The objective of the activity is to develop an independent and operational European capability to determine the attitude motion vector of an uncontrolled space object. This capability is necessary to support recovery actions after spacecraft contingencies leading to the loss of contact.

The vector should be derived from ground-based observations (SLR, radar, passive optical telescopes) within a short time frame (a few passes). The motion vector needs to be predictable with a given accuracy over the following passes. The attitude motion vector after loss of contact is essential in order to understand the current spacecraft mode and the overall accumulated amount of solar energy collected on the generator panels. For future active removal missions a precise a-priori knowledge of the attitude motion is essential for the design of the missions. This includes long-term forecasts of the tumbling motion.

 

When Europe still had no access to clarify the attitude of lost spacecrafts in order to optimize recovery attempts and improve re-entry predictions, the precursor GSTP study on ?Attitude Motion Measurements and Modelling? activity paved the way for an independent European capacity in this field. In fact, for the first time in Europe, it was possible to join measurements of SLR, passive telescope and synthetic aperture radar to fit a dynamic attitude model of the given spacecraft. This method is able to identify and predict the attitude motion of a fully defunct spacecraft within a few passes, which in contrast to the former method that relied on isolated single measurements, allows not only to ?measure? the attitude but also to ?understand? and predict it. Nevertheless, due to a meaningful number of European satellites being lost contact with each year, there is an increasing need for sensor support to clarify the attitude mode.

 

Therefore, the next important step to take is to expand and harden the method from an experimental setup to an operational one. In other words, the method needs to be made robust, along with an improvement on reaction and computation time for operational needs. Furthermore, in 2018/2019 there will be highly interesting test target (such as LEDsat, OPS-SAT and ELSA-D, which are equipped with either active LEDs or clusters of retro-reflectors), which provide unique opportunities to verify the methods.

 

In order to achieve this, the activity will refine the computer model IOTA (In-Orbit Tumbling Analysis) that is used to fit full 6-degree of freedom spacecraft dynamics to the measurements. In addition, the computation method needs to be accelerated by introducing look-up approaches in the computation of the aerodynamic cross-section and other measures for operational practicality. Also, data generation by SLR, light curve sources and ISAR radar need to be accelerated and calibrated along with reference targets such as LEDSat, ELSA-d, and a collaboration and emergency response mechanism shall be established as well.

 

Finally, the iteration of the 6-DoF model match to the measurements shall be automated, which requires a robust optimisation method, along with observation campaigns to verify the latest development steps and exercise the approach for increased operational robustness. Operational readiness shall be demonstrated along with modelling and observation of ESA operational reference targets, also in preparation of emergencies. The related target models for IOTA shall be established and tested for this purpose.