Abstract
In this simulation study we analyze the benefit of ground-space optical two-way links (OTWL) for Galileo precise orbit determination (POD). OTWL is a concept based on continuous wave laser ranging and time transfer with modulated signals from and to ground stations. The measurements are in addition to Global Navigation Satellite System (GNSS) observations. We simulate the measurements with regard to 16 Galileo Sensor Stations. In the simulation study we assume that the whole Galileo satellite constellation is equipped with terminals for OTWL. Using OTWL together with Galileo L-band, in comparison with an orbit solution calculated with L-band-only, demonstrates the advantage of combining two ranging techniques with different influences of systematic errors. The two-way link allows a station and satellite clock synchronization. Furthermore, we compare the ground-space concept with the satellite-to-satellite counterpart known as optical two-way inter-satellite links (OISL). The advantage of OTWL is the connection between the satellite system and the solid Earth as well as the possibility to synchronize the satellite clocks and the ground station clocks. The full network, using all three observation types in combination is simulated as well. The possibility to estimate additional solar radiation pressure (SRP) parameters within these combinations is a clear benefit of these additional links. We paid great attention to simulate systematic effects of all observation techniques as realistically as possible. For L-band these are measurement noise, tropospheric delays, phase center variation of receiver and transmitter antennas, constant and variable biases as well as multipath. For optical links we simulated colored and distance-dependent noise, offsets due to the link repeatability and offsets related to the equipment calibration quality. In addition, we added a troposphere error for the OTWL measurements. We discuss the influence on the formal orbit uncertainties and the effects of the systematic errors. Restrictions due to weather conditions are addressed as well. OTWL is synergetic with the other measurement techniques like OISL and can be used for data transfer and communication, respectively.
Highlights
Since the invention of the laser, optical communication links have been considered for space applications
We added a variety of systematic errors for all observation techniques and we investigated a possible expansion of the number of estimated empirical solar radiation pressure (SRP) parameters for the precise orbit determination (POD) solution
We evaluate the influence of a combined Galileo L-band and optical two-way links (OTWL) (Optical Two-Way Links) scenario for Galileo POD using 16 Galileo Sensor Stations
Summary
Since the invention of the laser, optical communication links have been considered for space applications. Laser technology in space experienced growing importance for future satellite missions. Optical links are perfect for point-to-point connection and can be used for communication, data transfer, clock synchronization and ranging, or synergetically for all applications. Due to a shorter wavelength compared to microwaves, a higher modulation rate is. The GRACE-FO (Gravity Recovery And Climate Experiment—Follow On) mission (Abich et al 2019) and LISA Pathfinder (McNamara et al 2008) are examples of inter-satellite optical frequency ranging applications.
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