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The next window opens around Nov 4, 2026, and the crossing takes about 265 days. Both are solved from the real orbits when the page loads — and the path is drawn above, framed on the flight.
Thu, August 13, 2026
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Distances from the sun are in AU — one AU is the Earth’s average distance, 149,597,870 km — and the angle is where the body sits around its orbit, measured from the March equinox direction.
The next one opens around Nov 4, 2026 and the crossing takes about 265 days, arriving Jul 27, 2027. After that you wait roughly 25 months for the next one — that is how long Earth takes to lap Mars.
| Leave | Arrive | Flight | Speed change | Burn from low Earth orbit | |
|---|---|---|---|---|---|
| Next window | Nov 4, 2026 | Jul 27, 2027 | 265 d | 3.08 km/s | 3.63 km/s |
| The one after | Dec 6, 2028 | Aug 14, 2029 | 252 d | roughly the same — the geometry repeats | |
A rocket cannot point at Mars and fire. It has to leave Earth on an orbit around the sun whose far side touches Mars’s orbit — half an ellipse — and it has to leave at the moment when Mars will have arrived at that far side by the time the ship gets there. That is what a launch window is, and it is why they come round only every 25.0 months.
Set Launch to: Mars on the rocket launches page to see the ellipse, where Mars is on launch day, and where it will be on arrival. Click the date to fly it.
It is a minimum-energy transfer: the cheapest possible path, half an ellipse with Earth’s orbit at one end and the target’s at the other, solved against where the planets really are — so the arrival lands on the planet’s real distance from the sun and its real position on the day it gets there, not on a circle standing in for its orbit.
It is not a mission plan, and three things are left out on purpose. The orbits are treated as flat, so the real inclinations — Mars is tilted 1.85°, Jupiter 1.3° — cost a plane change this ignores. Real missions trade fuel for a faster arrival, so they leave within days or weeks of these dates rather than exactly on them. And anything going past Jupiter usually steals speed from a planet on the way instead of buying it with fuel, which changes both the date and the path.
What it gets right is the thing worth teaching: why the window exists, why it comes round on the cadence it does, and why the cost of the trip is set by where two planets happen to be rather than by how far apart they are.
The cheapest route column is what a minimum-energy transfer from the same window would have taken, solved from the orbits rather than looked up — so the difference is the whole argument for gravity assists.
| Mission | Launched | Arrived | Actual flight | Cheapest route | Difference | Flybys on the way |
|---|---|---|---|---|---|---|
| Mariner 4 | Nov 28, 1964 | Jul 15, 1965 | 229 d | 257 d | 28 days faster | none |
| Viking 1 | Aug 20, 1975 | Jul 20, 1976 | 335 d | 281 d | 54 days slower | none |
| Mars Pathfinder | Dec 4, 1996 | Jul 4, 1997 | 212 d | 255 d | 43 days faster | none |
| Mars Reconnaissance Orbiter | Aug 12, 2005 | Mar 10, 2006 | 210 d | 282 d | 72 days faster | none |
| Curiosity | Nov 26, 2011 | Aug 6, 2012 | 254 d | 260 d | about the same | none |
| Perseverance | Jul 30, 2020 | Feb 18, 2021 | 203 d | 280 d | 77 days faster | none |
This is the flight. Mars itself — how big, how heavy, what goes round it and what is still unexplained — is its own page. Or see every destination and how they compare.
The date, the zoom, the span, the speed, the layers and any flight path are all in the address bar, so copying the URL shares exactly what is on screen. Set it up above, then take the link — it is the quickest way to hand a class one specific thing to look at.
This one is about the whole system. If the question is where the sun and the moon are from where you are standing — what time the sun comes up, why tonight's moon is the shape it is — that is the Sun, Earth & Moon movement simulator, which has a page for every city and a slider over a day, a week or a month. Between the two is the three bodies moving together — Earth going round the sun, the moon going round the Earth, on one screen and openly not to scale, keeping only the real ratio between the two periods.
And for why any of it stays up: the orbital velocity simulator takes one planet and lets you set its distance and its sideways speed by hand, so you can watch the balance that holds every orbit here — and break it, into an ellipse, an escape, or a fall into the sun.
Also: the classroom guide · sunrise & sunset by city · moon phase & moonrise · lunar eclipses · how the positions are worked out
When is the next launch window to Mars? The next minimum-energy window opens around Nov 4, 2026, with arrival about Jul 27, 2027 — a flight of roughly 265 days. That date is not written into this page: it is solved from the real orbits when the page is built and again in your browser when it loads.
How often does a window to Mars come round? About every 25 months. That is the synodic period — how long Earth takes to lap Mars — and only at that point are the two planets positioned for the cheapest transfer again.
How much speed does it take to reach Mars? About 3.08 km/s of change to leave Earth's orbit around the sun, or about 3.63 km/s as a burn from a 300 km parking orbit — less, because up there you are already moving fast.
Why can't a rocket just fly straight at Mars? Because it is already moving at about 30 km/s sideways, along with the Earth. A spacecraft does not leave the solar system's rules when it leaves the launch pad: it stays in orbit around the sun, and the only thing an engine can do is change the shape of that orbit. Getting to Mars means enlarging the orbit until its far side reaches Mars's — and then arranging to be there when Mars is.
Doesn't the curved path cost more fuel than a straight one? It costs far less — the curve is the free part. A rocket only spends fuel when it changes its speed or direction, and on this route the engine fires twice: once to leave, once to arrive. In between it is switched off for months, and the sun's gravity does all of the turning. A straight line is what an object does when NO force acts on it, and the sun is pulling the whole time, so holding a straight line to Mars would mean thrusting continuously for the entire trip just to cancel that pull — and cancelling the 30 km/s sideways motion the spacecraft inherited from Earth before it even started. The curve is not a detour. It is the shape of falling.