Astronauts prepare for first spacewalk of shuttle flight
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 18, 2008
Heidemarie Stefanyshyn-Piper and Stephen Bowen are gearing up for a planned six-and-a-half-hour spacewalk today to clean and lubricate a damaged 10-foot-wide solar array drive gear on the international space station. They also plan to begin replacing 11 of 12 bearings on the massive gear in a bid to restore the rotary mechanism to near normal service and improve electrical output from the lab's right-side solar arrays. The spacewalk is scheduled to begin around 1:45 p.m.
While the spacewalk is going on, shuttle and station crew members inside the lab complex will begin moving critical water recycling gear from a cargo module brought up by Endeavour and attached to the station Monday. The water recycling racks are designed to convert condensate and urine into pure water for drinking, food preparation, personal hygiene and oxygen generation, critical elements in NASA's plan to boost the station's crew size from three to six next year.
The water racks originally were scheduled for installation Wednesday, but the astronauts ran well ahead of schedule attaching and opening the multi-purpose logistics module Monday. Saving time on another front, mission managers decided Monday that no additional "focused" inspection of the shuttle's heat shield will be required, freeing up about 10-and-a-half hours of crew time Wednesday.
Going into Endeavour's mission, shuttle and station managers were holding open the option of extending the flight one day to complete installation of the water racks and a potable water dispenser. The goal is to activate the hardware and process the first water samples for return to Earth aboard Endeavour. Given the time saved so far, the astronauts might be able to get the gear hooked up and operating without needing the extra day.
"Yesterday, they got about eight hours ahead of schedule by being very efficient," station flight director Brian Smith said early today. "Now that trend probably won't continue because as we get further along into the mission, there's less and less opportunities for the crew to accelerate the transfer operations. They got us off to an excellent start, though."
Four spacewalks are planned for Endeavour's mission the first and third by Stefanyshyn-Piper and Bowen, the second by Stefanyshyn-Piper and Robert "Shane" Kimbrough and the fourth by Bowen and Kimbrough.
The bulk of the first three excursions is devoted to servicing the starboard solar alpha rotary joint, or SARJ. During the fourth spacewalk, Kimbrough will lubricate the port SARJ as preventative maintenance.
The station is equipped with two massive SARJ joints designed to rotate outboard solar arrays like giant paddle wheels, keeping them face-on to the sun as the lab complex orbits the Earth. Each SARJ features a 10-foot-wide toothed drive gear with a roughly triangular cross section with three faces, or bearing races: an inner canted race, a so-called "datum-A" surface and an outer canted race. Twelve trundle bearing assemblies, positioned around the drive gear grip the three bearing surfaces with rollers pushing against the gear with 1,000 pounds of pressure. A powerful motor called a drive lock assembly engages the drive gear to actually turn the outboard arrays.
The left-side SARJ is operating normally, but the drive gear on the right side has suffered serious erosion and degradation to its outer canted surface, subjecting the mechanism to high vibration and generating extensive metallic debris as it turns in the grip of the trundle bearings.
To avoid excessive stress and fatigue that might eventually lead to failure, the joint is no longer allowed to "auto-track" the sun and is only repositioned occasionally to improve electrical output. Based on analysis of collected debris and a trundle bearing removed earlier, engineers believe the problem was caused by a lubrication failure.
"We have concluded the most likely cause of this anomaly is due to high friction, which was caused by the loss of lubrication in the joint when it flew," said station Program Manager Mike Suffredini. "The way we lubricate that joint is we put a gold plating on the (trundle bearing) rollers. This is a very soft material and over time, it kind of wears off the roller and finds its way onto the race and fills in the very small microscopic holes and provides basically a lubricant that will wear over time. But it was intended to wear very slowly over time.
"We have found through a bit of research in the paperwork that was put together before we flew and some of the information we gained from the trundle bearing we returned home that we believe the gold prematurely came off these rollers, either because of a condition pre-flight or because of the process used to install the gold just wasn't adequate for the conditions that it saw, that we wore it off prematurely on the starboard side. We have proven through testing that once you take the lubrication off this joint, it will damage the race very, very quickly."
