CBS NEWS Coverage of STS-127

4:00 PM, 7/1/09, Update: NASA pleased with tanking test; agency pressing ahead for launch July 11

Sensors near a repaired hydrogen vent line attached to the shuttle Endeavour's external tank detected only the slightest traces of free hydrogen during a critical fueling test today, officials said, clearing the way for another launch attempt July 11.

The 7-inch vent line and the ground umbilical carrier plate used to connect it to a port on the side of the external tank will remain in their current configuration and engineers are confident the system will be leak free when Endeavour is fueled for launch on a space station assembly mission.

"We're in really good shape," said Mike Moses, the shuttle program launch integration manager at the Kennedy Space Center. "We're going to try on the 11th. ... We got it lined up just right and it doesn't leak."

The shuttle Endeavour after a fueling test Wednesday. The hydrogen
vent line is visible to the left. (Photo: NASA TV)

The vent line is used to carry excess hydrogen gas away from the shuttle when the tank is filled with super-cold propellant. A valve used to route hydrogen to the vent line is closed a few minutes before launch when the tank is pressurized for flight.

Endeavour was grounded June 13 and 17 when sensors near the umbilical attachment plate detected hydrogen concentrations of more than 60,000 parts per million, or 6 percent. The allowable concentration near the shuttle is 4 percent.

After the second launch scrub, engineers collected detailed measurements and concluded the problem was caused by an alignment issue between the hydrogen vent port on the tank and the vent line interface. To ensure a tight fit, engineers replaced a rigid Teflon seal with a more flexible design, modified the umbilical plate mounting pins and installed washer-like shims to counteract the alignment issue.

During the June launch attempts, the leaks occurred after the hydrogen section of the external tank was nearly full and fueling operations were transitioning from "fast fill" to "topping." In both cases, the leaks exceeded 60,000 parts per million.

During today's test, sensors detected a barely measurable 12 parts per million, a level so low it's not considered a sign of leakage.

"In this case, there were absolutely no leak indications and when we did transition all the way through the replenish operations, there were absolutely no leak indications whatsoever noted," said Launch Director Pete Nickolenko. The 12 parts per million reading was right at the limits of detectability, he said, and "we're calling that system tight, we show that as no leaks."

Moses said the same techniques used to ensure a near-perfect alignment of the vent line hardware will be used on all subsequent flights to prevent any repeat of the leaks that grounded Endeavour last month.

Assuming no other problems develop, NASA now plans to restart Endeavour's countdown at 10 p.m. next Wednesday, setting up a launch attempt at 7:39:33 p.m. Saturday, July 11. On board will be commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra.

Assuming an on-time liftoff, Polansky plans to guide the shuttle to a docking with the International Space Station at 3:25 p.m. on July 13. Five spacewalks are planned between July 14 and July 23, starting in the early afternoon to late morning U.S. time, to install a Japanese experiment platform, to replace aging solar array batteries and to store spare parts.

Kopra will remain behind aboard the space station when Endeavour undocks July 25, becoming part of the Expedition 20 crew. He will replace Japanese astronaut Koichi Wakata, who was launched to the station in March and who will return to Earth aboard Endeavour. Landing at the Kennedy Space Center is targeted for 12:15 p.m. on July 27.

As it now stands, NASA will only have four days to get the shuttle off the ground or the flight will slip to July 27 because of a critical Russian Progress space station resupply mission scheduled for launch July 24.

The Progress can "loiter" in orbit for five days, but it must dock by July 29. And that means Endeavour must take off by July 14 to complete its mission in time to undock by July 27, making way for the Progress.

Because of Endeavour's problems getting off the ground, the next flight in the station assembly sequence, mission STS-128, has slipped from Aug. 6 to around Aug. 18. NASA plans to close out the year by launching the shuttle Atlantis Nov. 12, although that flight may slip into December when all is said and done.

Engineers recently ran into an unusual problem with Atlantis when an astronaut work light attachment knob was lost during the shuttle's recent Hubble Space Telescope servicing mission. The hardware ended up lodged between a cockpit window pane and a flight deck instrument console. When the shuttle returned to Earth, the pressurized crew module contracted slightly and the knob was pinned against the glass.

The knob eventually was extracted by pressurizing the crew module and using dry ice to cool the metal enough to cause a slight amount of shrinkage. But the inner pressure pane in window No. 5 must now be inspected to make sure it did not suffer any structural damage.

Engineers are hopeful the window can be flown as is because replacing the inner pressure pane would take four to six months. Access is extremely tight and cockpit instrumentation would have to be disconnected, reconnected and retested after a window swap out.

With the shuttle program scheduled for retirement at the end of next year, a six-month schedule hit for one orbiter would require major replanning. But Moses said today NASA cannot complete the space station with just two shuttles, Endeavour and Discovery, and if Atlantis needs a window replacement, it will get one.

But engineers are hopeful it won't come to that.

10:30 AM, 7/1/09, Update: Fueling test complete; hydrogen vent line works normally with no signs of leakage

A gaseous hydrogen vent line attached to the shuttle Endeavour's external tank worked flawlessly during a critical fueling test today. Sensors detected no measurable leaks like those that twice grounded Endeavour in June, clearing the way for NASA to make a third launch attempt July 11.

The fueling test began at 6:48 a.m. when engineers began loading the external tank with a half-million gallons of liquid oxygen and hydrogen rocket fuel. By 9 a.m., the hydrogen section of the tank was 98 percent full.

It was around that point in fueling for launch attempts June 13 and 17 that sensors detected higher-than-allowable gaseous hydrogen concentrations near the ground umbilical carrier plate where the 7-inch vent line attaches to the tank.

A hydrogen vent line attached to the shuttle Endeavour's external tank
was leak free during a critical fueling test Wednesday. (Photo: NASA TV)

Precise measurements indicated the rectangular vent port housing was misaligned slightly during the tank's construction, preventing the umbilical plate that attaches the vent line from forming a tight seal when the hardware was exposed to ultra-low temperatures.

To fix the problem, a different type of seal was installed in the vent line quick-disconnect system, one that is more flexible, and shim-like washers were installed on the umbilical plate mounting points to provide additional pressure on the side believed to be pulling away slightly as the hardware contracted under cryogenic conditions.

The repair work apparently paid off. During today's test, no measurable leakage was detected near the carrier plate when the tank was filled and in "stable replenish" mode, with a vent valve cycling to route excess hydrogen gas away from the launch pad.

Mission Management Team Chairman Mike Moses and Launch Director Pete Nickolenko plan to brief reporters on the results of the test at 1 p.m. An updated status report will be posted after the briefing.

9:15 AM, 7/1/09, Update: Hydrogen vent line appears to work normally; no out-of-spec leakage detected

With the shuttle Endeavour's external tank loaded with super-cold rocket fuel, a gaseous hydrogen vent line that derailed two launch attempts in June appears to be working normally today midway through a critical test, with no signs of any leakage.

The test is not yet complete, but sensors near the 7-inch gaseous hydrogen vent line have not detected any measurable concentrations of free hydrogen in the area. NASA's safety limit of 4 percent, or 40,000 parts per million, was violated by this point during Endeavour's two previous launch attempts.

"Teams have not detected any leaks," said NASA commentator Candrea Thomas.

The test is scheduled to end around 10 a.m.

7:20 AM, 7/1/09, Update: Shuttle fueling test begins

Working by remote control, engineers at the Kennedy Space Center began pumping a half-million gallons of super-cold liquid oxygen and hydrogen rocket fuel into the shuttle Endeavour's external tank early today in a make-or-break test to make sure the leaky hydrogen vent line that grounded the ship twice in June has been fixed. The fueling procedure began just before 7 a.m.

If the 7-inch vent line attached to the side of the shuttle's external tank proves to be leak free, or at least tight enough to avoid exceeding NASA's 40,000 parts per million safety limit, the agency will press ahead for a third launch attempt July 11.

But if sensors detect concentrations of hydrogen gas greater than 4 percent near the vent line attachment point, Endeavour's 16-day space station assembly mission will face another lengthy delay, possible up to two months if the shuttle has to be attached to a different tank.

Engineers should know, one way or the other, by around 9 a.m. as the fueling process nears completion.

The space shuttle Endeavour at the start of a critical fueling test
(Photo: NASA TV)

Endeavour was grounded June 13 and 17 when the hydrogen section of the tank was nearing its full load and the vent line hardware was subjected to cryogenic conditions.

After the initial launch scrub, engineers replaced an internal seal in the vent line quick-disconnect fitting but that did not resolve the problem and another leak during fueling for a June 17 launch forced NASA to stand down for more extensive troubleshooting.

Precise measurements indicated the rectangular vent port housing where the external vent line attaches to the side of the tank was misaligned slightly during the tank's construction, preventing the umbilical plate that attaches the vent line from forming a tight seal.

To fix the problem, a different type of seal was installed, one that is more flexible, and shim-like washers were installed on the umbilical plate mounting points to provide additional pressure on the side believed to be pulling away slightly as the hardware contracts under cryogenic conditions.

Engineers are confident they understand the problem, but today's test was ordered to make sure the fixes will, in fact, prevent the vent line umbilical plate from leaking beyond the allowable 40,000 parts per million.

08:50 PM, 6/30/09, Update: NASA set for critical shuttle fueling test Wednesday to assess hydrogen vent line fix

Engineers at the Kennedy Space Center are preparing to load the shuttle Endeavour's external tank with liquid oxygen and hydrogen rocket fuel early Wednesday in a critical test that could either pave the way to launch July 11 or trigger another lengthy delay.

At issue is whether a different internal seal in an external tank gaseous hydrogen vent line, along with shims intended to offset an alignment problem, will prevent the sort of leaks that grounded Endeavour June 13 and 17.

If the line is leak free Wednesday, or at least tight enough to prevent concentrations higher than 4 percent near the vent line umbilical plate, NASA will press ahead with plans to launch Endeavour on a 16-day space station assembly mission July 11.

But if higher-than-allowable leakage is detected, shuttle managers could be forced to move Endeavour to a different external tank, a move that would delay launch up to two months or more in a worse-case scenario.

Engineers believe they understand the problem - the rectangular vent port housing in the side of the tank was riveted into place slightly out of alignment - and they are hopeful the alternate seal and shims will, in fact, keep the vent line quick-disconnect fitting from leaking.

Complicating the issue for troubleshooters, the leaks only show up when the hydrogen section of the tank is nearing a full load and the hardware in the vent line is subjected to ultra-low cryogenic temperatures. Shuttle Program Manager John Shannon ordered Wednesday's fueling test to assess the performance of the vent line fixes before committing to a full-up launch countdown.

Engineers began fueling test preparations Monday. If all goes well, super-cold liquid hydrogen will begin flowing from storage dewars to the shuttle around 7 a.m. EDT Wednesday. So-called "fast fill" operations will begin an hour later and the hydrogen section of the tank should be nearing its full load shortly after 9 a.m.

As of Tuesday evening, there were no technical problems of any significance at launch pad 39A, but forecasters say morning showers and thunderstorms may develop near the space center. For fueling, the probability of thunderstorms near the pad must be 20 percent or less.

NASA will provide television coverage of the fueling test starting at 7 a.m. A news briefing with Mission Management Team Chairman Mike Moses and launch director Pete Nickolenko is planned for 1 p.m. to discuss the results of the test.

Here is a timeline of major countdown events (in EDT; best viewed with fixed-width font):

EDT........EVENT

Wednesday, July 1

01:00 AM...Final preparations for fuel loading
03:00 AM...Personnel clear launch pad
06:00 AM...Countdown enters a one-hour hold
06:30 AM...External tank ready to load
06:30 AM...Mission Management Team meeting
07:00 AM...NASA television coverage begins
07:00 AM...Transfer line chill down
08:00 AM...Fast fill begins
09:15 AM...Liquid hydrogen tank 98 percent full
09:45 AM...Liquid hydrogen topping begins
10:00 AM...Launch pad walkdown
12:00 PM...Test team 'go' for tank drain
01:00 PM...NASA TV: Post-tanking test press briefing
01:30 PM...LH2 boil off (duration approximately 19 hours)
04:00 PM...Pad opened for limited access

In a bit of good news for NASA, engineers successfully extracted an astronaut work light attachment knob that was jammed between one of the shuttle Atlantis' cockpit windows and an instrument panel housing after the ship's just-completed mission to repair the Hubble Space Telescope.

The knob, apparently lost by the crew during the mission, was pressing against window No. 5's critical internal pressure pane. It apparently got lodged in place during re-entry when the pressurized crew module contracted slightly.

The knob had to be removed to allow engineers to assess what, if any, damage had been done to the pressure pane when the knob got stuck. Engineers initially tried to cool it with dry ice, but the knob refused to budge. They then attempted to reverse the effects of the shuttle's descent by pressurizing the crew module. That worked, and engineers were able to retrieve the troublesome knob without having to resort to more invasive measures.

The issue was potentially significant because replacement of a pressure pane would require engineers to remove or disconnect cockpit instrumentation and other structures, work that could take four to six months to complete. NASA managers are hopeful the knob caused no significant damage to the window, but tests are not yet complete.

7:15 PM, 6/24/09, Update: Tanking test targeted for July 1; engineers assess jammed knob in Atlantis window

Engineers plan to load the shuttle Endeavour's external tank with rocket fuel next Wednesday to test vent line fixes intended to stop, or at least reduce, gaseous hydrogen leaks that grounded the shuttle June 13 and 17, NASA officials said today. If the repairs work, the agency will press ahead with a third attempt to launch Endeavour on a space station assembly mission July 11.

