Double Gravity Assists

[Seeker89]

Today I wanted to do a double gravity assist; first by using mun and sling shooting me back to kerbin to get even a faster speed. My goal was to get into a close orbit to the sun without burning all that fuel needed for the speed.

What I did:

got into orbit around kerbin

use mechjeb to do a Hohmann transfer to mun.

maneuvered to head back to kerbin

before getting to kerbin, I used the engines to get to 10k m/s

use maneuvers to point to the sun.

In the end I failed flying off the sun going at 50k m/s.

Any tips for me?

Has other people tried this and got it?

Thanks

Seeker

[arq]

Mun won't be of much help in an assist to LSO. It is generally worth less than 100m/s. Your biggest asset here will be Moho. By repeatedly getting gravity assists from Moho, you can get down into a orbit that goes between Moho and LSO. From there, you must burn at LSO to circularize.

[voneiden]

Mun won't be of much help in an assist to LSO. It is generally worth less than 100m/s. Your biggest asset here will be Moho. By repeatedly getting gravity assists from Moho, you can get down into a orbit that goes between Moho and LSO. From there, you must burn at LSO to circularize.

Or Eve. Easier to reach and bigger gravity well. Though Moho has shorter period. Not sure which one would be faster, perhaps a good idea to consider both.

[arq]

Or Eve. Easier to reach and bigger gravity well. Though Moho has shorter period. Not sure which one would be faster, perhaps a good idea to consider both.

Eve would be good for some preliminary assists, but it has a higher orbit so you would want to do the later assists off Moho. Also, for the first pass by Eve, aerobraking (but do *not* capture) could also help.

[Sirrobert]

use maneuvers to point to the sun.

That's where you went wrong.

If you want to fall down towards the sun, you have to leave Kerbin's SOI along it's orbit, in retrograde direction.

Scott Manley explains why:

[Vector]

Your best bet is going to be Eve fly-by. From Kerbin to Eve you will leave Kerbin retrograde and arrive at Eve traveling prograde relative to Eve (probably with some radial and normal velocity too). An ideal fly-by of Eve will convert all the radial, normal, and prograde velocity into retrograde velocity relative to Eve, which will give you the lowest possible solar periapsis. (Aerobraking will give you less retrograde velocity and a higher solar periapsis.)

From there you just have to burn fuel to get closer to low solar orbit.

It is possible but rather involved to use gravity assists off multiple planets to lower your solar periapsis further.

[Traches]

I haven't had much luck with gravity assists from moho-- it's too light to affect my trajectory at the speeds I'm moving when I intersect.

OP, it's a whole lot easier to get an eccentric orbit that passes close to the sun than it is to get into a low orbit. Either way, a Bi-eliptic transfer will probably be the most efficient way to do it if you're aiming for really low orbits from kerbin. Start by raising your solar apoapse up high (like you're going to Jool), then when you get there burn retrograde to lower your periapse as low as you like. That actually doesn't take an insane amount of dV, but if you want to circularize at periapse that'll be a different story.