Planetary Launch Window Calculator
Find Hohmann transfer launch windows between any two solar system bodies.
Origin
Destination
Opens Nov 18, 2026 · Optimal Dec 3, 2026
Next window — Hohmann transfer from Earth to Mars
- Window opens
- Nov 18, 2026
- Optimal departure
- Dec 3, 2026
- Window closes
- Dec 18, 2026
- Estimated arrival
- Aug 19, 2027
- Transit time
- ~259 days (8.5 months)
- Next window after this
- ~25 months
Next 10 Earth–Mars transfer opportunities
| Optimal Departure | Arrival | Transit | Difficulty |
|---|---|---|---|
| Dec 3, 2026 Next | Aug 19, 2027 | 259 d | Moderate |
| Jan 6, 2029 | Sep 22, 2029 | 259 d | Moderate |
| Feb 8, 2031 | Oct 25, 2031 | 259 d | Moderate |
| Mar 17, 2033 | Dec 1, 2033 | 259 d | Moderate |
| May 8, 2035 | Jan 22, 2036 | 259 d | Moderate |
| Jul 26, 2037 | Apr 11, 2038 | 259 d | Moderate |
| Oct 5, 2039 | Jun 20, 2040 | 259 d | Moderate |
| Nov 19, 2041 | Aug 5, 2042 | 259 d | Moderate |
| Dec 25, 2043 | Sep 9, 2044 | 259 d | Moderate |
| Jan 26, 2046 | Oct 12, 2046 | 259 d | Moderate |
Comparison of transfer windows from Earth to each body
| Body | Next Window | Transit | Difficulty |
|---|---|---|---|
| Mercury | Aug 12, 2026 | 105 d | Hard |
| Venus | Jul 27, 2026 | 146 d | Moderate |
| Mars | Dec 3, 2026 | 259 d | Moderate |
| Ceres | Feb 5, 2027 | 472 d | Hard |
| Jupiter | Oct 29, 2026 | 998 d | Hard |
| Saturn | Jun 12, 2026 | 2208 d | Hard |
| Uranus | Aug 4, 2026 | 5858 d | Hard |
| Neptune | Jun 1, 2027 | 11182 d | Hard |
Click a row to switch destination.
How It Works
A Hohmann transfer orbit is the most fuel-efficient two-burn path between two circular orbits. A spacecraft departs the origin body at the correct phase angle, coasts along a half-ellipse, and arrives at the destination. Transit times range from ~100 days (Earth–Venus) to over a decade (Earth–Neptune via Hohmann).
Launch windows only open when the destination is at the right position for the spacecraft to arrive on time. These opportunities recur at the synodic period of the two bodies — the time for them to return to the same relative configuration.
ΔV (delta-v) is the change in velocity required to complete the transfer. It determines how much propellant a mission needs. Easy missions (<5 km/s total) require relatively little fuel; hard missions (>8 km/s) — like Earth–Mercury — demand either very powerful rockets or gravity assists from intermediate bodies.
This calculator uses simplified Keplerian orbital elements (NASA/JPL J2000 model) with a fixed-phase-angle Hohmann approximation. Windows may differ from actual mission dates by several weeks for low-eccentricity bodies or up to 90 days for high-eccentricity bodies like Mercury. Real mission planning uses numerical integration and porkchop-plot C3 analysis.
Related Tools
Frequently Asked Questions
What is a planetary launch window?
A launch window is the period when a spacecraft can depart Earth and arrive at another planet using a Hohmann transfer orbit — the most fuel-efficient two-burn path. The window opens when the planets are at the correct phase angle so the spacecraft arrives at the destination orbit when the target planet is there.
How often do Mars launch windows occur?
Every ~26 months, which is Mars's synodic period (the time for Earth and Mars to return to the same relative positions). This is why Mars missions cluster every two years — NASA's Perseverance (2020), Curiosity (2011), and Opportunity (2003) each launched in different windows.
What is delta-v (ΔV)?
Delta-v is the change in velocity (in km/s) required to complete a maneuver. It determines fuel requirements — the rocket equation means exponential fuel growth with ΔV. Earth-to-Mars requires roughly 3.6–4.0 km/s departure + ~0.9 km/s arrival = ~4.5–5.0 km/s total for a Hohmann transfer.
What is a Hohmann transfer orbit?
An elliptical orbit that connects two circular orbits using exactly two engine burns — one to leave the first orbit, one to enter the second. It is the most fuel-efficient path between two orbits but is not the fastest. Faster transfers (like those used for crewed missions) require more ΔV.