Delay Will Give Additional Time For Refining Procedures
NASA has decided to wait until Friday to conduct a spacewalk to
replace a failed ammonia pump module on the International Space
Station.
Flight Engineers (L-R) Tracy Caldwell Dyson and Doug
Wheelock prepare spacesuits in the ISS Quest airlock. NASA
Photo
Mission managers, program managers, flight controllers,
engineers, astronauts and spacewalk experts made the decision
Monday evening after continuing to analyze and refine engineering
requirements, and reviewing the results of an underwater practice
session.
Expedition 24 astronauts Doug Wheelock and Tracy Caldwell Dyson
currently are scheduled to start the repairs on the station’s
starboard truss Friday. Fellow astronauts Cady Coleman and Suni
Williams spent the afternoon in the Johnson Space Center’s
Neutral Buoyancy Laboratory practicing underwater the tasks needed
to restore the cooling loop over the course of two spacewalks.
Meanwhile, robotics experts are continuing to refine the
procedures that will be used by Expedition 24 flight engineer
Shannon Walker to guide Canadarm2 as she moves Wheelock into
position to swap the failed unit with a spare unit currently stored
on External Stowage Platform 2. That spare parts carrier is
attached to the Quest airlock that Wheelock and Caldwell Dyson will
use to exit and reenter the station.
The station today remains in a stable configuration. Most of the
crew's planned activities this week have been cancelled or deferred
in order to support spacewalk preparations.
Plans are in work to move the station’s Mobile Transporter
into position on the Starboard 1 truss on Tuesday. With the Mobile
Transporter positioned early, the team will be able to gather
additional data to confirm power resources are sufficient to use
the arm to support the spacewalk.
Each pump module weighs 780 pounds and is 69 inches long by 50
inches wide, and is 3 feet tall. The spacewalkers will need to
disconnect and reconnect five electrical connectors, four fluid
quick-disconnect devices, one fixed grapple bar and four bolts. The
spare pump module that will be used to replace the failed unit was
delivered to the station on the STS-121/Utilization Logistics
Flight-1 mission in July 2006.
The pump failed Saturday night after a spike in electrical
current tripped a circuit breaker. When the 780-pound pump failed,
it shut down half of the station’s cooling system. Efforts to
restart the pump, which feeds ammonia coolant into the cooling
loops to maintain the proper temperature for the station’s
electrical systems and avionics, were not successful. The
station’s crew worked with Mission Control to put the station
in a stable configuration.
In the first spacewalk, they will unbolt and remove the failed
pump module, and install the spare. A second spacewalk to hook up a
variety of electrical and fluid connections for the new pump module
is targeted for Monday.
Wheelock, who will be designated as EV1, or extravehicular crew
member 1, wearing the spacesuit bearing the red stripes, will be
making the fourth spacewalk of his career, while Caldwell Dyson,
designated as EV2, wearing the unmarked spacesuit, will be making
her first spacewalk.