Mars is having a busy month. Two spacecraft have already arrived on Mars, and the third one will reach on February 18. On February 9, the UAE became the fifth nation to enter the Red Planet’s orbit with the Emirates Mars Mission carrying an orbiter called Hope. This was the first interplanetary mission of the country. The following day, China’s Tianwen-1 entered the orbit around Mars. Tianwen-1 comprises an orbiter, a lander, and a rover. With the successful orbital insertions of Hope and Tianwen-1, all eyes are now on NASA’s Mars 2020 mission carrying the Perseverance rover and the Mars Helicopter Ingenuity.
The spacecraft is scheduled to land on February 18. Before Perseverance starts exploring Mars, it must complete the most challenging part of its mission: a soft landing. The spacecraft has been traveling in space for the past seven months. It will enter the Martian atmosphere at 12,000-13,000 miles per hour. That’s incredibly fast! At this time, the rover will be in a protective capsule. The sequence of maneuvers needed to land on Mars is often referred to as the “seven minutes of terror.” Here’s what will happen on Mars in those seven minutes.
The seven minutes of terror
Whenever there’s a mission in which soft landing is involved, the entry, descent, and landing (also known as the EDL) is a terrifying task assigned to the spacecraft. The EDL is known as the seven minutes of terror because it will roughly take seven minutes for the spacecraft traveling at thousands of miles per hour to come to rest and land on the Martian soil. In those seven minutes, everything has to be perfect. The margin of error is zero. If anything goes wrong, the spacecraft will dig a huge hole on the surface of Mars, an expensive one!
Mars is far away from us. Signals take about 14 minutes to reach there. Because of this delay, we cannot control the rover’s landing in real-time from Earth. The process will be automatic, governed by more than 500,000 lines of computer codes.
Entering the atmosphere
The first part of EDL is E, the Entry. It starts more than 100 km above Mars, where the Perseverance rover will encounter the first wisps of the atmosphere. In the next few minutes, the speed of the capsule will come down to 1 m/s. The first thing that will slow down the NASA spacecraft will be the atmosphere of Mars. As the capsule enters the atmosphere, it will experience an aerodynamic drag, thanks to its speed. Because of the intense friction created due to the atmosphere, the capsule’s heat shield will reach a temperature of 1600 degrees!
There’s a certain limit up to which the Martian atmosphere can slow down our capsule. Unlike the Earth’s atmosphere, it’s very thin. Hence, the aerodynamic drag alone won’t complete the job. The capsule will still be traveling at a thousand miles per hour, which is, of course, still too fast. If you are wondering how will NASA fly a helicopter in such a fragile atmosphere, watch this video that explains their technique.
Deploying the parachute
To further slow down the capsule, NASA will use a parachute. The parachute used in the mission is one of the largest and the strongest supersonic parachutes that engineers have ever built to date. The weight of the capsule must be reduced when the parachute is deployed. This is when the heat shield separates and falls. The shield had already completed its part when the capsule was entering the atmosphere of Mars. With the heat shield gone and parachute deployed, the radar can finally ‘see’ the surface. It has to correctly compute the altitude and velocity for the subsequent sequences of descent and landing to work perfectly.
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Cutting off the parachute
The parachute can slow down the capsule from 1,000 miles per hour to 200 miles per hour. It’s still too fast to land. The capsule must separate itself from the parachute by cutting it off. Don’t panic! The rover won’t free fall on Mars at such a high velocity. As soon as it gets rid of the parachute, it turns on its rocket motors. But there’s something that needs to be done immediately.
The divert maneuver
If the parachute is separated and rocket motors are turned on, the capsule will smack right back into the parachute. Hence, the capsule must initiate a divert maneuver – fly to the side away from the parachute. Once the divert maneuver is completed, the radar will search for an appropriate location to land in the Jezero crater.
The skycrane maneuver
The capsule cannot get too close to the surface of Mars with its rocket boosters turned on. The reason is apparent. The boosters would create a massive dust cloud that could land on the rover and damage its instruments way before operating. The solution to this problem is the skycrane maneuver.
As Adam Steltzer says, “Twenty meters above the surface, we have to lower the rover below us on a tether that’s 21-feet long and then gently deposit, on its wheels, on the surface.”
After the rover lands softly, there’s one last crucial task. The descent stage with its rocket boosters must be flown away from the rover to avoid a collision. Once it flies away from Perseverance, the EDL and the seven minutes of terror will complete.