22 Dec 2006
Astrium, the French optical satellite communications specialist, has demonstrated a record-breaking laser transmission between aircraft and a satellite.
Artemis, the European Space Agency's Advanced Relay and Technology Mission Satellite, has successfully relayed laser-based communications from an aircraft in early December.
These airborne laser links, established over a distance of almost 40,000 km during two flights at altitudes of 6000 m and 10 000 m, represent a world first. Typically the aircraft was travelling at around 500 kmh whilst transmitting 50 Mbit/s of data to the geostationary Artemis satellite orbiting at approximately 36,000 km above the Earth's surface.
"The primary achievement of the experiment has been the clear demonstration of the feasibility of an optical link between an airborne carrier and a geostationary satellite," said Vincent Cazaubiel, Lola's project manager.
"Applications could eventually include real time transmission of high resolution images from unmanned aircraft (UAVs) in remote locations for military, search and rescue, maritime, geological or agricultural purposes."
The relay was set up through six two-way optical links between a Mystère 20 aircraft equipped with the airborne laser transceiver Lola (Liaison Optique Laser Aéroportée) and the Silex laser link payload on board Artemis: a feat equivalent to targeting a golf ball over the distance between Paris and Brussels.
The tests were carried out by Astrium SAS (France), the prime constructor for both Lola and Silex, as part of the airborne laser optical link programme conducted by the DGA (French Ministry of Defence's procurement agency) from its Flight Test Centre at Istres, in the south of France. The ESA ground station of Redu, Belgium managed the Artemis Silex payload operations.
The laser communication system has been developed by EADS Astrium in Toulouse. The EADS team has benefited from the experience it gained on the Silex program in which two space laser terminals were constructed for the Artemis and Spot-4 satellites (see below).
Lola's laser transmitter technology uses Lumics' fiber laser diodes transmitting at 0.8 µm. PerkinElmer avalanche photodiodes are used on the receiver side. The laser signal is delivered with a total power of 300 mW.
So what is the innovation by EADS Astrium?
"Considering the relative speeds and distances of the plane and the satellite, the optical communication require the laser beam to be directed with a pointing accuracy below one micro-radian," Cazaubial told optics.org.
"The main challenge for the Lola program is to maintain such a pointing accuracy despite the high dynamic perturbations induced by the aircraft. This dynamic environment is 10 times more severe than that of satellite. Another significant achievement has been to establish and maintain the optical link despite the atmosphere around the aircraft. Optical propagation is disturbed by the high altitude turbulences and the air flow around the airplane."
"This new world first between a satellite and an aircraft is another demonstration of what can be achieved in Europe thanks to the ESA ARTES technology programme."
Optical technology has several advantages for data relay applications, including the capability to provide high data rates with low mass, low power terminals, combined with secure, interference-free communications. Earth observation can truly benefit from this new way of transmitting data around the planet.
• On a daily basis Artemis is also relaying data in the Ka-band from Envisat, the ESA earth observation satellite, providing, since 2002, a comprehensive view of the Earth's oceans, land, atmosphere and ice caps.
In November 2001, Artemis established a laser link with the French Earth Observation satellite Spot 4: imaging data was sent by Spot-4 using a laser beam as signal carrier to Artemis and from there by radio waves to the ground. This unprecedented link-up between satellites in space was done in the framework of the Silex development, an innovative payload which provides a laser beam as a data signal carrier.
Since November 2005, Artemis has been relaying optical signals from Kirari, the Japanese Optical Intersatellite Communications Engineering Test Satellite. This first ever two-way optical communication illustrated the value of this technology for the development of future Earth observation systems.