Mars transfer window — next departure
Spacecraft cannot leave for Mars whenever they like; they depart only in transfer windows that open about every 26 months, when Earth and Mars are in the right positions. The next one runs from late 2028 into early 2029, and Europe's Rosalind Franklin rover and China's Tianwen-3 are aiming for it.
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The story
Earth and Mars come close to each other about once every 26 months. A spacecraft that leaves during the transfer window that opens at that time can reach Mars using the least fuel. The route it follows is called a Hohmann transfer orbit, a stretched loop that goes half-way round the Sun. The next window runs from late 2028 into early 2029; miss it, and the next chance is early 2031.
The reason windows exist is simple. Earth goes round the Sun in 365 days and Mars in 687. Earth, on the inside track, moves faster and catches up with Mars about once every 780 days. The lowest-fuel route only works if the two planets stand at a particular angle at the moment of departure. That is why launches to Mars bunch into a few weeks, and missing them means waiting more than two years.
The window at the end of 2026 went largely unused, after SpaceX said in February 2026 that it would push its Mars plans back five to seven years and focus on the Moon. One mission aiming for the 2028 window is the European Space Agency's Rosalind Franklin rover, which is planned to launch in October 2028 and land on Mars in 2030. China's Tianwen-3 is also due to leave in this window, with a plan to bring Martian soil and rock back to Earth in 2031.
The answer to the question of when people will go to Mars also depends on this list of windows, because even a ready rocket has to wait for a window to open. Move the orbit view to December 2028 and the positions of Earth and Mars are reproduced, showing at a glance why this period is a window. Keep the replay running and Earth, on the inner orbit, can be seen chasing and overtaking Mars on the outer one.
Mission goals
Transfer windows are the calendar of Mars exploration. Rovers, orbiters and plans for crewed missions all set their budgets and building schedules to this 26-month rhythm, and a single delay pushes a whole mission back by more than two years. The Rosalind Franklin rover is an example. It was due to leave in 2022 in partnership with Russia, but after Russia's invasion of Ukraine that partnership ended and the launch slipped to 2028.
For a journey with people on board, the windows matter even more. Getting to Mars takes about seven to nine months, the crew must then wait on Mars for more than a year until a window for the return opens, and the trip home takes several more months. A round trip therefore lasts about two and a half years. Faster routes exist, but they need far more fuel.
Windows also differ from one another. Because Mars follows a slightly stretched orbit, its closest distance to Earth varies from about 56 million km to around 100 million km. Years when Mars comes especially close arrive every 15 or 17 years: 2003 and 2018 were such years, and the next is 2035. 2028 to 2029 is nearer the far end of the range. That is why the weight a given rocket can send changes from window to window.
Mission chronology and background
The Hohmann transfer is the lowest-fuel route worked out by the German engineer Walter Hohmann in 1925. Real missions adjust the route a little for their arrival date or for communications, but the window opens at almost the same time. Mariner 4 in 1964, Viking in 1975, Curiosity in 2011 and Perseverance in 2020 all left for Mars in windows like these.
In the July 2020 window three missions left together: America's Perseverance, China's Tianwen-1 and the United Arab Emirates' Hope. The 2022 window, by contrast, was left empty when Rosalind Franklin dropped out. SpaceX once aimed for the 2024 window, then moved to 2026, and in the end did not use the 2026 window either. Windows come round regularly, but only missions that are ready can use them.
Ways to depend less on windows are being studied. Engines that use a nuclear reactor to heat their propellant, or that run on electricity made from sunlight, could allow wider windows and shorter trips. No mission has yet reached Mars using such engines, though. Until one does, the Martian calendar runs in steps of 26 months.
Where to see it — sky and simulator
A transfer window is an event on the calendar more than an event in the sky. Still, as the window opens Mars is getting closer to Earth and growing brighter at night. In December 2028 Mars rises in the east late at night and is seen in the pre-dawn sky; by spring 2029, when it is closest to Earth, it rises at sunset and shines brightly all night like a red star.
Move the orbit view to 20 December 2028 and follow Mars, and the arrangement just before Earth on the inner orbit overtakes Mars is reproduced. Speed up the playback and the same arrangement comes round again about every 26 months. It is a direct way to see why the windows return so regularly. It also shows that no window opens while the two planets are far apart on opposite sides of the Sun.
Select Mars in the sky view to see what time it rises, how high it climbs and the path it takes across the sky over the day from your location. Step the date forward a few weeks at a time, and Mars is reproduced rising earlier and growing brighter from the time the window opens until spring 2029. Mars is brightest around its closest approach to Earth, then fades again as Earth pulls ahead.
See this for yourself — replay the moment in the orbit view
FAQ
Why can't we leave for Mars any time?
The lowest-fuel route only works if Earth and Mars stand at a particular angle at departure. Because the two planets circle the Sun at different speeds, that arrangement comes round only about once every 26 months.
How long does the trip take?
About seven to nine months on the lowest-fuel route. A crewed round trip, including the wait on Mars for a return window, takes about two and a half years.
Are any missions planned for the 2028 window?
The European Space Agency's Rosalind Franklin rover is planned to launch in October 2028 and land in 2030, and China's Tianwen-3 is due to leave in this window and return Martian samples in 2031. No date has been set for a Starship flight to Mars.
When is the window after this one?
Early 2031, then spring 2033. Windows come round about every 26 months.
Related
- ExoMars — Rosalind Franklin launch
- Tianwen-3 launch — Mars sample return
- MMX launch — Phobos sample return
- Perseverance launch
- Mars — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.