Programming Orbit Expansion: Change Radius w/ Centripetal Force

[rrfoote]

I am programming a game that involves objects orbiting in 3d space circularly around an axis. I have the orbits working for a fixed radius using centripetal forces, however, I want to be able to change the radius while the program is running. I have tried to just make the magnitude of the centripetal force = (mass*(velocity^2))/radius, however this fails if i change the radius during the program. What forces should I use to change the radius of the orbit?

 

[rcgldr]

You need at least two impulses to change the size of a circular orbit. The first impulse makes it an ellliptical orbit, the second impulse makes it a circular orbit again at a different radius.

http://en.wikipedia.org/wiki/Hohmann_transfer_orbit

 

[Fewmet]

I am programming a game that involves objects orbiting in 3d space circularly around an axis. I have the orbits working for a fixed radius using centripetal forces, however, I want to be able to change the radius while the program is running. I have tried to just make the magnitude of the centripetal force = (mass*(velocity^2))/radius, however this fails if i change the radius during the program. What forces should I use to change the radius of the orbit?

In reality, increasing the velocity increases the orbit radius. The orbital velocity equals the square root of the Universal Gravitational Constant x mass of attracting body (like the sun) divided by the radius of the orbit.

If the program is set up so that you need to change a force to change orbital radius, a lower centrifugal force will give a greater radius.