EVA-4 success with array repair – Atlantis rolls ahead of STS-122

by Chris Bergin

EVA-4 has been completed, successfully, after Doug Wheelock and Scott Parazynski’s epic repair effort on the P6 4B solar array. Parazynski ably completed his surgical tasks on the torn array, before it was finally deployed to its full length.

Meanwhile, Atlantis has concluded her STS-122 processing milestone, rolling over to the Vehicle Assembly Building (VAB) this morning. Atlantis is still on track to launch within the December window.

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EVA-4 Success:

As the Shuttle and International Space Station crews awoke for Flight Day 12 of STS-120 – to the fittingly apt wake up song of the theme to Star Wars – the epic spacewalk about to be conducted by Parazynski received rallying calls from NASA management.

Assisted by Wheelock, Parazynski will attempt to repair the P6 4B array – as outlined in previous articles on this site.

See live threads for up-to-the-second live STS-120 coverage.

Transported to the work site on the end of the SSRMS (Space Station Robotic Manipulator System) and OBSS (Orbiter Boom Sensor System) arms, he spent several hours freeing the snagged bays, before installing five cufflinks to allow for the full deployment – half a bay at a time – of the power generating panels.

The importance of EVA-4 should was never underestimated, with the successful repair ‘critical’ for the station. The level of importance earned a rallying call from NASA manager Kim Doering.

‘This is critical to ISS. Prioritized doing this above everything else,’ said Doering, on the latest Shuttle Stand-up/Integration report. ‘This brings out best in all the teams and really shows what working for NASA and contractors is about. Everyone needs to continue doing a great job on mission, because that’s what’s making it possible to focus on ISS.’

The priority of this EVA is obvious, with the latest information showing that the sensor package on the OBSS is now likely to be damaged, due to thermal limitations on the instruments, meaning it will not be fully functional for the post-undocking Late Inspection. This will be a small price to pay, should the spacewalk end in success. 

Several presentations were produced to show how the OBBS package might cope unpowered at the end of the SSRMS, with the latest – an 18 page overview – showing NASA will try several methods to help aid its survival, though it is still likely to suffer progressive sensor failings after about five hours.

‘Reasonable chance OBSS sensors won’t operate correctly afterwards, because they’ll be cold for longer than certified for,’ added Doering. ‘Program accepted potential additional risk of not doing complete late inspection with fully functioning sensors.’

Late Inspection will still be carried out, via cameras on the end of the Discovery’s robotic arm, with the one main area of interest on Panel 1L, which – according to the WLE (Wing Leading Edge) sensors – received a registered hit three times higher than any previous ‘impact’ seen on the new sensors that debuted on STS-114.

‘Array is important for ISS, and SSP (Space Shuttle Program) has ability to use Shuttle arm to look at panels of interest for late inspection,’ added Doering.

UPDATE: Three of the four main sensors survived EVA-4.


The coincidence of Atlantis’ rollover today – while EVA-4 took place – has major parallels, with the successful repair to the array helping STS-122’s push towards a launch attempt inside the December 6-13 launch window. At present, NASA remains confident that Atlantis can remain on track.

‘Cautioned everyone against jumping to conclusions about STS-122 launch date,’ noted NASA HQ in a memo to the Shuttle Program. ‘Have a good team for both SSP and ISS, and can work through challenges. Have a lot ahead of us both on STS-120 and the stage between here and STS-122. Have a good chance of making December 6 launch date or sometime within that window.’

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‘Looked at preliminary stage timeline. Have robotic activities and three staged EVAs still to be accomplished prior to STS-122. Puts EVA 11 one week later than previously planned; however, this is preliminary. They’re scrubbing timeline to shorten it and meet December 6 launch date,’ added Mission Operations at JSC.

‘Will know more in next few days on stage timeline and implications to STS-122. Would be a day-to-day slip of December 6 launch.’

Atlantis herself has no major issues, with a smooth processing flow, in addition to the successful implementation to the stacking of the Solid Rocket Boosters and ET-125 inside the VAB – which was initially a constraint until NASA worked a mitigation plan.

‘In position to rollout Orbiter Saturday morning. ET/SRB closeouts going well. Ready to pull platforms on Friday evening, allowing them to bring Orbiter over on Saturday morning,’ added processing information. ‘Weather isn’t cooperating this week, but have time to complete pad work and have integrated stack out. Working with payload folks to determine appropriate date to bring payload out.’

Prior to rollover, Atlantis had her RCC (reinforced carbon-carbon) panels scanned, a procedure that was called after the pre-launch deliberations that occurred with Discovery’s RCC panels.

A large PRCB (Program Requirements Control Board) meeting presentation found one area of interest, but deemed the results as holding the same ‘risks’ as was found with Discovery. This will likely make up part of the opening pre-FRR (Flight Readiness Review) meetings, which start next week.

Other items of interest relate to several presentations that resulted in a waiver for Main Propulsion System (MPS) LO2 prevalve CIL (Critical Items List) – relating to an increase of risk associated with a Critical Redundancy Separation Violation, after ‘surveillance inspection identified that two separate main power bundles were merged into a single wire bundle adjacent to Avionics Bay 5 (OV-103 & OV-104).’

Other items up for discussion include a problem with ordinance on STS-120’s SRBs, found during post flight inspections. This is still under review, but is not a constraint to mating.

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