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Spacewalk No. 3 begins BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: August 16, 2010 
Running 35 minutes ahead of schedule, astronauts Tracy Caldwell Dyson and Douglas Wheelock switched their spacesuits to battery power at 6:20 a.m. EDT to officially kick off a planned six-and-a-half-hour spacewalk to install a spare ammonia pump in the International Space Station's cooling system. For identification, Wheelock, call sign EV-1, is wearing a suit with red stripes around the legs and will be using helmet camera No. 19. Caldwell Dyson, EV-2, is wearing an unmarked suit and will be using helmet cam No. 20. The U.S. segment of the International Space Station features two coolant loops that circulate ammonia through huge radiators to dissipate the heat generated by the lab's electronics. The ammonia pump in loop A, mounted in the starboard one, or S1, truss segment, failed July 31, forcing the six-member crew to implement a widespread powerdown. Wheelock and Caldwell Dyson originally planned two spacewalks to repair coolant loop A, one to remove the old pump and install a spare and a second to complete the required ammonia line connections. But during their first excursion Aug. 7, one of four ammonia lines leaked, preventing the faulty pump's removal. Before a second spacewalk Aug. 11, flight controllers lowered pressure in the line to stop the leak and Wheelock was able to disconnect the balky M3 connector. The astronauts then unbolted the failed pump and Wheelock, anchored to the end of the station's robot arm, moved it to an attachment fitting at the base of the arm's mobile transporter. The primary goals of today's spacewalk are to remove a spare pump module from external stowage platform No. 2, install it in the S1 truss segment and reconnect the ammonia lines and five electrical cables. The spare pump, launched to the station in 2006, is the oldest of four stored aboard the space station as a hedge against coolant system failures. If time is available, the astronauts will install an electrical cable between the Quest airlock and the Unity module that is required before attachment of a cargo module during a shuttle flight in November. Here is an updated spacewalk timeline (in EDT and elapsed time; best viewed with fixed-width font): EDT........HH...MM...EVENT 06:20 AM...00...00...Suits to battery power 06:25 AM...00...05...Post depress/airlock egress 06:40 AM...00...20...EV-1: Tether swap; ingress robot arm (SSRMS); .....................loosen four bolts on spare pump module (PM); .....................release three bolts 06:40 AM...00...20...EV-2: Assist EV-1; remove caps 07:40 AM...01...20...EV-1: Release final bolt; remove spare PM from .....................external stowage platform No. 2 (ESP-2) 07:40 AM...01...20...EV-2: Assist EV-1; cleanup ESP-2 08:10 AM...01...50...EV-1: PM install in S1 truss; engage four bolts 08:10 AM...01...50...EV-2: Mate electrical cables 09:10 AM...02...50...EV-1: Mate PM quick disconnects (QDs); open valves; .....................install SPDs 09:10 AM...02...50...EV-2: Assist with QDs 10:35 AM...04...15...EV-1: Retrieve vent tool, PM stowage bags; .....................move to ESP-2 10:35 AM...04...15...EV-2: Cleanup S1 tethers; couple CETA carts 11:05 AM...04...45...EV-1: Remove SSRMS foot restraint; install on ESP-2 11:35 AM...05...15...EV-1: Install J612 extension cable between Quest .....................and Unity for cargo module attachment during .....................November shuttle flight 11:35 AM...05...15...EV-2: J612 extension cable install 12:20 PM...06...00...Cleanup/airlock ingress 12:45 PM...06...25...Airlock pre-pressurizationThis is the 150th EVA devoted to space station assembly and maintenance since construction began in 1998, the 14th so far this year, the sixth overall for Wheelock and the third for Caldwell Dyson. Going into today's outing, ISS spacewalk time stood at 937 hours and four minutes, or 39 days.
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VIDEO:
POST-SPACEWALK NO. 2 STATUS BRIEFING 