Changing inclination to match a ground base.

[7499275]

Building a base at minmus with fairly low tech. No MJ landing asistant plus I want to do it on my own. However, I do not know what to change my inclination to to line up with the base.

[Red Iron Crown]

Set a maneuver node on the ascending or descending node and use the retrograde and normal handles to plot a burn to match it. Execute that node and you'll overfly the base, at least on the next orbit or two. After that, Minmus' rotation will pull the base out from under your orbit.

Edit: Herpy derp, didn't notice you were using Mechjeb, and I think I might have given bad advice above anyway. Make a node at Ap (inclination change cheapest there) to adjust your inclination so the most northward portion of the orbit goes at least as far north as your base. When the base falls under that portion of the orbit, perform your deorbit burn and land.

Edited July 28, 2014 by Red Iron Crown

[7499275]

Set a maneuver node on the ascending or descending node and use the retrograde and normal handles to plot a burn to match it. Execute that node and you'll overfly the base, at least on the next orbit or two. After that, Minmus' rotation will pull the base out from under your orbit.

Okay, I THINK I get what you mean, not entirely sure. Could you please go into a little more detail as to what your saying? (sorry)

[Red Iron Crown]

Seem my edit above, I forgot that ground targets don't give you ascending descending nodes.

[Master Tao]

Make a node at Ap (inclination change cheapest there) to adjust your inclination ...

Shouldn't that be 90 degrees away in the orbit? Closer to the AP helps, but in this case the AP is almost directly opposite, so changing the inclination there won't move the orbit over the base.

[EdFred]

Looking at Minmus from above the north pole, put the base at the six o clock position, and when at the 9 o clock position burn north (normal). This will put your path over the base. However, Minmus orbits fast enough that will actually want your orbit to be slightly east of the base instead of directly over it. Then burn retrograde. Or you could combine the two and burn somewhere around 315 degrees rather than north while at the 9 o clock position.

[Mr Shifty]

Shouldn't that be 90 degrees away in the orbit? Closer to the AP helps, but in this case the AP is almost directly opposite, so changing the inclination there won't move the orbit over the base.

It will eventually be over the base as the moon rotates underneath your orbit. Moons are tidally locked, so it might take awhile, but it'll be there.

[EdFred]

I didn't think Minmus was tidally locked.

[Mr Shifty]

I didn't think Minmus was tidally locked.

You are right. I never knew that; I just assumed.

[purpletarget]

The inclination from the equator of a planet is directly related to the Max/Min latitudes that the ground trace will cover. So, your base at 1 degree 27' N, you will need a minimum inclination of 1 degree 27 minutes (1.45 degrees) for the top / northerly pass of your orbit to touch the latitude of your base....and then you just need to wait for the planet to rotate the base underneath the trace to make your landing.

If you do a higher inclination, then you will end up with 2 chances for the base to pass under the ground trace.....one on the way up, and one on the way down.

If you're on a tight orbit, and just want to change inclination and then land, you want to set your inclination change slightly more than 90 degrees from the base' longitude, so that the burn pushes the top of your orbit to the desired Lat just ahead of where the base is about to rotate under. By the time you get to the top and start to land, the base should be there to meet you.

[impyre]

If your base isn't exactly equatorial, you'll always be coming in at a slight angle no matter what you do... so inclination doesn't really matter all that much. Just eyeball it until the path crosses over the destination, and fine tune as you get closer. As long as you are pretty close, course corrections of that nature require very little fuel usually (at least with no atmosphere to interfere). In order to minimize the angle at which you are coming in, you could take one of two approaches. A) come in from a polar orbit laid ahead of your destination such that it will be there when you get there, or at 90 degrees phase (dawn or dusk), execute an inclination change whose degrees match the latitude of your destination, and ensure that your periapsis is over the target area, then burn for landing when the target site is at the noon position on the surface. Honestly, with either method your angle of attack due to descent will be greater than the angle of attack due to inclination difference.

If, however, you want to know more about method B, the trick is to get equatorial and point at your normal/antinormal node depending on situation. The number of degrees that node traverses will be equal to your change in inclination. (of course this requires a navball that shows normal/antinormal) So in your case, you'd burn normal or antinormal until the indicator moves about 1.5 degrees (which will be pretty difficult to nail unless using rcs.)

Now for my 2 cents:

I always go for insertion to polar orbit. You can land anywhere on the planet with minimal changes to your orbital inclination if you wait long enough. Also, if you do a mid-course correction, getting polar orbit is really cheap (anywhere between 5-40m/s depending on the situation). This, combined with not having to worry about post-arrival inclination changes and a variety of good alternate landing possibilities makes it an ideal situation.

[Kryxal]

In this case, it should be easy enough to combine the inclination burn with a deorbit burn ... a degree and a half isn't exactly much in any case, and it will be a lot easier to do an angled burn to get in the area then correct things on the way down.