Final spacewalk completed despite transporter trouble
Updated: November 30, 2002

In one of the more challenging space station assembly spacewalks to date, two astronauts managed to accomplish all of their primary objectives today even though problems moving the station's $290 million robot arm transporter prevented them from using the Canadarm2 space crane as originally planned.

"Things have gone very well today," said flight director Robert Castle. "We started off with a problem but basically, today has gone quite well, we accomplished all of our objectives. We are still on track for a hopefully quiet day tomorrow, an undocking on Monday and a landing on Wednesday. All of that remains on track."

After three spacewalks, the newly installed P1 solar array truss segment is now fully outfitted and operational, its ammonia cooling system ready for use as required starting next year. Likewise, the robot arm transporter is healthy and fully operational even though engineers were unable to immediately move it back to its starting point at the conclusion of today's seven-hour spacewalk.

But that was simply because an automatic software sequence was interrupted when the arm ran into a stowed UHF antenna before the spacewalk began. Once spacewalker John Herrington deployed the antenna, freeing the transporter to continue moving, flight controllers had to manually input commands and the process took longer than expected.

As standing policy, mission managers don't want to move the robot arm's transporter unless spacewalkers are available for troubleshooting if necessary. By the time the problems with the MT were resolved today, there was not enough time left to make the move under the supervision of Herrington and spacewalker Michael Lopez-Alegria.

The next station spacewalk is planned for early December and the transporter may be left where it is on the outboard side of the P1 truss before it is moved back to its normal stowage position on the central S0 truss.

"We got all of our mission objectives accomplished and more," said Kim Ulrich, launch package manager for mission STS-113. "We're very pleased with how this mission has gone. We've left the space station in a good posture for the next upcoming flight (in March)."

The original plan for today's spacewalk was to move the mobile transporter from work site 4 on the central S0 truss to work site 7 on P1. The Canadarm2 space crane then was to be walked off the Destiny lab module and onto the transporter to support today's spacewalk. Herrington planned to anchor himself on the arm to install 18 spool positioning devices on ammonia line quick-disconnect fittings to prevent problems related to internal leakage.

Because many of the SPDs had to be mounted in hard-to-reach areas, Herrington planned to use the arm to put him into the proper positions. Following the spacewalk, the arm was to walk off the transporter and back to a grapple fixture on the lab module before the MT itself was ordered to return to work site 4. The move back to work site 4 was planned so that the MT's long power cable, which unreels as the cart moves along the truss, would be rolled back up and thus less exposed to possible damage from space debris impacts.

But those plans went up in smoke shortly after the MT moved from S0 to P1 and unexpectedly stopped. After debating the issue, flight controllers attempted to restart the cart using a backup drive system, but it refused to budge. In the meantime, Herrington and Michael Lopez-Alegria had been cleared to press ahead with their spacewalk to install a total of 33 SPDs and to complete the P1's outfitting.

Herrington promptly discovered the problem: The MT had run into a stowed UHF antenna that was to be deployed during the December spacewalk by station commander Kenneth Bowersox and Nikolai Budarin. After a bit of a struggle, Herrington successfully erected the antenna, freeing the MT to resume its trek to work site 7.

But because the transporter's automatic control sequence had been interrupted, flight controllers had to manually enter all of the data and commands needed to get the MT back in action. All of that took longer than expected, but eventually the transporter was firmly locked down at work site 7, safely plugged into its power and data sockets.

By that point, however, there was not enough time left to make it worthwhile to move the robot arm onto the transporter. So it simply remained in place on the Destiny module while the spacewalkers worked without it.

In the end, it made no difference. Herrington and Lopez-Alegria were able to install all 33 SPDs, including the 18 needed for the hard-to-reach quick-disconnect fittings. They also reconfigured the truss' power supply, provided heater power to components on P1's radiator system and accomplished a handful of other tasks.

"It was another great EVA," said lead spacewalk officer Dana Weigel. "Although we ended up having to rearrange some of the tasks to accommodate the UHF antenna deploy, we did end up completing all of the nominal tasks, including two get-ahead tasks.

"The nominal tasks that we had planned that we did today was the installation of 33 spool positioning devices, that's a total of 43 for (Endeavour's mission). We also mated up ammonia tank lines to the truss, we mated up the nitrogen tank to the ammonia tank so the system's configured to be filled with ammonia on (an upcoming flight). We checked out the S1 and P1 DDCUs (DC-to-DC converter units) during the EVA and those both checked out nominally.

"We installed a DDCU thermal cover and we re-wired some harnesses to provide power to P3 when it arrives (next year). The two get-ahead tasks were deploying the UHF antenna and we re-wired the squib power unit to get redundant heater power to some components on the radiator beam."

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