Delta-v and upper stages

[valenti_scott]

Hello-
I've noticed something about the delta-v of upper stages of rockets. In the VAB, it may say the delta-v of an upper stage is say 100.

But then when the rocket actually gets out into space, the delta-v which is shown is about four-times that shown in the VAB, or about 400.

I assume the VAB calculation takes into account the effect of being on the surface of Kerbin, with the detriment of the thick atmosphere? Then when you get into orbit the delta-v shows a higher value?

Or is it something else? Has anyone noticed this?
-Scott

[vine]

It's what you suspect it to be. there's icons/buttons to change the orbiting body to which the dv will be computed, you can select altitude also. i don't have it in front of me but it's there where you get the readouts. just click around with curiosity.

[Quizzical]

Delta-v computations always assume that you'll stay at whatever altitude you're currently at. In the VAB, the default is sea level on Kerbin, but you can adjust it through the menus. In most cases, the vacuum numbers are what I look at, but I'll only use rockets intended for lower stages in thick atmospheres, so there isn't very much loss there other than on Eve.

[valenti_scott]

Ah, yes, I didn't notice the check-boxes, thx.

[GunsForBucks]

In the builder is a DV tool.

In the lower right click on the DV tab and you can set for vacuum or any altitude for any planet/celestial body so you can build it properly.

[koimeiji]

alternatively, install kerbal engineer redux or mechjeb 2 to get much more accurate and readable dV values

not to say that KSP's default dV count is bad or anything...it's just vastly inferior to the above two options

[vine]

Originally posted by 76561198050769806:

alternatively, install kerbal engineer redux or mechjeb 2 to get much more accurate and readable dV values

not to say that KSP's default dV count is bad or anything...it's just vastly inferior to the above two options

ideally both :)

[AIM-9X]

Yes, the delta-v calculated in the VAB is based off of the surface of kerbin, however you can change this. This is usually because upper stages tend to be more fuel efficent with low thrust (like the terrier, poodle, or the cheetah) meaning that in atmosphere, they have extremely low delta-v.