HYDRA Multiple Heads Star Tracker based on Active Pixel Sensor and the gyrometer assistance option

Paper number

IAC-06-C1.2.10

Author

Mr. Ludovic Blarre, EADS-Sodern, France

Coauthor

Mr. Nicolas Perrimon, EADS-Sodern, France

Coauthor

Mr. Laurent Majewski, EADS-Sodern, France

Year

2006

Abstract

A new generation of APS based Star Sensors with improved capabilities, greater flexibility, reduced size and mass and a high potential of cost reductions for future AOCS design is currently developed by Sodern.
The HYDRA Star Sensor design is based on two physically independent units, the Optical Head (OH) and the Electronic Unit (EU). The baseline of the HYDRA concept is an assembly of three OH’s and one redounded EU, but other configurations are possible since the EU can drive only one or up to five different OH’s. Each OH performs low level signal processing inside a FPGA in order to reduce the amount of EU data processing. The useful processed video signal is then transferred to the EU, at high data rates, for higher level computation like Star pattern identification, Star tracking and Attitude data computation, with update rates up to 30 Hz on the three heads.
Attitude tracking of HYDRA takes advantage of both high sampling rate (30Hz) and multiple head configuration to overtake single optical head star sensors capabilities. Single head architecture leads to more noisy orientation around boresight axis compared to cross boresight axes, while a three Optical Heads configuration gives better and true equalized 3-axis performances. Fused multiple head concept also extends star tracker field of view providing robustness to occultation of one or two Optical Heads from external bodies like Sun and Earth. The high sampling rate ensures robustness to rapid accelerations, and also acceleration changes that would be experienced in a highly agile mission or during thrusters firing for spacecraft de-spin.
This product is proposed with gyrometer assistance option, using either external on-board gyrometer equipments data or using internal low cost MEM’s vibrating gyrometer proposed in option with HYDRA product line. The use of gyrometers still enlarges the operational range of HYDRA. Improving star tracking in even harsher kinematics environment, it leads to extreme robustness to SET while offering better attitude accuracy by means of Kalman based hybridization algorithms.
As a conclusion, the SODERN approach for this new product is to propose a single attitude sensor for the AOCS which allows a large simplification of the system, by a reduction in the number of sensor required for the system to manage and the transfer of almost all Sensor related FDIR and data processing functions into the Sensor itself. The first ground demonstrator of this product is already realized and will be tested during first semester 2006, a complete EQM will be realized and tested in 2006.

Abstract document

IAC-06-C1.2.10.pdf

Manuscript document

IAC-06-C1.2.10.pdf (🔒 authorized access only).

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