Even as most of modern communication on Earth is moving toward 5G and broadband internet, space communications remain stuck in the 1990s. Satellites, probes and crafts, such as the International Space Station, rely on radio waves. And though radio waves share the electromagnetic spectrum with the same frequencies that make up 5G, they have limited capacity and diffuse over large distances. There is limited radio spectrum, and the signals can be received by unwanted listeners.
Radio is also slow. It takes about 2.5 seconds to send data to the Moon and back to Earth, several minutes from Mars and likely hours from the outer solar system, as Space Flight Insider notes. If humans are to usher in a new era of exploration to the Moon and Mars, beefing up space communication technology on satellites and spacecraft will be essential.
Lasers are the solution. These beams of invisible infrared light are more robust than radio waves and maintain signal strength over vast distances. The wavelengths are also 10,000 times shorter than radio waves, which means laser pulses can pump out more information per second. That could make data transfer rates 10 to 100 times faster, as FiveThirtyEight reports. A handful of national agencies, including NASA, the Japanese Space Agency (JAXA) and the European Space Agency (ESA), are all embarking on projects to put laser communication systems into orbit. The technology will improve data-transfer rates and lay the foundation for future missions to the Moon and beyond.
Mona Lisa on the Moon
Ever since the first U.S. satellite, Explorer 1, was launched into space 61 years ago, radio waves have been the go-to means of communication. But in 2013, NASA scientist Xiaoli Sun and his team used a laser to beam a digital image into space. They sent Leonardo da Vinci’s iconic painting, Mona Lisa, to the Lunar Reconnaissance Orbiter (LRO), which circles the Moon. To do it, they first divided the image into a grid that was 152 pixels side by 200 pixels tall. Each pixel was converted into a shade of gray that was represented by a number between zero and 4,095. One by one, the pixels were transmitted to the LRO with a laser pulse sent in one of 4,096 possible time slots. An instrument on the orbiter pieced together the image based on the arrival times of the laser pulses from Earth.
Although the data rate was only 300 bits, or 0.0003 megabits, per second, the experiment set the stage for the agency’s Laser Communications Relay Demonstration (LCRD), which will use lasers to beam data to and from a satellite. Technologies currently in development will be tested on two upcoming NASA missions. The first is called ILLUMA-T, which stands for the Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal. Scheduled for 2021, ILLUMA-T will be a fully operational end-to-end laser communications system that will be tested onboard the International Space Station. Another mission, called Optical to Orion (O2O), will use an optical modem to send high-definition video from NASA’s first crewed flight of the Orion spacecraft, scheduled for 2023, as Space Flight Insider reports.
In tandem, NASA scientists will also be developing a suite of laser-based instruments called the Deep Space Optical Communications package. These instruments are planned for the upcoming Psyche mission, a low-cost probe that will launch by 2023 and travel to the asteroid known as 16 Psyche, found between Mars and Jupiter. The spacecraft will analyze the rock body using an onboard imager, magnetometer and gamma-ray spectrometer, and it will transmit the data back to Earth using a laser-based communication system. In a NASA press statement, Lindy Elkins-Tanton, the principal investigator for the Psyche mission, said “the technology is mind-blowing and it brings out all my inner geek. Who doesn’t want to communicate using lasers, and multiply the amount of data we can send back and forth?”
Space Data Highway
Although NASA was the first to beam a digital image into space, the ESA was the first to establish an optical link in space. In 2001, the satellite Artemis used a laser signal to connect with the Earth observation craft, SPOT 4. The agency soon began setting two-way distance records for laser communication and, by 2008, had transmitted image data 28,000 miles between two satellites at a speed of 600 megabits per second, according to the ESA.
These early milestones paved the way for the European Data Relay System (EDRS), a laser communication infrastructure designed to deliver high bandwidth capability for Earth observation satellites as well as other spacecraft, such as the International Space Station. Dubbed the “Space Data Highway,” this infrastructure is the world’s first optical network in the sky based on laser technology. It’s made of two geostationary spacecrafts — with a third on the way — that orbit Earth at an altitude of about 22,000 miles. Their orbits match the orbit of the Earth, so they’re always fixed over the same location down below. That location has a network of ground stations that can transmit data at a rate of 1.8 Gbit/s — about three times faster than a radio connection, according to Wired.
The high-speed, high-capacity links are designed to serve spacecraft. Satellites that monitor Earth, for instance, orbit the planet lower than those in geostationary orbit and are never over the same location for very long. They typically relay the data they’ve collected when they’re in a direct line of sight with a ground antenna, which occurs about once every 100 minutes. “That can be a problem when you need information immediately, for example, when trying to provide aid during flooding or wild fires, or help ships navigating through ice sheets,” Michael Witting, EDRS project manager said in an ESA press briefing.
If these crafts transmit their data to the EDRS, the information can be sent immediately to researchers on Earth. Since the ESA’s relay system entered service in 2016, it has achieved more than 20,000 laser connections and downloaded more than 1 petabyte of data. The EDRS will soon start transmitting data from the International Space Station, and it’s available to be used by crewed missions to the Moon and beyond.
Tune in Tokyo
Compact discs seem as old school today as land lines and CRT televisions. But the laser technology inside hasn’t died. It’s going to space. Sony, which released the world’s first CD player in 1982, has partnered with JAXA to establish a long-distance laser communication system in space. The system will eventually support real-time communication between satellites, as well as between them and ground stations. JAXA’s and Sony’s interest lies in supporting future constellations of satellites that will beam broadband internet from Earth’s orbit to the ground. Unimpeded by terrestrial obstacles, such as mountains or oceans, these orbiting spacecraft will be able to send internet everywhere.
“Specifically, it can be used as a means of communication between the Earth and the International Space Station, the Moon, and Mars. There is a wide range of potential applications, such as communication with the Moon rovers,” Koichi Wakata, a JAXA vice president, said in a press statement.
As a first step toward creating the system, the partners sent a microwave-sized package in September 2019 to the International Space Station. Called SOLISS, for Small Optical Link for International Space Station, the device not only has optical communication capabilities but a 360-degree spherical camera to observe the laser tests, too. Any photos taken can be sent to the ground using SOLISS’s laser communication. JAXA and Sony should be releasing news of their demonstration in early 2020.
Putting lasers into orbit will increase the amount and speed of data that can be sent between satellites, as well as between them and the Earth. Although the technology is just beginning to emerge as a potential rival to radio waves, it could be years before it’s making its mark. But traveling vast distances along trajectories as straight as an arrow, lasers could one day deliver high-definition video from the Moon, Mars and planets as far away as Jupiter and Saturn.