Phase angles and launch windows

[Galileo Kerbonaut]

I've been playing KSP for a couple of months now. After landing on the Mun and Minmus, I went to Duna, Eve, Jool and Dres. But I'm not sure I'm doing everything right. The way I go to Duna now is by waiting for the correct phase angle (somewhere between 40º and 60º). So, I launch a ship into Kerbin orbit, time warp until I get the right phase angle and shoot it in a trajectory to Kerbin escape. From there I can plot my voyage to Duna...

My questions is: is there another more efficient (quick) way of doing this without waiting for the right angle? Or am doing everything right and do I HAVE to wait and time warp each time for the right phase angle in order to go to another planet? Is there a way I can launch a rocket to Duna without waiting forever or by using time warp?

[Awaras]

Basically, the farther away you are from the 'perfect' angle, the more dV (and therefore, fuel) you need to get where you want.

[KerbMav]

MOAR BOOSTAHS!

Sorry.

But yes, if you can built a ship powerful enough to get an encounter, you can start whenever you want - it is just not very efficient and maybe more difficult when it comes to designing the craft - also the voyage may take much much longer, hence again lots of time warping.

[andrewas]

The phase angle is needed if you want to do a hohmann transfer, since if your transfer orbit exactly touches the destination orbit, theres only one time you can launch and have the target planet be there when you get there.

But if you are willing to burn more deltaV, you can launch anytime. If you have a decent grasp of orbital mechanics, you can just play with the maneuver nodes until you get an intercept. Some angles will require an huge amount of deltaV, but you can usually get where you want to go if you have a reasonably powerful ship.

[J.Random]

More quick way to do this would be to timewarp at the launchpad instead of orbit.

[Galileo Kerbonaut]

If you have a decent grasp of orbital mechanics, you can just play with the maneuver nodes until you get an intercept.

I think this is my major problem, I'm not 100% sure of what I'm doing. Do you know any good tutorials that can help me with this?

[allmhuran]

Yep, you have to wait. You also don't want to wait around in *high* orbit, because your burn will be less efficient if you do it in high orbit. But if you're in low orbit you can only warp at 50x!

Easy solution follows.

After putting your interplanetary ship in low orbit, go to the VAB, grab a probe (don't bother making a rocket), and launch it. Now you go to maximum warp while sitting on the pad.

When things look good, you don't have to go all the way to the tracking station to switch vessels either. Just go into map view and click on your main ship. You will be presented with the option to "switch to".

If things still aren't quite right, just switch back to the probe on the pad and warp some more.

Now, just some extra bonus info for you on why we wait for launch windows.

If you're going interplanetary, then you no doubt already know how orbits basically work. To go higher, thrust prograde, to go lower, thrust retrograde.

Right, so, now think about how the planet Kerbin is moving around the Sun. The direction of Kerbin's orbit is "prograde". You therefore want to be accelerating in this direction in order to raise the apopasis on the other side of the sun to intersect with Duna. Clearly, this is going to require specific timing, just like intercepting with another ship in orbit around Kerbin requires specific timing.

Wait, don't go yet! There's slightly more to know about this.

When you burn your engines in Kerbin orbit, Kerbin's gravity is going to bend your trajectory. But you want to thrust prograde relative to your *solar* orbit! How can we do this if kerbin keeps changing which way is forward?

Well, the trick is this: What we want is for our *Kerbin escape trajectory* to be parallel with the orbit of Kerbin. In order to do this you actually take advantage of Kerbin's gravity, and start firing your engines when you are about 150 degrees (for duna) away from prograde. IE, you fire your engines about 30 degrees after passing the terminator and entering the night side of Kerbin.

The same is true to go to any "higher" planets, but since they are, of course, further away, the angles will vary slightly.

Edited October 22, 2013 by allmhuran

[Starwhip]

Yes. Watch Scott Manley's docking tutorials. Or go into the tutorials that KSP includes with the game when you start up. Both will help you tremendously.

[Iansoreta]

More quick way to do this would be to timewarp at the launchpad instead of orbit.

That's great idea, I always do that when I'm in a hurry.

Edited December 7, 2013 by Iansoreta
wrong title

[Liowen]

One thing I have done is if you are not good at guessing angles, then download the mod protractor. This will give you an angle or time till the best window for launch. I put one on a satellite and got it in a high enough orbit so that I could fully time warp to the next window without having to warp on the launch pad, bad things always happen when I am on the pad time warping it seems.