How do you set up an encounter with aerobrake trajectory?

[Xuixien]

Several times tried it with Duna, couldn't get any approach closer than 20m km. I do NOT have enough fuel to get into an orbit now. How do you get an encounter that takes you through the atmosphere??????

Edited October 28, 2015 by Xuixien

[Panzerbeard]

You probably won't be able to get an encounter that accurate immediately; the further away you are, the more sensitive the trajectory is to course changes and there's not much difference between smashing into the planet and missing the atmosphere entirely. As long as you've got the intercept, wait until you're closer before plotting the course adjustment (do it before you enter the SOI, though. Maybe 20-30 days out, or so, depending on how large a change you need to make). If you're coming in at a fairly low inclination you'll want to use the normal/antinormal nodes primarily.

[Red Iron Crown]

I toned down the thread title a bit.

If you have it within 20km you could wait until you are in Duna's SoI and do a radial - burn to lower your periapsis fairly cheaply and easily.

[Snark]

One technique that's very helpful when you're trying to fine-tune your approach to a planet while you're still outside its SoI:

1. Set up your maneuver node to get an intercept with the planet's SoI.

2. Click on the planet in map view and choose "Focus View". This centers the map view on the planet instead of your ship.

3. Assuming that you already got an SoI intercept in step #1, you can now see your new, post-maneuver-node trajectory going past the planet. You can rotate the camera around the planet to get a useful view.

4. Rotate the map view around until you can see your maneuver node in the background.

5. Slowly and gently, try adjusting the maneuver node. Tiny adjustments may make a big difference in how close to the planet your path goes. Try the various maneuver node grab handles-- at least one of them will drag your trajectory closer to the planet. (You can mouse over the grab handle and use the mouse wheel to make tiny adjustments, if you like).

6. Fiddle around until you get the trajectory to where you like it.

7. When you're done, hit the backspace key to return map focus to your ship.

[Yasmy]

1) Drop a 0 m/s maneuver node half way between Kerbin and Duna, or on the line of nodes if it is far enough away from Duna and you have a significant relative inclination.

2) Focus on Duna (in map mode, right click on Duna -> focus, or just hit Tab however many times it takes). Once you are focused, you can see what your encounter looks like.

3) Rotate the camera so you can see your encounter and the maneuver node. Mess with the maneuver node until you get the desired encounter. If tiny adjustments move your encounter by too much to manually fine-tune, move the maneuver node forward along the trajectory.

4) If your engines are too powerful to execute the maneuver with precision, temporarily limit their thrust. Or create a new maneuver closer to Duna.

Edit: ninjaed by snark!

[Xuixien]

One technique that's very helpful when you're trying to fine-tune your approach to a planet while you're still outside its SoI:

1. Set up your maneuver node to get an intercept with the planet's SoI.

2. Click on the planet in map view and choose "Focus View". This centers the map view on the planet instead of your ship.

3. Assuming that you already got an SoI intercept in step #1, you can now see your new, post-maneuver-node trajectory going past the planet. You can rotate the camera around the planet to get a useful view.

4. Rotate the map view around until you can see your maneuver node in the background.

5. Slowly and gently, try adjusting the maneuver node. Tiny adjustments may make a big difference in how close to the planet your path goes. Try the various maneuver node grab handles-- at least one of them will drag your trajectory closer to the planet. (You can mouse over the grab handle and use the mouse wheel to make tiny adjustments, if you like).

6. Fiddle around until you get the trajectory to where you like it.

7. When you're done, hit the backspace key to return map focus to your ship.

Wait, I can focus on the planet and it will show me where my trajectory will run, even before I'm anywhere near it????

[Vanamonde]

Wait, I can focus on the planet and it will show me where my trajectory will run, even before I'm anywhere near it????

Yes, and you can set your periapsis from the halfway point of the transit, though farther back than that is less efficient. My method is to set it to just graze the atmosphere, then save the game as soon as I enter the target's SOI. Then I try burns to set different altitudes until I get one that works.

[Snark]

Wait, I can focus on the planet and it will show me where my trajectory will run, even before I'm anywhere near it????

Yes, though it only works if your trajectory passes through the planet's SoI. So you have to get an intercept first.

Incidentally, you can take it further than that. Let's say you're going to Jool. You get your trajectory to hit Jool's SoI, then you focus on Jool to see it there. And suppose it happens to intersect Tylo's SoI as it goes through the Jool system: you could then focus on Tylo and see the path there, too-- even though your ship hasn't even gotten anywhere near Jool yet.

Not only does this show you the trajectory going past the planet: in this view you can even drop a maneuver node-- for example, at the periapsis over the planet, to set up your capture burn. This can be very helpful for planning your mission, so you'll know how much dV you'll need when you get there.

Edited October 27, 2015 by Snark

[satnet]

I couple of extra bits of advice. If you have RCS you can use it for a very fine tuned burn (turn on CAPS LOCK for precision and use translation controls). If you're as far out from Duna as I think you are, trying to use engines probably will result in an overshoot. When you focus on Duna (use Tab to change focus, backspace to return to your ship) I suspect you'll find that you couldn't get any closer because you have an inclination that takes you above or below Duna. Make sure to setup your maneuver to correct inclination first, then tweak it to get within the atmosphere. Combining the maneuvers is more efficient, but we're talking about very subtle changes so it may not be worth it. Assuming you aren't in Duna's SoI yet I would just try to get within the atmosphere and roughly equatorial (if you can get to a roughly 15 km Pe, that is great, but anything within +/- 10 km of that I probably wouldn't mess with). Fine tune it once you are in Duna's SoI.

I would also recommend installing Trajectories. It simulates your aerobraking trajectory and give you a projected orbit or landing site depending on how low your Periapsis goes. It makes aerobraking significantly easier/safer.

[mabarry3]

One thing about the SOI changes that I recently read though:

You need to install a text editor (nothing special) and go into the KSP folder, and go to the settings.cfg file and use the text editor to read it. Find the code line called "CONIC_PATCH_LIMIT" and change it from "= 3" to "= 5". If you're not tech-savvy and worried about messing something up, backup the file first.

This is (as far as I know) the only way you can see your trajectory in Duna's SOI while still in Kerbin's SOI or even in low Kerbin orbit. If you happen to run into a Mun or Minmus encounter while leaving Kerbin's SOI (unlikely, but possible I suppose), you can still see your trajectory after leaving that whereas normally the trajectory would stop at "Duna Encounter" or, in the case of a Mun/Minmus random interception, it could even stop at "Kerbin Escape".

[Xuixien]

Thanks everyone. Was playing around with your advice and it was all wonderful. I'm on my way to basic competency in KSP!