Pointing and Tracking systems

When it comes to optical communication between space-based stations fast acquisition and high precision pointing and tracking functions are the keys to success. Based on contracts with the European Space Agency and complemented by in-house developments, RUAG Space has developed state-of-the-art technologies for the exact alignment of the line of sights of optical transmitters and receivers to micro-radian accuracy. This involves both, the mechanisms and optics plus control electronics and software algorithms for optical beam alignment under environmental loads like micro-vibrations and thermal gradients.

Coarse Pointing Assembly (CPA)

The CPA is a very stable, critically damped mechanism based on novel drive technologies. RUAG Space offers two different types of CPA:

  • Single mirror configuration, small FoR
  • Periscopic configuration, hemispheric FoR

Next to the pure mechanism, also signal processing circuits and motion control electronics can be provided as one-stop solution.

Fine Pointing Assembly (FPA)

The FPA is based on a 2-axis tip-tilt beryllium mirror with a wide mechanical angular range of +/- 7 mrads and a signal bandwidth of 800 Hz @ +1/-3 dB, -10 deg. The full mirror diameter is 27 mm, the useful diameter is limited to 15 mm. The actuators are of Lorentz type while the position is sensed by four differential capacitive sensors. The FPA control electronics implement a cascaded feedback scheme with state space motion controllers and output current amplifiers to drive the actuators of the FPA. The FPA flew on Astrium's successful LOLA airborne optical link demonstration to ARTEMIS.

Fibre Nutator Tracking Sensor

The Fibre Nutator Tracking Sensor constitutes in the pointing and tracking chain the ultimate with regard to high bandwidth and efficient signal capture. It is based on the principle of fibre nutation and combines the tracking sensor with the receiver front end in one item. It provides a signal bandwidth of; 5 kHz (-3 dB, 90 deg) and a ultra-fine resolution of 20 nm. The tracking function is achieved by scanning the incoming wave front which leads to an amplitude modulation of the output signal carrier whose phase contains the tracking angle. This information is used by the tracking controller for high bandwidth tracking.