A laser that can beam data from Mars to Earth at 10 times the rate of current radio links will be sent to the Red Planet in 2009, say NASA scientists. The laser will be the first test of such technology in deep space and may usher in a new era of space communication.
鈥淚t is the next big thing,鈥� says Stephen Townes, deputy manager of the Mars Laser Communication Demonstration at NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California. 鈥淭here is the promise we will be able to get high data returns with lower power and lower mass than the typical systems out there.鈥�
NASA鈥檚 Mars Odyssey spacecraft currently boasts the highest data transmission rate at 128,000 bits per second. The new laser will beam back between one million and 30 million bits per second, depending on the distance between Mars and Earth.
Advertisement
That leap in capacity is due to the different wavelengths of light carrying the data. The laser will use infrared light with a wavelength of 1.06 microns, which is thousands of times shorter than radio waves. Since all light travels at the same speed through space, shorter wavelengths carry more information in the same time.
That is crucial for the increasing number of ambitious space missions, says Joss Bland-Hawthorn, head of instrument science at the Anglo-Australian Observatory in Sydney.
鈥淎stronomers are losing vast amounts of data from recent satellite missions to Mars,鈥� he told 快猫短视频. 鈥淲e collect a hundred times more than we can transmit back.鈥�
Cloudy skies
But so-called optical communication has certain drawbacks compared with time-tested methods. Unlike radio waves, clouds can block the laser鈥檚 photons. And laser beams are narrower than the distended radio wave cones that wash over the entire Earth, making precise pointing of the laser important.
The new Mars laser project will use two different sites to detect the laser on Earth 鈥� the 5-metre Hale Telescope in southern California and an array of four 0.8-metre telescopes whose location has yet to be determined. If the weather is overcast at one location, astronomers can try the next. Future projects are likely to have a dozen telescopes spaced around the world.
The laser will be transmitted from a 0.3-metre telescope on a spacecraft orbiting Mars, but the beam will spread to a width of a few hundred kilometres by the time it reaches Earth. That makes picking up the laser鈥檚 relatively weak signal 鈥渧ery difficult,鈥� says Townes, adding that the team is developing photon detectors that are orders of magnitude more sensitive than those now used.
Live footage
Despite the signal鈥檚 weak strength, 鈥渙ptical astronomers are quite alarmed about the prospect of this being generalised鈥�, says Tomas Gergely, electromagnetic spectrum manager at the National Science Foundation in Arlington, Virginia, US.
A few satellites orbiting Earth are already testing the technology to talk to each other or to send data to ground-based telescopes. A glut of such nearby lasers could bounce off the foil shrouds covering satellites and create light pollution, explains Gergely.
Bland-Hawthorn agrees that space-based lasers can cause unwanted light but adds that astronomers on Earth already cause similar problems by using laser dots for telescope calibration. He says that one day space agencies could send live video footage 鈥� which requires data rates of billions of bits per second 鈥� from Jupiter to Earth.
The new Mars laser, allocated $270 million from NASA, will undergo a design review in early 2005 and will fly on NASA鈥檚 Mars Telecommunications Orbiter in 2009. That spacecraft, which will also have traditional radio links, will be the first mission designed mainly for communication between other space missions.