A different sort of problem has cropped up for the shuttle Atlantis, just back from a successful mission to overhaul the Hubble Space Telescope. Sources say engineers recently discovered an astronaut work light attachment knob lodged between the inner pressure pane of cockpit window No. 5 and the back of an instrument panel housing.

The knob, used to mount a light on a bracket much like the knob on a tripod holds a camera, floated into a hard-to-see corner of the window area during the mission, when the crew cabin was pressurized to 14.7 pounds per square inch. It apparently got stuck between the inner window pane and the instrument panel housing when Atlantis returned to Earth and the cabin structure shrank slightly.

The knob is now firmly lodged against the inner pressure pane of window No. 5, the sources said. Because of uncertainty about whether the pane has been damaged, the knob must be removed - and the pane confirmed to be structurally sound - before Atlantis can fly again in November.

While the knurled knob is pressing against the pane in two locations, it's not yet clear whether the glass has suffered any measurable damage. But access is tight and engineers considering removal options must make sure they don't inadvertently damage the glass. Replacing a pressure pane, one official said, could take months because part of the cockpit instrumentation would have to be moved or disconnected to provide clearance.

Engineers have tried to cool the stuck knob with dry ice in hopes of getting it to shrink enough to permit removal, but that did not work. A variety of other techniques are under assessment and it's not yet clear what impact, if any, the issue might have for Atlantis' next mission. Launch is targeted for Nov. 12.

Endeavour was grounded twice June 13 and 17 by gaseous hydrogen leaks where a 7-inch vent line attaches to an umbilical plate on the side of the shuttle's external tank. Engineers believe the rectangular vent port housing built into the tank was misaligned slightly during the manufacturing process, preventing the umbilical plate and quick-disconnect fitting from achieving a tight seal.

To improve the vent line umbilical's ability to maintain a tight fit when the hardware is chilled to cryogenic temperatures, moving slightly as the mechanism contracts slightly, engineers are switching to an alternative two-part seal that is more flexible than the single-piece seal used earlier.

In addition, special washers will be installed on the umbilical plate's mounting points to act as shims, again to improve the system's ability to move slightly while maintaining a tight seal.

Hydrogen concentrations of up to 40,000 parts per million are allowable and engineers are hopeful the changes will eliminate the leakage, or at least reduce it to allowable levels. If so, NASA will press ahead with plans to launch Endeavour July 11.

Engineers plan to install a new flexible two-part seal in the vent line Thursday and to attach the quick-disconnect fitting Saturday. The "call to stations" to begin what amounts to a countdown to the fueling test is planned for Monday night. If all goes well, the tank will be loaded with super cold liquid oxygen and hydrogen rocket fuel Wednesday morning.

6:00 PM, 6/23/09, Update: Shuttle managers to meet Wednesday to review leak test plans; fueling test expected June 30 or July 1

Shuttle managers plan to meet Wednesday to review procedures for a fueling test next week to assess the performance of an alternative internal seal and shim-like washers intended to eliminate a leak in a gaseous hydrogen vent line that has twice grounded the shuttle Endeavour.

If the fueling test goes well and sensors don't detect hydrogen concentrations greater than the allowable 40,000 parts per million, NASA will press ahead for a third attempt to launch Endeavour on a space station assembly mission at 7:39 p.m. July 11.

If higher-than-allowable leakage is again detected, program managers could be forced to move Endeavour to a different tank and boosters, triggering more significant downstream delays.

Engineers believe they understand the problem - a slightly misaligned vent port housing built into the side of Endeavour's external tank - but it remains to be seen whether the proposed fix will, in fact, eliminate the leaks that have grounded Endeavour.

The 7-inch-wide hydrogen vent line in question is needed to carry away potentially dangerous hydrogen vapor that builds up in the tank as it is loaded with fuel. By cycling a valve in the vent line, the proper internal pressure is maintained and excess hydrogen gas is routed to a "flare stack" near the pad where it is harmlessly burned away.

The launch pad vent line is attached to the side of the tank with a ground umbilical carrier plate and a quick-disconnect fitting. At liftoff, an explosive bolt is detonated and the vent line drops away from the tank.

Endeavour was grounded June 13 and 17 when sensors detected hydrogen concentrations greater than 40,000 parts per million at the umbilical plate interface.

Engineers initially believed the problem involved a slight misalignment of the vent line umbilical plate and/or trouble with a Teflon seal in the quick-disconnect fitting. A similar problem grounded the shuttle Discovery for four days last March.

The seal was replaced, but the system leaked again during fueling for the June 17 launch try. After additional analysis, engineers concluded the rectangular vent port housing itself, which was riveted into the side of the tank about six-tenths of a degree out of vertical, was preventing the umbilical plate/quick-disconnect fitting from maintaining a tight seal under cryogenic conditions.

The proposed fix is to install a two-piece flexible seal in the quick-disconnect fitting in place of the more rigid single-piece Teflon seal used earlier. In addition, the umbilical plate that connects the vent line to the tank will be mounted using different shim-like washers to help counteract the effects of the vent port misalignment.

In so doing, engineers hope to maintain a tight fit at the vent line interface despite the temperature-induced shrinkage and flexing that occurs when the tank is filled with propellants. The leak only shows up when the equipment is exposed to cryogenic conditions.

To save time and minimize the chance of introducing any variables that might affect the test, Program Manager John Shannon told the engineering team to forego adding any additional instrumentation for the upcoming fueling test. Instead, Endeavour's tank will be in normal flight configuration when it is loaded with a half-million gallons of liquid oxygen and hydrogen rocket fuel.

Two fueling test timelines are under consideration but managers favor a plan that calls for installing the new seal late this week and re-rigging the umbilical plate attachments Saturday. The fueling test itself would be expected between 7 a.m. and 10 a.m. on either June 30 or July 1.

07:00 PM, 6/19/09, Update: Engineers believe minor misalignment in external tank vent line housing causing hydrogen leaks; use of different seal may correct problem; tanking test planned to make sure; Shannon optimistic about 7/11 launch target

A very slight "clocking" misalignment in the way a hydrogen vent port on the shuttle Endeavour's external tank was built into the structure is the leading candidate for what caused gaseous hydrogen leaks that derailed two launch attempts June 13 and 17, the shuttle program manager said today.

The use of a different type of seal where a launch pad vent line attaches to the side of the external tank may resolve the problem. The alternative seal design should provide a tighter fit that is less susceptible to the temperature-related mechanical shrinkage and motion that can put uneven stress on the interface and lead to leaks.

To find out, engineers are making plans for a fueling test at launch pad 39A, loading Endeavour's tank with super-cold hydrogen rocket fuel and measuring leak rates where the vent line connects to the side of the tank. The leaks typically show up when the mechanism is subjected to cryogenic temperatures.

Shuttle Program Manager John Shannon told CBS News Friday that if the tanking test goes well, Endeavour should be able to make its July 11 launch target.

"I'm pretty confident," he said in a telephone interview.

The hydrogen vent line attached to shuttle Endeavour's external tank.
A leak in the vent line interface derailed two launch attempts June 13 and 17.
(Photo: NASA TV)

NASA initially attempted to launch Endeavour June 13. But the night before, as the shuttle's tank was nearing its full load, sensors detected a significant gaseous hydrogen leak at the ground umbilical carrier plate where the vent line attaches to the tank with a quick-disconnect fitting.

Liquid hydrogen, at minus 423 degrees Fahrenheit, constantly "boils off" as the tank is being filled. The vent line is used to carry the potentially dangerous vapor away from the shuttle to maintain the proper internal pressure. At launch, an explosive bolt detonates and the vent line falls away from the tank.

While some leakage at the quick-disconnect fitting is acceptable, hydrogen concentrations higher than 40,000 parts per million are grounds for calling off a countdown.

That limit was exceeded during both of Endeavour's fuelings and after the second scrub, the flight was put on hold to make way for Thursday's launch of NASA's Lunar Reconnaissance Orbiter from the Cape Canaveral Air Force Station.

Endeavour's launch window closes this weekend, due to temperature constraints related to the space station's orbit. Assuming NASA can, in fact, fix the hydrogen vent line problem in time, the next launch window for the shuttle will open on July 11 at 7:39 p.m. EDT.

But the agency will only have four days to get the shuttle off the ground or the flight will slip to July 27 because of a critical Russian Progress space station resupply mission scheduled for launch July 24.

The Progress can "loiter" in orbit for five days, but it must dock by July 29. And that means Endeavour must take off by July 14 to complete its 16-day space station assembly mission in time to undock before the Progress arrives.

Shannon said three engineering teams have been set up to resolve the vent line seal issue. One team will begin precise measurements of the vent line interface this weekend before taking the mechanism apart next week. Those measurements are needed to confirm the root cause hypothesis.

Engineers at Lockheed Martin's external tank plant in Michoud, La., are making plans to replace the current rigid Teflon seal with the alternative flexible two-part seal, evaluating washer-like shims on the umbilical plate's mounting hardware to further counteract the clocking misalignment.

Finally, engineers at the Kennedy Space Center will be making plans for a tanking test. Shannon said it would take about 10 days to finalize those plans. The actual fueling test would take place shortly thereafter.

"The hardware is still, they call it 'quarantined,' it hasn't been touched since we scrubbed," Shannon said. "The vehicle and the pad have been secured. There was a lot of discussion, I think the underlying root cause, they at least have a plausible reason why we had a leak twice.

"The way the umbilical line that carries the hydrogen away from the tank, the way it attaches to the tank is there's a plate that's bolted on with a pyrotechnic bolt. And there's a receiving plate that's on the external tank and those two are lined up, there are two little pieces of metal that go down to these hinge pins that keep it from moving side to side. And there's a Teflon seal ... on the inside of that flange coming out of the tank. The line going into it pressure fits in."

When Endeavour's tank was delivered from the assembly plant, "they were doing measurements and that flange on the ET side is cocked counter-clockwise .65 degrees," Shannon said.

"What has happened, we are pretty sure, is that when you put that external plate with the line on it onto the ET flange, there's a pyrotechnic bolt that holds those two together. It's above that round pipe. That whole system can rotate about that pyro bolt. If the two plates are in perfect alignment, it's not going to rotate, it'll just move slightly up and down. But since it is cocked a little bit ... it pulls the entire structure to the right (when the hardware contracts at cryogenic temperatures) and that allows a leak on the left side."

The clocking problem was the leading suspect after the June 13 launch scrub, he said. Shims were used to provide a firmer connection, but the seal still leaked. Engineers believe the two-part seal that will be used for the upcoming tanking test will provide the strength needed to resist the temperature-induced asymmetrical loading believed to be responsible for the leaks.

The shuttle Discovery also was grounded by a vent line leak in March. But in that case, the misalignment was not as great and when the seal was replaced a subsequent fueling went well.

Shannon said engineers noted 18 to 20 gaseous hydrogen leaks at the ground umbilical carrier plate interface during previous fuelings but in all but two of those cases, cycling the vent valve caused enough vibration to help the seal seat itself.

The so-called "two-part seal" has been used on two previous shuttle fuelings, but NASA ultimately returned to the current Teflon seal design because it tended to leak less. But the leaks experienced by the two-part seal were within specification and did not require any corrective action.

If higher-than-allowable leakage is seen during the fueling test using the alternative seal design, Shannon said the team may have to consider more extensive work to remove, realign and re-attach the vent line flange on the external tank. In that case, Endeavour likely would be moved to a different tank and launch would face a more significant delay.

But engineers believe Endeavour's problem is a one-time issue related to this particular external tank. A spare vent line carrier plate was attached to external tanks currently in production and no similar clocking problems were found.

"There's nothing wrong with the tank," Shannon said. "It's just the alignment of the ground system is off from the flight system."

2:58 AM, 6/17/09, Update: LAUNCH SCRUBBED by gaseous hydrogen leak (UPDATED at 5:30 a.m. with news briefing; UPDATED at 6:15 a.m. with lunar launch reset for Thursday)

After a lengthy fueling delay because of stormy weather, launch of the shuttle Endeavour on a space station assembly mission was scrubbed early Wednesday when a presumably repaired hydrogen vent line umbilical began leaking potentially dangerous vapor for the second launch try in a row.

Given the apparent severity of the problem, and the planned launch of NASA's Lunar Reconnaissance Orbiter on Thursday atop an Atlas 5 rocket, Endeavour will be grounded until at least July 11 when the next shuttle-space station launch window opens.

"We've got to step back and try to understand this problem and we will do that," said LeRoy Cain, chairman of NASA's Mission Management Team. "It's going to take us a little time. As a result of this scrub, we will be targeting our next earliest available launch opportunity ... and that'll be as early as July 11. We'll go work this problem and once we get it fixed and we're confident we have a solution that's going to work and allow us to go fly safely, then we'll proceed forward."

He said shuttle engineers "will be relentless in terms of trying to go understand what's going on with this system. We'll fix it and we'll move forward once we have determined we can get in a safe configuration to go fly."

The vent line in question, attached to the side of the shuttle's external fuel tank, carries hydrogen gas away from the shuttle so it can be safely dissipated. A leak in the same mechanism scrubbed a launch attempt last Saturday.

Engineers replaced a seal in the gaseous hydrogen vent line umbilical plate Sunday and Monday and NASA managers were hopeful that would resolve the problem. A seal replacement worked last March when the shuttle Discovery was grounded by a similar leak.

While Endeavour's vent line passed leak checks at ambient temperatures, the seal replacement apparently wasn't enough to resolve the problem. During the initial stages of fueling, engineers observed a relatively small leak rate that, while unexpected, was within specification.

