Wed, Aug 11, 2010
Tough Repair Job Continues
Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell
Dyson spent Tuesday completing preparations for their second
spacewalk Wednesday out of the Quest airlock to replace the failed
ammonia coolant Pump Module on the S1 truss of the complex while
the International Space Station Mission Management Team gave its
final approval to proceed with the spacewalk.
NASA managers decided to begin Wednesday's spacewalk one hour
later than originally planned. The additional time will allow teams
to fine-tune robotic procedures and get some extra rest. NASA TV
coverage now will begin at 7 a.m., and the crew is scheduled to
switch to battery power at 7:55 a.m.
Overnight, ground controllers activated the Gaseous Pressure
Regulator Valve (GPRV) for the Loop A Nitrogen Tank Assembly,
lowering the overall pressure in the plumbing for the inactive
cooling loop in advance of Wednesday’s spacewalk by Wheelock
and Caldwell Dyson. The GPRV’s pressure reduction will assist
in the closure of quick disconnect valves at the S0/S1 truss
interface Wednesday by Wheelock and Caldwell Dyson as part of the
isolation of the line for the removal of the fourth and final fluid
line connector holding the failed pump module in place. The lowered
pressure will also facilitate the remate of all of the fluid lines
once the new pump is installed. That activity is targeted for the
third spacewalk no earlier than Sunday.
Once outside on Wednesday, Wheelock and Caldwell Dyson will
isolate the Loop A ammonia cooling line upstream from that final
connector by closing quick disconnect valves, then will use a tool
to vent residual ammonia from the failed Pump Module before the
final cooling line is disconnected. That will lead to the
disconnection of five electrical and data cables and four bolts
from the old pump so it can be extracted from the truss through the
use of a grapple bar and parked on a payload bracket on the
station’s Mobile Base System. If all goes as planned, the
spare pump will be installed during the third spacewalk.
Wheelock and Caldwell Dyson conducted final timeline reviews
Tuesday with flight controllers and moved into the Quest airlock
just before 4 p.m. EDT to begin their overnight
“campout” to reduce the nitrogen in their bloodstreams.
They will be awakened at 2 a.m. Wednesday to complete spacewalk
preparations and to suit up for their day’s work. This will
be the fifth spacewalk for Wheelock, who will wear the suit bearing
the red stripes, and Caldwell Dyson’s second spacewalk. She
will wear the unmarked suit.
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