The development of this receiver for high dynamics and space applications is based on the GPS Orion receiver design of Mitel (now Zarlink) Semiconductor. It serves as a prototype for industrial GPS receivers built around the Mitel GP2000 chipset and is supplemented by the GPS Architect Software Development Kit. A major advantage over other development kits is the availability of the receiver's source code, which is a fundamental prerequisite for the necessary software adaptations.
Core components of the GPS Orion are the frontend made up of the GP2015 R/F down converter and the DW9255 saw filter, the GP2021 Correlator and an ARM-60B 32-bit microprocessor. The receiver allows L1 C/A-Code measurements in 12 parallel channels and can be operated with common active antennas. For use with passive systems, a preamplifier with an 18-28 dB gain is required. Fig. 1 shows a sample flight unit built up at DLR for the IRDT mission. The main receiver board is supplemented by an interface board lying underneath, which, by default, provides two serial interface converters, a power regulator as well as a backup battery for real-time clock operation and non-volatile memory retention. The small size and the moderate power consumption of 2 W make the Orion receiver an ideal starting point for spaceflight applications. Here most functions of the standard interface board can be taken over by independent on-board systems, thus leaving a total receiver size of roughly 10cm x 5cm x 1cm. For use on low Earth satellites and other space applications numerous modifications and enhancements have been made to the original firmware by DLR. These include e.g.
The two versions also differ by their choice of FLL/PLL loop settings that are adapted to the specific application needs. A narrow bandwidth of the carrier tracking loop is chosen in the Orion-S receivers to achieve the most accurate carrier phase measurements under typical line-of-sight accelerations of 1 G. Wide bandwidth settings, in contrast are chosen in the HD receivers to accommodate the extreme dynamics of a powered flight and the re-entry shock.
For a validation of the software concept and the receiver hardware comprehensive tests have been conducted with GPS signal simulators at KT, UT/CSR and ESA/ESTEC.
The tests have proven the receiver's excellent hot start capability and demonstrated measurement accuracies of 0.4m (pseudorange), 0.7mm (carrier phase), and 0.08m/s (Doppler) for the latest software version designed for LEO satellite tracking (Fig. 3). For use on sounding rockets, slightly reduced accuracies (1m, 1.5mm, and 0.3m/s) apply in favor of an increased tracking robustness under high signal dynamics.
The Orion receiver has been tested to tolerate a maximum total ionizing dose of typically 15 krad, which makes it well suitable for spacecraft applications in low Earth orbit.
Montenbruck O., Leung S., Bruninga R.;GPS Operations on the PCsat Microsatellite;ION GPS 2002 Conference, 24-27 Sept. 2002, Portland, Oregon (2002).
Montenbruck O., Markgraf M., Leung S., Gill E.;A GPS Receiver for Space Applications;B1-Ax; ION GPS 2001 Conference, Salt Lake City, 12-14 Sept. 2001 (2001).
Markgraf M., Montenbruck O., Hassenpflug F., Turner P., Bull B.;A Low cost GPS System for Real-time Tracking of Sounding Rockets ;15thEuropean Symposium on European Rocket and Balloon Programmes and Related Research, Biarritz, 28 May - 1 June (2001).
Montenbruck O., Enderle W., Schesny M., Gabosch V., Ricken S., Turner P.;Position-Velocity Aiding of a Mitel ORION Receiver for Sounding-Rocket Tracking ;C5-5; ION GPS 2000 Conference, Salt Lake City, 19-22 Sept. 2000 (2000).
Montenbruck O., Markgraf M.;User's Manual for the GPS Orion-S/-HD Receiver;GTN-MAN-0110; Issue 1.0, DLR/GSOC (2003).
Montenbruck O.;Orion-S GPS Receiver Software Validation;GTN-TST-0110; Issue 1.0, DLR/GSOC (2003).
Markgraf M., Montenbruck O.;Total Ionizing Dose Testing of the Orion and Phoenix GPS Receivers;DLR-GSOC TN 04-01; Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen (2004).