From a 100km LKO orbit to jool needs a dV of 1986 m/s

From a 47,000km orbit (ie, where minmus is), one needs 2584 m/s!!!

This doesn't make sense to me...

This should also mean that a burn from heliocentric orbit to Jool will take more dV than a burn from LKO.

If:

A = burn to heliocentric orbit/a orbit to the edge of kerbin's SOI

B = the transfer burn from High SOI/heliocentric orbit

C = The transfer burn from LKO

I would expect that A+B > C, but that B < C, and A<C

If I refuel after A, then my craft should be able get by with lower dV capabilties... but this seems to be wrong.

But then I also have to consider some other things... like the oberth effect from orbiting Minmus, doing a bi-elliptic transfer (from minmus, lower PE to just above kerbin, then burn from there, but then the transfer window timing is even more complicated), departing from Mun instead... and so on.

But... something just seems intuitively wrong here... I really expect B < C...

Can anyone help me with the math to show why this is? Supply actual numbers, rather than just "Oberth effect, it just works out that way" (which I've already concluded)

So then I revised my plan: Going outward? fuel at Duna.... the math works out there to save (1986-1344) = 642 m/s of dV

Going Inward? Stop by Eve's system, fuel at Gilly... bit Gilly has miniscule gravity for an oberth effect, and is in a high orbit... does it work?

Kerbin @100km -> moho requires 5031 m/s, but from gilly's orbit, 3785 m/s is needed... a large difference... goog

Then I try different orbits from Eve -> Moho... the higher orbits always require less dV, as I would expect from my initial intuition...

Next I try the same thing, Eve -> Jool

From a 150km orbit of eve, it requires 2,508 m/s

From a 1,000km orbit of eve, it requires 2,480

From a 85,000 orbit of eve (ie, right on the SOI), it requires 3,211 m/s!?

There seems to be an "optimal" orbital height to depart from (assuming you can refuel prior to departure), on Eve, this seems to be about 600 km...

How does one calculate this (though the savings over just above the atmosphere are so small, I wouldn't bother moving to such an orbit, and then topping off)

This situation will reverse if one uses a bi-elliptic transfer correct? - ie starting from a higher initial orbit will require less dV to reach the target orbit (in another SOI).

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## Question

## KerikBalm 3,095

So, anticipating stock refueling, I've been planning on sending craft to minmus, where they would refuel, and then go on an interplanetary voyage...

I figured it had to take less dV to depart from the edge of Kerbin's SOI, than from LKO.

Sure, without refeuling, I figured its more efficient to do 1 burn from LKO - than to first burn to a high orbit, then do a 2nd transfer burn

But I figured the 2nd transfer burn would surely be smaller than the transfer burn needed from LKO.

But using this:

http://alexmoon.github.io/ksp/

I see its quite different...

Minus orbits at 47,000 km

From a 100km LKO orbit to jool needs a dV of 1986 m/s

From a 47,000km orbit (ie, where minmus is), one needs 2584 m/s!!!

This doesn't make sense to me...

This should also mean that a burn from heliocentric orbit to Jool will take more dV than a burn from LKO.

If:

A = burn to heliocentric orbit/a orbit to the edge of kerbin's SOI

B = the transfer burn from High SOI/heliocentric orbit

C = The transfer burn from LKO

I would expect that A+B > C, but that B < C, and A<C

If I refuel after A, then my craft should be able get by with lower dV capabilties... but this seems to be wrong.

But then I also have to consider some other things... like the oberth effect from orbiting Minmus, doing a bi-elliptic transfer (from minmus, lower PE to just above kerbin, then burn from there, but then the transfer window timing is even more complicated), departing from Mun instead... and so on.

But... something just seems intuitively wrong here... I really expect B < C...

Can anyone help me with the math to show why this is? Supply actual numbers, rather than just "Oberth effect, it just works out that way" (which I've already concluded)

So then I revised my plan: Going outward? fuel at Duna.... the math works out there to save (1986-1344) = 642 m/s of dV

Going Inward? Stop by Eve's system, fuel at Gilly... bit Gilly has miniscule gravity for an oberth effect, and is in a high orbit... does it work?

Kerbin @100km -> moho requires 5031 m/s, but from gilly's orbit, 3785 m/s is needed... a large difference... goog

Then I try different orbits from Eve -> Moho... the higher orbits always require less dV, as I would expect from my initial intuition...

Next I try the same thing, Eve -> Jool

From a 150km orbit of eve, it requires 2,508 m/s

From a 1,000km orbit of eve, it requires 2,480

From a 85,000 orbit of eve (ie, right on the SOI), it requires 3,211 m/s!?

There seems to be an "optimal" orbital height to depart from (assuming you can refuel prior to departure), on Eve, this seems to be about 600 km...

How does one calculate this (though the savings over just above the atmosphere are so small, I wouldn't bother moving to such an orbit, and then topping off)

This situation will reverse if one uses a bi-elliptic transfer correct? - ie starting from a higher initial orbit will require less dV to reach the target orbit (in another SOI).

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