Landing on Mars is hard. Two out of three missions to the red planet have failed. Hundreds of things have to go just right during this nail-biting drop. To get there, will have to fly through about 483 million kilometers (300 million miles) of deep space and target a very precise spot to land. Adjustments to their flight paths can be made along the way, but a small trajectory error can result in a big detour and or even missing the planet completely.
The space environment isn’t friendly. Hazards range from what engineers call “single event upsets,” as when a stray particle of energy passes through a chip in the spacecraft’s computer causing a glitch and possibly corrupting data, to massive solar flares, such as the ones that occurred this fall, that can damage or even destroy spacecraft electronics.
The road to the launch pad is nearly as daunting as the journey to Mars. Even before the trip to Mars can begin, a craft must be built that not only can make the arduous trip but can complete its science mission once it arrives. Nothing less than exceptional technology and planning is required.
If getting to Mars is hard, landing there is even harder. “One colleague describes the entry, descent and landing as six minutes of terror,” says Dr. Firouz Naderi, NASA’s Mars Program Office. So, the challenge of entry, descent and landing is how to get something that massive traveling at 19,300 kilometers per hour (12,000 miles per hour) slowed down in six minutes to have a chance of survival.”
Mars doesn’t exactly put out a welcome mat. Landing is complicated by difficult terrain. The martian surface is full of obstacles–massive impact craters, cliffs, cracks and jagged boulders. Even the toughest airbag can be punctured if it hits a bad rock. Unpredictable winds can also stir up further complications.
The risks are also great. “We do everything humanly possible and try to avoid human mistakes,” says Naderi. “That’s why we check, double check, test and test again and then have independent eyes check everything again. Humans, even very smart humans, are fallible particularly when many thousands of parameters are involved. But even if you have done the best engineering possible, you still don’t know what Mars has in store for you on the day your arrive. Mars can get you.”
“Perseverance is NASA’s most ambitious Mars rover mission yet, focused scientifically on finding out whether there was ever any life on Mars in the past,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. “To answer this question, the landing team will have its hands full getting us to Jezero Crater – the most challenging Martian terrain ever targeted for a landing.”
Jezero is a basin where scientists believe an ancient river flowed into a lake and deposited sediments in a fan shape known as a delta. Scientists think the environment here was likely to have preserved signs of any life that gained a foothold billions of years ago – but Jezero also has steep cliffs, sand dunes, and boulder fields.
What’s more, Perseverance has to handle everything by itself. During the landing, it takes more than 11 minutes to get a radio signal back from Mars, so by the time the mission team hears that the spacecraft has entered the atmosphere, in reality, the rover is already on the ground. So, Perseverance is designed to complete the entire EDL process by itself – autonomously.
After a seven-month, nearly 300-million-mile journey to Mars, NASA’s Perseverance rover successfully landed on Mars on February 18 2021. The rover also has a helicopter named Ingenuity strapped to its belly that will deploy shortly after a safe landing on the red planet.
Over the following days, engineers will also check on the health of the rover and deploy the remote sensing mast (otherwise known as its “head”) so it can take more pictures. The Perseverance team will then take more than a month to thoroughly inspect the rover and load new flight software to prepare for its search for ancient life on Mars. During the same period, the Ingenuity Mars Helicopter team will be making sure their small but mighty robot is prepared for the first attempt at controlled, powered aerodynamic flight on another planet.
Entry, Descent, and Landing – often referred to as “EDL” is the shortest and most intense phase of the Mars 2020 mission.
It begins when the spacecraft reaches the top of the Martian atmosphere, travelling 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 go from those speeds down to zero, in that short amount of time, while hitting a narrow target on the surface, requires “slamming on the brakes” in a very careful, creative and challenging way
Ten minutes before entering the atmosphere, the spacecraft sheds its cruise stage, which houses solar panels, radios, and fuel tanks used during its flight to Mars. Only the protective aeroshell – with rover and descent stage inside – makes the trip to the surface. Before entering the atmosphere, the vehicle fires small thrusters on the backshell to reorient itself and make sure the heat shield is facing forward for what comes next.
As the spacecraft enters the Martian atmosphere, the drag produced drastically slows it down – but these forces also heat it up dramatically. Peak heating occurs about 80 seconds after atmospheric entry, when the temperature at the external surface of the heat shield reaches about 2,370 degrees Fahrenheit (about 1,300 degrees Celsius). Safe in the aeroshell, however, the rover gets up to only about room temperature.
