ESA GNC Conference Papers Repository

Sodern’s HYDRA multi-head star tracker has achieved TRL-9 after being launched successfully aboard the French Spot-6 Earth observation satellite on September 9th 2012. HYDRA is the multiple head CMOS Active Pixel Sensor (APS) star tracker developed by Sodern under contract to the French Space Agency CNES and the European Space Agency . HYDRA is providing continuously for more than one year and without loss of tracking, a blended solution used in Satellite GNC loop. Analysis of Spot-6 in flight data has demonstrated that simulated performances are consistent with prediction and, on several major aspects, they are even better than simulation results; subarcsecond accuracy has been confirmed after Final In Orbit Validation. HYDRA is available in several configurations: up to four Optical Heads (OH) and one or two Electronic Units (EU) for redundancy, with cross-strapping for reliability enhancement. In order to address wider type of mission, two new HYDRA star tracker versions are now available. HYDRA-TC is designed to address Telecom market with a fully redundant Electronic Unit integrated into a single box and operating two Optical Heads. This is equivalent to a two conventional star sensors assembly, but with major advantages in terms of thermal interface, power consumption, robustness and accuracy. Re-use of generic HYDRA building blocks is very high, the main adaptations are limited to the Electronic Unit: new power supply, internal cross-strapping all together repackaged inside a single mechanical structure. HYDRA-M is an affordable, low consumption, low size solution for small satellites. It is derived from HYDRA from which it keeps the Optical Head design, the supplies and processing functions but without Thermo Electric Cooler. The number of Optical Heads is also limited to two. The HYDRA-M EU is smaller and lighter. It can be used alone or in redundancy with or without OH cross-coupling. The HYDRA-M OH is intended for use on LEO missions with regulated base plate temperature at up to 10 year life time, or shorter missions with no restriction on the temperature upper limit. Thanks to the re-use of HYDRA processing unit and software, the performance of both HYDRA-TC and HYDRA-M is identical to HYDRA flying on Spot-6.