Preparations for critical International Space Station repairs this week continue with another practice spacewalk by astronauts on the ground. In a giant Johnson Space Center swimming pool, veteran astronauts Rick Sturckow and Bobby Satcher will perform the rehearsal for a spacewalk fellow astronauts Doug Wheelock and Tracy Caldwell Dyson are expected Friday morning.
Wheelock and Caldwell Dyson will begin to replace an ammonia pump that failed last weekend, knocking out half the coolant system on the station's U.S. segment and requiring many systems to be powered down.
NASA is moving quickly to replace the pump module -- a difficult-to-maneuver, 780-pound box -- to avoid the worst-case scenario that another failure could shut down both coolant loops.
Suni Williams and Cady Coleman completed a first practice run in the pool known as the Neutral Buoyancy Lab on Monday. NASA later decided to delay the spacewalk from Thursday to Friday to allow for more planning time.
Managers plan to hold a readiness review Thursday before the first of two planned spacewalks to remove and replace the pump. If everything goes as planned Friday, Wheelock and Caldwell Dyson would complete the job Monday.
IMAGE: Last October, astronaut Tracy Caldwell, Expedition 23/24 flight engineer, attired in a training version of her Extravehicular Mobility Unit (EMU) spacesuit, participated in a spacewalk training session in the waters of the Neutral Buoyancy Laboratory (NBL) near NASA's Johnson Space Center. Divers are in the water to assist Caldwell in her rehearsal, which is intended to help prepare her for work on the exterior of the International Space Station.
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