Entry, Descent, and Landing (EDL) Technologies: Paving the Way for Mars Missions

Mars poses a set of extraordinary challenges for Entry, Descent, and Landing (EDL) systems, stemming from its unique environmental and logistical conditions. The planet’s thin atmosphere provides a paradoxical hurdle—it is dense enough to generate intense heating during entry but far too tenuous to offer sufficient aerodynamic braking. This limitation necessitates the use of advanced technologies, such as retropropulsion, to decelerate spacecraft effectively.

Mason Peck, former NASA Chief Technologist, aptly describes it:

“The atmosphere of Mars is really inconvenient. It’s too thick to ignore—so, aerothermal heating is important—but too rarefied to offer an easy descent by parachute.”

Compounding this issue is the sheer speed at which spacecraft enter the Martian atmosphere, often exceeding 20,000 kilometers per hour. At such velocities, heat shielding and deceleration mechanisms must endure and dissipate extreme thermal and mechanical stresses to ensure the spacecraft’s integrity. Additionally, the demand for precision is high, as landing zones on Mars are typically small, scientifically valuable areas. This necessitates sophisticated navigation systems capable of guiding the spacecraft to these targeted regions with minimal error.

Moreover, the vast distance between Earth and Mars introduces a communication delay of up to 20 minutes, leaving no room for real-time human intervention during critical EDL phases. As a result, these systems must operate autonomously, making rapid and accurate decisions to adapt to the dynamic conditions of the Martian environment.

For NASA’s Mars 2020 mission, the EDL phase, lasting approximately seven minutes, was pivotal. This phase began as the spacecraft entered the thin Martian atmosphere at a speed of nearly 12,500 mph (20,000 kph) and ended with the Perseverance rover safely stationed on the surface of Jezero Crater. Accomplishing this requires advanced autonomous systems capable of managing the complex series of maneuvers without real-time human intervention due to the 11-minute communication delay between Earth and Mars.

Together, these challenges underscore the complexity of Mars exploration and drive innovation in spacecraft design and simulation technologies.

Mars poses a set of extraordinary challenges for Entry, Descent, and Landing (EDL) systems, stemming from its unique environmental and logistical conditions. The planet’s thin atmosphere provides a paradoxical hurdle—it is dense enough to generate intense heating during entry but far too tenuous to offer sufficient aerodynamic braking. This limitation necessitates the use of advanced technologies, such as retropropulsion, to decelerate spacecraft effectively.

Compounding this issue is the sheer speed at which spacecraft enter the Martian atmosphere, often exceeding 20,000 kilometers per hour. At such velocities, heat shielding and deceleration mechanisms must endure and dissipate extreme thermal and mechanical stresses to ensure the spacecraft’s integrity. Additionally, the demand for precision is high, as landing zones on Mars are typically small, scientifically valuable areas. This necessitates sophisticated navigation systems capable of guiding the spacecraft to these targeted regions with minimal error.

Moreover, the vast distance between Earth and Mars introduces a communication delay of up to 20 minutes, leaving no room for real-time human intervention during critical EDL phases. As a result, these systems must operate autonomously, making rapid and accurate decisions to adapt to the dynamic conditions of the Martian environment. Together, these challenges underscore the complexity of Mars exploration and drive innovation in spacecraft design and simulation technologies.

The Key Phases of EDL

The Entry, Descent, and Landing (EDL) process for Mars missions is a meticulously orchestrated sequence of events designed to safely deliver spacecraft to the planet’s surface. Each phase addresses unique challenges posed by Mars’ thin atmosphere and harsh conditions, employing advanced technologies to ensure mission success.

Atmospheric Entry and Heat Shield Protection: 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. Despite these intense conditions, the rover remains safely insulated at near-room temperature within the protective aeroshell. The heat shield’s ablative design effectively dissipates heat, ensuring the spacecraft’s structural integrity during this critical phase.

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.

Guided Entry: Navigating the turbulence of the Martian atmosphere requires precision. Small thrusters onboard the spacecraft make real-time trajectory adjustments during guided entry, ensuring it stays on course. This system enables the rover to target its landing zone accurately despite the unpredictable dynamics of atmospheric entry.

Parachute Deployment: To reduce velocity further, a supersonic parachute deploys at an altitude of approximately 7 miles (11 kilometers). This parachute, designed to operate under extreme conditions, dramatically slows the spacecraft. Utilizing Range Trigger technology, the system calculates the optimal deployment point to maximize precision, ensuring the spacecraft reaches its intended landing site.

As the descent stage maneuvers, it diverts laterally to avoid collision with the parachute and backshell. The direction of this diversion is determined by TRN, which identifies the safest target location. Terrain-Relative Navigation (TRN) : A key innovation in Mars missions, Terrain-Relative Navigation (TRN), enables the spacecraft to autonomously map and analyze the Martian surface in real-time. By comparing live terrain images to preloaded maps, TRN allows the rover to identify and avoid hazardous areas, ensuring it selects the safest possible landing site.

