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The TerraSAR-X/TanDEM-X Formation Acquisition–from Planning to Realization

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Abstract

On June 21, 2010 the TanDEM-X satellite (TDX) was injected into orbit at 15,700 km distance from its twin satellite TerraSAR-X (TSX), which has been in orbit since 2007. Already one month later TDX acquired a formation with TSX in order to build up the first single-pass radar interferometer in space. Within three years of close formation flying with flexible baselines ranging from 150 m to a few kilometers the twin satellites will collect interferometric radar measurements for the generation of a global digital elevation model with unprecedented accuracy. This paper elaborates on the TDX pre-launch analysis performed in the fields of collision assessment during orbit injection and target formation acquisition. To avoid a critical close approach shortly after TDX separation, the risk of collision between the already flying TSX satellite and the newly injected elements (DNEPR upper-stage, gas dynamic shield, and TDX satellite) had to be carefully analyzed. Further, the paper discusses a fuel-saving formation acquisition strategy, for which the maneuver budget is analyzed as a function of launch day and launch injection accuracy. Finally, flight results are presented to illustrate the successful formation acquisition realized in July 2010 and the formation reconfiguration process from the 20 km wide formation into the 300–400 m close formation performed in October 2010. This reconfiguration marked the start of the bi-static TDX/TSX instrument operation.

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Notes

  1. Remark: Although a small adjustment of the launch time depending on the cycle-day would be beneficial in terms of RAAN correction (e.g. a 1 s change translates into a 0.1 deg RAAN change) this option was not implemented in order to ease interface specifications with the launch provider.

  2. Note that the analysis was initially performed for the launch into 5 km higher altitude (i.e. TSX altitude). Here the probabilities for collision of TSX and GDS were significantly larger and radial distances below 100 m were found.

  3. The data is calculated using Eqs. (8) and (9), which will be introduced in the next section.

  4. The start of the commissioning phase was foreseen on cycle-day 1 within 3 cycles after TDX launch.

  5. Note that we consider day 6 as compliant too, because the maximum maneuver budget for the 1-σ dispersion exceeds the 18.5 m/s limit by less than 1 %.

  6. The relative SMA is nominally zero for all formations.

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Acknowledgments

The TanDEM-X project is partly funded by the German Federal Ministry for Economics and Technology (Förderkennzeichen 50 EE 0601) and is realized in a public-private partnership (PPP) between German Aerospace Center (DLR) and Astrium GmbH.

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Authors and Affiliations

  1. German Space Operations Center (GSOC), Deutsches Zentrum für Luft- und Raumfahrt (DLR), 82234, Wessling, Germany

    Ralph Kahle, Benjamin Schlepp, Florian Meissner, Michael Kirschner & Reinhard Kiehling

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  1. Ralph Kahle
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  2. Benjamin Schlepp
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  3. Florian Meissner
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  4. Michael Kirschner
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  5. Reinhard Kiehling
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Corresponding author

Correspondence to Ralph Kahle.

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Kahle, R., Schlepp, B., Meissner, F. et al. The TerraSAR-X/TanDEM-X Formation Acquisition–from Planning to Realization. J of Astronaut Sci 59, 564–584 (2012). https://doi.org/10.1007/s40295-014-0003-3

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