As the numbers of satellites in orbit continue to rise there is a greater need for effective communication solutions that can handle increasing data volumes. Optical communications may hold the answer, enabling operators to get more data from space to Earth faster and more efficiently.
The drive for optical communication is also due to the crowding of traditional radio options in frequencies such as the S-band and X-band, which have been used for decades for satellite communication.
Space-space and space-ground communications are the primary use cases for optical laser communications (lasercom) and in this article we take a look at how the technology works and share some of the products available on the market today.
In the article below we provide a gentle primer of optical communications systems for satellites discussing their history and giving the advantages and disadvantages that they bring, as a quick guide to understanding the promise of the technology. If you are familiar with the technology and would prefer to skip down to see the product listings, please click here.
Do you know of any optical communication products for small satellites that we’ve missed? Please drop us a note at [email protected] or on Twitter. Alternatively, if you’d like to list your products and services on satsearch, get started here.
Early history
Early demonstrations of optical communications technologies date back to the mid-90s. The Communications Research Laboratory (CRL) in Japan successfully demonstrated the Laser Communication Experiment (LCE) on the Japanese Engineering Test Satellite-VI (ETS-VI) satellite in 1994 with the first purpose-built lasercom satellite for demonstrating space-to-ground laser communications.
The ARTEMIS program, a European-led mission, demonstrated bi-directional laser communication between a geostationary orbit and the European Space Agency (ESA) Optical Ground Station (OGS). This incorporated narrower beam divergences than the LCE mission, which allowed higher data rates and enabled a better understanding of atmospheric impairments, particularly at low zenith angles.
The geostationary satellite-based missions allowed for the use of a fixed ground terminal to conduct repetitive measurement of link parameters over many days and have enabled the improvement of propagation models and design changes of subsequent lasercom missions.
Laser communications on small satellites
Small satellites predominantly operate in Low Earth Orbit (LEO) and offer a low-cost platform for researchers to test technologies such as satellite laser communications. For example, the National Institute of Information and Communications Technology (NICT) in Japan and the German Aerospace Centre (DLR) have used such platforms to successfully demonstrate laser communications using satellites in LEO over the last few years.
Table 1: Recent significant missions incorporating small satellite laser communication terminals
| SOTA | OSIRISv2 | |
|---|---|---|
| Operator | NICT, Japan | DLR, Germany |
| Launch date | May 24, 2014 | June 22, 2016 |
| Satellite | SOCRATES (48 kg) | BIROS (130 kg) |
| Mass | 5.9 kg | 5 kg |
| Size | 18×11×10 cm | 25×20×10 cm |
| Beacon | 1 µm unmodulated | 1560 nm modulated |
| Downlink | 800, 980, 1549 nm | 1545, 1550 nm |
| Modulation | On-Off Keying | On-Off Keying |
| Max. bitrate | 10 Mbit/s | 1 Gbit/s |
Laser communications on CubeSats
As satellites are getting smaller the need to fit in communications systems that will allow the reduced form factor at lower power and with higher data rates has generated significant interest in laser communications for CubeSats.
The first (brave) attempt to demonstrate laser communication on a CubeSat was on-board FITSAT-1, a 1U system developed at the Fukuoka Institute of Technology in Japan. The satellite carried two arrays of high-power light-emitting diodes (LEDs) along with an experimental RF transceiver and was deployed in October 2012 by the robotic arm of the International Space Station (ISS).
FITSAT-1 used a neodymium magnet as a passive attitude control system with a panel containing 50 green 3W LEDs, achieving 200-W pulses and modulated with a 1-kHz Morse-code signal.
A photomultiplier coupled to a 25 cm ground telescope was used to receive the signals on the ground. Interestingly, the flight model of the FITSAT-1 laser communication payload was tested between the beach of the Fukuoka and the rooftop of the eight-story building of the university which were 12 km apart from each other.
In August 2018, The Aerospace Corporation in the US tested a laser communication system during a mission named Optical Communications and Sensor Demonstration (OCSD) with two LEO CubeSats known as AeroCube-7B and Aerocube-7C. The satellites successfully transmitted data at a rate of 100 Mbps.
Today there are various lasercom products available or approaching the marketplace that have built on these early developments, bringing some significant benefits compared to existing solutions.
Advantages of optical communication
Optical communication systems have several advantages over traditional radio equipment including:
- Higher data rates, so more information may be transmitted in less time and using lower power
- Better signal/noise ratio (weather-dependent) due to higher directivity
- Lack of interference
- Smaller antennae
- Lower overall power requirements
- Increased spectrum availability
- Narrow beams are difficult to intercept and jam
- No International Telecommunication Union (ITU) coordination needed
Disadvantages
On the other hand, there are some aspects of optical satellite communications products that can cause issues such as:
- Higher pointing accuracy is needed for satellites
- Potential weather-based disruptions
- Increased mission complexity and risk
- The Sun is a noise source for optical detectors
Commercial optical communications providers
As commercial-off-the-shelf (COTS) componen
