Automation challenges of the Mission Planning System and the Ground Station Network and their Interoperability within the combined TerraSAR-X/TanDEM-X Ground Segment

Kurzfassung

The successful launch of the TDX satellite on June 21st, 2010 marked the beginning of the challenging TerraSAR-X add-on for Digital Elevation Measurement mission (TanDEM-X). Its primary mission goal is the consistent generation of a high accuracy world-wide global digital elevation model. The satellites TSX and TDX were therefore flown for about four years in a close configuration to form a single-pass (bistatic) spaceborne radar interferometer in a stable baseline configuration. Since the TanDEM-X data taking required both satellites, the on-going TerraSAR-X mission also had to be based on both satellites to counterbalance the TSX interferometric usage. In 2014, the DEM data acquisition was successfully completed. Since then, different flight configurations yielding various perpendicular baseline conditions are used to support the secondary TanDEM-X mission goal, the acquisition and generation of radar data products for a number of science and new technology related applications while the TerraSAR-X mission is still on-going. As the original TerraSAR-X mission already lead to some challenging solutions within its ground segment to fulfill its demanding requirements, the TanDEM-X mission required just as many new ideas and solutions for the acquisition of the DEM data within the combined TerraSAR-X/TanDEM-X ground segment. The operation of the new TanDEM-X ground station network asked for elaborate workflows and interfaces with the mission planning system (MPS). And the TanDEM-X Science Phase following the DEM Acquisition Phase since 2014 even put the complexity one level further and again led to an upgrade of the interfaces and workflows between the ground station network and the MPS. One of the major challenges results from the need to consistently handle the different flight formations. The close formation (about 1km or less) of the two satellites enables the ground station to receive data from both spacecrafts within one contact. In the far configuration (about 50 km or more) a ground station with two antennas is able to receive data from both satellites in parallel. Furthermore, in the near formation (something between about 1 and 50km) a ground station with only one antenna can receive data from one satellite only, thus, a reception from both satellites is without specific enhancements in the antenna control, for example already implemented on the German Antarctic Receiving Station (GARS) in O’Higgins, in general only possible using two antennas. In a very specific formation, the so called “close formation with large horizontal baseline”, both spacecrafts are close when they are nearby the poles, and then they take a near formation when they are nearby the equator. Thus, a specific operation type had to be developed for each ground station individually depending on its geographical position and its physical properties. In this presentation, the analysis carried out in close collaboration with the flight dynamics group for the selection of the appropriate operations type per ground station and contact is shown. The outcome of this analysis was a heterogenic pattern of all the ground station contacts of that network. As TanDEM-X data acquisition produces the same amount of data on each of the two satellites, a more homogenous distribution of the downlink time was necessary and thus another complex analysis had to be carried out. The outcome of this secondary analysis will be the main topic of this presentation. In particular, we will discuss the necessity of the adaptation of the various interfaces and workflows between the ground station and the mission planning system. These adapted workflows still allow timeline horizons of several months down to reaction times of only about an hour between the mission planning output and the readiness of the ground station. Based on the information given by the MPS, the ground station is able to optimize its used resources. Furthermore, not only is the recording of the received data driven by the input of the MPS, also, the subsequent quality check of the data is completed within one hour. At the end of the talk, the downlink-scheduling within the MPS will be briefly described. This includes the ground station pool concept and specific features supporting near real-time applications. Here again, the focus will be on the resulting workflows and interfaces of the two missions, TerraSAR-X and TanDEM-X, between mission planning and the ground station.