Another possibility to use the continuously transmitted and freely available signals of the GNSS satellites is the so-called occultation measurement. Here, a GNSS satellite disappears on the horizon as seen from the receiver, and in the process, the navigation signal passes through the Earth’s atmosphere. From the doubling shift of the signal as a function of time, profiles of the diffraction angle and the refractivity, respectively, pressure and temperature of the atmosphere can be determined.
CORE OBJECTIVES AND UNIQUE FEATURE
Both occultation and reflectometry measurements require a stable reference source since very small changes in phase or frequency must be measured. New developments in oscillator technology make it possible to provide new-space oscillators with small dimensions, low weight and low power consumption. Therefore, an ultra-stable new-space oscillator will be tested and characterized for the SeRANIS satellite ATHENE1, which meets the frequency stability requirements for GNSS-ROX.
In addition, a test environment will be set up in the laboratory where new methods and algorithms for the evaluation of GNSS-ROX measurements can be developed and tested. Reflectometry measurements will also be performed using a downscaled model version of the GNSS-ROX experiment payload on a quadrocopter to test the developed algorithms of the simulation/planning software package and data analysis software.
The GNSS-ROX experiment is part of the Radioscience (RS) research group at the Institute of Astronautics at the Universität der Bundeswehr München (University of the German Armed Forces in Munich). The RS group has been and is involved in Radio Science experiments on several interplanetary space missions such as Venus Express (VeRA), Mars Express (MaRS), Rosetta (RSI), LUCY (REX), and JUICE (3GM). The knowledge and developments from GNSS-ROX will thus also find their application in future interplanetary missions.