ENR CTIO Blanco 4-m 2014-10-25

SISPI hung at about 11:40 local time. Study of the log files indcated that OBSTAC was failing to choose the next OBSTAC field, and was not populating the observing queue. Eric Neilsen also found that because we are having a **very** good seeing night, that OBSTAC's use of a pre-configured instrumental seeing of 0.65 -- which is subtracted in quadrature from the seeing value returned by Image Health -- results in a non-physical, imaginary number (or negative number) which is returned during those instances of very good seeing (like is occurring tonight), with Image Health values of < 0.65 arcsecs.

This return of a non-physical number caused OBSTAC to hang/crash and not populate the observing queue. However it is not clear why this would cause SISPI to freeze. Klaus will need to take a look at the OCS code.