VECTRONIC Aerospace offers with the VST-41M a high performance 3-axis star tracker for small satellite applications with the technical capabilities and radiation tolerance suitable for LEO, GEO and even for interplanetary missions. The sensor has been successfully used in several small satellite missions with outstanding in-orbit performance.
The star tracker consists of two main elements: (1) The optical head with the high quality lens system (Leica) and the baffle in front of it. (2) The star tracker processing electronics with the on-board star catalogue.
The VST-41M performs direct and autonomous measurement of the spacecraft attitude in the body fixed star tracker reference frame relative to the inertially fixed celestial reference system.
Core element of the sensor’s processing electronics is a 512 x 512 pixel rad-hard CMOS sensor, especially developed for space applications, which transforms star images detected through the lens into electrical information. After the A/D conversion the CPU analyses the incoming data through a chain of several algorithms, which eliminate fixed pattern noise, objects that are to bright like the Moon or planets and then determine star positions using a barycentric algorithm.
With a focal length of 50 mm the sensor’s FOV is around 14°x14° which guarantees at least 10 visible stars independent of the current attitude. After the first acquisition, which takes typically 800 ms, the sensor, operating with an update rate of 4 Hz, calculates the attitude with a 2σ accuracy of better than 18 arcsec for each individual star frame.
The probability of attitude acquisition at spacecraft angular rates lower than 0.3 deg/sec is better than 99.7%. The attitude information is provided together with other status telemetry in the form of quaternions and Euler angles. The communication interface comprises two independent asynchronous SCI’s with a baud rate up to 1 Mbit.