But as the tank filled and the temperature of the vent line kept dropping, the leak worsened. Engineers stopped the flow of hydrogen and cycled a valve in the system in hopes of clearing the problem, but they were not successful.

They then resumed hydrogen "fast fill" operations to collect additional data. When the vent valve was opened again, however, higher-than-allowable levels of hydrogen gas were detected, up to 60,000 parts per million. Additional vent valve cycles also were out of limits.

Finally, at 1:55 a.m. EDT, Launch Director Pete Nickolenko, overseeing his first countdown, reluctantly ordered a scrub.

"We are scrubbing the launch attempt for today," said launch commentator Mike Curie. "The troubleshooting efforts have not resulted in a significant decrease in the amount of gaseous hydrogen that's being detected outside of the ground umbilical carrier plate, the same area where we experienced a leak the last launch attempt."

Because of the conflict with this week's launch of NASA's Lunar Reconnaissance Orbiter, NASA only had one shot at getting Endeavour off the ground before the end of its current launch window.

The shuttle's normal launch window extends through Saturday. A launch on Sunday would be possible if mission managers eliminated one of the crew's five planned spacewalks. The window is defined by temperature constraints related to the space station's orbit.

After the shuttle countdown was called off Wednesday, launch of the LRO mission, originally planned for Wednesday but bumped to Friday by the shuttle, was moved up one day to Thursday.

Had the shuttle been grounded by bad weather, it might have been possible to make another launch attempt at the back end of the window, assuming the LRO mission got off on time. But given the nature of the hydrogen leak, it was a moot point.

Endeavour's crew - commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra - took the delay in stride and planned to fly back to Houston later in the day.

"I'm sure you all know that we postponed again," Polansky said in a Twitter feed. "It's a reminder that spaceflight is NOT routine. We will fly home to Houston this morning."

The goals of Endeavour's mission are to attach an experiment platform to a Japanese research module, to replace aging solar array batteries, to deliver critical spare parts and to ferry Kopra to the station to replace Japanese astronaut Koichi Wakata.

Wakata, launched to the space station last March aboard Discovery, was informed of Endeavour's launch delay - and his extended mission - earlier today.

"OK, it is great that this international crew will continue," he said. "Another month for me!"

With Endeavour now delayed to at least July 11, launch of the next space station assembly flight, currently targeted for Aug. 7, likely will be delayed as well in a downstream domino effect.

And that assumes engineers can resolve the umbilical plate problem in time for a July 11 launch. With today's scrub, leaks have developed at the vent line interface in three of the last five shuttle fuelings, indicating a potentially more serious problem than misalignment issues or isolated damage to a seal.

"It's too early for me to give you any idea of level of confidence," Cain said. "The direction we gave to the team today after our scrub was we need to step back from this problem and try to understand what is different in our process, if anything. Somehow, we've introduced some other variable or some change, albeit very small. But our sense is something has changed and something is different and we need to go re-evaluate."

Because of the earlier problems with Discovery in March and the leak Saturday, engineers already were looking into "the procedures, the materials, the techniques, everything from A to Z associated with this part of the system," Cain said.

"It could be something as simple as a heat treatment to some material part in the system, it could be some change in a vendor that was done years ago that is just now being introduced because of a part number," he said.

"I don't want to speculate, there are a whole myriad of things that it could be. But that's the whole idea of stepping back and trying to determine what it is, if anything, that has changed."

2:45 AM, 6/17/09, Update: Senior Launch Director says gaseous hydrogen leak 'way out of spec'

Senior Launch Director Mike Leinbach, serving as deputy to Pete Nickolenko for the shuttle Endeavour's countdown, said the gaseous hydrogen leak that grounded the spacecraft Wednesday for the second time in four days was too severe to continue with a launch attempt. Speaking on NASA television, Leinbach explained what happened leading up to the launch scrub.

"We got into tanking and everything looked like it was going fine until we were about an hour away from the end of tanking and we picked up the hydrogen leak at the umbilical again," he said. "This time, it was a little bit different. We were actually picking up the leak before we got into the topping sequence, which is where we've seen this leak before.

"So at that time, we knew we had a little bit different signature. We watched the data very closely, we did our standard troubleshooting techniques by cycling the valve to see if we could clean up that leak again and indeed, it never cleaned up. The signature was a little bit different, but that doesn't surprise me. With cryogenic leaks it would be very unusual to have an identical leak.

"And so the fact that this one was a little bit different and we thought we might be able to work our way through it, that didn't surprise me we were trying to do that.

"The team did an outstanding job over these last four days to get to this point," Leinbach said. "I sure wish we could have rewarded them and the astronauts and everybody with a launch this morning. But the leak was way out of spec again and so we were just not comfortable pressing on. As much as we tried to fix the leak, we just couldn't do it so we had to scrub and secure again.

"We're in the process of draining the external tank now. ... Sometime tomorrow evening, we'll be able to get our hands on this disconnect again and go into taking it apart. I imagine we'll put together a more detailed troubleshooting plan this time and go execute that once we get our hands on the disconnect again.

02:00 AM, 6/17/09, Update: LAUNCH SCRUBBED by gaseous hydrogen leak

After a lengthy fueling delay because of stormy weather, launch of the shuttle Endeavour on a space station assembly mission was scrubbed early Wednesday when a presumably repaired hydrogen vent line umbilical began leaking potentially dangerous vapor.

The vent line, attached to the side of the shuttle's external fuel tank, carries hydrogen gas away from the shuttle so it can be safely dissipated. A leak in the same mechanism scrubbed a launch attempt last Saturday.

The gaseous hydrogen vent line attached to Endeavour's external tank.
(Photo: NASA TV)

Engineers replaced a seal in the gaseous hydrogen vent line umbilical plate Sunday and Monday and NASA managers were hopeful that would resolve the problem. A seal replacement worked last March when the shuttle Discovery was grounded by a similar leak.

While Endeavour's vent line passed leak checks at ambient temperatures, the seal replacement apparently wasn't enough to resolve the problem. During the initial stages of fueling, engineers observed a relatively small leak rate that, while unexpected, was within specification.

But as the tank filled and the temperature of the vent line kept dropping, the leak worsened. Engineers stopped the flow of hydrogen and cycled a valve in the system in hopes of clearing the problem, but they were not successful.

They then resumed hydrogen "fast fill" operations to collect additional data. When the vent valve was opened again, however, higher-than-allowable levels of hydrogen gas were detected, up to 60,000 parts per million. Additional vent valve cycles also were out of limits.

Finally, at 1:55 a.m. EDT, Launch Director Pete Nickolenko, overseeing his first countdown, reluctantly ordered a scrub.

"We are scrubbing the launch attempt for today," said launch commentator Mike Curie. "The troubleshooting efforts have not resulted in a significant decrease in the amount of gaseous hydrogen that's being detected outside of the ground umbilical carrier plate, the same area where we experienced a leak the last launch attempt.

"STS-127 Launch Director Pete Nickolenko has just given the team a 'go' to scrub the launch attempt after two more attempts to open the vent valve once again displayed much higher than expected amounts of gaseous hydrogen."

Because of a conflict with the launch of NASA's Lunar Reconnaissance Orbiter, scheduled for takeoff Friday atop a United Launch Alliance Atlas 5 rocket, NASA is not expected to get another chance to launch Endeavour until July 11 at the earliest.

The shuttle's normal launch window extends through Saturday and a launch on Sunday would be possible if mission managers eliminate one of the crew's five planned spacewalks. The window is defined by temperature constraints related to the space station's orbit.

But the Air Force Eastern Range, which provides required telemetry and tracking support, cannot reset its systems in time to support a shuttle launch Sunday even if the LRO mission took off on time Friday.

At least that's what reporters were told earlier. NASA managers have not yet said when another attempt to launch Endeavour might be possible.

Either way, it was a frustrating disappointment to Endeavour's crew - commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra - and to the NASA launch teams at Kennedy and the Johnson Space Center in Houston.

If Endeavour is, in fact, delayed to July 11, launch of the next space station assembly flight, currently targeted for Aug. 7, would be delayed as well in a downstream domino effect.

And that assumes engineers can resolve the umbilical plate problem in time for a July 11 launch. With today's scrub, leaks have developed at the vent line interface in three of the last five shuttle fuelings, indicating a potentially more serious problem than a misaligned seal.

Additional information will be posted here as it becomes available.

01:00 AM, 6/17/09, Update: Engineers monitoring leak near gaseous hydrogen vent line umbilical

Engineers stopped loading liquid hydrogen into the shuttle Endeavour's external tank today at 1:02 a.m. because of a leak in the gaseous hydrogen umbilical that connects a vent line to the side of the tank. Launch remains targeted for 5:40:52 a.m. if the problem can be quickly resolved, but because fueling began nearly three hours late, there is little time available.

"At this time, engineers here in the launch control center at the Kennedy Space Center are monitoring a leak in the area of the ground umbilical carrier plate," said NASA launch commentator Mike Curie. "It's a leak in the amount greater than we would anticipate at this time (in the fueling procedure) and we'll keep our eyes on it."

Engineers cycled the valve in hopes of clearing the leak, but an initial attempt was not successful.

11:10 PM, 6/16/09, Update: NASA clears shuttle for fueling

Running nearly three hours late because of thunderstorms near the Kennedy Space Center, engineers finally were cleared to begin pumping rocket fuel into the shuttle Endeavour's external tank just after 11 p.m. While the delay means little time is available to handle unexpected problems, launch on a space station assembly mission remains targeted for 5:40:52 a.m. EDT Wednesday.

Fueling had been scheduled to begin at 8:15 p.m., but severe thunderstorms across central Florida, and electric activity near the spaceport, forced Launch Director Pete Nickolenko to hold off in hopes conditions would improve.

NASA safety rules prohibit fueling if lightning is within 5 miles of the launch pad or if the forecast is worse than 20 percent "no-go." At 8:15 p.m., the forecast was 40 percent no-go.

But nearly three hours later, the storms finally dissipated and conditions improved enough for NASA managers to clear the launch team to start the three-hour fueling procedure. Transfer line chill down, the first step in the fueling sequence, began at 11:04 p.m.

There are no technical problems of any significance at pad 39A and forecasters continue to predict an 80 percent chance of good weather at launch time.

Engineers pulled a protective gantry away from the shuttle Endeavour and restarted the orbiter's countdown Tuesday, setting the stage for launch Wednesday on a delayed space station assembly mission.

Countdown clocks at the Kennedy Space Center began ticking backward at the T-minus 11-hour mark at 1:15 p.m. EDT, setting the stage for a launch attempt at 5:40:52 a.m. Wednesday, roughly the moment Earth's rotation carries launch complex 39A into the plane of the space station's orbit.

There are no technical problems of any significance and forecasters are predicting an 80 percent chance of good weather at launch time.

The space shuttle Endeavour, exposed to view on pad 39A
(Phot0: NASA)

Because of a conflict with NASA's Lunar Orbiter Reconnaissance mission, Endeavour's crew will only have one shot at getting off the pad. If the weather or some other problem delays launch, the shuttle team will stand down to give the LRO team a launch opportunity Friday at 6:41 p.m.

Endeavour's normal launch window closes on June 20 and even if the LRO mission took off on time Friday, Endeavour would not get another launch opportunity until July 11, after a so-called "beta angle cutout" defined by the angle between the sun and the plane of the space station's orbit. During beta cutouts, temperature constraints can be violated when the shuttle is docked to the lab complex.

Hoping for the best, engineers plan to begin loading a half-million gallons of liquid oxygen and liquid hydrogen rocket fuel into Endeavour's external tank starting with transfer line chill down at 8:15 p.m. The remotely-controlled fueling procedure should be complete by around 11:15 p.m.

It was during fueling overnight last Friday that a significant leak showed up in an umbilical where a vent line attaches to the shuttle's external tank. The vent line is used to carry hydrogen gas from inside the tank to a flare stack well away from the shuttle where it can be safely burned away before launch.

The repaired hydrogen vent line attached to Endeavour's external tank.
(Photo: NASA TV)

The leak occurred as the hydrogen section of the external tank was nearing a full load late Friday and the umbilical plate that connects the vent line to the side of the tank was subjected to extremely low temperatures. A similar problem grounded the shuttle Discovery for four days last March.

Engineers are not sure what caused either problem, but in this case they suspect an internal seal might have been damaged when the umbilical was connected, disconnected and then reconnected when Endeavour was moved from pad 39B to 39A last month. In any case, the seal in question was replaced and engineers are hopeful the quick-disconnect fitting will be leak free the second time around.

If all goes well, commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra will begin strapping in around 2:20 a.m. Wednesday to await liftoff.

The goal of Endeavour's 16-day mission is to attach a sophisticated experiment platform to a Japanese research module, to replace aging solar array batteries, to store critical spare parts on the space station for future use and to replace one of the lab's six crew members. Kopra will remain behind aboard the station when Endeavour departs and Japanese astronaut Koichi Wakata, launched to the complex last March, will return to Earth in his place.

