Picture: The EDL process for NASA’s Perseverance Rover. Image Credit: NASA/JPL
In a few days from now, on February 18th, NASA’s Jet Propulsion Laboratory (JPL) will once again attempt the daring feat of landing on Mars. This is a challenge which has been attempted ~15 times, by multiple agencies. However, only ten landers have made it safely to the surface. And two of those experience deployment failures, despite making it to the ground. So how will NASA accomplish this? And what do you need to know before the landing?
Entry, Descent, and Landing
NASA terms the Mars landing process as Entry, Descent, and Landing (EDL), or alternatively, the Seven Minutes of Terror. While NASA has landed other missions on Mars, Perseverance will still be a challenge. It is the heaviest mission ever sent to Mars, clocking in at a whopping 1,025 kilograms (compared to Curiosity’s 899). It will use a very similar landing method as Curiosity, but upgraded for the new mission.
EDL begins as Perseverance comes in at a blistering 20,000 kilometers per hour (about 12,500 miles per hour). The spacecraft must orient itself at just the right angle, otherwise it could bounce off the atmosphere like a stone skimming off a lake. It uses special control jets to point its heat shield towards the surface. As it falls, it continues to use these jets to maintain its orientation and guide itself towards the landing zone.
About four minutes later, the parachute deploys. This is the largest supersonic parachute NASA has ever used, and one of the largest in the world. At this point, the heat shield will have done its work and will be detached to fall to the ground below. Throughout the whole process, Perseverance will be imaging and scanning the surface to determine where to go.
Although Mars’s atmosphere is thick enough that it necessitates bringing along a heavy heat shield, it is thin enough that it cannot slow down the spacecraft enough to land it. That’s when it’s time to start the jets. The descent stage will identify a suitable area to set the rover down, one that’s free of boulders, cliffs, and other hazards.
The lander will bring Perseverance to about 20 meters above the surface. After that, it’s time to start the sky crane. This technique, first used by Curiosity, is necessary to avoid kicking up too much dust which could damage sensitive instruments. Curiosity and Perseverance are far too large to use the bouncing airbags employed by the Mars Exploration Rovers, Spirit and Opportunity.
Once the sky crane has verified that the rover is solidly on the surface, explosive bolts will fire to detach the rover from the descent stage. The sky crane will then fly off, so that it does not crash into the rover. This whole process takes about seven minutes, hence the nickname.
Remember that through the whole process, Mars is about 198 million kilometers away from Earth. It takes light 22 minutes to make the round-trip journey from the Earth to Mars and back. It is impossible to control any of the EDL process from the Earth. We must rely entirely on the rover’s onboard guidance system. Meanwhile, the crew at the JPL Space Flight Operations Facility (SFOF) will be anxiously biting their nails and monitoring the telemetry transmissions as they come back in. It’s a good thing that they’ve got some lucky peanuts.
The tradition of keeping peanuts at the SFOF dates back to the early days of the Space Race. NASA was working on the Ranger Program – a set of probes designed to take close-up pictures of the moon before crashing into it. After all, in order to land on the moon, you’ve got to be able to hit it first. The Ranger Program was initially plagued with problems. The first two probes failed to launch, two more missed the moon, and two impacted, but malfunctioned.
During the launch of Ranger 7, Dick Wallace, the Mission Trajectory Engineer, decided to hand out some peanuts to the scientists in the control room. Lo and behold, the probe performed spectacularly, sending back some of the first close-up pictures of the surface of the moon. Ever since then, it’s been a tradition to keep peanuts on hand in the control center at all times. Keep an eye out while watching the stream; you’ll definitely see a few jars here and there.
Once Perseverance is safely on the ground, NASA will have to run many checks and tests to ensure that all the systems are functional. After that, it’s time to begin the science.
While on Mars, Perseverance is slated to do some extra special experiments. Among them include setting up for a sample-return mission, searching for life, and testing a helicopter.
“Wait a second, did you say that Perseverance has a helicopter?” I did indeed. The Ingenuity helicopter is a technology demonstration to test the feasibility of such a device. In order to fly, Ingenuity must provide powerful lift, as Mars’s atmosphere is less than 1% as dense as Earth’s. It must also be strong enough to survive the trip. And, as with everything onboard Perseverance, it must be able to operate entirely autonomously. If Ingenuity is successful, future missions may make use of similar drones to aid in exploration.
However, Perseverance’s main goal is to continue the investigation started by the Viking Landers into whether or not Mars had life. Perseverance’s landing site is Jezero Crater, the site of an ancient lake bed. Images from the HiRISE camera aboard the Mars Reconnaissance Orbiter show evidence that a river once flowed into the crater. MRO’s CRISM spectrometer has also detected clays which form in the presence of water, further indicating that this location may have supported life.
Throughout the mission, Perseverance will be collecting and storing samples onboard. These will be placed in special containers and carried aboard the rover as it travels. NASA plans to send a follow-up rover to collect these samples and bring them back to a special Mars Ascent Vehicle, which will launch them into orbit. From there, they will be collected by an orbiting spacecraft and brought back to Earth. Once they’ve been returned, scientists can analyze them using more powerful machines than could ever be carried aboard a rover. NASA hopes to complete this mission by 2031.
Watch the landing!
Of course, in order to accomplish all this glorious science, Perseverance has to make it to the ground in one piece. You can follow along with the action straight from the SFOF through NASA’s broadcasts.
Tune in to the livestream, starting at 11:15 a.m. PST. I recommend watching on the NASA TV Public Channel, though you can also watch on YouTube and several other sites. You can ask questions by sending them to @NASA on Twitter and tagging them #CountdownToMars.
During the livestream, NASA scientists and engineers will explain Perseverance’s design and goals. Meanwhile, the crew members will be closely monitoring the telemetry coming in from the Deep Space Network. They’ll be tracking Perseverance’s progress as it descends, making callouts after confirming key events.
Should everything go well, Perseverance should be sitting on the surface by 4:00 p.m. PST. So grab your peanuts, and join the rest of the space exploration community as NASA once again challenges the limits of science and engineering.