published by Jules Bercy
About seven months after taking off, NASA’s last vehicle, Perseverance, will still have to survive « seven minutes of terror, » as the ultra-perilous maneuver preceding its landing on Mars is dubbed.
The chosen location, Jezero Crater, is the most dangerous landing site ever attempted. In seven minutes, the rover must go from a speed of 20,000 km / h to zero.
The landing will take place at 8:55 p.m. GMT Thursday (3:55 p.m. Washington).
-130km: entry into the atmosphere-
Ten minutes before entering the Martian atmosphere, the vessel separated from the cruise stage which supplied it with fuel during the trip.
It is then only composed of a rear shield, a heat shield at the front, and, caught between the two, the descent stage, connected to the rover itself.
At about 130km altitude, it enters the atmosphere at a speed of 20,000km / h, causing friction raising the temperature to 1,300 ° C. The heat shield protects the rover from this infernal heat.
-11km: opening of the parachute-
But the atmosphere is not enough to slow the ship enough, which is still going at 1,500 km / h.
At about 11km altitude, at an opportune moment calculated according to the distance remaining to the landing place, a huge supersonic parachute 21 meters in diameter, located in the rear shield, is deployed.
This slows down the ship to about 300 km / h.
-9km: heat shield released-
20 seconds after opening the parachute, the heat shield is released: the rover it was protecting is exposed for the first time to the Martian atmosphere.
A whole new technology, called “Terrain Relative Navigation” (TRN), comes into play: the images recorded live by the cameras of the vessel are compared to maps recorded in its system, where the dangerous zones to be avoided are pre-defined. Taking these data into account, the ship decides on the final landing place.
-2km: retro-propelled phase-
At an altitude of around 2km, the rear shield – and its parachute – are dropped.
The rover is no longer attached to the descent stage, equipped with eight motors pointed downwards, which light up to finish slowing it down. After performing a maneuver to get away from the parachute, the rover ended up descending vertically, right above its landing site.
-20m: separation of the rover-
At about 20m from the ground, it reached a speed of 2.7km / h, slower than that at which a man walks. The rover then descends along the cables thanks to a system of pulleys, during a final fifteen seconds (stage called « skycrane »).
The vehicle deploys its wheels at this time. When the latter feel the ground, the lines are cut and the descent stage makes a final push to crash as far as possible.
Because of the transmission delay between Earth and Mars, when the landing will be confirmed by NASA, it will actually have taken place several minutes earlier.
Source: Orange with NASA