Here is a timeline of major events in the shuttle's countdown to launch (in EDT; best viewed with fixed-width font):

EDT...........EVENT

Tue  06/16/09

01:15 PM......Resume countdown
01:45 PM......Pad clear of non-essential personnel
01:35 PM......Hydraulic power unit bite test
02:25 PM......Fuel cell activation
03:15 PM......Booster joint heater activation
03:45 PM......Master events controller test
04:00 PM......Tanking weather update
04:45 PM......Final fueling preps; launch area clear
05:15 PM......Red crew assembled
06:00 PM......Fuel cell integrity checks complete

06:15 PM......Begin 2-hour built-in hold (T-minus 6 hours)
06:25 PM......Safe-and-arm circuit test
06:45 PM......Crew wakeup
07:15 PM......External tank ready for loading
07:40 PM......Mission management team tanking meeting
07:45 PM......Crew medical checks
08:15 PM......Resume countdown (T-minus 6 hours)

08:15 PM......LO2, LH2 transfer line chill down
08:25 PM......Main propulsion system chill down
08:25 PM......LH2 slow fill
08:55 PM......LO2 slow fill
09:00 PM......Hydrogen engine cutoff sensors go wet
09:05 PM......LO2 fast fill
09:08 PM......Crew medical checks
09:15 PM......LH2 fast fill
11:10 PM......LH2 topping
11:15 PM......LH2 replenish
11:15 PM......LO2 replenish

11:15 PM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
11:15 PM......Closeout crew to white room
11:15 PM......External tank in stable replenish mode
11:30 PM......Astronaut support personnel comm checks
11:55 PM......Crew photo op (recorded)

Wed  06/17/09

12:00 AM......Pre-ingress switch reconfig
12:30 AM......NASA TV coverage begins
01:18 AM......Final crew weather briefing
01:28 AM......Crew suit up begins
01:45 AM......Resume countdown (T-minus 3 hours)

01:50 AM......Astronauts leave crew quarters
02:20 AM......Astronauts strap in
03:10 AM......Astronaut comm checks
03:35 AM......Hatch closure
04:05 AM......White room closeout

04:25 AM......Begin 10-minute built-in hold (T-minus 20m)
04:35 AM......NASA test director countdown briefing
04:35 AM......Resume countdown (T-minus 20m)

04:36 AM......Backup flight computer to OPS 1
04:40 AM......KSC area clear to launch

04:46 AM......Begin final built-in hold (T-minus 9m)
05:16 AM......NTD launch status verification
05:31:52 AM...Resume countdown (T-minus 9m)

05:33:22 AM...Orbiter access arm retraction
05:35:52 AM...Launch window opens
05:35:52 AM...Hydraulic power system (APU) start
05:35:57 AM...Terminate LO2 replenish
05:36:52 AM...Purge sequence 4 hydraulic test
05:36:52 AM...Guidance units to inertial
05:36:57 AM...Aerosurface confidence checks
05:37:22 AM...Main engine steering test
05:37:57 AM...LO2 tank pressurization
05:38:02 AM...Gaseous oxygen vent arm retraction
05:38:17 AM...Fuel cells to internal reactants
05:38:22 AM...Clear caution-and-warning memory
05:38:52 AM...Crew closes visors
05:38:55 AM...LH2 tank pressurization
05:40:02 AM...Orbiter to internal power
05:40:21 AM...Shuttle computers take control of countdown
05:40:31 AM...SRB steering test
05:40:45 AM...Main engine start (T-6.6 seconds)
05:40:52 AM...SRB ignition (LAUNCH)

NASA managers today formally cleared the shuttle Endeavour for a delayed launch Wednesday on a space station assembly mission. Launch of the agency's Lunar Reconnaissance Orbiter was delayed to June 18 or 19 to make room for the shuttle in an effort to maximize launch opportunities for both missions.

Endeavour was grounded Saturday when a gaseous hydrogen vent line umbilical seal leaked potentially dangerous vapor during fueling. Engineers replaced the seal and while the schedule is tight, NASA managers decided today to retarget the shuttle for launch at 5:40:50 a.m. EDT Wednesday.

The shuttle's countdown will be restarted at the T-minus 11-hour mark at 1:15 p.m. Tuesday and forecasters are predicting an 80 percent chance of good weather.

As it now stands, the Endeavour astronauts will have one shot at getting off the ground Wednesday. After that, the Air Force Eastern Range, which provides critical telemetry and tracking support, will reset its systems for launch of the Lunar Reconnaissance Orbiter on Friday. In that case, Endeavour's mission likely would be delayed to July 11 because of temperature constraints related to the International Space Station's orbit.

"The agreement we've made with the Range and the Atlas LRO folks is that we will have one opportunity on the 17th and then stand down and allow them to play through," said NASA Test Director Steve Payne.

"We always plan a couple of days in the future in case some unforseen thing happens and (if) we have an opportunity, we're ready. The vehicle will be ready to make multiple attempts. Our only constraint is Range right now. If for some reason the constraint were lifted, we may have other opportunities."

But as of this writing, that does not appear likely as long as the $583 million Lunar Reconnaissance Orbiter mission stays on track.

A technician at pad 39A works to reconnect a hydrogen vent line
to a repaired umbilical plate on the side of shuttle Endeavour's
external tank. (Photo: NASA TV)

While the shuttle team presses ahead with work to ready Endeavour for launch, the LRO/LCROSS team is continuing processing for takeoff aboard a United Launch Alliance Atlas 5 rocket at launch complex 41 at the nearby Cape Canaveral Air Force Station.

"We will monitor shuttle's progress," said Charles Dovale, the NASA launch manager. "If shuttle were to begin their count and scrub for any reason prior to midnight (Tuesday), LRO/LCROSS and Atlas can maintain June 18 as the earliest date."

But if the shuttle stays on track, LRO will slip to June 19.

The LRO spacecraft is scheduled to map the moon's surface in unprecedented detail from an orbit around the lunar poles just 31 miles above the cratered terrain. A companion mission, the Lunar Crater Observation and Sensing Satellite, or LCROSS, is designed to look for evidence of water ice and other materials by crashing the Atlas 5's Centaur upper stage into a crater near the moon's south pole.

A small "shepherding satellite" will monitor the Centaur's demise, flying through the cloud of debris thrown up by the crash, before following it to a similar fate.

The primary goals of Endeavour's 16-day five-spacewalk mission are to attach an experiment platform to a Japanese research module, to replace aging solar array batteries, to mount critical spare parts on the station and to replace station flight engineer Koichi Wakata with NASA astronaut Timothy Kopra.

Endeavour's launch window opened June 13 and closes June 20. A launch on June 21 is possible, but one of the crew's spacewalks likely would have to be deleted to ensure an undocking before temperature constraints were violated.

The LRO/LCROSS launch window also closes on June 20. The decision to give the shuttle a launch opportunity Wednesday still leaves at least two opportunities to launch LRO/LCROSS before its window closes.

4:29 PM, 6/14/09, Update: NASA aims for Wednesday shuttle launch, but official decision on Endeavour versus lunar mission deferred to Monday

NASA managers Sunday deferred making a formal decision on whether to reschedule the delayed shuttle Endeavour for launch Wednesday or whether to press ahead instead with launch of the agency's $583 million Lunar Reconnaissance Orbiter mission aboard an unmanned Atlas 5 rocket.

But with both missions facing tight launch windows, Mission Management Team Chairman LeRoy Cain said the agency's preference was to launch Endeavour on Wednesday, if possible, to maximize the number of launch opportunities for both programs.

"If shuttle goes first on the 17th, then the most opportunities we can give LRO is two, and that would be on the 19th and 20th," Cain said. "If LRO goes first on the 17th, then the most opportunities we could get for the shuttle is one opportunity, and that would be on the 20th."

Engineers prepare a gaseous hydrogen umbilical plate for seal replacement.
A leak in the vent line umbilical grounded Endeavour Saturday.
(Photo: NASA TV)

A final decision on how to proceed must be made Monday to provide enough time for the Air Force Eastern Range, which provides required tracking and telemetry support for all rockets launched from Florida, to set up its systems to support one launch or the other.

But Cain said if no additional problems develop, and if work to repair a leaky hydrogen vent line umbilical plate on Endeavour's external tank goes smoothly, NASA likely will opt to press ahead with an attempt to launch the shuttle at 5:40:50 a.m. Wednesday.

"In plan A, which is shuttle launching on the 17th and LRO has attempts on the 19th and 20th, we have three total launch opportunities between the two missions," Cain said. "In Plan B, LRO on the 17th and shuttle on the 20th, we only have two total launch opportunities between the two missions. So from an agency standpoint, we're trying to maximize our opportunities.

"We're going to see how the processing goes. If we have some good fortune, if we have some good weather, or at least not too much bad weather, in the next 24, 36 hours, then we think it's achievable for us to get to a (shuttle launch) on the 17th."

Engineers at launch pad 39A at the Kennedy Space Center worked Sunday to replace a seal inside the vent line umbilical plate that leaked during fueling Saturday, delaying Endeavour's launch on a space station assembly mission.

At the nearby Cape Canaveral Air Force Station, United Launch Alliance engineers pressed ahead with work to ready the Lunar Reconnaissance Orbiter for launch from complex 41 on a mission to map the moon in unprecedented detail. The LRO launch window opens Wednesday at 3:51 p.m. and closes at 4:11 p.m.

The forecast for Wednesday calls for a 70 percent chance of good weather for the shuttle's pre-dawn launch window and a 60 percent chance of acceptable conditions for the lunar orbiter's window Wednesday afternoon.

"The final decision on which mission we're going to launch on the 17th is in front of us," Cain said. "We didn't make it today because we don't have to, because the Range reconfiguration requirement deadline is not until sometime tomorrow. And so we're both proceeding in parallel paths toward the 17th. If nothing changes, it looks like the preference would be to maximize the opportunities, shuttle first. Again, a decision will be made tomorrow."

If LRO is not off the ground by June 20, the flight will slip to the end of the month. If Endeavour is not off the ground by June 20 or 21 at the latest, the shuttle launch will be delayed to July 11 because of temperature constraints related to the space station's orbit.

If the shuttle does indeed get the nod for a Wednesday launch try, Endeavour's interrupted countdown would resume at the T-minus 11-hour mark at 1:15 p.m. Tuesday.

Endeavour was grounded during fueling overnight Friday when the gaseous hydrogen vent line umbilical plate on the side of the shuttle's external fuel tank began leaking potentially dangerous vapors as the hydrogen section of the tank was filled.

A technician inspects the gaseous hydrogen vent line on the
shuttle Discovery's external tank. (Photo: NASA TV)

Some of the supercold liquid hydrogen propellant inside the tank constantly turns into a gas that is routed overboard through a vent line to a flare stack near the pad where it is harmlessly burned away. The vent line attaches to the tank at an umbilical plate that pulls away at liftoff.

During an attempt to launch the shuttle Discovery last March, a gaseous hydrogen leak in the umbilical plate triggered a four-day delay. Engineers were unable to duplicate the leak under ambient conditions - it only occurred when cryogenic hydrogen was filling the tank - but after replacing a critical internal seal, the umbilical worked normally and Discovery was able to take off.

A virtually identical scenario is playing out with Endeavour. Engineers were unable to duplicate the leak after the tank was drained and mission managers decided to press ahead with a seal replacement.

Launch Director Pete Nickolenko said engineers discovered small areas where the seal in question appeared to have pulled away from the external tank slightly, possibly due to exposure to cryogenic conditions. The gaps seen are similar to those found during troubleshooting of the leak that grounded Discovery in March.

Engineers are trying to figure out what caused seal problems in two of the last three shuttle flights, but in the meantime, "we are on the path of installing a new quick-disconnect and a new flight seal," Nickolenko said.

The work is expected to be finished early Tuesday.

"In summary, the team is processing on the path towards a launch attempt on the 17th," Nickolenko said. "The team is optimistic that our quick-disconnects and seal removal and replacement will fix the problem. THe schedule that we're moving toward is very tight, but it is achievable. All other turnaround activities are proceeding nominally."

3:10 AM, 6/13/09, Update: Endeavour launch delayed at least four days; conflict with launch of lunar mission yet to be resolved

Launch of the shuttle Endeavour, grounded by a gaseous hydrogen leak during fueling Saturday, is off until Wednesday at the earliest. But because of the already planned launch of NASA's Lunar Reconnaissance Orbiter satellite Wednesday, the shuttle team could be delayed to June 20, the last day this month Endeavour can be launched.

Mission managers plan to meet later this weekend to discuss troubleshooting and to assess their options, including negotiations with the Lunar Reconnaissance Orbiter project and the Air Force Eastern Range that provides telemetry and tracking support for all rockets launched from Florida.

"Obviously, the 17th is a range problem, there's a conflict out there with LRO/LCROSS," said Mike Moses, shuttle integration manager at the Kennedy Space Center. "We haven't even begun to work that yet. ... We'll start those negotiations tomorrow and see where we get, both with the Range and with the NASA payload."

In the meantime, shuttle engineers will press ahead with troubleshooting to figure out what went wrong during fueling.

Engineers began the three-hour fueling process at 9:52 p.m. Friday. As the hydrogen section of the tank fills up, some of the liquid turns into a gas that is carried away by a vent line. As Endeavour's tank was being topped off, sensors indicated higher-than-allowable levels of gaseous hydrogen at the ground umbilical plate, or GUP, that connects the vent line to the side of the shuttle's external tank.

A television view of the ground umbilical plate on the side of the
shuttle Endeavour's external tank that leaked during fueling.
(Photo: NASA TV)

The problem, which only shows up when supercold cryogenic propellants are flowing, was virtually identical to a leak in March that grounded the shuttle Discovery for four days, NASA officials said. In that case, engineers disassembled the umbilical and replaced a critical seal. While the "root cause" of the problem was never determined, the system worked normally during Discovery's subsequent launch attempt.

"We got into tanking on time," senior Launch Director Mike Leinbach said early Saturday. "Everything was going perfectly fine, per plan. But just like on the STS-119 mission, we suffered a leak at the ground umbilical carrier plate just as soon as we got into the topping part of the sequence on the hydrogen load.

