Dual-frequency space-based GPS receivers have many mission-enabling capabilities as compared to their single-frequency counterparts. The ionosphere-corrected range measurement allows precise orbit determination (POD) of the spacecraft to centimeter level, which has been successfully demonstrated in several space missions that have studied the Earth. Furthermore, the dual-frequency measurement allows observation of the ionospheric delay, which supports GPS radio occultation and space weather experiments. With the emergence of a second civilian GPS signal, dual-frequency measurements may be used for future real-time space applications such as autonomous formation flying, satellite networks, and cooperative control (e.g., satellite inspection and rendezvous).

While dual-frequency GPS receivers have been used in space for more than two decades, the size, power, and cost of this technology is an important driver for future space missions. The growing availability of launch opportunities for very small satellites known as nanosatellites and CubeSats raises the possibility of more affordable access to space measurements if the observation quality is sufficient to support the user’s needs.

This paper presents the initial development and testing of the Fast, Orbital, TEC, Observables, and Navigation (FOTON) receiver: a small, reconfigurable, dual-frequency, space-based GPS receiver. Originally developed as a science-grade software receiver for monitoring ionospheric scintillation and total electron content (TEC), this receiver was designed to provide high-quality GPS signal observations. The original receiver hardware was miniaturized and the software has been adapted for low earth orbit (LEO) operations. FOTON now fits within a 0.5U CubeSat form factor (8.3 x 9.6 x 3.8 cm), weighs 400 g, and consumes 4.5 W of instantaneous power, which can be reduced to 1 W orbit average power with on-off duty cycling. The receiver has been designed with commercial parts to keep manufacturing costs low.

Significant testing of FOTON has been performed with live signals and with signals generated by a Spirent GPS signal simulator. Initial terrestrial tests demonstrate behavioral consistency with the original heritage high performance receiver. Several LEO simulations are presented, demonstrating FOTON’s single- and dual-frequency positioning, Kalman filter based POD, and GPS radio occultation observation capabilities. In addition, its acquisition and reacquisition performance is presented; on average, FOTON’s time to first fix is approximately 45 seconds. Finally, an orbital Kalman filter is introduced to enable navigation in geostationary orbit (GEO), which is a challenging application for space- based GPS navigation. Extensive testing demonstrates that FOTON is a robust, versatile, high-precision dual-frequency space receiver. Its low cost, size, weight, and power requirements are key enablers for future small-satellite missions.

Cite and download the paper:
Joplin, A.J., E.G. Lightsey, T.E. Humphreys, "Development and Testing of a Minaturized, Dual-Frequency GPS Receiver for Space Applications," Proceedings of ION ITM, Newport Beach, California, 2012.

Download the presentation here [pdf].