The FASTRAC Satellites: Software Implementation and Testing

The Formation Autonomy Spacecraft with Thrust, Relnav, Attitude, and Crosslink (FASTRAC) project from the University of Texas at Austin has developed two nanosatellites as the winner of the University Nanosat-3 Competition. Both satellites have been manifested for a launch provided by the Space Test Program (STP) in December of 2009. The FASTRAC satellites will demonstrate the following enabling technologies for nanosatellites: (1) on-orbit real-time GPS relative navigation via real-time crosslink data exchange; (2) on-orbit real-time attitude determination using a single frequency, C/A-code, reprogrammable GPS receiver; (3) a micro-discharge plasma thruster; and (4) a distributed ground station network. In this paper, the design and testing of the FASTRAC command and data handling system (C&DH) is described. The C&DH system is divided into four subsystems, each controlled by one Atmel Atmega128 microcontroller: communications, electrical power, GPS, and thruster or IMU (depending on the satellite). The major functionality of the C&DH software is presented: automatic crosslink, dual uplink frequency support, user command capabilities, automatic beacon updates, automatic storage and retrieval of experimental data, and support for all mission phases. By using commercially available off the shelf components and leveraging freely availably software, it was possible to build and deliver two low-cost, fully functional satellites. The major hardware and software testing and debugging tools, including the Flatsat electronic test-bed and the FASTRAC GUI Debugging Program, are discussed. Finally, the challenges encountered during the design process and the lessons learned through the numerous design iterations are presented.