Spacewalkers to remove tank, experiments today
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: September 1, 2009
Astronauts John "Danny" Olivas and Nicole Stott are gearing up for a planned six-and-a-half-hour spacewalk to remove a massive 1,300-pound ammonia coolant tank from the International Space Station's solar power truss..
"Today's a big transfer day," said space station Flight Director Royce Renfrew. "We're right where we want to be with the transfer ops for this flight."
Flight controllers, meanwhile, implemented an alternative procedure overnight to help maintain the orientation of the shuttle-station "stack" with the station's control moment gyroscopes while nitrogen was vented overboard from the lab's coolant pressurization system in preparation for today's spacewalk.
The station normally would rely on small vernier steering jets aboard the docked shuttle to compensate and maintain the lab's orientation, or attitude, during a propulsive venting, but Discovery's vernier jets suffered a failure after launch and are out of action. Using Russian thrusters for a large maneuver earlier in the mission used up more fuel than expected and engineers implemented an alternative gyro control technique overnight for the nitrogen venting.
"The prop savings was on the order of 50 to 75 kilograms ... using the 'desats enabled" (technique) rather than just using the Russian segment thrusters last night," Renfrew said. "That all worked fine."
Today's spacewalk is the 131st devoted to station assembly and maintenance since construction began in 1998, the 12th so far this year and the first of three planned by Discovery's crew. Going into today's EVA, 90 astronauts and cosmonauts representing the United States, Russia, Canada, Japan, France, Sweden and Germany had logged 810 hours and 36 minutes of station assembly spacewalk time, or nearly 34 days.
For identification, Olivas, call sign EV-1, will be wearing a spacesuit with red stripes around the legs. Stott, EV-3, will be wearing a suit with no stripes. The spacewalk was scheduled to begin at 5:49 p.m. EDT.
Stott and Olivas spent the night in the space station's Quest airlock at a reduced pressure of 10.2 pounds per square inch to help purge nitrogen from their bloodstreams and prevent the bends after working in NASA's 5-psi spacesuits.
The primary goals of the excursion are to remove a depleted ammonia tank assembly, or ATA, and attach it to the space station's robot arm for temporary storage. The spacewalkers also will retrieve two experiment packages mounted on the European Space Agency's Columbus lab module. A new ATA charged, with 600 pounds of ammonia and tipping the scales at 1,702 pounds, will be installed during a second spacewalk by Olivas and Christer Fuglesang Thursday and the old tank will be mounted in the shuttle's payload bay for return to Earth.
The old tank would weigh 1,295 pounds on Earth - including 200 pounds of residual ammonia - and is one of the most massive space station components ever handled by spacewalking astronauts.
"In zero G (gravity), we sort of think of everything as being weightless and being easy to move around," said Zeb Scoville, the lead spacewalk officer at JSC. "The thing to remember is that although those things have no weight, they still have mass. ... They're going to have to try to manipulate that mass so it doesn't try to pull them out of their foot restraints. Keeping control of this is certainly a challenge, again because of the mass, the inertia and the fact that it sometimes wants to resist being turned or re-oriented."
Another issue is potential ammonia contamination.
"Before the first spacewalk, the fluid lines that run internal to the ammonia tank and also run from that ammonia tank along the truss structure into the fluid system, a section of that line (was) vented so there will only be residual bits of ammonia inside, there won't be the large pressurization volume of ammonia in those lines when they are demated," Scoville said. "So the amount of ammonia that could potentially leak is limited in that regard.
"If a crew member does get sprayed, we'll have time outside, exposed to the sun, the warm external environment, to bake off any ammonia ice that may be stuck on the suit. Beyond that bake-out scenario, we have some testing hardware once the crew ingresses the airlock. They can do a test at 5 psi that will detect any ammonia that may be off gassing from the suit. So, we'll be able to verify the crew is in a clean configuration before they come inside."
Stott and Olivas will disconnect the old ammonia tank from the port-1 truss segment and pull it out. Holding it in their gloved hands, the astronauts will orient the tank so shuttle pilot Kevin Ford, operating the station's robot arm, can lock on. The tank will remain on the end of the station arm until after the new ammonia tank is installed during the crew's second spacewalk. After that, the old tank will be mounted on a cargo carrier in the shuttle's payload bay for return to Earth, refurbishment and relaunch next year.
