While in safe-mode, preservation of a spacecraft is the number one priority. Essential AOCS input needs to be provided by high reliable sensors. For this purpose, Spacetech offers a thermo-optical Coarse Earth and Sun Sensor (CESS), available in two versions:

Heritage CESS (HCESS): used in numerous successful LEO space missions e.g. CHAMP, GRACE, TerraSAR-X, TanDEM-X, Paz, Cryosat, SWARM

Advanced CESS (ACESS): Design improvements result in superior sensor performance and extend the range of application (orbit height, satellite accomodations).

HCESS Alone // ACESS Alone

Sensor at a glance:
  • Dimensions: < 100 mm x 50 mm x 40 mm (width x depth x height)
  • Mass of approx 80 (120) g for HCESS (ACESS)
  • Two OSR surfaces (black and mirror) with known solar absorbance α and emittance ε
  • 6 PT1000 thermistors on the OSR backside
  • Low power consumption of 0.1 W for temperature read-out
  • Simple yet robust design

For more detailed information, find our product datasheet.

Working Principle

 A set of six orthogonal accomodated CESS can be used to determine the relative earth and sun vector in the following way:

  1. Perform a continous measurement of the temperatures of all OSRs by probing the Pt1000 thermistors
  2. Extrapolate temperatures to steady-state
  3. Estimate the irradiated infra-red and solar flux, both for black and mirror OSRs via their respective values for α and ε
  4. Calculate Earth and Sun Vectors by combining the six respective vectors and apply appropriate filters.

 04SPADESPoster Description bearb 02







Thermal vacuum test setup

STI CESS Template

ACESS development has been performed in STI thermal vacuum facilities and represenative environmental conditions:

  • Heritage and advanced CESS tested simultaneously in thermal vacuum test chamber
  • (p < 10-5 mbar)
  • 2 kW light source used for sensor illumination and heatable spacecraft I/F (+60 K)
  • Thermal modelling for numerous test cases, such as irradation with variable angle of incidence


Flight data correlation


  • Thermal testing allows to state a mathematical thermal model (TM) for sensors
  • Models are used to correlate CESS to satellite (GRACE) housekeeping data in order to check consistency
  • Excellent agreement of simulation and data
  •  Modeling allows to simulate and analyse the sensor performance in arbitrary orbits



Sensor Performance
  • ACESS outperforms the HCESS by approx. 50 % in peak and mean error for different orbits and sun positions
  • Using CERES data (earth albedo infrared map) with GRACE housekeeping data results in the following earth vector errors




Our Products