Laser communication is the most disruptive solution to improve the telecom capabilities of nanosatellites, as high data rate links (up to some Gbit/s) can be obtained through very light and compact devices which can fit on such small spacecraft. In fact, the narrow beamwidth and the high carrier requency – respectively in the order of few microradians and hundreds of THz – result in very high transmission gain with small apertures (few tenths of millimiters). Radio system with equivalent peformance can be realized with so huge and heavy antennas that cannot be embarked on a nanosatellite bus.
However, the very stringent pointing accuracy demanded by laser communication, combined with the limited performance of the typical attitude control system of nanosatellites, requires the development of a dedicated stabilization and pointing system for the laser. In this context, we propose the realization of a miniature, 2-dof active system based on the parallel platform configuration, to be used as a fine pointing stage for a miniature lasercom terminal for nanosatellite missions. Such device will orient the laser beam with a given, high accuracy while rejecting the vibration disturbances coming from the satellite bus.
LOW COST SPACE NETWORKS
The inherent low cost of nanosatellites could encourage the realization of telecom LEO networks affordable to private users for commercial applications (voice/video calls, monitor of private assets). Optical links could be used even to provide internet access to airliner passengers, as optical communication do not interfere with the avionics.
Lasercom terminals which flew on large satellites (e.g. SILEX, OICETS) were mounted on 2-axis moving gimblas with large rotational range for pointing the laser transmitter/receiver indipendently from the satellite atittude control.
On miniature satellites, this is impractible as the satellite bus does not provide a stable base and moving gimbals can significantly affect the spacecraft attitude control. Our approach is to break-up the coarse pointing task between the ACS of the nanosatellite bus (+/- 5 deg), and a dedicated robotic device based on the parallel platform configuration, with pointing accuracy up to +/- 100 microradians .
A simplified prototype has been developed and exploited for preliminary test activities and technology validation. It consists in a shaker rotary stage, representing the host satellite bus, and a a 1-D stabilization stage; both feature a linear stepper motor and a dedicated controller. The test campaign demonstrated the capability of the system to keep the pointing error of the stabilization stage within the +/- 100 microradians band.