SUMO, or Spacecraft for the Universal Modification of Orbits, is a risk reduction program for an advanced servicing spacecraft sponsored by the Defense Advanced Research Projects Agency and executed by the Naval Center for Space Technology at the Naval Research Laboratory in Washington, DC. The purpose of the program is to demonstrate the integration of machine vision, robotics, mechanisms, and autonomous control algorithms to accomplish autonomous rendezvous and grapple of a variety of interfaces traceable to future spacecraft servicing operations. The laboratory demonstration is being implemented in NRL's Proximity Operations Test Facility, which provides precise six degree of freedom motion control for both the servicer and customer spacecraft platforms. This paper will describe the conceptual design of the SUMO advanced servicing spacecraft, a concept for a near term low-cost flight demonstration, as well as plans and status for the laboratory demonstration. In addition, component requirements for the various spacecraft subsystems will be discussed.

The Subsumption Architecture is a special case of behavior based control for robotics. Behavioral modules are added as "layers" with each layer performing a complete behavior. Higher level behaviors override lower level ones by taking control of their effectors or manipulating their internal states. The control layers are built up out offinite state machines connected by links that act essentially like wires. To test this architecture on a reasonably complex problem, a prototype airplane controller was developed. This controller jlies a simulated aircraft from take-off to landing and was run on a "C" based implementation of the subsumption architecture. Several lessons where learned from this effort. The subsumption architecture as currently defined is not sufiiently modular. A clean interface between different behaviors would be desirable. And finally, a more general relationship than strict hierarchy between high level and low level modules is required. None of these problems is insoluble within the behavior based approach but all must be solved i f realistic problems are to be dealt with. Some candidate solutions are given.

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Results are described of an ongoing project whose goal is to provide advanced Computer Vision for small low flying autonomous aircraft. The work consists of two parts; range-based vision for object recognition and pose estimation, and monocular vision for navigation and collision avoidance. A wide variety of range imaging methods were considered for the former, and it was found that a promising approach is multi-ocular stereo with a pseudorandom texture projected with a xenon flash. This provides high range resolution despite motion, and can be small and light. The resulting range images, taken at a few meters range, would support the use of Tripod Operators, an efficient and general method for recognizing and localizing surface shapes in 6 DOF. This would provide the ability to recognize immediately upon encounter many kinds of targets. The monocular navigation system is based on finding corresponding features in successive images, and deducing from these the relative pose of the aircraft. Two methods are under development, based on horizon registration and point correspondences, respectively. The first can serve as a preprocessor for the second. This approach aims to continuously and accurately estimate the net motion of the vehicle.