During Endeavour's mission, Stefanyshyn-Piper, Bowen and Kimbrough, working in two-person teams, plan to replace the remaining 11 trundle bearing assemblies, or TBAs, on the right side SARJ. Using grease-impregnated wipes, the spacewalkers will attempt to blot up the metallic shavings contaminating the race. Dry wipes will be used to finish the job and grease guns will be used to lay down beads of lubricant on all three bearing surfaces. The drive gear will be turned between spacewalks to let the bearing rollers distribute the grease across all three bearing surfaces and position fresh sections for cleaning.
A major challenge will be to keep the grease under control and prevent debris from floating away, contaminating the crew's spacesuits or possibly working its way into other delicate mechanisms.
"We want to make sure we get the grease where it's supposed to go and that's on the race rings to help lubricate the SARJ," Stefanyshyn-Piper said. "When you go out there to do this work, even though it's not a fine, delicate task, it is a fine, delicate task in the sense that you don't want to get grease all over yourself and everywhere else. And so you've just got to work slowly and very deliberately on what you're doing."
If the cleaning and lubrication go smoothly, engineers hope to be able to use the starboard SARJ in a manual mode and, when power requirements are high, to auto track for short periods. While both SARJ mechanisms include a backup drive gear for redundancy, NASA managers want to operate the starboard SARJ on its primary gear as long as possible.
"Once we get this all cleaned up, we'll look at the vibrations," Suffredini said. "We're assuming the vibration levels will be very low and that will allow us, if there come times when we need short intervals of auto track in order to get the power we need for utilization, then we'll do that.
Today's spacewalk will begin when Stefanyshyn-Piper and Bowen, floating in the station's Quest airlock module, switch their spacesuits to battery power. Stefanyshyn-Piper, call sign EV-1, will be wearing a suit with red leg stripes. Bowen, EV-2, will be wearing a suit with no stripes.
This will be the 115th spacewalk devoted to station assembly and maintenance since construction began 10 years ago Thursday and the 16th so far this year. Going into today's outing, total spacewalk time stood at 718 hours and 48 minutes by astronauts representing the United States, Russia, Japan, Canada, Germany, France and Sweden.
Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision C of the NASA television schedule):
EST........DD...HH...MM...EVENT 11/18/08 08:55 AM...03...13...00...Crew wakeup 09:30 AM...03...13...35...EVA-1: 14.7 psi airlock repress/hygiene break 10:20 AM...03...14...25...EVA-1: Airlock depress to 10.2 psi 10:40 AM...03...14...45...EVA-1: Campout EVA preps 10:50 AM...03...14...55...ISS daily planning conference 12:10 PM...03...16...15...EVA-1: Spacesuit purge 12:10 PM...03...16...15...Cargo module (MPLM) transfers resume 12:25 PM...03...16...30...EVA-1: Spacesuit pre-breathe 01:15 PM...03...17...20...EVA-1: Crew airlock depressurization 01:45 PM...03...17...50...EVA-1: Spacesuits to battery power (START) 01:50 PM...03...17...55...EVA-1: Airlock egress/setup 02:15 PM...03...18...20...EVA-1: Nitrogen tank assembly (NTA) removal 03:10 PM...03...19...15...EVA-1: NTA installation in shuttle cargo bay 03:40 PM...03...19...45...EVA-1/EV2: Flexible hose rotary coupler (FHRC) removal 03:40 PM...03...19...45...EVA-1/EV1: Solar alpha rotary joint (SARJ) preps 04:00 PM...03...20...05...EVA-1/EV1: FHRC installation/SSRMS cleanup 04:05 PM...03...20...10...EVA-1/EV2: FHRC installation/SSRMS cleanup 04:25 PM...03...20...30...EVA-1/EV1: Remove Kibo berthing covers 04:40 PM...03...20...45...EVA-1/EV2: SARJ cleaning, TBA R&R 05:10 PM...03...21...15...EVA-1/EV1: SARJ cleaning, TBA R&R 07:40 PM...03...23...45...EVA-1: Cleanup and ingress 07:55 PM...04...00...00...ZSR installation 08:15 PM...04...00...20...EVA-1: Airlock pressurization 08:25 PM...04...00...30...Spacesuit servicing 10:00 PM...04...02...05...Mission status briefing on NASA TV 10:10 PM...04...02...15...Evening planning conference 11/19/08 12:25 AM...04...04...30...ISS crew sleep begins 12:55 AM...04...05...00...STS crew sleep begins 01:00 AM...04...05...05...Flight day 5 video highlights reel on NASA TV 07:30 AM...04...11...35...Flight director update on NASA TV 08:55 AM...04...13...00...Crew wakeup
Before beginning the SARJ servicing, the spacewalkers will spend about two hours installing a spare coolant system component, called a flexible hose rotary coupler, on an external stowage platform located on the station's main power truss. They also will remove a now-depleted nitrogen tank assembly, or NTA, used to help pressurize the coolant system. The nitrogen tank will be returned to Earth aboard Endeavour.
