# How to Perform an Orbital Transfer

Four Methods:Raising Your Orbit with a Hohmann TransferRaising Your Orbit with a Bi-Elliptical TransferLowering Your Orbit with a Hohmann TransferLowering Your Orbit with a Bi-Elliptical Transfer

An orbital transfer is a maneuver used to change the height of your orbit around a planet, moon or other body. Although you'll probably never need to use this knowledge in real life, it comes in very handy if you're using a simulator like the Kerbal Space Program.

## Steps

### Method 1 Raising Your Orbit with a Hohmann Transfer

- 1
**Decide if you should use a Hohmann transfer.**In general, you should use a Hohmann transfer if: desired radius/current radius < 11.95. - 2
**When you reach your periapsis (the lowest point of your orbit), burn prograde (in the direction of travel).**This has the effect of raising your apoapsis (the highest point of your orbit). Burn until your apoapsis reaches the height of your desired orbit. You can calculate the delta-v for this burn using the formula in the picture. - 3
**When you reach apoapsis, burn prograde until your periapsis reaches the desired height.**This should cause your orbit to circularise. Again, you can use the equation to calculate the delta-v for this burn.

### Method 2 Raising Your Orbit with a Bi-Elliptical Transfer

- 1
**Decide if you should use a bi-elliptical transfer.**You should use this method if: desired radius/current radius > 11.95 - 2
**When you reach periapsis, burn prograde until your apoapsis is near the edge of the planet's sphere of influence.** - 3
- 4
**When you reach periapsis, burn retrograde (opposite the direction of motion) until your apoapsis falls to the height of the desired orbit.**

### Method 3 Lowering Your Orbit with a Hohmann Transfer

- 1
**When you reach apoapsis, burn retrograde until your periapsis reaches the height of the desired orbit.**You can use the equations from method one to calculate the delta-v for this and the next step. - 2
**When you reach periapsis, burn retrograde until your apoapsis falls to the height of the desired orbit.**

### Method 4 Lowering Your Orbit with a Bi-Elliptical Transfer

- 1
**When you reach periapsis, burn prograde until your apoapsis is near the edge of the planet's sphere of influence.**You can use the equations from method two to calculate the delta-v needed for these steps. - 2
**When you reach apoapsis, burn retrograde until your periapsis reaches the desired height.** - 3
**When you reach periapsis, burn retrograde until your apoapsis falls to the height of the desired orbit.**

## Tips

- Periapsis: the lowest point of your orbit
- Apoapsis: the highest point of your orbit
- Prograde: the direction in which you are moving (not necessarily the direction in which you are facing)
- Retrograde: opposite the direction in which you are moving
- Sphere of influence: the zone of space in which the gravity of a body is dominant over other gravity sources.

## Warnings

- When performing a bi-elliptical transfer, make sure that your apoapsis doesn't leave the planet's sphere of influence! If it does, you'll escape the planet's gravity and go flying off into space.

## Article Info

Categories: Classical Mechanics | Astronomy