Third spacewalk contains “windshield wiper maneuver”

William Atkins
Sunday, 08 June 2008 20:51

Science - Space

Besides the replacing of the nitrogen tank, Fossum will inspect the normally-operating left-side (port side) solar alpha rotary joint (SARJ).

Fossum will use tape to collect debris around the 10-foot (3-meter) drive gear so NASA scientists and engineers back home on Earth can take a more detailed look at them.

Although the left-side (port-side) SARJ is working ok, Fossum noticed some debris built up on it while performing a spacewalk on Thursday, June 5, 2008. The debris appears to be grease and gray dust. The left-side SARJ, one of two joints on the Station, rotates solar arrays in order to track the Sun.

The right-side (starboard side) SARJ has had continuing problems in the past, with damage found on the surface of the drive gear.

In other work during the spacewalk, the two astronauts will re-install a television camera on the power truss of the Station and remove launch locks and insulation from the robotic arm on the JAXA Kibo laboratory module.

Fossem comments on both SARJs, "I don't believe it looks at all like the starboard side. The starboard side definitely has metal shavings that show up and you can see some damage to the metal surface. There's just some things look different on the side we looked at the other day, the port side. It really looks to me like a little bit of grease, which is not a terribly big surprise when you're dealing with a bearing surface.” [SpaceFlight Now]

But the major objective of today's work is to replace a nitrogen tank assembly, or NTA, used to pressurize the station's ammonia coolant loops. The depleted tank is located in the right side S1 segment of the station's power truss while the replacement, launched earlier, is mounted on an external stowage platform - ESP-3 - on the left side of the truss.

At of 10:28 a.m. EDT the two spacewalkers are preparing to swap out the new nitrogen tanks. The spacewalk (or EVA—extravehicular activity) can be seen live on NASA TV.

During an earlier NASA interview Garan stated, "This is going to be an absolutely spectacular EVA. What's going to happen is I'm going up to the (right side of the) truss, to S1, where the old NTA is and I'll do the final preparations to pull it out of the truss. Meanwhile, Mike is going to translate all the way out to (the left side of the power truss) where the spare is and he's going to make the final preparations to receive the old NTA and to get the new NTA ready to move.” [Space.com]

He continues, "So when everything is all set, I'm going to get onto the end of the space station's robotic arm and I'm going to pull the NTA out of the truss as the arm is backing away from the truss. And so when we get out a safe distance away from the truss, I'll have this 550-pound box in my hand and the space station's robotic arm is basically going to do what we call the ‘windshield wiper maneuver' and it's going to go over the top over to ESP-3. So this maneuver takes about 20 minutes and on the top here I'll be almost (six stories) above the station looking straight down on the aft side of the station and the Earth (210) miles below. So it'll be a pretty spectacular view and, and pretty spectacular ride over to ESP-3." [Space.com]