Circularizing from a very elliptical Solar orbit

[Mmmmyum]

I've tried messing around with gravity assists to achieve a bi-elliptical transfer, and I've currently gotten myself into a 998.929Gm by 63.6351Gm orbit after doing a 150km pass of Jool with a burn at closest approach to speed up.

What kind of breaking burn am I looking at to circularize my Solar orbit at a very low periapsis? And is there some way of speeding up my 34 year wait till apoapsis? Krag's Planet Factory doesn't seem to have it's higher time warps enabled.

Edited January 10, 2014 by Mmmmyum

[Epthelyn]

Your braking burn will be a burn retrograde relative to your trajectory around the star...in 34 years.

It's as simple as that, I'm afraid.

You could edit the persistence files to change the position of the craft in orbit to apoapsis, effectively skipping 34 years of in-game time, or just leave your computer running for ~3 hours on max warp.

[FenrirWolf]

Maybe you could bisect Eve's atmosphere for a big ol' slowdown should you manage an encounter, but other than that I figure you'll have have to burn at PE and hope you have enough fuel.

[Kasuha]

I think you overcomplicated things a bit. If you used gravity assist, you could have pretty much slipped around Eve, getting your low Sun periapsis and decent low apoapsis in one go.

The braking burn you'll need depends on the periapsis you set up. The lower you set it, the bigger burn you'll need regardless of what apoapsis you'll be coming from.

[Smidge204]

For speeding up time, you can use Cheat Engine to hack the time warp. I've successfully tweaked it to 100,000,000,000x making my trip to 40.7Tm take under 5 min or so. Be warned that this may break the in-game mission clock.

And do not set time warp to a value less than 1. That makes the Kraken very angry.

=Smidge=

[Mmmmyum]

I think you overcomplicated things a bit. If you used gravity assist, you could have pretty much slipped around Eve, getting your low Sun periapsis and decent low apoapsis in one go.

The braking burn you'll need depends on the periapsis you set up. The lower you set it, the bigger burn you'll need regardless of what apoapsis you'll be coming from.

Half the reason I did it was because I wanted a bi elliptic transfer

[thereaverofdarkness]

You can actually circularize at any point in the orbit. At apoapsis, you burn prograde. At periapsis, you burn retrograde. At half past periapsis, you burn straight toward the center of your orbit. At half past apoapsis, you burn straight away from the center of your orbit. You might note that all of these involve pointing your ship in the same direction. Once you know what that direction is, you can circularize at any point in your orbit.

You may have to adjust your heading during the circularization burn for best efficiency.

[draeath]

Set up a maneuver node to get the required delta-v, and give the firemarshal script in my signature a try to figure out if you've the fuel for it.

[Mmmmyum]

I was more hoping for an estimation of delta v required...

[draeath]

Have you tried plopping a maneuver node down and fiddling with it? You should be able to get it in the ballpark and refine it. The idea is once you know what you want to do, you can use the script to confirm you can do it (and what you'll be left with) and exactly how long of a burn it should be, to help you with timing.

You could do the math to compute the delta-v for the orbit adjustment, but frankly that part of it is beyond me.

[Smidge204]

You need the vis-viva equation, use or conservation of energy.

=Smidge=

[Kasuha]

I was more hoping for an estimation of delta v required...

That depends on what periapsis you choose. The best answer for "low periapsis" is "a hell lot of dv".

For given periapsis it's the difference between orbital speed at that height and parabollic escape spees with that periapsis.

[Mmmmyum]

I want to go down to around under a few thousand kilometres.

[thereaverofdarkness]

If you thrust retrograde, you will lower your periapsis. If you thrust in the direction I described in my previous post here (page 1) then you raise your periapsis. either one will lower your apoapsis. If you want to keep your periapsis where it is but lower your apoapsis, pick a direction somewhere in between. It doesn't have to be exact, you can adjust as you go.

[Kasuha]

Escape velocity at given distance r is SQRT(2*G*M/r)

Orbital speed for circular orbit at given distance r is SQRT(G*M/r) which is also <escape_speed>/SQRT(2)

Escape speed on Sun surface is 94,672 m/s, orbital speed on its surface is 66,943 m/s and the difference by which you need to slow down is 27,728 m/s

At distance of few thousand kilometers it will not be significantly different.

[Yasmy]

Nice analysis, Kasuha!

Correct to about 1%, since he is almost, but not quite on a Kerbol escape trajectory.

Beautiful back of the envelope calculation.

For your rocket, with about 10.8 km/s delta-v left, you can circularize at about 1.6 Gm above the solar surface.

As smidge204 says, use the vis-viva equation.