STS-133 mission preview (UPDATED)

CBS News

KENNEDY SPACE CENTER, Fla. -- Three-and-a-half months after the shuttle Discovery was grounded by potentially dangerous cracks in its external tank, the orbiter is finally back on track for launch Feb. 24 to deliver critical spare parts, supplies and a final U.S. module to the International Space Station.

During an executive-level flight readiness review Feb. 18, senior NASA managers cleared Discovery for blastoff Feb. 24, at 4:50:24 p.m. EST (GMT-5), following an exhaustive safety analysis of the modifications used to beef up suspect ribs, or stringers, in the tank's central "intertank" section.

The shuttle Discovery atop pad 39A at the Kennedy Space Center. (Credit: CBS News/William Harwood)
"This is probably one of the most difficult technical issues, I think, we've ever faced because the answers were not obvious," shuttle commander Steven Lindsey said in a NASA interview. "It wasn't obvious what was wrong, why it was wrong, or how to fix it, and then you had the additional, if you will, pressure of the shuttle program winding up and we keep slipping and slipping and slipping.

"But to the space shuttle program's credit, they've really done due diligence on this one and really focused on the engineering, following the data, figuring out what was wrong. ... It's just been very impressive to watch them, not get rushed, focus on the data, focus on the engineering. When they didn't understand something, they did a lot of testing.

"You can write a thousand computer programs, but one test makes all the difference because that tells you what's really going on," he said. "So I think they've done a great job with it."

Lindsey and his five crewmates -- pilot Eric Boe, Nicole Stott, Michael Barratt and spacewalkers Stephen Bowen and Alvin Drew -- flew to the Kennedy Space Center Sunday to prepare for the start of the shuttle's countdown at 3 p.m. Monday.

A veteran of two previous shuttle flights, Bowen joined Discovery's crew in January after Timothy Kopra, the mission's original flight engineer and lead spacewalker, suffered what sources said was a broken hip in a bicycle accident near his home in Houston.

"It was actually a sad story," Bowen said in a NASA interview. "Tim had worked for well over a year putting this thing together and had an accident. He's unable to make the launch time frame (and) we needed to find somebody to fill his role. ... It was not what you expected, not what you want. Tim worked really hard."

Bowen, a veteran submariner with five previous spacewalks to his credit, was a natural choice to replace Kopra on short notice. He flew aboard the most recent shuttle mission and served as the lead astronaut in the spacewalk office at the Johnson Space Center.

He underwent accelerated training for the two spacewalks planned for Discovery's mission, joining Drew for four simulation runs in NASA's huge neutral buoyancy training pool near the Johnson Space Center.

Because of time constraints, Bowen did not attempt to assume Kopra's duties as flight engineer. Instead, Drew will take on that role for launch and Stott will serve as flight engineer for Discovery's re-entry and landing.

"I get to concentrate on just the EVA portion," Bowen said. "Tim and Drew had put together a great plan. I literally told the EVA team don't change a single word of the plan, I'm going to follow what he wrote. I've been watching the videos of what Tim did in the (training tank) and I’ve been talking to Tim as well and learning how to do these EVAs."

Kopra plans to help out in mission control during the flight, providing advice as needed based on his own experience training.

The primary goals of the 133rd shuttle mission are to deliver critical spare parts, supplies and a final U.S. module to the International Space Station. It will be Discovery's 39th and final flight as NASA presses ahead with plans to retire the fleet after just three more missions.

The shuttle Discovery's crew (left to right): Nicole Stott, Michael Barratt, Stephen Bowen, Al Drew, pilot Eric Boe, commander Steven Lindsey. (Credit: CBS News/William Harwood)

"Discovery's a workhorse, the fleet leader in number of flights, done a lot of famous flights, all the return-to-flight test missions," Lindsey said before the crew's initial launch attempt. "Yet when you walk inside Discovery, it still looks like a new car even after almost 30 years of service. It's a great machine, a great vehicle. It's a privilege for us to be able to fly it on the last flight."

Assuming an on-time launch, Lindsey and Boe will oversee a two-day rendezvous with the lab complex, carrying out a now-routine heat-shield inspection the day after liftoff before guiding the shuttle to a docking at the station's forward port around 2:16 p.m. on Feb. 26. It will be Discovery's 13th and final docking.

Waiting to welcome the shuttle astronauts aboard will be Expedition 26 commander Scott Kelly, Alexander Kaleri, Oleg Skripochka, Catherine Coleman, Dmitry Kondratyev and Italian astronaut Paolo Nespoli.

