Preliminary timeline for pump replacement spacewalk (EVA-1)
Flight planners at the Johnson Space Center are continuing to fine tune the timeline for a planned spacewalk Friday by Expedition 24 astronauts Tracy Caldwell Dyson and Douglas Wheelock to replace a faulty ammonia pump that failed Saturday, shutting down one of the space station's two primary coolant loops.
Under the current plan, Wheelock, call sign EV-1, and Caldwell Dyson, EV-2, will switch their spacesuits to battery power at 6:55 a.m. Friday, officially kicking off a planned seven-hour spacewalk. It will be the fourth EVA for Wheelock and the first for Caldwell Dyson.
The primary objectives of the spacewalk are to remove the faulty 780-pound pump module; temporarily stow it on a nearby payload attach fitting; and install the new pump module on the starboard one - S1 - truss segment on the right side of the International Space Station.
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pm/pm3.jpg)
Viewed from just ahead of the International Space Station, the faulty loop A
pump module -- PM1 -- is located in the starboard one, or S1, truss segment.
(Credit: NASA)
Along with unbolting the faulty pump, the astronauts also will have to demate electrical cables and four ammonia lines. The first two ammonia lines to be disconnected - M3 and M4 - will be connected to a "jumper box" that will prevent the loop A coolant system from over pressurizing during temperature swings in orbit. After installing the new pump module, the astronauts will reconnect the data and electrical lines.
During a second spacewalk Monday, Wheelock and Caldwell Dyson will reconnect the ammonia lines to finish the repair.
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pm/pm2.jpg)
Four ammonia lines leading to the faulty pump module must be disconnected,
along with bolts and electrical cables. (Credit: NASA)
The timeline for Friday's spacewalk may change pending additional analysis at the Johnson Space Center in Houston, but here is a preliminary version (in EDT and elapsed time):
Engineers at the Johnson Space Center are refining guidelines for the spacewalk, including what to do in the event of ammonia leaks or problems mating/demating any of the fluid lines. Even though the loop A coolant system is out of action until repairs are complete, the crew should have normal use of the station's robot arm -- Wheelock will ride on the end of the arm during the EVA while Caldwell Dyson will free float -- and near-normal television views are expected.
Under the current plan, Wheelock, call sign EV-1, and Caldwell Dyson, EV-2, will switch their spacesuits to battery power at 6:55 a.m. Friday, officially kicking off a planned seven-hour spacewalk. It will be the fourth EVA for Wheelock and the first for Caldwell Dyson.
The primary objectives of the spacewalk are to remove the faulty 780-pound pump module; temporarily stow it on a nearby payload attach fitting; and install the new pump module on the starboard one - S1 - truss segment on the right side of the International Space Station.
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pm/pm3.jpg)
pump module -- PM1 -- is located in the starboard one, or S1, truss segment.
(Credit: NASA)
Along with unbolting the faulty pump, the astronauts also will have to demate electrical cables and four ammonia lines. The first two ammonia lines to be disconnected - M3 and M4 - will be connected to a "jumper box" that will prevent the loop A coolant system from over pressurizing during temperature swings in orbit. After installing the new pump module, the astronauts will reconnect the data and electrical lines.
During a second spacewalk Monday, Wheelock and Caldwell Dyson will reconnect the ammonia lines to finish the repair.
![](http://www.cbsnews.com/network/news/space/ISS/iss24/iss24graphics/pm/pm2.jpg)
along with bolts and electrical cables. (Credit: NASA)
The timeline for Friday's spacewalk may change pending additional analysis at the Johnson Space Center in Houston, but here is a preliminary version (in EDT and elapsed time):
EDT........HH...MM...EVENT
08/06/10
06:55 AM...00...00...Spacesuits to battery power
07:00 AM...00...05...Post depress/airlock egress
07:25 AM...00...30...Tool and tether setup
07:45 AM...00...50...EV-1: Pump module (PM) removal preps
07:55 AM...01...00...EV-2: CETA cart preps
08:35 AM...01...40...EV-1: Station arm (SSRMS) prep and ingress
08:45 AM...01...50...EV-2: PM jumper vent
09:00 AM...02...05...Initial PM quick-disconnect (QD) operations
09:30 AM...02...35...QD demate
09:50 AM...02...55...Thermal shrouds on all QDs
10:05 AM...03...10...EV-1: Retrieve AGB (adjustable grapple bar)
10:10 AM...03...15...EV-2: Prep failed PM for removal from S1 truss
10:50 AM...03...55...Install AGB on failed PM
11:10 AM...04...15...EV-1: Failed PM moved to payload attachment fitting
11:10 AM...04...15...EV-2: Spare PM preps
11:30 AM...04...35...EV-1: Spare PM preps
11:50 AM...04...55...BINGO for spare PM removal
12:20 PM...05...25...Remove spare PM from external storage platform No. 2
12:50 PM...05...55...Install spare PM in S1 truss
01:25 PM...06...30...Cleanup and ingress
01:50 PM...06...55...Pre-airlock repress
01:55 PM...07...00...Airlock repress
Engineers at the Johnson Space Center are refining guidelines for the spacewalk, including what to do in the event of ammonia leaks or problems mating/demating any of the fluid lines. Even though the loop A coolant system is out of action until repairs are complete, the crew should have normal use of the station's robot arm -- Wheelock will ride on the end of the arm during the EVA while Caldwell Dyson will free float -- and near-normal television views are expected.