HORACE (Horizon Acquisition Experiment) was an experiment flying on REXUS 16, a rocket that is designed for student experiments by the REXUS/BEXUS programme, a collaboration between the German Aerospace Center (DLR), the Center of applied space technology and microgravity (ZARM), the Swedish National Space Board (SNSB) and the European Space Agency (ESA).
The aim of our experiment is to develop a sensor system, which is supposed to evaluate autonomously its attitude relative to the earth. What we wanted to determine during the rocket flight was whether this approach is really apt to acquire the attitude even under stress conditions. The Experiment was designed and implemented by a team of six students at the University of Wuerzburg, Germany. Thereby the students were supported by the Chair of Computer Science VIII, the DLR and ZARM.
(left to right: Jochen Barf, Thomas Rapp, Sven Geiger, Arthur Scharf, Florian Wolz, Matthias Bergmann )

(left to right: Jochen Barf, Thomas Rapp, Sven Geiger, Arthur Scharf, Florian Wolz, Matthias Bergmann )


Why we were doing such an experiment
On today’s way to completely autonomous satellites a satellite’s attitude determination and control system (ADCS)  must work autonomously not only during nominal phases of the mission but also in unexpected situations or emergency cases. These include, among others, situations during which the satellite’s main ADCS is corrupt itself or during which the main ADCS’s capability does not suffice any more, e.g. when the satellite is spinning and tumbling uncontrolled with high rates.


Experiment Setup
The System consists of a (off-the-shelf-)camera and an embedded system that captures and saves the image data. These image frames are then processed by the algorithm, which is trying to recognise the horizon of the earth and its curvature to calculate a vector to the earth centre (the so-called nadir-vector). Using several processed image frames the attitude can be determined.


From the technical and operational point of view, the experiment was a full success, since the subsystems were fulfilling their purpose, and most requirements were met (we had some minor technical issues, though, but nothing that would have affected our or other experiments). The scientific results, however, were kind of poor since our cameras took overexposed images.
(For a detailed evaluation please see the results report)


But luckily EXPLORE, a former REXUS-projects provided us with some real footage they shot during their experiment launch on board of REXUS 11, so we were able to test our horizon sensing algorithm with some real data, see video below:



And of course we captured a lot of stills and videos during the whole campaign, with the rocket launch as highlight!