# OrbitableVelocity¶

When any Orbitable object returns its VELOCITY suffix, it returns it as a structure containing a pair of both its orbit-frame velocity and its surface-frame velocity at the same instant of time. To obtain its velocity as a vector you must pick whether you want the oribtal or surface velocities by giving a further suffix:

structure OrbitableVelocity
Members
Suffix Type
ORBIT Vector
SURFACE Vector
OrbitableVelocity:ORBIT
Type: Vector Get only

Returns the orbital velocity.

OrbitableVelocity:SURFACE
Type: Vector Get only

Returns the surface-frame velocity. Note that this is the surface velocity relative to the surface of the SOI body, not the orbiting object itself. (i.e. Mun:VELOCITY:SURFACE returns the Mun’s velocity relative to the surface of its SOI body, Kerbin).

Note

Special case instance, the Sun: Because the Sun has no parent SoI body that it orbits around (Kerbal Space Program does not simulate the existence of anything outside the one solar system), that means that the Sun’s surface velocity is just hardcoded to be the same thing as its orbital velocity. This may or may not be entirely correct, but the “correct” answer to the question, “What is sun:velocity:surface?” would technically be “I refuse to answer. That’s an invalid question.” Rather than crash or throw an exception, kOS just returns the same as the orbital velocity in this case.

Examples:

SET VORB TO SHIP:VELOCITY:ORBIT
SET VSRF TO SHIP:VELOCITY:SURFACE
SET MUNORB TO MUN:VELOCITY:ORBIT
SET MUNSRF TO MUN:VELOCITY:SURFACE


Note

At first glance it may seem that Mun:VELOCITY:SURFACE is wrong because it creates a vector in the opposite direction from Mun:VELOCITY:ORBIT, but this is actually correct. Kerbin’s surface rotates once every 6 hours, and the Mun takes a lot longer than 6 hours to orbit Kerbin. Therefore, relative to Kerbin’s surface, the Mun is going backward.