Astronauts given to-do list for today's station spacewalk
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 21, 2009
Astronauts Joseph Acaba and Steven Swanson are preparing for a revised six-and-a-half-hour spacewalk today. The major goals of the excursion, the second of three planned for the shuttle Discovery's mission, are to prepare a set of solar array batteries for replacement in June; to deploy storage platforms on the international space station's solar power truss; to install a GPS navigation system antenna on a Japanese module; and to photograph two sets of radiator panels with an infrared camera. Insulation on one radiator panel has pulled away and engineers want to assess the health of the system.
Today's spacewalk, the 122nd devoted to station assembly and maintenance since construction began in 1998, is scheduled to begin at 12:43 p.m. when Swanson and Acaba, floating in the station's Quest airlock module, switch their spacesuits to internal battery power. For identification, Swanson will be wearing a suit with red stripes and use the call sign EV-1. Acaba, EV-2, will be wearing a suit with broken red stripes.
Overnight, engineers at the Johnson Space Center in Houston continued checking out the newly deployed S6 solar array wings that were successfully extended Friday. Pat Ryan, the overnight mission control commentator, said checkout was proceeding smoothly. Engineers are charging and conditioning the batteries that store power from the new arrays when the station is in Earth's shadow, but that power is not yet being fed into the station's electrical distribution system.
"The new arrays are gathering solar energy and converting it to electrical power, but at this point that electrical power is being used only to charge the batteries out there," Ryan said. "The plan is that these two new power channels will not be incorporated into the station power grid until after the completion of today's spacewalk. That's a precautionary measure to prevent any disruption of station systems while crew members are outside."
Discovery's mission originally included four spacewalks, but one had to be eliminated when launch was delayed from Feb. 12 to March 15, putting the shuttle mission in conflict with upcoming Russian flights to rotate space station crew members. Facing a March 25 deadline to undock and make way for the Russians, one spacewalk had to be eliminated.
NASA flight planners re-prioritized the tasks planned for Discovery's spacewalkers, moving some work up and deferring other activities.
The first item on the agenda today is work to prepare batteries on the port 6, or P6, solar array truss segment for replacement during assembly mission STS-127 in June.
"What the crew will do is, they'll go out to that worksite and break the torque on those batteries and install some foot restraints and pre-stage some tools that they'll use to save the crew of the next mission some time when they go to do the complex operations to replace those batteries. So we're going to do that get-ahead task," said lead flight director Kwatsi Alibaruho.
"We'll also deploy external cargo carriers, one cargo carrier on the port side, one on the starboard side. They are to prepare for installation of cargo or payload carriers on a future flight. Finally, we'll install a prox ops GPS antenna on the Japanese experiment module. This will be the second of two installations of these antennas. And this is in preparation for the launch and rendezvous of the H2 transfer vehicle from Japan later on this year."
Unlike the shuttle, Russian Soyuz and Progress vehicles and the European Space Agency's Automated Transfer Vehicle, which rendezvous and dock with the station, the unmanned Japanese H-2 Transfer Vehicle is designed to approach the lab complex and then wait for the station's robot arm to grab it and move it to a docking port. The GPS antennas are part of the Japanese proximity navigation system that will be used for those missions.
"We'll also do some additional EVA get-aheads to include some imaging, infrared imaging of the port and starboard radiators, as well as reconfiguration of an electrical patch panel that provides power to the station's control moment gyros," Alibaruho said.
Swanson will carry out the radiator photo documentation while Acaba installs the GPS antenna on the Japanese module.
"We've noticed one of the panels on our radiators, which help us basically release heat out into space, has begun to peel back," spacewalk coordinator Richard Arnold said in a NASA interview. "We don't really yet understand what that means, how it was caused and how it's impacting our ability to get rid of excess heat off the station."
"So (Swanson will) head aft, get in a foot restraint and take some infrared thermal images of both the radiators. That's to see if we can get some data that helps us understand what's going on with the radiators and why this panel is peeling back and how that's affecting us."
Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision I of the NASA television schedule):
EDT........DD...HH...MM...EVENT 03/21/09 07:43 AM...05...12...00...Crew wakeup 08:18 AM...05...12...35...EVA-2: 14.7 psi repress/hygiene break 09:08 AM...05...13...25...EVA-2: Airlock depress to 10.2 psi 09:13 AM...05...13...30...ISS daily planning conference 09:28 AM...05...13...45...EVA-2: Campout EVA preps 10:58 AM...05...15...15...EVA-2: Spacesuit purge 11:13 AM...05...15...30...EVA-2: Spacesuit prebreathe 11:33 AM...05...15...50...Distillation assembly install part 1 12:03 PM...05...16...20...EVA-2: Crew lock depressurization 12:43 PM...05...17...00...EVA-2: Spacesuits to battery power 12:48 PM...05...17...05...EVA-2: Airlock egress 01:03 PM...05...17...20...EVA-2: Setup 01:43 PM...05...18...00...EVA-2: S6 battery R&R preps 02:43 PM...05...19...00...EVA-2: P3 nadir UCCAS deploy 03:58 PM...05...20...15...EVA-2/EV-2: JLP GPS antenna B install 03:58 PM...05...20...15...EVA-2/EV-1: S1/P1 radiator imaging 04:18 PM...05...20...35...Water recycling system rack closed 04:58 PM...05...21...15...EVA-2/EV-2: Z1 patch panel reconfig 05:28 PM...05...21...45...EVA-2: S3 PAS deploys 06:28 PM...05...22...45...EVA-2: Cleanup and airlock ingress 07:13 PM...05...23...30...EVA-2: Airlock repressurization 07:28 PM...05...23...45...Spacesuit servicing 08:00 PM...06...00...17...Mission status briefing 08:48 PM...06...01...05...Crew choice downlink 09:08 PM...06...01...25...Evening planning conference 10:43 PM...06...03...00...ISS crew sleep begins 11:13 PM...06...03...30...STS crew sleep begins