Discovery is scheduled to spend seven days docked to the space station, departing on March 5 and landing back at the Kennedy Space Center around 12:44 p.m. on March 7.

But U.S. and Russian space managers are expected to approve a one-day mission extension for an out-of-this-world photo opportunity.

The idea is to insert a new flight day 10 in the crew's timeline -- March 5 -- so Kelly, Kaleri and Skripochka can undock in the Soyuz TMA-01M spacecraft and photograph the space station with the shuttle and a full complement of European, Japanese and Russian cargo ships and crew capsules attached.

Discovery's mission is the last time all of the international spacecraft will be docked at the station at the same time before the shuttle fleet is retired later this summer.

Assuming the fly-around is approved -- and no decisions are expected until after Discovery reaches the space station -- Discovery would undock on March 6 and land in Florida around 11:35 a.m. on March 8.


NASA originally hoped to launch Discovery on Nov. 1, but the flight was delayed to Nov. 5 by bad weather and technical problems.

The ship was fueled for launch Nov. 5, but the countdown was called off when sensors detected a gaseous hydrogen leak in a quick-disconnect fitting used to attach a vent line to the side of the tank. That problem was quickly resolved, but engineers also discovered cracks near the tops of two adjacent structural rib-like "stringers" near a flange in the external tank that supports the upper liquid oxygen tank. More cracks were found later, after Discovery was returned to NASA's Vehicle Assembly Building for more detailed inspections.

Tracing the manufacturing history of the tank, engineers discovered that most of the original 108 stringers in the "intertank" section that separates the tank's oxygen and hydrogen sections were made using an aluminum-lithium alloy from a lot that was more brittle than usual and more susceptible to temperature-induced fractures when the tank is loaded with super-cold propellants.

That weakness, engineers concluded, along with subtle manufacturing issues, were the most likely causes of the observed cracks.

In the most invasive repair of an external tank ever attempted, engineers installed structural stiffeners, called radius blocks, to better secure the top few inches of 105 stringers to prevent cracks from forming when the tips of the stringers are pulled inward due to the contraction of the liquid oxygen tank.

Engineers install radius block stiffeners to beef up structural rib-like stringers in the shuttle Discovery's external tank to make them less susceptible to stress-relief cracks. (Credit: NASA)

The goal was twofold: to ensure the tank's overall structural integrity and to prevent cracks that could cause foam insulation to pop off during the climb out of the dense lower atmosphere when debris impacts pose the greatest threat to Discovery's fragile heat shied.

The addition of the radius blocks more evenly distributes stresses in the stringers and reduces the strains on the top few fasteners.

The tank was designed to be structurally "fail safe" even if three adjacent stringers developed cracks. Data from a Dec. 18 fueling test, elaborate laboratory tests and an exhaustive engineering analysis showed the tank would remain structurally sound even if more than three stringers developed cracks greater than four inches in length as long as they were separated by undamaged stringers.

The tank's calculated factor of safety is not precisely known, but it is greater than one in all cases, meaning that even with extensive modifications and stringers that are more brittle than usual, the structure's strength is sufficient for flight.

Testing also showed cracks greater than four inches long were most likely to occur during fueling, when the hardware is "shocked" by extreme low temperatures and that any such fractures likely would cause visible cracks in the tank's insulation. With the radius block modifications, engineers do not expect such cracks to form. But during Discovery's countdown, cameras will be focused on the liquid oxygen flange area to look for any signs of insulation damage. If any cracks are seen, the countdown will be called off.

Bill Gerstenmaier, director of space operations at NASA headquarters, praised the NASA and contractor engineers and technicians who did the troubleshooting, analysis and repairs of Discovery's tank. Many members of the repair team were called in from Lockheed Martin's Michoud Assembly Facility near New Orleans where the giant tank was built. With only three more shuttle flights planned, the production line has been shut down.

"They did a phenomenal job of doing this testing and pulling the work together," Gerstenmaier said. "I couldn't be prouder of what they've done. ... A lot of these folks, some of them in the tank world, were laid off, they were already in other jobs and we called them back to do some of this work. ... There was no question about their dedication. They really want to see this vehicle fly."


Discovery's delayed launching comes at a historic moment for NASA and its international partners. On April 12, NASA will mark the 30th anniversary of the first shuttle flight and the Russian space program will celebrate the 50th anniversary of Yuri Gagarin's launch on the first manned space flight.

