Abstractdeep space navigation is an evolving technology which must constantly meet new challenges. During the 1960's, Mark‐I navigation, involving ground‐based radio tracking and flight path control, was adequate to meet the needs of various lunar, Venus, and Mars missions. During the 1970's, Mark‐II navigation, involving a combination of ground‐based radio and onboard optical measurements, but still utilizing ground‐based control, will be adequate for such missions as Viking 1975, Mariner Jupiter Saturn 1977, Pioneer Venus 1978, Mariner Jupiter Uranus 1979, and even a “standoff” asteroid or cometary‐nucleus flyby. In the 1980's and beyond, however, reaction time becomes more important for many of the advanced missions under consideration by NASA. Examples include precision asteroid/comet flybys and rendezvous, probe delivery, outer planet satellite tours, landers, rovers, sample returners, and other mission options. It is thus necessary to develop Mark‐Ill navigation, which can use onboard computation and control to avoid both round‐trip‐light‐time and certain earth‐based delays in data processing and decision making during time‐critical mission phases.In order to prepare for the era of autonomous navigation, this paper first examines existing techniques for spacecraft navigation by describing the basic elements of the Mark‐I and II navigation technologies. The remainder of the paper deals with identification of criteria which necessitate onboard navigation, and with promising solutions now under consideration. An attractive solution possibility is proposed which utilizes narrow‐angle optics, a charge‐coupled device area‐array image sensor, a small advanced onboard flight computer, and a simplified set of software algorithms. Onboard commands would be derived and sent to the appropriate spacecraft attitude control, propulsion, and science platform pointing subsystems. The proposed autonomous navigation system does not address all mission options, but focuses primarily on precision approach trajectory control and adaptive science instrument pointing for asteroid, cometary, and outer planet satellite missions. Excluded mission options include landing, surface rovi