Arriving at Mars: Orbital Insertion, Descent, and Landing
After seven months of interplanetary travel covering roughly 480 million kilometers, the crew faces one of the most technically demanding moments in all of spaceflight: arriving at Mars. The planet offers no calm welcome. Its thin atmosphere — about 1% the density of Earth's — is too thick to ignore during descent but too thin to rely on for braking alone. Its gravity, at 3.72 m/s², is enough to pull a spacecraft in fast and hard. Getting humans safely to the Martian surface requires a precisely choreographed sequence that pushes aerospace engineering to its current limits.
Mars Orbit Insertion
The spacecraft doesn't simply fall into Mars orbit — it must be actively captured. As the vehicle approaches Mars, the crew and mission controllers execute a Mars Orbit Insertion (MOI) burn. This retrograde engine firing, lasting roughly 20 to 30 minutes depending on vehicle mass and target orbit, bleeds off enough velocity to allow Mars' gravity to capture the spacecraft rather than let it fly past.
The target is typically a highly elliptical capture orbit — perhaps 500 km by 33,000 km — which is then gradually lowered through a series of subsequent burns over several days. This phased approach conserves propellant and gives engineers time to assess spacecraft health before committing to entry. For a human mission, NASA's Design Reference Architecture 5.0 outlines placing the crew in a safe parking orbit while pre-deployed surface assets are confirmed operational. There's no landing on Mars until mission controllers on Earth — with a one-way communication delay of 3 to 22 minutes depending on planetary alignment — have verified that the habitat, power systems, and life support on the surface are ready.
The Seven Minutes of Terror — Scaled Up
The phrase "seven minutes of terror" was coined during the 2012 Curiosity rover landing, describing the time between atmospheric entry and touchdown — a window during which the spacecraft is entirely autonomous and Earth has no real-time ability to intervene. For a human mission, that window remains, but the stakes are categorically different.
A crewed entry vehicle for Mars would be far heavier than any robotic lander to date. Curiosity weighed about 900 kg at landing; a crewed vehicle with life support, habitat provisions, and return propellant could mass 20,000 to 40,000 metric tons — or more in some architectures. That scale makes every previous Mars Entry, Descent, and Landing (EDL) system inadequate as a direct template.
Entry: Riding the Atmosphere
Atmospheric entry begins at roughly 125 km altitude, where the spacecraft first meaningfully interacts with Martian air. The vehicle enters at approximately 5.5 to 6 km/s. A large aeroshell — likely a blunt-body design derived from heritage going back to the Viking landers of 1976, but scaled dramatically — generates aerodynamic drag that converts kinetic energy into heat. Peak heating can exceed 2,000°C on the heat shield surface, requiring advanced Thermal Protection Systems (TPS) such as NASA's HEEET (Heat shield for Extreme Entry Environment Technology) or Phenolic Impregnated Carbon Ablator (PICA), which has flown on Dragon capsules and Mars Science Laboratory.
One promising concept is the Hypersonic Inflatable Aerodynamic Decelerator (HIAD), a large deployable structure that increases the effective diameter of the entry vehicle without the mass penalty of a rigid aeroshell. NASA has tested HIAD technology through the LOFTID mission, which successfully demonstrated the concept in Earth's atmosphere in November 2022. A large enough HIAD — potentially 15 to 20 meters in diameter — could provide sufficient drag to slow a crewed vehicle meaningfully before powered descent begins.
Descent: The Hardest Problem in Mars EDL
Even after a successful aerocapture phase, a heavy crewed lander arrives at lower altitudes still traveling at supersonic speeds — and Mars' thin atmosphere means conventional parachutes, effective on Earth, are largely insufficient here. The Perseverance rover used a 21.5-meter supersonic parachute to decelerate from about 450 m/s to 100 m/s; for a vehicle ten or twenty times heavier, even a vastly larger parachute cannot do enough work.
This is why powered descent — rocket engines firing to kill the remaining velocity — is unavoidable for large Mars landers. SpaceX's Starship architecture, which NASA selected for the Artemis Human Landing System on the Moon, is designed around propulsive landing and is one candidate vehicle discussed for Mars human missions. Starship uses six Raptor engines burning liquid methane and liquid oxygen (a combination called methalox), which has the added advantage that methane can theoretically be produced on Mars using the Sabatier reaction — combining atmospheric CO₂ with hydrogen to produce CH₄ and water.
Terrain Relative Navigation
Autonomous precision landing is non-negotiable. The crew cannot manually fly a vehicle through supersonic descent in real time, and Earth-based guidance is ruled out by communication delays. Terrain Relative Navigation (TRN) — a system that compares onboard camera imagery to pre-loaded surface maps to determine exact position — was flight-proven by the Perseverance rover during its 2021 landing in Jezero Crater. For a crewed mission, TRN must be more capable still, guiding the lander to within tens of meters of a pre-established surface outpost where infrastructure already waits.
Touchdown: The Surface of Mars
Landing site selection will have been made years in advance, balancing scientific value, resource availability (particularly near-surface water ice), and terrain safety. Candidate regions include Hellas Planitia, Isidis Planitia, and mid-latitude sites where subsurface ice has been mapped by the Mars Reconnaissance Orbiter's SHARAD radar. Elevation matters too: lower-lying sites offer more atmosphere for deceleration.
When the lander finally settles on Martian soil — after a descent sequence lasting roughly seven to twelve minutes from entry interface — the crew will have survived the most dangerous phase of any Mars mission outside of a catastrophic failure scenario. Communications with Earth will be delayed. The environment outside is lethal. But they will be on Mars.
"The entry, descent, and landing problem for humans on Mars is not yet solved. It is the single largest technical gap between where we are and where we need to be." — NASA Mars Architecture Study Team, paraphrased from public roadmap documents