Black Jack GPS Receiver

The Black Jack (BJ) receiver is the revolutionary flight Global Positioning System (GPS) receiver developed by NASA to fill future needs for orbit-based GPS science. These range from a receiver to determine precise (1-cm radial accuracy goal for JASON-1) orbits, to missions using the GPS signals for remote sensing of the Earth's atmosphere. The BJ receiver follows the TurboRogue space receiver, which was successfully used in collaboration with engineers and scientists at JPL on five satellite missions. While the TurboRogue was initially designed as a high-accuracy ground receiver, the BJ was designed from the start as an instrument for use from orbit. The BJ contains many innovations to better suit it to this application. In order to simplify the analog electronics, it directly samples the amplified and filtered RF (radio-frequency) signal. This sampling produces two sample streams in quadrature for improved SNR (signal-to-noise ratio). The BJ semicustom Application Specific Integrated Circuit (ASIC) uses a full matrix switch so that inputs from multiple antennas can be directed to any of 48 tracking channels. Other ASIC capabilities are telemetry reception, tone tracking, and precise time tagging of external events. Although the receiver is designed as a science instrument rather than for mission-critical operation, it does contain innovative features such as the capability to operate in a bit-grab mode. In the event the highly-redundant digital processing fails, the main processor stops, or the spacecraft can no longer power the GPS receiver, the BJ can turn on for less than a second every hour, and still transmit data to the ground allowing sub-100-m orbit determination. The BJ receiver is designed with excess processor capacity to allow it to perform non-GPS functions; for example, on the GRACE mission, the BJ controls an intersatellite K-band link and also processes the output of a star camera to determine spacecraft attitude.