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."

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."

"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.

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.

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.

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