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Scientists push for laser links in space

31 Jul 2002

Laser telemetry holds the key to transmitting increasing amounts of data back to Earth, argue scientists in the 26 July issue of Science.

Switching from radio links to laser telemetry could solve an impending communication bottleneck in space, say scientists in Australia and the US. (Science 297 523)

Satellites and space stations will soon be gathering more data than they can transmit back to the Earth. If current trends continue, within five years only 0.3% of all collected data could be sent home.

"Our opinion is that in the long term, optical communications will be more efficient than radio telemetry," said Andrew McGrath from the Anglo-Australian Observatory. "To deploy a deep space optical communications link on a 15-year timescale, the enabling technologies must be pushed for today."

The root of the problem for radio-telemetry devices is bandwidth. Transmitting over more frequencies, that is increasing the bandwidth, boosts the amount of information a signal can carry. But as the carrier frequency increases, atmospheric absorption comes into play.

With next generation spacecraft capable of collecting gigabits of information every second, the range of radio waves that penetrate the atmosphere is not enough to carry all the information home.

Lasers could be the answer. According to McGrath, more research is required to decide on ideal wavelengths and technologies. "We could take advantage of established technologies at 1300 and 1550 nm," he says. "But shorter wavelengths offer high efficiencies in the long term."

In November 2001, the European Space Agency (ESA) established the world's first optical data link between two orbiting satellites using a laser beam as a signal carrier. This test had a data rate of 50 megabytes per second (Mbps).

The researchers claim that data transfer rates can be increased by several orders of magnitude without basic changes in principle. But this will require increased signal power, a suitable transmitter and adequate onboard memory. Well-separated mountaintop receiving stations around the globe will also be required. Six stations will guarantee cloud free operation says McGrath.

The estimated total cost is likely to be comparable to one medium-sized space mission. This comes in between USD 300 million and USD 400 million.

"Work toward a near-infrared telemetry system carries little risk and will pay for itself in the efficiency with which data can be gathered and transmitted," the team conclude in their paper. "However, progress will only come about with the allocation of sufficient resources by NASA and ESA and the attention of the scientific community."

Hawthorn and colleagues hope to win AUS 10 million to fund their research over the next five years.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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