How big is the launch window?

[Tokay Gris]

I am planning (and building) several interplanetary missions at the moment.

Using Mechjeb, I get specific launch windows for each mission.

So: Can I (using Mechjeb) send more than one vessel per launch window? Or do I either have to wait for the next one or do it manually for the second one to be in the same launch window?

[Shrike42]

If you have all your vehicles ready at once, you can launch quite a few in a caravan, provided you get your ship into orbit before you go back to launch the next.

If Mechjeb is giving you only one possible launch window, that's the OPTIMAL window, but you've got time both before and after that you can manually launch and then do some minor in-flight corrections.

I'd estimate that you've got an in-game window of +- 2 hours for launches, as the interplanetary phase angles won't change too much in 4 hours to make a mission impossible.

Note: I haven't used mechjeb, since I'm still at the stage where I'm not yet bored by launches and trying to get all my navigation sorted out by hand/maneuver nodes, so I'm guessing based on a handwavey general understanding of why those launch windows exist. It doesn't make sense that there's only one time at which you can reach another planet, since I've gone all over by launching craft whenever.

Now, the bigger concern I'd have is how mech jeb would react to being told to get craft in orbit to another planet. I must admit it would be an amazing feat if you had to juggle multiple missions manually to follow a mechjeb mission in one long train of craft.

Edited May 30, 2013 by Shrike42
distractions make me forget to finish thoHEYWHAT'S THAT?

[Xaver]

Yes you can. Start a little bit before and there is no problem sending more then one vessel to jool duna eve from a low Kerbin orbit because the vessels dont need long time around to the burning point. The inclinided planets are more difficult to reach because you need inclinided burn with every vessel.

Hint: the kerbal clock from spaceport helps a lot when you want to send more vessels at once.

[Vanamonde]

Launch windows never actually end; they just become less efficient the further you are from the ideal moment. You can fly from any point to any other point at any time, provided you have enough dV, so launch windows are actually nothing more than the least-fuel-expensive moments to go somewhere.

[nerdboy64]

There isn't an actual "launch window," per se. However, the farther away you are from the ideal phase angle you are, the more dV you will have to expend to make the trip. A difference of a few in-game days isn't that large on the planetary timescale, so it as long as you're pretty close, you should be able to get an encounter.

[Tokay Gris]

I think it was more of a Mechjeb question.

If done by hand, it is of course possible... but does anyone know how Mechjeb handles that window?

The vessels will all be in orbit around Kerbin, of course.

[Mihara]

There isn't an actual "launch window," per se. However, the farther away you are from the ideal phase angle you are, the more dV you will have to expend to make the trip. A difference of a few in-game days isn't that large on the planetary timescale, so it as long as you're pretty close, you should be able to get an encounter.

I think it would be very useful to know just how fast the dV requirements increase as you miss the launch window, and nobody seems to give any clear information on that. Assume I've had a trip planned with 10% safety margin on fuel. How long should I dawdle before it becomes worthless to go?

[OUScooby]

If you have MechJeb turned on and auto piloting through all your maneuver nodes to get to another planet, will MechJeb continue to fly and execute maneuvers if you switch away from that ship to another?

[Mihara]

If you have MechJeb turned on and auto piloting through all your maneuver nodes to get to another planet, will MechJeb continue to fly and execute maneuvers if you switch away from that ship to another?

Nope. As long as you stay within 2.3km physics distance MechJeb will remain active, at least SmartASS will. But I don't think the current version continues to execute maneuvers in this case. I'd need to doublecheck that though... The moment your current vessel goes out of physics distance, the ship is packaged and turned into a dummy mass on a stable, never changing orbit - until it bumps into something, that is.

I am quite definite that you can send a multiple-ship mission to a planet in the same launch window because I have done it myself, though -- my mission to Duna, by happenstance, consisted of the prepared lander-transfer ship, the airship that wasn't finished in time for a place to be designed for it on that ship, and a tanker just in case I messed up on fuel. All three went out with about 4 hours difference as I switched between them and executed their burns, and all three made it at times spread out by about a week.

[kahlzun]

Interestingly, the 'later' you send your ship, the earlier it will arrive and vice versa.

So, if you send a ship one hour before the window, and one hour after, the second one will arrive hours or days before the other!

[Tokay Gris]

Hm.... maybe I should takle it like this and still make it easier:

I could get the fleet of ships (minimum two to Jool, more like thriee or more and the two to Duna) outside Kerbins sphere of influence and into Kerbols. In the front, I think...

This way, I could use "plan Hohmann transfer to target" and not the "go to another planet"-feature. It should work.... I will try it with the Jool mission. One craft for that journey is already assembled and ready to go. I could place it in an orbit leading Kerbin.

This would also allow me to send another one from Kerbin orbit using direct thrust.

This is the first one to go: The "Colin Campbell", ready for launch.

[alexmun]

Coincidentally, I've just finished up a tool specifically designed to show you how big your launch window is. You can give it a shot at http://alexmoon.github.io/ksp. It creates what's known as a porkchop plot which shows how the delta-v required to execute a transfer varies with your departure date and time of flight.