Astronauts gear up for dramatic spacewalk
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 28, 2007
Running an hour ahead of schedule, astronauts Scott Parazynski and Dan Tani suited up and made final preparations for a dramatic six-and-a-half-hour spacewalk today to disconnect a 35,000-pound solar array segment for a two-day move to the far left end of the space station's main power truss.
The port 6, or P6, truss segment will remain on the end of the space station's robot arm overnight before being handed off to the shuttle's arm on Monday. The station arm then will ride a transporter to the far left end of the power truss and re-grapple P6. If all goes well, the arm will maneuver the truss into position for attachment to the P5 segment Tuesday during the crew's third spacewalk.
With the arm fully extended, operator Stephanie Wilson will have little or no visibility of the attachment interface. Instead, she will rely on guidance from spacewalkers Parazynski and astronaut Doug Wheelock. Once the truss segment is bolted in place, it's two huge solar panels will be re-extended to accomplish one of the primary goals of Discovery's mission.
"It's a big truss," lead flight director Rick LaBrode said Saturday. "Putting it outboard of P5 is pretty tricky. The robotic ops involved are complex, the arm is pretty nearly reached out and you're working essentially at the very end of its capability. And then the visuals are non existent. So for the most part, we're relying on the (spacewalkers to guide) it into place. So you have this big truss, the arm's fully extended and you're trying to thread a needle without really good visuals. So it is extremely complex, but ... I have every bit of confidence we're bgoing to pull this off."
Said Wheelock in an interview with CBS News: "Our confidence level is very high. We're very excited, we've trained and trained for this task and we are ready. We're even ready for any contingencies we might see. We're very excited about our spacewalk (Sunday) with Scott and Dan going out the door. (Stephanie Wilson) and I will be backing them up on robotics and we're just real, real excited."
For today's excursion, Parazynski and Tani, after disconnecting P6, will focus on outfitting the newly installed Harmony module. Tani also will spend an hour or so inspecting a massive rotary joint on the right side of the power truss to look for any signs of whatever might be causing excessive friction in the mechanism that turns outboard solar panels to track the sun.
"We're seeing some increased currents, which are indicative of some increased friction on that joint," said Kirk Shireman, deputy manager of the space station program. "We've collected most of the data we can collect with the sensors that we have in place and what we need to do is get some visual inspection of that joint. So ... we made a decisoin to send one of the crew members out to that interface during EVA-2 and actually go 360 degrees around that joint and look at specific bolts and thermal blankets and make sure they're all in configuration."
For today's spacewalk, Parazynski (call sign EV-1) will be wearing a spacesuit with red stripes around the legs. Tani's suit has broken red stripes. His call sign is EV-3.
This is the 94th spacewalk devoted to station assembly and maintenance since assembly began in 1998, the 17th so far this year and the second of five planned for Discovery's mission. Going into today's excursion, 73 astronauts and cosmonauts representing the United States, Russia, Canada, Japan, Germany, France and Sweden had logged 574 hours and 13 minutes of EVA time building and maintaining the lab complex.
Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision D of the NASA television schedule):
EDT........DD...HH...MM...EVENT 10/28/07 01:08 AM...04...13...30...STS/ISS crew wakeup 01:43 AM...04...14...05...EVA-2: Airlock repress to 14.7 psi 02:53 AM...04...15...15...EVA-2: Campout EVA prep 04:23 AM...04...16...45...EVA-2: Spacesuit purge 04:38 AM...04...17...00...Station arm (SSRMS): walkoff lab to mobile transporter 04:38 AM...04...17...00...SSRMS: ungrapples lab module 04:38 AM...04...17...00...EVA-2: Spacesuit pre-breathe 04:53 AM...04...17...15...SSRMS: grapples P6 05:28 AM...04...17...50...EVA-2: Crew lock depressurization 06:03 AM...04...18...25...EVA-2: Airlock egress 06:18 AM...04...18...40...EVA-2: Disconnect Z1/P6 umbilicals 06:43 AM...04...19...05...EVA-2: EV-1: Detach P6 solar array 06:58 AM...04...19...20...EVA-2: EV-3: Detach P6 solar array 07:13 AM...04...19...35...Crew meals begin 08:03 AM...04...20...25...EVA-2: EV-3: Airlock ops 08:13 AM...04...20...35...EVA-2: EV-1: Node 2 outfitting 08:13 AM...04...20...35...SSRMS: P6 demate 08:43 AM...04...21...05...EVA-2: EV-3: Starboard SARJ inspection 09:43 AM...04...22...05...EVA-2: EV-3: S1 SFU 10:03 AM...04...22...25...EVA-1: EV-3: Spare power switching unit installation 10:13 AM...04...22...35...EVA-2: EV-3: Circuit breaker replacement 10:43 AM...04...23...05...EVA-2: Node 2 grapple fixture installation 11:58 AM...05...00...20...EVA-2: EV-1: Node 2 outfitting 12:18 PM...05...00...40...EVA-2: Airlock ingress 12:38 PM...05...01...00...EVA-2: Airlock repressurization 12:48 PM...05...01...10...Spacesuit servicing 02:30 PM...05...02...52...Mission status briefing on NASA TV 04:08 PM...05...04...30...ISS crew sleep begins 04:38 PM...05...05...00...STS crew sleep begins 05:00 PM...05...05...22...Video highlights reel on NASA TV 10:30 PM...05...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 needs to move 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.
Complicating the work, the station's robot arm cannot reach far enough on its own to make the move. So the station arm, after handing P6 off to the shuttle's space crane, will be moved by the station's mobile transporter to the far end of the power truss. At that point, the shuttle arm will hand the truss segment back to the station arm and Parazynski and Wheelock, making their third spacewalk by that point, will oversee its attachment to the P5 truss segment.
"Moving the P6 solar array will be a major activity," shuttle commander Pam Melroy said in a NASA interview. "On our second spacewalk - our first spacewalk is all about node 2 - we'll be using the robotic arm in one location to actually reach around and pull P6 off ... with the assistance of our spacewalkers.
"Once the P6 has been detached from the space station, then the robotic arm will move it around to the port side of the shuttle, at which point it will be handed off to the shuttle arm. The shuttle robotic arm will take control of the P6 truss while the space station robotic arm is reconfigured and rolled out on the mobile transporter, the mobile platform, all the way to the far end of the port truss. And then, we'll use the station arm to take it back and install it in its final location.
"This is pretty nearly the design-limiting case for the robotic arm of the space station, so it's out at its full extension, trying to get that truss out there," Melroy said. "We'll have the help of the spacewalkers on the third spacewalk to do that. So, all these activities will actually span three days, three full days, two spacewalks with robotics in the middle."
Last December, attempts to stow the folding blankets making up one side of the P6 array ran into problems when several of the slats making up the blankets folded the wrong way along their creases. The astronauts ultimately were successful and engineers don't anticipate major problems re-extending the arrays.
They'd better be right. The station's robot arm will be fully extended just to attach P6 to P5. It will not have the reach necessary to position a spacewalker beyond the lowest few feet of the huge arrays if any major problems are encountered.
"One of perhaps the most audacious things we've ever done in space is this P6 solar array truss relocation," said Parazynski, an emergency room physician and veteran spacewalker making his fifth shuttle flight. "We're powering down this major element, something that we've never done before, basically shutting off the lights, shutting off the computers, turning off the cooling, unbolting it, disconnecting all the fluid and electrical and data lines and then via a process of EVA and very complex robotics we're going to take it to the very tip of the space station and then reverse the process: bolt it together, hook up connectors, deploy solar arrays, deploy a radiator.
"One of the things I love about NASA is we plan for success but we prepare for failure. And so we are very well prepared. A lot of people, a lot of smart rocket scientists around the Johnson Space Center ... have spent a lot of time figuring out what could go wrong and what we might do to address those things. We have a very long list of procedures we can run if things don't go exactly to plan."
A fourth and final set of solar arrays - S6 - will be mounted on the starboard, or right, side of the main truss during a shuttle flight next year.