Velocity difference between a craft and some other planet.

[cicatrix]

Is there a way I could know the difference in velocities between my craft and some other planet? I select a target then click the speed until 'Target' reading appears but it always shows 0 m/s.

I need this reading to estimate the dV I will need to kill when I'm using a warp drive.

[Pecan]

Velocity relative to what?

If you're interested in your sun-relative orbital velocity while in orbit around, say, Kerbin then it's just, on average, exactly the same as Kerbin's (you are in a sun-orbit with a slight wobble - being your orbit around Kerbin). More accurately, that's +your Kerbin orbital velocity at the prograde point of your Kerbin orbit and -orbital velocity at retrograde. The orbital velocity of your target planet is fixed and presumably none of the usual transfer rules apply if you're using a warp drive? (Might as well use hyperedit?)

[Snark]

If you're using a warpdrive, I think you're basically out of luck-- the game's not designed for that, the UI doesn't really offer any help. Seems like something to suggest to the warpdrive mod author that they add.

If you were flying there conventionally, then the reason you'd care about your relative velocity would be "how big a burn will I need to capture when I get there," and that would be easy to answer: just click on the planet, set your focus there (which will show your trajectory sweeping past it), and drop a maneuver node to see how big it needs to be to get the orbit you want.

[cicatrix]

Velocity relative to what?

If you're interested in your sun-relative orbital velocity while in orbit around, say, Kerbin then it's just, on average, exactly the same as Kerbin's (you are in a sun-orbit with a slight wobble - being your orbit around Kerbin). More accurately, that's +your Kerbin orbital velocity at the prograde point of your Kerbin orbit and -orbital velocity at retrograde. The orbital velocity of your target planet is fixed and presumably none of the usual transfer rules apply if you're using a warp drive? (Might as well use hyperedit?)

Ok, relative to the Sun, I suppose, but direction also matters. My speed vector and the target speed vector, I need the difference in m/s between them. Similarly when you are making an intercept maneuver you get the speed relative to target. I want basically the same thing, but with another planet being my target.

When you use warp drive for direct travel you usually end up near your target with circularization maneuver costing you 12-25 km/s of dV (you retain your initial momentum after the jump). If, from the other hand, I can move to a certain point within the system and wait there for the right moment (when our speeds are nearly matched) and then make the transfer to the target. It's not by any means cheaty. It requires very careful navigation and the mistake is measured in km/s of dV.

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If you're using a warpdrive, I think you're basically out of luck-- the game's not designed for that, the UI doesn't really offer any help. Seems like something to suggest to the warpdrive mod author that they add.

Hmm, I think I will need to calculate it by myself

If you were flying there conventionally, then the reason you'd care about your relative velocity would be "how big a burn will I need to capture when I get there," and that would be easy to answer: just click on the planet, set your focus there (which will show your trajectory sweeping past it), and drop a maneuver node to see how big it needs to be to get the orbit you want.

I would prefer knowing it BEFORE I turn on the drive

[RocketPropelledGiraffe]

The thing is, warp (basically a teleport) actually does cost a lot of delta-v.

When you teleport from Kerbin orbit to Jool, you have 5000 m/s of velocity to kill just from this transfer alone. (Kerbins orbital velocity is ~9 km/s, Jool has ~4 km/s around Kerbol.)

When you do the warp you basically step outside the regime of orbital mechanics for a moment and enter again at a completely different position in phase space - in this example that would be a very high Kerbol orbit close to Jool which you have to reduce to get into orbit.

[DancesWithSquirrels]

Can you just use the navball and look at your velocity relative to your target (toggling orbital/surface/target)? Or isn't that valid past a certain distance or outside the SOI?

Edited May 26, 2015 by DancesWithSquirrels