Atlantis has rolled back out to Pad 39A for her re-aligned STS-125 mission to the Hubble Space Telescope. First motion for the stack was registered at 3:54am local time, for a 11am arrival at the pad, after which the vehicle will undergo a hotfire of all three of her Auxiliary Power Units (APUs) tonight. Meanwhile a Flow Control Valve (FCV) plan has been created for Atlantis’ May 12 launch.
Atlantis, mated with ET-130 and her twin Solid Rocket Boosters (SRBs), began rolling out on top of the Mobile Launch Platform (MLP) and Crawler Transporter (CT) for the seven hour journey to the pad.
“A5214, rollout of STS-125 to Pad A, call-to-stations was completed at 0001L this morning. MLP first motion occurred at 0354L,” noted Tuesday morning processing information on L2. “MLP hard-down at the pad is targeted for 1100L.
“S0009, Launch Pad Validation: Call-to-stations is scheduled for 1030L this morning. All 3 APUs will be hot-fired on 3rd shift tonight. RSS rotation to mate position is scheduled for 0900L Wednesday.”
Atlantis will be joined by her younger sister Endeavour, when she rolls out to Pad 39B – following the approval to opt for the dual pad scenario for STS-400 LON (Launch On Need support.
Due to a “mission duration change” being worked by the SSP (Space Shuttle Program) for her primary STS-127 mission, Endeavour’s rollout date in April is undergoing fine-tuning. However, both vehicles remain on the flow timeline to support the May 12 NET (No Earlier Than) target for Atlantis’ final servicing mission to the HST.
“A mission-duration change will be brought forward for STS-127/2JA,” noted the latest Shuttle Stand-Up/Integration report on L2. “There are several sidewall payloads and a DTO (Detailed Test Objective) that have been worked and will meet the “early rollout date” on OV-105 (Endeavour).”
Flow Control Valve Status:
It was Endeavour’s previous flight on STS-126 that raised the questions surrounding the three LH2(G) Flow Control Valves (FCVs), following the liberation of a small part of the valve’s poppet during ascent.
Click here for NASASpaceflight.com articles on the FCV issue since STS-126.
The liberation failed to cause any issues for Endeavour, notably via the other two valve’s ability to keep the LH2 tank at the required pressure, and no damage was suffered to the internal plumbing of the Main Propulsion System (MPS) from the liberation – which is the main concern surrounding the FCV’s during ascent.
For STS-119, Discovery was fitted with three “cherry picked” valves, which have previously flown multiple times. These valves exhibited no signs of cracking, which is understood to be the first sign of a potential liberation threat on a future ascent.
All three of Discovery’s FCVs worked nominal during ascent, earning deserved praise for the multi-center effort utilized to create the Flight Rationale for STS-119.
Engineers are now looking ahead to the next two flights with Atlantis and Endeavour, in order to guarantee both orbiters have a good set of valves, to “ensure we have the right plan in place to get our assets for STS-125, STS-125(400) LON, and STS-127,” as per the Orbiter Project Office status on the FCVs on L2.
“Will also talk forward plan and make sure there is a good long-term plan to finish out the program.”
At present, Atlantis and Endeavour will require their replacement valves by the start of May, before a long term plan – surrounding newly produced valves at the contractor Vacco – kicks in. For the upcoming missions, previously flown valves have been “cherry picked”, including the re-use of Discovery’s three good FCVs from STS-119.
“Issue: Due to STS-126 GH2 Flow Control Valves (FCV) failure, Orbiter team reviewing options to support near-term requirements. Limited spares with no cracks and rapid flight sequence (STS-119 to STS-125 and STS-127),” noted a SSP overview of the current status.
“In the process of restoring new poppet production capability at Vacco, and they turned on to reinitiate their GN2 test stand capability. It will much more efficient to test and build the valves at Vacco.
“STS-125 and STS-125 LON mission need FCVs by approx May 1, 2009. Orbiter Team reviewed options to install unflown poppets as soon as possible. Current schedules projects FCV delivery in late May/early June as full production capability is restored.”
Discovery’s three nominally performing FCVs will be removed from the vehicle and donated to Endeavour, while Atlantis will fly with three valves that have flow between eight and 12 missions each – all with a nominal track record and no signs of cracking on their poppets, confirmed following extensive testing.
“Orbiter Team recommends the following preliminary FCV configurations: STS-125: (number of flights: 8/12/12, (S/N (Serial Numbers) 1007, 1022, 1023),” added the OPO report. “STS-125(400) LON/STS-127: 5/6/13 (S/N 1006, 1015, 1002) – recycle of STS-119 valves.”
One flown valve and another spare are being prepared to support any issues with the six valves that are to be installed on Atlantis and Endeavour, while other unflown/new valves are being targeted for use with Discovery on STS-128.
“Team working to clear S/N 1017 (10 flight valve) and/or deliver single zero flight poppet valve early as usable spare,” added the OPO. “Schedule supports the 5/1 need date for the STS-125 valves. Team still working to determine exact delivery date for STS-125 LON valves.
“Due to STS-119 valve recycle, date for unflown poppets will move to right. Date should support August STS-128 launch.”
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.