Mars EDL is widely recognized as one of the most demanding technical challenges for human Mars missions. The fundamental difficulty arises from Mars having enough atmosphere to generate significant aerothermal heating during entry but insufficient atmospheric density to decelerate large masses to safe landing speeds using aerodynamic drag alone.

Heritage and the scaling gap:

All successful Mars landers to date have been robotic and relatively low mass. The progression from Viking (approximately 600 kg landed mass, 1976) to Curiosity (approximately 900 kg, 2012) to Perseverance (approximately 1,025 kg, 2021) represents steady but incremental advancement. Human-class payloads require landed masses at least 20 times greater than anything achieved to date, representing a fundamentally different engineering regime.

The Mars EDL sequence for robotic landers has relied on a combination of aeroshell-based atmospheric entry, supersonic parachute deployment, and terminal descent (retrorockets or the sky crane system used for Curiosity and Perseverance). This architecture does not scale to human-class masses because parachute systems become impractically large and heavy.

Supersonic retropropulsion (SRP):

SRP, using rocket engines to decelerate the vehicle while still traveling at supersonic speeds through the atmosphere, is the leading candidate technology for large-mass Mars EDL. SpaceX has accumulated extensive operational experience with SRP through Falcon 9 and Falcon Heavy booster landings on Earth, though Mars atmospheric conditions (lower density, different gas composition) require dedicated adaptation and testing. Computational fluid dynamics modeling and limited wind tunnel testing have explored SRP in Mars-relevant conditions, but full-scale Mars-atmosphere validation remains to be accomplished.

Thermal protection systems (TPS):

Larger vehicles with different ballistic coefficients and entry corridor geometries impose different thermal loads than current robotic entry vehicles. Both ablative TPS (PICA-X, SLA-561V heritage) and potentially reusable TPS concepts (ceramic tiles, metallic heat shields) are under development. SpaceX's Starship heat shield tile system represents an active development program for reusable TPS at relevant scale, though Mars entry velocities and atmospheric composition differ from Earth reentry conditions.

Precision landing:

Human missions must land at specific prepared sites where pre-deployed infrastructure, ISRU systems, and cached supplies are waiting. This requires terrain-relative navigation, hazard detection and avoidance, and landing accuracy within tens of meters, all demonstrated at smaller scale on Mars 2020 (Perseverance) and further developed through lunar programs (Artemis HLS).

Aerocapture:

An alternative to direct entry from interplanetary trajectory is aerocapture, where the vehicle uses a single atmospheric pass to decelerate into Mars orbit before conducting a controlled descent. This approach can save significant propellant mass compared to propulsive orbit insertion but requires precise aerodynamic performance and thermal protection for the capture maneuver.

Mars Ascent Vehicle (MAV):

EDL is paired with the challenge of Mars ascent. Crew must be able to launch from the Martian surface to orbit for the return trip. MAV design drives propellant production (ideally via ISRU) and imposes constraints on surface habitat siting and launch infrastructure.