Perseverance Rover Entry Descent and Landing Nightmare
There are three spacecraft that were sent to Mars in 2020 and after a 6 months journey, they are finally arriving at their destination. The first to reach Mars is Hope orbiter which is the first rocket to Mars sent from the United Arab Emirates. It is a satellite orbiter that will observe the weather patterns of Mars from its outer orbit. The second to arrive is the China Mars probe which comprises an orbiter and a lander. Finally, Perseverance, which we will look into in more detail.
What makes Perseverance Rover the most interesting one of the three is the fact that it will be the first of the three to try to land on the surface of Mars which is the most high-risk part of the mission. This will see the spacecraft enter the surface at 7 times the speed of a bullet and autonomously slow down to a gentle landing on the surface in only seven minutes, popularly known as the ‘Seven Minutes of Terror’.
The process will start with the cruise stage separation ten minutes before the spacecraft enters Mars’ atmosphere travelling at 12000MPH. The friction from the atmosphere will reduce this speed while also creating a lot of heat on the heat shield covering the rover to about 1,300 degrees Celsius making it look like a shooting star from the surface of Mars.
While still firing thrusters to steer itself to the right landing target location with a guided entry, the spacecraft will launch a parachute 21.5 Meters in diameter that inflates in half a second reducing the entry speed even further up to 360MPH. At this stage, the spacecraft will drop the heat shield to prevent the heat from transferring to the rover which is comfortably at room temperature at this point.
With onboard cameras at the bottom of the rover, it will take pictures of the ground and compare them to high-resolution images taken from orbit to try to figure out its current location. This is a high-speed image processing technique called Terrain Relative Navigation. In about 2.4 seconds, the rover will have known where it is and how it needs to fly to land at the desired destination.
After knowing where to land, the rover detaches from the backshell and fires up some thrusters to start the powered descent stage. The jetpack-like backpack will steer it away from the backshell and closer to the landing location. The rover can not land using the thrusters because one, it will not provide a stable landing, and two, it will raise a lot of dust covering the rover which might destroy some of the rover’s instruments.
The final stage of EDL is the sky crane maneuver about 20 meters high and 12 seconds before touchdown, which involves the rover being lowered down by three cords. As soon as the rover senses that its wheels have touched the ground, it quickly cuts the cables connecting it to the descent stage. The jetpack flys away to fall at a safe distance and this marks a successful landing and the end of the seven minutes of terror.
With all this autonomously happening, the rover will be sending information back to earth but after landing, Earth will have set so the rover will only be able to communicate with earthlings through overhead orbiters. The orbiters can transfer more data but we will have to wait longer to get all the images, videos and Martian sound(for the first time) back on earth.