Interplanetary departing from Minmus

[Warzouz]

I usually start my interplanetary transfers from LKO, using fuel from Kerbin. Some people starts from Minmus, but I don't really understand how.

- How do you get a working encounter ?

- How do you handle the long revolution of Minmus around Kerbin (to get proper ejection angle)

- How do you handle narrow windows ?

Is is really efficient ?

Edited September 7, 2015 by Warzouz

[Starhawk]

To get the encounter, just use Alexmoon's KSP Planner and input Minmus altitude as the orbit you're leaving from.

Because Minmus gravity well is so small and it's orbital velocity is only 274 m/s, you can eject into the desired angle at any time without too much trouble.

If you're already at Minmus (because you have a refueling base there, for instance), then it's efficient. Otherwise, no.

Happy landings!

[Warzouz]

OK, so you ignore you orbot Minmus, but you consider you orbit Kerbin at Minmus altitude.

Is it precise enought to target narrow window (Moho) ?

[Tazin]

How would the ejection angle work in that case? Since i am technically orbiting kerbin, the proper ejection angle means i have to wait for minmus to be in the right place during its annual period? What about accounting for minmus orbital inclination?

[tbarcello]

How would the ejection angle work in that case? Since i am technically orbiting kerbin, the proper ejection angle means i have to wait for minmus to be in the right place during its annual period? What about accounting for minmus orbital inclination?

Yes, close to Kerbin it has a huge influence on your trajectory.

But what you have to understand is you are almost escaping Kerbin SoI when you orbiting Minmus. So as long as Kerbin is not on your way it doesn't matter where exactly are you. Even it's better if kerbin is on your way, because you can slingshot then, which is fun....

All you have to do is burn, until your escape trajectory is parallel to Kerbin current pro or retro and be at the transfer window.

Take care of inlination issue though. Fixing inclination is more expensive than changing direction of an escape burn. Time is on your side in interplanetary, so if inclination is funny, fix it early.

Edited September 7, 2015 by tbarcello

[mhoram]

A while ago there was a discussion about exactly this problem including the timing issue:

http://forum.kerbalspaceprogram.com/threads/78254

But what you have to understand is you are almost escaping Kerbin SoI when you orbiting Minmus. So as long as Kerbin is not on your way it doesn't matter where exactly are you. Even it's better if kerbin is on your way, because you can slingshot then, which is fun....

Going from Minmus -> Kerbin -> Interplanetary is not a gravitational slingshot. This one however is a gravitational slingshot utilizing the Mun:

[Coga19000]

A while ago there was a discussion about exactly this problem including the timing issue:

http://forum.kerbalspaceprogram.com/threads/78254

Going from Minmus -> Kerbin -> Interplanetary is not a gravitational slingshot. This one however is a gravitational slingshot utilizing the Mun:

http://i.imgur.com/ynquTiO.jpg

This is... not an interplanetary slingshot, though.

[tbarcello]

A while ago there was a discussion about exactly this problem including the timing issue:

http://forum.kerbalspaceprogram.com/threads/78254

Going from Minmus -> Kerbin -> Interplanetary is not a gravitational slingshot. This one however is a gravitational slingshot utilizing the Mun:

http://i.imgur.com/ynquTiO.jpg

Correct. My bad. It's not a slingshot, because you were always in Kerbin SoI all along.

[mhoram]

@Coga19000: right. An interplanetary slingshot would involve

1. Being in an orbit around the Sun.

2. Entering the SOI of a planet

3. Leaving the SOI of said planet.

4. Being in a different orbit around the Sun.

The picture was just there to illustrate that a gravitational slingshot involves entering and exiting a SOI.

[cantab]

The fuel-efficient way to depart is to leave Minmus's SOI and put your periapsis low over Kerbin, then burn at that periapsis to get on your interplanetary trajectory. Of course that takes some planning. You'll need to wait for Minmus to move into position so your periapsis is in about the right place, there's some room for error but not by much. Departure timing should be fine for all destinations but Moho.

Done well, that burn at periapsis is about 800 m/s less than if you departed directly from LKO, which means you can use a smaller interplanetary ship.

Of course if fuel isn't an issue *cough* ions *cough* you can go straight from Minmus orbit.

[Warzouz]

I understand there is no easy way to do it.