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Sat contracts and LAN of moons


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How do you determine what time for an injection burn so you arrive at the moon's proper Longitude of Ascending Node for a sat contract? Ive been trying to figure this out since yesterday. Have you ever layed a protractor on your screen trying to determine angles? lol , surely there is some sort of formula you can use to figure this out. It doesnt have to be perfect. It just needs to be close and not 90 degree's off from where I need to be. :) I couldnt seem to find the numbers I need in Mechjeb or KER. This is a Minmus contract which isnt as hard as trying to figure it out for the similar Duna contract I have as well. So how does one do this?

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Seconding ZL647's response. Get the bird there, then fine tune the orbit. I don't think you'll save much delta-v doing it in a single burn.

And it would be a GAN (_G_lobal _A_rea _N_etwork) rather than  a LAN (_L_ocal _A_rea _N_etwork). At least on the Duna or Kerbin segments of it. The standards body is currently... debating... vigorously as to if the moons count as part of the parent body GAN, or they should each be their own GAN. Yeah, I know a bureaucratic distinction that will fade in the field.

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I usually try to get some point of my trajectory within the moon's SOI to somewhat line up with the target orbit, so I will be at least moving in somewhat the right direction in the right place, then do a few corrections once I make orbit.

If you set your map view camera focus to the target body you can see your trajectory inside of its SOI, and can correct it well before you arrive.

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7 minutes ago, Hydrothermalventclam said:

If you set your map view camera focus to the target body you can see your trajectory inside of its SOI, and can correct it well before you arrive.

Are you absolutely sure it works like that? By that method it shows that I will arrive at almost 90 degree's to the intended orbit. Im not sure that it shows you that correctly for the time you are arriving. I think it shows you what it currently is and not the future position. Wish I knew for a fact that it works that way. I might have to do some testing to determine that. Im not nearly as concerned about arriving at Minmus at the correct time as I am about arriving at Duna at the correct time. I dont think there is any way I would have enough Dv to make a major correction at Duna. I see from my searching that a few others want to know the same thing. I bet there is a formula for figuring this out.

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OK, your right, I knew you was but it didnt seem right what it was showing me. So, I wait for 11 days and do my burn and it will arrive there just a few degree's off if that.

 

Still, Im sure there is some formula for working this out. Much more reading required I think. Maybe someone here knows where that info is.

 

 

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14 minutes ago, Kevin Kyle said:

Still, Im sure there is some formula for working this out. Much more reading required I think. Maybe someone here knows where that info is.

It's a series of calculations. Maybe someone else knows a simplified way to calculate it, or you can derive a simpler way by working through the formulas and canceling as much as you can and setting some of its parts to be constant for just kerbin and the target body.

Here's a good place to start though, hope it helps.

http://www.braeunig.us/space/orbmech.htm

 

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2 hours ago, Kevin Kyle said:

I dont think there is any way I would have enough Dv to make a major correction at Duna.

Ike makes 'corrections' at Duna.  Very active moon that, can't keep out of anything.  Usually that's an annoyance but it can also be used to advantage.

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8 hours ago, Kevin Kyle said:

Thanks to you both. I bookmarked that link. Maybe my head wont explode. :)

Thanks for the heads up on using the moons, wasnt even thinking about that. I see some flight planning is going to be involved for this one.

Anecdotally at least Ike is (in)famous for interfering with most trips to/from Duna.  Usually it's a mild deflection but by the same token it's very easy to intercept Ike instead of the planet itself*.  That gives you an easy way to wait in the SOI until you have an easy transfer to the Duna orbit you really want.

(*Unless you're trying to get to Ike, in which case it always hides behind Duna.  Life's like that *sigh*).

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@Kevin Kyle, I usually just focus view on the target planet and try to get as close to the correct plane as possible.  For Mun and Minmus, if it's going to be really far out of plane, it's easy to just delay the transfer and loiter in Kerbin orbit until the alignment improves.  For a transfer to Duna, that' really not possible.  You have to go when it's time to go or you'll miss the window.  So I don't worry about it to much.  I just try to get an intercept and then perform a correction(s) to match the plane of the target orbit as close as possible.  There's only so much that can be done in that regard, so instead I try to line it up so I can do the plane change at the same time as the orbit insertion.  The key is to make sure the periapsis of your incoming trajectory touches somewhere on the orbit line that you're trying to match.  You then just place a maneuver node on the Pe and perform a burn the includes both the retrograde and normal components.  You can also include a radial component if necessary.  By performing a combination burn you can save much delta-v.  It's a Pythagorean thing.  If you have a 1000 m/s retrograde burn, 500 m/s normal burn, and 200 m/s radial burn, you can perform all three at once for SQRT(1000^2+500^2+200^2) = 1136 m/s.  I can often match the target orbit close enough with one big burn to fulfill the contract requirements.

 

Edited by OhioBob
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