When an expedition reaches Mars, braking is required to enter orbit. Two options are available – rockets or aerocapture. Aerocapture at Mars for human missions was studied in the 20th century. One of the considerations for using aerocapture on crewed missions is a limit on the maximum force experienced by the astronauts. The current scientific consensus is that 5 g, or five times Earth gravity, is the maximum allowable deceleration

Rocket-Powered Descent and Skycrane Maneuver: Once the spacecraft separates from the parachute, the descent stage activates its retrorockets to slow its speed to just 1.7 mph (2.7 kph). The final stage, known as the Skycrane Maneuver, involves the descent stage lowering the rover to the surface using cables. This innovative approach minimizes the risk of surface impact and ensures a gentle landing. After the rover is safely deployed, the descent stage flies away to a safe distance, completing the EDL sequence.

Through these meticulously planned phases, EDL systems achieve the extraordinary feat of landing spacecraft on Mars, paving the way for groundbreaking exploration and scientific discovery.

Key EDL Technologies for Mars Missions

The success of Entry, Descent, and Landing (EDL) on Mars depends on the integration of cutting-edge technologies designed to overcome the planet’s unique challenges. Additionally, landing at lower elevations is preferable because the denser atmosphere provides more drag, aiding deceleration. However, even under optimal conditions, slowing down from orbital speeds to a safe touchdown velocity requires a combination of aerodynamics, parachutes, retrorockets, and precision navigation.

Each component plays a vital role in ensuring safe and precise landings, particularly as missions become more ambitious with larger payloads and human exploration on the horizon.

1. Heat Shields and Thermal Protection Systems (TPS)

During atmospheric entry, spacecraft encounter intense heating caused by friction with the Martian atmosphere. Heat shields, often composed of ablative materials, protect the vehicle by dissipating heat through controlled material erosion. Modern TPS systems are designed to withstand extreme temperatures and aerodynamic forces, ensuring the spacecraft remains intact during this critical phase.

Porous Microstructure Analysis (PuMA): NASA’s PuMA software uses micro-CT imaging to analyze how extreme heat and pressure affect spacecraft materials. This tool aids in designing reliable thermal protection systems, ensuring mission success even under the harshest conditions.

2. Supersonic Parachutes

Following initial deceleration through atmospheric drag, supersonic parachutes deploy to further slow the spacecraft. These parachutes are engineered to handle the extreme forces of deployment at speeds exceeding Mach 2. For instance, NASA’s Mars Perseverance rover utilized the largest supersonic parachute ever built, capable of withstanding dynamic pressures unique to the Martian atmosphere.

3. Powered Descent Systems

The final phase of descent often employs powered descent technologies, utilizing retropropulsion to reduce speed and enable precise positioning. This system, famously used during the landing of the Curiosity and Perseverance rovers, includes innovations like the “sky crane,” which gently lowers rovers to the Martian surface while minimizing the risk of damage.

4. Guidance and Navigation Technologies

Sophisticated guidance and navigation systems ensure the spacecraft maintains its intended trajectory and lands safely. Advanced techniques, such as Terrain-Relative Navigation (TRN), allow spacecraft to autonomously compare real-time surface images with preloaded maps, enabling them to detect and avoid hazards like rocks, slopes, and craters.

NASA continues to enhance landing precision through innovative technologies like the Navigation Doppler Lidar (NDL). Developed by NASA’s Langley Research Center, NDL is a laser-based navigation technology that calculates a spacecraft’s exact velocity and position. Its precision enables safe and hazard-free landings on planetary surfaces. NDL is part of the Safe & Precise Landing – Integrated Capabilities Evolution (SPLICE) project, which aims to improve precision landing and hazard avoidance. The technology has been licensed for commercial applications, further demonstrating its versatility for both terrestrial and space missions.

5. Inflatable Decelerators

Emerging technologies like Low-Density Supersonic Decelerators (LDSDs) are designed to address the challenges of Mars’ thin atmosphere. These inflatable, disk-shaped structures expand the spacecraft’s surface area, generating additional drag and allowing for the safe landing of heavier payloads.

In November 2022, the Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) demonstrated an alternative approach to deceleration and thermal protection. NASA’s LOFTID mission, tested in 2022, demonstrated an inflatable heat shield capable of handling the intense pressures and temperatures of atmospheric entry.  Launched aboard an Atlas V 401 rocket alongside the JPSS-2 weather satellite, LOFTID successfully inflated to a diameter of 6 meters (20 feet) and endured the intense heat and pressure of Earth re-entry. The inflatable system, composed of seven toroidal chambers covered with a flexible silicon carbide fabric, splashed down in the Pacific Ocean near Hawaii. Launched aboard an Atlas V 401 rocket alongside the JPSS-2 weather satellite, LOFTID successfully inflated to a diameter of 6 meters (20 feet) and endured the intense heat and pressure of Earth re-entry. The inflatable system, composed of seven toroidal chambers covered with a flexible silicon carbide fabric, splashed down in the Pacific Ocean near Hawaii.

