The Bruce Murray Space Image Library
Hohmann transfer orbit diagram
Filed under explaining technology, trajectory diagrams, Mars
A Hohmann transfer orbit can take a spacecraft from Earth to Mars. The orbit is an elliptical one, where the periapsis is at Earth's distance from the Sun and the apoapsis is at Mars' distance from the Sun. The transfer orbit has to be timed so that when the spacecraft departs Earth, it will arrive at its orbit apoapsis when Mars is at the same position in its orbit. Earth and Mars align properly for a Hohmann transfer once every 26 months.
Original diagram found here.
More information on Hohmann transfer orbits at the Basics of Space Flight
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