Station power truss juggled between robotic arms
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 29, 2007
The space station's robot arm handed a 35,000-pound solar array truss segment to the shuttle's arm today as part of a carefully choreographed, step-by-step procedure to move the stowed arrays to the far left end of the station's main power truss.
Detached from its central mounting point during a spacewalk Sunday, the P6 array will be held by the shuttle arm until a transporter on the front face of the power truss can carry the station arm 80 feet or so to an outboard work site. Once in place, the station arm will take the array truss back and hold it in place until a spacewalk Tuesday to bolt P6 to the P5 spacer truss on the outboard side of an identical set of arrays known as P4.
At that point, the stowed solar panels will be re-extended, a radiator will be deployed and the left side of the station's power truss will be complete. A final set of arrays for the right side of the truss, S6, will be attached next fall.
Earlier today, flight controllers sent commands to deploy two folding radiator panels on the S1 truss segment as part of an ongoing procedure to fully activate the station's power and cooling systems. Additional radiators on the port side of the power truss will be deployed later.
The astronauts will enjoy four hours of off-duty time this morning, winding up with a joint crew meal at 8:08 a.m. After lunch, the station arm will lock onto the P6 solar array to complete the handoff procedure.
The entire crew plans to participate in a spacewalk review session this afternoon to go over the flight plan for Tuesday's excursion by Scott Parazynski and Doug Wheelock to bolt P6 to the station's main power truss.
In an overnight message to the astronauts, flight controllers said the timeline for Tuesday's spacewalk had been amended to let Parazynski carry out a brief inspection of the station's left-side solar alpha rotary joint to collect data for comparison to the right-side SARJ. The two SARJ joints turn the station's solar arrays to keep them face-on to the sun.
During an inspection of the starboard SARJ Sunday, spacewalker Dan Tani reported seeing what appeared to be metal shavings or filings on the joint's 10-foot wide outboard drive gear and bearing race. He also reported an apparent discoloration, or mottling, of the bearing race ring. Engineers asked for the inspection because of recently observed vibration and higher-than-normal power consumption, both signs of unwanted friction in the mechanism.
The source of the debris is not clear and engineers at the Johnson Space Center are evaluation a variety of options for additional inspections on an upcoming spacewalk. For Tuesday's outing, the only additional task is an inspection of the port SARJ, which is operating normally, to see if any similar debris and discoloration might be present.
"Anytime we run into these unknowns we end up with a lot of options on the table at once initially and we have to sort through them," station flight director Heather Rarick said late Sunday. "One of the things we've talked about is sending someone during the next EVA to the port side and see the SARJ, or the rotational ring out there, and find out what it looks like nominally because we haven't experienced any issues out there. That's one of the things we're considering doing."
The revised flight plan for Tuesday now includes a 40-minute block of time for Parazynski, starting just over five hours into the EVA, to remove one of 22 thermal blankets and inspect the interior of the port SARJ.
"Big picture for EVA 3: On the way back from deploying the P6 radiator, Scott will be stopping by the port SARJ, removing cover 12, and performing an inspection, picture snapping (with flash!) and sample-taking similar to EVA 2," flight controllers said in the overnight message to the crew. "This will give us a baseline to use for comparison in the (starboard) SARJ troubleshooting activities."
Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision E of the NASA TV schedule):
EDT........DD...HH...MM...EVENT 01:23 AM...05...13...45...S1 radiator deploy 12:38 AM...05...13...00...STS/ISS crew wakeup 02:38 AM...05...15...00...Spacesuit resizing 03:08 AM...05...15...30...Shuttle arm (SRMS): P6 grapple 03:38 AM...05...16...00...Station arm (SSRMS): P6 ungrapple 03:53 AM...05...16...15...Mobile transporter moves SSRMS to work site 8 04:08 AM...05...16...30...Spacesuit swap 04:18 AM...05...16...40...Nespoli ham radio opportunity 04:38 AM...05...17...00...Shuttle crew off duty 05:38 AM...05...18...00...Station crew off duty 08:08 AM...05...20...30...Joint crew meal 09:08 AM...05...21...30...SSRMS: P6 grapple 09:28 AM...05...21...50...Equipment lock preps 09:38 AM...05...22...00...Harmony module avionics rack outfitting 09:53 AM...05...22...15...SRMS: P6 ungrapple 10:13 AM...05...22...35...EVA-3 tools configured 10:30 AM...05...22...52...Mission status briefing on NASA TV 12:38 PM...06...01...00...EVA-3: Procedures review 01:43 PM...06...02...05...ABC, NBC, CNN crew interviews on NASA TV 02:38 PM...06...03...00...Crew choice downlink 02:53 PM...06...03...15...EVA-3: prebreathe and tools configured 04:08 PM...06...04...30...ISS crew sleep begins 04:38 PM...06...05...00...STS crew sleep begins 05:00 PM...06...05...22...Daily video highlights reel 10:30 PM...06...10...52...Flight director update on NASA TV
Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly.
Now, with identical solar panels in place on the left and right sides of the main power truss, NASA is moving P6 to its permanent position on the far left end of the beam. The segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June. Power and cooling lines were disconnected during an August flight, setting the stage for the massive truss's detachment, relocation and re-extension during Discovery's mission.
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