"The signature was almost identical to what we had two flows ago. The guys on console cycled the valve as they did previously, they cycled the valve four times trying to clear up that leak. In the past, every now and then that'll work for us. This time, again, it didn't work for us. We were out of spec leakage at that disconnect.

"It's a four-day scrub turnaround is what we're estimating right now," he said. "That's a preliminary plan, but I would not expect it to be any shorter than that. ... It's going to be very, very similar to what we went through last time on STS-119."

Moses said engineers were surprised to encounter the same problem in two out of three launch campaigns. After the March leak, "we measured how that seal fits, we looked at it under a microscope, we looked at it under cryo conditions, we didn't really find anything that would tell us what common cause is."

"But obviously, something is going on, the second time in three flights, something is going on. So teams are being kicked off to go look at that. ... But really, our plan is going to be pretty much what it was last time, which is just R-and-R that seal and then we really have to tank again to see what happens."

That means Endeavour will be grounded until Wednesday at the earliest. But NASA's Lunar Reconnaissance Orbiter currently is schedulejd for launch atop an Atlas 5 rocket at 3:51 p.m. Wednesday.

It takes the Eastern Range two days to reconfigure its systems to support a different launch. If the LRO mission stays on track and takes off Wednesday afternoon as planned, the next opportunity for Endeavour would be before dawn on June 20.

But in that case, NASA would only have one day to get Endeavour off the ground or the flight would slip to July 11 because of temperature constraints related to the orbit of the International Space Station.

NASA managers want to get Endeavour off as soon as possible to avoid downstream delays for upcoming space station assembly missions as the shuttle program winds down toward retirement in 2010. But the LRO mission is a high priority as well and it's not yet clear how NASA might ultimately resolve the conflict.

"They only have a four-day window, it's a lunar rendezvous, so they have those four days and if they don't make that they have to wait two weeks before they could go again," said Moses.

"So there are two parts to that. One, we don't want them to miss their lunar rendezvous window because that's very difficult to replan around. The other thing is, the Range is kind of backing up, especially on the Atlas pad, there are a lot of payloads that are waiting for LRO to get going and having a payload that needs to wait every two weeks for its launch window to reopen could cause some problems. We're going to have those negotiations, I can't begin to foretell how they're going to go.

"We had pretty much agreed ahead of time that we would probably not bump them off the Range, but it would all depend on why we needed to scrub in the first place," Moses said. "We didn't really talk about a failure like this, we were mostly thinking weather. So we'll go and re-talk again. But I don't expect that we'll make them go away and we'll take that whole window. But if we do, we'd try the 17th and could go all the way through the 20th."

12:30 AM, 6/13/09, Update: LAUNCH SCRUBBED

Saturday's launch of the shuttle Endeavour has been scrubbed due to a hydrogen leak at or near a gaseous hydrogen umbilical plate on the side of the external tank that leaked during a launch a launch campaign in March. The scrub was called during fueling when sensors detected higher-than-allowable levels of hydrogen.

If the problem cannot be resolved in time for launch attempts Sunday or Monday, the flight will be delayed until after the planned June 17 launch of NASA's Lunar Reconnaissance Orbiter.

If the lunar orbiter takes off on time, NASA may be able to make additional attempts to launch Endeavour on June 19 and 20. After that, the flight would slip to July 11 because of temperature constraints related to the space station's orbit.

During the March launch of the shuttle Discovery, a gaseous hydrogen leak in the same area took four days to resolve when seals in a vent line had to be replaced and re-torqued. It is not yet clear, however, what will be needed to resolve Endeavour's problem.

Additional details will be posted as soon as possible.

10:00 PM, 6/12/09, Update: Shuttle fueling begins

Engineers began pumping a half-million gallons of liquid oxygen and hydrogen rocket fuel into the shuttle Endeavour's external tank late Friday, setting the stage for launch Saturday at 7:17:19 a.m. There are no technical problems of any significance at pad 39A and forecasters are continuing to predict near ideal weather at launch time. The three-hour fueling process started with transfer line chilldown at 9:52 p.m. The huge tank should be topped off and in stable replenish mode by around 1 a.m. Saturday. NASA television coverage of the final hours of Endeavour's countdown is scheduled to begin at 2 a.m. Commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra plan to don their bright orange pressure suits and head to the launch pad at 3:27 a.m. to begin strapping in. If all goes well, the shuttle's hatch will be closed a few minutes past 5 a.m.

12:40 PM, 6/12/09, Update: Shuttle Endeavour prepped for fueling

A protective gantry was rolled away from the shuttle Endeavour today, exposing the orbiter to view atop launch pad 39A and setting the stage for fueling and liftoff Saturday on a space station assembly mission.

The rotating service structure, which protects the shuttle from the elements during pad processing, was pulled away at 10:39 a.m. EDT while engineers in the launch control center 3.2 miles away worked through the final day of a smooth-ticking countdown.

"They haven't had any kind of issues," said a NASA spokeswoman. "The weather has been fantastic."

Shuttle Endeavour poised for launch atop pad 39A.
(Photo: Stephen Clark/Spaceflight Now)

If all goes well, engineers will begin loading the shuttle's external tank with a half-million gallons of supercold liquid oxygen and hydrogen rocket fuel starting around 9:52 p.m. The three-hour process should be complete by around 12:52 a.m. Saturday when the countdown will go into a standard two-hour 30-minute hold at the T-minus three-hour mark.

NASA television coverage is scheduled to begin at 2 a.m. and Endeavour's seven-member crew - commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra - plans to begin strapping in a few minutes before 4 a.m.

Launch is targeted for 7:17:19 a.m., roughly the moment Earth's rotation carries the launch pad into the plane of the International Space Station's orbit. Forecasters are continuing to predict near-ideal weather for launch.

Here is a timeline of countdown highlights (in EDT; best viewed with fixed-width font):

EDT...........EVENT

12:00 PM......Final thermal protection system, debris inspection
12:00 PM......Ascent switch list configured
02:52 PM......Resume countdown
02:52 PM......Cockpit configured for launch
03:22 PM......Pad clear of non-essential personnel
03:12 PM......Hydraulic system bite test
04:02 PM......Fuel cell activation
04:52 PM......Booster joint heater activation
05:22 PM......Master events controller pre-flight bite test
05:37 PM......Tanking weather update
06:22 PM......Final fueling preps; launch area clear
06:52 PM......Red crew assembled
07:37 PM......Fuel cell integrity checks complete

07:52 PM......Begin 2-hour built-in hold (T-minus 6 hours)
08:02 PM......Safe-and-arm PIC test
08:52 PM......External tank ready for loading
09:15 PM......Mission management team tanking meeting
09:52 PM......Resume countdown (T-minus 6 hours)

09:52 PM......Liquid oxygen (LO2), liquid hydrogen (LH2)
.............. transfer line chilldown
10:02 PM......Main propulsion system chill down
10:02 PM......LH2 slow fill
10:32 PM......LO2 slow fill
10:37 PM......Hydrogen low-level sensors go wet
10:42 PM......LO2 fast fill
10:52 PM......LH2 fast fill

Sat  06/13/09

12:47 AM......LH2 topping
12:52 AM......LH2 replenish
12:52 AM......LO2 replenish

12:52 AM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
12:52 AM......Closeout crew to white room
12:52 AM......External tank in stable replenish mode
01:07 AM......Astronaut support personnel comm checks
01:37 AM......Pre-ingress switch reconfig
02:00 AM......NASA TV coverage begins
02:52 AM......Final crew weather briefing
02:57 AM......Crew suit up begins
03:22 AM......Resume countdown (T-minus 3 hours)

03:27 AM......Crew departs O&C building
03:57 AM......Crew ingress
04:47 AM......Astronaut comm checks
05:12 AM......Hatch closure
05:42 AM......White room closeout

06:02 AM......Begin 10-minute built-in hold (T-minus 20m)
06:12 AM......NASA test director countdown briefing
06:12 AM......Resume countdown (T-minus 20m)

06:13 AM......Backup flight computer to OPS 1
06:17 AM......KSC area clear to launch

06:23 AM......Begin final built-in hold (T-minus 9m)
06:53 AM......NTD launch status verification
07:08:19 AM...Resume countdown (T-minus 9m)

07:09:49 AM...Orbiter access arm retraction
07:12:19 AM...Launch window opens
07:12:19 AM...Hydraulic power system (APU) start
07:12:24 AM...Terminate LO2 replenish
07:13:19 AM...Purge sequence 4 hydraulic test
07:13:19 AM...IMUs to inertial
07:13:24 AM...Aerosurface test profile
07:13:49 AM...Main engine steering test
07:14:24 AM...LO2 tank pressurization
07:14:29 AM...Gaseous oxygen vent arm retraction
07:14:44 AM...Fuel cells to internal reactants
07:14:49 AM...Clear caution-and-warning memory
07:15:19 AM...Crew closes visors
07:15:22 AM...LH2 tank pressurization
07:16:29 AM...Orbiter to internal power
07:16:48 AM...Shuttle computers take control of countdown
07:16:58 AM...Booster steering test
07:17:12 AM...Main engine start (T-6.6 seconds)
07:17:19 AM...Booster ignition (LAUNCH)

3:10 PM, 6/11/09, Update: Endeavour set for launch (mission preview)

The shuttle Endeavour is poised for blastoff Saturday on one of the most complex space station assembly missions yet attempted, a grueling 16-day flight to attach a Japanese experiment platform, deliver critical spare parts, replace massive solar array batteries and swap out a station crew member.

Five spacewalks by four astronauts will be required, along with carefully choreographed, near daily use of three robot arms, two on the station and one aboard the space shuttle, to move equipment, spare parts, experiments and spacewalkers from one work site to another.

Complicating the choreography, the station must host a combined crew of 13 - six full-time station astronauts and seven shuttle visitors - for the first time, putting the lab's life support systems, including its new water recycling system, toilets, oxygen generators and carbon dioxide scrubbers, to the test.

"It's like having your family descend on you for the holidays, right? And they're going to stay for a very long time. And they come, and they're bringing all their stuff," said Mike Moses, director of shuttle integration at the Kennedy Space Center.

But he said the combined crews are "more than ready" for the challenge, adding that with six full-time station astronauts on board, "I think what we're going to see is probably some unprecedented efficiencies" because "they know where to go, they know what the procedures are, they know how to get things done."

The Endeavour astronauts at launch pad 39A. (Photo: NASA)

"With the shuttle program ending in 2010, we had to pack the mission as much as we could. So our mission is probably reaching the limits of what one crew can do on a 16-day mission: five different spacewalks, we're basically operating at least two (robot) arms every day of the mission except for one, it is extremely intensive in the choreography that we do.

"But it is a construction mission," said Payette, making her second shuttle flight. "We are crane operators, we're construction workers, we're going to replace elements of the station, install new elements on the station, transfer equipment inside the station, we're going to disturb life for two weeks and then we're going to go home."

Lead spacewalker David Wolf, a physician-astronaut and Mir veteran making his fourth spaceflight, said the complexity of the mission is "not just from EVA (spacewalks). It's doing the EVA and robotics and the other internal transfer work that we have planned, all at once in a very complex choreography."

"It is busy, it is a sprint race for us and it's very interactive, it takes everyone (of the astronauts), mission control and the engineering teams to be with it real time, tracking as we go, to pull this off," he said.

Endeavour is scheduled for liftoff on the 127th shuttle mission at 7:17:15 a.m. Saturday, roughly the moment Earth's rotation carries launch pad 39A into the plane of the space station's orbit.

Joining Payette on the shuttle's upper flight deck will be veteran commander Mark Polansky, making his third flight, rookie pilot Douglas Hurley and first-time flier Christopher Cassidy, a Navy SEAL with combat experience in the caves of Afghanistan. Based on seat positions, Hurley will be the 499th individual to reach orbit and Cassidy will be the 500th.

Strapped in on the lower deck will be Wolf, physician-astronaut Thomas Marshburn and space station flight engineer Timothy Kopra, both making their first flights.

Kopra will trade places with Japanese astronaut Koichi Wakata as a member of the Expedition 20 crew, remaining behind aboard the International Space Station when Endeavour departs. Wakata, launched to the station in March aboard the shuttle Discovery, will take Kopra's place aboard the shuttle for the trip back to Earth.

"If I had to cherry pick a mission to be part of, it would be this one," Kopra, an Army helicopter pilot, told CBS News. "A fabulous space shuttle crew, it's very complex like a lot of our station missions, five EVAs using three robotic arms, transition to six-person crew and then to be part of that six-person crew and stay for a few months, I'm just really thrilled."

Along with the crew swap, the primary goals of the mission are to attach a porch-like external experiment platform to the Japanese Kibo laboratory module, to equip it with three experiment packages and to hook up TV cameras, data and electrical connections. Attachment of the Japanese Exposed Facility, or JEF, will complete the assembly of the station's most sophisticated laboratory suite.

The main Japanese lab module is equipped with its own airlock and its own robot arm to move experiments out to the exposed facility and back inside as needed.

"The Japanese Exposed Facility, or JEF as we tend to call it, is very impressive," Wolf said in a NASA interview. "It's a large external porch to the space station where high quality experiments can be conducted in the high vacuum of space. It's really an exceptionally valuable piece of real estate. It has its own robotic arm, the ability to do observations of the Earth and of the sky, astrophysics experiments, a very wide range of abilities."

Protecting against failures down the road, the astronauts also plan to mount a spare S-band antenna assembly on an external storage platform, along with a spare cooling system pump module and a replacement drive unit for the station's robot arm transporter.

