Scientists demonstrate first quantum communication with microsatellite
A team of researchers from the National Institute of Information and Communications Technology (NICT) in Tokyo, Japan, has recently reported that they succeeded in demonstrating the first quantum communication between a microsatellite and a ground station. The signal was sent by a quantum communication transmitter on board the SOCRATES satellite.
The instrument, known as the Small Optical TrAnsponder, or SOTA, is the world’s smallest and lightest quantum communication transmitter. It has a mass of roughly 13.22 pounds (6 kilograms) and its dimensions are 7 by 4.5 by 10.6 inches (17.8 by 11.4 by 26.8 centimeters). This shoebox-sized tool is capable of transmitting a laser signal to the ground at a rate of 10 million bits per second from an altitude of about 370 miles (600 kilometers) while orbiting at a speed of approximately 15,660 mph (25,200 km/h).
SOTA was launched into space as part of the Space Optical Communications Research Advanced TEchnology Satellite (SOCRATES) microsatellite in May 2014. The mission’s main goal was to test a standard microsatellite bus technology applicable to missions of various purposes. SOTA has successfully completed its objectives by demonstrating its quantum communication capabilities.
“We are proud to say that the SOTA mission fulfilled all the success levels as foreseen and more than doubled its originally designed working life of one year,” Alberto Carrasco-Casado of NICT’s Space Communications Laboratory told Astrowatch.net.
According to Carrasco-Casado, four different success levels were established for the SOTA instrument: minimum success, success, full success, and extra success. The minimum success level required a basic check-up of all the lasercom subsystems, while the success level consisted of acquiring the laser beams transmitted from SOTA to the ground station by using different wavelengths and performing basic communication tests.
In order to achieve the full success level, a real data transmission from SOTA to the ground station by using error correcting codes to deal with variable atmospheric conditions was needed. When it comes to the most desired extra success level, SOTA needed to successfully conduct lasercom experiments with different ground stations around the world and the quantum-limited communication experiment that was recently described in the Nature Photonics journal.
“The main achievement of SOTA was to be the first lasercom terminal in a microsatellite. Being such a tiny lasercom terminal, we could test several technologies and perform different experiments,” Carrasco-Casado noted.
The scientists used three wavelengths for communications: 800-nm, 980-nm, and 1,550-nm bands – each of them through a different aperture (small lenses to transmit the 800-nm and 980-nm band lasers, and a 5-cm Cassegrain telescope to transmit the 1,550-nm laser). Also, they used two different pointing technologies: a coarse-pointing gimbal for the 800-nm and 980-nm band lasers, and an additional fine-pointing system for the 1,550-nm, the latter being able to deliver a higher power to the ground.
The researchers were able to gather a great deal of atmospheric-propagation data using these technologies, which is critical to characterize the atmospheric channel for future missions. They managed to replicate the experiments in different ground stations around the world (Canada, Germany, and France), thereby achieving promising results.
For instance, regarding the French ground station, the French Space Agency (CNES) group demonstrated an adaptive-optic system to compensate the atmospheric perturbations suffered by the SOTA signals. Finally, they were able to carry out the first quantum-limited communication experiment from space.
“All these technologies are key for the future development of space optical communications and quantum communications,” Carrasco-Casado said.
He underlined that space lasercom will play a more and more important role in satellite communications in the future, and all the technologies that SOTA demonstrated are key to these future developments. For example, the SpaceX constellation plans to use over 4,000 satellites, and those satellites will use laser communications to communicate with each other. Moreover, many other constellations and communication networks are being designed at the moment where free-space lasercom plays a key role, with private companies like Google or Facebook investing a great deal of effort in their deployment.
“If Quantum Key Distribution (QKD) and lasercom systems can be miniaturized following the heritage of SOTA, this technology could be spread massively, enabling a truly secure global communication network. Prior to the commercialization of this technology, research organizations like NICT have to demonstrate its feasibility, which was the goal of the SOTA mission. In line of this endeavor, NICT is also actively collaborating in the standardization of lasercom technologies through the Consultative Committee for Space Data Systems (CCSDS), and the data obtained with SOTA is another important result of this mission,” Carrasco-Casado concluded.
Currently, the Space Communications Laboratory and the Quantum ICT Advanced Development Center in NICT are working together toward future missions that will leverage the expertise and knowledge acquired with the SOCRATES/SOTA mission in technologies related to space laser communications, quantum communications, and physical-layer cryptography.
Tomasz Nowakowski is the owner of Astro Watch, one of the premier astronomy and science-related blogs on the internet. Nowakowski reached out to SpaceFlight Insider in an effort to have the two space-related websites collaborate. Nowakowski’s generous offer was gratefully received with the two organizations now working to better relay important developments as they pertain to space exploration.