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Erbal k

Advanvced intercepts in different spheres of influence.

Question

I'm looking for advice on planning intercepts between different orbital objects in different shperes of influence. 

Long story short I am using real solar system and have an orbital satalite in low orbit around Mars with an orbital inclination of about 23° that I want to transfer to from an orbital installation from each with an oi of about 26°. I also have mechjeb and a few other planner mods but so far the only thing I have been able to do is spend a ton of time setting up a chain of nodes to get somewhat (usually not very) close to the intercept objects orbital plain and then waist tons of dv for final alignment. If there is a better way to achieve this or a better tool to use I would definitely appreciate the advice! Thanks.

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Not sure if I understand you... I think you're asking "how do  plan a transfer so that I will match the inclination of something that's already in orbit around the destination body".

The honest answer is that I don't know how to properly plan for it, but am certain that in many cases it simply is not possible.

You are limited by which way you're coming from when approaching the target body. Which essentially is determined by the launch window. You can get some leeway by doing the transfer a few weeks sooner or later than the ideal hohman transfer window, but this usually won't have much of an effect. Even with the best planning tools, there's a lot of target orbits you simply cannot reach on any given transfer window.

If you're lucky, you can make it so that your PE at capture very nearly coincides with an AN/DN. If that is possible, do it, never mind the relative inclination. Capture into a highly eccentric orbit, then do a cheap plane change at apoapsis (which, in this scenario, also happens to coincide with an AN/DN).

But often, the cheapest way of getting to the target orbit is this:

  1. capture into a highly eccentric orbit around Mars
  2. circularize to a very high orbit, as close to the SOI edge as you dare
  3. wait until you come across AN/DN, then lower PE and match inclinations in one maneuver.

Steps two and three together require considerably less than 1km/s, IIRC. I had to do that a few times, but it's been a while and I seem to have lost my notes.

 

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You can't do it with maneuver nodes. Matching planes is always a question of timing. There are two times a year when you can transfer and end up in the correct plane. However, those two times do not correspond to your optimal launch windows. So there is no way to get anything like an optimal dV transfer.

So, the best way is to use a gravitational slingshot past some CB to change your plane during your trip, and save you some dV at the same time. This is enormously tricky, and requires even more precise timing for your transfer.

The second best way, as said above, is to do the transfer at a good window and then use all the tricks at the destination and during your midcourse correction burn to minimize the cost of your plane change. This is easy and fast and has very little in the way of timing requirements.

 

 

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