Using a delta V map...?

[Scottiths]

So I used a delta v map to calculate how much fuel I needed to carry for a Moho mission. I don't know where I went wrong though because the map said 2200 to get orbital capture and when I actually got there I needed 3500 to get captured. Did I come in too close? Is there a trick to keeping dv requirement low once you get an encounter? I basically came in parallel to Moho's orbit, so maybe thats the problem (I essentially did a flyby with almost no bending of my path at all).

So whats the trick for low fuel consumption orbital captures? Should I have tried to come in with a higher Pe?

[EndlessWaves]

Which way did you burn to slow down?

[maltesh]

Moho's a hard target, and 3.5 km/s of relative velocity on arrival is fairly good, all things told. It sounds like you did fairly well. You want a periapsis as low as possible on arrival, and you /want/ to come in as close to the direction of Moho's travel as you can.

Basically, the Delta-V map assumes that Moho is in an equatorial circular orbit whose radius is equal to the semimajor axis of Moho's actual inclined, elliptical orbit, and that you do a perfect Hohmann transfer to this hypothetical object.

When you descend on a Hohmann transfer deep into the sun's gravity well, you're arriving much faster than an object running around down there, which results in a high relative velocity on arrival. If you aren't moving in exactly the same direction as Moho when you arrive (because you're not exactly in the same plane, or because you had to cut inside its orbit to catch up with it) that cranks up the relative velocity. If you hit Moho when it's near Apoapsis, it's moving much slower than the circular velocity for its orbit, and that cranks up relative velocity.

The delta-V maps are fairly good for many destinations, but you generally need to take them with a fist-sized rock salt crystal with Moho.

[RoboRay]

The numbers on the delta-v charts are minimums (although the one I use shows around 2600m/sec for a Moho capture in a low circular orbit). If you're thrusting in a direction other than along your velocity vector (prograde/retrograde line), you incur losses. Did you also try to make an inclination change during the capture burn?

The lower your Pe the better for capture burns as well as the transfer burns.

[Scottiths]

No, I came in at Moho Pe I think. I was almost perfectly parallel to its orbet and my Pe was 500Km. I only had 2600 m/s of dv and I needed 3500 (according to my manuver node) to get captured at all. I'll keep in mind that it is minimums I guess and just build in a few thousand extra dV. The sad part is that I was trying to land a base there to mine Kethane so that I could go there without having a lot of fuel later. I thought I had over engineered (because I left with 5,500 total dV and the map said I only needed something like 5k). I used protractor to give my my launch window and spent 1800. My correction burn was 1,000 ish and then my capture was demanding 3500 ish. I was so close, but now I have kerbals trapped in solar orbit

[tomf]

I was just doing the maths for my own moho mission and I found that the minimum total dv required to escape Kerbin and get a 30km Moho orbit varies between 3791 and 4461, depending on where in Moho's orbit the Hohmann transfer intersects it. that doesn't include the plane change to cope with Moho's inclination though.