Astronauts to make solar array repair spacewalk today
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 18, 2006
Astronauts Robert Curbeam and Christer Fuglesang, Sweden's first man in space, are preparing for a fourth spacewalk today to help coax a recalcitrant solar array to fully retract. The astronauts are running a few minutes ahead of schedule and the spacewalk, the 77th devoted to station assembly and maintenance since construction began in 1998, is expected to begin around 2 p.m.
This will be Curbeam's fourth spacewalk during this mission - a space shuttle record - and his seventh overall. He currently ranks 13th on the list of most experienced spacewalkers with 38 hours and 56 minutes of EVA time.
"This is the first time that one crew member has been asked to do four spaceswalks in one (shuttle) mission," said lead EVA planner Tricia Mack at the Johnson Space Center. "And really, if anyone can do it, it's Beamer. He is rock solid. ... he's calm under pressure, he is just a machine, he is an EVA machine. He does everything right, he says all the steps and he can do other people's tasks, he works quickly and effectively, he reacts well to change."
Curbeam, call sign EV-1, will be wearing a suit with red stripes around the legs. Fuglesang, call sign EV-2, will wear an unmarked suit. Here is a timeline of today's activity (in EST and mission elapsed time; includes items from rev. F of the NASA TV schedule):
EST........DD...HH...MM...EVENT 09:17 AM...08...12...30...STS crew wakeup 09:47 AM...08...13...00...ISS crew wakeup 09:52 AM...08...13...05...EVA-4: 14.7 airlock repress 10:12 AM...08...13...25...EVA-4: Hygiene break 10:37 AM...08...13...50...EVA-4: 10.2 airlock depress 11:02 AM...08...14...15...EVA-4: Campout preps 12:32 PM...08...15...45...EVA-4: Spacesuit purge 12:47 PM...08...16...00...EVA-4: Spacesuit oxygen pre-breathe 01:37 PM...08...16...50...EVA-4: Airlock depress 02:12 PM...08...17...25...EVA-4: Spacesuits to battery power 02:17 PM...08...17...30...EVA-4: Airlock egress 02:42 PM...08...18...00...EVA-4: P6-4B troubleshooting/retraction 05:42 PM...08...21...30...EVA-4: Payload bay cleanup 06:12 PM...08...23...25...EVA-4: Airlock ingress 06:37 PM...08...23...50...EVA-4: Airlock repress 08:47 PM...09...00...00...Rendezvous tools checkout 10:30 PM...09...01...43...Mission status briefing on NASA TV 12:47 AM...09...04...00...STS/ISS crew sleep begins 01:00 AM...09...04...13...Daily video highlights reel on NASA TV 08:47 AM...09...12...00...STS crew wakeup
The P6 solar array, made up of two wings known as 2B and 4B, was attached to the station six years ago to provide interim power during the initial stages of assembly. Construction has now reached the point where the arrays need to be moved to the station's main solar array truss and wired into the lab's permanent power system.
To do that, the two wings are being folded up one at a time, with 4B scheduled for retraction during Discovery's mission and the still fully extended 2B wing during a shuttle mission next March. In September, another crew plans to move the stowed arrays to the left end of the main truss and re-extend both wings.
The Discovery astronauts attempted to retract the 4B wing on Wednesday but they were only able to pull it in about half way. Several of the slats in the folding blankets, held in alignment by guide wires similar to the cords in pleated blinds, failed to fold evenly, stopping the process in its tracks. Repeated attempts to free a presumably jammed grommet and guide wire were unsuccessful.
On Saturday, during a spacewalk by Curbeam and Sunita "Suni" Williams to finish the Discovery crew's goal of re-wiring the space station, NASA's Mission Management Team approved a fourth spacewalk to help get the P6-4B wing retracted. Curbeam and Williams, meanwhile, finished their electrical work early and ventured up to the stalled array for an up-close inspection.
The spacewalkers then repeatedly shook the solar array storage box, setting up ripples in the hinged slats of the solar cell blankets, freeing up stuck grommets and permitting their crewmates inside to retract the central mast an additional six bays. But they eventually ran out of time and had to call it a day, leaving 11 of the mast's 31 open-framework bays still extended.
For today's spacewalk, Curbeam and Fuglesang will be equipped with a variety of tools, all insulated with non-conducting tape, to free grommets and guide wires as needed. The solar array will be shunted to lower its electrical potential. In addition, Curbeam will work from the end of the station's robot arm, allowing him to access possible trouble spots that otherwise might be beyond his reach.
NASA has budgeted three hours for the repair work, but the spacewalk can be extended several hours if necessary.