Editing Phobos program (section)

==Phobos 1==
{{Main|Phobos 1}}

''Phobos 1'' operated nominally until, a few weeks into the cruise to Mars, an expected communications session on September 2, 1988, failed to occur. The failure of controllers to regain contact with the spacecraft was traced to an error in the software uploaded on August 29/August 30, which had deactivated the attitude thrusters.<ref>{{Cite web|url=https://apnews.com/article/8e65a6dc038aa841808008a62593a9f3|title = Soviet Mars Probe Lost in Space Because of Controller's Error|website = [[Associated Press]]}}</ref> By losing its lock on the Sun, the spacecraft could no longer properly orient its solar arrays, thus depleting its batteries.

Software instructions to turn off the probe's attitude control, normally a fatal operation, were part of a routine used when testing the spacecraft on the ground.  Normally this routine would be removed before launch.  However, the software was coded in [[Programmable read-only memory|PROM]]s, and so removing the test code would have required removing and replacing the entire computer.  Because of time pressure from the impending launch, engineers decided to leave the command sequence in, though it should never be used.  However, a single-character error in constructing an upload sequence resulted in the command executing, with subsequent loss of the spacecraft.<ref name=ScienceMag>{{Cite journal|url=http://catless.ncl.ac.uk/Risks/9.24.html#subj3|title=The RISKS Digest, Volume 9 Issue 24|first=Peter G.|last=Neumann|date=September 14, 1989|journal=The RISKS Digest|volume=9|issue=24|via=catless.ncl.ac.uk}}</ref>