posted 10-28-2007 05:08 PM               

About 50 days ago, a station flight controller just happened to notice that a camera mounted to the starboard solar array truss was vibrating ever so slightly. Upon investigating the issue, it was discovered that the 10-foot wide joint assembly was requiring more electricity to rotate than what was considered normal. This suggested to mission managers that something was impeding its movement.

The only way to know for sure would be to get a firsthand look, so flight controllers took advantage of STS-120 being at the station and today, during the second of the mission's five planned spacewalks, asked newly-arrived ISS Expedition 16 flight engineer Dan Tani to inspect the Solar Alpha Rotating Joint (SARJ, pronounced "sarge") that was giving them trouble (the additional inspection still allowed for Tani and his spacewalking partner Scott Parazynski to complete their pre-scheduled activities, with the exception of connecting the electrical wiring to a new robotic arm grappling point on the Harmony module).

After looking over the exterior of the SARJ, which appeared normal, Tani unbolted one of the 22 thermal covers that protects the joint's gears and made a discovery.

"It's quite clear," radioed Tani, "there's metal-to-metal scraping, or something, and it's widespread."

Tani observed what he believed to be metal shavings. At the suggestion of flight controllers, he used tape to collect some of the debris to bring it inside to be photographed and then returned to Earth on shuttle Discovery for further study.

The leading theory as to the source of the filings, at least as of now, is the aluminized mylar foil that lines the bottom of the thermal covers. If that material rubbed up against the teeth of the SARJ, it could have been gradually but thoroughly shredded to cause the debris observed by Tani.

Mission managers are considering their options, including have a later spacewalk go out and inspect the remaining 21 covers for signs of the shredded mylar. If they can locate the culprit, they can remove it and then deal with cleaning up the debris.

In the meantime, they have stopped the joint from tracking the sun and, with the exception of a few movements necessary for thruster firings and when the shuttle undocks, can safely leave the arrays in a static position. Even with half of them parked in place, the solar arrays generate enough electricity to support the current configuration of the station.

Which leaves the question of future additions, including ESA's Columbus module, scheduled to launch in December. According to Michael Suffredini, NASA's ISS manager, even without a functioning starboard SARJ, the station should be able to support Columbus' arrival, though further study is needed to determine if enough power is present for the European laboratory's science payloads to be activated once on orbit.

posted 10-28-2007 05:28 PM               

Additional reporting:

• CBS/Spaceflight Now: Spacewalker finds debris in critical station truss joint

• SPACE.com: NASA Eyes Worrisome Debris in Space Station Joint

• New York Times: Space Station Has Power System Damage

posted 10-28-2007 09:14 PM               

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Originally posted by GACspaceguy:
The Engineer on the panel (I don't remember his name) let him off easy by saying he would take him aside later and talk to him about using a vacuum in a vacuum!

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posted 10-28-2007 09:34 PM               

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Originally posted by Jay Chladek:
Now that is funny, but also sad considering the education of some of these reporters covering space flight.

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posted 10-28-2007 11:31 PM               

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Originally posted by Robert Pearlman:
You need to understand the context.

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posted 10-29-2007 10:58 AM               

On Tuesday, during STS-120's third (of five planned) spacewalks, Scott Parazynski will conduct a similar inspection to the one conducted by Dan Tani on Sunday, only this time it will be at the port (left side) SARJ, which has been operating without problem. Parazynski will remove the corresponding thermal cover to the one removed by Tani on the starboard SARJ, in an attempt to establish a "baseline" or normal condition for the joint. Normal wear and tear is expected to have created some particulate (just not as much as observed by Tani), thus Parazynski will use kapton tape to take samples of whatever debris is present.

Some of the shavings collected by Tani, as pictured above, were carefully transferred by the ISS crew to a piece of white paper and a magnet was passed underneath. The filings responded to the magnet, which indicates the presence of a ferrous metal (which would exclude the aluminized mylar from that specific sample, though mylar could still be in the shavings they didn't test).

Parazynski's inspection should only take about 40 minutes, still allowing time for the completion of the pre-scheduled spacewalk activities.

Looking beyond EVA 3, station managers have recommended devoting the fourth spacewalk to inspecting the starboard SARJ, removing the remaining 21 blankets and collecting shaving samples if they appear to be different from what was gathered by Tani. This would require extending the length of EVA 4, which was originally intended to test a space shuttle tile repair technique, and thus would require lengthening the STS-120 mission by one day. A decision on this proposal is expected to be made later on Monday.

The station program has also put forth a few ideas about changing out equipment in the starboard SARJ for the purpose of bringing the installed hardware home for study, but that work is much more complicated is not as likely to be approved.

posted 10-29-2007 07:43 PM               

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Originally posted by Jay Chladek:
Does each array have its own independent SARJ or does one SARJ control the whole group on one side?

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posted 10-29-2007 08:38 PM               

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Originally posted by Robert Pearlman:
The latter: there are only two SARJ assemblies, port and starboard.

