ISS SARJ Joint solution?

[MeteorWayne]

<p>From Spaceflightnow:</p><p>&nbsp;http://www.spaceflightnow.com/shuttle/sts126/080925sarj/</p><p><strong><font size="5" color="#000033">Station to get new ring for damaged solar rotary joint<br /></font></strong><font face="VERDANA, ARIAL, HELVETICA, SANS-SERIF" size="-2"><strong>BY WILLIAM HARWOOD</strong><br />STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION<br />Posted: September 25, 2008</font></p><p>Engineers believe they have finally pinned down the cause of metallic contamination and degradation in a critical solar array rotary joint mechanism aboard the international space station, Program Manager Michael Suffredini said today. The problem apparently was caused by the premature loss or breakdown of a gold plating intended to lubricate the joint. </p><p>During the next station assembly flight in November, shuttle astronauts will replace bearings in the joint, attempt to clean up the contamination and apply a lubricant to the surface of the bearing race. </p><p>The idea, Suffredini said, is to stabilize the joint, reducing stress and vibration so it can be periodically moved to maximize solar energy generation. While the starboard solar alpha rotary joint, or SARJ, features a redundant, uncontaminated race ring, Suffredini said the long-range solution is what amounts to major surgery: astronauts will partially disassemble the joint and insert a new race ring to take over from the one that has been damaged. </p><p>"It is our intention today ... to essentially not go to outboard ops and use the redundant ring that exists on orbit today," Suffredini said. "We intend to bring up another race and we will attach it to the race that's damaged and then roll on that race and save the outboard race for later in the life of the international space station." </p><p>During the next shuttle assembly flight, scheduled for launch Nov. 16, "we intend to go on the starboard side and remove the remainder," Suffredini said. "There are 12 trundle bearings, we've replaced one. We intend to remove and replace 11 other trundle bearings in order to bring those all home to help us with root cause. </p><p>"We will take that opportunity to clean up that race and then we'll also lubricate that race. What we're doing here is we're trying to modify the system just enough so that when we do have to rotate it, we minimize both the vibrations associated with the damage to the race and the contamination that's currently on the race, that helps us with structural life. In addition to that we want to reduce the amount of current required to drive this joint to make sure we never reach the maximum current the motor can drive to. So that's what these two steps do." </p><p>As a precaution, the astronauts also plan to lubricate the port-side SARJ. </p><p>"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," Suffredini said. "The way we lubricate that joint is we put a gold plating on the (TBA) 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. </p><p>"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. We have proven through testing that once you take the lubrication off this joint, it will damage the race very, very quickly." </p><p>Up to this point, the only long-range option appeared to be switching to the outboard race ring. But Suffredini said installing a new race will permit the station to continue operating with its current software and still preserve a backup in case of additional problems down the road. </p><p>"The downside to that is we have to basically separate the truss at a joint that wasn't made to separate on orbit," he said. "This is not the joint we put together on orbit, this is a joint that was assembled prior to flight and flew as an integrated truss. We referred to it at the time as S3/S4. </p><p>"We have a technique for doing that," he said. "We have to build the hardware, basically build some jack screws and we'll attach them to where we had some launch locks. And we'll basically separate this joint about 10 inches and we'll slip this new race ring in, install it and then pull it back together. To do all that, it won't happen tomorrow. It'll probably take us to late in 2010 before we have all this hardware ready to go and can get this race ring on orbit. But that is the current plan." </p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[Testing]

<p>Aeropace daily says the Bearing Trundle preload was excessive.</p><p><table border="0" class="Discussion_PostTitleTable"><tbody><tr><td class="Discussion_PostTitleTableIcon"><img src="http://sitelife.space.com/ver1.0/Content/images/forums/comment.gif" alt="" />

 

[JonClarke]

Graphite? <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>