Lunar Orbit Simulator
Set periapsis and apoapsis altitudes to build a simplified lunar orbit. The simulator calculates the semi-major axis, eccentricity, orbital period and speeds at the low and high points of the orbit, then draws the resulting ellipse around the Moon.
What the simulator calculates
The model treats the Moon as a spherical body with a mean radius of 1,737.4 km and uses a lunar gravitational parameter of 4,902.800118 km³/s² from NASA/JPL reference data. For an elliptical orbit, the periapsis and apoapsis radii determine the semi-major axis and eccentricity. The vis-viva equation then gives orbital speed at each point, while Keplerian two-body dynamics provide the period.
Why a real lunar orbit is more complicated
The Moon's gravity field is uneven. Mass concentrations beneath large basins, commonly called mascons, perturb spacecraft orbits. Earth and solar gravity also matter, especially for higher and more unusual cislunar trajectories. NASA has repeatedly used orbit-maintenance strategies and specialised orbit families because a simple two-body ellipse does not capture every long-term effect.
This tool therefore answers a specific educational question: what would the orbit look like in an idealised Moon-spacecraft two-body model? It does not predict where a real spacecraft will be at a future time.
Useful experiments
- Set periapsis and apoapsis both to 100 km to see a low circular orbit.
- Keep periapsis at 100 km and raise apoapsis to see eccentricity increase and apoapsis speed fall.
- Compare orbital periods as you raise the entire orbit.