Today, NASA will try to land Perseverance Mars Rover on the Red Planed. The success rate is 40% – more than half of the missions that tried failed. Why is it so difficult to land on Mars?
To be more accurate, NASA has an excellent success rate with 8 out of 9 successful landings. The overall rate drops as Russia (and former Soviet Union) and ESA (European Space Agency) have 8 and 2 failed attempts. The United States is the only country which has successfully sent a spacecraft to the surface of Mars.
Watch the video animation, that we’ll describe below: Entry, Descent and Landing. The whole process takes 7 minutes – “seven minutes of terror” before the spacecraft safely reaches the surface of the Red Planet.
From the top of the atmosphere down to the surface it takes 7 minutes. But it takes 11 minutes for the signal to reach Earth. So when we are warned that we’ve touched the top of the atmosphere, the vehicle has already landed …or crashed. Seven minutes to go from above 20,000 km/h to zero, “slamming on the brakes” in perfect sequence, perfect choreography, perfect timing – and the computer has to do it all by itself.
The process of landing on Mars. Credit: BBC
Small trajectory corrections during the seventh month journey in space, have ensured that the spacecraft enters Mars atmosphere at exactly the right spot at exactly the right angle, which is around 12 degrees. Mars atmosphere is 100 times thinner than Earth’s. Mars has just enough atmosphere that you have to deal with, otherwise it will destroy the spacecraft, but it’s not thick enough to adequate slow it down.
Due to atmospheric friction the speed is reduced within two minutes from 20,000 km/h to 1,600 km/h, while the external temperature reaches 1,300 degrees Celsius. And all this time small thrusters fires on the backshell adjusting the angle and direction of lift, in a “guided entry” technique so the spacecraft stays on the path to its downrange target.
Around 11 km above the ground a large parachute is deployed and the heat shield separates and drops away. The rover is exposed to the atmosphere of Mars for the first time, and its landing radar bounces signals of the surface to figure out its altitude, while new Terrain-Relative Navigation technology uses a special camera to quickly identify features on the surface, compares these to an onboard map, and determine exactly where it’s heading.
In the thin Martian atmosphere, the parachute is only able to slow the vehicle to about 320 kilometers per hour. Perseverance must now cut itself free of the parachute, around 2 km above the ground, and ride the rest of the way down using rockets.
As the rover slows to its final descent speed of about 2.7 kilometers per hour, it initiates the “skycrane” maneuver. With about 12 seconds before touchdown, at about 20 meters above the surface, the descent stage lowers the rover on a set of cables 6.4 meters long.
Meanwhile, the rover unstows its mobility system, locking its legs and wheels into landing position.
As soon as the rover senses that its wheels have touched the ground, it quickly cuts the cables connecting it to the descent stage. This frees the descent stage to fly off to make its own uncontrolled landing on the surface, a safe distance away from Perseverance.
Landing Site of Perseverance Mars rover – Inside the Jezero crater, in front of an ancient river delta deposit. The rover will later travel up into the valley that cuts through the crater rim. The Perseverance Mars rover will land near this delta to search for evidence of past life and collect samples that could be returned to Earth by a later mission. Deltas form when flowing water is slowed down by encountering standing water, causing sediment to be deposited. On Earth, deltas are excellent at concentrating and preserving evidence of life, making this delta on Mars an appealing target. The image is composed of multiple precisely aligned images from the Context Camera on the Mars Reconnaissance Orbiter, and has a resolution of 6 meters per pixel. The large crater on the delta has a diameter of roughly 1km. Credit: NASA/MSSS/USGS
SAVE THE DATE: February 18, 2021 — “Seven Minutes of Terror” the Entry, Descent, and Landing for Perseverance will be broadcast live as the rover arrives at Mars.