Station solar joint cleaning continues on today's EVA
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 20, 2008
Marking the international space station's 10th anniversary, the Endeavour astronauts are gearing up for a second spacewalk today, a planned six-and-a-half-hour excursion to service the station's robot arm, to continue cleaning and lubricating a damaged solar array rotary joint and to make preparations for the next shuttle assembly flight in February.
Astronauts Heidemarie Stefanyshyn-Piper and Robert "Shane" Kimbrough spent the night in the station's Quest airlock module at a reduced pressure of 10.2 pounds per square inch to help purge nitrogen from their bloodstreams and prevent the bends after a day working in NASA's 5-psi spacesuits. If all goes well, they will switch their suits to internal battery power at 1:45 p.m. to officially kick off the 116th spacewalk since station assembly began 10 years ago today.
As of 10:50 a.m., the astronauts were running about 40 minutes ahead of schedule in their preparations.
The spacewalkers have modified the plan for today's excursion in the wake of a lost $100,000 tool kit that slipped away from Stefanyshyn-Piper during a spacewalk Tuesday. Spacewalker Stephen Bowen did not notice the bag was untethered inside a larger container before the spacewalk began and Stefanyshyn-Piper, struggling to clean up a grease leak in the bag, inadvertently let it slip away.
Two grease guns, a scraper tool, a caddy to clean grease off the scraper and contain debris and a large trash bag were lost. As a result, Stefanyshyn-Piper and Kimbrough will share a single set of tools cleaning and lubricating the right-side solar alpha rotary joint during today's spacewalk.
Because one of the remaining grease guns is needed to lubricate snares on the station's robot arm, Stefanyshyn-Piper plans to use a different technique to contain debris scraped off the rotary joint's 10-foot-wide drive gear. Instead of laying down a bead of grease to contain the scraped-off debris, she will use grease-impregnated wipes to accomplish the same purpose.
"EVA number two is going to consist of some more cleaning and maintenance on the starboard solar alpha rotary joint, or SARJ," said flight controller Brian Smith. "They did some of that work on EVA-1, they'll do more of it again on EVA-3. In addition to the EVA, of course, we're going to have some more work (inside the station) associated with the regenerative ECLSS (environmental control and life support) system and we're also going to get the total organic carbon assembly installed. The TOCA, as this is referred to, is used to sample the water that comes out of the regenerative ECLSS system. ... The TOCA is a box that will independently verify the quality of that water."
The regenerative ECLSS hardware Smith was referring to is designed to turn urine into potable water, a requirement for NASA's plan to boost station crew size from three to six next year. The astronauts installed the equipment Wednesday and if all goes well, the first tests will begin later today. The goal is to generate samples from two parts of the system for return to Earth aboard Endeavour. At least three months of testing are planned before any astronauts will actually sample the recycled water.
While water system activation is in work inside the station today, the spacewalk will be going on outside.
The space station is equipped with two SARJ mechanisms designed to rotate outboard solar arrays like giant paddle wheels to stay face-on to the sun as the lab complex orbits the Earth. The port-side SARJ is operating normally, but the starboard joint has suffered extensive damage to drive gear because of a lubrication failure.
The surface layer of one of the gear's three bearing surfaces, the so-called outer canted surface, has suffered significant erosion, generating widespread clumps of metallic filings. The debris and the roughness of the bearing surface cause life-limiting vibration and higher-than-usual motor currents when the joint is used to track the sun.
The goal of the Endeavour spacewalks is to clean off ground-up debris, to lubricate the big gear's bearing surfaces and to replace 11 of the 12 trundle bearings that grip the gear on three faces with pressure-loaded rollers.
"The race ring's going to be cleaner and it's going to have some new bearings in place," Smith said. "Now what that means operationally, we'll see. On flight day nine (Saturday, after a third spacewalk), we're going to conduct a test to see how the maintenance worked and if the cleaning had any effect.
