Hohmann Transfer Orbit

For two circular orbits around the same central body, a Hohmann transfer ellipse is tangent to each orbit at opposite ends. Its periapsis lies on the smaller orbit and its apoapsis on the larger one. The vehicle makes an initial velocity change to enter the ellipse, then coasts through half of that ellipse before a second velocity change circularizes its path at the destination. For a transfer inward, the spacecraft instead reduces speed to enter the lower-energy ellipse and adjusts again on arrival.

In the ideal case of circular, coplanar starting and ending orbits and two impulsive burns, the Hohmann maneuver minimizes the total velocity change among two-impulse transfers. A smaller required velocity change generally means less propellant for a given propulsion system. This does not imply it is the fastest possible route: spacecraft may use other trajectories or additional burns when mission duration, geometry, launch capability or arrival conditions matter.

A transfer between planets is planned around their motion, not simply their locations at launch. For an ideal Earth-to-Mars Hohmann transfer, the spacecraft follows a solar orbit whose perihelion is near Earth's orbital distance and whose aphelion reaches Mars's orbital distance. Mars must be positioned so it arrives near the spacecraft's destination at the same time. NASA's educational treatment gives an approximate 259-day half-ellipse travel time under simplified circular-orbit assumptions; actual mission plans vary and include additional navigation and arrival requirements.

The elementary Hohmann model assumes two-body motion, circular coplanar orbits and instantaneous velocity changes. Real planetary orbits are elliptical and slightly inclined; spacecraft propulsion is finite, and launch and arrival conditions matter. Mission designers therefore use more complete trajectory calculations and may choose paths that trade extra energy for shorter travel, operational flexibility or a required encounter geometry.