In April 2026, four astronauts on Artemis II swung around the Moon and came home, travelling farther from Earth than any humans before them. It was a genuine milestone. It was also, at its farthest point, about 400,000 km from home. Mars never comes closer than roughly 55 million km, and for much of its orbit it is several hundred million kilometres away.
That gap, more than a hundred times the Moon's distance at best, is the whole story. Nearly every obstacle to reaching Mars comes down to how far it is, how long the trip takes, and how little help is available once you arrive.
You Can't Just Go When You're Ready
Earth and Mars both orbit the Sun, at different speeds. The most fuel-efficient route between them, the kind of trajectory every Mars mission has used, only works when the two planets line up in a particular geometry. That alignment comes around roughly every 26 months.
Miss a window and you wait two years. That single fact shapes everything. Mission schedules snap to a two-year grid, and a delay of a few weeks can turn into a delay of two years. It is why every Mars programme's history reads as a list of windows that were targeted and then missed.
A transfer on one of these efficient trajectories takes roughly six to nine months each way. A crewed mission can't simply turn around on arrival either: the planets have to line up again for the trip home, which typically means waiting on Mars for over a year. A realistic first crewed mission lasts well over two years from launch to landing back on Earth.
Distance from Earth: roughly 55 to 400 million km, depending on orbital positions. One-way radio delay: about 3 to 22 minutes, so no real-time help from mission control. Surface gravity: 38% of Earth's. Atmosphere: about 1% of Earth's surface pressure and mostly carbon dioxide, too thin to breathe or to slow a heavy spacecraft easily, but thick enough to cause severe heating on entry.
The Landing Problem
Mars is awkward to land on. Its atmosphere is too thin for parachutes to do the job alone, but thick enough that arriving spacecraft must be shielded from intense heating. Every successful Mars landing so far has used some combination of heat shield, parachute, and rocket braking, and the heaviest thing ever landed there, NASA's Perseverance rover, weighs about a tonne.
A crewed mission needs to land dozens of tonnes: habitats, life support, vehicles, and a rocket to leave again. That's a leap of more than an order of magnitude over anything achieved so far. SpaceX's answer is Starship, which is designed to hit the atmosphere belly-first, shed most of its speed through drag, then flip upright and land on its engines. It is an elegant idea that has never been tried on another planet.
Radiation: The Problem With No Easy Fix
On Earth, the planet's magnetic field and thick atmosphere shield us from most cosmic radiation. Astronauts on the International Space Station are still inside much of that magnetic protection. On the way to Mars, there is none.
NASA's Curiosity rover carried a radiation detector during its cruise to Mars in 2011 and 2012. Scientists estimated from its readings that a round trip would expose astronauts to roughly 0.66 sieverts from the journey alone, before counting time spent on the surface. That's many times what radiation workers are permitted in a year, and enough to meaningfully raise lifetime cancer risk.
Shielding helps against some radiation but not the most energetic particles, and heavy shielding costs mass, which is the one thing a Mars mission has least of. Solar storms add acute risk: a crew caught in the open during a major solar event would need to shelter somewhere well protected. No mission architecture fully solves this. It is accepted as a risk and managed.
๐ค Space weather matters beyond Earth. The solar activity our space weather tracker reports, the kind that produces auroras here, is a genuine hazard for anyone travelling between planets.
Living Off the Land
The most important idea in Mars planning has an ugly acronym: ISRU, in-situ resource utilisation. It means making what you need on Mars instead of bringing it from Earth.
The biggest prize is propellant for the trip home. Carrying return fuel all the way from Earth is prohibitively heavy. But the Martian atmosphere is mostly carbon dioxide, and Mars has water ice. Combine carbon dioxide with hydrogen from that water and you can make methane and oxygen, which is exactly the propellant Starship burns. That's no coincidence; SpaceX chose methane partly because it can be made on Mars.
The concept has been demonstrated at small scale. NASA's MOXIE experiment, carried on the Perseverance rover, pulled oxygen out of the Martian atmosphere on repeated runs, producing about 122 grams in total. That proved the chemistry works on Mars. Scaling it up to the tens of tonnes a return flight would need is a completely different engineering problem, and nobody has done it.
Why SpaceX Pivoted to the Moon
For years, Elon Musk described SpaceX's purpose in terms of Mars, and as recently as 2025 he talked about sending uncrewed Starships during the window that opens in late 2026. In early 2026, the company changed course. SpaceX told investors it would prioritise the Moon, describing a lunar settlement as achievable sooner, and would attempt Mars later. The late-2026 Mars window will pass without a SpaceX landing attempt.
The reasoning holds up. The Moon is three days away, not six months. A launch window opens every few weeks, not every two years. Problems can be fixed with a resupply flight. And the hardest technologies Mars needs, above all refuelling Starship in orbit with propellant from tanker flights, are also required for the lunar landers NASA has contracted SpaceX to build. When SpaceX changed plans, Musk himself pointed to orbital refuelling as the main obstacle standing between Starship and Mars.
Watching the Mars hardware get built. Every Starship test flight moves the Mars question forward or back. Our Starship page tracks upcoming flights, and the live launch countdown shows the next one.
A Realistic Timeline
History argues for caution. SpaceX once targeted an uncrewed Mars landing for 2018, then the early 2020s, then 2026. NASA's own crewed Mars plans have drifted toward the late 2030s for decades. None of this is failure, exactly: rockets, landers, and life-support systems have all improved enormously. But the deadlines have consistently arrived before the hardware.
A reasonable reading of where things stand: uncrewed Starship landings on Mars are plausible in one of the next few windows, once orbital refuelling works reliably and the Moon programme has proven the lander. Crewed missions would follow only after cargo landings succeed, likely in the 2030s. A permanent settlement is a far longer project than any single landing.
The honest answer to "when will humans walk on Mars?" is that it depends on a short list of specific, unsolved engineering problems. Watch those, not the announcements: propellant transfer in orbit, heavy landings through a thin atmosphere, radiation protection, and making fuel on the surface. When those are solved, the dates will start meaning something.