The Mobile Asteroid Surface Scout (MASCOT) is a small landing package build by the German Aerospace Center (DLR) jointly with the French National Center for Space Studies (CNES). MASCOT is flying aboard the Japanese space probe Hayabusa-II, built by the Japan Aerospace Exploration Agency (JAXA). The probe has been launched on December 3rd, 2014 for a five year sample return mission to the Near-Earth Asteroid Ryugu (1999 JU3). The lander is equipped with four science instruments which will take detailed close-up pictures and make a variety of in-situ measurements. MASCOT has a cubic shape, roughly 29 x 27.5 x 20 cm, and weighs about 10 kg. An internal mechanism with an eccentric tappet can be used to reorient MASCOT if needed and relocate to a different site to change and increase its investigation area.
After arrival and characterization of the asteroid, MASCOT will be dropped from the Hayabusa-II mothership and will land passively on the asteroid surface. Before starting science measurements, MASCOT must lie on the correct side.
The attitude determination system consists of two types of sensors: solar cell-based Sun sensors on each side of MASCOT as well as five optical proximity sensors (OPS). The latter consists of a LED and a photodiode which can detect the reflected LED light when MASCOT is in proximity to the surface.
A histogram filter is used for attitude determination and multi-sensor data fusion. It is a Bayesian filter used to estimate states which can be divided in a finite number of possible values. This is useful for MASCOT, since all that is needed is an estimation of the side on which it is lying.
The GNC systems department is responsible for this attitude determination system. This includes concept design, sensor selection and procurement, algorithm development, simulation, software requirements, testing on software level as well as Hardware-in- the-Loop and mission support.