Shuttle managers continue evaluations – RSS retracted

by Chris Bergin

With less than a day to go before the lift-off of STS-117, Shuttle Atlantis is having her final issues resolved, as S0007 Launch Countdown procedures enter the final stages.

The Rotating Service Structure (RSS) has been rolled back to reveal a floodlit Atlantis on Pad 39A, as managers continue to approve flight rationale surrounding the final few issues surrounding the vehicle.

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With the RSS now retracted, work will be carried out in preparation for tanking tomorrow. Technicians will arrive at work in the early hours to follow the process.

Only a few IPRs (In Process Reviews) remained by the end of day on Thursday, with one – a leak observed in the Ground Support Equipment (GSE) during PRSD (Power Reactant Storage and Distribution) loading – receiving a waiver.

The major bulk of Mission Management Team (MMT) and OPO (Orbiter Project Office) meetings have been related to the ‘suspect’ MSBLS (Microwave Scanning Beam Landing System), or MLS (Microwave Landing System). Orbiters have three MLS’ on board, with number three being the ‘suspect’ in question.

The MMT met to discuss the MLS issues, before the OPO looked at historical data surrounding the system. The late OPO meeting ended without a resolution, but will ‘tag-up’ Friday morning to finalize their evaluations. A positive conclusion is expected.

‘MLS#3 – failed S/T yesterday for Range. Performed 20 additional S/Ts that all passed,’ noted manager Steve Poulos on the L-1 Day MMT overview presentation (on L2). ‘Leading theory is ingestion of gas that caused start up transient, later gas heated up and cleared.

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‘We were ready to R&R (Remove and Replace) last night, but weather didn’t cooperate, causing delays in PRSD loading. LCC (Launch Commit Criteria) still go even if call MLS failed.’

The OPO meeting looked back at historical data relating to this number three MLS, which included the history of power up transients and hardware. This MLS number three had its decoder box removed and replaced earlier in the month and suffered some issues at that time.

Poulos noted that there is ‘a need to go look back and see if hardware is telling us something. Still go for MLS #3.’

Manager Leroy Cain – at the MMT – noted the two string ability even with one failure (number 3), which keeps the MLS within the LCC requirements for launch, as there is redundancy even if MLS 1 or MLS 2 fails during the mission.

‘MOD (Mission Operations Directorate), Firing room and Orbiter will think about what we want to do if we see something in the count,’ he added. ‘Don’t have a LCC violation if we declared MLS failed. We have not declared MLS#3 failed yet for purposes of the count.’

Other managers, and even astronaut Steve Lindsey, gave their opinions on how to deal with a failure of the MLS system during landing (or abort), with references to the GPS (Global Positioning Satellite) system.

‘GPS is great tool, but not a MLS replacement,’ added one manager. ‘MLS takes precedent at lower altitudes, but in a pinch could take GPS if we lost all MLS. LCC/FR maintain MLS for both single and three string GPS flights.’

The focus now appears to be on whether to actually class MLS number 3 as failed, given it had passed 20 tests without an error being found. If managers decide to class the system as failed – as opposed to suspect – then Atlantis can still launch, although extra focus will be placed on the MLS system as a whole during the mission.

‘(We are) not declaring it failed, there is work to do before get into final countdown. I consider it suspect,’ noted Cain. ‘As to whether we declare it failed we need to do some more work. That’s where I think we are.’

The full evaluation transcript was extensive, allowing comments from all who wished to make one – another example of the professionalism and openness of NASA evaluations and meetings that is now common place. This was also the subject of praise from Space Shuttle S&MA.

‘Thanks for all the dissenting opinions that helped make good flight rationale. We have a well trained – and after their long wait – I am sure they are ready to go. Looking forward for having Sunni (Williams) home.’

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