Discovery's docking with the International Space Station will come just over 12 years after the Nov. 20, 1998, launch of the station's first component, the Russian Zarya module, and 10 years after the first three-man crew arrived aboard a Russian Soyuz spacecraft Nov. 2, 2000.

Since then, the space station has grown to include 13 pressurized modules and a huge solar array power truss stretching the length of a football field and tipping the scales at nearly 900,000 pounds. The lab has been continuously manned by rotating two-, three- and now six-person crews.

"I delivered the airlock on my first flight to space station," Lindsey said in a NASA interview. "It had just barely started and I remember thinking about all of the missions and all the components we still had to fly up there to fully build this thing out. At times it seemed like we were never going to get there. It was just, there were so many missions.

The International Space Station. (Credit: NASA)

"When I look back at it now and see this fully assembled space station operating with six people and doing all the science and stuff like that, I'm just amazed at what this big team has accomplished and really excited about what it's going to accomplish in the future.

"Getting an opportunity to go up there again, which I never thought was going to happen, and see this fully assembled space station I've worked on most of my professional career here at NASA is just going to be something fantastic. I hope that the rest of the world appreciates what we have."

When Lindsey and his crewmates were named to the crew of shuttle mission STS-133, NASA intended Discovery's flight to be the program's final voyage, following a Bush administration mandate to finish the space station and retire the shuttle fleet by the end of fiscal year 2010.

That somewhat arbitrary deadline was relaxed a bit when Congress, worried about the possibility of schedule pressure on flight safety, promised an additional $600 million in funding to cover shuttle operations through the end of the calendar year. NASA managers later said internal cost-savings initiatives would allow shuttle operations to continue into early 2011 if necessary.

As it turned out, problems with a $2 billion particle physics experiment scheduled for launch aboard the shuttle Endeavour during the next-to-last fight in July 2010 forced NASA to revise the end-of-program shuttle manifest.

Because of work to replace the powerful magnet in the particle physics experiment, Endeavour's flight leap-frogged Discovery's, slipping to late November and eventually to Feb. 27, 2011. Discovery's flight, in turn, slipped from mid September to Nov. 1, in part to accommodate work to modify a cargo transport module for permanent attachment to the space station.

Discovery's launching then was delayed to Nov. 5 by bad weather and technical snags. The ship has been grounded since then because of the stringer cracks.

In the midst of Discovery's long launch campaign, NASA won political support for a third and final mission with the shuttle Atlantis to deliver additional supplies and equipment to the station. That flight, the shuttle program's final voyage, is targeted for launch June 28.

After the shuttle fleet is retired, NASA will rely on smaller unmanned Russian, European and Japanese cargo ships, along with new commercial spacecraft that are currently in development, to deliver the supplies and equipment needed by the space station to support a full-time crew of six.

"From a logistics standpoint, 2012 is going to be a real challenge for (the station program)," said shuttle Program John Shannon. "If there are delays in any of the new vehicles that are expected to deliver cargo to the station, that problem is just going to be exacerbated. It's hard to compare vehicles and capabilities. But my operations guy said one shuttle flight is roughly equivalent to about seven (Russian) Progress flights. So if you think about that, you can do pretty well on one shuttle.

"So getting to fly (Atlantis) late is going to give the space station margin from a logistics standpoint to keep six crew (members) up, to keep doing the research, to keep doing the utilization even if some of those new vehicles are delayed by some period of time."

If the Atlantis mission is not launched "and the new vehicles that are going to deliver cargo are delayed, and we end up having a logistics shortfall in 2012, and we have to go down to three crew, and we're not doing research, we have made a major error, in my opinion," Shannon said.

Faced with an uncertain budget, Shannon is struggling to reduce the shuttle workforce as required while maintaining flight safety and maximizing resupply of the space station.

Despite extensive layoffs, "the program is very healthy," Shannon said. "But I have a very high sense of paranoia that this is a very difficult time for the team, and we need to be incredibly vigilant, and any little noises that you hear you've got to go pay attention to and really make sure you fully understand what is going on. Because it's a very complex process and it's very unforgiving.

"So far, the team has done an outstanding job and we're going to continue to stay focused. The team really wants to preserve the legacy of the shuttle program and end on a really high note."


As originally planned, Discovery's flight did not include any spacewalks. But with the schedule revision and the initial slip to November, NASA managers added two spacewalks, or EVAs, with Drew and Kopra -- now Bowen -- and scheduled additional work to maximize the resupply effort.

