23 Sep 09:54 2013

## Re: [tz] Deep Impact: wrong time zone?

```Reddit[1] making a guess:

Put another way, if you represented time as the number of tenths of a second since midnight on January 1,
2000, then you would hit 4294967296 tenths of a second on August 11, 2013[2]. 4294967296 is significant
because it's 2^32, which is the smallest number that can't be represented as a 32-bit integer. Generally
this will wrap around to 0 (as in calculating 4294967295 + 1 will give you 0).

[2] http://www.wolframalpha.com/input/?i=2%5E32+*+0.1+seconds+after+midnight+on+jan+1%2C+2000

-----Original Message-----
From: tz-bounces <at> iana.org [mailto:tz-bounces <at> iana.org] On Behalf Of Paul Eggert
Sent: 22 September 2013 23:37
To: Arthur David Olson; tz <at> iana.org
Subject: Re: [tz] Deep Impact: wrong time zone?

Deep Impact's chief mission scientist Mike A'Hearn said, "Basically, it was a Y2K problem, where some
software didn't roll over the calendar date correctly."
The fault-protection software misread any dates after 2013-08-11, and the misreads triggered an endless
series of computer reboots.

The failure was in the fault-protection software -- i.e., if they hadn't tried to prevent failure, Deep
Impact would still be working.

What timescale wraps around on 2013-08-11?  Perhaps it was something mission-specific, such as the number
of deciseconds since the mission began, or the number of milliseconds since the previous reboot, and this
was bowdlerized into "calendar date" for the general public.

My source:

Vargano D.
NASA Declares End to Deep Impact Comet Mission.
National Geographic 2013-09-20
http://news.nationalgeographic.com/news/2013/09/130920-deep-impact-ends-comet-mission-nasa-jpl/

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Gmane