Realtime coverage of shuttle fueling test

CBS News

Editor's note...
For a detailed overview of the goals and objectives of today's shuttle fueling test, please see our preview story.

03:00 PM, 12/17/10 Update: Shuttle tanking test complete; instrumentation worked well with no major surprises

Data from temperature sensors attached to the skin of the shuttle Discovery's external tank closely matched predictions from computer models, engineers said Friday as a critical fueling test drew to a close, and no unusual stresses were noted from strain gauges on or near structural ribs, or stringers, that cracked during a Nov. 5 launch attempt.

The shuttle Discovery atop pad 39A as a fueling test came to a close. (Photo: NASA)

The fueling test began at 7 a.m. EST (GMT-5) and ended at 2:25 p.m. with the countdown holding at the T-minus 31-second mark. The liquid hydrogen and oxygen tanks were pressurized as they would be in a real launch countdown to collect additional data on the tank's performance.

After draining the propellants, engineers planned to move a rotating gantry back around the space shuttle around 10:30 p.m. in preparation for starting work to ready the ship for roll back to the Vehicle Assembly Building early Tuesday. Once in the VAB, X-ray equipment will be used to look for any signs of cracks or other damage that might have escaped detection to this point.

NASA managers plan to meet Tuesday to discuss whether to order installation of structural stiffeners on 36 stringers, nine to either side of the two booster-attachment thrust panels, that experience the most stress during launch. If all goes well and no other major problems are found, NASA hopes to haul Discovery back to the launch pad in mid January for work to ready the ship for launch Feb. 3 on a space station resupply mission.

A detailed assessment of the data collected during today's test is not expected until later. But a senior shuttle manager said the instrumentation operated normally throughout the test, collecting data to better understand how the tank responds to the shock of ultra-low temperature propellants. An inspection by engineers at the launch pad found no obvious problems, reporting that freshly sprayed foam insulation over the sensors performed well.

One of two stereo cameras focused on thousands of small dot-like targets to detect any movement in the structure due to shrinkage or other factors apparently moved during the test and it's not yet clear if those data will be useful. The other camera apparently worked well.

10:30 AM, 12/17/10 Update: External tank full, in 'stable replenish' mode; no obvious problems seen

The shuttle Discovery's external tank has been fully loaded with more than a half-million gallons of liquid oxygen and hydrogen rocket fuel. The three-hour fueling procedure began at 7 a.m. EST and ended at 9:59 a.m. when both the hydrogen and oxygen tanks were in "stable replenish" mode. Sensors on the huge external tank will continue to collect temperature and stress data throughout the afternoon.

Wiring from sensors on the skin of the shuttle Discovery's external tank can be seen in this view of the tank during a fueling test Friday. (Photo: NASA)
So far, no problems have been seen. A hydrogen vent line that leaked during a Nov. 5 launch attempt is operating normally today and engineers have not spotted any problems with the tank's foam insulation.

Launch Director Mike Leinbach said engineers are recording data from strain gauges and temperature sensors, but it will take time to evaluate the information and draw any conclusions about the tank's structural integrity and the effects of ultra-low temperatures on vertical ribs, or stringers, where cracks developed during fueling for the November launch attempt.

"Everything's going extremely well," said Leinbach. "We got into tanking on time and we're processing through the standard tanking procedure, not doing anything different to fill up the tank today. And everything's going really, really well. The ground umbilical carrier plate is working fine, no leaks there. That was one of our major objectives and that guy's performing perfectly fine now.

"We haven't seen any issues with the foam. We've talked to the guys looking at the sensors and the data's being processed right now. Too early to draw any conclusions, of course, but we're getting great data from the tank. So we're pressing on, we feel good about it. ... We're looking forward to the real thing. Hopefully in February we'll do that."

Just like with a real launch countdown, a team of technicians was sent to the pad 39A after that tank was full to begin a close-up inspection, looking for any signs of trouble with the foam insulation. During the Nov. 5 launch attempt, cracks in two stringers making up the ribbed intertank section caused a large crack to appear in the tank's foam insulation.

The cracks were repaired by splicing in undamaged segments and then bolting on doublers to provide additional strength. But engineers looking into what caused the cracks have not found an obvious "smoking gun." Based on an exhaustive investigation, it appears the cracks were the result of a "stack up" of tolerance problems during the tank's construction that resulted in pre-loaded stress in the hardware. Today's fueling test may help engineers confirm that hypothesis.

"So we have stringers instrumented in the repair area so we can look and see how that repair performs under a cryo load," said Mike Moses, the shuttle integration manager at the Kennedy Space Center. "We have stringers instrumented next to that repair that aren't damaged so we can see how they perform. That'll give us some information about the general area to see if there are any non-linearities. And then on the opposite side of the tank, we've instrumented stringers to kind of go to a control type theory to say over here in a completely different area, here's how the tank performs.

"Really what we want to look for, in additional to the details, it's really that big picture," he said. "Does the left side and the right side of the tank compare to each other, do both sides perform the way the models show they would?

"We're looking for non linearities, is something obviously not tracking what we think it's going to, are the temperature profiles what we think, is there a spike in stress or strain that we do not expect to see? That would be an indication that there might be a different problem other than the stringer itself having a flaw or a defect that would put us in that second family where the stringer was the victim here and not the cause.

