In-depth processing flow charts and information acquired by NASASpaceflight.com show that both Discovery and Atlantis are in a smooth launch processing flow, with only a few issues in works.
The move to a July window for the second Return to Flight test mission, STS-121, has given a margin of contingency that has aided the processing of the two orbiters, targeting missions in July and August respectively. Threats to reducing the amount of contingency in the launch flow are tagged green, yellow and red. Only items noted as red have the potential to impact on the launch window. On the red side of processing towards July 1, the document indicates that only the issues of Tin Whiskers (RJD) and Window Bruising (windows 6,7 and 11) – added to any major issues found during and after the Tanking Test on June 1 – have the potential for impacting on the launch flow to July 1.
The following information was collated from two documents, the primary dated April 27. Selected scans are available (click images below – full documents available on L2).
Ultimately, the processing of both orbiters has to remain on track to allow Discovery’s mission to proceed as planned, due to Atlantis supporting role on the standby STS-300 rescue mission. A document, dated April 27 shows Discovery is on target for the opening of her launch window, as it noted the ‘overall processing schedule is assessed to a July 1st launch date,’ with ‘the assessment of critical path items assumes some level of contingency or margin in the schedule, based on the July 1st launch date.’
One of the buzz words in early launch processing, the gap filler pull, test and replace work, is on schedule for Discovery, with one of the remaining areas in works (1A upper), added to pre-rollover inspections.
Discovery is set to make her short trip to the VAB (Vehicle Assembly Building) on May 12, leaving the VAB as the STS-121 stack for the trip to the launch pad a week later. (Live rollover event pages)
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Atlantis appears to be in even better shape, as she finalises her preparations for being available to support her sister on the LON (Launch On Need) requirement date of August 4. Atlantis will be stood down from that mission requirement a few days into Discovery’s mission, following TPS (Thermal Protection System) inspections.
Her External Tank (ET-118) is scheduled to ship from the Michoud Assembly Facility (MAF) on May 30 – arriving at the Kennedy Space Center (KSC) well in time for mating with the twin Solid Rocket Boosters on June 29.
July 18 is the date scheduled for Atlantis to be mated with her ET and SRBs – easily achieving a large amount of contingency for the LON requirement date.
On Atlantis’ current OPF (Orbiter Processing Facility) flow, gap filler work is classed as ‘green’ – with TPS bond plan and Gap Filler Priority 1 in work, as is window (2,4, and 5) replacement.
Atlantis will also see one of her SSMEs (Space Shuttle Main Engines) replaced, (SSME 2047 vs 2058) which is scheduled for early June.
The primary mission for Atlantis (STS-115) will see the long-awaited re-start to assembly missions to the International Space Station (ISS), as she carries the P3/P4 truss uphill for installation into the outpost.
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