AUVSAT: An experimental platform for spacecraft formation flying
- Paper number
IAC-08.C1.8.9
- Author
Mr. Thomas R. Krogstad, Norwegian University of Science and Technology, Norway
- Coauthor
Dr. Jan Tommy Gravdahl, Norwegian University of Science and Technology, Norway
- Coauthor
Ms. Kristin Y. Pettersen, Norway
- Coauthor
Mr. Even Boerhaug, Norway
- Year
2008
- Abstract
In this paper we present the design and building of an experimental platform for validation of relative attitude control schemes for spacecraft. The spacecraft simulator is one of two systems which constitutes the AUVSAT laboratory, the other being the SKARV and MUNIN autonomous underwater vehicles (AUV). Both of which are fully developed and currently undergoing pool trials. Having used the same hardware and measurement systems, we are able reuse control, measurement and communication systems, only changing the control algorithms, saving time in the development process.
The experimental platform consists of 3 autonomous underwater vehicles, with 3-axis rotation control capabilities. Each vehicle is internally actuated by means reaction wheels on all three axes and measures the attitude using an inertial measurement unit, merging gyro and magnetometer measurements through an embedded Kalman filter. In addition an internal ballast system is used in combination with a pressure sensor to control the depth of the vehicles in the test pool, to ensure that the vehicle is fully submerged.
To be able to rely on internal actuation it is necessary to minimize the effect of the restoring torques, i.e. torques resulting from displacement of the center of gravity from the center of buoyancy. The vehicles are therefore designed with this specification when placing the components, and also contains movable lead weights for fine tuning. This goal was obtained by designing the whole system accurately in a CAD application. The simulator is therefore a good approximation to a space environment, with regards to torques acting on the vehicle.
Mechanically each vehicle is built of a spherical glass pressure hull, minimizing drag moments, and removing the effect of added mass, a phenomenon effecting all submerged or semi-submerged vehicles, due to the interaction between the body and the surrounding fluid. Inside the spheres, a mounting platform is provided for the hardware, fitted with three reaction wheel assemblies, inertial measurement unit, power supply battery, ballast system and on-board computer.
The on-board computer, is a PC104 stackable computer, including a CPU card, solid state hard drive, an IO communication card, a serial communication card and power supply. The QNX Momentix operation system is chosen for its real-time capabilities, required to execute control commands and collect sensor data in a timely manner. This on-board computer is connected through tcp-ip to an on-shore host computer running Matlab Simulink and real-time workshop. Giving us the opportunity to follow measurements and control inputs in real-time, give set-points, and start and stop the experiments, without having to surface the vehicles.
We are currently in the final phases of assembly of the vehicles, and expect to have experimental data in time for the final paper.
- Abstract document
- Manuscript document
IAC-08.C1.8.9.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.