NAVIGATION FOR THIl NEW MII , LENNIUM : AUTONOMOUS NAVIGATION FOR DEEP - SPA CE - I

The first flight of NASA’s New Millennium Program, DeepSpace1, will include a new navigational technology: a fully autonomous optical navigation system. The DSI Navigation system will be the first use of autonomous navigation in deep space. The task for this system is to 1) perform interplanetary cruise orbit determination, using images of distant asteroids, 2) control and maintain the orbit of the spacecraft using the ion propulsion system (IPS, another technology never applied to deep space) and conventional thrusters, 3) perform approach orbit determination and control using images of the science targets, 4) perform late knowledge updates of target position during close fast flybys in order to facilitate a high degree of quality data return from 2 targets: asteroid McAuliffe and comet West-KohoutekIkemura. Additionally, an encounter with Mars will probably performed with possibly a close flyby of one of the Mart ian moons , Phobos or Deimos. In order to accomplish these tasks, several functional components are necessary. These include Picture Planning and Image Processing, Dynamical Modeling and Integration, Planetary Ephemeris and Star Catalog Handling, Orbit Determination Data Filtering and Estimation, Maneuver Estimation, Spacecraft Ephemeris Updates and Maintenance, and general Interaction with the other Onboard Autonomous Systems. INTRODUCTION Autonomous onboard optical navigation will be a necessary component of autonomous spacecraft operations for many future planetary exploration missions. Because of light-travel times, there are experiments and even missions that cannot be performed or have limited data potential unless autonomous navigation systems are incorporated. Close orbits around, or very fast flybys of, small poorly characterimd objects are examples of such missions. Reducing operational complexity and costs is another goal of autonomous navigation systems. In a not-too-distant future, many small robotic missions may be simultaneously exploring the solar system. To increase the efficiency of these missions, the spacecraft themselves must take on more of the responsibilities of their own maintenance, including navigation. Adapting many of the techniques provmr for optical navigation for Voyager and Galileo, the New Millentaium DS1 onboard navigation system must autonomously plan picture sequences, perform image analysis, estimate the trajectory and calculate trajectory corrections using the low-thrust Solar Electric Propulsion system. New Millerwiurn DS1 will be the first planetary exploration mission to autonomously navigate al l mission phases. The engineering of such a navigation system poses a number of very significant challenges. An overview of Optical Navigation and how it will be applied to DS1 is given in Ref. 1. The presence of an autonomous navigation system onboard a spacecraft imposes certain requirements on the onboard control system, and in turn, the capabilities and function of the control system will influence the architecture of the “Navigator” In fact, one of the more challenging developments of the navigation system is the construction of this interface. The nature of the interaction is to balance the resource needs of the navigation system with those of equally important onboard engineering and mission science objectives. These resources include use of the camera, slew time, mass storage capacity, fuel use, use of the system computer and total time in the sequence of events. The amount of resources devoted to the Navigator will often translate directly into performance of the system. DSI MISSION ATTRIBUTES An overview of the New Millennium Program andDSI in particular is given in Ref. 2. The DS1 mission includes a very ambitious and challenging set of mission objectives and activities. There are probably three planetary targets intended for flyby encounters: asteroid McAuliffe, Mars, with possibly a close flyby of one of the Martian moons, and comet West-Kahoutek-lka moura. Currently, it is anticipated that launch will occur in July of 1998. The McAuliffe encounter will happen late January of 1999, the Mars flyby in late May of 2000, and the comet encounter about six weeks later. Figure I shows a heliocentric view of the mission trajectory, with