6. Entry Capsules for Payload Protection

The aerodynamic design of entry capsules is critical for protecting delicate instruments and payloads during the turbulent entry phase. These capsules are optimized for stability, shielding the payload from intense heat and mechanical stresses while maintaining a smooth descent trajectory.

Innovations for Future Mars Missions

The success of Perseverance’s EDL showcased the evolution of Mars landing technologies. Yet, as missions grow more ambitious—aiming for crewed landings and heavier payloads—innovations like inflatable heat shields, advanced lidar systems, and enhanced material analysis will play pivotal roles. As Mars missions evolve, EDL technologies must advance to accommodate larger payloads, enhance precision, and ensure the safety of human crews and equipment.

Hypersonic Inflatable Aerodynamic Decelerators (HIADs)

HIADs represent a next-generation approach to heat shields, offering increased aerodynamic drag to handle heavier payloads. This technology is critical for landing the larger equipment required for crewed Mars missions, such as habitats and life support systems.

Reusable Entry Systems

The future of Mars exploration may involve reusable EDL systems to lower costs and improve mission reliability. These systems would be designed to endure multiple missions, supporting long-term exploration and the establishment of permanent bases on Mars.

Autonomous Landing Technology

Advances in artificial intelligence and machine learning are driving the development of highly autonomous landing systems. These technologies will enhance landing precision, reduce mission risks, and allow spacecraft to access previously unreachable regions on Mars.

Supersonic Retropropulsion

Originally tested by SpaceX on Earth, supersonic retropropulsion is being adapted for Mars missions. This technology uses forward-firing engines to decelerate vehicles at supersonic speeds, potentially replacing or supplementing parachutes for future missions.

The continued innovation in EDL technologies is essential for meeting the demands of future Mars missions. From advanced heat shields to autonomous navigation systems, each development pushes the boundaries of what is possible, bringing humanity closer to sustained exploration and habitation of the Red Planet.

Supercomputers and the Challenge of Simulating Mars Landings

Landing spacecraft on Mars is no easy task, and it becomes exponentially more difficult when the goal shifts from robotic missions to human exploration. The Red Planet’s thin atmosphere and unique environmental challenges mean traditional parachute-based deceleration isn’t viable for the massive spacecraft required for human missions. Instead, engineers at NASA are turning to retropropulsion—using forward-firing rockets to slow a spacecraft as it approaches the Martian surface.

A number of challenges come with using retropropulsion. The high-energy rocket engine exhaust interacts with both the vehicle and the Martian atmosphere. Those dynamics change how the team needs to guide and control the vehicle. In addition, engineers can’t fully replicate how a flight on Mars would go on Earth. While they can test spacecraft in wind tunnels and use other tools, those tools aren’t a perfect replacement or direct analog for the Martian environment.

To address the complexities of landing large vehicles on Mars, NASA is working with the Department of Energy’s Oak Ridge Leadership Computing Facility (OLCF) and its state-of-the-art supercomputers. These machines simulate the intricate physics of retropropulsion, filling in gaps that physical testing on Earth cannot replicate.

The journey began in 2019 with OLCF’s Summit supercomputer. Using the FUN3D software suite, originally developed in the 1980s and continuously improved since, scientists modeled fluid dynamics to analyze rocket exhaust interactions with the Martian atmosphere. Early simulations focused on fixed conditions, exploring variables like flight speeds and engine settings. Despite generating petabyte-sized datasets, these were only partial representations of actual flight dynamics.

The introduction of NASA’s Program to Optimize Simulated Trajectories (POST2) represented a significant leap. POST2 enabled dynamic simulations, allowing researchers to simulate real-time vehicle flight. This required collaboration with Georgia Tech’s Aerospace Systems Design Laboratory, which had expertise in coupling POST2 with high-fidelity aerodynamic models. Additionally, integrating POST2 involved resolving major cybersecurity and system interoperability challenges, as the software was restricted to NASA systems.

The project reached a new milestone with the move to OLCF’s Frontier supercomputer, the world’s first exascale system. Frontier’s unmatched processing power allowed for a 35-second closed-loop simulation of a spacecraft’s descent, dynamically controlling its trajectory using eight main engines and four reaction control modules. The simulation covered the critical phase from 5 miles to 0.6 miles altitude, reducing the spacecraft’s speed from 1,200 to 450 miles per hour.

These advanced simulations are laying the groundwork for future human missions to Mars. By overcoming the challenges of retropropulsion and creating highly detailed models of flight dynamics, NASA and its partners are paving the way for safer and more efficient Mars landings. This collaboration between engineers, researchers, and supercomputing facilities highlights the transformative role of cutting-edge technology in expanding human presence beyond Earth.