After a 6-month, 480,000,000-kilometre journey through deep space, NASA’s Perseverance rover finally reached Mars in the morning hours of February 19th, 2021. It endured the entire EDL (Entry, Descent, Landing) process and executed each step flawlessly as planned, reaching the surface of Mars in Jezero Crater at 9:55am NZT.
Millions of people were watching around the world, as mission control called out each step during the process. Cheers erupted in mission control once the call was given; “Touchdown confirmed! Perseverance safely on the surface of Mars ready to begin seeking the signs of past life”. While the most hazardous part of the mission is now over, the mission itself has only just begun.
A socially distanced celebration at mission control as NASA mission specialists erupt in cheers after the successful landing of Perseverance was called. (NASA)
The ‘7 Minutes of Terror’
Getting a car-sized rover to another planet is no easy feat and landing it safely on the surface is even harder. NASA dubbed the EDL process on Mars the ‘seven minutes of terror’ – as after all those months and hundreds of thousands of kilometres, it all comes down to the final seven minutes from atmospheric entry until planetary touchdown.
The most terrifying fact is that the rover is on its own during this process, we can do absolutely nothing from Earth to help it. Mars may be our neighbouring planet, but space is big and the distance between our two worlds is vast even at their closest points. Signals travelling at the speed of light still can take over 20 minutes to reach Mars from Earth, and in Perseverance’s case the planet was about 11 light-minutes away when it began to enter the Martian atmosphere. This means that the rover was completely on its own, relying solely on pre-programmed commands and sensors to tell it exactly when to execute key steps to get onto the surface. If something were to go wrong, our signals to Perseverance would take too long to correct any error and it would have already crashed by the time it heard us.
Watching the video of mission control, you can see the intense nerves on the faces of the team as each step was called out when the signals reached Earth. The scientists can merely read out information as it comes in, hoping that nothing goes wrong. Thankfully, the process was executed flawlessly, and Perseverance sent back the ‘I’m okay!’ signal just seconds after touching the ground. Mars landings are extremely complex, but their success is a true triumph of science and engineering after years of planning and testing.
Entry, Descent, Landing
Mars is an interesting world, and it has some unique conditions that make landing there quite difficult. Only 40% of missions to Mars have been successful. When astronauts landed on our Moon, their spacecraft did not need heat shields to protect them because the Moon has no atmosphere. The spacecraft could fly directly down without ever experiencing heating from re-entry. Mars however does have an atmosphere, but one so thin that it is roughly 1% the thickness than Earth’s.
All spacecraft that have ever made it down to the surface of Mars were enclosed in a heatshield to protect them from the intense heat of atmospheric entry. As Perseverance plunged into the atmosphere it was travelling at speeds of 20,000km/ph. The thin air is used to create drag to slow the rover down, but this process causes intense heat, with temperatures reaching 1,300c on the heatshield.
The heatshield slows the spacecraft from 20,000kmph down to just 1,600kmph. At this point the capsule is still travelling faster than the speed of sound. A supersonic parachute is deployed to further reduce its speed. The parachute itself is an incredible 21m across; the largest supersonic parachute ever made. It must be this size as the Martian air is exceptionally thin. Once the parachute is deployed, the heatshield separates and drops away. This exposes the rover to the Martian atmosphere for the first time, and it could now ‘see’ where it is. Using a special camera to quickly identify features on the surface, the rover compared these to an onboard map to determine exactly where it was heading.
Mission team members had mapped in advance the safest areas of the landing zone. If Perseverance could tell it was heading for more hazardous terrain, it would pick the safest spot it could reach and get ready for the next dramatic step. At this time, the rover had slowed down to about 320kmph. Much slower than supersonic speeds, but still way too fast to safely land. A parachute on Earth could be used to land on our planet’s surface because we have a substantial atmosphere, but Mars’ air is so thin that a third stage is required to get the rover down safely.
This is when Perseverance executed another crucial step to landing on Mars. The rover cut itself free from the parachute and aeroshell using its descent stage. This descent stage acts somewhat like a jetpack that the rover is attached to. The ‘jetpack’ has 8 engines that fire to slow the rover down further while flying directly down to the surface. The descent stage quickly diverted to one side to avoid being impacted by the parachute and backshell coming down behind it.
You’d think that this powered stage would be able to bring the rover all the way down to the surface, right? Nope. The engines would cause too much dust and debris close to the ground which could potentially damage the rover, so one final step was required: the Skycrane.
The descent stage brought the rover all the way down to Mars until it was just 20m above the surface. The descent stage then lowered the rover on a set of cables about 6.4 meters long until it touched the ground. As Perseverance was slowly lowered down it unlocked its wheels and readied itself to touchdown on the red planet. As soon as Perseverance touches the ground, it cuts the 3 wires attaching itself to the descent stage at which point the Skycrane fired its engines once again to fly away and crash at a safe distance from the rover.
So many things can go wrong during a landing, but everything must go right for it to work. Luckily for Perseverance, the entire process went flawlessly, and Perseverance is now in its new home of Jezero Crater on Mars.
Perseverance’s’ view looking up towards the skycrane as it lowered it down to the surface. (NASA)
Haven’t we done this before?
The daring task of landing Perseverance on Mars was not the first time it had been done. The rover’s predecessor, Curiosity, used the same EDL process to land successfully back in 2012. Curiosity was a pioneer in this new landing technique as it had never been tried. Earlier rovers had used an airbag-type system, but both Perseverance and Curiosity were too large to use this system.
When Curiosity landed in 2012, it had 1 single low-quality camera to image its descent. Perseverance was the first to carry a slew of HD cameras to capture the entire process on video, and from multiple angles like we’d never seen before. Just days after landing, NASA released the entire video which is an incredible watch. It is like watching something out of a sci-fi movie, only real. This is all science, no fiction.
The MRO orbiter captured the rover along with all the stages used to get it down to the surface from space. (NASA/JPL-Caltech/University of Arizona)
The search for life begins
Perseverance is a unique rover, and the first of its kind. The Spirit & Opportunity rovers were designed to explore geology on Mars and tell us about surface conditions. The Curiosity rover is continuing to show us that Mars was once a water-covered world. Now, Perseverance has been designed and tasked specifically to search for past signs of life on Mars. Its landing site was chosen as it is an ancient river delta. Water once flowed in the exact area that Perseverance landed, and we know that water is the key ingredient for all life.
The success of Perseverance brings us closer than ever to answering profound and fundamental questions in science. Did life ever exist on Mars, and are we alone?