Airbus Defence and Space


STOS, Star Tracker stimulator

"µSTOS is directly mounted on top of sensor baffle (left) and then positioned in front of STR optics, inside the baffle (right)

Star Tracker Optical Stimulator The µSTOS is a test equipment that was developed to operate the whole star tracker chain on ground, either in a stand alone configuration for sensor characterization, or as part of global AOCS closed loop and real time test environment.

Features / technical details

Principle: Using attitude commands, STOSPilot application software, computes sky images in real time (real star constellation from star catalogue or customised pattern) and send them to a specific opto-mechanical assembly involving collimating lens and filters, acting like a dynamic planetarium. Images are visualized by the sensor just like a real sky. High performances and compatibility: The alignment procedure guarantees perfect alignment between frames as well as magnitude offset adjustment. Mechanical interface between STR and STOS can be customized for any STR. Easy to control: Local control through dialog boxes enables to manually define real sky or customized pattern simulation cases. Data files can be used as input in order to make the STOS use pre-computed attitudes and simulate real time testing. An optional real time communication link can be provided to achieve remote control and real time close loop testing. Characteristics

LCOS Microdisplay : DVI interface, 85 Hz refresh rate and 1280 x 1024 pixel resolution
Standard PC (minimum : 2GHz Pentium IV processor is recommended), Windows NT, 2000 or XP

Through Windows dialog boxes or command files (for complex dynamics)


For close loop testing, attitude commands can be sent up to 128 Hz through a specific remote link (Ethernet, VME-PCI,RS232 / 422, USB …).


Star catalogue

Any STR catalogue with instrumental magnitude can be used (up to 15000 stars).

Star magnitude

A range of 4.5 magnitudes (with a typical precision of +/-0.3) is available. It can be adjusted with a global bias obtained with optical densities.

Field of view

Optimized for 25 deg in diameter. Other FOV can be studied.


Better than 0.001 deg.

Star position

Error for individual star positioning on STOS is less than 0.005 deg at 2 sigmas


Up to 8 deg /s. No constraint on acceleration.

Synchro/ Delay

In remote control, the delay between command reception and the corresponding image update is less than two monitor update periods.

Planets&  Bodies

Planets and bodies like satellites or debris can be simulated like additional stars (up to 32) or extended objects (up to 16).


Can be simulated like a white disk or with a specific model for a better rendering.

Residual background

At least 2 magnitudes higher than the highest magnitude in the useful range. Light-proof.

Stray light simulation

Stray light can be simulated with uniform grey levels [0 - 255] or using specific dynamic Earth or Sun models. Use of background movie-like  images is also available.


Solar flares or SAA effects (direct or streak impacts on detectors) are dynamically simulated with up to 8192 events per image

Satellites & debris

Up to 128 satellites or debris with random linear trajectories can be simulated

Operating Conditions


Temperature  0°C to 35°C (32°F to 95°F)
Humidity  5% to 90% (non-condensing)
Cleanness STR optics and baffle are protected. Compatible with use in clean-room.
Life Long life: Up to 50,000 hours of reliable operations for critical
Dimensions & Weight

 < 2 kg (total weight to be mounted on top of baffle) with typical dimensions Æ0.2m, length 0.3m



  • Development and characterisation of new optical sensors (Star trackers but also navigation sensors…)
  • Attitude and Orbit Control System (AOCS) validation (Open and closed loop testing
  • Spacecraft integration : sign tests, functional tests …

Reference customers

ESA (ATV), Airbus Defence and Space (PLEIADES, THEOS, Microsats), Thales Alenia Space (Spacebus), NSPO (ROCSAT)