Words By Amy-Rose Collins
At 20:56 GMT yesterday evening NASA’s Jet Propulsion Laboratory (JPL) received confirmation that the wheels of the Perseverance rover had safely touched Martian soil. The Mars 2020 spacecraft left Earth in July last year, then cruised through space for a little over 6 months. In the last few minutes of its journey, known as “7 minutes of terror”, Perseverance plummeted towards Mars at a top speed of 12,500mph, with nothing but a parachute and a high-tech jet pack to slow itself down. It is now exploring the area known as Jerezo crater, with the main aims of collecting rock samples for return by an ESA mission in the 2030s, and searching for signs of ancient martian life.
“We have a camera in the front and rear of the spacecraft […] you can see the wheels there. They’re a little dirty because we’ve got glass covers over these cameras, [and] we took these seconds after landing so there’s still dust in the air after our landing event.” – Chief Engineer Rob Manning, during NASAs live stream
Despite matching, mission logo adorned face coverings hiding half of every face in the room at the Jet Propulsion Lab (JPL) – and lack of high-fives-all-around, jumping all over each other style celebration to go viral – the enthusiasm, joy, and relief of the hundreds of people who have been working on the Mars 2020 mission for years now was as easily felt as ever. Swati Mohan, Operations Lead, acknowledged the many empty seats: “we had to rethink and redesign what it meant to operate a spacecraft in flight when we couldn’t all be in the same room”. Thankfully, Chief Manning smuggled in the traditional lucky peanuts despite the extra coronavirus restrictions.
Landing on Mars is no easy feat. With an atmosphere 100 times thinner than that of Earth, there is little air resistance to slow a speeding craft down. Even so, the craft is travelling so fast that friction from the air resistance heats up whatever is pointing down to up to 1,300°c. Then, there’s the rocky surface; a collection of jagged edges and crevasses to impale or otherwise smash the precious equipment on.
To make matters worse, by the time a spacecraft is at Mars the delay in sending a signal from Earth to the craft and vice-versa is 11 minutes. It takes just 7 minutes to descend from Martian orbit to the surface. This means that the craft surfed down entirely by itself. By the time the engineers at the JPL received the signal that it had entered the atmosphere, it was already on the ground. Previously, only 40% of Mars landing attempts had been successful. With a little Perseverance it seems that figure can be improved.
The basic construction of Mars 2020 is the same as that of the Mars Science Lab (Curiosity Rover), which landed in 2012. Perseverance and its precious cargo were encapsulated in the “aeroshell” (the top and bottom pieces of the image). The aeroshell is made up of the heat shield that protects the craft from the extreme temperatures of atmospheric entry – the rover itself only ever reaches room temperature! – and a backshell, which contains the parachute and sideways maneuvering thrusters. The descent stage (second piece from top) has 8 downwards-facing engines (AKA high-tec jet pack) and cables which are attached to the rover itself.
Thankfully, NASA had done this all before, with their Curiosity rover in 2012. The Mars 2020 landing borrowed from Curiosity’s success, with a couple of notable improvements. The “Range Trigger” allows flexibility in the timing of parachute deployment, which brings the rover closer to its ideal landing spot. If Range Trigger detects that Perseverance is further away than ideal from Jerezo crater, it will delay parachute deployment so valuable ground is gained. Conversely, it can pull the parachute sooner so it doesn’t overshoot. Because Perseverance moves slowly once on the ground, NASA say that this technique could have saved the rover up to a year of travel time to their primary region of interest.
The other major improvement to the landing sequence was “Terrain-Relative Navigation”. Perseverance obtained a map of the Martian surface from satellites in orbit, and additional logs of both dangerous and safer areas to land. Terrain-Relative Navigation takes pictures of the surface during descent and compares them to the onboard maps. It is able to fire sideways thrusters on the descent stage to course-correct if it detects that the craft is getting too close to a dangerous area.
Now Perseverance is on the ground, it will begin collecting data to fulfill its main mission. “The most important question for me is, really; was there ancient life on Mars during the time where it evolved on Earth? And for me, that question will be ultimately answered in ‘31 when the labs have the samples that are coming back from Mars.” – Dr Thomas Zurbuchen, speaking with BBC Science Correspondent Jonathan Amos 14/02/21. Perseverance will collect data with its onboard cameras, microphones, radar, drills, and multiple instruments capable of analysing material composition. It will also leave some samples behind for collection and return to Earth by another mission at a later date. Several small experiments are also onboard, including a drone named Ingenuity which will be attempting the first solo powered flight on another planet; “MOXIE”, a device designed to convert carbon dioxide into oxygen; and even a spacesuit designed specifically for potential future human use.
The adrenaline of the evening’s events subsiding, the little rover has some big wheel tracks to fill. With the likes of Spirit and Curiosity having both sent back compelling evidence for the existence of water on Mars, could Perseverance be the one to send us evidence for life?