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Kerbol polar orbit


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I think you only need 1.41 * Kerbin orbital velocity + 950 m/s.

950 m/s is the dv required to leave Kerbin SOI from LKO.

Happy landings!

How much of the plane change could you get with gravity assists? Say you escape Kerbin into a slightly eccentric orbit in the vicinity of Kerbin's, so that about a year later you intercept Kerbin. When you do, you come in under the south pole or over the north pole so Kerbin gives you as much plane change as possible. You might have to do this several times, meaning small burns to get the intercepts, and you'd probably have to burn some to keep your Ap and Pe in the right general area, but if you don't mind waiting a few years you might could get the desired orbit cheaper this way.

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For a Kerbol-Polar orbit, you would need to exit Kerbins SOI at a velocity of 9284.5*sqrt(2) m/s (=13130 m/s).

In the scenario that you burn in a 100km LKO (and assuming that you have the correct inclination and ejection angle) you will need a LKO velocity according to the Vis-Viva equation of 13505,9 m/s.

Based on the usual LKO velocity of 2250 m/s you have to burn about 11260 m/s in LKO.

Compared with a 13130 m/s burn outside of Kerbins SOI you get away with around 1900 less dV.

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Based on the usual LKO velocity of 2250 m/s you have to burn about 11260 m/s in LKO.

Compared with a 13130 m/s burn outside of Kerbins SOI you get away with around 1900 less dV.

I'm sure you can do better than that with gravity assists. Even going out to Jool, using it to fling you into a polar Kerbol orbit, then burning to get your Pe and Ap back down to the size of Kerbin's orbit, would be way cheaper than that.

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I'm sure you can do better than that with gravity assists. Even going out to Jool, using it to fling you into a polar Kerbol orbit, then burning to get your Pe and Ap back down to the size of Kerbin's orbit, would be way cheaper than that.
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@mhoram : So I should even start burnig inward as if I was going to Eve, because I'll need to cancel my (Kerbol prograde) velocity ?

Burning as if you were going to Eve does not change your inclination, so this will not bring you to a polar orbit.

You should burn in such a way that you leave Kerbins SOI with a Retrograde and Normal velocity component (ideally at a 45° angle).

BTW is there a way to calculate how much dV a Jool gravity assist is worth ?

Take the velocity vectors (relative to the sun) before entering Jools SOI and after leaving Jools SOI.

A vector-subtraction between the two gives you a Delta-Velocity vector which is approximately the amount of dV you gained by the Graviy assist.

This approximation does not take the altitude-difference between entering and exiting the SOI into account, but I don't know how that could be even calculated in terms of dV gain.

Also your velocity change is at most twice Jools orbital velocity. Since Jools orbital velovity is between 3 927 and 4 341 m/s, this value is at most ~8700 m/s (in the case that you leave the SOI in the opposing direction as you enter)

These numbers can be enlarged by a certain amount by utilizing further gravity assists from Jools moons (which would be tricky to set up).

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Theoretically the highest velocity one can get in a gravity assist is half the orbital speed of given planet. This is of course lowered by the fact you're not passing by the planet's core but above its surface, and by entry and departure angles which will rarely be optimal.

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What would it take to put something into Kerbol polar orbit around Kerbin radius ?

Using measured speeds from practical testing , starting at about 120km orbit around Kerbin.

Cheapest is:

1) from low orbit, go to infinity-1 Kerbol apogee. (about 2750m/s)

2) change plane to desired angle (about 0m/s)

3) circularise. (about 3875m/s)

i.e. about 6625m/s

(and something like 500 years.... orbit to infinity-something is very very slow)

by formula, i expect its something like:

.414 of LKO speed to just barely escape kerbin. (850m/s)

.414 of Kerbin orbital speed to get to infinity. (3843m/s)

0 to change plane

.414 of kerbin orbital speed to slow down to circular orbit (3843m/s)

Note that the second term gets massive gains from oberth effect of combined Kerbin orbital speed + LKO orbital speed, as the entirety of this burn is done at LKO altitude and speed.

note also that as infinity is not practical, one uses something a lot less. in my test, about 4* eeloo orbit distance. The plane change in term 3 was then about 150m/s, but reduces term 2 and 4 by less than 5m/s each

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