Repair work planned today for stalled water system gear
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 23, 2008
Space station commander Mike Fincke and Endeavour astronaut Don Pettit will attempt repairs today that may resolve on-going problems with the station's newly installed urine recycling equipment. The rest of the shuttle crew, meanwhile, will enjoy a half-day off this morning before making preparations for a fourth and final spacewalk Monday by astronauts Stephen Bowen and Robert "Shane" Kimbrough.
Fincke, shuttle commander Christopher Ferguson and pilot Eric Boe will participate in round-robin network interviews beginning at 4:05 p.m. followed by NASA's daily mission status briefing at 4:30 p.m.
One of the major goals of Endeavour's mission was to deliver, install and activate a new water recovery system designed to convert condensate and urine into potable water for drinking, meal preparation, personal hygiene and oxygen generation. An operational recycling system is required before NASA can boost station crew size from three to six next May, a long-awaited milestone in the lab's evolution.
The installation went smoothly, but engineers have been troubleshooting potentially serious problems with the urine processor assembly. After about two hours of operation, the motor powering a centrifuge in the UPA's vacuum distillation sub-assembly shuts down, apparently because of thermal expansion that causes a speed sensor to come in contact with the centrifuge.
The astronauts managed to coax a urine sample through the system Saturday by running it for about an hour and 45 minutes at a time. That sample, and a condensate sample, will be returned to Earth aboard Endeavour for a detailed chemical analysis.
It's a bit confusing as to what engineers believe is actually causing the UPA problem. Flight director Ginger Kerrick said late Saturday that telemetry indicates the problem occurs because of thermal expansion that causes a speed sensor to come in contact with the centrifuge after the system warms up. That causes the motor to work harder and draw more current, triggering a shut down.
One possible solution, she said, was to remove the vibration dampers the centrifuge is mounted on. By "hard mounting" the unit to its shelf in the water recovery system rack, engineers believe they can eliminate a frequency mode that contributes to the problem. How that relates to thermal expansion, however, is not clear.
In any case, Fincke and Pettit plan to remove the vibration dampers today starting around 12:55 p.m. Once the unit is locked down on its shelf, flight controllers then will carry out additional tests to determine if that resolved the problem.
"Yesterday, we successfully collected the first set of samples from the water recovery system, so that was a big milestone," Flight Director Brian Smith said early today. "That accomplishment is sometimes overshadowed by the attention being received to the urine processing assembly that we're still having some trouble with. So it should be noted we had a very successful run of the water processing assembly and we were able to collect our samples."
Smith then added that "the water processing assembly did experience an issue and it did go into a shutdown mode. We're looking into that. This may not prove to be that significant a problem, but we're going to play close attention to it."
Whether Smith was referring to a new problem with a different part of the system or reprising the UPA trouble was not immediately known. The NASA commentator interviewing Smith in mission control did not follow up and no additional details were immediately available.
As for the UPA repair, Smith said the work to lock down the distillation sub-assembly is relatively straight forward.
"Mike is going to execute a maintenance procedure we developed that's essentially going to change the way the distillation assembly is mounted inside the rack," Smith said. "The distillation assembly slides in on a shelf. This shelf is mounted into the rack and the way it's mounted is where we focused our attention. It's current mounting scheme contains some dampers and we're going to remove some of those dampers and re-attach the shelf to the rack. We call that a hard mount, it'll be mounted in a much more rigid way than it was originally. The theory being that that will change the vibrations that occur while the centrifuge is running and if we can change the characterization of those vibrations, we may be able to prevent what we believe is some physical interference with that centrifuge as it spins."
Along with collecting testable samples of reprocessed urine and condensate from the water recovery system, the astronauts also plan to hook up, activate and collect samples from a new potable water dispenser. The water recovery system racks, a new toilet and the potable water dispenser are all connected to a common water bus in the Destiny lab module.
The astronauts plan to hook up the potable water dispenser after the final spacewalk Monday.
