Orbit Determination Performance Evaluation of the Deep Space 1 Autonomous Navigation System

NASA’s New Millennium Program involves a series of missions whose primary purpose is to demonstrate the feasibility of new technologies for spaceflight. Deep Space 1, the first mission in the New Millennium Program, will demonstrate, among other things, an Ion Propulsion System to provide thrust, and an autonomous onboard navigation system to guide the spacecraft. The mission plan is to flyby an asteroid, Mars, and a comet using these and other new technologies. The onboard navigation system, in order to be as self-contained as possible, uses images of asteroids taken by the spacecraft’s camera as its sole data type in determining the spacecraft’s trajectory. These images are clustered at intervals varying from hours to a week depending on the phase of the mission, with up to 12 different asteroids sighted per cluster. T h e images are then incorporated into a least-squares filter a t periodic intervals to estimate spacecraft orbit parameters. The orbit determination solutions are in turn used by the navigation system to compute maneuvers required to guide the spacecraft to its targets. Since this navigation strategy has never been used in flight before, it is important to perform pre-launch assessments of its performance. This is accomplished by the use of Monte Carlo simulations which drive the navigation software with a truth model of the spacecraft trajectory and the observables. The truth model simulates realistic errors for both which are expected in flight, and individual realizations of these errors are drawn from random samplings of the errors with provided statistics. This technique is used to analyze the first leg of the mission, the flyby of the asteroid McAulliffe. T h e results indicate that, under nominal conditions, the combined orbit determination/maneuver computation strategy is capable of navigating the spacecraft to a safe flyby. In addition, the propulsive events required are within the abilities of the hardware to provide.