In one of the more challenging tasks faced by the spacewalkers, six 375-pound batteries will be replaced in the station's oldest set of solar arrays on the far left end of the lab's main power truss. The battery replacement will be spread over two spacewalks.

"The P6 batteries have been up there since December of 2000, so they've been up there quite a while," said Kirk Shireman, deputy director of the space station program at the Johnson Space Center. "They're reaching the end of their life (and) we need to swap them out. We'll be doing that for the first time, it's very challenging."

The spacewalkers also will attempt to rewire a gyroscope circuit, install another television camera to provide additional external views and deploy a jammed external storage mount on the left side of the power truss. The crew plans to deploy two others on the right side of the station that are needed to hold spare parts and equipment being stockpiled as the shuttle program winds down toward retirement in 2010.

Finally, the astronauts will make preparations for the debut flight of a Japanese cargo ship in September. The HTV spacecraft is designed to be plucked out of open space by the station's robot arm for docking to the Harmony module's upper port.

Wolf and Kopra will carry out the mission's first spacewalk, followed by EVAs with Wolf and Marshburn, Wolf and Cassidy and then a final two excursions by Cassidy and Marshburn. Polansky, Hurley and Payette will operate the shuttle and station robot arms, moving from the orbiter to the station and back as needed, assisted by Wakata.

In several cases, robot arm operations and equipment transfers will be going on while the spacewalkers are doing something else at a different location.

"It's an extremely challenging, complex mission," Polansky told CBS News. "The robotics that are interlaced with the spacewalks are complicated, we do complicated robotics every single day of the mission, starting with the first full day in orbit all the way through. We just never get to come up for air. It's something I think about a lot."

And with a combined crew of 13 aboard the space station, the pace will be hectic to say the least.

"It'll be very interesting to see how we're going to adapt to that many people inside a relatively small vehicle," Payette said. "I mean, it's very roomy compared to the comfort of the space shuttle, but it's still a very confined environment. There will be growing pains, how to adapt to one another, not to step on one another, not to all speak on the communications loops at the same time.

"But I think it'll be awesome for the first time to have that many people in space. It will really be the beginning of a permanent settlement in space, because that's what it will be in the future and we're trying it out for the first time. It'll be very interesting, the social aspects of having that many people on board from different nationalities."

Said Wolf: "We're kind of having a population explosion in space, you know, with the 13 or so people will be up there. That will be interesting. ... We're going to have to learn to operate and keep all that organized. And these are busy schedules, with a lot of activity going on, so it's important that we learn how to handle that, manage it."

Endeavour's road to orbit began in April when the shuttle was hauled out to launch pad 39B to serve as an emergency rescue vehicle for the crew of the shuttle Atlantis, launched May 11 on a fifth and final mission to service the Hubble Space Telescope.

Toward the end of Atlantis' mission, engineers started a countdown for Endeavour to protect against the possibility of damage spotted late in the Hubble mission. When it became clear a rescue flight would not be needed, the countdown was halted and engineers moved Endeavour to pad 39A for work to ready the ship for launch Saturday.

Other than interruptions prompted by stormy weather, Endeavour's processing has been relatively smooth. While engineers were unable to trace the cause of an avionics short circuit that knocked out a redundant flight control system during Atlantis' launch, NASA managers said Endeavour's wiring is newer and has been inspected more recently. No similar problems are expected.

Assuming an on-time launch, Endeavour will dock with the space station around 3:55 a.m. on Monday, June 15. The mission will be conducted during the deep overnight hours in the United States, with the five spacewalks beginning between 1:42 a.m. and 10:12 p.m. on June 16, 18, 20, 21 and 24. Undocking is expected around 8:11 p.m. on June 26 with landing back at the Kennedy Space Center scheduled for 12:18 a.m. on June 29.

"I sum it up this way," Payette said. "Six people, five EVAs, three (robot) arms, seven (payload) handoffs, 16 days. It is going to be an action-packed flight. So if you're bored, please tune in."

Endeavour's mission is being flown against a backdrop of high anxiety as NASA's post-Columbia drive to develop a new rocket system to replace the space shuttle comes under renewed scrutiny. The first public hearing by a presidential panel charged with assessing NASA's manned space program is scheduled for June 17.

The Bush administration ordered NASA to complete the space station and retire the shuttle by the end of 2010 to free up funds to pay for development of a new rocket system that would be safer and cheaper to operate. The ultimate goal of the program was to establish Antarctica-style bases on the moon beginning in the early 2020s.

Under the leadership of former Administrator Mike Griffin, NASA opted to develop the Ares 1 rocket, using a shuttle solid-fuel booster as a first stage and a hydrogen-fueled second stage, to launch Orion crew capsules to low-Earth orbit. A giant unmanned rocket called the Ares 5 is envisioned to propel lunar landers and attached Orion spacecraft to the moon.

But the Bush administration provided little in the way of additional funding to pay for the new rockets and NASA expects a five-year gap between the end of shuttle operations and the debut of Ares 1/Orion. In the interim, U.S. astronauts will have to hitch rides to the space station aboard Russian Soyuz ferry craft.

Despite the Apollo heritage of the new upper stage and the remarkable safety record of space shuttle boosters - one failure in 127 shuttle missions, or 252 booster flights - critics have relentlessly attacked the Ares/Orion architecture, arguing that alternatives based on heavy lift Delta or Atlas rockets, or a new family of liquid-fueled boosters, makes more sense.

Emotions run high on all sides, fueled by the internet and bloggers, the perception of technical problems with the Ares program, distrust of the NASA bureaucracy and supporters of commercial rocket agendas.

The Obama administration recently ordered an independent assessment of NASA's manned space program, a review headed by former Lockheed Martin CEO Norman Augustine, that is expected to be completed by August.

In the meantime, the White House Office of Management and Budget has deleted $3.1 billion from NASA's projected budget through 2013. That money is needed to begin development of the Ares 5 moon rocket and without it, NASA managers say, the moon program will be deferred if not eliminated.

Administration officials say money can be returned to the projected budget depending on the conclusions of the Augustine review. But for now, the future of NASA's manned space program is uncertain, including use of the International Space Station. As it now stands, U.S. participation in the project will end in 2015 unless additional funding is approved.

NASA has resolutely moved ahead with its ongoing programs and launch of a sophisticated satellite to begin mapping the moon in unprecedented detail is scheduled for June 17, the same day the Augustine panel will hold its first public hearing.

The Endeavour astronauts will be asleep, facing their second spacewalk in the deep overnight hours as NASA presses ahead with a final eight shuttle missions to complete the space station and stock it with the supplies and spare parts needed to keep it viable after the shuttle is retired.

Endeavour's mission comes on the heels of the May 27 launch of a Russian Soyuz capsule that ferried three additional crew members to the space station, boosting the lab's full-time crew to six for the first time.

Station commander Gennady Padalka, NASA flight engineer Michael Barratt and Wakata were joined by cosmonaut Roman Romanenko, European Space Agency astronaut Frank De Winne of Belgium and Canadian Space Agency astronaut Robert Thirsk.

"Six-person crew is a milestone in the history of the International Space Station," Thirsk said before launch. "In a big way, the International Space Station will be able to fulfill it's primary purpose, which is to function as a world-class orbiting laboratory for medical science and materials science."

The lab complex has been stocked with enough food to last the expanded crew through October even if subsequent shuttle and unmanned resupply missions get delayed. Oxygen is generated on board by U.S. and Russian systems and fresh water is delivered by shuttle crews and automated Russian supply ships.

But in a major milestone, a sophisticated water recycling system was installed late last year and, after startup problems were resolved, the new hardware was cleared for everyday use. The system recycles condensate and urine from a U.S. toilet in the Destiny lab module, generating ultra-pure water for drinking, crew hygiene and oxygen generation.

The water recycling system will be critical to sustaining a six-person crew after the space shuttle is retired late next year.

"It will be a challenge for everybody to make sure we can sustain six persons on orbit," De Winne said before launch. "I think it shows a great example to the rest of the world that if nations want to work together for something great, for something wonderful, for something for the future of our kids, that we can achieve incredible things."

Coping with a combined crew of 13 during Endeavour's mission will be another challenge, one that will pose a severe test of the station's life support systems.

"Oxygen, plenty of oxygen supplied by the O2 supplies on board the shuttle, we have the oxygen generation system on board the U.S. segment, which is functioning, and the Elektron, which is the Russian system. So oxygen production is not an issue," Shireman said.

"Carbon dioxide, we have the Vozdukh, which is the Russian carbon dioxide scrubber, we have the CDRA, the carbon dioxide removal assembly aboard the U.S. segment. Those two together cannot take care of 13 completely, so we'll actually be utilizing two lithium hydroxide canisters on board the shuttle every day to keep the carbon dioxide within its limits. We have a stockpile plus margin aboard ISS, so that's not an issue.

"In terms of food preparation, we have basically three galleys, the shuttle has a galley, the ISS in the U.S. segment has a galley and then there's the Russian segment galley and food warmers, all those things are functional. We'll have plenty of food preparation capability so we don't expect any difficulties there.

"To the best of our ability, we've tried to think of all those things that having additional people on board dictate," Shireman said. "I think we have a good plan at this point in time. I expect we'll learn and adapt during the mission as we see it unfold."

As for bathroom management, Shireman said he did not expect any problems.

"We've been planning for this for quite some time," he said. "We have the whole thing choreographed. When the shuttle crew arrives, there's actually three functioning bathrooms, so there's actually more bathrooms per person than we've had in the past, if you think about it."

Up until now, the station's science output has been limited because assembly was ongoing and the lab's three full-time crew members were busy simply maintaining the growing complex. With a crew of six, the time devoted to scientific research is expected to triple, jumping from 20 hours a week to more than 70.

"We've been building the International Space Station for 10 years now and we've finally gotten to a point now where it has some incredible laboratory facilities and six people on board the station to do some science," Thirsk said. "So you're going to see over 1,000 hours (in the near term) of crew time devoted to research and development."

More than 100 experiments are planned for the Expedition 20 crew.

"We're going to be doing life science work, we're going to be doing medical operations, plant biology, fluid physics, materials processing, exploiting this weightless environment of space," Thirsk said. "We're ... doing some great, fundamental science for preparing humans for the next venture into space."

But for now, it's not clear what that next venture will be.

11:30 AM, 6/10/09, Update: Countdown begins; weather improves to 90 percent 'go' for Saturday launch

The countdown began today for the shuttle Endeavour's launch Saturday on a complex 16-day space station assembly mission. There are no technical problems of any significance at launch complex 39A and forecasters are predicting a 90 percent chance of good weather.

"The launch team and the flight crew are all very excited to be in launch countdown, we've worked hard to get here and we're all eager to get Endeavour and her crew on the way to the International Space Station," said NASA Test Director Steve Payne.

"Right now, Endeavour's in great shape, the launch countdown is progressing nominally, the weather looks like it might cooperate and we are ready to fly this mission."

Commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra flew to the Kennedy Space Center from Houston late Monday to prepare for launch.

The countdown began on time at 9 a.m. today, setting up a launch attempt at 7:17:15 a.m. EDT Saturday, roughly the moment Earth's rotation carries launch pad 39A into the plane of the space station's orbit. The shuttle has enough power to launch five minutes to either side of that "in-plane" time, but NASA targets the middle of the 10-minute window to maximize ascent performance.

Forecasters are predicting virtually ideal weather Saturday, with light winds and only a 10 percent chance of cumulus clouds that could raise a concern about rocket-triggered lightning. NASA's emergency runways in New Mexico, California, Spain and France are all expected to be "go" for launch.

On Sunday and Monday, the forecast drops to 80 percent go, with cumulus clouds and showers possible within 20 nautical miles of the Shuttle Landing Facility. Conditions at three of NASA's five backup landing sites also are expected to deteriorate, but at least one site should be available in both Europe and the United States.

"Right now, weather's looking very good for launch time," said Air Force Lt. Col. Patrick Barrett, a forecaster with the 45th Weather Squadron at nearby Patrick Air Force Base. "I think the weather is cooperating very well for us and we should be good to go."

NASA only has three days to get Endeavour off the pad or the flight will be delayed until after the planned June 17 launch of NASA's Lunar Reconnaissance Orbiter.

If the launch is delayed, and if the lunar orbiter takes off on time, NASA may be able to make additional attempts to launch Endeavour on June 19 and 20. After that, the flight would slip to July 11 because of temperature constraints related to the space station's orbit.

3:15 PM, 6/9/09, Update: Endeavour set for start of countdown Wednesday; weather 80 percent 'go' for Saturday launch (COMBINING with earlier story about crew arrival Monday)

Engineers at the Kennedy Space Center are gearing up to start the shuttle Endeavour's countdown Wednesday, with forecasters predicting an 80 percent chance of good weather for launch Saturday on a space station assembly mission.

Endeavour's crew - commander Mark Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra - flew to the Kennedy Space Center from Houston late Monday, landing at the shuttle runway just before midnight.

"Thanks for coming out at the lovely hour of just past, let me see, what time is it, midnight here at KSC," Polansky told reporters. "The STS-127 crew, we're absolutely thrilled to be down here in preparation for Saturday's launch of Endeavour."

NASA Test Director Charlene Blackwell-Thompson said today there are no technical problems of any significance at pad 39A that would interfere with the start of Endeavour's countdown at 9 a.m. Wednesday. Endeavour's liftoff is targeted for 7:17:15 a.m. Saturday.

"It's only been a little over a week since we've been at pad A," said Blackwell-Thompson. "We arrived at pad A on May 31 and last week, the flight crew was in town to do the terminal countdown demonstration test. We completed that Thursday, where we rehearsed late countdown operations, and that all went very well."

