Busy ISS Ops

Normally I would include all the news and statuses of the ISS mission in my Friday Links post tomorrow, but it’s been such a busy week that I think it deserves to stand alone.

On Tuesday, May 14, the second half of the Expedition 31 crew launched into the clear Kazakhstan sky.

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The launch meant that a great deal of planning that had been done for their docking late Wednesday night was validated. Due to various constraints, we did last night’s Soyuz docking a little differently than we have before. It is a three-day affair, still not over, with large attitude maneuvers the day before and the day after docking.

The maneuver on Tuesday was performed successfully, but not without some unexpected technical hiccups, so I hear. But alls well that ends well, and the Soyuz approached ISS late last night and docked around 11:30 PM Houston time.

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ISS will perform the second big maneuver back to our normal attitude today.

While all of this was going on, other teams are preparing for a SpaceX launch on Friday that will finally bring their Dragon capsule on a close approach mission to ISS. NASA held an FRR (Flight Readiness Review) on Monday and gave a go for launch. Sounds simple, except that in the 11th hour, as they say, the ISS Motion Control System has been having some issues that directly affect SpaceX launch commit criteria. From the ISS on-orbit Status for the 12th:

GPS Failure:     On 5/10, GPS-1 (Global Positioning System 1) of SIGI (Space Integrated GPS/Inertial Navigation System) locked up and stopped producing attitude information, potentially due to an internal hardware issue.  Controllers on the ground power-cycled it twice (turned it off/on), but it did not come back on.  GPS-1 is drawing power but is not communicating with the GNC MDM (Guidance, Navigation & Control Multiplexer/Demultiplexer) computer.  There is another good spare onboard for an R&R (removal & replacement), as well as a degraded spare.  On 5/14 (Monday), the crew will access the SIGI GPS and perform the R&R to increase redundancy in preparation for SpaceX launch and berthing if the decision to do it is made by tomorrow.  Last April, when Burbank & Kuipers replaced the SIGI GPS in the Lab Aft Endcone, they ran into a couple of issues, and the R&R took eight hours of crew time split over two days using two crewmembers.

The GPS system on ISS is needed for SpaceX approach and rendezvous. The two vehicles each have their own set of GPS hardware and use the calculations for precise relative navigation, until Dragon gets close enough to use laser ranging. Fortunately, the removal and replacement (R&R) of the GPS was done successfully on Monday, and we’re back in business.

All of that and today is only Thursday. Dragon should launch on Friday and do a close approach Monday, with capture on Tuesday… and then an ATV reboost on Wednesday. We’ll get a bit of relief before Dragon unberths and comes home later in the month.

And if SpaceX has a successful mission this month, ISS ops are sure to get even more exciting in the near future!

May 17, 2012 6:39 am

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