"None of our experts believe that to be the problem, none of our analysis or data mining to date shows that that's going to be the case. This tanking test hopefully will give us the final set of data that lets us kind of declare that to be true."

Engineers are hopeful the instrumented fueling test, along with exhaustive analysis and additional testing will clear the way to launch in early February even in the absence of a single obvious cause of the cracks.

"It looks like what we probably had happen was during assembly we introduced stress such that this part was kind of pre-loaded with some stress and then the extra stress of cryo loading was enough to then break it and exceed its capacity," Moses said.

When the stringers are attached to the skin of the intertank, he said, "you kind of clamp it together. There could be gaps between the parts such that when you then rivet it up with ... something like a 5,000-pound load, you could trap a lot of that force into the part if there's a gap.

"When you stack up that there might have been a gap there, and you stack up that you might have clamped it down a little too hard, which made the feet splay out a little, and then when you look at the stringer itself, this particular stringer ... is like a tenth of an inch farther up the tank than the other stringers. These things are pre-formed with a bend in them, that bend is now in a different place than it was supposed to be. So you have these groupings of things that if they line up on you could cause a problem.

"We're not probably going to come out of here with a smoking gun, but we're going to come out of here with a family of failures and we're going to have a lot of testing to then make sure we're not fooling ourselves."

09:15 AM, 12/17/10 Update: Hydrogen vent line appears to be leak free

A 7-inch gaseous hydrogen vent line attached to the side of the shuttle Discovery's external tank that leaked during a Nov. 5 launch attempt is working normally during today's fueling test.

Engineers earlier traced the leak to an alignment problem with the quick-disconnect hardware used to attach the vent line to a fitting in the intertank section of the external tank. Replacement hardware was installed and carefully aligned and engineers were confident any leak paths had been eliminated.

At 8:56 a.m. EST, the liquid hydrogen tank was 98 percent full, roughly the point where the leak developed during the Nov. 5 launch attempt. But this time around, sensors near the attachment fitting showed no discernible free hydrogen.

07:10 AM, 12/17/10 Update: Shuttle fueling test begins

Working by remote control, engineers began pumping liquid oxygen and hydrogen through transfer lines to the space shuttle Discovery at 7 a.m. EST (GMT-5) to begin a planned seven-and-a-half-hour test to verify the structural integrity of the ship's external tank and to test the strength of repairs to two cracked ribs, or stringers, that were discovered after a Nov. 5 launch scrub.

The propellants, flowing through transfer lines to the shuttle's aft engine compartment, through main engine plumbing and then into the external tank, will subject the tank's lightweight aluminum-lithium alloy components to ultra-low temperatures that will be measured by thermocouples mounted on the tank's skin.

Strain gauges will measure the stresses acting on the stringers near two booster attachment thrust plates, including the two ribs that cracked during fueling Nov. 5. Those data will be used to verify the tank's ability to withstand the thermal stresses of fueling, confirm the strength of the repaired stringers and help analysts validate ascent safety margins.

The tanking test also will allow engineers to verify the performance of a 7-inch gaseous hydrogen vent line that leaked during fueling Nov. 5. The vent line quick-disconnect hardware was replaced and alignment problems thought to have caused the leak were corrected.

Discovery will be hauled back to the Vehicle Assembly Building Tuesday for additional X-ray inspections and possible modifications to beef up 36 stringers -- nine on either side of the two thrust plates where the shuttle's solid-fuel boosters are attached. If no other major problems are found, NASA hopes to move the shuttle back to the pad in mid January for work to ready the ship for launch Feb. 3 on a space station resupply mission.

Here is the timeline for today's activity:


01:00 AM...Final fueling preps
03:00 AM...Pad clear

06:00 AM...Begin a one-hour built-in hold
07:00 AM...Resume countdown

07:00 AM...Liquid oxygen/hydrogen transfer line chill down begins
07:10 AM...Liquid hydrogen slow fill begins
07:40 AM...Liquid oxygen slow fill begins
07:45 AM...Hydrogen engine cutoff sensors "wet"
07:50 AM...Liquid oxygen fast fill begins
08:00 AM...Liquid hydrogen fast fill begins
09:15 AM...Liquid hydrogen topping (98 percent full)
09:45 AM...Liquid hydrogen replenish
10:00 AM...Liquid oxygen stable replenish

10:00 AM...Begin a one-hour built-in hold
10:00 AM...Final inspection team at the launch pad
11:00 AM...Resume countdown

01:00 PM...Final inspection team departs launch pad

01:40 PM...Begin a 10-minute hold at T-minus 20 minutes
01:50 PM...NASA test director briefing
01:50 PM...Resume countdown

02:01 PM...Begin a 10-minute hold at T-minus 9 minutes
02:05 PM...NASA test director launch status verification
02:11 PM...Resume countdown

02:11 PM...Ground launch sequencer auto sequence start
02:16 PM...Terminate liquid oxygen replenish
02:18 PM...Tank pressurization
02:19 PM...Begin a five-minute hold at T-minus 31 seconds
02:24 PM...Fueling test ends
02:50 PM...Liquid oxygen drain begins
02:55 PM...Liquid hydrogen drain begins