Spaceflight Now

Station crew to do spacewalk chores on Atlantis visit
Posted: July 6, 2011

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While the astronauts begin work to unload the MPLM, Garan and Fossum will be gearing up for a planned spacewalk on flight day five, the only EVA planned for Atlantis' mission. The primary goals of the spacewalk are to install a robotic refueling demonstration kit; to move a failed ammonia coolant system pump module back to Atlantis for return to Earth; and installation of a materials science space exposure experiment.

Credit: NASA
Garan and Fossum also will hook up a data cable needed by a robot arm attachment fixture that was mounted on the Russian Zarya module during a spacewalk by the shuttle Endeavour's crew in May.

"This will be the first shuttle mission where the EVA is performed by the space station crew," Edelen said. "The reason we did that was because with a small shuttle crew of four, we wanted to off load the training tasks on the shuttle crew and sort of level the load. So we took advantage of the EVA experience of Mike Fossum and Ron Garan. They've actually done three spacewalks together on previous shuttle missions (and they) were able to get up to speed very quickly on this EVA."

Returning the failed pump module is a high priority objective for NASA. The space station is equipped with two coolant loops that circulate ammonia through huge radiators to get rid of the heat generated by the space station's electrical systems. Last July 30, the pump in one coolant loop failed, forcing the crew to implement an emergency powerdown.

"I remember it because I was on console when it failed. It was one of those moments where on a quiet Saturday and the crew's off duty and getting ready to go to bed and everything's going real well and it all changed in a second when that pump module failed. All the caution and warnings started going off and the crew had to very quickly scramble to reconfigure the systems and power down some of the systems in order to keep the station limping along on one remaining cooling loop.

"That was a major failure in the history of the space station program, the first major failure that required (U.S.) spacewalks without a shuttle present to fix a problem."

Over the course of three spacewalks, the pump module was successfully replaced by a pre-positioned spare. But the coolant system is critical to the station's long-term health and engineers want to find out what went wrong in the pump that failed. After troubleshooting, engineers plan to repair the pump and re-launch it aboard a Japanese cargo ship.

After mounting the pump module in Atlantis' payload bay, Fossum and Garan plan to move an experimental robotic refueling apparatus from the shuttle to a storage platform used by the Canadian Special Purpose Dexterous Manipulator, or SPDM, a robot arm extension also known as DEXTRE.

"We are taking up a payload, it's called the robotics refueling module, this is to demonstrate a capability for the Special Purpose Dexterous Manipulator, which hasn't seen a whole lot of use on the International Space Station to date, but we hope to turn that all around with this payload," Ferguson said.

"I've kind of likened it to a Fisher-Price play toy for a robot. And I don't mean that in a negative sense, it is really an opportunity for the SPDM to get in there and use several different tools and prove the capability to do something extremely novel, and that is to refuel satellites in orbit that were never designed to be refueled.

"So the manipulator will actually go in and pick up special cutter tools and cut safety wire, it has a drill that can actually drill into a fuel tank so there's some very unique capabilities that will be demonstrated using this. What capability will robots provide to us in the future? To think about going out there and perhaps grappling a satellite that was never designed to be refueled ... and refill it and use it for an additional five or 10 years is a dramatic example of how robotics can modify what we're doing in space."

With the spacewalk behind then, the astronauts will spend the next four days unloading the shuttle's crew cabin and the MPLM, repacking it with more than 6,000 pounds of gear and trash for return to Earth.

Finally, if all goes well, the crew will finish its work on July 13, staging a final shuttle farewell ceremony before moving back aboard Atlantis. The next day, around 1:59 a.m., Atlantis will undock and pull directly away in front of the shuttle for a half-lap photo documentation fly around.

In all previous shuttle departures, the orbiter flew up above, directly behind and below the station, looping around the long axis of the outpost at right angles to the lab's solar power truss. For the shuttle's final departure, Hurley will pause directly in front of the station while the lab is reoriented so Atlantis can loop from one end of the power truss to the other at right angles to the long axis formed by the station's pressurized modules.

"She'll perform a modified fly around," Alibaruho said. "We're actually very excited about this. Normally, the shuttle will undock from the International Space Station and fly around the station taking photographs in the undocking orientation.

"What's going to happen this time, Atlantis will hold at about 600 feet while the station performs a 90-degree yaw maneuver. What this does for us is this allows us to present a side of the space station the shuttle does not normally get to see on undock and fly around, so the crew can take high-resolution engineering-quality photos of sections of the spacecraft that we have not seen before on fly arounds.

"This will enable us to evaluate other areas of the space station for micrometeoroid and orbital debris impacts as well as assess the overall health of those parts of the spacecraft. After that half lap fly around, Atlantis will sep and go on her merry way."

The next day, flight day 12, will be one of the crew's busiest as they pack up the shuttle, launch a small solar cell test satellite, check out Atlantis' re-entry systems, talk to reporters and rig the ship for re-entry and landing.

"Right after we undock, we're deploying the picosat, we have to get the cabin ready for return, we have to wind up some of the last-minute science we're doing, we have standard before-landing checks, it's an extremely busy day and there's no cushion in the timeline," Magnus said. "So we could probably use an extra pair of hands or two that day. The ground's going to help us out a lot and we'll get through it, but we're going to be very, very busy at a very, very high pace at the end of the mission."

Added Ferguson: "We have to turn the orbiter back into an airplane, we have to set the seats up, we have to run cooling lines, we have to pack everything away so it's not going to fall when we re-enter. So, there's our big challenge day followed closely by flight day two, which is (heat shield) inspection day, which we normally pull off with about six people."

PART 8: The final shuttle re-entry -->