The aeroshell designed to protect Perseverance during entry into the Martian atmosphere includes a heat shield and a cone-shaped back shell. The former must withstand temperatures of more than 2,700 degrees Fahrenheit (about 1,480 degrees Celsius). The technology’s 28 sensors are positioned across the heat shield and backshell of the Mars 2020 entry vehicle. During the seven minutes of atmospheric entry – when the spacecraft slows from 12,500 miles per hour to just under 2 (from about 20,100 kilometers per hour to 3.2) – the sensors will continuously record heat and pressure across the entry vehicle. These will be NASA’s first-ever measurements of the heat experienced by the backshell of an entry vehicle.
As it begins to descend through the atmosphere, the spacecraft encounters pockets of air that are more or less dense, which can nudge it off course. To compensate, it fires small thrusters on its backshell that adjust its angle and direction of lift. This “guided entry” technique helps the spacecraft stay on the path to its downrange target.
The heat shield slows the spacecraft to under 1,000 miles per hour (1,600 kilometers per hour). At that point, it’s safe to deploy the supersonic parachute. To nail the timing of this critical event, Perseverance uses a new technology – Range Trigger – to calculate its distance to the landing target and open the parachute at the ideal time to hit its mark. The parachute, which is 70.5 feet (21.5 meters) in diameter, deploys about 240 seconds after entry, at an altitude of about 7 miles (11 kilometers) and a velocity of about 940 mph (1,512 kph).
The impressive parachute is a combination of nylon, Technora and Kevlar fibers and it was created by the Jet Propulsion Laboratory’s ASPIRE project after a thorough series of tests. “Mars 2020 will be carrying the heaviest payload yet to the surface of Mars, and like all our prior Mars missions, we only have one parachute and it has to work,” said John McNamee, project manager of Mars 2020 at JPL in a statement.
Zeroing In on Landing
Twenty seconds after parachute deployment, the heat shield separates and drops away. The rover is exposed to the atmosphere of Mars for the first time, and key cameras and instruments can begin to lock onto the fast-approaching surface below. Its landing radar bounces signals of the surface to figure out its altitude. Meanwhile, another new EDL technology – Terrain-Relative Navigation – kicks in.
“TRN is a new subsystem that allows the lander to figure out its position and where it’s going to land by taking images while it’s on the parachute,” said Andrew Johnson, manager for the guidance, navigation, and control subsystem at NASA’s Jet Propulsion Laboratory in Southern California. “Past missions haven’t had this capability.”
Using a special camera to quickly identify features on the surface, the rover compares these to an onboard map to determine exactly where it’s heading. Mission team members have mapped in advance the safest areas of the landing zone. If Perseverance can tell that it’s headed for more hazardous terrain, it picks the safest spot it can reach and gets ready for the next dramatic step.
This autopilot technology uses a map of the designated landing ellipse created from pictures taken by the Mars Reconnaissance Orbiter. Landmarks and hazards are identified, and the annotated maps are loaded on the TRN computer. TRN uses a camera designed to take a picture in one-tenth of a second, resulting in clear pictures even during rapid descent. To enable fast image processing, the system includes a high-performance computer that uses algorithms to compare the descent pictures with data previously loaded via the onboard map.
In the thin Martian atmosphere, the parachute is only able to slow the vehicle to about 200 miles per hour (320 kilometers per hour). To get to its safe touchdown speed, Perseverance must cut itself free of the parachute, and ride the rest of the way down using rockets.
Directly above the rover, inside the backshell, is the rocket-powered descent stage. Think of it as a kind of jetpack with eight engines pointed down at the ground. Once it’s about 6,900 feet (2,100 meters) above the surface, the rover separates from the backshell, and fires up the descent stage engines.
The descent stage quickly diverts to one side or the other, to avoid being impacted by the parachute and backshell coming down behind it. The direction of its divert maneuver is determined by the safe target selected by the computer that runs Terrain-Relative Navigation.
As the descent stage levels out and slows to its final descent speed of about 1.7 miles per hour (2.7 kilometers per hour), it initiates the “skycrane” maneuver. With about 12 seconds before touchdown, at about 66 feet (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 unstows its mobility system, locking its legs and wheels into landing position.
