Laser beams have been used for space communication systems since their inception in 1960. Scientists believed that laser had the potential to transfer data at very high speeds, but also needed specific advancements in systems engineering and component performance, particularly for space-compatible hardware. Developments in data formatting, component technology and system architecture over the last couple of years have made laser communication systems in space a viable and attractive option for inter-satellite link applications. The speed and amount of data laser communications can transfer is several times greater than radio frequency systems.
Features of Laser Communication Systems
Digital data are entered into electronic data systems which modulate the transmitting laser beam. Indirect or direct modulation techniques are used depending on the type of laser. The beam produced goes through an optical system and directed into a channel. The optical system shapes and directs the laser beam into a projected path along signal processing, and detector electronics.
Laser space communication systems connect wirelessly throughout the atmosphere. They operate similar to fiber optics except they are wireless and their beams are transmitted across open space. A high-powered laser diode or LED generates the energy needed for signal transmission. These systems work in the infrared area of a spectrum at wavelengths between 770 and 920nm. To enable communication, two beams; one for transmitting and one for receiving data are used.
Laser space communication systems follow three stages: tracking, communication and acquisition. Tracking is normally the easiest stage to employ and acquisition the most difficult. Communication largely depends on bandwidth, a higher bandwidth relates to increased difficulty. What makes acquisition difficult is the size of its laser beams. Beams are smaller than the region of uncertainty and it becomes difficult for satellites to locate. Everything in space communications moves to some level of uncertainty, and signal searches cannot go on for long otherwise the reference signal will be lost.
Acquisition can be made easier by operating several laser beams at high power and low cycle turns. This is because low pulse rates are required for acquisition than for communications and tracking. High power pulses easily affect the receiver threshold, keeping the false alarm rate at minimum levels. A low cycle transmitter provides high power but requires less power, making it the ideal basis for acquisition.
The Future of Space Communication Systems
Big companies like NASA use laser space communication systems, and currently steps are being taken towards developing high speed data transfer of space. More like the “internet of space,” when complete it will enable data transfer speeds 10 to 200 times faster than they do currently. The future of space communication is bright.