Example Data Table
| Origin |
Target |
Current Phase |
Parking Altitude |
Expected Phase |
Transfer Time |
| Kerbin |
Duna |
0° |
80 km |
44.36° |
302.04 Kerbin days |
| Kerbin |
Eve |
0° |
80 km |
305.87° |
170.35 Kerbin days |
| Kerbin |
Jool |
0° |
80 km |
96.58° |
1122.81 Kerbin days |
Formula Used
The calculator uses a circular Hohmann transfer model. It estimates a practical transfer window, not a perfect n-body trajectory.
Transfer semi major axis: a = (r1 + r2) / 2
Transfer time: T = π × √(a³ / μ)
Mean motion: n = √(μ / r³)
Required phase angle: φ = 180° - n2 × T
Synodic period: S = 2π / |n1 - n2|
Wait time: wait = angular difference / relative angular speed
Parking burn estimate: burn = √(v∞² + vesc²) - vcircular
How to Use This Calculator
Select an origin body and a target body. Enter the current phase angle from your map view. Use positive degrees when the target is ahead along its orbit.
Enter your current UT day. Add departure and arrival parking orbit altitudes. Leave custom orbit fields empty for stock values. Use them only for modded systems or special challenges.
Press the calculate button. The result appears above the form. Review the desired phase angle, wait time, transfer duration, and burn estimates. Download the table when you need records.
Why Transfer Windows Matter
A transfer window is the moment when two orbits line up. In Kerbal Space Program, a good window reduces wasted fuel and makes the arrival cleaner. This calculator uses a Hohmann style estimate. It treats the origin and destination as circular paths around the same central body. That keeps the method fast, readable, and useful for mission planning.
What the Result Means
The desired phase angle tells where the target should sit compared with the origin. A positive angle means the target is ahead along its orbit. The wait time shows how long until that angle repeats from your current phase. The transfer time estimates the coast time after the ejection burn. The synodic period shows how often similar windows return.
Burn Planning Notes
The listed heliocentric burn values describe the ideal change in orbital speed around the star. The departure and capture estimates use parking orbit altitude and body gravity. They are patched conic approximations, so real launches may differ. Inclination, aerobraking, moon encounters, and piloting accuracy can change the final cost. Use the value as a planning guide, not as a perfect autopilot command.
Better Mission Workflow
Start with stock Kerbin to Duna data. Change the current phase angle to match your map view. Enter your parking orbit altitude. Then compare several upcoming windows. Choose the one that fits your mission supplies and crew schedule. Export the table before launch. Keep the file with your craft notes, staging plan, and maneuver node settings. For difficult targets, test a save first. Small correction burns after departure are normal. A mid course adjustment can save a messy arrival. This page also accepts custom orbit radii and central gravity. That makes it useful for modded systems, unusual challenges, or educational examples. Always check units before trusting the output. Orbit radii use kilometers in the form. Calculations convert them internally to meters. The result table returns common mission values in days, degrees, and meters per second. Record the chosen window beside your contract goal. Note the target altitude and planned inclination. When the craft is heavy, add a fuel reserve. When the target is small, add more correction budget. Patient launches often beat rushed burns in careful planning.
FAQs
What is a KSP transfer window?
It is the launch timing when the target body is at a useful phase angle. Launching near that angle reduces fuel waste and improves arrival planning.
What does phase angle mean?
Phase angle is the angular gap between the origin and target. In this calculator, positive degrees mean the target is ahead along its orbit.
Why is my desired phase above 180 degrees?
That usually happens for inward transfers. It means the target is effectively behind the origin when measured along the orbit direction.
Does this match every in-game transfer exactly?
No. It uses a circular Hohmann estimate. Inclination, eccentricity, piloting, aerobraking, and moon encounters can change the final result.
What is a Kerbin day here?
This page uses a six hour Kerbin day. The internal time conversion is based on 21,600 seconds per Kerbin day.
Can I use custom orbit radii?
Yes. Enter custom origin and target orbit radii in kilometers. Leave those fields blank when you want the stock body values.
What is the synodic period?
It is the time between repeated alignments of two orbiting bodies. Similar transfer windows return after about one synodic period.
Why are burn estimates approximate?
The page uses patched conic math and parking orbit estimates. Real burns depend on ascent profile, maneuver accuracy, inclination, and capture strategy.