MARS OBSERVER ORBIT DETERMINATION ANALYSIS

Orbital accuracies throughout the Mars Observer mission are summarized and a plan is developed for achieving navigation objectives. These objectives are 1) to navigate the Mars Observer spacecraft to Mars and achieve accurate targeting at Mars, 2) to propulsively maneuver the spacecraft into a three-day period, capture orbit, 3) to navigate the spacecraft into a short-period (1.96 h), low-altitude, nearly circular mapping orbit, and 4) to maintain Mars Observer in the mapping orbit throughout 687 days devoted to scientific data acquisition. During the orbital phase, gravity field and atmospheric drag perturbations will control the spacecraft's orbital evolution. They are also the major factors influencing the accuracy of the prediction and reconstruction of the spacecraft' s orbital motion. Initially, the current best estimate of the Mars gravitational field model will be used during flight operations. However, this will be superseded by a 20th degree and order model developed by the navigation team early in the mapping phase. With this implementation, spacecraft reconstructed position errors will be improved significantly. In addition, estimates of the average atmospheric density (over four to five orbits) will be possible throughout Mars' perihelion.