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Spacewalk choreography to replace station's coolant tank BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: April 8, 2010 
Astronauts Rick Mastracchio and Clay Anderson are set for a planned six-and-a-half-hour spacewalk Friday, the first of three excursions required to install a 1,700-pound ammonia coolant tank on the International Space Station's solar power truss.
For identification, Mastracchio, call sign EV-1, will be wearing a suit with red stripes around the legs. Anderson, EV-2, will be wearing an unmarked spacesuit. The International Space Station features two independent coolant loops that circulate ammonia through huge radiator panels to dissipate the heat generated by the lab's electrical systems. Each loop features a nitrogen pressurization system and an ammonia reservoir that must be periodically replaced. "It's like Freon in your air conditioner at home, but we use ammonia on the outside of the station," Anderson said. "So we have a huge tank. It's about eighteen hundred pounds. It's probably the size of a double refrigerator-freezer component. There are actually two, one on the right and one on the left. The one on the left has recently been changed out by another shuttle crew. So we're going to change the one on the right." Mastracchio said the biggest challenge is the coordination required to swap out the massive components. "The real challenge here is this ammonia tank that we're moving is taking three EVAs, or part of three EVAs, to get it done," he said. "Our first EVA, we'll remove the new ammonia tank from the shuttle and get it onto the station (where) we'll temp stow it. The second EVA, we'll actually swap the two ammonia tanks, the new one for the old one and then on the third EVA, we'll be moving the old tank from the space station into the space shuttle's payload bay for return." During Friday's spacewalk, Anderson and Mastracchio first will disconnect ammonia and nitrogen pressurization lines from the old tank, then move to the shuttle's cargo bay where they will detach the new ammonia tank assembly from its mount and hand it off to the station's robot arm. Stephanie Wilson and shuttle pilot James Dutton, operating the space station's robot arm, will move the new ATA to a temporary mounting point on the crane's mobile base. While that is going on, the spacewalkers will install a replacement rate gyro assembly, a device that helps the station's computers determine the lab's orientation in space. "During each of the EVAS, we have to hold the ATA, this ammonia tank, up over our
heads," Mastracchio said. "Clay's going to do it on EVA-1 then I do it on EVA-2.
We're going to be holding this tank over our heads, trying to control it while Jim
and Stephanie come in and grapple it. So I'm a little concerned about trying to have
the stability to hold that tank nice and firm and steady ... so they can come in and
grapple it."
But mission managers opted to delete the battery work after an analysis showed the possibility of an electric shock hazard involving the mini work stations attached to the astronauts' suits that hold tools and other gear. Devices called plasma contactor units operate during space station EVAs to prevent dangerous charge buildups. But at the far ends of the power truss, depending on the station's orientation with respect to Earth's magnetic field and a variety of other factors, a shock hazard remains a possibility. As a result, the battery work was deleted from Friday's spacewalk. Long term, the astronauts who will remove the batteries during the next shuttle mission will use equipment that is better insulated to eliminate the threat. While Anderson and Mastracchio are working outside the station, the astronauts inside the lab will be working to unload the Leonardo multi-purpose logistics module. Among the items scheduled for transfer during the spacewalk are an experiment sample freezer, known by the acronym MELFI, a muscle loss experiment and a new crew cabin, the fourth and final U.S. cabin to be moved to the station. NASA's original plan was to equip the sleep station with a curtain-like liner to turn it into a bathing and hygiene cabinet. "It's a space shower," said Kirk Shireman, deputy manager of the space station program at the Johnson Space Center. "We don't really take showers on board the ISS, but people need to bathe and shampoo their hair and because it can release free water, we like to do it in a place that won't allow the water to float and get into avionics, electrical equipment, that can cause damage. "So we actually put a liner in there. It's not as simple as you would think. It's not just a shower curtain, it's a little more complicated than that. But it's a station with privacy where the crew members can go and clean up. A very important thing from a health standpoint and also a psychological standpoint." But with the arrival of the Soyuz TMA-18 spacecraft last weekend, the Expedition 23 crew includes three Russians. The Russian segment of the station only has two crew sleep stations and a third will not be available until 2012 when a new Russian lab module is launched. NASA may let the Russians use the new U.S. crew cabin as needed until then and instead use the toilet compartment in the Tranquility module as a hygiene station. Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision C of the NASA television schedule; best viewed with fixed-width font): EDT........DD...HH...MM...EVENT 04/08 08:51 PM...03...14...30...Crew wakeup 09:26 PM...03...15...05...EVA-1: Airlock repress/hygiene break 10:16 PM...03...15...55...EVA-1: Airlock depress to 10.2 psi 11:31 PM...03...17...10...MPLM transfers 04/09 12:06 AM...03...17...45...EVA-1: Spacesuit purge 12:21 AM...03...18...00...EVA-1: Spacesuit prebreathe 01:11 AM...03...18...50...EVA-1: Crew lock depressurization 01:41 AM...03...19...20...ZSR transfer 01:41 AM...03...19...20...EVA-1: Spacesuits to battery power 01:56 AM...03...19...35...EVA-1/EV-1: FBG retrieve 01:56 AM...03...19...35...EVA-1/EV-2: S1 ATA FQD release 02:06 AM...03...19...45...ZSR deploy 02:26 AM...03...20...05...EVA-1/EV-1: Payload bay ATA release preps 02:41 AM...03...20...20...EVA-1/EV-2: Payload bay ATA preps 03:11 AM...03...20...50...EVA-1: ATA release and handoff 03:36 AM...03...21...15...MELFI transfer 03:56 AM...03...21...35...EVA-1/EV-1: JEM seed retrieval 03:56 AM...03...21...35...EVA-1/EV-2: Payload bay cleanup 04:36 AM...03...22...15...Crew quarters transfer 04:41 AM...03...22...20...EVA-1: ABG retrieve and install 05:26 AM...03...23...05...EVA-1: S0 RGA R&R 05:56 AM...03...23...35...EVA-1/EV-2: P1 FHRC clamp release 06:41 AM...04...20...00...EVA-1/EV-1: WIF EXT RLCT 07:11 AM...04...50...00...EVA-1/EV-2: Get aheads 07:41 AM...04...01...20...EVA-1: Cleanup 07:56 AM...04...01...35...EVA-1: Airlock ingress 08:06 AM...04...01...45...MARES transfer 08:11 AM...04...01...50...25...EVA-1: Airlock repressurization 08:26 AM...04...02...05...Post-EVA servicing 08:56 AM...04...02...35...WORF preps 10:21 AM...04...04...00...ISS crew sleep begins 10:30 AM...04...04...09...Mission status briefing on NTV 12:51 PM...04...06...30...ISS daily planning conference 01:21 PM...04...07...00...STS crew sleep begins 02:00 PM...04...07...39...Daily highlights reel on NTV 06:30 PM...04...12...09...Flight director's update on NTV 09:21 PM...04...15...00...Crew wakeup
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The crew patch for Discovery's flight delivering