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posted 10-30-2007 08:42 AM               

"The raceways themselves look like they are brand new machines, no wear on any of the teeth. Looking at the raceways themselves, very, very smooth and no particulate matter there, no galling."

posted 11-24-2007 12:24 PM               

The addition of the inspection to the spacewalk, which was primarily scheduled to complete outfitting of the Harmony module, came late in the week as flight controllers are still weighing their options for similar or more extensive activities during the next shuttle mission, STS-122, set to launch early in December.

After removing thermal cover no. 7 from the SARJ assembly, Tani reported seeing similar damage to what he had earlier seen under cover no. 12 in October. As with his previous report, the debris appeared to be magnetized, however upon touching the shavings, Tani was unable to detect what material he had displaced.

"So it does look like the race ring may be pitted, or at lest somehow damaged," ISS Expedition 16 commander Peggy Whitson observed, having joined Tani at the inspection site. Samples of the shavings collected by Tani and returned to Earth by STS-120 were subsequently identified as the same metal alloy as the race ring, the track on which the joint rotates.

"I agree it's damaged," Tani replied. "I don't think it's just on top."

posted 11-24-2007 02:29 PM               

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Originally posted by jameskelley97:
How are going to come up with idea on what may be wrong with it?

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What I gathered from today, and of course the engineers are going to go off and talk about this in great detail, but basically the damage is significant and is widespread. I'm not qualified or ready to draw conclusions here today, but we know that the damage is consistent around the race ring. The crew did report the gear teeth themselves looked clean and did not appear to be damaged or rubbed in any off-nominal way, which I took to be good news.

What we've done is put the program in a better position on STS-122 to understand what they need to do in terms of either SARJ cleaning or SARJ repairs, etc. So we've gathered additional data, verified the extent of the damage and now the folks have some work to do to quantify and plan exactly what they're going to do to address the SARJ issues on their mission.

In a worst-case scenario, the 12 bearing assemblies and two drive motors could be moved to the redundant gear during three to four spacewalks. But engineers do not want to consider such a drastic step until they figure out what is causing the problem with the active gear and race ring.

The problem is not serious in the near term because the station's arrays can generate enough power even with the starboard blankets locked in place. But the starboard SARJ must be back in operation by next April when NASA plans to launch Japan's Kibo research module.

posted 12-06-2007 06:29 PM               

They illustrate the nature of the metal filings and the observed pitting damage to the starboard solar alpha array joint.

They were provided to collectSPACE by a reader.

posted 12-18-2007 11:34 AM               

The spacewalkers looked for the cause of partial loss of electrical power to one of the station's two Beta Gimbal Assemblies (BGAs) for the starboard solar wings. They also examined damage to the starboard Solar Alpha Rotary Joint (SARJ).

On Dec. 8 the BGA's primary power was lost after three circuit breakers tripped. A backup power source still functions, but because of the loss of redundancy, the device was latched with the wing in a position suitable for docking of shuttle Atlantis on STS-122.

With the cables disconnected the circuits remained closed, apparently clearing the cables as suspects. Whitson reconnected them late in the spacewalk.

For the BGA inspection, the spacewalkers entered the truss from opposite sides, but remained together to be able to warn one another of obstructions in that confined area. That inspection took about 45 minutes.

Next the spacewalkers moved to the SARJ. Working together, they removed two large drive lock assembly covers and inspected the race rings and bearings beneath them. Then they removed and inspected beneath most of the remaining 22 covers. Their inspection on Tuesday showed various degrees of contamination under the individual covers. Generally it was similar to what had been seen previously.

Finally, they removed trundle bearing assembly No. 5, one of the 12 that move along the race ring, and returned it to the station's interior.

The spacewalk was the 100th for the construction and maintenance of the station.

posted 01-30-2008 12:14 PM               

Whitson and Tani also continued their earlier inspections of the starboard solar alpha rotary joint.

Most of the spacewalk focused on replacement of the motor, the Bearing Motor Roll Ring Module (BMRRM). Called the 'broom," the motor drives the starboard solar wings as they tilt along their axis to follow the sun for optimal power generation as the station orbits the Earth.

Mission Control reported good electrical continuity to the new BMRRM. While spacewalkers were still outside, flight controllers completed a planned 3-degree rotation and then did a 360-degree rotation of those solar wings.

Major activities of the BMRRM replacement took place during the night part of the orbit, when less voltage is generated by the solar wings than when they are exposed to the sun. The replacement BMRRM was retrieved from its stowage place in Pressurized Mating Adapter-3 early this month in preparation for the spacewalk.

The motor is part of the Beta Gimbal Assembly, which experienced electrical failures Dec. 8. The removal and replacement of the BMRRM took about 3 hours, including pauses during the daylight part of the orbit.

posted 09-29-2008 09:12 AM               

According to Bill Harwood's story posted on Spaceflight Now, a repair option is being devised including installation of a new race ring. This ambitious repair plan will take until 2010 to get all components into orbit.

posted 09-29-2008 09:16 AM               

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Originally posted by PowerCat:
This leads to another question... will this force NASA to extend the shuttle program to complete these tasks?

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