Need documentation on expected input units

[ReeceHumphreys]

Currently there is no documentation on expected input units. Currently the units are as follows:

Current units for input:

• Satellite mass [km]
• Min. Characteristic Length [m]
• Position [m]
• Velocity [m/s]

There needs to be documentation to indicate this. Additionally, ODAP and other python packages tend to use kilometers for position and kilometers per second for velocity. There needs to be a better way to handle this other than changing the units on the Satellite implementation.