"We have met the original goal for this mission with the samples that we collected yesterday," Smith said. "But all along, we have been challenged to hook up the potable water dispenser and collect some samples associated with that. So we are still on track to do that. The crew's got some more work to do to continue hooking up the potable water dispenser and then we will do another run of the water processing assembly and be able to generate the samples. So we've got a plan that will accomplish that before the hatch is closed and that's what we spent some of tonight doing, figuring out where some of those activities are going to go.
"We talked to the crew for quite a while before they went to bed last night about what they experienced when they started the routing procedure for the hoses associated with the potable water dispenser and based on their feedback, we think the remaining routing that needs to be done is going to be a little more complicated and a little more intrusive to some systems we're going to need for EVA-4. So we made the decision to postpone the continuation of that routing work for the potable water dispenser until after EVA-4 is done. Even with that postponement, we still have time to get it hooked up, run some water through it, collect our samples and we've got margin in case we experience a problem."
Bowen and Kimbrough plan to spend six-and-a-half hours outside the station Monday to complete the cleaning and lubrication of the lab's damaged right-side solar array rotary joint; to prepare the Japanese Kibo module for attachment of an external experiment platform next year; to install GPS antennas on the module; and to lubricate the station's left-side rotary joint.
Work to finish up the starboard alpha rotary joint servicing includes installation of a final bearing assembly and the cleaning and lubrication of a 30-degree segment of bearing races on the 10-foot-wide drive gear. In one bit of added work, problems with the retraction of a berthing latch needed next year to lock down the Kibo experiment platform will be manually retracted by one of the astronauts.
"The fourth spacewalk has changed a little bit from what we envisioned it to be pre flight," Smith said. "The first thing we need to get taken care of is the remaining work on the starboard solar alpha rotary joint. This is the work that wasn't completed on EVA-3. We left covers 17 and 18 off on the starboard SARJ. We had pulled trundle bearing three out. So on EVA-4, we need to go back to that location, clean the area, install a new trundle bearing assembly number three and then lubricate, reinstall the covers and then we'll be complete with the starboard SARJ work.
"Also added onto EVA-4 is a new task," he said. "The other day, our colleagues in the Japanese control center were checking out the exposed facility berthing mechanism (on the Kibo lab module). One of the structural latches deployed as planned but did not retract and that's an issue on assembly mission 2J/A. The exposed facility is going to be brought up by the shuttle and it's going to be berthed using this mechanism. That latch needs to be retracted before the start of that operation. So we have added in a new task to have the crew member, who was already going to be in that vicinity installing a cover over that mechanism, use his pistol grip tool ... to drive a bolt that will retract that latch manually."
Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision I of the NASA television schedule):
EST........DD...HH...MM...EVENT 08:55 AM...08...13...00...Crew wakeup 10:40 AM...08...14...45...ISS daily planning conference 11:05 AM...08...15...10...Flight director conference 12:05 PM...08...16...10...Crew off duty time begins 12:55 PM...08...17...00...Urine system maintenance (Fincke/Pettit) 04:05 PM...08...20...10...Crew meal 04:05 PM...08...20...10...CBS News/ABC News/NBC News interviews 04:30 PM...08...20...35...Mission status briefing on NASA TV 05:05 PM...08...21...10...Cargo transfers resume 05:20 PM...08...21...25...Spacesuit swap 05:25 PM...08...21...30...SAFER jet backpack checkout 06:05 PM...08...22...10...Equipment lock preps 06:50 PM...08...22...55...Tools configured 08:50 PM...09...00...55...EVA-4: Procedures review 09:50 PM...09...01...55...Evening planning conference 11:20 PM...09...03...25...EVA-4: Nitrogen purge protocol 11/24/08 12:05 AM...09...04...10...EVA-4: Airlock depress to 10.2 psi 12:25 AM...09...04...30...ISS crew sleep begins 12:55 AM...09...05...00...STS crew sleep begins 01:00 AM...09...05...05...Flight day 10 highlights 07:30 AM...09...11...35...Flight director update 08:30 AM...09...12...35...HD flight day 10 highlights 08:55 AM...09...13...00...Crew wakeup