The Perseverance is the fifth robot that NASA sent to Mars after Sojourner, Spirit, Opportunity and Curiosity. Curiosity, which landed in August 2012, and Perseverance, which did so during the current month of February 2021, are the only ones that are currently active. All NASA rovers have sent photos to Earth, and their communications are really complex. So how do these robots manage to send images of Mars to Earth?
All previous rovers have sent critical information back to Earth, including spectacular photographs . The Perseverance, being the most modern, has the most advanced photography system of all rovers, with 19 cameras. Among them we find the Navcams, which the robot uses to drive and position the tools, and which have a resolution of 20 megapixels (5120 x 3840 pixels), occupying up to more than ten MB. To send all the information and images, the Perseverance has three antennas.
Three antennas with different speeds and properties
The first one is a UHF antenna that operates at around 400 MHz . This antenna sends the signal to one of the five orbiters that revolve around Mars. There is hardly any delay between the orbiter and the rover because they are very close to each other. However, between Earth and Mars it is where there is more delay. Depending on the position of the planets, sending radio frequency signals between Mars and Earth takes between 5 and 20 minutes. The sending speed is around 2 Mbps between the rover and the orbiter.
The second is a high gain antenna that operates in the X band . This antenna is motorized, and it can send information directly to Earth without having to move the robot’s body. The X band that it uses operates between 7 and 8 GHz , and through it the information is sent directly to the Deep Space Network. This network is made up of several groups of antennas located in Madrid, California and Canberra, so that there is always an antenna accessible at all times, being 120 degrees apart between each one. The sending speed is between 0.16 and 0.5 Kbps for antennas of 34 meters in diameter, and between 0.8 and 3 Kbps for antennas of 70 meters in diameter.
Finally, we have a third antenna that also operates in the X band, but with a lower gain . This antenna operates in all directions regardless of where it is oriented, being an ideal antenna for long distances . Thanks to this, it is more reliable, but its speed is much slower. This speed is 0.01 Kbps for antennas of 34 meters in diameter, and 0.03 Kbps for those of 70 meters.
Elon Musk wants to also cover Mars with satellites
As we can see, the main way to send the files to Earth is to use the orbiters , and these in turn send the information to Earth. Currently, the so-called Mars Relay Network is made up of five orbiters: three from NASA (Mars Reconnaissance Orbiter, Mars Odyssey and MAVEN) and two from ESA (ExoMars Trace Gas Orbiter (TGO) and Mars Express). These orbiters are not geostationary, which implies that the time in which the rover can communicate with them is quite limited, and hence the sending of photos and videos is not very fast. In turn, they cannot always be sending information back to Earth.
In the future, it is to be expected that transfer speeds will increase, since Elon Musk wants to create with SpaceX a satellite network similar to Starlink , but on Mars. Thanks to this, communications will have a greater flow and can be done 24 hours a day (terrestrial), although the delay will continue to be more than 5 minutes due to the distance that separates both planets.