Exiting the airlock, Stefanyshyn-Piper will hook up 85-foot-long tethers connected to the front face of the S0 solar array truss segment and collect a robot arm foot restraint stowed outside. She will make her way to external stowage platform No. 3 on the solar array truss and provide guidance cues for Don Pettit and Sandra Magnus, operating the station's robot arm, as they maneuver the space crane into position. Once the end of the arm is positioned, Stefanyshyn-Piper will attach the foot restraint to its latching end effector.
Assisted by Bowen, Stefanyshyn-Piper then will clip her boots into the foot restraint. At this point, the 1,100-pound nitrogen tank assembly will be pulled out of its mounting and the station arm will move Stefanyshyn-Piper and the NTA down to the back end of the shuttle Endeavour's cargo bay. While she's in transit, Bowen will make his way down, pausing to close a flap over a berthing mechanism on the Unity module. Then he will join his crewmate in the cargo bay.
Working together, the NTA will be mounted on a cargo carrier for return to Earth. The flexible hose rotary coupler then will be removed from the carrier and carried by Stefanyshyn-Piper back up to ESP-3. Bowen will meet her there and the two will stow the FHRC on the external stowage platform to serve as a critical spare. Rotary couplers allow the station's big ammonia coolant radiators to turn away from the sun, maximizing heat rejection.
At this point, Stefanyshyn-Piper will get off the arm and fold the foot restraint, leaving it in place for use during spacewalk No. 4. Bowen will move out to the starboard end of the station's power truss to begin the long-awaited servicing of the right-side solar alpha rotary joint.
Stefanyshyn-Piper, meanwhile, will move along the top of the Destiny module to the forward end of the station and the Japanese Kibo lab module attached to the Harmony module's left port. Making her way to the outboard end of the Kibo module, she will remove four small covers from a berthing mechanism that will be used next year to attach an external experiment platform. She also will temporarily remove a larger cover from the aft end cone that will be reinstalled later in the mission. Once she's done, she will make her way to the starboard SARJ.
Going into the spacewalk, the SARJ drive gear, protected by 22 thermal covers, was parked at an angle of 105 degrees. Working on the top side of the mechanism, Stefanyshyn-Piper will remove cover No. 7. Cover No. 8 was removed during an earlier mission to provide a viewing port for a robot arm camera.
Reaching inside, Stefanyshyn-Piper will remove a trundle bearing assembly and stow it in a bag for return to the airlock. Using a terry cloth glove impregnated with Braycote vacuum grease, she will attempt to collect metallic shavings littering the outer canted race. She'll then use a scraper tool to remove debris that has been crushed down on the surface by the roller bearings.
Switching to dry wipe, Stefanyshyn-Piper will clean up any remaining grease and debris, cleaning all three races as best she can - the undamaged inner canted race and the datum A surface and the damaged outer canted race. She then will begin lubricating all three races, using a grease gun to lay down beads of lubrication. A J-hook nozzle will be ued to reach the inner race of the drive gear.
The starboard SARJ will be rotated later to evenly distribute the grease.
With the first section under covers 7 and 8 now cleaned and lubricated, Stefanyshyn-Piper will install a new trundle bearing assembly. Bowen, meanwhile, will be doing the same thing on the other side of the SARJ, working on the races under covers 1 and 22. He will remove and replace TBA No. 6. After covers are reinstalled, the spacewalkers will make their way back to Quest and call it a day.
If time is available, Stefanyshyn-Piper may be able to clean and lube under covers 9 and 10 where TBA No. 11 resides, and possibly under cover 11. Between the first two spacewalks, the SARJ will be rotated from 105 degrees to 60 degrees. This will position the SARJ drive motors and adjacent areas of the gear for the second spacewalk.
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