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This illustration shows the events that occur in the final minutes of the nearly seven-month journey that NASA’s Perseverance rover takes to Mars. Hundreds of critical events must execute perfectly and exactly in time for the rover to land safely on Mars on February 18, 2021. Credit: NASA / JPL-Caltech
Entry, descent and landing – often referred to as “EDL” – is the shortest and most intense phase of the March Mission 2020. It begins when the spacecraft reaches the top of the Martian atmosphere, traveling nearly 12,500 miles per hour (20,000 kilometers per hour). It ends about seven minutes later, with Perseverance stationary on the Martian surface. To safely shift from those zero speeds in that short amount of time while hitting a narrow target on the surface requires “slamming the brakes” in a very careful, creative and challenging way.
Discover entry, descent and landing
Real time simulation: Fly alongside Perseverance in this 3D demo of his entry, descent and landing. See the full experience ›
Landing on Mars is difficult. Only about 40% of missions ever sent to Mars – by any space agency – were successful. Hundreds of things must go perfectly during this gnawing drop. In addition, Perseverance has to manage everything on its own. During landing, it takes over 11 minutes to retrieve a radio signal from Mars, so by the time the mission team learns that the spacecraft has entered the atmosphere, in reality, the rover is already on the ground. . Thus, Perseverance is designed to complete the entire EDL process on its own – on its own.
How the landing is going
Final preparations
Ten minutes before entering the atmosphere, the spacecraft abandons its cruise stage, which houses solar panels, radios, and fuel tanks used on its flight to Mars. Only the protective spray – with the rover and the descent stage inside – makes the trip to the surface. Before entering the atmosphere, the vehicle fires small thrusters on the rear hull to reorient itself and ensure that the heat shield is facing forward for afterwards.
Atmospheric inlet
When the spacecraft enters the Martian atmosphere, the drag produced slows it down considerably – but these forces also heat it up considerably. Peak heating occurs approximately 80 seconds after atmospheric entry, when the temperature at the outer surface of the heat shield reaches approximately 2370 degrees Fahrenheit (about 1300 degrees Celsius). Safe in the aerosol, however, the rover only reaches room temperature.
Perseverance Rover Decelerating in the Martian Atmosphere (Illustration): In this illustration of its descent to Mars, the spacecraft containing NASA’s Perseverance rover slows down using the drag generated by its movement in the Martian atmosphere. Credit: NASA / JPL-Caltech
As it begins to descend into the atmosphere, the spacecraft encounters more or less dense pockets of air, which can cause it to deviate from its trajectory. To compensate, it triggers small thrusters on its rear hull that adjust its angle and direction of lift. This “guided entry” technique helps the spacecraft stay on track with its descending target.
Parachute deployment
The heat shield slows the spacecraft to less than 1,000 miles per hour (1,600 kilometers per hour). At this point, it is safe to deploy the supersonic parachute. To nail the timing of this critical event, Perseverance uses new technology – Range Trigger – to calculate its distance from the landing target and open the parachute at the perfect time to hit its target.
Perseverance Parachute Test: The massive supersonic parachute from the Mars 2020 mission is being tested in the world’s largest wind tunnel at NASA’s Ames Research Center. Credit: NASA / JPL-Caltech / Ames
The parachute, which measures 21.5 meters in diameter, deploys approximately 240 seconds after entry, to an altitude of approximately 11 kilometers and a speed of approximately 940 mph (1,512 km / h).
Zeroing on landing
Twenty seconds after the parachute deploys, the heat shield separates and falls. The rover is being exposed to Mars’ atmosphere for the first time, and key cameras and instruments may begin to lock onto the rapidly approaching surface below. Its landing radar bounces signals from the surface to determine its altitude. Meanwhile, another new EDL technology – Terrain-Relative Navigation – kicks in.
Using a special camera to quickly identify surface characteristics, the mobile compares them to an on-board map to determine exactly where it is heading. Members of the mission team mapped the safest areas of the landing zone in advance. If Perseverance can tell he’s heading for more dangerous terrain, he chooses the safest spot he can reach and prepares for the next dramatic step.
Motorized descent
In the thin Martian atmosphere, the parachute can only slow the vehicle down to about 200 miles per hour (320 kilometers per hour). To reach safe touchdown speed, Perseverance must free itself from the parachute and rocket the remainder of the descent.
Directly above the rover, inside the rear hull, is the rocket-powered descent stage. Think of it as a sort of jetpack with eight engines pointed at the ground. Once about 6,900 feet (2,100 meters) above the surface, the rover separates from the rear hull and fires the engines for the descent phase.
Motorized Descent for Perseverance (illustration): NASA’s Perseverance rover fires its descent stage motors as it approaches the Martian surface in this illustration. Credit: NASA / JPL-Caltech
The descent stage quickly deviates to one side or the other, to avoid being struck by the parachute and the rear hull which descends behind it. The direction of its diversion maneuver is determined by the safe target selected by the computer performing Terrain-Relative navigation.
Skycrane maneuver
As the descent phase stabilizes and slows down to its final descent rate of approximately 1.7 miles per hour (2.7 kilometers per hour), it initiates the “skycrane” maneuver. About 12 seconds before touchdown, about 20 meters above the surface, the descent stage lowers the rover on a set of cables about 21 feet (6.4 meters) long. Meanwhile, the rover uninstalls its mobility system, locking its legs and wheels in the landing position.
As soon as the rover feels that its wheels have touched the ground, it quickly cuts the cables connecting it to the descent stage. This allows the descent stage to fly up to make its own uncontrolled surface landing, a safe distance from Perseverance.
Save this date
Known to the team as “Seven Minutes of Terror,” the Entrance, Descent and Landing for Perseverance will be broadcast live when the rover arrives on Mars on February 18, 2021.
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