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Telecoms and frequencies used for the exploration of the planet Mars.

Telecoms and frequencies used for the exploration of the planet Mars.

1-Telecoms used around the planet Mars

The distance between the Earth and the planet Mars varies over time and depends on the position of the two planets in relation to the sun. The distance which separates the Earth from Mars is the smallest when the Earth is positioned between Mars and the Sun. In this specific case, the distance is the smallest and only 3 minutes and 7 seconds are needed for a telecom signal sent by the DSN earth station (1) to reach Mars. But when Earth and Mars are furthest apart, it takes 20 minutes and 57 seconds to transmit the same radio signal. In any case, it is impossible in the current state of telecom technology to communicate between Earth and Mars in real time. In addition to these constraints, engineers from NASA and the other countries involved are required to choose the period outside of the time span when Earth and Mars are in conjunction. That is, in the situation where the Sun produces a lot of radio interference, making radio communications virtually impossible between Earth and Mars. Rovers (2), which are mobile robots whose objective is to carry out various missions on Mars, communicate with the various satellites (probes) installed around Mars but they can also communicate in certain cases directly with DSN earth stations.

The Rovers establish radio communications links to the closest orbital probes orbiting around Mars, for example using the Mars Odyssey or Mars Global Surveyor as a relay, known as Orbiters (3). Indeed, generally it is these Orbiters which transmit the data to the Earth when it is in the field of their antennas. In turn, the orbital probes can also relay messages transmitted by the DSN to the attention of the Rovers. The advantages of using orbital probes are primarily related to the fact that the Orbiters are much closer to the Rovers than the antennas of the DSN. The communication of Rovers with Orbiters, i.e. space probes, is very useful because these probes fly only 400 km above the surface of Mars. With these probes orbiting around Mars, among other things, Rovers can save energy because communicating through space probes is not the same thing as when Rovers communicate directly with DSN stations on Earth. According to NASA expert Nacer Chahat when, in rare instances Rovers communicate with Earth, they do so through all three antenna systems: a low gain antenna (LGA), an ultra-high frequency (UHF) antenna, and a high gain antenna (HGA). As for DSN earth stations on Earth; they communicate with space probes orbiting around Mars using the S, X and K bands as the following.

 The S band which is used by NASA in various applications in particular to ensure communications among DSNs and Orbiters and rovers at 2.2 Ghz frequencies.

The X band: The X band is also used in the space sector, where its very long range in space is used in particular by NASA for telecoms in the 8.4 Ghz band.

The K-band: NASA uses it in this case in the 32 Ghz band.

Communications between Rovers on Mars are made in X-band via UHF antennas. Rovers communicate with orbiters and also with DSN earth stations thanks to UHF X-band antennas which are short range antennas used at low power.

2- Artificial satellites around Mars

 Orbiters or artificial satellites around the planet Mars, which serve as relays for telecommunications with the modules placed on the ground of Mars and on earth with the DSN, are currently around ten as it could be seen in the table below:

In the years to come, NASA is planning a new telecommunication system based on lasers, which is very different from the one currently in use and based on radio communication. With this the laser technology, the travel time of a communication between a Mars probe and the DSN on Earth can be up to 20 minutes. This delay cannot be reduced with radiocommunications currently in use. To reduce these delays, NASA and the Massachusetts Institute of Technology (MIT) are working on a laser-based system that is said to be 10 times faster than transmission by radio waves. This new laser-based communication system is also capable of transmitting up to 30 million bits per second between the two planets Earth and Mars. If this new system is operationally successful, NASA plans to use it on all of its space communications systems.

3-The liberalization of telecommunications around the planet Mars 

As it has done for travel to the ISS, NASA plans to privatize the telecommunications used around the planet Mars. The space agency (NASA) has already started the process for the liberalization of telecoms around Mars. Time is running out because NASA does not plan any Orbiter by 2025.

 (1) DSN: The Deep Space Network is a telecom system with deep space, made up of three earth stations equipped with parabolic antennas owned by NASA. This system is used for communications with probes installed on the planet Mars.

(2) The Rovers: On Mars, NASA installs so-called Rovers devices which are mobile robots with the objective of carrying out various missions on Mars. Perseverance is one of the Rovers that landed on Mars in 2020. On February 18, 2021, the Perseverance rover landed in Jezero crater on Mars. It will study the composition of rocks, the subsoil and the climate. Each Rover weighs around 200 kg and travels on six wheels using solar electric power. It is equipped with cameras used for navigation and several scientific instruments. Rovers communicate with the various satellites (probes) installed around Mars but they can also communicate in some cases directly with DSN earth stations.

(3) The Orbiter: is a space probe orbiting the planet Mars. The orbit is equipped with a telecommunication system that should allow it to transfer very large volumes of data to Earth and act as a relay for the data collected by the Rovers. The other main purpose of the Orbiter is to map the surface of Mars. The large orbiter (more than 2 tons) which has to fulfill this objective of the HIRISE telescope, allows to obtain images with a great resolution.

(*) Richard Rayan, telecom engineer, working with US companies close to NASA.

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