| Radii ( m ) | |
| Moon | 1,738,000 |
| Mars | 3,397,000 |
| Earth | 6,378,000 |
Radius is the radius of the body which the spacecraft is launching from. Since orbital velocity is equal to the square root of the product of radius and gravity and since, for a given density, gravity is proportional to the radius; therefore for a given density, orbital velocity is proportional to the radius.
These radii are from Physical Solar System Data. Radius is used to calculate ground orbital velocity, orbital velocity at an altitude and the planetary rotation boost.
ground orbital = sqrt( radius * gravity )
low drag orbital = ground orbital * sqrt( radius / ( radius + low drag altitude ) )
orbital = ground orbital velocity * sqrt( radius / ( radius + altitude ) )
rotation boost = 2 * pi * radius * rotation period * cos( latitude )
This is used in atmospheric spacecraft, multi stage spacecraft, and spacecraft cost.