NASA defer New Year’s Eve YERO test

by Chris Bergin

NASA managers have re-scheduled a YERO (Year End Rollover) test involving the Mission Control Center (MCC), after it was originally set to take place on New Year’s Eve.

Capability to handle a YERO event is now a Space Shuttle Program (SSP) requirement, although major headway has been made on understanding the both the technicalities and required contingencies.

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Notes and Presentations, including: Year-End Roll-Over (YERO) MCC New Year’s Eve Test (now not NYEs) – Dec 21. PRCB: STS-116 Year End Roll-over (YERO) Options (Nov 2).
STS-116 YERO (Year End problem) outline and troubleshoot plan – available to download on L2.

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The problem relates to the shuttle orbiter’s computers needing to reset through a change of year, which could cause a glitch on orbit, first highlighted when managers decided to reduce Discovery’s STS-116 launch window to avoid having the orbiter on orbit during the change of year.

‘When somebody designed the General Purpose Computers (GPCs) that we use to basically run the shuttle, nobody thought that you needed to have the timer such that it needed to reset itself when it went from one year to the next,’ noted STS-116 commander Mark Polansky.

The conflict between the GPC’s software and the MTU (Master Timing Unit) is what caused NASA to look at the YERO issue, which could – in the worst case scenario – shut down the orbiter’s computers for a short period of time whilst on orbit.

‘The two talk to each other and say, ‘Wait a minute, you are at zero and I am at day 366 – something is wrong so we are going to have to shut ourselves down,” added Polansky.

October YERO simulation testing showed that the likelihood of problems arising with the orbiter were small. However, had Discovery failed to launch within the shorter launch window on STS-116, NASA were open to possibly launching within the longer window. Had that of occurred, she would have remained safely docked to the International Space Station (ISS) as a contingency during the change of year.

The New Year’s Eve YERO test was to be the first of a number of simulations to ensure ground support capabilities could handle a change of year event while an orbiter was in space. This will now take place later in 2007, with a PRCB (Program Requirements Control Board) meeting late in January to decide on the new schedule.

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Following the October tests, the November 2nd PRCB meeting noted that further evaluations would be required, including the capability to mitigate further modifications and upgrades to both the flight software and ground support upgrades.

‘The team is also working plans for future YERO. Potential to reduce on-board YERO impacts with Flight Software changes. Potential to reduce ground YERO recycle impacts with additional testing,’ noted a late December presentation announcing the decision to defer the New Year’s Eve test.

Carrying out the test on New Year’s Eve would have made sense due to the parallel timeline to the event occurring in a real scenario, but this would not be the ultimate conclusion to understanding YERO, given the test would need to be conducted again after the MWSOR (MCC Workstation/Server/Ops Replacement) upgrade – a replacement for the current DEC Alpha workstations.

‘There will continue to be MCC hardware and software changes between now and the time that YERO is needed. Most significant is MWSOR (MCC Workstation/Server/Ops Replacement), replacing workstations and servers along with re-hosting software from UNIX to Linux.

‘Currently underway – user software will be ready for testing in Spring of 2007. Replacements will continue through 2009. This makes it highly desired to be able to simulate MCC YERO response without being constrained to a single opportunity on New Year’s Eve.

‘Further testing and analysis can reduce the procedure footprint. Current procedure is brute-force recycle of everything. YERO testing, simulations and training to increase awareness and confidence across the community.’

The late December presentation also noted that the previous tests only provided data on the orbiter’s YERO events, whereas further testing would aid the understanding on how MCC events can be mitigated.

‘Further testing can reveal unknowns – SAIL and SMS testing that has been performed to date has only changed Orbiter-based time, not local MCC time (SGMT is used in sims).

‘Multiple ways to tell time can make it difficult to clearly identify YERO vulnerabilities. Based on this, MOD is planning to perform additional YERO testing and simulations to support YERO readiness efforts.

‘The goal of the test is to evaluate MCC hardware and software during time rollover at GMT and Local midnight. Focus is on MCC response to YERO, so on-board procedures will not need to be executed during the test.’

While the rationale to defer the test was not explained, NASA scheduled the test for New Year’s Eve to primarily reduce the impact of the test to MCC operations. The re-scheduled test is likely to take place at a weekend to ensure impacts are kept to a minimum.

While the orbiters are set to be retired in 2010, the NASA insistence that no short cuts are taken by the impending finale of the veteran ships is self evident, with the decision to make a YERO solution a program requirement – regardless of the fact that the remaining manifest of missions may not even see an orbiter on orbit during a change of year.

‘Additional YERO tests and simulations will be scheduled as required to achieve program requirement of having YERO capability through the end of Shuttle,’ concluded the latest presentation.

‘Expectation of SSP is clear – YERO capability is a requirement.’

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