Autonomous Docking Of Small Satellites In Large Space-structure Construction

Paper number

IAC-07-C1.I.09

Author

Mr. Keita Sawayama, University of Tokyo, Japan

Coauthor

Mr. Takashi Matsuzawa, Japan

Coauthor

Mr. Yohsuke Tsutsumi, Japan

Coauthor

Dr. Toshiaki Iwata, National Institute of Advanced Industrial Science and Technology, Japan

Coauthor

Dr. Kazuo Machida, University of Tokyo, Japan

Year

2007

Abstract

We propose a method for the construction of a large space structure, such as a solar-powered satellite (SPS), in which a small satellite and a large-scale deployment mechanism are used. The construction strategy is as follows: (1) unfolding of the large-scale deployment structure, (2) approach to the proper position and orientation using thrusters and reaction wheels on the small satellite, and (3) connection to other deployment mechanisms using connection assemblies. 

On-orbit construction of the structure is expected to be executed autonomously. Many autonomous abilities are required for on-orbit construction, autonomous satellite docking being the most critical and challenging. We develop a method for controlling the satellite to achieve autonomous docking, and verify the method in a ground experiment using an air table and small satellite models. In this paper, we present a summary of the small satellite models and the control architecture. 

The small satellite models have eight thrusters and one reaction wheel as the actuators, an angular velocity/acceleration sensor and a CCD camera as sensors, and the connection assemblies. The actuators and sensors are controlled with a laptop PC via serial interfaces. The thrusters and the air-bearing are operated individually by small air compressors. The relationships between thruster power and acceleration/rotation acceleration and between reaction wheel rotation and satellite rotation were investigated. A vision system that consists of the camera module and a target marker plays a major role in observing the relative positions and orientations of the satellites. The connection assembly uses a grapple fixture and a snare-type mechanism. This assembly utilizes the mechanism employed by the end effector of the space shuttle robot arm. 

We present the architecture by which the autonomous satellite docking is controlled. Because thruster fuel is a limited resource, it is desirable to minimize thruster fuel consumption during the approach and docking operations. It is also required to satisfy some constraints, such as a vision constraint (i.e., whether the camera can detect the target marker) and a docking constraint (i.e., whether the connection assembly is aligned adequately and satellite relative speed is slow enough not to damage other satellites). It is difficult to satisfy these constraints because of the high dimensionality due to the coupling of the position and orientation of two satellites. We will present a path planning method which minimizes the fuel consumption and satisfies the constraints. The results of simulation and ground experiments will be presented.

Abstract document

IAC-07-C1.I.09.pdf

Manuscript document

IAC-07-C1.I.09.pdf (🔒 authorized access only).

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