Hohmann Transfer Orbit

A Hohmann transfer orbit is the cheapest way, in terms of fuel, to move a spacecraft from one circular orbit to a larger or smaller one around the same body. It is the quiet workhorse behind everything from delivering TV satellites to sending rovers to Mars.

Quick facts

• What it is: a two-burn maneuver between two circular, coplanar orbits (orbits in the same flat plane) of different size around the same central body.
• First described: by German engineer Walter Hohmann in his 1925 book Die Erreichbarkeit der Himmelskörper (The Attainability of Celestial Bodies).
• LEO to GEO (Earth): from about a 300 km low orbit up to geostationary altitude of 35,786 km; total delta-v (the change in speed an engine must supply) about 3.88 km/s; coast time about 5.3 hours.
• Earth to Mars (around the Sun): a transfer ellipse from about 1 AU at Earth to about 1.52 AU at Mars, where an AU (astronomical unit) is the average Earth-Sun distance; coast about 8 to 9 months.
• Launch windows for Mars: roughly every 26 months (NASA cites about 25 months for Mars, 19 for Venus).
• Plane changes: the classic transfer stays in one plane; any change of orbital tilt (inclination) costs extra fuel.

How it works

The maneuver uses two short engine burns, both fired along the direction of travel so they change only speed, not heading.

First, in the lower orbit, the spacecraft fires forward (prograde). This adds energy and stretches its circular path into an ellipse whose far point, the apoapsis, just touches the higher target orbit. Then the engine shuts off and the craft coasts for half of that ellipse, climbing and naturally slowing as it trades motion for altitude, exactly as Kepler’s laws and the conservation of energy predict. Think of a ball thrown upward: it rises and slows, then needs a second push to keep moving at the top. At apoapsis, where the ellipse grazes the destination orbit, the craft fires forward again to speed up and round the path into the new circular orbit.

To reach a lower or inner orbit, such as toward Venus, the burns are fired backward (retrograde) to lower energy instead. For trips between planets, the planets’ paths around the Sun act as the two circular orbits, and the burn must be timed so the destination planet arrives at the meeting point at the same moment. That timing is what creates launch windows.

Why it’s used

It uses the least propellant for moving between two circular orbits, and propellant is the single biggest cost and mass driver of a mission. By changing only the size of the velocity and not its direction, with just two burns, the spacecraft rides the lowest-energy ellipse that touches both orbits. That keeps missions affordable and within reach of existing rockets. It is the default method for lifting satellites from low orbit to geostationary orbit, where the Geostationary Transfer Orbit is simply the first half of a Hohmann transfer, and for low-cost trips between planets when a longer travel time is acceptable.

Notable missions

• Geostationary satellites: launchers such as Ariane 5 inject payloads into a Geostationary Transfer Orbit, the first leg of a Hohmann transfer, then an apogee burn circularizes the orbit at GEO.
• NASA Mars rovers: Spirit, Opportunity, and Curiosity flew Hohmann minimum-energy Earth-to-Mars transfers, coasting roughly 7 to 9 months.
• 2020 Mars window: the UAE’s Hope (Al-Amal) orbiter and China’s Tianwen-1 launched onto Earth-to-Mars Hohmann trajectories.
• India’s Mars Orbiter Mission (Mangalyaan): used a Hohmann-like minimum-energy transfer to Mars.
• Early probes: Mariner and Viking used Hohmann-type paths to Mars and the inner planets.

The trade-off is simple: a Hohmann transfer saves fuel but takes time, from hours for low-orbit-to-geostationary trips to about nine months for Mars. When speed matters more than economy, mission planners spend extra propellant on faster, higher-energy routes instead.