Last August, Masahide Sasaki and his team instructed a satellite to shoot laser beams at a suburb of Tokyo. No, not like that. The laser beam, made of infrared light, was invisible to the human eye. By the time it had traveled through hundreds of miles of outer space and atmosphere, the light was harmless: It had spread out like a spotlight, about as wide as 10 soccer fields. Some of that light made its way into the end of a telescope, where it bounced off mirrors and flew through lenses and filters onto a photon-measuring detector.
Someday, Sasaki hopes, that light could be more than invisible wavelengths hitting a telescope—it could be encoded with information. Today, the radio waves beamed in satellite communications have limited bandwidth, which means they can’t transmit a lot of data at once. But if you can encode a message in infrared photons, you can transmit a million times more data per second, says Sasaki, a physicist at the National Institute of Information and Communications Technology in Japan.
For years, space scientists have proposed this kind of laser-beaming sat, which could make it possible to communicate with unmanned space rovers on faraway planets faster than radio waves allow. But laser light will die out as it travels 55 million miles to Mars—only a few photons might actually reach a receiver on a rover. So scientists first need to be able to read encoded information from a single quantum of light.
Capturing and reading individual photons from a satellite is a tough experiment that took Sasaki’s group seven years to pull off—and by then, someone else had already done it. Physicists in China published in Science last month that they’d managed an even more difficult version of the experiment, where their satellite beamed two photons to two different cities at the same time. But the Japanese group’s claim to fame, published in Nature Photonics, is that they did their experiment in a tiny satellite known as a microsatellite—a cube that weighs about 100 pounds, somewhere between the size of a microwave and a refrigerator. “The microsatellite weighs less than one-tenth of the Chinese satellite,” Sasaki says.
That weight difference also means it’s a lot cheaper to launch: you can launch a 100-pound satellite for about 2 million dollars, as opposed to hundreds of millions for larger satellites. That price point is appealing to a lot of companies. “Many companies that are not specialists in space technology can enter this new field,” Sasaki says.
Sasaki’s group is working with a company in Japan that wants to launch a network of small sats. It wants to investigate laser communication as a technique for sending messages within its network, as well as a fringey encryption technique known as quantum cryptography to secure those messages. Sasaki won’t name the company, but it’s definitely not the only game in town: US company Planet launched 88 small satellites in February, though its focus is imaging, not communications. Japanese company Axelspace has also launched a few, with a grand plan of a network of 50. Even Canon has a 110-pounder up there right now, carrying photography system based on one of its DSLR cameras. In 10 years, Sasaki expects 4,000 of these tiny satellites will be in low Earth orbit, many of which might need secure communication technology.
All these companies are interested in launching small satellites because they’re cheap—and now that tech is finally small enough to fit on them (thanks, Moore’s law!) there’s not much holding them back. “You can actually start to do significant things in small satellites that you could only do before in a large satellite,” says Todd Harrison, a space security expert at the Center for Strategic and International Studies.
The US military might, for example, be able to use a laser-beaming sat to communicate with drones, Harrison says. Military drones take lots of high-resolution photographs and need fast, secure data transmission. So you could launch a dedicated microsatellite for downloading and delivering drone data. Laser communication, unlike radio waves beamed from conventional satellites, delivers a targeted beam, which means it’s best used in a one-on-one setting.
These small satellites could also change military satellite networks, which consist of a handful of conventional large satellites. “We’re heavily dependent on each individual satellite,” says Harrison. “To make [the network] more resilient, instead of building a small number of large satellites, you could build a large number of small satellites.” Last week, The New York Times reported that the US government was planning to launch a fleet of small satellites to watch for North Korean missile tests.
Still, Sasaki’s communications tech is far from deployment. To send a message fast, they have to be able to detect as many photons as quickly as possible, and their group could only detect about one in every hundred million photons sent from the satellite. “This time, we decided to widen the laser beam to make the experiment more feasible,” Sasaki says. “But it’s kind of an embarrassing specification.” Right now, they can’t do their experiment in the daytime because the sunlight completely drowns out their tiny signal, even with filters. They’re planning to shrink the size of the laser beam so that more of it goes in the telescope. Then maybe they can send that good morning text to Mars.
