Troubleshooting required for Discovery

by Chris Bergin

NASA is working towards a smooth transition for the launch of their third flight of the year with Discovery on STS-116, although she has some remaining issues that require troubleshooting, prior to rollover in a few weeks time.

Meanwhile, the major work load on Atlantis comes in the form of plugging the hole, created by a debris strike to a radiator panel during STS-115.

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Processing for Discovery is still targeting a November 1 rollover of the orbiter to the Vehicle Assembly Building (VAB), where she’ll join the awaiting ET-123 and twin Solid Rocket Boosters stack.

However, Thermal Protection System technicians are working at a pace to complete ‘bonding’ of Discovery’s tiles that came back with cavities in them, following the conclusion to her STS-121 mission earlier in the year,

‘Still working in OPF (Orbiter Processing Facility) toward November 1, 2006 rollover,’ noted the Stand-up/Integration flow report for the first half of this week. ‘Tile in forward area on nose landing gear and chin will probably be worked up until rollover. On landing gear, working back-and-forth between tiles and mechanical checks to make sure everything in spec.

‘Twenty-one of 167 cavities remain to bond. Expect to complete bonding cavities by October 23, 2006.’

The External Tank door on the belly of Discovery has been repaired, although some electrical issues have been spotted – which will require a level of troubleshooting.

‘ET door system was put together, tile checks in work, and ET door functional should be performed later this week. Payload bay doors closeout out by October 19, 2006, which should close out mid-body,’ added the report.

‘Newly installed WSB (Water Spray Boiler) failed functional test run test late last week, and controller failed retest. Will require troubleshooting, and may need to R&R (Repair and Replace) WSB. Troubleshooting at Hamilton-Sunstrand on original WSB having anomaly on flight showed sensor bad (repeatable). Working on why it’s bad.’

‘AC3 current spike occurred and AC3 lost. Powered down and will troubleshoot. UAs (Unexplained Anomalies) on past such occurrences closed and determined to be inverter R&Rs.’

Atlantis also needs to remain on track, despite her primary mission (STS-117) being moved back a month. Her LON (Launch On Need) rescue mission support for Discovery (STS-317) has not changed in the schedule, meaning she will be required to support early in February.

Inspecting the orbiter’s TPS is almost complete, and appears to be on track to produce far less cavities than her sister. Removal and replacement of her windows are also progressing well.

‘Tile processing about 97 percent complete with tile inspection. Have 78 cavities so far. Windows 1 thru 6 R&R’d. Complete windows 2 and 3 this week. Windows 7 and 8 inspected. Appears must remove window 7.’

Pokeouts from her last mission (STS-115) also gain a mention, with the removal and replacement of the troublesome Fuel Cells – which – in the case of FC1 on Discovery – ultimately performed without issue on two of its three phases, plus the plugging of the hole caused by a debris hit whilst on orbit.

‘FC3 removed and being replace. Waiting for spare for FC1,’ continued the report. ‘Major work item on OV-104 (Atlantis) is MR plug for radiator repair.’

Also making an unwelcome entrance into the report was a note about Tin Whiskers, although the specific issue is not deemed serious.

‘On tin whiskers, ASA (Aerosurface Survo Amplifier) boxes 1 and 3 removed. Will install new boxes. Scratches found on cold plate. Under engineering evaluation. First report is will be acceptable as is.’

The issue of Tin Whiskers led to a self-titled dissenting opinion presentation from the Aerospace Corporation, in turn rebuffed by NASA, prior to STS-121.

Tin Whiskers are small slices of metal which can fall off on to the circuit boards – which could cause shorts in the orbiter’s electrical components, with the potential loss of vehicle and crew.

However, on the ASA issue noted in the Standup Report, it was recognised that the systems involving the Aerosurface Survo Amplifier (ASA) have a mitigated risk, due to redundancy through the need of three failures being required to affect the same actuator signal, before loss of function occurs. These systems are only used during launch and landing.

On the ET front, MAF (Michoud Assembly Facility) and Lockheed Martin and pushing ahead with the next two tanks due to arrive at the Kennedy Space Center, namely ET-124 – required for Atlantis’ STS-117 and LON-117, plus ET-117 – set to fly with Endeavour’s return to flight mission STS-118.

‘ET-124 – Tank due out December 17, 2006. No major issues, and production activities generally on schedule. Critical path still thru bipod mods. RTF (Return to Flight) mods in progress. Started grip lip spraying. Assessing other areas.

‘ET-117 – This is next tank following ET-124. Vertical in Cell A. Using accelerated production flow thru Cell A, and are on schedule. Completed most sub work in plant, including pocket spray. Puts them in good shape for upper spray next week.’

Interestingly, while NASA claim the changes made to the Shuttle manifest relate to ET backlog, Lockheed Martin appear to be picking up the pace, noting that ‘nine tanks (are) actively in production,’ at MAF.

The other major point of interest with the tanks is the upcoming final decision on the IFR (Ice Frost Ramp) design, which will affect around three or four of the ramps, with the aim of further mitigating foam liberation concerns.

‘On ice/frost ramp testing, completed series of tests with no collars Thursday, and first series of tests with collars Friday,’ noted the report. ‘Both tests successful. Will run another series of tests with collars.

‘Found out last week the bureau of mines will shut down helium pipeline for November 2006. Assessing now, but think we have enough helium for testing required for CDR (Certification Design Review).’

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