Spacewalker says cleaning damaged joint a 'big job'
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: June 9, 2008
The powder-like debris dusting the outer edge of the space station's left-side solar array rotary mechanism does not appear to represent a serious problem, spacewalker Mike Fossum said today. He said the grease and debris seen on the port solar alpha rotary joint does not look anything like the much more severe contamination that has hobbled the station's right-side SARJ.
"There's really no similarity because on the starboard side, the damage is extensive and apparent," Fossum said during a crew news conference aboard the station. "The bearing surface itself is severely eroded, maybe not very thick but there's definitely a lot of damage there. On the port side, you really didn't see that at all. You see a little bit of the grease that some expected, and some didn't. It's really unclear.
"The particles over there (on the port drive gear), it's just a few fine, almost powder-like particles. On the starboard side, it's metallic particles that are clinging to things, you can see magnetic pattern kind of features in there, the way they cling to corners and things like that. On the port side, there's nothing like that. It's more like just a little bit of dust, maybe kind of like the dust you have on your brakes."
The international space station is equipped with two motor-drive 10-foot-wide SARJ gears, one on either side of the lab's main power truss, that are designed to rotate outboard solar arrays like giant paddle wheels to track the sun. The devices are crucial for maximizing the electricity the station's solar panels can generate.
Last summer, engineers began noticing higher-than-usual vibration levels in the right-side joint mechanism, along with electrical current spikes indicative of increased friction as the gear rolled through 12 trundle bearing assemblies. During a subsequent spacewalk inspection, astronauts discovered extensive metallic contamination covering the active drive gear and degradation, or erosion, of at least one of the gear's bearing surfaces.
Despite extensive troubleshooting, engineers still don't know what might be causing the damage. One possibility is a small crack or breakdown in the hardened bearing surface that produced debris that was then crushed as it passed through the trundle bearings, causing more damage and creating more debris. Whatever the cause, it is a serious problem and flight controllers no longer operate the right-side SARJ in "auto-track" mode.
The left-side SARJ is operating normally, but Fossum spotted buildups of grease during an inspection Thursday. Photographs also indicted small amounts of an unknown material dusting the outer edge of the drive gear.
Engineers believe the grease may be coming from one or more of the trundle bearings the gear rolls through and it may be beneficial in slowing or preventing the sort of surface breakdown that has damaged the right-side gear. In any case, the grease is not thought to be an issue. The source of the powder-like material is not yet known, but Fossum collected samples during a spacewalk Sunday.
Each SARJ is made up of two identical drive gears, only one of which is used at any given time. NASA managers are holding open the option of moving all 12 trundle bearings and two drive motors to the backup gear in the right-side SARJ, but they don't want to take that step without first knowing what happened to the current drive gear to make sure the problem doesn't crop up again.
In the near term, astronauts may attempt to clean up the contamination in the starboard SARJ using grease and cloth wipes to get as much mileage out of the damaged gear as possible before switching to the backup gear. Fossum tested cleaning procedures during a spacewalk last Tuesday and while they seemed to work, "that's going to be a big job."
"What you'd really like to do is go out there with a shop vac, but that's not going to work for obvious reasons," Fossum said today. "And they don't want to use a brush that would cause all those particles to end up just in other places or perhaps clinging to solar arrays and causing other problems.
"So the grease looks like it's a pretty good answer. It's going to be a lot of work, but you can lay down a bead of grease, kind of wipe it across the surface you're trying to clean, and then scrape that up to get most of (the debris) and then go over it with essentially a terry cloth wipe, It's kind of a mitt with terry cloth on one side to clean up most of the grease. Maybe we see from the port side that a little bit of grease isn't a bad thing."
Fossum and his crewmates - commander Mark Kelly, pilot Kenneth Ham, flight engineer Ronald Garan, Karen Nyberg, Japanese astronaut Akihiko Hoshide and returning space station flight engineer Garrett Reisman - spent the day replacing spacesuit battery chargers in the Quest airlock module, testing the Japanese Kibo module's robot arm and re-opening a storage module that was bolted to the top of Kibo on Friday.
Reisman's replacement - Gregory Chamitoff - will remain behind aboard the station with Expedition 17 commander Sergei Volkov and Oleg Kononenko when Discovery undocks Wednesday. Hatches between the two spacecraft will be closed Tuesday evening.
"This is so much fun," Chamitoff said today. "The station is huge and there's plenty or room here for 10 people to work hard and do what we've done. I think when they leave, it's going to be very sad for me to see them go. I think that one moment, when we close the hatch, that's going to be the hard moment. After that, I'm with really good friends that I've spent years training with and they've already been here for two months, so they know how to do it and they'll show me the ropes."
Reisman, launched to the station in March, said he's looking forward to getting back to Earth.
"As far as what I'm looking forward to the most, that's easy. I can answer that with two words and it's Simone Francis, who's my wife," he said, laughing. "No doubt about that. And our cat, Fuzzy. ... Let's see, as far as what I'll miss most, it's definitely just floating. We call it floating, but really it's more like flying because as soon as you push off, you're moving through the air like some kind of super hero and being able to do that every day as you're commuting to work, it's unreal. That's what I'll miss the most.
"As far as what I'm looking forward to eating the most, of course, I would love to have a good slice of pizza. We don't really have much bread on board," he said. "We eat mostly tortillas because bread makes too many crumbs. So a nice, big, fat hamburger bun or something like that would be great. And that's what I think about.
"But the truth is, adjusting back to gravity is not so easy. Just like adjusting to weightlessness takes some time, adjusting to gravity takes some time, too. So even though I have visions of stepping off the shuttle and chowing down on a giant T-bone steak or something, that's not going to happen. But eventually it will, and I'm looking forward to that day where I can enjoy my favorite foods and do some of the things I love to do that I haven't been able to do from up here."