OFJ Field Journal from Lou D'Amario - 10/13/95
NEW ROUTINES FOR OPTICALLY NAVIGATINGNormally, I would not have made another journal entry so soon. The last one was only a week ago. However, because of the Galileo tape recorder problem, I felt I should put my current thoughts into a journal. I am hopeful that the problem can be solved.
In any case, we can accurately navigate Galileo through the orbital tour without the tape recorder. The reason for this is that optical navigation (OPNAV) pictures taken with the Galileo camera during the orbital tour are not stored on the tape recorder (as science pictures are). The information we need from each of the OPNAV pictures is extracted by a new program in the main computer; this takes only about 20 minutes. Then only the extracted information is immediately returned to Earth. It takes no more than about one hour for the data to get from Galileo to the Earth. The new program will be sent to Galileo's computer in April 1996.
There are three OPNAV pictures taken during Jupiter approach to improve the navigation accuracy at the Io flyby (which occurs about four hours before Jupiter closest approach). The processing of these OPNAV pictures cannot take advantage of the new method described above. These pictures are first stored on the tape recorder. Then pieces of each picture are read off the tape recorder and returned to Earth over a span of about two weeks. Losing these three OPNAV pictures would decrease the accuracy of the Io flyby somewhat, but only in the latitude direction. It would have no effect on the Probe mission or getting Galileo into orbit about Jupiter.