Robert A. Jacobson (1944- ) is a noted authority on spacecraft navigation techniques, and he is currently developing ephemerides for natural satellites at the Jet Propulsion Laboratory. He was instrumental in generating the accurate satellite ephemerides used by the Voyager 2 spacecraft project during its encounters with Uranus and Neptune. These ephemerides were developed using both ground-based astrometry and spacecraft optical navigation data. Citation prepared by D. K. Yeomans, a colleague of the honoree.