Over the weekend, "we finished up our payload activities, all our testing work is complete, our closeouts were finished up on Saturday and we closed the payload bay doors on Saturday afternoon. Our ordnance operations also were worked over the weekend, we completed them Sunday and we began putting on the flight doors, they were completed yesterday, and all of the aft closeouts, aft confidence checks, are now complete. I'm happy to report both the midbody and the aft are closed out for flight."

The shuttle's main propulsion system was pressurized early today and "in summary, all of our systems are in great shape, our launch countdown preparations are complete, I have no issues to report,' she said. "The STS-127 flight crew, Endeavour and the launch team are all ready to proceed."

Forecasters with the 45th Weather Squadron at nearby Patrick Air Force Base are predicting an 80 percent chance of acceptable weather Saturday, Sunday and Monday. The Spaceflight Meteorology Group at the Johnson Space Center in Houston will issue its initial forecast Wednesday.

As it now stands, NASA only has three days to get Endeavour off the pad or the flight will be delayed until after the planned June 17 launch of NASA's Lunar Reconnaissance Orbiter.

If the shuttle launch is delayed past Monday, and if the lunar orbiter takes off on time next Wednesday, NASA may be able to make additional attempts to launch Endeavour on June 19 and 20. After that, the flight would slip to July 11 because of temperature constraints related to the space station's orbit.

The goals of the 16-day five-spacewalk mission are to deliver and attach a Japanese experiment platform; to replace aging solar array batteries; to deliver critical spare parts; and to ferry Kopra to the lab complex to replace Japanese astronaut Koichi Wakata.

"Thank you for taking the time to come and see us at this ungodly hour," Payette told reporters at the shuttle runway late Monday. "This represents, of course, one of those flights where we have to shift in a completely different time zone in order to synch up with the space station. And for that, we become a bit of a stealth flight."

The mission will be conducted in the deep overnight U.S. time with the first of the crew's five spacewalks beginning around 1:40 a.m. on June 16. The astronauts have been sleep shifting to prepare for the overnight work hours and all seven said they were eager to take off.

"I just think it's really incredible to be part of a team that has six people in orbit now on the International Space Station and when we get there, we'll have 13 on board for the very first time," Polansky said. "We'll have all of the major international partner space agencies represented at once. And if that's not enough, we're going to be challenged with five spacewalks, coupled with complicated robotics using three different (mechanical) arms, all at the same time.

"So we're really happy to be a part of that," Polansky said. "As astronauts, we often get a lot of the spotlight, but this mission is a really great reminder of the countless number of men and women around the globe who work so tirelessly to go ahead and prepare missions like this and others, and that's something that I think we're all really proud to be a part of."

03:05 PM, 6/4/09, Update: Astronauts practice countdown procedures; station spacewalk on tap early Friday

The Endeavour astronauts, wearing bright orange pressure suits, strapped in aboard the shuttle today for a dress-rehearsal countdown that sets the stage for launch June 13 on a space station assembly mission. The station crew, meanwhile, prepared for a spacewalk early Friday, the first of two needed to rig the Russian Zvezda module for attachment of a new docking port.

The Endeavour astronauts pose for pictures before heading to launch
pad 39A Thursday for a dress-rehearsal countdown.
(Photo: NASA)

At the Kennedy Space Center, the practice countdown highlighting the crew's terminal countdown demonstration test, or TCDT, ended with the simulated ignition and shutdown of the shuttle's main engines.

"I personally have always thought it's a really important, necessary part of what the entire team does," commander Mark Polansky said Wednesday. "It focuses the team, it certainly gets them to look at a lot of things they're going to see on launch day. If there are going to be any glitches, now is the time to find it out.

"From the crew perspective, for some people, they've never, ever gotten up to a vehicle and strapped in one before. So, I think it gives you a certain familiarity that will pay dividends when you do it for real."

Polansky, pilot Douglas Hurley, Canadian flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra planned to fly back to Houston late today and to enter medical quarantine Saturday.

If all goes well, the astronauts will fly back to Florida next week for the start of their countdown at 9 a.m. Wednesday. Launch is targeted for 7:17 a.m. June 13.

Aboard the space station Thursday, commander Gennady Padalka and NASA flight engineer Michael Barratt prepared for a spacewalk early Friday to install docking system antennas on the upper port of the Russian Zvezda command module. Padalka and Barratt plan a second, internal spacewalk Wednesday to make interior modifications.

A new docking module, known as MRM-2, is scheduled for launch atop a Soyuz rocket on Nov. 10. Once attached to the station, it will add a fourth Russian docking port to support the increased traffic required by a full-time crew of six.

For Friday's five-hour excursion, Padalka, call sign EV-1, will be wearing an upgraded Russian Orlan MK suit with red stripes while Barratt, EV-2, will be wearing a suit with blue stripes. The spacewalk is scheduled to begin around 2:45 a.m. EDT.

This will be the 124th spacewalk devoted to station assembly and maintenance since construction began in 1998, the fifth so far this year, the seventh overall for Padalka and the first for Barratt. Going into Friday's excursion, more than 80 astronauts and cosmonauts representing the United States, Russia, Japan, Canada, Germany, France and Sweden had logged 775 hours of space station EVA time.

The KURS antennas being installed by Padalka and Barratt are passive elements in a system that will enable the MRM-2 docking module to home in on the station, line up and dock at the zenith port of the Zvezda command module.

At present, two three-seat Soyuz lifeboats are docked at the station, one at Zarya and the other at Zvezda's aft port. An unmanned Progress supply ship is attached to the Pirs docking module on Zvezda's Earth-facing port. The MRM-2 docking module scheduled for launch in November will go on the zenith port directly above and across from Pirs.

Yet another docking module, known as MRM-1, is scheduled for launch next year aboard a space shuttle. It will be attached to Zarya's downward facing port, providing the clearance needed for planned U.S. Orion crew capsules to dock at a downward-facing port in the station's U.S. Unity module.

Two spacewalks are planned to outfit the upper docking port of the
Russian Zvezda module for attachment of a new docking module.
(Photo: NASA)

During the upcoming spacewalks, the station crew will be split up to make sure everyone has access to a Soyuz lifeboat at all times. Wakata will join Barratt and Padalka in the Russian segment of the station, with access to the Soyuz docked at the command module's aft port, while Frank De Winne, Robert Thirsk and Roman Romanenko remain in the forward U.S. segment of the lab, with access to the Soyuz docked to the Zarya module's Earth-facing port. The hatchway between Zarya and Zvezda will be closed.

"The antennas installed on the station are the passive system where the active antenna are on the arriving vehicle," said David Korth, NASA's Expedition 20 spacewalk director. "For this particular EVA, the first set of antennas ... are for range, range-rate and roll misalignment. The second antenna block to be installed (is) a relative attitude measurement antenna.

"So we'll be installing both of these antennas, routing all the cabling externally. Several weeks ago, the crew began performing internal cable routing so at the end of this EVA, these will be functional antennas. In fact, toward the end of the EVA we will be performing a quick continuity check to verify all the signal paths are correct."

At the end of the spacewalk, Barratt will anchor himself to a telescoping Russian crane and Padalka will extend his crewmate up above Zvezda's zenith port. Barratt then will photograph the area to help Russian engineers confirm the new antennas are properly oriented.

"Once he takes the photos, he will come back in," Korth said. "At this point, this is when the Russian ground team will perform the continuity checks of the antennas to make sure everything is wired correctly. And then the crew will head back into the Pirs docking compartment, thus ending EVA-22."

NASA graphic showing Barratt, on the end of the Russian Strela boom,
photographing the Zvezda module's zenith port.
(Photo: NASA)

For the spacewalk Wednesday, Gennady and Barratt will remain inside the Zvezda module's forward transfer compartment, sealed off from the rest of the station and working in vacuum while connected to umbilicals. The ball-shaped transfer compartment connects Zvezda to the Zarya module and features upward- and downward-facing hatches. Pirs is attached to the Earth-facing port while the new MRM-2 module will be attached to the zenith port.

The goal of the second EVA on June 10 is to install a docking cone on the zenith port to complete preparations for the new module's arrival in November. The internal spacewalk is expected to last about an hour. A few hours after its conclusion, NASA plans to start Endeavour's countdown to launch.

7:45 PM, 6/3/09, Update: Shuttle Endeavour cleared for June 13 launch; astronauts review emergency procedures; practice countdown on tap

While the shuttle Endeavour's crew reviewed emergency procedures at the launch pad Wednesday, NASA managers held an executive-level flight readiness review and cleared the ship for blastoff June 13, at 7:17:15 a.m., on a complex space station assembly mission.

NASA Launch Director Pete Nickolenko, directing his first shuttle launch campaign, said there is no contingency time left in the schedule to handle unexpected problems. But so far, the shuttle's systems are checking out normally and the team is optimistic about starting the countdown next Wednesday, at 9 a.m., for a launch try one week from Saturday.

"We're running on all cylinders right now," Nickolenko said. "We're hitting our stride. The pace that we are challenged to work towards to make the manifest is going to require us to keep on pace and keep that work flowing. ... But it's all doable, manageable, the teams are seasoned and I believe they're focused."

Over the past month, NASA launched the shuttle Atlantis on a successful mission to service the Hubble Space Telescope, the Russian space agency launched an additional three crew members to the International Space Station, Endeavour was moved from pad 39B to pad 39A for final processing and Atlantis was returned to Florida from California where it landed May 24.

Endeavour's crew - commander Mark Polansky, pilot Douglas Hurley, flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra - flew to Florida Tuesday and reviewed emergency procedures at the pad Wednesday. All seven plan to strap in aboard the shuttle Thursday for a dress-rehearsal countdown.

Endeavour's crew at pad 39A. (Photo: William Harwood)

Aboard the space station, meanwhile, commander Gennady Padalka and NASA flight engineer Michael Barratt plan to carry out two spacewalks, one Friday and the other next Wednesday, to rig the Zvezda command module for the eventual attachment of another docking port.

"It's been a really amazing schedule over the last couple of months," Polansky said today at the launch pad. "It's tight from the standpoint that we're here in Florida to climb in the vehicle tomorrow. We're going to go back home, take a day off, go into quarantine Saturday, come back down here Monday night and launch next Saturday. I mean, that's really tight.

"But I know from a training perspective, we're ready," he said. "It would be great if we could just climb in and go tomorrow, but I think our families would be a little upset because they're not here!"

The 16-day flight features five spacewalks to install an external experiment platform on the Japanese Kibo research module, to swap out batteries in the station's oldest set of solar arrays and to deliver critical spare parts. Endeavour also will ferry Kopra to the lab complex for an extended stay and bring Japanese station flier Koichi Wakata back to Earth.

Endeavour was hauled to pad 39B in April to serve as a rescue vehicle for the crew of Atlantis. In the Hubble Space Telescope's orbit, the Atlantis astronauts could not seek safe haven aboard the space station if any major problem developed that might prevent a safe re-entry.

Engineers actually started a countdown for Endeavour late in Atlantis' mission to keep the rescue option open as long as possible. As it turned out, no such flight was needed and after bad weather blocked multiple attempts to bring Atlantis back to Florida, the ship was diverted to Edwards Air Force Base, Calif.

NASA flight directors and mission operations managers, at the Kennedy
Space Center for a flight readiness review, watch Atlantis' return to Florida.
(Photo: Ben Cooper/Spaceflightnow.com)

But the wisdom of processing Endeavour in parallel was made clear during a post-landing inspection of Atlantis. Space debris, a greater threat at Hubble's high altitude, apparently hit one of the shuttle's braking rocket nozzles, damaging the inner and outer surfaces. The shuttle spent much of the mission flying tail first to shield more sensitive areas from debris impacts.

As it now stands, NASA will only have three days to get Endeavour off the pad or the flight will be delayed until after the planned June 17 launch of NASA's Lunar Reconnaissance Orbiter. Going into the campaign, Nickolenko said the team would make two back-to-back attempts if necessary, but not three.

If the launch is delayed, and if the lunar orbiter takes off on time, NASA may be able to make additional attempts to launch Endeavour on June 19 and 20. After that, the flight would slip to July 11 because of temperature constraints related to the space station's orbit.

"The folks have done just a tremendous job getting ready to go fly again," said Bill Gerstenmaier, chief of space operations at NASA headquarters. "The Atlantis mission was a tremendous success and it really enabled us to be here. As we went through the flight readiness review today, it became really obvious that Atlantis was a very clean vehicle, it had very few anomalies. ... We didn't have a lot to talk about. The vehicle was really in great shape."

One question mark after Atlantis' flight was what caused the failure of an avionics box just before liftoff May 11. The box in question, one of four used to control the movement of the shuttle's elevons and rudder-speedbrake assembly, shut down moments after main engine ignition, the apparent victim of a short circuit.

The failure did not affect the shuttle's climb to orbit or its re-entry. But engineers wanted to make sure the issue was understood in case it was the result of some fleet-wide problem, or wiring deficiency, that might affect Endeavour.

An inspection of the wiring leading into and out of the box in question was carried out at Edwards and no obvious shorts were found. Likewise, a resistance test found no issues that would confirm a short. Engineers now plan to inspect the box itself as soon as it can be removed from Atlantis' aft avionics bay.

In the meantime, a detailed analysis was carried out indicating the odds of a similar problem aboard Endeavour were sufficiently remote to press ahead for flight. Unless an obvious problem is found aboard Atlantis that would raise a concern for Endeavour, the launch team plans to proceed with flight.

