Ran a quick search on this thread and didn't see anyone else with this issue, so i figure i might as well put it up for consideration. I'm trying a conventional start for laughs, and to get some surveying done while the shipyard builds up enough to launch surveyors, i made a series of geosurvey buoys to be launched from the starting ICBM bases. However, i noticed that buoys with no engines are listed as having a maximum survey points output of zero. Reactor space is still assigned.
I tested it real quick, and the probes appear to last until the survey is complete. So, it's just that it the value listed in the missile design screen seems to be simply (engine endurance time) * (survey sensor value), ignoring the role of stationary survey buoys.