The TanDEM-X Mission Operations Segment: Close Formation Flight, Preparation and First Experiences

Abstract

In 2007 the TerraSAR-X satellite was successfully launched. Its payload consists of an earth observing Synthetic Aperture Radar, which supplies high resolution radar images. The yet to be launched TanDEM-X mission extends the TerraSAR-X mission with a second satellite of very similar capabilities. The two satellites will be flying in close formation (250m-500m), such that the radar instruments can be synchronized (bistatic mode). This bistatic mode allows the generation of three dimensional pictures and thus a high resolution elevation model of the observed area (according to HRTI-3 specifications), which in the end should cover the whole earth. TanDEM-X is the first project worldwide to fly a close formation with a minimum distance of only a few hundred meters. During the development and integration of the ground segment, it became obvious that the amount of security measures have to be significantly increased to ensure safe operations. One of the main influences is the satellite orbit and attitude control system that is based on active control via hydrazine thrusters. The activation of the thrusters for attitude control possibly also changes the orbit, which leads to a change of the relative positions. Consequently two problems can appear, either mutual radar illumination which might damage electronic equipment or if the impulse is large enough, a collision.

Dual satellite operations in close formation flight

“…Secondly, the master timeline is double checked against illumination risks before upload by an independent application. As a third step an on-board check based on the argument of latitude is established 18 . However, overall payload operations are not restricted due to the EZ since TSX and TDX EZ do not overlap.…”

TerraSAR-X/TanDEM-X Mission Planning: Handling Satellites in Close Formation

“…In intermediate phases, where the satellites are positioned in formations with greater distances, not all of the given requirements are applicable or different requirements will be needed. For detailed background information, especially on the security issues, see [6].…”

“…The German Space Operations Center (GSOC) designed the operations concept, implemented the necessary facilities and software and will operate the two-satellite mission throughout its lifetime [6]. This paper concentrates on the mission planning aspects.…”

“…Other off nominal cases might occur if one of the satellites deviates from its orbit or is not operational for a certain time period. The measurements taken are described in detail in [6].…”

TerraSAR-X/TanDEM-X Mission Planning - Handling Satellites in Close Formation

“…For each session, the mission Space Ops 2010, 2010-1989 17 planning system has to provide two execution timelines, one for the TerraSAR, one for the Other off nominal cases might occur if one of the satellites deviates from its orbit or is not operational for a certain time period. The measurements taken are described in detail in [6].…”