Space Travel Calculator

About orbital space travel

Travel between two circular Earth orbits can be approximated with a Hohmann transfer, a fuel-efficient maneuver made from half of an elliptical orbit. The spacecraft first performs a tangential burn to leave its initial circular orbit and enter the transfer ellipse. At the opposite apsis, a second tangential burn circularizes the trajectory at the target radius. This calculator adds the magnitudes of those two velocity changes to report total ideal delta-v. The calculation uses Earth's standard gravitational parameter, 398600.4418 km³/s², and orbit radii measured from Earth's center rather than altitude above the surface. A spacecraft at 300 km altitude therefore has a radius of roughly 6671 km after adding Earth's mean radius. Circular and transfer-orbit speeds follow the vis-viva equation. Transfer time is half the period of the ellipse whose semi-major axis is the average of the initial and target radii. Propellant is estimated with the Tsiolkovsky rocket equation. Specific impulse measures engine efficiency in seconds, and dry spacecraft mass is treated as the final mass after the maneuver. The calculator solves for the propellant needed to provide the ideal transfer delta-v. Higher specific impulse sharply lowers propellant demand, while a larger delta-v increases the required mass ratio exponentially. The estimate assumes one propulsion system, constant effective exhaust velocity, and no unusable residual propellant. A real mission needs additional delta-v for launch dispersions, plane changes, rendezvous, navigation corrections, finite-duration burns, station keeping, atmospheric drag, gravity losses, and safety reserves. Hohmann transfers also assume coplanar circular orbits and impulsive burns. They are not necessarily fastest, and they may be unsuitable when time, eclipse, radiation, or operational constraints dominate. Use this result for education and preliminary mission comparison. Detailed planning requires high-fidelity trajectory propagation, current celestial ephemerides, vehicle performance margins, and review by qualified mission analysts. Radius inputs must remain within physically meaningful Earth-orbit regimes; trajectories intersecting the planet are not viable missions.

Space transfer examples

How to estimate a space transfer

1. Convert both orbit altitudes to radii measured from Earth's center.
2. Enter initial and target radii in kilometres.
3. Enter final dry mass and propulsion specific impulse.
4. Select Calculate to estimate ideal delta-v, transfer time, and propellant.