On 24 January 2021 at 16:00 CET, the PIXL-1 small satellite was successfully launched from the US spaceport at Cape Canaveral on board a Falcon 9 launcher from US company SpaceX. The satellite is carrying the world's smallest laser communications terminal. Known as OSIRIS4CubeSat, this terminal enables data transmission up to 100 times faster than conventional radio links and was developed by researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in close collaboration with German telecommunications company Tesat-Spacecom (TESAT), which is based in Backnang, near Stuttgart. The laser terminal provides an important platform for investigating matters of scientific interest. It has been designed for mass production and is marketed by TESAT under the name 'CubeLCT'. This is creating new value chains in Germany, reinforcing the country's profile as a prime location for industry.
Data transmission using lasers can be seen as a 'wireless fibre-optic connection' and will open the way for far more efficient data transfer to and from satellites in the future. It will also enable an array of new applications in the field of communications. At the same time, it paves the way for new options in the fields of satellite navigation and quantum cryptography. With the PIXL-1 mission, the project partners want to demonstrate that optical communications from space to ground can be achieved with even the smallest of satellites. The German Space Operations Center (GSOC) in Oberpfaffenhofen is responsible for operating the satellite.
"By developing OSIRIS4CubeSat, we have prepared the groundwork that will offer new options in terms of data rate for many future missions, while providing DLR with an ideal basis for scientific measurements and the next technological steps for scientific projects," says Christopher Schmidt, Project Manager at the DLR Institute of Communications and Navigation.
A decisive step forward
Until now, laser terminals have been too large to be used on small satellite platforms such as CubeSats. They also required too much power. The launch of PIXL-1 opens up new horizons in satellite communications and expands the potential offered by small satellites. OSIRIS4CubeSat and the CubeLCT product, with dimensions of just ten by ten by three centimetres, fits perfectly onto small satellites but can also be adapted for larger platforms. The systems are optimised for five-year missions in low Earth orbit. The technological advancement has been achieved through end-to-end miniaturisation of the technologies, with the optics, mechanics and electronics closely interlinked for that very purpose. The DLR Institute of Communications and Navigation has brought its findings and experience obtained through around 15 years of research to the project.
"The functionality and miniaturisation that we have achieved with CubeLCT advances small satellites into a new capability class and allows us to assign more complex tasks to satellite constellations," says Christoph Günther, Director of the DLR Institute of Communications and Navigation.
Numerous scientific objectives are to be investigated as part of the PIXL-1 mission. In addition to a basic demonstration of the technologies, the transmission channel itself will be researched in more detail to optimise error-protection mechanisms. These findings will serve as an important basis for the international standardisation of the technology and a further increase in data rates of up to one gigabyte per second on future missions. This is particularly in demand for Earth observation, where ever-increasing quantities of data need to be transmitted.
Small satellites can function individually or in mega-constellations. In the latter case, a large number of satellites work together as part of an overall mission, such as the worldwide distribution of broadband internet connection. One of the next steps is to advance optical communications so that this type of connection between small satellites is possible.
Another special feature of optical communications technologies is that they can be used for the distribution of quantum keys. With this technique, any form of digital communication can be protected against eavesdropping. The DLR Institute of Communications and Navigation is a leader in this area of research and will use this new technology platform in space to further develop quantum key distribution between transmitters and receivers.
Receiving stations – building a network
One major challenge in laser-based communications is the weather, as laser signals cannot be transmitted through clouds. A worldwide network of optical ground stations, mainly situated at locations with little cloud cover, is to be set up to overcome this limitation. DLR is supporting this approach through its pioneering PIXL-1 mission, and will be testing locations and expanding the receiving network over the coming months. The network’s first two ground stations are currently being established at two European locations by the GSOC in collaboration with an industry partner.
Two different radio frequency bands are used for communicating with and controlling the PIXL-1 small satellite. During the initial in-orbit demonstration phase, communications will be conducted in the Ultra-High Frequency (UHF) band, using a new GSOC antenna set up for that purpose. During the mission itself, the satellite will communicate in S-band frequencies, so that the control centre will be able to use its normal ground stations and integrate the satellite into the standard processes as smoothly as possible. During regular operations, GSOC will control the satellite from Oberpfaffenhofen, calibrate the laser terminal and ensure that the data are forwarded to researchers at the Institute of Communications and Navigation.
Industry collaboration with TESAT
DLR and TESAT have been working very closely and successfully together since 2016. Through its Optical Space Infrared Downlink System (OSIRIS) programme, the Institute of Communications and Navigation is developing miniaturised laser communications terminals with compact designs. These can be used for direct optical downlinks from the satellite to Earth. As a client, TESAT has been involved in the development work from the start. The company is a world leader in optical satellite communications and is planning to expand the market for small satellites in the context of these developments. The launch of PIXL-1 marks a major advancement for this technology. After completion of the development phase, TESAT will commence mass production of the compact satellite laser terminal.
"At TESAT, we have a clear vision of our products overcoming borders and bringing people together. We have come one crucial step closer to achieving this with the launch of PIXL-1. The CubeLCT is the result of the highly successful cooperation between the DLR Institute of Communications and Navigation and TESAT," says Marc Steckling, CEO of Tesat-Spacecom.