"We started out as an eight-day mission," Lindsey said. "We were just going to go up, dock with space station, offload some payloads and (do) a lot of transfer and basically leave station in the best logistic state possible because when we were originally assigned we were going to be the very last shuttle mission.

"They've added a couple of spacewalks to our flight so what we've had to do is lengthen the mission from eight days to eleven days nominal with a plus one if we need it. We're having to pick up and train (for) those two spacewalks, which we hadn't been training for before. We've also added a whole bunch of robotics that go along with that.

"As a result of that, I've had to move crew members into different tasks to make the timeline fit. ... We have a good schedule in place, and we've worked out all those details. It's just going to take us a little bit longer to get there, but we still have a good plan and I feel pretty comfortable with what we're doing."

The shuttle Discovery's payload bay. (Credit: NASA)

At the heart of the mission is the permanent multi-purpose module, or PMM, that will be carried aloft in Discovery's cargo bay. The Italian-built module, dubbed Leonardo, was originally designed to serve as an up-and-down cargo transport canister that could be temporarily docked to the space station and then returned to Earth aboard the shuttle.

Then called a multi-purpose logistics module, or MPLM, Leonardo was not designed to remain permanently attached to the station. But with shuttle flights coming to a close, program managers ordered modifications, beefing up Leonardo's insulation, adding increased orbital debris shielding and arranging for power, lights and ventilation. The result is the PMM.

"I think it's going to be a really outstanding addition to the station," said Stott. "Anybody who's lived and worked up there has at one time or another felt like wow, if we just had a closet where we could stick this, or we just had designated storage for these particular items it would be such a great thing.

"And I think what it's going to do is provide that, but it's also going to give us the opportunity to go through station and look at where we have stuff and maybe better distribute so we make even more space available. So I think it's going to be a really, really nice addition."

Mounted in Discovery's cargo bay, the PMM measures 21 feet long and 15 feet in diameter and tips the scales at 21,817 pounds, including 6,536 pounds of equipment and supplies. Another 1,568 pounds of station-bound gear is mounted in the shuttle's crew cabin.

The station-bound hardware includes an experiment rack, a heat exchanger for the lab's temperature and humidity control system, a spare pump for the station's internal cooling system, a large fan, a water processing assembly storage tank, a waste water tank and an experimental robot known as Robonaut 2.

Shaped like a human's upper torso, Robonaut 2 weighs about 300 pounds and measures nearly four feet from waist to head and nearly three feet across the shoulders. The robot will be operated remotely by engineers on the ground.

Describing the robot as a technology demonstrator, Barratt said "this is very much a first step. We'll be identifying some breadboard tasks over the next few years to figure out how best to use a humanoid robot in space."

Robonaut (left). (Credit: NASA)
"When you look at some of the tasks we're asked to do, and what a robot could do, you're thinking of things that would be perhaps dangerous for a human to do or repetitive tasks that would wear a human out," he said. "So if you were to go around the station, for instance, and identify scenarios where it was risky to send a human in, whether you had a suspected fire or a toxic release and what you needed was a switch throw or to discharge a fire extinguisher into the right fire port, that's the kind of thing we could eventually envision sending Robonaut in to do.

"I'd much rather send a robot in than go in myself on a gas mask," he said. "But again, we're very early, and we'll be mapping those tasks to the capabilities that Robonaut demonstrates over the years. And it will be years before we figure all this out. So we're excited to see this all start."

Discovery also is carrying up an 8,161-pound external storage platform carrying a folded set of radiators that will serve as a spare in case of future problems with the station's external cooling system. The station features two independent coolant loops that circulate ammonia through huge radiators to dissipate the heat generated by the lab's electronics.

The spare radiator panels weigh 2,475 pounds and are mounted on an external logistics carrier known as ELC-4. Barratt and Stott, operating the station's robot arm, will lift ELC-4 out of Discovery's cargo bay a few hours after docking on flight day three. They will hand it off to Boe, operating the shuttle's robot arm, and then reposition the station arm. After re-grappling the cargo carrier, Barratt and Stott will mount it on the right side of the station's power truss.

The next day, Barratt and Stott will use the station arm to pull the shuttle's heat shield inspection boom out of the cargo bay before handing it off to Boe and the shuttle's arm where it will remain for possible use later in the mission. Inside the station, the astronauts will begin work to repair one of the U.S. segment's carbon dioxide removal systems.