As soon as the rover senses that its wheels have touched the ground, it quickly cuts the cables connecting it to the descent stage. This frees the descent stage to fly off to make its own uncontrolled landing on the surface, a safe distance away from Perseverance.
No matter how hard it is, getting to Mars is just the beginning. “The challenge after we land,” says Rob Manning, manager of Mars Exploration Rovers entry, descent and landing operations, “is how to get the vehicle out of its cramped cocoon and into a vehicle roving in such a way as to please the scientists.”
Perseverance is a robotic scientist weighing about 2,260 pounds (1,025 kilograms). The rover’s astrobiology mission will search for signs of past microbial life. It will characterize the planet’s climate and geology, collect samples for future return to Earth, and pave the way for human exploration of the Red Planet.
Atmospheric Nitty-Gritty MEDA camera
The Mars Environmental Dynamics Analyzer, or MEDA, will fill gaps in atmospheric data that pose risks for human exploration. Manuel de la Torre Juárez, deputy principal investigator for MEDA at JPL, explained that international collaboration is behind the suite of instruments.
The U.S. contribution is a camera dedicated to one of the most significant factors in Martian weather: dust. The MEDA camera will take measurements of the Martian atmosphere throughout the day and night. These readings will augment the data already collected by other rovers and landers.
“Those measurements are going to inform us about the aerosols,” he said, adding that both dust and ice have previously been observed in the Martian atmosphere. “What is the particle size of these aerosols? How do they change within the same day? This is something that we could not measure regularly on the other missions,” said de la Torre Juárez.
The Martian dust contains perchlorates, which are toxic to humans, and thus introduce another challenge for human explorers. MEDA measurements could help inform technologies to keep this pesky dust from contaminating habitats, space suits, and surface systems.
Learning when and how various atmospheric conditions occur and interact with the dust cycle will influence the design of infrastructure such as power systems, so they perform consistently in all conditions. One method for identifying the type and physical properties of particles in the air is to examine how sunlight is transformed by the atmosphere. The intensity of solar radiation, how it changes depending on its angle, and the color distribution that reaches the surface all yield information.
These measurements will also provide important details about the ultraviolet (UV) light filtered out by dust and ozone in the Martian atmosphere. This is important for future astronauts. UV radiation can cause skin cancer in humans, but it also might kill any bacterial contamination people bring. This information can help fine-tune the protective habitat, clothing, and other resources astronauts bring to Mars.
When astronauts set foot on the Red Planet for the first time, they’ll rely on technologies tried and tested by their robotic predecessors. The Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, is one of the instruments arriving with Perseverance that will demonstrate a new, critical capability: making oxygen directly from the Martian atmosphere. This means access to air for breathing, but more importantly, vast quantities of it that could be used to burn the fuel of a return rocket.
MOXIE is the first demonstration of its kind – the first test of an in-situ resource utilization technology to generate mission products with local resources – on another world. The instrument is like a miniature electronic tree on the rover, producing oxygen from the carbon dioxide in the Martian atmosphere. MOXIE will produce oxygen by transforming carbon dioxide into carbon monoxide and oxygen molecules.
MOXIE works in a three-step process. The instrument collects carbon dioxide from the atmosphere using a compressor, or pump. Next, it separates the molecule into carbon monoxide and oxygen via a catalytic reaction. Then, electrical current applied to a hot, permeable membrane – in this case, a type of ceramic – selectively pulls the negative oxygen ions from one side to the other, leaving behind the carbon monoxide. The pure oxygen is then collected, analyzed, and released back into the Martian atmosphere, while the carbon monoxide is sent to an exhaust along with any unused carbon dioxide.
“It’s like a fuel cell operated in reverse,” said Jeff Mellstrom, instrument manager at JPL. “A fuel cell will use fuel and an oxidizer to generate electricity and exhaust gas. We take in what would normally be considered an exhaust gas, the carbon dioxide, applying electricity to generate fuel and oxidizer, carbon monoxide, and oxygen, respectively.”
Testing MOXIE on Mars will validate how the technology functions outside of a lab, after the stressors of launch and traveling through space, and how it adapts to the harsh environment on the Martian surface. Scientists and engineers built the instrument to be robust enough to work through these conditions. The primary goal for this technology is to prove that it could be feasible to make liquid oxygen propellant in situ, on Mars. Before astronauts even land on Mars, a larger system could begin producing metric tons of rocket fuel.