Hohmann Transfer Calculator

The calculator first finds the semi-major axis of the elliptical transfer orbit, a = (r1 + r2) / 2, then uses the vis-viva equation, v = √(GM(2/r − 1/a)), to find the spacecraft's speed on that ellipse at both r1 and r2. Comparing those speeds to the circular orbital speeds at r1 and r2 gives the size of each burn: Δv1 at departure and Δv2 at arrival. Adding them gives the total delta-v — the standard measure of how much propellant the maneuver costs, independent of the spacecraft's actual mass. The transfer time follows from Kepler's third law: half the period of an orbit with semi-major axis a, or π√(a³/GM).

The calculator takes three inputs: the central body's mass in kilograms, and the two circular orbit radii in kilometers, measured from the center of the body (not its surface). For Earth orbits, remember to add Earth's radius (~6,371 km) to the satellite's altitude above the surface. Because masses and radii for astronomical bodies span many orders of magnitude, the mass field accepts scientific notation (e.g. 5.972e24). The transfer works in either direction — enter a larger r1 than r2 to compute a de-orbit transfer instead of a raise.

This calculator assumes both orbits are circular and coplanar (no inclination change) and that each burn is instantaneous (an idealization — real burns take finite time and lose some efficiency to gravity losses). It also assumes a two-body system with no perturbations from other bodies. For very large radius ratios (roughly above 11.94), a three-burn bi-elliptic transfer can actually use less total delta-v than a Hohmann transfer, though it takes longer. For everyday satellite-repositioning and interplanetary-transfer estimates, though, the Hohmann transfer formula is the standard first-order approximation used throughout orbital mechanics.