Optical Satellite Communications | Seminar Topic
Optical Satellite Communications
Satellite cross links generally require narrower bandwidths
for increased power concentration. We can increase the power concentration by
increasing the cross link frequency with the same size antenna. But the source
technology and the modulation hardware required at these higher frequency bands
are still in the development stage.
Use of optical frequencies will help to overcome this
problem with the availability of feasible light sources and the existence of
efficient optical modulation communications links with optical beams are
presently being given serious considerations in inter-satellite links.
And
establishing an optical cross link requires first the initial acquisition and
cracking of the beacon by the transmitting satellite followed by a pointing of
the LASER beam after which data can be modulated and transmitted.
The European Space Agency (ESA) has programmed underway to
place Satellites carrying optical terminals in GEO orbit within the next
decade. The first is the ARTEMIS technology demonstration satellite which
carries both microwave and SILEX (Semiconductor Laser Intro satellite Link
Experiment) optical inter orbit communications terminal. SILEX employs direct detection
and GaAIAs diode laser technology;
the optical antenna is a 25cm diameter reflecting telescope.
The SILEX GEO terminal is capable of receiving data modulated on to an incoming
laser beam at a bit rate of 50 Mbps and is equipped with a high power beacon
for initial link acquisition together with a low divergence (and un-modulated)
beam which is tracked by the communicating partner. ARTEMIS will be followed by
the operational European data relay system (EDRS) which is planned to have data
relay Satellites (DRS). These will also carry SILEX optical data relay
terminals.
