[tilly]

He's right that the period vs comma is likely wrong. But it is a legend based on a real event.

For details see http://en.wikipedia.org/wiki/Mariner_1 or http://catless.ncl.ac.uk/Risks/5.65.html#subj1 for more details. Here is a summary. The Mariner 1 probe was destroyed because it veered off course shortly after launch on July 22, 1963. By July 28 the NY Times was reporting that the cause was due to a missing hyphen. NASA submitted a report to Congress the next year that confirms this.

The comma vs period version likely arose as a misremembering of which typo caused the problem. Or possibly by confusing it with another incident. (There are anecdotal reports of such a bug being caught in Project Mercury. Whether they are true is a different story.)