The initial phase of testing and troubleshooting on the issue known as YERO (Year End Rollover) has been successfully completed, but not to the point where NASA are satisfied they can allow Shuttle Discovery to be on orbit through the change of year.
NASA presentations from Thursday’s PRCB (Program Requirements Control Board) meeting notes recommendations that STS-116 should not launch after December 17, reducing Discovery’s launch window to 10 days.
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On the same day Shuttle managers confirmed that other mission elements would allow STS-116’s window to stretch from December 7 to December 24, the on-going evaluations with YERO – which affects orbiter software through the change of year – are not at the stage where they are confident they have dismissed the ‘unknowns’ of how Discovery will handle the change from 2006 to 2007.
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YERO testing has gone well, but the ‘unknowns’ have led managers to conclude that Discovery should not be launched after December 17, allowing the orbiter and crew to be back on Earth before the new year.
‘Shuttle MCC Platform and Orbiter ‘YERO recycle’ have been successful in the limited testing performed to date,’ noted the overview of a fascinating 54 page presentation of the YERO troubleshooting. ‘Procedures continue to mature with each test.’
‘Concerns of ‘unknowns’ due to limited testing (no failures introduced during MCC Platform or Orbiter YERO recycle). Unknowns could have a major impact to accomplishing the STS-116/12A.1 mission objectives (most challenging assembly flight to date).’
The setting of the launch window in relation to all mission elements, including YERO, will be confirmed at the upcoming Flight Readiness Review (FRR) for STS-116. However, the pre-emption of what will be recommended at the FRR is already taking place, with the Flight Operations Integration Control Board (FOICB) stating Discovery should not be launched past December 17.
‘At FOICB MOD (it was) recommended YERO should not be used to extend Launch window past 12/17/06,’ continued the overview, whilst adding their is a possibility of accepting the unknown risks, so long as Discovery launches over the Christmas period – so as to allow her to remain docked to the ISS during the change of year.
‘If program accepts additional risks, recommendation is to use launch dates that have YERO occurring docked (12/23, 24, 25, 26).’
Given that testing has gone well, it is not inconvincible that managers will wish to protect the current manifest flow for the upcoming salvo of missions, in which case YERO testing will continue with the aim of supporting STS-116 through the New Year, with a bottom line message from those carrying out the testing that, ‘Bottom Line â€“ Committed to performing YERO procedures if launch into YERO window!’
However, the presentation makes it clear that the orbiters are simply not designed to operate during this timeframe, and it is highly unlikely Shuttle managers will want to place any additional risk to the mission.
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