Timelines and Power – Epic EVA-4 to begin major ISS challenge

by Chris Bergin

In what is being characterized as the most important spacewalk since the repair to the Skylab solar array in 1973, Scott Parazynski and Doug Wheelock are now in their ‘campout’ ahead of EVA-4.

The spacewalk is the opening challenge for the smooth continuation of International Space Station (ISS) assembly, a challenge tasked to the program regardless of how well the repair is conducted on Saturday.

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P6 4B Repair proceedure latest: 

Ground testing on the repair procedure has been non-stop, with NASA now confident they have a good chance of being able to bring the P6 4B array back into a nominal configuration.

Working night and day, engineers have been tasked with the repair procedure, and also the complex ballet of robotics involved with ensuring Parazynski is able to carry out the repair safely, as he reaches over to the array on the end of the SSRMS (Space Station Remote Manipulator System) and OBSS (Orbiter Boom Sensor System) robotic arms.

The tools that will be used are being constructed by the crew on the ISS – tools which will utilize ‘cufflinks’, made out of aluminium shim stock, covered in kapton and fiberglass tape, with a loop of 10 gauge electrical wire passing through two holes in the taped-up shim.

The procedure was successfully carried out on a set of full scale array bays back on Earth, with tests showing the repair is at least as strong as the original design, after engineers pulled on the entire array with its repair straps, with over three times the nominal full-tension load in the arrays, without any issues.

However, the challenge facing Parazynski on orbit should not be underestimated. Parallels are already being drawn with Pete Conrad’s EVA during the Skylab 2 mission in 1973, when he pulled a solar array wing free on the Skylab station, required to save the mission. EVA-4’s task is to save the smooth continuation of ISS assembly.

If the array isn’t repaired:

NASA engineers – as always – have been working hard on contingencies, should the task of repairing the array fail. Due to the problem relating to the starboard SARJ (Solar Alpha Rotary Joint) adding to the power consumption issues for the station, rationing would be required.

‘Conservative assumptions were made for the analysis: Port SARJ Directed Position Only. Unable to use power from 4B: 10A Stage: Preliminary availability assessment indicates all 10A stage activities can be supported with these assumptions,’ noted one evaluation presentation.

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‘Worst availabilities occur at low beta (0) on November 16 and 17. Stage activities may need to be strategically located based on beta. Next step is detailed analysis with the specific loads.

‘STS-122/1E Joint Mission: Preliminary availability assessment indicates 1E will have impacts if Autotrack is not used on the Port SARJ. High priority payloads will be impacted (SOLAR, UTEF, EPM, and EDR).

‘The nominal Columbus activities may also be impacted. This concern is caused by the low power availabilities combined with the expected constraints for the location of 4B during dynamic events.’

Columbus could still launch with Atlantis next month, although evaluations would need to be conducted on the status of P6 4B’s structural integrity, for Atlantis’ docking.

Tight Stage timeline ahead of STS-122:

STS-122 is on track to launch on December 6 as per ground processing, with the rollover of the orbiter to the Vehicle Assembly Building (VAB) recently advanced to Saturday.

However, this is no longer the restraining factor, with the requirement of work on the ISS now the priority before Atlantis can launch, regardless of how successful the array repair goes.

‘Quick Look Timeline: 11/5 – Undock. 11/9 – EVA 5. 11/13 – PMA2 relocate. 11/15 – Node2/PMA2 relocate. 11/21 – EVA 10. 11/25 – EVA 11: This puts EVA 11 exactly 1 week later then originally planned on 11/18,’ noted the latest timeline presentation.

‘The week is accounted for with +1 extra docked day, +4 days for EVA prep and execution, and +2 for post EVA prior to Robotics. The team will scrub through the plan details and determine if this timeline can be shortened in any way. With only EVA 4 planned on 10A, the team will look at 11/8 as an EVA 5 option.’

Should the array repair be completed, the challenge next facing NASA will be the reduction of the timeline in the stage, now that it has that addition of EVA-5 added to the worksheet. The goal will be to reduce the stage timeline, ready to receive Atlantis and Columbus in the first half of December, before the STS-122 window closes on December 13.

More will follow ahead of EVA-4. Array Repair Testing Images, MMT and Team 4 presentations now uploaded into L2.

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