Bowen and Drew will end the day by camping out in the station's Quest airlock module at a reduced pressure of 10.2 pounds per square inch. The camp out procedure is used to help purge nitrogen from the bloodstream before spacewalks are conducted in NASA's 5-psi spacesuits.

The first major objective of the mission's first spacewalk on flight day five is to install a 10-foot-long power cord between the Quest airlock and the Harmony module directly across the station on the other side of the Unity module. The power line, which might be needed in the future if Harmony ever needs to be undocked for repairs, cannot be installed after the PMM is attached to Unity's Earth-facing port.

The permanent logistics module attached to the International Space Station. (Credit: NASA)
With the power line in place, Bowen and Drew will retrieve a failed ammonia pump module that was left temporarily stowed on the robot arm's mobile base system after a three-spacewalk repair job last August. After moving the module back to a stowage platform, Drew will install a vent line that will be used during the crew's second spacewalk to dump about 10 pounds of residual ammonia overboard.

Most of the remaining tasks were left over from earlier missions.

"On my last flight and on the next flight, there's not a lot of time to do all the tasks that have just built up over the past year," Bowen said. "Originally when this flight was assigned, there were no EVAs on it but they wisely saw they had the talent with Tim and Al and Mike and Nicole to put a good team outside and use that talent to get some work done.

"These were two EVAs that were not originally in the plan, that they've taken advantage of the fact that they have these guys on board. They're going around, and we will be doing a lot of items, a lot of stuff. It’s going to be busy."

With the pump module safely stowed, Drew and Bowen plan to carry out a variety of maintenance tasks, adjusting the insulation on the upper Z1 truss, attaching a tool stanchion and a wedge to tilt a camera away from ELC-4, providing additional clearance when hardware arrives aboard future supply ships.

Before ending the spacewalk, Bowen and Drew will open a Japanese container and "fill" it with the vacuum of space in a project known as "message in a bottle."

"It's a Japanese piece of hardware and the intention here is to use this outside space station and all we want to do is open a valve," Kopra said before the crew's initial launch attempt. "It's kind of unique and a thoughtful sort of experiment the Japanese have designed where we're just going to fill it with the vacuum of space. ... Clearly a vacuum is a vacuum whether it's space or if it's in a vacuum chamber here at NASA. But this is a little bit special, especially for the Japanese because it's the vacuum of space. So we'll do that, capture in pictures and provide that to the Japanese once we come home."

The next day, flight day six, Stott and Barratt, operating the station's robot arm from inside the multi-window cupola, plan to pull the PMM out of Discovery's payload bay and attach it to Unity's Earth-facing port. That afternoon, a block of time is set aside for a so-called "focused" inspection of the shuttle's heat shield if any problems are spotted after launch or during approach to the station.

That night, Bowen and Drew will camp out in Quest to prepare for another spacewalk the next morning.

The goals of the second excursion are to vent residual ammonia from the failed pump module, to retrieve a European experiment package from the outboard end of the Columbus laboratory module, to install protective lens covers on external cameras that could be "plumed" by approaching cargo ships and to troubleshoot problems with mounting hardware that could be needed in the future for radiator repairs or replacement.

A spare radiator panel will be stored on the lower side of the outboard starboard power truss (circled). (Credit: NASA)

Inside the station, the astronauts will complete outfitting the vestibule between Unity and the PMM, opening the hatch and floating inside for the first time. Unlike normal MPLM missions, the crew will be in no hurry to unload the supplies and equipment ferried aloft in the PMM. Robonaut 2, for example, is not expected to be activated for several months.

Over the next two days, the astronauts will enjoy a bit of off-duty time, participate in multiple interviews and a traditional joint crew news conference. What happens after that depends on whether the Soyuz fly-around is approved.

The pre-launch flight plan called for Discovery to undock from the station around 7:37 a.m. on March 5. After looping around the outpost for a photo-documentation inspection, the shuttle crew would depart and pull away before carrying out a final heat shield inspection to look for any signs of damage since the initial inspection the day after launch.

Discovery's 39th and final landing would be targeted for around 12:36 p.m. on March 7.

If the Soyuz fly-around is approved, however, undocking and landing would be delayed one day and a new flight-day 10 would be inserted into the timeline for March 5.


"I don't think you can take a final voyage of a ship of exploration and not take some moments to celebrate its history," Barratt said. "As many people know, our ship Discovery, which is a ship of exploration, was named after several predecessor ships, all named Discovery, all ships of exploration.

