By Leo Farrell, Senior Writer, Red Planet Bound
Landing a craft on Mars is one of the most scientifically advanced feats of engineering humanity has ever pulled off. A handful of rovers have touched down, and these successes, along with modern efforts like the Artemis II mission, signify the leaps and bounds researchers have made in forging resilient spacecraft.
Eventually, a human will set foot on the red planet because of a next-generation machine, thanks to the years of research and effort teams have made.
The Challenges of Landing on Mars
Mars’s atmosphere is challenging for a machine to wade through. Because of its composition, the spacecraft must be able to land on the surface without human input. Experts have referred to this drop in communications as the seven minutes of terror for years, representing a mismatch in comms as it touches down.
The planet’s thin atmosphere complicates matters even more. Without it pushing up against the spacecraft as it descends, the machine reaches the surface much faster. When a spacecraft comes to Earth, part of the landing maneuver is accounting for aerobraking, or the drag the atmosphere creates.
Landing a craft on Mars is different. Instead, it enters at speeds of up to 13,000 mph, with only a short window to slow down. Additionally, a heat shield must protect it from temperatures of thousands of degrees Celsius. During this time, real-time communication from Earth is impossible due to delays.
Therefore, space engineers need to implement autonomous measures so the Mars spacecraft can navigate the terrain on its own. If it cannot trigger the mechanisms to adjust its speed, it will crash and render the mission moot.
The Entry, Descent and Landing (EDL) Sequence
The EDL process, or the seven minutes of terror, is an intricately choreographed series of commands in the spacecraft’s computer. Though it is automated, it is one of the most complex parts of any Mars mission.
Atmospheric Entry
The EDL sequence begins when it touches the atmosphere. An aeroshell surrounds it, comprising a heat shield in the front and a shell in the back. The material is critical because it must simultaneously withstand extreme heat from the immense friction and slow the craft down. Typically, they are ablative materials that dissipate heat as they dissolve from the spacecraft’s main body.
Parachute Deployment
A Mars spacecraft needs more than a heat shield to withstand both the atmosphere and landing. It is also equipped with parachutes to reduce its speed and help the machine find its center of gravity and maintain stability and control amid chaotic flight dynamics. The parachutes are made of a material that can withstand supersonic speeds alongside the thin atmosphere. However, it will need more help if the landing is going to proceed safely.
Powered Descent
Many space enthusiasts have witnessed the rocket separate from the main body of the ship. Mars crafts execute a similar separation after the parachute has slowed them down enough. What remains of the aeroshell will split from the rover, triggering a series of rockets that serve as the next braking system. This continues to slow it down, but it also helps the rover adjust its position and trajectory.
As it continues to descend, the onboard computer measures velocity and altitude to inform the rockets’ power.
Touchdown
Touchdown technology can vary from one rover to another. Rovers like Spirit and Opportunity have airbags that enshroud them and allow them to softly bounce to the surface. Others, like Curiosity, have a mechanism called a sky crane. This is a series of cables that lowers the rover’s body to the surface. Once it lands, a jetpack cuts the ropes and flies out of range of the rover.
The Impact of Mars’s Gravity
Most of the struggle for EDL has been due to atmosphere, but gravity is another vital consideration. The gravity on Mars is only 38% of Earth’s, which helps and hurts a craft’s chances of landing safely. The gravity of any planet will make landing a rover more difficult, as engineers must account for additional forces acting on the rover.
This is evident in mechanisms like parachutes. The lower gravity, combined with the reduced atmospheric density, makes them less reliable. They will not have the same impact as if they were entering the Earth’s atmosphere. There is less air resistance acting on the parachute, which is why it is not reliable throughout the entire EDL process.
The lower gravity becomes beneficial during the propulsion phase. The Mars spacecraft does not need as much fuel to have a safe descent. If it were combating Earth’s gravity, it would need far more to push against the forces. Having less fuel on board helps the rover remain as lightweight as possible.
Case Studies of Successful Mars Landings
These successful missions have laid the groundwork for the future, letting professionals know what works and where there are areas for improvement.
1975’s Viking 1 and 2
These were among the first rovers to demonstrate the effectiveness of the aeroshell-parachute-rocket sequence. This would inspire the many missions that came after. Because of this planning, Viking 1 and 2 landed softly on their legs without damage. Viking 1 achieved this by incorporating a radar altimeter, so the machine was always aware of its altitude. Then, it throttled its rockets and adjusted its position with more data.
1997’s Pathfinder Rover
Pathfinder was a revolutionary mission because it would lay the foundation for the airbag landing system. At around 330 feet above Mars’s surface, it inflated a massive cloud of airbags around the rover. Once it hit the ground, the rover rolled 15 times before coming to a stop. Then, the airbags deflate, revealing the rover, camera masts and ramps for its inevitable departure.
2004’s Spirit and Opportunity Rovers
This rover pair was one of the largest designs in NASA’s history, meaning it had to improve upon the airbag-based EDL used by Pathfinder. The two were still going to bounce and roll onto the surface, but their heft required a better cushion even when split. Opportunity would not have lasted over 14 years if its landing had not been perfected.
This mission also proved the airbag method was scalable beyond its original conception, though it was reaching its limit.
2021’s Perseverance Rover
Because of Perseverance’s size, it could not rely on airbags. This mission catalyzed the development of the sky crane maneuver, which enabled NASA to reach parts of Mars that were previously too dangerous.
Even the most advanced airbags could not compensate for Mars’s intensely rough terrain, but the sky crane could hover and lower Perseverance delicately onto the surface. After it split from the cables, the crane could fall to the surface, crashing a safe distance away from the rover.
The Beginning of the Journey
Every piece of tech that finds its way to Mars’s surface has to battle against several stressors before it can begin its work. From low gravity to intense friction, scientists need to find the right materials and configurations to bring technologies to the surface. Every step of the process is a balancing act between physics and materials science, alongside advances in communication and engineering.
Eventually, these insights will culminate in a spacecraft that contains humans, leading to their first Martian spacewalk.
Author’s Personal Note: I (and perhaps many of you, too) recently visited my local theater to see the film Project Hail Mary. I quite enjoyed it, but more pertinently, the film was what served as the inspiration for this article idea. The film was a strong reminder that there are so many unique technical layers and scientific considerations that go into what can, at first glance, appear to be quite simple.
I find it fascinating to dive into these subjects and come to a greater understanding of just how much time, effort, knowledge, skill, and trial-and-error is required for something as ‘simple’ as landing a spacecraft on the Red Planet!
