Calculator Inputs
Use altitude mode for above-surface values or radius mode for center-to-spacecraft orbital radius values.
Example Data Table
| Scenario | Body | Input mode | Start (km) | Target (km) | Burn 1 (km/s) | Burn 2 (km/s) | Total Δv (km/s) | Time (hours) |
|---|---|---|---|---|---|---|---|---|
| LEO to GEO | Earth | Altitude | 400 | 35,786 | 2.397473 | 1.456487 | 3.853959 | 5.2913 |
| 200 km to 1,000 km | Earth | Altitude | 200 | 1,000 | 0.219996 | 0.213771 | 0.433766 | 0.8057 |
| Mars parking to high orbit | Mars | Altitude | 250 | 17,032 | 1.037511 | 0.651033 | 1.688545 | 5.5689 |
Formula Used
Transfer semi-major axis: at = (r1 + r2) / 2
Circular orbit speed: v = √(μ / r)
Transfer speed at departure orbit: vt1 = √[μ × (2 / r1 − 1 / at)]
Transfer speed at arrival orbit: vt2 = √[μ × (2 / r2 − 1 / at)]
Burn magnitudes: Δv1 = vt1 − vc1, Δv2 = vc2 − vt2
Total mission delta-v: |Δv1| + |Δv2|
Transfer time: t = π × √(at3 / μ)
Optional propellant estimate: mf = m0 / eΔv / (Isp × g0), propellant = m0 − mf
This calculator assumes two impulsive burns between coplanar circular orbits around the same central body. It does not model finite burn losses, plane changes, atmospheric drag, or multi-body gravity effects.
How to Use This Calculator
- Select the central body preset or choose custom values.
- Pick altitude mode for above-surface values, or radius mode for full orbital radius.
- Enter the starting and target orbit values in kilometers.
- Review or edit the body radius and gravitational parameter if needed.
- Add spacecraft mass and specific impulse to estimate propellant demand.
- Press Calculate Transfer to show the result section above the form.
- Use the export buttons to download CSV or PDF summaries.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates the two burn magnitudes, total delta-v, transfer time, phase angle, and optional propellant usage for a classic Hohmann transfer between circular coplanar orbits.
2. When is a Hohmann transfer appropriate?
It is appropriate when both orbits are circular, lie in the same plane, and the mission favors minimum impulsive delta-v over the fastest travel time.
3. Can I use altitude instead of orbital radius?
Yes. Altitude mode automatically adds the central body radius to each altitude so the orbital mechanics equations use full center-to-spacecraft radius values.
4. Why are some burns labeled retrograde?
A retrograde label appears when the signed burn is negative. That happens in descending transfers, such as moving from a higher circular orbit to a lower one.
5. Does the calculator include plane changes?
No. Plane change costs are excluded. If the orbit inclination changes, you need additional delta-v analysis beyond the simple Hohmann transfer model.
6. How is propellant mass estimated?
The propellant estimate uses the Tsiolkovsky rocket equation with your spacecraft mass, specific impulse, and standard gravity to convert total delta-v into mass consumption.
7. What units does the calculator expect?
Orbital distances use kilometers, the gravitational parameter uses cubic kilometers per second squared, velocity uses kilometers per second, and propellant outputs use kilograms.
8. Why does transfer time remain large for outer orbits?
The half-ellipse gets much larger as target radius increases. A larger semi-major axis raises orbital period, so the transfer arc takes more time.