to calculate distance traveled for an ascending rocket - what ref frame for velocity to use?

[Drew Kerman]

I have my equation to calculate distance traveled, my only remaining question is whether I should be starting with surface velocity and transitioning at some point to orbital velocity to calculate my acceleration, or exclusively using one or the other

Edited November 14, 2015 by Gaiiden

[Snark]

I'm having trouble understanding your question. What exactly is it that you're trying to accomplish or figure out? (i.e. when you say you want to calculate distance traveled, why do you want it? what do you plan to do with the number?)

For example, if you care about air resistance, then only surface-relative velocity matters; but if you care about orbital mechanics, then only orbital velocity matters. If you care about World First accomplishments for downrange distance traveled, I believe that it's surface-relative distance that matters.

[Gooru]

Well, velocity is allways relativ to a reference point.

And so is the distance traveled.

You simply can´t say "a rocket traveled this distance"

So a geostationary satelite for example does not move at all (as the word stationary implies) if you look from the surface of the planet.

If you look from outside it travels a full circle around the planet.

[MarvinKitFox]

The most *correct* measurement is relative to the stationary point that is the center of the current SOI.

This is not the most convenient!

[Snark]

Which is precisely my point. "Velocity" and "distance" are meaningless terms in isolation, they're always with respect to a particular frame of reference.

So to know the answer, you need to choose what frame of reference you want the answer in.

The OP's question is "which frame of reference should I use?", but he didn't say use for what. Different frames of reference are useful for different purposes. Therefore, "which one is the right one" completely depends on what you want to use the numbers for.

So it's really not possible to provide any answer to the OP that's more useful than "it depends," without finding out that crucial bit of information.

Edited November 13, 2015 by Snark

[Greenspan]

It's pretty clear what he's trying to do, he's integrating the velocity to solve for distance. Technically, it should not matter what reference frame you use, there is always a constant of integration; but you will have to subtract that out to get the answer you want for some reference frame.

If you want to calculate the distance traveled relative to KSC use Surface.

If you want to calculate the distance traveled relative to the center of Kerbin use Orbital.

The result will be the same except Orbital will include the additional distance traveled due to the rotation of Kerbin.

The key is DO NOT change the reference frame in the middle of doing your integration.

[Drew Kerman]

The key is DO NOT change the reference frame in the middle of doing your integration.

I probably should have just focused the question on this. I'll keep my suborbital sounding rockets on surface and anything heading up into space to stay on orbital.

This is all just for the sake of knowing. I like knowing things like it took one of my Minmus probes approx 359,997km (it's in a tooltip for the Last Update text) since leaving the launchpad to get into orbit I've been relying on Persistent Trails to tell me my distance traveled to orbit (then KSPTOT for precise distance traveled once in orbit) but it reduces its output to km every few seconds at long distances, so I wanted to get a more accurate calculation I could log via kOS.

Edited November 14, 2015 by Gaiiden