27-01-2016, 08:50 PM
Abstract
Lasers have been considered for space
communications since their realization in 1960.
Specific advancements were needed in
component performance and system engineering
particularly for space qualified hardware.
Advances in system architecture, data formatting
and component technology over the past three
decades have made laser communications in
space not only viable but also an attractive
approach into inter satellite link applications.
Information transfer is driving the requirements
to higher data rates, laser cross -link technology
explosions, global development activity,
increased hardware, and design maturity. Most
important in space laser communications has
been the development of a reliable, high power,
single mode laser diode as a directly modulable
laser source. This technology advance offers the
space laser communication system designer the
flexibility to design very lightweight, high
bandwidth, low-cost communication payloads for
satellites whose launch costs are a very strong
function of launch weigh.
This feature substantially reduces blockage of
fields of view of most desirable areas on
satellites. The smaller antennas with diameter
typically less than 30 centimeters create less
momentum disturbance to any sensitive satellite
sensors. Fewer on board consumables are
required over the long lifetime because there are
fewer disturbances to the satellite compared with
heavier and larger RF systems. The narrow beam
divergence affords interference free and secure
operation.
Background
Until recently, the United States government was
funding the development of an operational space
laser cross-link system employing solid-state
laser technology. The NASA is developing
technology and studying the applicability of space
laser communication to NASA's tracking and
data relay network both as cross-link and for
user relay links. NASA's Jet Propulsion
Laboratory is studying the development of large
space and ground-base receiving stations and
payload designs for optical data transfer from
interplanetary spacecraft. Space laser
communication is beginning to be accepted as a
viable and reliable means of transferring data
between satellites. Presently, ongoing hardware
development efforts include ESA's Space satellite
Link Experiment (SILEX) and the Japanese's
Laser Communication Experiment (LCE).
The United States development programs ended
with the termination of both the production of the
laser cross-link subsystem and the FEWS
satellite program. Satellite use from space must
be regulated and shared on a worldwide basis.
For this reason, frequencies to be used by the
satellite are established by a world body known
as the International Telecommunications Union
(ITU) with broadcast regulations controlled by a
subgroup known as World Administrative Radio
Conference (WARC). An international consultative
technical committee (CCIR) provides specific
recommendations on satellite frequencies under
consideration by WARC.
The basic objective is to allocate particular
frequency bands for different types of satellite
services, and also to provide international
regulations in the areas of maximum radiation's
level from space, co-ordination with terrestrial
systems and the use of specific satellite locations
in a given orbit. Within these allotments and
regulations an individual country can make its
own specific frequency selections based on
intended uses and desired satellite services.
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