<title>Autonomous docking algorithm development and experimentation using the SPHERES testbed</title>

Abstract

The MIT Space Systems Laboratory (SSL) has developed a testbed for the testing of formation flight and autonomous docking algorithms in both 1-g and microgravity environments. The SPHERES testbed consists of multiple microsatellites, or Spheres, which can autonomously control their position and attitude. The testbed can be operated on an air table in a 1-g laboratory environment, in NASA's KC-135 reduced gravity research aircraft and inside the International Space Station (ISS). SPHERES launch to the ISS is currently manifested for May 19 2004 on Progress 14P. Various types of docking maneuvers, ranging from docking with a cooperative target to docking with a tumbling target, have been developed. The ultimate objective of this research is to integrate the different algorithms into one program that can assess the health status of the target vehicle, plan an optimal docking maneuver while accounting for the existing constraints and finally, execute that maneuver even in the presence of simulated failures. In this paper, results obtained to date on the ground based air table using the initial version of the program will be presented, as well as results obtained from microgravity experiments onboard the KC-135.

Flight Testing of Multiple-Spacecraft Control on SPHERES During Close-Proximity Operations

“…4), which can autonomously control their relative positions and orientations in a 6-DOF environment. The testbed is primarily designed to operate inside the ISS, but it can also operate onboard NASA's reducedgravity aircraft as well as in a two-dimensional environment (3-DOF motion) on a flat floor (such as the one at the NASA Marshall Space Flight Center Flight Robotics Laboratory) or on a laboratory air table [34][35][36]. By operating inside the ISS, SPHERES exploits the microgravity environment to represent the dynamics of distributed satellite and docking missions while preventing the testbed from experiencing unrecoverable failures when real or simulated guidance, navigation, and control (GNC) failures occur.…”

“…The subtraction of these states from the chaser states provides the relative navigation information necessary to the LQR/APF algorithm. The forces commanded by the algorithm, combined with torques commanded by the attitude controller, are processed by a pulse-width modulator and converted into thruster on/off times at the control frequency [10,34].…”

Mobile Robotic System for Ground-Testing of Multi-Spacecraft Proximity Operations

“…1 The Synchronized Position Hold Engage and Reorient Experimental Satellites (SPHERES) project has made use of air bearings in the testing of an actual space-based micro satellite in a ground-based testbed. 2 Relative motion of 6 degree-of-freedom (DOF) micro satellites has been ground tested in 3-DOF using a laboratory air bearing table and two of the SPHERES micro satellites. For spacecraft reorientation dynamics and control, friction-free rotational motion can be achieved using a spherical air bearing and using reaction wheels or control moment gyroscopes.…”

Design of an algorithm for autonomous docking with a freely tumbling target

“…There are Earth-operated platforms like blimp units, 1 underwater vehicles 2 and robotic facilities like the 12-DOF facility developed at the Naval Research Institute (NRL). 3 There are also space-operated platforms like the Synchronized Position Hold Engage and Reorient Experimental Satellites (SPHERES) testbed, 4,5,6 the platforms developed through the University Nanosatellite Program, 7 and larger platforms designed for a specific mission like the Japanese ETS-VII satellites 8 and the XSS-10 Micro-Satellite. 9 Because of its accessibility and its ability to operate both on the ground in a 2-D environment and inside the International Space Station (ISS) in a 3-D environment, the SPHERES testbed was selected to implement and demonstrate the algorithms developed throughout this research.…”