System design, modelling, and tracking filter for bearings only analog camera

The formation control testbed (FCT) is a ground based multiple robot testbed for simulating the dynamic interaction of spacecraft formations in a representative 6-DOF environment. Linear and spherical air bearings are used to mimic the drag free space environment. Each robot is fully autonomous with a self contained supply of float gas, integrated battery power, and a complete suite of onboard avionics including IMU (3-axis gyro), wireless interspacecraft and ground communication links, cold-gas thrusters, and reaction wheels. For attitude determination an analog camera is used to image IR beacons fixed to the walls and ceiling of the test facility. These navigation beacons act as an artificial star field. Due to the close proximity of these beacons, the camera direction measurements are coupled to both translation and attitude maneuvers of the robot. This allows unique determination of each quantity, provided enough beacons are in the camera FOV. We have come to refer to this sensing scheme as the "celestial sensor". In this paper, each subsystem of the celestial sensor is discussed with emphasis given to the filtering algorithms. A detailed sensor model is described that is used to predict the performance of the sensor. Frame based simulations using this model are presented that predict 1-sigma errors on the order of 3.0 arc minutes in attitude (per axis) and 4.0 millimeters in position (per cartesian coordinate). Preliminary results from the production system are given that demonstrate uncalibrated functional operation of the system.

I. INTRODUCTION

The problem of indoor navigation has been motivated by a number of diverse applications including virtual reality, photogrammetry, aircraft assembly, and robotic operations. Researchers have characterized these applications in two categories, “outside-looking-in” applications, such as photogrammetry, where the sensing is done external to the vehicle or target of interest and “inside-looking-out” applications where the sensing of external landmarks is done on-board. Examples of the latter are the Arc Second Constellatiorr^3DiIndoor-GPS^TMsystem [1], [2] and the UNC HiBall Tracker [3]. The FCT robots require the “inside-looking-out” architecture as they must have onboard knowledge of their positions and attitudes.