Minmus via Mun

[DeathSabre]

Ok. so I've done some googleing and i can't seem to find an answer for this anywhere.

I want to Maximize efficiency in going to Minmus. my Idea, is to launch at the correct time to burn to the mun, (slingshot around the mun) probably make a correction burn when in mun's SOI in order to bring my Apoapsis up to Minmus so i intersect Minmus's orbit at its ascending or decending node, as minmus gets there.

Thereby giving me an encounter without plane corrections and more efficiently than burning straight for it.(without the mun slingshot.)

What i need to know is: what phase angle Minmus needs to be at reletive to the mun, when i Do my burn from LKO (75km ish).

I'm assuming the phase angle will change depending one how close you get to the mun on your slingshot.

unless i'm totally understanding this incorrectly and that's not the most efficient way to get there. (fuel efficient not time efficient)

Thanks in advance for the feedback.

Fly Safe.

[mhoram]

I did not do the calculations but the formula for Angular alignment on this wikipedia page should help you get started:

http://en.wikipedia.org/wiki/Hohmann_transfer_orbit

Have you thought about the following idea:

Plan to encounter the Mun while it is in the same plane as Minums. That way you can use the gravity of the Mun in order to do the planechange and do not depend on exact timing for Minmus being on its ascending or descending node.

[KerikBalm]

Thereby giving me an encounter without plane corrections and more efficiently than burning straight for it.(without the mun slingshot.

I suppose if it were done ideally, it would be pretty close to the mun-> minmus transfer windows (mnus a few hours to get to the mun).

But its easy enough to get to minmus with no plane change, launch at the AN/DN directly into the same plane, or select a launch window such that you arrive at minmus as it crosses the AN/DN node.

Beyond that, a transfer to the mun or minmus only differ by about 100 m/s... I wouldn't bother with the slingshot to save that little dV

[soulsource]

The difference might be just 100 m/s, but in case of single stage missions a gravity assist indeed does pay off. All my trips to Minmus with my Peacock plane design (unmodded 0.23.5 game) included a gravity assist, either at the trip to, or while returning from Minmus, and without that gravity assist the crew would have been stranded in orbit around Kerbin more than once...

Sadly I've always planned these by the bare eye, and cannot tell you what exact angle is required... Nevertheless the screenshots linked above might help you get an idea how the two moons should be aligned.

[Oafman]

Things like this are always good practice, even if they don't save much dv

[DeathSabre]

Hi guys. Thanks for the replys

Plan to encounter the Mun while it is in the same plane as Minums. That way you can use the gravity of the Mun in order to do the planechange and do not depend on exact timing for Minmus being on its ascending or descending node.

That's Genius, why didn't i think of that.

I suppose if it were done ideally, it would be pretty close to the mun-> minmus transfer windows (mnus a few hours to get to the mun).

But its easy enough to get to minmus with no plane change, launch at the AN/DN directly into the same plane, or select a launch window such that you arrive at minmus as it crosses the AN/DN node.

Beyond that, a transfer to the mun or minmus only differ by about 100 m/s... I wouldn't bother with the slingshot to save that little dV

I Usually just go straight there. but i want to do a mun slingshot partly for efficiency and partly coz i think it would be cool to do.

The difference might be just 100 m/s, but in case of single stage missions a gravity assist indeed does pay off. All my trips to Minmus with my Peacock plane design (unmodded 0.23.5 game) included a gravity assist, either at the trip to, or while returning from Minmus, and without that gravity assist the crew would have been stranded in orbit around Kerbin more than once...

Sadly I've always planned these by the bare eye, and cannot tell you what exact angle is required... Nevertheless the screenshots linked above might help you get an idea how the two moons should be aligned.

Wow ok. that pic tells me there is a lot more leeway than i thought there was. allthough travelling all they way out past minmus like that strikes me as a tad inefficient.

So far what I've worked out is that a Mun minmus transfer minmus needs to be about 90 degrees ahead. so if i launch with minmus a little more than 90 degrees ahead, and adjust my encounter with the mun so my plane change is done by the muns gravity. I should be able to get pretty close to the mun.

I'm going to leave this as unanswered for a while longer to see if anyone has the actual calc's done with exact windows. But i'm going to give this approach a go when i get home.

Thanks again for the help everyone.

fly safe.

[metaphor]

I think it's about 90 degrees, but I'm not sure, would have to try it in game. It's not the same as a Hohmann transfer from Mun to Minmus since you have a good bit of velocity over Munar escape velocity, so after the Mun assist you would be in an elliptical orbit with periapsis inside the Mun's orbit (and apoapsis at Minmus's orbit).

If you want to save even more delta-v (maybe like 20 m/s extra), you can also use Minmus gravity assists after the Mun assist to get your orbit closer to Minmus's orbit before capture.

For that matter, the most efficient way to get to the Mun from LKO is to use a Minmus gravity assist.

Edited October 29, 2014 by metaphor

[MarvinKitFox]

If you want to be absurd, you *can* get to a Minmus-orbit from a LKO that *just* touches Mun's SOI.

Using, literally, zero additional propulsion.

This part uses at least 3 mun encounters, and 5 minmus encounters.

In practice though... not worth it.

The savings headed to MinMus are at best about 85m/s, as compared to a direct transfer from LKO.

Still it could serve as good training for getting around the solar system using gravity assists.

There, theoretically, you can achieve orbit around any body in the Kerbol system, for only about 1200m/s from LKO.

(One exit from LKO to Mun, slings out to Eve, from there to the universe.)

The discontinuities in gravity field encountered in the patched-conics gravity model allows for virtually infinite free maneuver opportunities, given the right planning.

And patience. Plenty of patience.

Disclaimer:

No I'm not nearly good enough at mathemagics to have calculated this...

Rather than calculate the optimal route, I simply tried them all.

http://forum.kerbalspaceprogram.com/threads/69816-A-preliminary-study-into-the-Migratory-Habits-of-the-common-Octo-2

[Yakky]

One other thing you can do via the Mun slingshot is change your plane much more efficiently. You can add an up or down out-of-plane component to your slingshot with a little tweaking: basically a small out-of-plane alignment on the want into the Mun can be amplified into a much larger out-of-plane departure. Using this technique, it's not strictly necessary to line yourself up to arrive at Minmus exactly at the ascending or descending node.

[metaphor]

That is an awesome experiment MarvinKitFox.

Did you get anything that orbits Minmus though? I think you can get bound orbits and weird gravity assists if you pass through SOI boundaries at high time warp values. But that's not really repeatable.

[Red Iron Crown]

Rather than calculate the optimal route, I simply tried them all.

http://forum.kerbalspaceprogram.com/threads/69816-A-preliminary-study-into-the-Migratory-Habits-of-the-common-Octo-2

Best kerbal science I've seen in a while, love it!