"We're going to put the starboard solar alpha rotary joint into what we call an auto-track mode, where we're going to let it constantly rotate and track the sun. Right now, we do not do that, we pick one position and we leave it there. But for this test, for two orbits, we're going to let it fully rotate and we're going to monitor the vibrations seen on the space station. We've got sensors to do that as well as an external camera that we'll be using. We're also going to measure the current draw on the motor that's driving that joint."
If the test shows reduced vibration and current draw, flight controllers will be cleared to put the starboard SARJ in auto-track mode from time to time as required to improve solar array power output. But because of the damage to the outer canted surface that has already occurred, full-time auto-track operations will not be permitted.
Today's spacewalk comes on the 10th anniversary of the launch of the Russian-built, NASA-financed Zarya module that marked the beginning of station assembly. Zarya was launched from the Baikonur Cosmodrome in Kazakhstan aboard a Proton rocket at 1:40 a.m. EST on Nov. 20, 1998.
Since then, the station has grown to 10 pressurized modules - three Russian, four U.S., one European and two Japanese - with a habitable volume of 12,626 cubic feet and a mass of 661,857 pounds. Including Endeavour's mission, 27 space shuttle assembly flights have been launched, two Proton heavy-lift rockets, 17 Soyuz crew ferry craft, one Soyuz assembly flight, 30 unmanned Progress supply ships and one European Space Agency automated transfer vehicle.
"Even from 40 miles away, you can tell the beauty and the grandeur and the enormity of this vehicle," Endeavour commander Christopher Ferguson said in a pre-taped anniversary message downlinked from the lab. "As you get closer, it only gets larger. Post-docking, when we were able to come inside and explore the expanse of the vehicle, it's overwhelming, the size and the enormity of this ship in space.
"This crew, this fine crew, and its cargo will enable the space station to plus up to a crew of six people living full time, international partners working hand in hand for years on end. After 10 years, we wish the international space station a happy birthday and we hope to see many, many more."
Going into the Endeavour crew's second spacewalk today, 115 station assembly and maintenance EVAs had been carried out totaling 725 hours and 40 minutes by more than 80 astronauts and cosmonauts representing the United States, Russia, Japan, Canada, Germany, France and Sweden.
The station has traveled some 57,000 orbits, or roughly 1.5 billion miles, over the past 10 years, enough for 3,000 round trips to the moon or a one-way flight just shy of Uranus. Some 167 U.S. and partner country astronauts and cosmonauts have visited the lab complex over the past decade and some 19,000 meals have been served.
"Today is a special day aboard the space station, we're celebrating the 10th anniversary of the first launch of the first module of the international space station," said Expedition 18 commander Mike Fincke. "Since then, our space station has gotten larger and larger. ... And along the way, we've learned how to live in space for a long time and we've learned how to act and work together as international partners. I know myself and my crew are really proud to be here on this special date."
Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision E of the NASA television schedule):
EST........DD...HH...MM...EVENT 11/20/08 01:40 AM...05...05...45...10th anniversary of ISS first launch Flight Day 7 (Updated 11/20/08) 08:55 AM...05...13...00...Crew wakeup 09:30 AM...05...13...35...EVA-2: 14.7 psi repress/hygiene break 10:15 AM...05...14...20...EVA-2: Airlock depress to 10.2 psi 10:25 AM...05...14...30...Russian PAO event 10:40 AM...05...14...45...EVA-2: Campout EVA preps 10:55 AM...05...15...00...ISS daily planning conference 11:35 AM...05...15...40...TOCA assembly 11:50 AM...05...15...55...MPLM transfers resume 12:10 PM...05...16...15...EVA-2: Spacesuit purge 12:25 PM...05...16...30...EVA-2: Spacesuit prebreathe 01:15 PM...05...17...20...EVA-2: Crew lock depressurization 01:45 PM...05...17...50...EVA-2: Spacesuits to battery power 01:50 PM...05...17...55...EVA-2: Airlock egress 02:05 PM...05...18...10...EVA-2: Setup 02:15 PM...05...18...20...EVA-2: CETA cart relocation 04:00 PM...05...20...05...EVA-2/EV1: