Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR
Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR

Strong Partner for Space Missions: TIRA Supports Controlled Re-Entry of the Aeolus Satellite

With Aeolus, ESA carried out for the first time an assisted re-entry into the Earth’s atmosphere for a satellite that was not originally designed for such maneuvers. On behalf of the Space Situational Awareness Centre, which collaborates closely with ESA, the Space Observation Tracking and Imaging Radar (TIRA) provided crucial mission support – through time-critical tracking data and high-resolution radar images – for the preparation and execution of the re-entry, as well as for future missions.

© FRAUNHOFER FHR
Radar images of Aeolus, taken with the Space Observation Radar TIRA. During the assisted re-entry of the ESA satellite, Fraunhofer FHR supported ESA and the Space Situational Awareness Centre with TIRA’s imaging capabilities. The images show Aeolus on one of its final orbits around the Earth. The vertical patterns originating from the center of the image are caused by multiple reflections of the radar signal in the telescope cavity of the ALADIN instrument.
© ESA - P. Carril, 2010
Artwork of the Aeolus satellite. The side-mounted solar panels and the large round opening for the ALADIN instrument are clearly visible.

More and more satellites are being launched in low Earth orbit, and the amount of space debris is increasing exponentially. Consequently, many retired satellites are returned to Earth under control, where they largely burn up. Today, most satellites are designed for re-entry. However, not Aeolus: The older weather satellite was not designed for this procedure. Nevertheless, ESA achieved its targeted re-entry. The capabilities of the large radar TIRA contributed to this success.

Mission support through orbital data and radar images

To bring Aeolus back, ESA performed targeted orbit correction maneuvers with the remaining fuel to place it in the best position for re-entry. It was supported by TIRA, which tracked the mission whenever Aeolus was visible from Germany. Immediately after each radar observation, the data were sent to the Space Situational Awareness Centre and ESA: Did the maneuvers achieve the intended effect? Based on this, it was assessed whether the next steps would proceed as desired. Fraunhofer FHR also provided predictions of the re-entry time and location. TIRA not only produced tracking information but also images of the satellite: What is the status of Aeolus? Are there any damages? This did not appear to be the case: the radar data clearly showed the large ALADIN telescope, the main payload, as well as the solar panels. Another finding: In the final phases of re-entry, the satellite exhibited a slight intrinsic rotation, i.e., it rotated slowly.

Relevant data for future satellite re-entries

The data collected during the mission with TIRA were not only important for the Aeolus re-entry, they also provide a valuable basis for the simulation and modeling of future missions. The information helps to better understand satellite re-entries, reduce uncertainties, and produce more precise forecasts, thereby increasing planning and decision security for future controlled re-entry missions.