"Nicole and Danny have a lot of work to do to disconnect the plumbing and electrical and all that stuff and make sure the (old) tank's vented and everything," Ford said. "It's going to be interesting, they're going to actually hold that tank out there and position it in their hands while I grapple it with the big arm. Then I'll take that away from them and I'll hold onto that until almost the end of EVA-2."
With the old ammonia tank safely locked to the station's robot arm, Stott and Olivas will move to the outboard end of the Columbus module and retrieve two experiment packages, mounting them in Discovery's cargo bay for return to Earth.
While the spacewalk is going on, the station crew will be busy moving supplies and equipment from the Leonardo cargo module into the lab complex, including the storage rack, an astronaut sleep station, the COLBERT treadmill and the new carbon dioxide removal rack.
The space station currently is equipped with four small crew cabins, two in the Russian Zvezda command module, used by commander Gennady Padalka and cosmonaut Roman Romanenko, and two U.S.-built cabins on the port and starboard side of the Harmony module, used by Michael Barratt and Stott. European Space Agency astronaut Frank De Winne uses a temporary sleep station, or TeSS, in the U.S. Destiny laboratory module while Canadian Robert Thirsk bunks in a similar makeshift cabin in the Japanese Kibo module.
Thirsk will use the new NASA crew cabin, which will be temporarily mounted in Kibo and eventually moved to Harmony. A fourth U.S. sleep station will be launched next year and installed in Harmony as well.
The U.S. sleep stations have a volume of 54 cubic feet, about the same as a large refrigerator. They are sound-proofed and feature their own lighting, air ducts, computer ports, communications gear and alarm systems. Eventually arranged in a ring around Harmony, plastic sheathing at the back of each cabin also provides radiation shielding.
"They are very cool," Stott said before launch. "I think it's going to be nice. You show some people the space that's available and they're like, oh my gosh, how could you possibly do that? You think about it, though, it's like this volume that's available to you, it's the whole volume, you're not relying on sticking to a wall somewhere or anything like that. Just like the station in general, you have this whole volume to use."
Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision G of the NASA television schedule):
EDT........DD...HH...MM...EVENT 09/01 12:59 PM...03...13...00...Crew wakeup 01:34 PM...03...13...35...EVA-1: 14.7 psi repress/hygiene break 02:24 PM...03...14...25...EVA-1: Airlock depress to 10.2 psi 02:29 PM...03...14...30...ISS daily planning conference 02:44 PM...03...14...45...EVA-1: Campout EVA preps 04:14 PM...03...16...15...EVA-1: Spacesuit purge 04:29 PM...03...16...30...EVA-1: Spacesuit prebreathe 04:29 PM...03...16...30...ISS: Zero G rack transfer 05:19 PM...03...17...20...EVA-1: Crew lock depressurization 05:24 PM...03...17...25...ISS: COLBERT treadmill transfer 05:49 PM...03...17...50...EVA-1: Spacesuits to battery power 05:54 PM...03...17...55...EVA-1: Airlock egress 06:09 PM...03...18...10...EVA-1: Setup 06:34 PM...03...18...35...EVA-1: P1 ammonia tank release 06:44 PM...03...18...45...ISS: Crew quarters rack transfer 08:19 PM...03...20...20...EVA-1: EUTEF retrieval/stow 08:59 PM...03...21...00...ISS: Air rack transfer 10:09 PM...03...22...10...EVA-1/EV-1: MISSE 6 retrieval/stow 10:09 PM...03...22...10...EVA-1/EV-3: Station arm reconfig 10:34 PM...03...22...35...EVA-1/EV-3: MISSE 6 PEC stow 10:59 PM...03...23...00...EVA-1/EV-3: Get aheads 11:39 PM...03...23...40...EVA-1: Cleanup/airlock ingress 09/02 12:19 AM...04...00...20...EVA-1: Airlock pressurization 12:34 AM...04...00...35...Spacesuit servicing 01:44 AM...04...01...45...ISS evening planning conference 03:00 AM...04...03...01...Mission status briefing on NTV 03:59 AM...04...04...00...ISS crew sleep begins 04:29 AM...04...04...30...STS crew sleep begins 05:00 AM...04...05...01...Daily highlights reel 10:00 AM...04...10...01...Flight director's update 12:29 PM...04...12...30...Crew wakeup
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