Another issue that was discussed at the flight readiness review was the loss of foam insulation from Atlantis' external tank that impacted the ship's forward right wing in an area known as the chine. While the debris caused minor impact damage to several heat-shield tiles, it did not pose any threat to the crew and no in-flight repairs were needed.

But because the foam came from the upper liquid oxygen section of the tank, which poses more of a threat to the shuttle's heat shield, engineers are paying close attention to make sure the issue is understood and that it's not a sign of a more serious problem.

Most other foam losses experienced in recent flights have come from the liquid hydrogen section of the tank, caused by temperature changes as the fuel is consumed. In those cases, foam releases occur late in the ascent, after the shuttle is out of the thick lower atmosphere, and pose little or no threat to the heat shield.

That mechanism does not explain foam losses from foam on the oxygen tank, or its main feed line, like that seen during Atlantis' ascent.

"The other foam losses we've seen have been back on the hydrogen tank, where it's the cryo-pumping foam loss that occurs typically late," Gerstenmaier said. "If foam comes off in this area (of the oxygen tank), it's going to come back to the chine area like we saw on Atlantis, or it'll come back to the (wing leading edge) area. So this is a very sensitive area from a transport standpoint.

"So again, it's not out of family. In fact, it's consistent with what we've seen before, there's no real indications here we've got a problem. But in the spirit of preventing a future problem, (we're looking at) is there something we can learn from this?"

11:30 AM, 6/1/09, Update: Atlantis heads for Florida

The space shuttle Atlantis, bolted to the back of a NASA 747 jumbo jet, began its two-day trip from California to the Kennedy Space Center Monday at 11:06 a.m. EDT. Atlantis closed out a Hubble Space Telescope repair mission May 24 with a landing at Edwards Air Force Base, Calif., because of stormy weather in Florida.

Atlantis begins its trip back to the Kennedy Space Center
(Photo: NASA TV)

Engineers are anxious to get Atlantis back to Florida to troubleshoot an avionics failure during launch May 11. The problem with a redundant aerosurface actuator control box caused no problems for Atlantis, but engineers want to make sure there is no generic wiring issue that could affect the shuttle Endeavour, scheduled for launch June 13.

12:00 PM, 5/31/09, Update: Shuttle Endeavour moved to pad 39A

The space shuttle Endeavour was moved from pad 39B to nearby pad 39A Sunday for launch June 13 on NASA's next space station assembly mission. The 3.4-mile trip atop an Apollo-era crawler-transporter began at 3:16 a.m. and was completed by 11:42 a.m.

The shuttle Endeavour reaches launch pad 39A
(Photo: NASA TV)

Endeavour's crew - commander Mark Polansky, pilot Douglas Hurley, flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra - plans to fly to the Kennedy Space Center Tuesday to review launch pad emergency procedures and to participate in a practice countdown Thursday.

NASA managers, meanwhile, will hold an executive-level flight readiness review Wednesday to assess Endeavour's launch processing. One item on the agenda will be a discussion of a presumed short circuit during the shuttle Atlantis' launch May 11 that knocked out one of four avionics boxes used to control the hydraulic positioning of the shuttle's elevons and rudder/speedbrake.

The short had no impact on Atlantis' launch or re-entry, but engineers want to make sure there is no generic wiring problem that could affect Endeavour.

Atlantis was diverted to a California landing May 24 and its cross-country ferry flight back to Florida was not expected to begin until Monday. As a result, engineers will have little time to inspect Atlantis and trace the failure before the start of Endeavour's countdown to blastoff.

NASA only has three days to get Endeavour off the ground in June or the flight will be delayed one month. The short window is the result of a conflict with another high-priority mission - launch of NASA's Lunar Reconnaissance Orbiter on June 17 - and temperature constraints due to the space station's orbit.

4:00 PM, 5/29/09, Update: NASA managers decide to press ahead with Endeavour launch preparations; June 13 launch target still possible, officials say, despite processing delays

NASA managers met Friday and decided to press ahead with work to ready the shuttle Endeavour for launch June 13 on a five-spacewalk space station assembly mission while continuing an analysis of a short circuit that knocked an avionics unit off line during the shuttle Atlantis' liftoff May 11.

An executive-level flight readiness review is planned for next Wednesday to assess the status of launch processing and to set an official launch date. While the short circuit analysis is not complete, engineers are optimistic it will have no impact on Endeavour's launch.

The weather, however, is another matter. To make the June 13 target, Endeavour must be moved from pad 39B, where it was on stand-by for emergency rescue duty during Atlantis' Hubble Space Telescope servicing mission, to pad 39A on Sunday.

Rollover had been targeted for Friday, but it has now slipped to Sunday, primarily because of stormy weather that delayed rollover preparations. With no contingency time left in the processing schedule to handle unexpected problems, another rollover delay - or any other significant issue - likely would delay launch.

As it now stands, NASA only has three days to get Endeavour off the ground in June or the flight will be delayed one month. The short window is the result of a conflict with another high-priority mission - launch of NASA's Lunar Reconnaissance Orbiter on June 17 - and temperature constraints due to the space station's orbit.

If Endeavour misses the three-day June launch window, the flight will slip to around July 11, based on the most recent analysis of the station's trajectory.

Along with moving Endeavour to pad 39A Sunday, NASA also plans to begin the shuttle Atlantis's ferry flight back to the Kennedy Space Center from Edwards Air Force Base, Calif., where the orbiter landed last weekend.

Because of its diversion to California and the time needed to prepare the ship for its cross country flight atop NASA's 747 transport jet, engineers have not yet gained access to the aft avionics bay where aerosurface actuator No. 1, the unit that failed during launch, is located.

Based on telemetry, engineers believe a short circuit in the wiring leading to or from the box triggered the failure, not a problem with the box itself. The unit is part of a redundant system used to move the shuttle's elevons and rudder/speedbrake and its failure had no impact on Atlantis' climb to space or subsequent re-entry.

But engineers want to make sure the short is not the result of any kind of fleet-wide wiring problem. As a result, ASA-1 will be pulled from Atlantis after its return to Florida next week and subjected to inspections and electrical tests to help isolate the issue.

Built to replace the shuttle Challenger, Endeavour is NASA's newest space shuttle and engineers are confident its wiring is in good shape. But if any problems are found, engineers will re-assess the launch schedule and what, if anything, might be needed to clear the ship for flight.

Hoping for the best, Atlantis commander Mark Polansky, pilot Douglas Hurley, flight engineer Julie Payette, David Wolf, Christopher Cassidy, Thomas Marshburn and space station flight engineer Timothy Kopra plan to fly to Florida Tuesday to review launch pad emergency procedures and to participate in a practice countdown Thursday.

The primary goals of Endeavour's mission are to attach an external experiment platform to the Japanese Kibo laboratory, to replace batteries on the space station's oldest set of solar arrays, to deliver critical spare parts and to perform a variety of get-ahead tasks for upcoming assembly flights.

The space station program achieved a major milestone Friday with arrival of three fresh crew members, boosting the lab's full-time crew to six.

Before Endeavour's arrival, Expedition 20 commander Gennady Padalka and Michael Barratt plan to carry out two spacewalks June 5 and 10 - the day Endeavour's countdown is expected to begin - to prepare the Russian Zvezda command module for the attachment of a new docking port.

Delayed two days by stormy Florida weather, the shuttle Atlantis glided to a California landing today, closing out a successful mission to overhaul the Hubble Space Telescope with a picture-perfect Mojave Desert touchdown.

With commander Scott Altman and pilot Gregory C. Johnson at the controls, Atlantis crossed the coast of California northwest of Los Angeles on a steep descent to Edwards Air Force Base, rattling the countryside with twin sonic booms.

Taking over manual control at an altitude of about 50,000 feet, Altman guided the shuttle through a sweeping 200-degree left-overhead turn to line up on runway 22 at the fabled Air Force test center.

As Altman flared the shuttle's descent and pulled its nose up slightly on final approach, Johnson lowered the landing gear and Atlantis settled to a smooth touchdown at 11:39:05 a.m. EDT to close out NASA's final mission to Hubble.

Space shuttle Atlantis on final at Edwards Air Force Base (Photo: NASA TV)

"Houston, Atlantis, wheels stopped, Edwards, 22!" Altman radioed mission control at the Johnson Space Center as Atlantis rolled to a halt.

"Welcome home, Atlantis," astronaut Gregory H. Johnson replied from Houston. "Congratulations on a very successful mission, giving Hubble a new set of eyes that will continue to expand our knowledge of the universe."

"Thank you, Houston, it was a thrill from start to finish," Altman said. "We've had a great ride. It took a whole team across the country to pull it off. Our hats are off to you all. Thank you so much."

Mission duration was 12 days 21 hours 37 minutes and nine seconds for a flight covering 5.2 million miles and 197 complete orbits since blastoff May 11 from Florida's Kennedy Space Center.

Altman, Johnson, flight engineer Megan McArthur and spacewalkers John Grunsfeld, Michael Massimino, Andrew Feustel and Michael Good planned to fly back to Houston late today or early Monday for reunions with family and friends.

"Now and only now can we declare this mission a total success," said Ed Weiler, NASA's associate administrator for space science. "We've now entered the second chapter of the great American comeback story.

"This mission ... was canceled Jan. 16, 2004," he said, referring to post-Columbia safety concerns. "If you'd have told me on that day I'd be sitting here five years later with a totally successful five-EVA mission, with a brand new Hubble once again that will probably operate well into the third decade of its life, I wouldn't have bet you a penny. But Hubble is the great American comeback story, chapter two."

Weiler said engineers at the Goddard Space Flight Center's Space Telescope Operations Control Center are in the process of testing Hubble's new instruments and subsystems and "everything is going very smoothly, no problems so far."

Landing in California will add a week to 10 days to Atlantis' processing for its next mission in November and cost NASA about $1.8 million. It also will delay access to an electronics box that failed at launch May 11. Engineers want to make sure a short circuit affecting the aerosurface actuator in question will not affect any systems aboard the shuttle Endeavour, scheduled for launch June 13.

Mike Moses, director of shuttle integration at the Kennedy Space Center, said he is confident the issue will be resolved in time for Endeavour's flight. Likewise, launch Director Mike Leinbach said Atlantis' diversion to Edwards will have no direct impact on Endeavour's processing.

Because Endeavour was on hot standby for launch on an emergency rescue mission in case the Atlantis astronauts ran into any major problems, much of its launch processing is already complete.

"One of the key things we did in the processing meetings was make sure we had a sufficient work force to go out to California, process Atlantis and get her ready to come home in addition to processing Endeavour here," he said. "When you think about it, there's not much left to do on Endeavour."

Engineers plan to move Endeavour from launch pad 39B to pad 39A next Friday. A flight readiness review is on tap June 3.

"A lot of the work on Endeavour's already done, we've got a good head start on that," Leinbach said. "Without a doubt, we have sufficient people to process them, make that 13th launch date. It's just not an issue for us."

Altman and company had hoped to close out the 126th shuttle mission Friday with a landing at the Kennedy Space Center. But low clouds and thundershowers at the Florida spaceport forced entry Flight Director Norm Knight to order a waveoff in hopes of better conditions Saturday.

The astronauts ran into more of the same Saturday. Knight considered diverting the crew to Edwards then, but ended up deciding the wave off another day in hopes of better weather Sunday. Atlantis had enough on-board supplies to remain in orbit through Monday and forecasters were predicting slightly better conditions in Florida for the crew's third attempt.

Conditions were, in fact, better but with offshore clouds and rain threatening to move into the landing zone, Knight ordered another waveoff and diverted the crew to Edwards to close out a high-stakes mission that left the Hubble Space Telescope in its best health since launch in 1990.

Over the course of five back-to-back spacewalks, the Atlantis astronauts installed two new instruments, repaired two others, replaced the observatory's six batteries and stabilizing gyroscopes, installed a new star sensor, a replacement science computer and three insulation panels.

Engineers at the Space Telescope Operations Control Center say it will take weeks to calibrate and test the new instruments and return Hubble to normal service. The first images from the refurbished telescope are expected in early September.

"Hubble has been a roller coaster ride going all the way back to the '80s," Weiler told CBS News. "It's mighty sweet to see (Atlantis' mission) happen, it's even sweeter to see it happen successfully."

The upgrades should permit Hubble to operate an additional five years, and possible 10, Weiler said.

"We've got new gyros, new instruments, old instruments that were dead and are now alive, what more could you ask for?" he said. "It's sad to know this is the end of an era. It's not the end of Hubble, it's the beginning of the new Hubble. But it's the last time we'll be servicing the Hubble with (the shuttle). And that's sad.

"But on the other hand, we've had a good ride. It was supposed to be a 10- to 15-year mission. We're in our 19th year, we may get 29 years. That's not a bad return on investment."

Atlantis' landing kicks off a busy few weeks for NASA. On Wednesday, at 6:34 a.m. EDT, the Russians plan to launch the Soyuz TMA-14 spacecraft from the Baikonur Cosmodrome carrying three additional astronauts and cosmonauts to the International Space Station, boosting the lab's crew to six for the first time.

Expedition 19 commander Gennady Padalka, flight engineer Michael Barratt, a NASA physician-astronaut, and Japanese astronaut Koichi Wakata will be joined by Roman Romanenko, a second-generation cosmonaut, European Space Agency astronaut Frank De Winne of Belgium and Canadian Space Agency astronaut Robert Thirsk.

At the Kennedy Space Center, meanwhile, engineers plan to follow the Soyuz launch with Endeavour's takeoff on a five-spacewalk assembly mission. Because of temperature constraints related to the station's orbit, NASA will only have one week to get Endeavour off the ground or the flight will be delayed to mid July.

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