Lasers Boost Space Communications

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Tim Mousseau, an evolutionary SPACE SCIENCE geneticist at the University of South Caro- lina in Columbia, says that more studies like these are sorely needed. He is heading to Fukushima this week to begin his third Lasers boost space season of field work since the meltdown, tracking birds, insects and other small ani- mals. His team saw die-offs in some insects and declining numbers of some bird popu- communications lations after one season’s work (A. P. Møller et al. Environ. Pollut. 164, 36–39; 2012). He hopes soon to publish three years of Optical systems set to handle planetary science’s big data. observations. For funding, Otaki says he has had to BY DEVIN POWELL more information, allowing orbital broadcasts turn mostly to private foundations. “I to transmit hundreds of megabits of infor- think maybe this is a very touchy issue, efore NASA even existed, science-fic- mation per second. Lasers, which operate at politically,” he says. Mousseau has received tion writer Arthur C. Clarke in 1945 higher frequencies still, can reach gigabits per money from a German biotechnology com- imagined spacecraft that could send second (see ‘Tuned in’). And unlike the radio pany and is now working with researchers Bmessages back to Earth using beams of light. portion of the electromagnetic spectrum, supported by the Finnish government. But After decades of setbacks and dead ends, the which is crowded and carefully apportioned, he says that US government grants are dif- technology to do this is finally coming of age. optical wavelengths are underused and unreg- ficult to secure. The Department of Energy Two spacecraft set for launch in the com- ulated. has largely stopped funding its research ing weeks will carry lasers that allow data to be Efforts to develop laser communication programme in low-dose exposure, and transferred faster than ever before. One, sched- systems struggled for much of the twentieth the National Science Foundation and the uled for take-off on 5 September, is NASA’s century: weak lasers and problematic detec- National Institutes of Health have awarded Lunar Atmosphere and Dust Environment tors derailed project after project. But recent few grants on the topic. “The only people Explorer (LADEE), a mission that will beam advances in optics have begun to change the who seem to be doing any research are video and scientific data from the Moon. The situation. “The technology has matured,” adventurous, opportunistic and independ- other, a European Space Agency (ESA) project says Frank Heine, chief scientist at Tesat- ent,” Mousseau says. “They have some flex- called Alphasat, is due to launch on 25 July, and Spacecom, a company based in Backnang, ibility in what they do and are just doing it will be the first optical satellite to collect large Germany. on their own without official support.” amounts of scientific data from other satellites. In the 1980s, Europe took advantage of Other scientists take issue with the reports “This is a big step forward,” says Hamid improved lasers and optical detectors to begin of ecological harms from Fukushima. They Hemmati, a specialist in optical communica- work on its first laser communication sys- say that Otaki’s research is flawed, because tions at NASA’s Jet Propulsion Laboratory in tem, the Semiconductor Laser Intersatellite wing shape and other butterfly traits vary Pasadena, California. “Europe is going beyond Link Experiment (SILEX). Equipped with the naturally with geography. “This study’s demonstrations for the first time and making system, the ESA satellite Artemis received 50 sensational claims should not be used to operational use of the technology.” megabits of information per second from a scare the local population into the errone- These lasers could provide bigger pipes for French satellite in 2001 and then exchanged ous conclusion that their exposures to these a coming flood of space information. New messages with a Japanese satellite in 2005. The relatively low environmental radiation doses Earth-observation satellites promise to deliver project taught engineers how to stabilize and put them at significant health risk,” Timothy petabytes of data every year. Missions such as point a laser in space. But it was abandoned Jorgensen, a molecular radiation biologist at the Mars Reconnais- after its intended application — a constellation Georgetown University in Washington DC, sance Orbiter (MRO) “Laser of satellites to provide Internet services — was wrote in a comment on Otaki’s 2012 paper. already have con- communication dropped in favour of the network of fibre-optic Mousseau’s report of harms to birds one straints on the vol- becomes more cables now criss-crossing the globe. year after Fukushima has been criticized ume of data they can advantageous Since then, Heine’s team at Tesat-Spacecom for including only one sampling period and send back because the farther out has created a laser terminal for satellite- lacking baseline data. of fluctuations in you go.” to-satellite communication, at a cost to the Richard Wakeford, an epidemiologist at download rates tied German Aerospace Center of €95 million the University of Manchester, UK, thinks to a spacecraft’s varying distance from Earth. (US$124 million). The laser, amplified by that ecological research on the Fukushima “Right now, we’re really far from Earth, so we modern fibre-optic technology, achieves a disaster’s effects will prove as confounding can’t fit as many images in our downlink,” power of watts — compared with the tens of as efforts to detect health effects in humans says Ingrid Daubar, who works on the MRO’s milliwatts reached by SILEX. In 2008, termi- exposed to low doses of radiation. Many HiRISE camera at the University of Arizona in nals mounted on two satellites transferred ecosystems and their species are altered Tucson. Laser data highways could ultimately information at gigabits per second over a few after human evacuations in ways that have allow space agencies to kit their spacecraft with thousand kilometres. nothing to do with radiation, he says. more sophisticated equipment, says John Kel- ESA’s Alphasat will extend the range of this Wayne says post-Fukushima research ler, deputy project scientist for NASA’s Lunar laser terminal to tens of thousands of kilome- needs more support to boost its quality. Reconnaissance Orbiter (LRO). That is not yet tres once it is positioned high in geostationary She and her colleagues are drafting a white possible, he says. “We’re limited by the rate at orbit. Future satellites that sport laser terminals paper to establish better standards for col- which we can download the data.” in lower orbits will be able to beam as much lecting, analysing and sharing data. “We Today’s spacecraft send and receive mes- as 1.8 gigabits per second of information up don’t want disasters to happen so we can sages using radio waves. The frequencies used to Alphasat, which will then relay the data collect more data,” she says. “But as it has are hundreds of times higher than those put to the ground using radio waves. Alphasat’s happened, we should learn from it.” ■ out by music stations on Earth and can cram in geostationary orbit means that it can provide

