The Navigation and Occultation Experiment - GPS Receiver Performance On Board a LEO Satellite

Kurzfassung

The small satellite “Technologie-Erprobungs-Träger 1” (TET-1) is the first spacecraft developed for the German Aerospace Center (DLR) On-Orbit-Verification (OOV) program, which provides flight opportunities dedicated to testing and qualification of new technologies in space. The satellite was lifted into a low-Earth orbit (LEO) on July 22, 2012, from the launch site in Baikonur, Kazakhstan. TET-1 carries various technology demonstration payloads, among them the Navigation and Occultation eXperiment (NOX). This payload consists of a geodetic-grade GPS receiver, which is connected via an antenna selector to two GPS L1/L2 patch antennas. One of the antennas is mounted on the satellite’s zenith panel and receives signals primarily used for precise orbit determination (POD) experiments. The second antenna is pointed towards the anti-flight direction of the satellite for collecting measurements of low elevation satellites for ionospheric and tropospheric occultations. The antenna switch allows to select either the POD or the occultation antenna for signal reception. This article describes the NOX payload on board the TET satellite in detail and analyzes the receiver’s tracking performance and the accuracy of its navigation solution. It also presents the initial tracking results of the occultation antenna, which demonstrate that GPS signals can be tracked through the ionosphere below the satellite’s local horizon — at a minimum, even down to the upper part of the atmosphere — with commercial off-the-shelf (COTS) equipment.