Astronauts prepare for mission's final spacewalk
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: June 8, 2008
Astronauts Michael Fossum and Ronald Garan are preparing for a third and final spacewalk today, a six-and-a-half-hour excursion highlighted by a dramatic robot arm ride over the top of the international space station to replace a nitrogen tank. Dubbed the "windshield wiper maneuver," the ride from one side of the station to the other will put Garan "clearly on top of the world," said arm operator Karen Nyberg, as he carries the 550-pound tanks.
"If you think about it, I'm going to be on the end of the arm and as we're doing this windshield-wiper maneuver right here at the top, I'll be 80 feet above the station looking down at the station, looking down at the Earth," Garan said before launch. "It's going to be really exciting, it's going to be really challenging, but I'm really looking forward to it."
Fossum will stow the old tank and hand Garan the fully charged replacement. Fossum also plans to re-visit the left-side solar alpha rotary joint, or SARJ, remove a thermal cover and use Kapton tape to collect samples of dust-like debris he spotted on the joint's big drive gear during an inspection Thursday.
The space station is equipped with two 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 right side SARJ has suffered considerable damage to the surfaces of the 10-foot-wide drive gear that are gripped by 12 three-roller trundle bearings.
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 10-foot-wide 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 dust-like material was somewhat of a surprise, Fossum said, but it is nothing like the damage and debris seen in the right-side SARJ.
"I don't believe it looks at all like the starboard side," Fossum told a reporter Saturday. "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.
"Through the photographs, there might be a little bit of dusting of some other deposits around there. We plan to go out with a little bit of special tape and collect some of that dust from around the edge of the bearing. But really, that bearing looks to be in pretty darn good shape."
The crew was awakened at 5:32 a.m. by a recording of "The Mickey Mouse Club March" beamed up from mission control. The spacewalk, the 112th devoted to station assembly and maintenance since construction began in 1998, was scheduled to begin at 10:32 a.m. (as of 7:30 a.m., the astronauts were running about a half-hour ahead of schedule).
Along with the nitrogen tank swap out and SARJ work, the spacewalkers also plan to re-install a repaired TV camera on the power truss and remove launch locks and insulation from the Japanese robot arm on the outboard end of the Kibo lab module.
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.
After exiting the Quest airlock module, Fossum will make his way to ESP-3 to prepare the new tank for handoff while Garan proceeds to the right side of the truss to pull out the depleted tank.
"This is going to be an absolutely spectacular EVA," Garan said in a NASA interview. "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.
"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."
Nyberg, assisted by Japanese astronaut Akihiko Hoshide, will be operating the station arm.
"It's going to be a fun ride for him because the arm is going to go completely stretched out up in a big arc over to the other side of the truss and so he'll be clearly on top of the world at that point."
Once on Fossum's side of the power truss, "we will stow the old nitrogen tank assembly on ESP-3," Garan said. "I'll grab the new one and we'll just do the maneuver right back to the other side where I'll install it back on S1. Meanwhile, Mike's out and tying up ESP-3, making sure that that NTA is ready to come back to Earth when we're ready to do that on a later mission. So that's the big thing that we're going to do.
"After that, we've got a number of other tasks, a whole bunch of maintenance of tasks on the station. Mike's going to go back out to the Japanese laboratory and finish some of the work on the robotic arm that we couldn't do because on EVA-2 it was in the launch configuration and we couldn't get at some of the covers and some of the fasteners that we needed to undo."
Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision K of the NASA television schedule):
EDT........DD...HH...MM...EVENT 06/08/08 05:32 AM...07...12...30...Crew wakeup 06:02 AM...07...13...00...ISS daily planning conference 06:12 AM...07...13...10...EVA-3: 14.7 psi repress/hygiene break 06:57 AM...07...13...55...EVA-3: Airlock depress to 10.2 psi 07:22 AM...07...14...20...EVA-3: Campout EVA preps 08:57 AM...07...15...55...EVA-3: Spacesuit purge 09:12 AM...07...16...10...EVA-3: Spacesuit prebreathe 10:02 AM...07...17...00...EVA-3: Crew lock depressurization 10:32 AM...07...17...30...EVA-3: Spacesuits to battery power 10:37 AM...07...17...35...EVA-3: Airlock egress 11:07 AM...07...18...05...EVA-3: Fossum: Retrieve ESP-3 NTA 11:07 AM...07...18...05...EVA-3: Garan: Remove S1 NTA 12:17 PM...07...19...15...EVA-3: Fossum: Stow S1 NTA on fram 12:27 PM...07...19...25...EVA-3: Garan: S1 NTA install 12:47 PM...07...19...45...EVA-3: Fossum: Cleanup ESP-3 worksite 01:22 PM...07...20...20...EVA-3: Garan: SSRMS cleanup 01:27 PM...07...20...25...EVA-3: Fossum: Kibo robot arm (JRMS) insulation and launch lock removal 02:07 PM...07...21...05...EVA-3: Garan: S1 NTA connections 02:42 PM...07...21...40...EVA-3: Fossum: Kibo launch locks 02:42 PM...07...21...40...EVA-3: Garan: TV camera installation 02:57 PM...07...21...55...EVA-3: Fossum: Deploy micrometeoroid shields 03:02 PM...07...22...00...Logistics module vestibule outfitting 04:27 PM...07...23...25...EVA-3: Cleanup and airlock ingress 04:52 PM...07...23...50...EVA-3: Airlock repressurization 05:02 PM...08...00...00...Spacesuit servicing 07:00 PM...08...01...58...Mission status briefing on NTV 08:32 PM...08...03...30...ISS crew sleep begins 09:02 PM...08...04...00...STS crew sleep begins 10:00 PM...08...04...58...Daily video highlights reel on NTV; repeated hourly