KSP Orbital Period Planning
Orbital period is the time needed to complete one full path around a body. In Kerbal mission design, it affects transfers, rendezvous timing, relay spacing, and rescue windows. A small change in apoapsis can shift the period enough to miss a target orbit. This calculator helps you test those changes before launch.
Why Semi-Major Axis Matters
The semi-major axis is the average of the apoapsis radius and periapsis radius. Radius means distance from the center of the planet or moon, not height above the surface. That detail is important. KSP shows apoapsis and periapsis as altitudes. The tool adds the body radius first. It then applies the standard orbital period equation.
Advanced Mission Uses
You can use the result to build resonant orbits. For example, a satellite with half the target period will meet the same point every two revolutions. A craft with one third of the period can help place constellations. The comparison field also helps you match a station or carrier. Enter the desired period and review the difference.
Reading The Outputs
The period appears in seconds, minutes, hours, and Kerbin days. Mean motion shows angular travel per second. Periapsis and apoapsis speeds come from the vis-viva equation. These speeds help estimate burn size near each point. Specific orbital energy gives another compact way to compare similar paths.
Practical Accuracy Notes
KSP patched conics are simplified. They ignore many real perturbations. That makes this equation very useful in the game. Still, burns, atmosphere, terrain, and sphere of influence changes can alter the final path. Treat the output as a planning value. Recheck after each maneuver node. For low orbits, keep periapsis above the atmosphere. For custom bodies, enter the correct gravitational parameter and radius. Use consistent distance units. This version works in kilometers, so the gravity value must be in cubic kilometers per second squared. Export the result when you want a quick mission note, contract record, or constellation plan.
Start with known stock values when possible. Switch to custom mode only for modded systems. Save each test with clear notes. That habit makes later corrections easier. Compare tanker routes before committing extra fuel reserves. Exported notes keep long campaigns organized for later planning.