Navigation and Occultation Receiver Experiment (NOX)

Schematic of the NOX payload onboard TET-1. Two antennas are switched via the RF relay and the signal is amplified via an LNA prior to the GPS receiver. The payload includes also a power supply, a latch-up protection system as well as serial line drivers.

As part of the first German Technologie Erpropungsträger mission (TET-1) the GNSS Technology and Navigation Group will validate the use of commerical-off-the-shelf (COTS) GPS receiver technology for low-budget science missions.

Primary mission goal of the NOX experiment is the demonstration of COTS receiver operation under the conditions of a space environment (radiation, latch-up, thermal conditions). Secondary objectives comprise the collection of scientific measurements for precise orbit determination at the 10 cm level and for occultation measurements. The latter data are of great interest for the determination of neutral atmospheric parameters (temperature and pressure) as well as for the estimation of ionospheric electron density. In order to reach the secondary objectives in an optimum way, the data from the GPS receiver will be shared with external partners including the GeoForschungsZentrum (GFZ), Potsdam, and the Universitat Politecnica de Catalunya (UPC), Barcelona.

The Navigation and Occultation Experiment (NOX) on TET-1 is based on a PolaRx2 dual-frequency receiver with a switchable antenna system. During normal operation, a zenith facing antenna provides optimum visibility of the GPS constelaltion for orbit determination purposes. For occultation measurements, in contrast, the receiver is connected to an antenna pointing in anti-flight direction. This allows tracking of setting satellites in the vicinity of the horizon.

The Septentrio PolaRx2 GPS receiver is a geodetic grade receiver providing highly accurate pseudorange and carrier phase measurements on the L1 and L2 frequency. For use within the NOX experiment, the receiver has undergone extensive environmental tests including thermal-vacuum, ionizing radiation and vibratuon testing.

Further Reading

Garcia-Fernandez M., Montenbruck O., Markgraf M., Leyssens J.;
Affordable Dual-Frequency GPS in Space;
16th International ESA Conference on Guidance, Navigation and Control; 17-21 Oct. 2005, Loutraki, Greece (2005).

Leyssens J., Markgraf M.;
Evaluation of a Commercial-Off-The-Shelf Dual-frequency GPS Receiver for use on LEO Satellites;
ION GNSS 2005 Conference; 13-16 Sept. 2005; Long Beach, California (2005).

Montenbruck O., Garcia-Fernandez M., Williams J.;
Performance Comparison of Semi-Codeless GPS Receivers for LEO Satellites;
GPS Solutions 10, 249-261 (2006). DOI 10.1007/s10291-006-0025-9