Features of laser communication
Extremely high bandwidth and large information throughput available many times greater than RF communication. Modulation of helium-Neon laser (frequency 4.7 x 1014) results in a channel bandwidth of 4700 GHz, which is enough to carry a million simultaneous TV channel.
Small antenna size requires only a small increase in weight and volume of the satellite. This reduces blockage of fields of view of most desirable areas on satellites. Laser satellite communication equipment can provide advantages of 3:1 in mass and 2:1 in power relative to microwave systemsNarrow beam divergence affords interference free and secure operation. The existence of laser beams cannot be detected with spectrum analyzers. Antenna gain made possible by narrow beam, enables small telescope aperture to be used. The 1550nm-wavelength technology has added the advantage of being inherently eye-safe at the power levels used in the free space systems, alleviating the health and safety concerns often raised with using lasers in an open environment where human exposure is possible.Laser technology can meet the needs of a variety of space missions, including intersatellite links, Earth to near-space links, and deep space missions. The vast distances to deep space make data return via conventional radio frequency techniques extremely difficult.
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Two-way laser communication in space has long been a goal for NASA because it would enable data transmission rates that are 10 to 1,000 times higher than traditional radio waves. While lasers and radio transmissions both travel at light-speed, lasers can pack more data. It's similar to moving from a dial-up Internet connection to broadband.
"We've been trying to do this kind of thing for about a decade," said David Smith, a researcher from Goddard Space Flight Center who was involved in the experiment. "We attempted to do it on one of our Mars probe but either we got weathered out or the spacecraft misread some stars and everything closed down."
The Mars Telecommunications Orbiter spacecraft, set to launch in 2010, but cancelled last summer due to budget problems, would have used lasers to transmit data between Earth and Mars at a rate of between 1 to 30 million bits per second, depending on how close the two planets are to each other.
Currently, the maximum data rate between Earth and Mars is about 128,000 bits per second.
Cheers,
Marvin
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