Progress made towards STS-119 flight rationale – March 11 NET possible
Engineers are scheduled to begin the installation of the three replacement Flow Control Valves (FCVs) into Discovery on Tuesday, following their arrival from Vacco. Meanwhile, managers are preparing to meet at Wednesday’s Special Program Requirements Control Board (PRCB) meeting, buoyed by encouraging data on the path towards flight rationale that may even allow for a March 11 launch date.
The arrival of the replacement valves – all of which have flown with Discovery over previous flights – is in time for the required retest work to be completed, post installation, ahead of the requirement to continue the pad flow towards launch.
“Flow control valves were shipped out yesterday and are expected to arrive at KSC today,” noted Tuesday morning processing information on L2. “Inspection, installation, and retest work will begin today.”
With the Special PRCB meeting on Wednesday, ahead of the second – and hopefully final – Delta Flight Readiness Review (FRR) on Friday, engineers are picking up preparations at Pad 39A to support a potential launch next week.
Range-Safety confidence testing was performed on Sunday. However, a few issues were noted during the test – notably on the Command Receiver/Decoder- which required a re-run. The second run proved to be successful.
“S5009 Range Safety confidence test: SRSS open/closed loop tests and flight code loads were successfully completed. Range Safety ordnance connections are complete,” added Tuesday processing information.
“S0007 Launch countdown preps will pick up today, and continue through the week. S0071 MPS/SSME and OMS/RCS pressurization for flight is scheduled for Friday night, following the completion of the flow control valve work.”
The FRR on Friday now appears to have the option of launching a day earlier than the previously announced work-to date, or NET (No Earlier Than) of March 12, with managers evaluating a March 11 launch.
Efforts at the Johnson Space Center (JSC) Flight Control Office also protected the contingency of launching up to and including March 17 – based on a shorter docked phase of the mission. March 11 through 13 would allow for a nominal four EVA mission timeline.
“We are preserving the option to launch on March 11 if possible, so schedules for both a March 11th and March 12th launch are shown (presentation on L2),” noted KSC’s Launch and Landing Division.
“We will brief both options at the barchart review and at the pretest briefing and be prepared to execute whichever option we are asked to support. Because of the potential call to stations on Sunday, March 8th, we will move up our barchart review and pre-test briefing to the dates/times.”
Click here for NASASpaceflight.com articles on the FCV issue since STS-126.
Although the FRR reserves the right to delay the launch out of the March window, which would likely be based on a call to redesign the FCVs ahead of STS-119 – as opposed to the plan to defer the redesign to later missions – positive news has been noted by the engineering teams working towards viable flight rationale for Discovery’s mission.
Firstly, the Orbiter Project Office (OPO) believe they have full confidence in the “health” of the three FCVs that are to be installed into Discovery on Tuesday, after testing proved the valves have avoided any sign of cracking – and thus less likely to liberate part of their poppets as seen on STS-126 – despite being flown four to five times already.
“The eddy current testing of the poppets for the FCVs continues to develop confidence,” OPO noted on the latest Shuttle Stand-up/Integration report on L2. “It has been used on the three valves that will fly (S/N 1002 to fly in LV56, 1006 to fly in LV57, and 1015 to fly in LV58), with no indications of cracking.”
Secondly, OPO believe that their testing procedure has the ability to find signs of cracking in the valves, in turn providing additional confidence for ensuring Discovery is flying with three good FCVs.
“Inspections were also performed on four other valves that had not been polished and rigorously tested (S/N 1011, 1013, 1014, and 1021). Each of these showed eddy current results that indicated cracking,” OPO added.
“After high-fidelity polishing, etching, magnetic particle and simulation inspection, all four valves showed cracking consistent with the eddy current results.
“It is believed that eddy current testing will point out cracks that exist in the poppets.
“As a result, the rigorously tested items to be used for STS-119 are believed to have no cracks within our ability of detection. This will be part of the flight rationale used to support the mission.”
Flight rationale, which will be approved for just STS-119 for the interim, will also be based on risk assessments on the ability to protect against a scenario where a liberation still occurs during Discovery’s ride uphill.
“In speaking with the team from MSFC (Marshall Space Flight Center) that is working to bound the particle size, it appears that this task is really coming into focus,” added the Stand-up. “Crack growth and propagation have been studied using analytical tools and testing. This data set provides some confidence regarding one-flight safety.
“The teams have been working to determine how best to bound the particle size. Over the past weekend, the various teams have been able to tie together all of the test data to present a cohesive story.
“Fracture mechanics analysis and hydrogen environment testing results have enabled us to say that for a single initiation site, we can bound particle size to 125 degrees. This determination received unanimous support from all supporting team members.”
And to ensure the orbiter’s Main Propulsion System (MPS) plumbing – notably the 90 degree elbow immediately downstream of the FCVs – is protected, should a poppet liberate during ascent, the installation of a doubler plate to the line appears to be close to being given a green light. The current plan is to install the protective plate on Discovery around March 5.
“Work on the doubler is progressing well. Over the weekend, an NSLD team drilled a 0.1” hole in the elbow, to test the efficacy of the doubler installed with an o-ring. It passed a 650 psi leak-check. The doubler is holding pressure with an O-ring.
“More testing of the doubler will be performed, using various backing plates,” added the Stand-up. “The goal is to deliver the doublers on March 4, for installation on the vehicle the following day.”
The Special PRCB will review the data, with a goal of creating full outline presentations for Friday’s Delta FRR. However, it is currently thought that STS-119 will gain the required flight rationale to launch next week.
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.