Aerocapture around Duna

[Drunkrobot]

Hello friends. See this?

This is my first mothership-lander interplanetary system. Right now, it is tearing through the cold void to Duna. It will enter orbit around Duna, the lander will detach, and make history. Then it will make the climb back into orbit, redock to the mothership, and come back home.

But first:

During my entire voyage, my mother ship can only use 3,616 m/s of delt-v. Already, I've used about 1,020 m/s for trans-Duna injection. The less I can use to enter a stable orbit around Duna, the better. So, aerocapture is the best way to go. However, if the entry into the atmosphere is too shallow, I'll just skip off, going back into Solar orbit. Too deep, and the whole thing will rendezvous with the ground.

My question is: Assuming a near-perfect TDI (I had the assistance of protractor), what should my closest approach be to enter a nice, relatively low orbit around Duna (closer than Ike), without assistance from thr main engines?

(Yes, I know that I'll need the engines to raise the periapsis after the aerocapture.)

Edited July 8, 2013 by Drunkrobot
Been answered.

[RocketPilot573]

Based on my own experience, 10.5 Km is the perfect altitude to aim for. However, Dunas atmosphere is very picky, going just slightly too low will have disastrous consequences,. And going only a few Km to high will hardly even be an aerobrake. So I'd recommend 11 Km, and remember to quicksave!

[Drunkrobot]

Ok, I'll try 11 km right now. <presses F5>

[Nibb31]

It depends on your entry velocity. Other than making some complicated calculations, the best option is probably to try several altitudes and see how it works out.

On my last mission, I found that a planned periapsis of 11km was to deep and I crashed. 15 was too shallow and I didn't bleed off enough speed. After some trial and error, I settled with 12km.

[Nimelrian]

To add: If you're using MechJeb, you can activate the landing guidance and check the "show landing site" and "show aerobrake nodes" options, which will give you convenient maneuver nodes at your periapsis that show you how the atmosphere will influence your orbit.

[allmappedout]

I've had success around 12km, but it's obviously dependant on your entry trajectory.

[pizzaoverhead]

There's a calculator you can use to find the correct altitude for aerobraking. Try it out here.

[Drunkrobot]

I'VE DONE IT! Lucky number 13 km was the one for me. I'll link the mission report in the first post when I've finished the mission.