I suck with launch windows.

[jros83]

As the title says, I have no idea what I am doing when it comes to choosing the right time to launch for a particular target.

With the Mun, I pretty much have it figured out. But anything beyond, including even just Minmus, I really do not have a sense as to when are good launch windows. I recently went for Minmus with an unmanned exploratory probe in Career, and frankly it was comical. Though I had enough fuel to get captured, establish an orbit (with a "high above" apo and a very, VERY close peri so I was able to get some science from both tiers), and return to it to Kerbin, I feel as if I had to make too many adjustments and fine tuning. I knw, had I launched at the appropriate time, I could have made it much easier on myself.

Now that I have grasped the fundamentals of rocket building and fuel management, I really would like to know the secrets of efficient launch windows. I know this will be crucial as I finally, FINALLY start looking past the Kerbin system.

[Gaarst]

For Minmus, the best way to get there without worrying too much about transfer windows is to match its inclination (either during ascent or with a manoeuvre while in orbit).

If you want to do it during the ascent, then you'll have to launch when Minmus' orbit is directly over the KSC, and head towards whatever direction the orbit is to get in a coplanar orbit. If you do the manoeuvre thing, just put a node at the AN or DN, and burn normal or anti-normal until the relative inclication is 0°.

Once you match Minmus' inclination, going there is basically just like getting to the Mun.

For interplanetary destinations, you will have to use transfer windows. There is a very useful mod that allows you to plan them in game: it will show you when to launch, and in what direction to make your ejection burn to have an encounter with a planet; from then, with a little tuning, you'll be able to get to any planet you want.

[Snark]

My favorite tool for interplanetary transfers is http://ksp.olex.biz.  Dead simple to use, easy to understand.  Just tell it what body you're orbiting, what altitude your parking orbit is, and where you're headed, and it will tell you how much, when, and in what direction to burn.

For Minmus:  It's basically the same rule as for the Mun: do your ejection burn when you're just slightly less than 90 degrees before Minmus in its orbit.  In other words, if you go to map view and rotate it so you're looking down on Kerbin's north pole, rotate it so that Minmus is just shy of 3 o'clock.  Do your burn when your ship is at 6 o'clock.  You'll meet Minmus at the 12 o'clock position.  There's inclination to consider, but you can drop a node about halfway between Kerbin and Minmus to correct for that.  It'll be a lot cheaper in terms of dV than doing an inclination match when you're in LKO.

[Alshain]

For equatorial planets, it's quite easy. 

1.  Use the tool Snark linked to find a window. 
2. Launch your craft just before the window.
3. Create a maneuver and drag prograde until the maneuver Delta V is equal to what the tool says it should be.
4. Zoom out and set your planet as a target.
5. Roll the maneuver node around Kerbin till you find a close approach, which should be there, then tweak it with the prograde/retrograde.

Moho, Dres, and Eeloo will be a bit more challenging due to their inclination, you have to include more than just prograde and retrograde.  Start with Duna or Eve though.  Graduate up from there. (Just be careful, you can't easily get back off the surface of Eve)

Edited December 6, 2015 by Alshain

[maceemiller]

All the above are correct however I like the Protractor Mod. Simple to use and hits your target every time.

[GoSlash27]

For figuring out interplanetary transfer windows without calculating, I use what I call a "pathfinder" probe.

It's a simple probe that just barely escapes Kerbin's SoI.

Once it's established in Kerbin's orbit about the sun, I can use it's maneuver nodes to find launch windows to various planets.

Best,

-Slashy

[Waxing_Kibbous]

32 minutes ago, GoSlash27 said:

For figuring out interplanetary transfer windows without calculating, I use what I call a "pathfinder" probe.

It's a simple probe that just barely escapes Kerbin's SoI.

Once it's established in Kerbin's orbit about the sun, I can use it's maneuver nodes to find launch windows to various planets.

Best,

-Slashy

This in interesting, can you elaborate more? Is it a probe in a very similar orbit as Kerbin that flies ahead a bit that you just fiddle with once in a while?

