Radio in Space

Written by Helena Furgoni

10th July 2019

State-of-the-art

Today (and for about 60 years), the most common way to communicate with a spacecraft is to use radio waves, as they are the most efficient for long-distance communications.

Let us take the example of the ISS (“International Space Station”). Located at an altitude of approximately 36,000 km, in a geostationary orbit, relay satellites provide communication with the space station. This orbit actually allows satellites to stabilize on a fixed line above the Earth’s surface.

We can differentiate three types of radio communication in space: communication between astronauts, communication between astronauts and the Earth, and finally communication between the ship itself and the Earth. The latter requires the most advanced technology, being a crucial factor for the mission’s success.

As for broadcasting to the public, the images we receive from the station may have been broadcast live, they still have a (slight) delay of about 30 seconds. Delayed due to the processing and broadcasting of the signal. This signal, once transmitted, is actually processed via tracking and data relay satellites (more commonly referred to as “TDRS”, for “Tracking & Data Relay Satellite”), and then routed (among the other destinations) directly to Houston.

IoT Constellations

There are today dozens of satellite constellations (several satellites operating synchronously in a synchronized way), including positioning systems, telecommunications services and remote sensing. These constellations all are owned by major players in the aerospace industry, and more recently, political powers, while China plans to launch 72 nanosatellites dedicated to IoT within 3 years, in the same way as Russia and Europe. . However, after the deployment on the ground of LoRa, Sigfox or even the most advanced cellular technologies, operators are looking to the stars. Several companies are now considering launching their own nanosatellites.

Among these operators are Objenious and Sigfox, which in 2018 signed a partnership agreement with Eutelsat to take advantage of the nanosatellites already launched by the latter, and to develop its own new network called “0G”. Objenious, on the other hand, intends to create a hybrid network combining terrestrial and satellite networks.

Be aware that the idea is not to create a new IoT protocol, but to make existing protocols compatible with spatial frequency bands. Objenious does not plan to put aside the development of its LoRa module, and is determined to have, ultimately, only one module that supports several technologies. 

Ambitious, isn’t it? By this, operators intend to cover the entire territory, and notably the areas not served by the current solutions. Among these areas, there is a large part of the maritime territory, for which deploying a satellite network would be less expensive than installing antennas. . If we add to this objective the advantageous taxation associated with spatial exploitation, the entry of operators into this 21st century space race seems to be one of the major trends of the years to come.

But how far will we go?

Have you ever heard of the Voyager program? It is a space program developed by NASA to explore the most remote planets (such as Saturn, or Jupiter). Voyager 1 is one of the two probes sent into space in 1977. It left the solar system in 2012. Even today, and over 20 billion kilometers from Earth, the probe is still able to communicate certain information with us. So how is that possible? The communication system is enabled by a parabolic antenna with a diameter of over 3.7m, which allows radio waves to be transmitted and received from the Earth.

Today, the probe only transmits a very small amount of information, which takes more than 20 hours to reach Earth.

The optical solution

Last year, the European Space Agency announced the deployment of a telecommunications satellite to become the main relay between low orbits and the Earth. Until then, these satellites in low orbit (below 36,000 kilometers from the Earth’s surface) had to be over a relay point on Earth to communicate. This new satellite would retrieve this information and send it itself to ground relay points, more easily accessible from its high geostationary orbit.

While communications between space and Earth are usually via radio waves, the innovative character of the project is the use of a laser, allowing a much higher throughput than the technology used until then (10 to 100 times faster), and a lower energy consumption. But NASA is not to be left out, and wishes to deploy a new network by 2020 by installing a photonic modem (allowing the use of an optical solution) on existing satellites and the ISS. NASA would then benefit from a smaller and less expensive solution.

Optical communications thus have a bright future ahead of them, because in addition to allowing a dialogue between space objects and the Earth, they also help to advance scientific research in several fields (especially meteorology), and an immediacy still impossible today. NASA has even announced the possibility of sending videos from the surface of other planets!

 

The end of radio waves?

However, the radio waves have not said their last word. They still offer many advantages, such as better resistance to climatic conditions. Indeed, light beams are currently not reliable enough in snow or rainy weather and can be disturbed by a single cloud (not to mention the atmospheric conditions of other planets!). Furthermore, this technology is only relevant when the communications require a high throughput.

And installation is expensive! All the ground infrastructure has to be designed, as the lasers have a totally different technology than radio, which is based on NASA’s “Deep Space Network” (an international antenna network). So, in order to be able to extend the use of optical communication, there is no choice but to build new stations in areas where the weather is good. In other words, there is still a long way to go.

Did you know ?

Space Hackers

From the 1940s the American army wanted to take advantage of the ionized trails left by meteorites when they entered the atmosphere, to perform long-distance communications. These ionized trails have the ability to bounce waves.

It should be pointed out that space is not only the playground of the world’ great forces! From 1953, space hackers, those passionate about radio communication, became interested in this topic. Most communications are possible when stations “make an appointment” to transmit and receive waves. But since it is almost impossible for them to define whether the meteor track is in the appropriate location for radio communication, the same messages are usually sent continuously until the receiver station confirms receipt of the same message… By also sending this information continuously. However, protocols have been established to regulate these transmissions.

By using the ionized trails of the meteors, space hackers were able to propagate radio messages without having to wait for the receiving stations to be prepared in advance. By voice or Morse code, countless messages were exchanged until the 2000s, when computer programs replaced these methods, which were considered archaic, with ever more sophisticated transmission systems.

Photo by Adam Riser on Unsplash