Matching Minmus orbit at launch

[CaptainKipard]

So i plan on visiting Minmus a lot, since it's a prime location for mining pure green.

Can I save some delta-v by matching minmus orbit during insertion without having to do any (or much) correcting after I establish a parking orbit? If so what do i need to do in order to match the inclination and longitude of the ascending node of minmus? I'm guessing I have to launch at a specific time and yaw/pitch towards the right heading, but I don't know exactly.

Thanks for helping.

Edited June 21, 2013 by Cpt. Kipard

[DMagic]

Yeah, I do this whenever I launch to Minmus. You need to launch to an inclination of +/- 6^o depending on whether you are at the ascending or descending node with Minmus.

To figure this out, and to launch at the right time, select Minmus as your target when you're on the launch pad, its orbit should then be highlighted in green on the map screen. So just warp ahead until the KSC is directly opposite from where this green path intersects Kerbin (You can use either the Mun or a satellite in an equatorial orbit to make sure you are looking straight down at the KSC). If you are at a descending node (Minmus' orbit should go down on the right side of the map screen if you are looking directly down on the KSC) then you launch to -6^o, the opposite if you are at the ascending node.

To change your inclination just turn to a direction slightly above or below 90^o during launch. You can watch the map screen and check one of the ascending or descending nodes to monitor your inclination relative to Minmus.

[HoY]

It only costs 70 m/s to correct from a non optimal intercept for a total of just under 1000m/s,, not counting circularizing. If you launch at the optimal window it costs 900ish m/s (from 80km)and usually a tiny 1.5-3 m/s correction.

Bottom line, you Can shave off a little but if dV requirement but saving a maximum of 70-80 m/s may not be worth the effort of time warping to the proper place

[DMagic]

I guess the take away should really be, don't correct your inclination when in LKO. This will take 200 or 300 m/s. You can either launch into the correct inclination, or worry about it later when you are much further away from Kerbin and the inclination change takes very little delta-v.

[zanzibar196]

If you are trying to hit the mun or minmus... don't worry about it on launch... match it from Kerbin orbit. Much easier to do that way!

[CaptainKipard]

If you are trying to hit the mun or minmus... don't worry about it on launch... match it from Kerbin orbit. Much easier to do that way!

I'm going for efficient, not easy. It'll come in handy when career mode arrives.

If you are at a descending node (Minmus' orbit should go down on the right side of the map screen if you are looking directly down on the KSC) then you launch to -6^o, the opposite if you are at the ascending node.

Hmm. Well I'm looking straight down on KSC and Minmus orbit looks tilted right, so it's orbital plane is at 96^o relative to kerbin north right now. Surely that means I must head towards east +6^o and not -6^o right?

That's a minor detail anyway. At least now I know when to launch. You and HoY get rep for answering, because it's not a very easy question.

[DMagic]

Yeah, plus 6^o, a little above 90 on the navball. But it's easy to see if you're going in the wrong direction, just check the nodes on the map.

[Razor235]

If you want the most efficient way, just timewarp until Minmus is ~90 degrees from the ascending/descending node. No extra fuel spent and no headaches adjusting at launch.

[CaptainKipard]

If you want the most efficient way, just timewarp until Minmus is ~90 degrees from the ascending/descending node. No extra fuel spent and no headaches adjusting at launch.

I don't get it. How does minmus position help me here?

[Razor235]

You don't have to change inclination at all.

[CaptainKipard]

Oh. well actually the sweep angle for this hohmann transfer is closer to about 60something degrees. I get your point here but this method makes me wait days rather than the hours needed for kerbin to rotate. I'll try it some time though. Rep for you too.