Laser, dedicated protocol and material: the future of space telecoms

Telecommunications play a crucial role in space exploration. Dependant upon technologies designed to work in extreme environments, they will soon be based on an interplanetary communication protocol designed to cover astronomical distances and adapted to very different conditions from those on Earth. The International Space Station (ISS) may currently be using a network of telecommunications satellites, but in a few years’ time it is a true 4G network that should see the light of day on the Moon.

The role of space telecommunications is to establish contact between astronauts and mission control centres, as well as to retrieve data from the scientific research carried out in space or that gathered by the various space vehicles (equipped with measuring instruments, cameras, etc.). With human presence set to become permanent and more intense, it is also about providing crews with mainstream functionalities: streaming of high-definition videos of space, communicating with loved ones, and using social networks to share their everyday lives in zero gravity.

In 2010, the International Space Station (ISS) crew was provided with a direct personal access to the internet; Timothy Creamer sent the first ever tweet from the ISS. In 2013, millions of internet users enjoyed Canadian astronaut Chris Hadfield’s version of the song Space Oddity, recorded on board the ISS.

The ISS communicates with Earth via radiofrequency, relying on a constellation of satellites placed in geosynchronous orbit (meaning they move in the same direction as the Earth), called “Tracking and Data Relay Satellite” (TDRS), and antennas on the ground in the United States, in New Mexico and Guam, an island in the Pacific Ocean. Europe, Russia, and China also have systems fulfilling the same function, respectively named “European Data Relay System” (EDRS), Loutch, and Tianlian. Modernisation of the equipment and software in the space station and the ground stations has enabled the American agency to gradually increase the amount of data that can be exchanged, reaching a rate of data sent and received of 600 megabits per second in 2019, a rate that is higher than that provided by optical fibre in most homes.

From radio waves to infrared lasers

The space projects that are currently underway and those planned concern the low Earth orbit in which the ISS is situated (408 Km), as well as areas a thousand times (the Moon) and even hundreds of thousands of times (Mars) further away. These missions generate and gather volumes of data that are also much larger. Such factors are leading to increasing capacity requirements for communications both with and within space, which today are mainly based on radio waves.

Space agencies are currently experimenting with laser communications, which should increase bandwidth ten to one hundredfold, all the while reducing the size and weight of communication tools as well as the electrical power needed for them to run. In 2014, NASA’s Opals (Optical Payload for Lasercomm Science) mission proved the feasibility of data exchange between space vehicles and earth stations via optical communication systems.

The next NASA demonstrator, called the “Laser Communications Relay Demonstration” (LCRD), should enable testing of these systems’ capacities for use cases similar to those of the TDRS system. First of all, it must “train” by relaying data between two stations on the ground, situated in California and Hawaii. As of June 2021, on board an experimental satellite of the US Air Force placed in orbit by the Atlas V 551 launch system, it is to relay data between space missions and Earth. The first planned operational use consists in transmitting data received via Illuma-T to a station on the ground. Illuma-T is an optical terminal hosted on the ISS that receives high resolution scientific data collected as part of experiments and by the instruments on board the laboratory.

A protocol dedicated to space telecommunications

Since 1998, Vint Cerf, co-founder of the TCP/IP protocol, and NASA have been working on an “interplanetary internet” project that aims to define a new protocol suite adapted to the space environment, enabling data exchange between different regions of the solar system.

In effect, the internet protocol used on Earth is not quite adapted to the conditions encountered in space. Firstly, astronomical distances make latencies inevitable (up to 24 minutes for Mars). What’s more, celestial bodies are not always aligned. Several other phenomena, such as solar radiation or the rotation of planets, can potentially deteriorate transmission quality.

Vint Cerf and his team have chosen to work on a DTN network, which means “Delay/Disruption-Tolerant Networking”. At the heart of this delay/disruption-tolerant network is the “Bundle Protocol”, which is based on packet switching that makes it possible to bundle data in order deliver it from source to destination by a “store-and-forward” mechanism.

With this technique, data is sent to a relay station, or “node”, where it is stored and forwarded later to the final destination (or to another node). A data packet travelling from Earth to Jupiter might, for example, go through a relay on Mars. Once on Mars, if the two planets are not aligned, the data is stored until its transmission is possible.

4G on the Moon

“Reliable, resilient and high-capacity communications networks will be key to supporting sustainable human presence on the lunar surface,” said Marcus Weldon, Chief Technology Officer at Nokia and Nokia Bell Labs President, in a press release in October 2020. The Finnish telecoms manufacturer thus announced that it had been selected by NASA to develop and deploy a 4G/LTE mobile network on the surface of the Moon by the end of 2022.

The network imagined includes an LTE base station equipped with an EPC (Evolved Packet Core) network, LTE terminals (“user equipment”), RF antennas, and high-reliability operations and maintenance (O&M) control software. The solution, which on the whole is quite similar to terrestrial networks, must nevertheless meet very stringent size, weight, and power constraints for it to be delivered by the lunar lander developed by American company Intuitive Machines. It has been designed to resist both take-off and Moon landing phases as well as to function in the extreme conditions of space. The Moon is subject to huge temperature variations as well as moonquakes.

Once on the Moon, the network has to self-configure in order to provide the communication capacities needed to carry out a certain number of essential activities such as the use of control-command systems, real-time navigation and telemetry, remote control of the lunar rovers and the deployment of sensors, as well as high-resolution video streaming. In the future, it could evolve towards 5G.

What about on Earth?

Technologies developed for space lead to terrestrial applications. Throughout its history, the ISS has been a place of experimentation for various communication technologies that are used notably for satellite internet. Thus, DTN could be deployed on Earth in places where connection is intermittent due to a difficult environment.

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