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There is a claim circulating on Facebook that space shuttles couldn't fly near the end of the year because its onboard computers could not handle a year turnover.

Searching for the claim, I found Y2K-like fears create shuttle scheduling crunch, which says,

The space shuttle's computer software is about 30 years old and does not recognise when the calendar year switches. On 1 January 2007, for example, it will think it is day 366 of 2006 - a problem NASA calls 'year-end rollover'.

To reset the time, the shuttle's main computers would have to be 'reinitialised', which would mean a period without navigation updates or vehicle control, a situation NASA obviously wants to avoid.

As a programmer I know I should always store time as a Unix timestamp or some other T+x time representation, so I don't need to deal with timezones or other stuff. I only need to convert to or from actual date and time when presenting it or when parsing user input.

So I cannot believe NASA made such a mistake in that critical software.

Peter Mortensen
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Calmarius
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  • NASA does indeed use day and time-of-day. Day is sometimes expressed as Julian day, which is supposed to rollover at the end of the year, but more frequently uses mission day, which is always monotonically increasing. – Ben Voigt Jan 02 '15 at 19:12
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    When I look through a list of Space Shuttle missions, I see none have been in orbit during New Year, and the one that took place latest in a year, was [STS-103](http://en.wikipedia.org/wiki/STS-103) which lifted off (after some abandoned attempts) 1999 December 19 and landed December 27 (local Florida time; this was December 20 to December 28 according to UTC). – Jeppe Stig Nielsen Jan 02 '15 at 22:50

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From an archive from NASASpaceflight.com (which is not an official NASA web site), NASA solves YERO problem for shuttle:

By Chris Bergin, 2/19/2007 6:35:00 PM

Shuttle orbiters can now enjoy a happy New Year's Eve on orbit, following the recommendation to implement a YERO (Year End Rollover) solution that was recently designed by NASA engineers.

The recommendation, which was presented in the form of a 45 page presentation to the all-powerful PRCB (Program Requirements Control Board), involves the implementation of a modification to flight software on the orbiters, and new ground procedures.

The above is a synopsis, see the hyperlink above for the "full story".

Community
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ChrisW
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    "*The YERO plan may actually remain unused if all of the remaining shuttle missions launch away the small window that is affected.*" Reading through [the list of missions](https://en.wikipedia.org/wiki/List_of_Space_Shuttle_missions), it would appear they never needed it. I wonder if it was ever implemented. – Schwern Jan 03 '15 at 02:32