STS-132 L-2 MMT: IFAs Cleared Ahead of Atlantis’ Launch
With S0007 (Countdown) operations underway for Friday afternoon’s scheduled 14:20:07 EDT launch of Atlantis, Program managers have completed the customary L-2 MMT (Mission Management Team) meeting – officially clearing Atlantis for launch. Among the items discussed and cleared at the various FRRs (Flight Readiness Reviews) for STS-132 this past month were the previous IFAs (In-Flight Anomalies) from the STS-129 flight (last flight of Atlantis) and the STS-131 mission.
Previous Vehicle and Program Flight IFA Review:
In all, 10 IFAs were declared from Atlantis’ previous flight – the STS-129 mission in November 2009. Of those 10 IFAs, five were from Atlantis herself.
These IFAs, none of which were discussed in depth during the STS-132 FRR process, included a failed Mid-Starboard Payload Bay floodlight, a premature stop to a waste dump, a dislodged fire extinguisher, damage to MDU PLT1 Screen Glass, and an unexpected water temperature operation of an APU water tank heater.
Since these IFAs were dispositioned before Endeavour’s STS-130 flight in February and were of no concern for Atlantis’ STS-132 flight, a detailed discussion of these IFAs was not required during the SSP (Space Shuttle Program) and SOMD (Space Operations Mission Directorate) FRRs.
However, four IFAs from Discovery’s STS-131 flight (the previous Program flight) did require discussion and review prior to their official clearance for STS-132.
The first of these IFAs related to the failure of the Forward and Return Links on Discovery’s (OV-103’s) Ku-Band antenna.
“During STS-131, OV-103’s Ku-Band system did not operate in Comm or RADAR mode,” notes the Orbiter Project Office presentation to the SSP FRR – available for download on L2.
STS-132 Specific Articles: http://www.nasaspaceflight.com/tag/sts-132/
Numerous attempts to troubleshoot the Ku-Band antenna on-orbit were unsuccessful and recovery of the Ku antenna was not possible.
Testing on Discovery’s Ku-Band antenna in OPF-3 (Orbiter Processing Facility bay 3) at the Kennedy Space Center in the last three weeks suggests that the probable cause for the failure is either the Deployed Electronics Assembly (DEA) or the Electronics Assembly 1 (EA-1).
A troubleshooting plan was initiated on April 27 and further isolated the problem to the Deployed Assembly (DA).
Testing of the DA revealed that the Q6 transistor in the DEA exciter was the cause of the problem – which carried the same P/N as the transistor that caused the previous Ku-Band failure on Discovery during the STS-92 mission in October 2000.
In terms of STS-132 and Atlantis (OV-104), the SSP FRR and SOMD FRR Orbiter presentations both note that “OV-104 Ku-Band system hardware has had considerable flight experience and there is no evidence to suggest a trend in performance degradation.” Moreover, “All Ku-Band system OMRSD testing has been successfully completed.”
Confidence is high that the problems that plagued STS-131 will not reoccur since Atlantis’ Ku-Band antenna has passed all self-tests in the OPF and “No trend … in review of OV-103 or OV-104 mission or turnaround test data (back 3 flights on each vehicle) that could suggest the failure seen during STS-131” has been noted. Nonetheless, should the problem reoccur during Atlantis’ flight, workarounds – as seen during STS-131- are available to the 132 crew.
The second STS-131 IFA to gain note in the STS-132 SSP and SOMD FRRs was the partial loss of part of a Rudder Speed Brake (RSB) TPS (Thermal Protection System) tile during ascent.
Since only a portion of the TPS tile was lost during the 131 ascent, and on-orbit photography from the ISS confirmed that adjacent tiles were intact, the partially missing tile was not a concern for reentry as the aft portion of the Orbiter experiences more heating during ascent than descent and entry temperatures would not exceed any material limits for the exposed areas.
A review of SSP flight history further revealed that this was the first time that part of a TPS tile liberated out of 225 tiles that cracked during flight. As such, the chance of a cracked TPS tile liberating is “limited.”
Moreover, an entry analysis (from an Orbiter controllability perspective) revealed that even if two complete RSB TPS tiles liberated during ascent, controllability of the vehicle would be maintained during Entry, Descent, and Landing.
The third IFA reviewed by the SSP FRR pertained to the Left RCS (Reaction Control System) Fuel Helium Isolation B Value.
“During the post-waveoff RCS helium system reconfiguration, the Left RCS Helium B Isolation valves were being taken from OPEN to CLOSED,” notes the Orbiter presentation. “When cockpit switch was taken to CLOSE, the Ox Helium B Iso Valve indicated closed nominally (< 1 sec); however, the Fuel Helium B Iso Valve remained OPEN for 46sec before finally indicating CLOSED.”
Furthermore, there was no pressure difference across the valve during the anomalous OPEN indication. The valve operated nominally when it was re-opened for entry; the valve also worked properly during post-flight valve testing.
To be certain that this problem is understood, an IPR (Integrated Problem Report) was opened for the STS-133 flow (dubbed IPR 133V-0006).
STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/
For Atlantis, all RCS He Iso Valve were verified functional during the flow toward STS-132. Parallel pressure paths are available should one valve fail closed and cross-feed capability exists in the event that both valves fail closed. Further, a “Series [of] redundant regs and [a] relief valve prevent overpressurization for [a] failed open valve,” notes the SSP FRR presentation.
Finally, the last IFA from STS-131 pertained to the Forward RCS (FRCS) Fuel Helium ISO A Valve.
“During post-flight valve test, the Forward RCS Helium A Isolation valves were being taken from OPEN to CLOSED. When cockpit switch was taken to CLOSE, the Ox Helium A Iso Valve indicated closed nominally (< 1 sec); however, the Fuel Helium A Iso Valve remained OPEN for 82sec before finally indicating CLOSED,” notes the Orbiter presentation.
Previously, the valve had performed flawlessly during the entire STS-131 mission. A nearly identical signature was seen during post-flight inspection from the STS-119 mission in March 2009; however, the signature did not repeat during the remainder of the ground flow toward STS-128.
To make sure that this signature is understood as well as can be, an IPR has been opened for the STS-133 flow (IPR 133V-0007).
Again, since all RCS Helium Iso valves were verified functional during the flow toward STS-132 and since parallel pressure paths exist should a valve fail closed, this problem is not a concern for the STS-132 mission.