TUNED IN Interplanetary data transmission rates have shot up 10 orders of magnitude in the past 50 years, thanks in part to higher frequency bands of radio waves. Optical transmissions with lasers promise to extend that pace, to the point at which high-de nition television broadcasts from Jupiter might be possible. 108 HDTV FAST INTERNET 106 SOURCE: NASA/JPL-CALTECH

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Planetary mission data rates (bits per Planetary mission data rates Ka band –6 Optical second), referenced to Earth–Jupiter distance second), referenced 10

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a constant flow of data to its ground station Laser beams, by contrast, keep their focus, — unlike low-Earth-orbit satellites, which allowing them to shuttle the already greater can commuicate with the ground for only an quantities of information they encode over hour or two each day as they race by overhead. longer distances without using the extra “Other satellites will be able to buy time on our power needed by radio transmitters. “Laser laser terminal,” says Philippe Sivac, Alphasat’s communication becomes more advantageous acting project manager. the farther out you go,” says Donald Cornwell, One client will be another ESA mission mission manager for the Lunar Laser Com- due to launch this year: Sentinel-1, the first munication Demonstration project on LADEE of several spacecraft to be sent up for Europe’s at NASA’s Goddard Space Flight Center in new global environmental-monitoring pro- Greenbelt, Maryland. gramme Copernicus. It will beam weather In 1992, the Galileo probe, on its way to data to Alphasat until the end of 2014. At that Jupiter, spotted laser pulses sent more than point, Europe plans to start deploying a net- 6 million kilometres from Earth. A laser on work of dedicated laser-relay satellites that Earth pinged the Mars Global Surveyor in will ultimately handle 6 terabytes of images, 2005. Another struck the MESSENGER mis- surface-temperature measurements and other sion en route to Mercury, which responded data collected every day by a fleet of Sentinel with its own laser pulses. In January this year, spacecraft. the Lunar Reconnaissance Orbiter received But Europe’s space lasers have a significant the first primitive message sent by laser to the drawback. Although they can shuttle infor- Moon — an image of the Mona Lisa that trav- mation between spacecraft, they have trouble elled pixel by pixel in a sort of Morse code. talking to the ground — a task that must still LADEE carries NASA’s first dedicated laser be performed by radio waves. This is because communications system. With a bandwidth of these lasers encode information by slightly 622 megabits per second, more than six times varying the frequency of light in a way analo- what is possible with radio from the distance gous to modulating an FM radio station. A of the Moon, the system can broadcast high- beam modulated in this way is protected from definition television-quality video. But even solar interference but is vulnerable to atmos- though its AM optical system is good at pene- pheric turbulence. trating Earth’s turbulent atmosphere, it will still The laser on NASA’s upcoming LADEE need a backup radio link for cloudy days when mission will communicate directly with Earth the laser is blocked. To minimize this problem, using a different approach that is less suscep- LADEE’s primary ground station is in a largely tible to atmospheric interference. It encodes cloudless desert in New Mexico, with alterna- information AM-style by tweaking the ampli- tive sites in two other sunny spots: California tudes rather than the frequency of a light wave’s and the Canary Islands. ■ SEE EDITORIAL P.254 peaks. NASA hopes that the LADEE demonstration will extend laser communications beyond CORRECTION Earth’s immediate vicinity, to the Moon and The News story ‘Teething troubles at huge other planets. Deep-space missions currently telescope’ (Nature 499, 133–134; 2013) rely on radio transmissions. But radio waves mistakenly gave Natural Resources Canada spread out when they travel long distances, as the source for the graph instead of weakening the signal and reducing the data- National Research Council Canada. transfer rate.