[GoSlash27]

1 minute ago, Waxing_Kibbous said:

This in interesting, can you elaborate more? Is it a probe in a very similar orbit as Kerbin that flies ahead a bit that you just fiddle with once in a while?

Exactly. I just put it in Kerbin's orbit around the sun and just ahead of Kerbin. If I want to go somewhere, I just use the maneuver node to set up a hohmann transfer for the probe and then drag it around until I have an encounter. The time to burn gives me the transfer window.

Best,

-Slashy

 

[Superfluous J]

I do similar, but never actually send the probe into Sun orbit. It stays in LKO and I use the method Slashy described to find transfer windows* but do it with 2 maneuver nodes instead of actually performing the burns.

As a bonus, you can use it to plan the actual burn, and then when you launch your real ship you can target it, and see where the maneuver node is. Then you can place your real maneuver node right on top of it and get your encounter without much fuss.

*Actually, I use the transfer planner. But when I'm not using it for some reason (challenges, it's not updated, whatever) it's nice to have this to fall back on.

[Renegrade]

Re: Minmus specifically - my personal favorite technique to get to Minmus is to use a pair of maneuver node - a 920-ish delta-v one from a 0-inclination, and then a much smaller one (30-60) to correct the inclination outside of the Mun's orbit (normal/anti-normal, ie pink triangles).  I eyeball the first one's position, set up the correction, and then drag the first node around until I get a nice encounter.  Once the first burn is complete, I then re-tweak the second one to compensate for any errors (prograde/retrograde to line Minmus up, more normal/anti-normal to compensate for any inclination error).

It's not as cheap as launching directly into the correct orbit, but my "perfect" memory always remembers to do something one step too late (thus I remember that I'm supposed to be launching into an inclined orbit just as I finish circularization of the non-inclined one, or remember to empty the 'rescuee' seats once the rocket is sitting on the pad, etc).

 

5 minutes ago, GoSlash27 said:

Exactly. I just put it in Kerbin's orbit around the sun and just ahead of Kerbin. If I want to go somewhere, I just use the maneuver node to set up a hohmann transfer for the probe and then drag it around until I have an encounter. The time to burn gives me the transfer window.

That's not unlike something that 5thHorseman does;  the only difference is that he sets up the pathfinder orbit via a pair of nodes (one just barely escaping, and then one to find the encounter).

If anybody's interested, I believe it's in this video: https://www.youtube.com/watch?v=q4tPfWmFOeM

 

[jros83]

Thanks all. Some great options here to check out. Cheers.

[Dfthu]

I don't bother with Tranfers.

[Superfluous J]

12 hours ago, Renegrade said:

If anybody's interested, I believe it's in this video: https://www.youtube.com/watch?v=q4tPfWmFOeM

That feel when someone else pimps your videos for you

The funny part was, I was going to post that myself but didn't want to seem like I was just here to advertise.

[satnet]

I would also suggest http://alexmoon.github.io/ksp/ for planning a transfer burn. It is similar to olex's, but it tells you the in-game time when the transfer window will occur. It also makes it obvious that it is a window where you have times that are really optimal and some around it that are not as optimal, but OK. There is also a mod that does nearly the same thing (Transfer Window Planner?).

[Renegrade]

13 hours ago, satnet said:

I would also suggest http://alexmoon.github.io/ksp/ for planning a transfer burn. It is similar to olex's, but it tells you the in-game time when the transfer window will occur. It also makes it obvious that it is a window where you have times that are really optimal and some around it that are not as optimal, but OK. There is also a mod that does nearly the same thing (Transfer Window Planner?).

The mod is actually based on alexmoon's code - and it's a bit faster to boot.  The magic of open source

 

13 hours ago, 5thHorseman said:

That feel when someone else pimps your videos for you

The funny part was, I was going to post that myself but didn't want to seem like I was just here to advertise.

Well, it's a clever concept, worth re-posting

I just love it how it can be done with a stock install.   Great for those windows after a new release when mods aren't updated