What IS Prograde?

[Tompete Kerman]

So, I'm trying to develop a sci-fi inspired "Inertial Brake" mod, that will ideally find the current vessels prograde vector, and it's speed, and then "magically" apply a PID-controlled counterforce/resistance to the craft to slow it to a set speed. My issue is figuring out exactly which of the vaguely defined variables in the vessel API is what I'm looking for. So far the most likely candidates are srf_Velocity, srfRelRotation, and srfSpeed. If anyone has any insight/experience with these, or has an idea on how to find these variables, I'd greatly appreciate the guidance.

[HebaruSan]

2 hours ago, Tompete Kerman said:

srf_Velocity, srfRelRotation, and srfSpeed

I couldn't find those in the API docs, but a web search found them on the out of date wiki docs. Might want to check the up to date ones:

https://kerbalspaceprogram.com/api/class_vessel.html

My money's on GetObtVelocity() or velocityD.

[Tompete Kerman]

10 hours ago, HebaruSan said:

...out of date wiki docs...

My money's on GetObtVelocity() or velocityD.

That would explain a lot of my confusion and frustration. As for the variables you mentioned, I can logically suss out what GetObtVelocity() would get me, but velocityD isn't as well described. Can you help pre-enlighten me as to what it is before I experiment with it?

[HebaruSan]

15 minutes ago, Tompete Kerman said:

velocityD isn't as well described. Can you help pre-enlighten me as to what it is before I experiment with it?

I assume it's the velocity represented as a Vector3d, SQUAD's 64-bit vector class.

[Tompete Kerman]

I suppose that would make sense, I'll have to finagle with it a bit when I'm back at my workstation. In the meantime, any more insight from anyone is greatly encouraged.