"It's the culmination of a great heritage, really, and we hope there are future ships bearing that name. We will be carrying a medallion from the Royal Society that was struck in honor of Captain Cook. On Cook's third voyage, there was a ship called Discovery and that's the main ship for which our ship took its name. We'll be doing a few other taped commemoratives on it as well. But again, you cannot not celebrate the history and the heritage of this ship."

The shuttle Discovery, on the way to its final flight. (Credit: CBS News/William Harwood)

The contract authorizing construction of Discovery was awarded Jan. 29, 1979, and initial work to begin building the crew module began the following August. The spacecraft was completed at North American Rockwell's Palmdale, Calif., plant in October 1983 and was ferried to the Kennedy Space Center Nov. 9, 1983.

Following an on-pad main engine test firing June 2, 1984, NASA attempted to launch Discovery on its maiden voyage the following June 26. But in a moment of high drama, the shuttle's main engines shut down seconds after ignition because of a sluggish fuel valve.

The problem was corrected, and commander Henry Hartsfield and his crew, including Challenger astronaut Judith Resnik, finally blasted off Aug. 30, 1984, on a successful mission to deploy three commercial communications satellites and to test space station construction techniques.

Over the next 26 years and 38 flights, Discovery carried out four military missions, two Spacelab science flights, two visits to the Russian Mir space station, one Mir docking and 12 missions to the International Space Station. At least 24 civilian and military satellites were carried into space, including the Hubble Space Telescope.

During Discovery's final mission, the ship will make its 13th docking with the space station, and its crew will carry out the orbiter's 50th and 51st spacewalks.

Veteran of two on-pad launch aborts, Discovery also flew the return-to-flight missions following the 1986 destruction of the shuttle Challenger and the 2003 loss of Columbia. In addition, two stranded communications satellites were plucked out of orbit by spacewalking astronauts and brought back to Earth for repairs in November 1984 in what many veterans consider the most daring shuttle mission ever attempted.

Going into its final flight, Discovery had logged 142,917,535 miles traveled over 5,540 orbits, carrying 246 astronauts and cosmonauts into space, including former senator and Mercury astronaut John Glenn and Eileen Collins, the first woman to pilot and later command a space shuttle.

"When you really look at the space shuttle and its capability, it can do everything, everything you can think of in space except for one thing, it can't leave low-Earth orbit, but it can do everything else," Lindsey said in a NASA interview. "It can do robotics. It can do science. It can go dock. When you dock with the space station, in the end you have to maintain a three-inch corridor and one degree of attitude error and you can easily fly the shuttle manually and maintain that. I mean, that's unbelievable for a 120-ton vehicle.

"I don't think there's going to be another one that's ever going to match the versatility of the space shuttle, and I think that's the legacy. All the systems we've developed and things we've done on space station, or on space shuttle, have all had impacts in our society. I mean, literally any room you walk in, anything you do during the day, you can point at things in that room and say, 'That came out of the space program. This came from shuttle. This came from Apollo. This came from space station' and you can see it all around you.

The shuttle Discovery in orbit. (Credit: NASA)

"The public's not real aware of all of that ... and it's very hard to measure, but it's all there if you really think about it, and I think that's the legacy. I think the legacy is that all these things came out of it, and people take all of those things for granted."

NASA managers are considering a variety of options for Discovery's post-landing processing. Some have suggested maintaining the orbiter in a flight-ready state for as long as possible. Others have recommended using the orbiter for spare parts until Atlantis and Endeavour complete their final missions. Shannon favors a combination of approaches.

"We're in the middle of a very significant effort to identify hardware off of Discovery and also in the spares (inventory) that could be used for some future as yet unknown program, or that we would want to maintain as spares for Endeavour and Atlantis," Shannon said.

"We're also going to pull some off as engineering teaching units so that future generations will be able to take the hardware that was flown on the shuttle and dissect it and understand the engineering and how it was put together. We're also going to go in and look at some hardware on Discovery that has flown for 30 years that we've never looked at before. Things like actuators and some structural areas that are impossible to get to.

"Those will be fairly invasive, it will take time and it will take money," he said. "But I think that's one of the legacies the shuttle can provide. ... So even after Discovery lands, we will not be finished learning about the space environment. That's my goal, to start immediately on that."

No matter how the end game plays out, Discovery eventually will be shipped to a museum and put on display. But with nearly two dozen museums vying for one of NASA's three orbiters, it's not yet clear where Discovery will end up. A decision is expected later this year.