SARJ cleaning and TBA R&R 04:00 PM...05...20...05...EVA-2/EV3: Robot arm lubrication 05:00 PM...05...21...05...EVA-2/EV3: SARJ cleaning and TBA R&R 07:45 PM...05...23...50...EVA-2: Cleanup and ingress 07:55 PM...06...00...00...GPS antenna assembly 08:15 PM...06...00...20...EVA-2: Airlock repressurization 08:25 PM...06...00...30...Spacesuit servicing 10:00 PM...06...02...05...Mission status briefing on NASA TV 10:10 PM...06...02...15...Evening planning conference 11/21/08 12:25 AM...06...04...30...ISS crew sleep begins 12:55 AM...06...05...00...STS crew sleep begins 01:00 AM...06...05...05...Flight day 7 highlights 06:00 AM...06...10...05...HD flight day 7 highlights 07:30 AM...06...11...35...Flight director update 08:55 AM...06...13...00...Crew wakeup
Going into the flight, the SARJ repair plan was to use grease-impregnated wipes to dab up loose debris on the races of the rotary joint's drive gear. Then, after laying down a bead of grease with a grease gun, the spacewalkers, working on opposite sides of the joint, would use a scraper to chip off debris that had been crushed onto the damaged bearing race by the rollers that hold the big gear in place. Then, after using dry wipes to clean up any remaining debris, additional lubrication would be applied to reduce rolling friction in the mechanism.
Two types of grease gun are required. One with a straight nozzle to lubricate the outer canted surface and the so-called datum-A bearing race, and a second gun with a curved "J-hook" nozzle to reach the inner canted surface.
During the first spacewalk Tuesday, Stefanyshyn-Piper and Bowen used up about a quarter of a cartridge in each of the two remaining grease guns. Flight director Ginger Kerrick said the crew still has six full cartridges of Braycote vacuum grease available, which should be more than enough to complete the servicing.
During today's spacewalk, Stefanyshyn-Piper will use the grease-impregnated wipes to collect and contain debris on the damaged outer canted surface of the rotary joint while Kimbrough uses the lone straight-nozzle grease gun to lubricate the capture snares on one end of the station's robot arm. Then, working together, they'll share tools again.
"We only have one set of SARJ guns," said station flight director Ginger Kerrick. "We wanted to try to minimize the amount of sharing that's required. When you're cleaning the the ring, to scrape off the debris, requires you to lay down a line of lube before you use the scraper to scrape off the debris. In talking to Heide after (the first EVA) she thought it might be just as useful to take a wet wipe, which has been pre-lubricated with that same lubricant, and dab that on the ring and that would apply just enough grease to contain the items we're scraping off the ring.
"So we're going to give that a try on EVA-2. The reason we're trying this, Shane needs the lube gun with the straight nozzle to perform the (robot arm) lubrication. And Heide will be at the SARJ worksite already, so she would not have that gun in her possession. So we're going to try this technique. If this technique works, we do anticipate being able to complete not only the planned activities on EVA-2, but also the timelined activities on EVA-3."
Today's spacewalk was scheduled to begin around 1:45 p.m. from the Quest airlock. The first item on the agenda is to move two carts on the front side of the station's solar power truss to the other side of the mobile transporter that moves the lab's robot arm from one worksite to another. The carts need to be moved so the arm can be positioned on the starboard end of the truss for attachment of a final set of solar arrays in February.
Kimbrough will ride on the end of the robot arm, carrying each cart to the other side of the transporter where Stefanyshyn-Piper will help lock them back down on their rails.
At this point in the spacewalk, Kimbrough and Stefanyshyn-Piper will split up. Kimbrough will use a straight-nozzle grease gun to lubricate the snares in the end of the robot arm to help them retract more smoothly. Stefanyshyn-Piper, meanwhile, will head to the starboard SARJ to begin a second round of cleaning and lubricating, using the grease-immpregnated wipes instead of a grease gun.
Overnight, the SARJ was rotated from 105 degrees to 60 degrees to expose more of the drive gear's contaminated races. Kimbrough will join her after he's done servicing the robot arm.