FICHE SED36 A4 - Sodern

SED36
STAR TRACKER
The SED36 is the very high accuracy star
tracker developed for the PLEIADES satellite,
the follow-on to the SPOT family of Earth
observation satellites developed by the
CNES.
The design is derived from the already
flight proven SED26. It uses the same basic
sub-assemblies, but instead of a single box
it is split into three parts with minimum
thermal coupling effects on the optical head.
This specific thermal and mechanical
concept was required to improve performances,
with direct mounting of the Optical
Head on the instrument, thermally isolated
from the electronic box and the baffle.
Ultimate Accuracy
Fully Autonomus
Separated Head
Thanks to this specific thermo-mechanical
design, plus local distortion calibration,
updated star catalogue, and increased
number of tracked stars, the SED36 can
achieve the ultimate attitude low frequency
error of better than 1 arcsec at 3σ end of
life.

ULTIMATE ATTITUDE ACCURACY
Among all the error classes of a Star Tracker, the most penalizing for the
attitude control of the satellite is the Low Frequency Error (LFE) since unlike
Noise Equivalent Angle (NEA) or Bias, it cannot be compensated.
• On SED36, several improvements have been performed:
- An optimized thermo-mechanical design
- A local, more accurate calibration of optical distortion
- An update of the star catalogue
- An increased number of tracked stars
• Attitude accuracy (full performances - 3σ - EOL):
- Cross boresight axes: 1 arcsec LFE – 2.6 arcsec/√Hz NEA
- Boresight axis: 6 arcsec LFE - 17 arcsec/√Hz NEA
OTHER PERFORMANCES
• Attitude Acquisition:
- Autonomous in less than 3 seconds
- With angular rates up to 10°/s
• Attitude tracking:
- Up to 14 stars simultaneously
- Update rate up to 8Hz
• Robustness:
- Operating with Moon and Planets in FoV
- Operating in tracking with Solar flares or in SAA
- Baffles for 30° and 25° Sun Exclusion Angles
ENVIRONMENTAL CARACTERISTICS
•Temperatures:
- Full performances 20°C ± 3°C (STR-O only)
- Operating -20°C to +60°C
- Storage -30°C to +70°C
• Mechanical loads:
- Random 18.4g rms along Z and 10g rms along X/Y
- Shock 1500 SRS @ 2 KHz
MECHANICAL INTERFACES
The SED36 is made of three parts, the Optical Head
(STR-O), the Electronic Box (STR-E) and the Baffle
(STR-B). Distance of up to 2.5 meter between STR-O and
STR-E.
• STR-O: 1.3 Kg, Φ130x110 mm (AlSiC)
• STR-E: 1.5 Kg, 160x130x110 mm 3 (Aluminium)
• STR-B: