Spacecraft observations of NEOs: a Mars Express demonstration

To demonstrate the astrometric capability of the Mars Express Super Resolution Channel for observing Near Earth Asteroids, asteroid 4 Vesta was imaged against a star field in two five-picture sequences. While at a solar phase angle of 40.5 degrees and visual magnitude of 7.2, Vesta was imaged along with a 7.4 and 8.2 visual magnitude reference star in all ten pictures. Mars Express centered astrometric observations of Vesta were then produced using flight camera geometric calibrations, optical photogrammetric techniques, and the Tycho 2 star catalog. The astrometric measurements, validated to an accuracy of 0.4 arc-sec, were delivered to the IAU's Minor Planet Center. Such observations provide geometrically powerful samples of the target body's state vector when combined with Earth-based astrometric observations, substantially improving orbit reconstruction and prediction compared to data obtained while viewing from the Earth direction only. Based on this success, Mars Express will routinely image Near Earth Objects, asteroids and comets passing within 20,000,000 km of Mars that are brighter than 9th magnitude to support the Near Earth Object Observation program