Multidisciplinary Control of a Sparse Interferometric Array Satellite Testbed

Abstract

The MIT Adaptive Reconnaissance Golay-3 Optical Satellite (ARGOS) is a wide-angle Fizeau interferometer spacecraft testbed. Designing a space-based interferometer, which requires such high tolerances on pointing and alignment for its apertures, presents unique multidisciplinary challenges in the areas of structural dynamics, controls and multi-aperture phasing active optics. In meeting these challenges, emphasis is placed on modularity in spacecraft subsystems and optics as a means of allowing expandability and upgradeability. For the interferometer to function properly, unique methods of coherent wave front sensing are developed and used for error detection in control of the Fast Steering Mirrors (FSMs). The space environment is simulated by floating ARGOS on a frictionless air-bearing that allows it to track fast moving satellites such as the International Space Station (ISS), planets or point stars. A System Identification is performed on ARGOS to determine its dynamic properties and to design optimal controllers for the Attitude Control System (ACS). ACS sensors include an electronic compass with a 2-axis tip-tilt sensor, a viewfinder camera with centroiding algorithm, and a 3-axis rate gyroscope. Nonlinear, quaternionbased control is employed using reaction wheels as the spacecraft's actuators.

ARGOS testbed: study of multidisciplinary challenges of future spaceborne interferometric arrays

“…Based on the linear model obtained, the pointing and tracking controller was successfully designed and implemented performing a large angle slew maneuver. 21 The controller calculates the error quaternions 22 from the rate gyroscope, the electronic compass/inclinometer and the viewfinder centroiding CCD mixing the mechanical sensors with the optical sensor ͑the viewfinder CCD in Figs. 1 and 13͒.…”

An Air Bearing Facility for Antenna Pointing Mechanism

“…Traditional simulator can also unload the gravity of each link of robot arm. MIT has built several 3-DOF (degree of freedom) air bearing simulators to test the control method of small satellites formation flight [5][6][7]. Those simulators can move on the horizontal plane and rotate around the vertical axis.…”

Automatic Mass Balancing of Air-Bearing-Based Three-Axis Rotational Spacecraft Simulator

“…In fact, many recently built spacecraft simulators either employ automatic mass balancing systems already [2][3][4][5] or plan to upgrade in the future [14]. The automatic mass balancing system is composed of three proof masses on three individual linear stages, which can alter their positions relative to the spacecraft body.…”

“…To overcome the difficulties associated with the manual balancing, automatic mass balancing systems have been considered in many references [2][3][4][5][6][7][8][9][10][11][12][13]. In fact, many recently built spacecraft simulators either employ automatic mass balancing systems already [2][3][4][5] or plan to upgrade in the future [14].…”

“…Ground-based spacecraft simulators often use air bearings to simulate frictionless and microgravity space environments. Various air-bearing-based spacecraft simulators have been developed in the past ( [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]), and a historical review is presented in [17]. Planar air-bearing systems use a set of air pads mounted under the test article to achieve frictionless sliding over a smooth surface.…”