John Herrington's third spacewalk overcomes problems
John Herrington's third spacewalk, on November 30th, was supposed to be the simplest and least glamorous of the three. Herrington and his spacewalking partner Mike Lopez-Alegria were scheduled to spend most of their six-and-a-half hours installing Spool Positioning Device (SPD) adapters. The SPDs compensate for a design flaw by Boeing, the company which designed the space station's truss and cooling system.
The Space Station is cooled by ammonia -- not the 3 percent household ammonia used for cleaning, but 99 percent pure ammonia. Each hose has a "quick disconnect" connector which can be easily operated by an astronaut wearing a spacesuit glove. The quick disconnects were designed with dual seals in case one seal failed. But after the design was finished engineers realized one of the seals could leak resulting in a build-up of ammonia between the two seals. This would make it very difficult to open up the quick disconnect lever in the future, like trying to unscrew a garden hose while the faucet is open.
So engineers developed the SPDs. They squeeze around the quick-disconnect and hold them half way open, enough to let the ammonia leak past one seal but not the second. So spacewalking astronauts have been tasked with installing scores of SPDs wherever different components mate.
Herrington was assigned the task of installing the SPDs on the newly installed P1 Truss. The plan called for the Mobile Transporter (MT), a railcar/work platform to move from the center of the space station to the end of the P1. The space station's robot arm would grab on to the MT and provide a stable work platform for Herrington to install his SPDs.
So much for the best laid plans of mice and men and NASA. The MT started moving down its rails but suddenly stopped. Initially flight controllers thought it was a software problem but when they turned on the secondary motors the MT ground to a halt, indicating that something was blocking the way. Camera views couldn't find anything obstructing the path though.
So mission control asked Herrington to inspect the area and see what he might find. Herrington quickly discovered what had happened, saying: "Houston, I've found the problem. On the MT, it looks like the IUA (interface umbilical assembly) is bumping into the UHF antenna. I can deploy the UHF antenna and you'll have free clearance."
Mission control gave Herrington approval to deploy the antenna, even though it wasn't one of their planned tasks. Herrington had to remove three bolts and a pin which held the UHF antenna in its storage location. Herrington had to push the antenna in place when it was stuck. Lopez-Alegria complimented him saying, "Good job John, way to go."
Because the Mobile Transporter was so late in getting to its worksite there wasn't enough time for the robot arm to move into position to act as a work platform for Herrington. Turning bolts and using tools in space is a bit like working while standing on wet ice. If you turn a wrench you're just as likely to turn yourself the opposite direction as to loosen a bolt. The robot arm acts as a stable platform to give the astronaut something to push against while working in a spacesuit. Instead Herrington had to install his SPDs while free-floating. Instead of the robot arm, Herrington used his "Body Restraint Tether" which held him in place, the equivalent of having a friend wrap his arms around you to hold you in place.
It turned out that Herrington and Lopez-Alegria were so efficient, even without the robot arm, that they were able to complete all of their scheduled tasks, plus two additional tasks.
Astronaut Paul Lockhart, within the crew cabin, monitored the spacewalkers to keep them on their timeline and warn them if they were about to bump into something. At one point Lockhart started to warn Herrington, "John there's ..." and Herrington finished his thought, "a grapple fixture above me?" Lockhart replied, "You got it" and Herrington responded, "Thank you, good eyes."
While Herrington was concentrating on his tasks he had two personal items to note. His sister Jennifer Monshaugen had given birth to a baby girl, Ashley Joyce, the day before. In addition his parents Jim and Joyce Herrington were celebrating their wedding anniversary. He said, "It's my parents anniversary -- happy anniversary." Lopez-Alegria asked, "You think they're watching college football?" Herrington replied, "Probably."
At 8:37 p.m. astronaut Don Pettit, within the shuttle's cabin said, "It looks like we're about 10 minutes from sunset." Lopez-Alegria remarked, "Your last sunset EVA John for a while." Herrington added "Mine too." On their three spacewalks Herrington and Lopez-Alegria got to see the incredible sights of sunset in space through just the single transparent layer of their spacesuit helmets about a dozen times. Nobody knows when they'll have the opportunity to make a spacewalk in the future.
Even with all of their additional tasks the spacewalk only went half an hour longer than originally planned, clocking out at 7 hours. That gives Herrington a total spacewalking time of 19 hours and 55 minutes. While Herrington was a rookie just a week ago, he's now the 19th most experienced U.S. spacewalker.