Airbus Defence and Space


STOS, Star Tracker stimulator

A high performance miniaturized Star Tracker Optical Stimulator

Application fields

  • Development and/ or characterisation of new optical sensors.
  • Attitude Control System validation (Open and Closed loop testing).
  • Spacecraft integration: functional tests, sign tests …


Starting from attitude commands, a calculator is used to builds sky images (star constellations from star catalogue or customised pattern). These images are sent to an opto-mechanical assembly (OMA) which includes a micro-display component and a collimating optical system. The OMA is mounted in front of the sensor optical head and acts like a dynamic planetarium.

One product, three main components

  • The software: STOSPilot is running on a PC calculator to build the images in real time using current attitude and a star catalogue.


  • The opto-mechanical assembly (OMA) produces the collimated images thanks to the miniaturized “image display unit” and the necessary optics.


  • The Interface mounting device (IMD) enables OMA safe mounting on top of sensor baffle. Only the part in contact with the baffle may vary from one sensor to another.


The STOS main application software is a very powerful and user-friendly application which enables simulating stars in a very realistic way. It includes simulation of main disturbances the sensor can find in orbit: Sun blinding, Moon stray light, planets, extended objects masking stars, satellites or debris crossing the field of view, protons impacts on detectors and even dynamic stray light or background predefined images.





LCOS technology with standard DVI /HDMI video input interface. Up to 225Hz monochrome image refresh rate with 1280 x 1024 pixel resolution


PC / Software

STOSPilot application is running under Windows XP or W7 on a standard PC. Distance between PC and OMA can be as long as 20m (65 ft) or even more if required.



Through Windows dialog boxes or command files (for complex dynamics)
For close loop testing, attitude commands can be sent with a refresh rate up to 128 Hz through a standard Ethernet link.


Star catalogue

Any sensor catalogue containing star position and instrumental magnitude can be used.

Star magnitudes

Useful range is as at least 4.5 magnitudes large. In this range, maximum typical error is usually lower than 0.2 mag. Offset is adjusted by software (brightest star is usually set around magnitude1.5 so that the faintest star is about magnitude 6.0).

Field of view

FOV is optimized for 25 deg in diameter which is compatible with most STR in the market.


Residual bias is lower than 0.001 deg after fine alignment is performed.

Star position

Error in star positioning is less than 0.005 deg for more than 90% of stars.


Motions up to 18 deg /s can be simulated. No constraint on acceleration.

Synchro /Delay

In remote control mode, the typical delay between command reception and the corresponding image update is around 60 ms. Thanks to internal attitude buffering and temporal interpolation, when commands are periodic there is no time jitter.

Planets & bodies

Planets, satellites or debris can be simulated like additional stars (up to 32) or extended objects (up to 16). International Space Station (ISS) masking stars is simulated like an extended object.


For best rendering including masking area and stray light, a specific model is provided.

Background Stray light

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


Impact of protons in image degradation (direct or streak impacts) is dynamically simulated with up to 8192 events per image.

Satellites & debris

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



-10°C to 35°C (14°F to 95°F) in ambient pressure conditions (1 bar)


5% to 90% (non-condensing)


sensor optics and baffle are protected. Compatible with use in clean-room.


Compatible with use in vacuum when OMA chassis is thermally controlled in the range [+5°C, +30°C] (from 41°F to 86°F)



<2 kg (total weight to be mounted on top of baffle) with typical dimensions diameter 0.2m, length 0.35m
Up to 20m distance or even more between calculator and the opto-mechanical assembly


With the µSTOS, “end to end” indoor star tracker testing has become reality

Simulations are very realistic:

The µSTOS package includes a very powerful software with high level of image rendering.

The µSTOS is compatible with most star trackers:

The same stimulator can be reused to stimulate and possibly compare various star sensors : only the interface mounting device and possibly the OMA baffle length are specific to a given sensor.

The µSTOS is easy to install and operate:

Its light weight enables direct and safe mounting on top of sensor baffle. µSTOS can be used during all integration steps, from “flat-sat” until late operations on launch pad.

The µSTOS is easy to align:

No mechanical alignment procedure is required. Fine alignment is completely done by software using a simple star alignment pattern or real sky constellation. Whenever sensor telemetry is available, the STOSPilot integrated self-alignment function makes alignment very fast and precise.

The µSTOS is easy to control:

Use of dialog boxes or local command file is user friendly. Thanks to a simple protocol and free source sample codes (STOSClient application), developing a user remote control application has also become very easy.

Useful additional tools

STOSPilot includes post-processing capabilities:

Attitudes and other commands are recorded in such a manner that the file containing recorded data can be used as a command file to replay the test sequence or to perform fine analysis the simulation image by image.

STOSCmdTool enables controlling multiple headed sensors:

This application accepts spacecraft attitudes and uses them to control multiple stimulators accordingly with the geometrical configuration of optical heads on the spacecraft platform.



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Platform Data HandlingAOCS