Martin Dunstan

Image Processing for Near Earth Object Optical Guidance Systems

A feature tracking algorithm is described, which is designed to support optical navigation of autonomous spacecraft. The algorithm is based on an existing system designed for use in planetary entry, descent, and landing (EDL) scenarios and includes several extra processing steps aimed at improving the performance. The algorithm is tested against the original by processing synthetic image streams of an asteroid and a lunar-type surface, taking care to use realistic surface reflectance models. The tracked features are processed to extract estimates of the camera motion between frames, and the results are compared with the ground truth to assess the robustness and accuracy of the feature tracking.

Modeling cratered surfaces with real and synthetic terrain for testing planetary landers

The autonomous guidance of a spacecraft lander requires extensive testing to develop and prove the technology. Methods such as machine vision for navigation and both vision and LIDAR for hazard avoidance are being studied and developed to provide precise, robust lander guidance systems. A virtual test environment that can simulate these instruments is a vital tool to aid this work. When available, terrain elevation models can provide a base for simulation but they frequently contain artifacts, gaps, or may not have the required resolution. We propose novel techniques to model heavily cratered surfaces for testing planetary landers by combining crater models and fractal terrain to create a multiresolution mesh for simulating a spacecraft descent and landing. The synthetically enhanced models are evaluated by comparing enhanced terrain based on Clementine/RADAR data with higher resolution terrain models from the Selene and the Lunar Reconnaissance Orbiter (LRO) to show that the artificial models are suitable for testing planetary lander systems.

Asteroid Modeling for Testing Spacecraft Approach and Landing

Spacecraft exploration of asteroids presents autonomous-navigation challenges that can be aided by virtual models to test and develop guidance and hazard-avoidance systems. Researchers have extended and applied graphics techniques to create high-resolution asteroid models to simulate cameras and other spacecraft sensors approaching and descending toward asteroids. A scalable model structure with evenly spaced vertices simplifies terrain modeling, avoids distortion at the poles, and enables triangle-strip definition for efficient rendering. To create the base asteroid models, this approach uses two-phase Poisson faulting and Perlin noise. It creates realistic asteroid surfaces by adding both crater models adapted from lunar terrain simulation and multiresolution boulders. The researchers evaluated the virtual asteroids by comparing them with real asteroid images, examining the slope distributions, and applying a surface-relative feature-tracking algorithm to the models.

SpaceWire Satellite Onboard Data-Handling Networks

Abstract SpaceWire is a communications network being widely used onboard current spacecraft. It is designed to connect high data-rate sensors, large solid-state memories, processing units and the downlink telemetry subsystem providing an integrated onboard, data-handling network. SpaceWire links are serial, high-speed, bi-directional, full-duplex, point-to-point data links which connect together Space Wire equipment. Application information is sent along a SpaceWire link in discrete packets. Control and time information can also be sent along Space Wire links. This paper introduces the SpaceWire standard and describes the key features of SpaceWire. Development and test equipment designed to support users of SpaceWire is also described.