Remote Access in Deep Space: How NASA Speeds Interplanetary Communications


On November 26, 2018 at 2:52:59, NASA started again. The agency's InSight probe managed to land on Mars after an entry, descent and landing maneuver dubbed "six and a half minutes of terror". NASA engineers did not know right away if the spacecraft had safely reached the surface because of the current delay (about 8.1 minutes) in communications between Earth and Mars. During this period, InSight could not rely on its more modern and powerful antennas – instead, everything depended on old-fashioned UHF communications (the same method used for a long time, from TV antennas to walkie-talkies in the UK). through Bluetooth devices).

Finally, critical data relating to the state of InSight was transmitted in the form of 401 586 MHz radio waves to two CubeSats, WALL-E and EVE, which relayed them at 8Kbps to D & # 's. 39, huge 70-meter antennas on Earth. The CubeSats had been launched on the same rocket as InSight and they followed the trip to Mars to observe the landing event and immediately return the data. Other orbits of the Mars planet, such as Mars Reconnaissance Orbiter (MRO), were out of place and could not initially establish real-time communications with the LG. This is not to say that all landing coverage was based on two experimental CubeSats (each of a briefcase size), but the MRO would have relayed the landing data from InSight only after an additional delay.

The complete landing of InSight has truly put the whole NASA communication architecture, called the Mars network, to the test. The signal that the InSight lander returned to the relay orbiters was certain to reach Earth, even if one or more of these orbiters were failing. WALL-E and EVE were there to immediately transmit information, and that's what they did. If these CubeSats were not working for any reason, the MRO was ready to respond. Each room functioned as a node in an Internet-like network, which allowed routing of data packets via multiple terminals composed of different types of hardware. At the present time, the most efficient tool is the MRO satellite, which can relay data at a maximum speed of 6 Mbps (a current record for planetary missions). But NASA has had to work with much less communication power in the past – it will also need a lot more in the future.

<img alt = "Just like your local ISP, NASA allows Internet users to check real-time connectivity between the Earth and its various space explorers. "src ="×366.png "width =" 640 "height =" 366 "srcset =" .31-PM-1280×732.png 2x "/>
Enlarge / Like your local ISP, NASA allows Internet users to check real-time connectivity between the Earth and its various space explorers.

The network of deep space

As NASA expands its footprint in space, better space communications systems seem to be gradually extending coverage: the goal was first a low Earth orbit, then a geosynchronous orbit and the Moon, and sooner in the future. distant space. It all began with crude portable radio tracking stations deployed by the US military in Nigeria, Singapore and California to receive telemetry data from Explorer 1, the first artificial satellite that the United States has successfully launched into orbit in 1958. And slowly but surely, this base has evolved into today's advanced communication systems.

Douglas Abraham, Head of Strategic Prediction and Systems at NASA's Interplanetary Network Directorate, today underlines three independently developed space communication networks. The nearby terrestrial network supports spacecraft in low Earth orbit. "It's a collection of antennas, mostly between 9 and 12 meters in. There are some larger ones that are 15 and 18 meters tall," explains Abraham. Then, slightly above the geosynchronous Earth orbit, there are several satellites for telecommunication tracking and data relay (TDRS). "They can look at the low-Earth orbiters and communicate with them, and that information is then relayed to the ground by the TDRS satellites," says Abraham. "This is the satellite traffic and data transmission system, commonly referred to as NASA's space network."

But even TDRS was not enough to communicate with another plane flying beyond the Moon to other planets. "So we had to create a network covering the entire solar system. It's the Deep Space network, "explains Abraham. The Mars network is an extension of the DSN network.

Given its scope and ambitions, the DSN is the most complex of these systems. The DSN consists of a series of very large antennas with a diameter of 34 to 70 meters. Several 34-meter antennas and a 70-meter antenna operate in each of the three DSN sites. One site is located in Goldstone, California, another outside Madrid, Spain and the third outside Canberra, Australia. These facilities are located approximately 120 degrees away around the world to provide 24/7 coverage for all spacecraft beyond the geosynchronous orbit.

The 34-meter antennas are the daily pilots of DSN. They come in two variants: old high efficiency antennas and relatively modern waveguide antennas. The difference is that the waveguide version has five precision radio frequency mirrors that reflect signals along a tube to the control room below the ground, where the electronics that analyze these signals are better protected from all sources of interference. 34-meter antennas working separately or in groups of two or three antennas can close most of the links that NASA must close. But for special occasions where the distance is too great, even for some 34-meter antennas working together, DSN users use their 70 meter monsters.

"They are important in many situations," explains Abraham about larger antennas. The first is when a spaceship is so far away from Earth that it would be impossible to close the link with a smaller satellite dish. "The New Horizons mission, which has moved from Pluto or the Voyager spacecraft beyond the solar system, are good examples, only 70-meter antennas can reach them and send their data back to Earth." Abraham explains.

The 70-meter satellite dishes are also used when a spacecraft can not communicate with its high-gain antenna, either because of a planned critical event, such as an orbit insertion, or because of a serious problem. A 70-meter antenna was used to safely bring Apollo 13 back to Earth, for example. He also received Neil Armstrong's famous message, "It's a small step for a man, a giant step for humanity". Even today, the DSN is the most advanced and sensitive telecommunications system in the world. "But for a number of reasons, it's close to its limits," warns Abraham, "There is not much room to improve the radio frequency technology that the DSN is supporting. of hand. "

Image by NASA Ames

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