A BRIEF HISTORY OF OPTICAL NAVIGATION AT JPL

Optical navigation-the use of onboard imaging to aid in the determination of the spacecraft trajectory and of the targets' ephemerides-got its start at JPL as an experiment on the Mariner 6 and 7 mission to Mars in 1969. The justification for opnav was to ensure quality navigation results at the outer planets: as radio tracking data are geocentric, a radio-only orbit determination solution will tend to become less accurate with increasing distance from the earth. Opnav was used operationally for both Viking orbiters at Mars, but it came into its own with the Voyager missions to the outer planets. Pictures of the Galilean satellites of Jupiter, of Titan and the smaller icy satellites of Saturn, of the five classical Uranian satellites, and of Triton, Nereid and Proteus (S/1989 N 1) at Neptune helped immensely to shrink the size of the B-plane error ellipse. Optical navigation engineers were also responsible for several of Voyager's discoveries. The serendipitous discovery of volcanic plumes on lo is best known, but we also found new satellites at all four outer planets and determined their orbits. Both hardware and software advances have occurred since the 1970s. Vidicon television cameras have given way to CCDs. Ground data processing has moved from mainframes to minicomputers and now to workstations. We once used special frame buffers and monitors for display; now, our workstations bring up pictures inside an X window. The software has progressed from a mixture of Fortran 66 and assembly language to Fortran 77 and C, and some of it is now being rewritten in C++ and Python. Perhaps the most promising advance in optical navigation technology is the migration from ground processing to onboard processing. Our onboard autonomous navigation system was demonstrated on Deep Space I and used on Stardust. Autonav's greatest success to date was on Deep Impact, where it ran on both the Impactor and Flyby spacecraft and guided the Impactor onto a collision course with the nucleus of comet 9P/Tempel 1 while the Flyby spacecraft was taking pictures of the event. Opnav figures to play a prominent role in every future JPL mission to a small body. Whether the processing is done on the ground or onboard, whether the imager is our group's own Opnav Camera (first own on Mars Reconnaissance Orbiter) or a science instrument, optical navigation data will continue to enable the kind of precision navigation which is required for mission success.