Station boss happy with SARJ and water recycler repairs
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 25, 2008
Work to replace bearings and re-lubricate the space station's damaged right-side solar array rotary joint went better than expected, a senior manager said today, resulting in remarkably smooth operation that may permit the agency to forego building, launching and installing costly replacement hardware.
Space station Program Manager Mike Suffredini also said the station's newly installed water recycling system, including an initially cantankerous urine distillation assembly, appears to be operating normally and that the Endeavour astronauts will be able to bring some six liters of processed urine and condensate back to Earth for chemical analysis, more than engineers expected before launch.
"When we went into this mission, we said there were two primary objectives we needed to take care of," Suffredini said. "One was to repair the SARJ (solar alpha rotary joint) and prepare the port SARJ for continued operations. And of course, the other major objective was to get started on our regenerative ECLSS (environmental control and life support) system, get it going in preparation for six-crew operations in the May timeframe. I'm happy to report today that we're well on our way in both of those cases."
Early today, flight controllers activated the right-side solar alpha rotary joint and commanded it to operate in normal "auto-track" mode for two full orbits. In auto-track, the station's two SARJ mechanisms rotate outboard solar arrays like huge paddle wheels to keep them face on to the sun.
Engineers first noticed problems with the starboard SARJ last year when sensors measured increased vibration levels and power usage in the drive motor. Inspections by spacewalking astronauts later showed one of the gear's three bearing races was heavily damaged, apparently because of a lubrication breakdown that generated extensive metallic contamination.
One of the 12 trundle bearings that grip the gear was replaced last June to help engineers troubleshoot the problem. During parts of four spacewalks, the Endeavour astronauts replaced 10 bearing assemblies and re-installed the 11th, cleaned off the metallic debris and re-lubricated all three races.
Going into the flight, Suffredini said engineers believed the outer canted bearing race was too damaged to permit resumption of around-the-clock auto-track operations. The goal was to lower vibration and friction levels enough to permit periodic operations to boost power when needed.
But it now appears the bearing swap-out and re-lubrication might permit more routine operations than originally expected. That's a major issue as NASA transitions to full-time operations with an expanded crew of six and a full slate of experiments that require all the power the lab's solar arrays can generate.
Along with bringing the old bearings down for a comprehensive failure analysis, the goal of the servicing work was to "clean up the race and lubricate it and see what we could do about reducing the currents on the motor to drive this joint (and) to see if we could reduce the vibrations," Suffredini said. "One of the things that's not immediately obvious to you is the vibrations induced by rotating this joint had the potential to put extensive life (reduction) on the structure. So that was another big driver for not operating in auto track.
"And so we performed both of those tasks and we found that the current dropped dramatically, in fact the currents are now much, much closer to where they were when we started off," he said. "We've seen as low as 0.17 amps since we lubricated it. It was as high as 0.7 to 0.9 in some cases. These are the peak numbers, we average the lower numbers. This particular joint, when it first started out, was operating at about 0.15 amps. So you can see the data is suggesting we're awfully close to our original drive currents.
"We took vibration data that we're looking at now. So I can't tell you what that data tells us, but I can tell you anecdotally, one of the ways we discovered this problem, one of the cameras on the starboard truss would vibrate, you could look at an image with this camera and you'd see it vibrate when the joint was rotating. And that particular camera is still now. So if you want to take that as an indication that we reduced vibrations, we certainly have."
Suffredini said it will take weeks of engineering analysis and additional auto-track test runs to fully characterize the behavior of the joint. But if the initial results hold up, the agency may be able to stop work on a long-range plan to build a new bearing race that would be launched on the last planned shuttle mission and installed over multiple spacewalks.
"If, in fact, we could keep the currents down through a lubrication process that's not extensive, that we wouldn't have to do every three or four months but maybe once every year or two, perhaps we could choose that avenue as opposed to replacing that race," he said. "So this is a very positive step for us. It's very possible we could save ourselves quite a bit of time and effort and get this joint in auto-track sooner than we had hoped."
The Endeavour astronauts also lubricated the station's port SARJ. That mechanism has been operating normally, but engineers wanted to add fresh lubrication to prevent problems like those experienced by the starboard joint. The astronauts reported seeing signs of very slight damage on one bearing race, but Suffredini said it appeared to be normal wear and tear.
As for the urine processor, Suffredini said it appears the removal of rubber vibration isolators and additional work to hard mount the distillation assembly to its mounting bracket paid off. Initial startup problems appear to be related to subtle harmonic effects as an internal centrifuge spins in a vacuum distillation assembly. The vibration dampers were put in place to reduce noise, but taking them off apparently prevented the motions that contributed to an unwanted balance issue, allowing the system to operate in a more normal fashion.
"So now we believe where we are is that we'll keep the distillation assembly on orbit and we will look to methods to mount it perhaps a little stiffer to the structure, we'll see if there's anything we want to do different, if we want to perhaps build some sort of bracket we bring to orbit to stiffen up the structure," Suffredini said. "We may choose to do that. But right now, the thinking is we'll probably leave this distillation assembly on orbit and we'll nurse it along the way we have been and learn from the system."
Today, the astronauts hooked up a potable water dispenser that is connected to the same water "bus" as the water recycling gear. A new toilet will be connected to the bus after the shuttle departs, routing urine to the processor for conversion into pure water for drinking, food preparation, personal hygiene and oxygen generation.
Flight Director Holly Ridings said the astronauts will bring down about six liters of processed water for detailed chemical analysis to determine purity and to help calibrate an analyzer on the space station. No one will drink any processed water until after additional samples are brought down next February.
Assuming the equipment continues working normally, NASA will be clear to boost crew size to six next May as planned.