Transfering from one planet to the next.

[Melonfish]

I'm concious that I'm doing it all wrong and wasting precious Delta-V, let me run this down.

I make orbit around Kerbin then burn prograde on the dark side 90° until i leave the SOI, this takes me into a slighly lower Kerbol orbit than Kerbin, from here i go round until i find a good spot with the planning tool and burn for my target, be it prograde to raise apoapsis or retrograde to lower periapsis.

I'm concious this is mahoosively inefficient as I'm burning for 11 mins to get an intersect, granted my ship has like 50 minutes of burn time with 8 nuke engines and I can afford it but it'd be nice to get these mythical 1500 odd delta V burns that Transfer planner says I can do it'd mean I can build smaller ships.

I take it we just sort of wait for the proposed window (I have some KAC alarms set) and burn light side 90° and it should intersect directly?

Thanks

Pete

Edited October 20, 2015 by Melonfish
answered.

[KerikBalm]

You should make your burn from low-ish kerbin orbit, and not simply light side or dark side... actually its going to be more or less near the terminator (+/- 25 degrees normally).

Going into heliocentric orbit first is massively inefficient.

If long burn times are a problem, then you'll want to perapsis kick and get everything set up a few days before the intended transfer window (but there's no sharp cutoff, if you elave a few days early or late, its fine.

Perapsis kicking your orbit nearly out to Mun is normally a good compromise, as the orbits are still rather fast, and its not so much of a burn needed at perapsis to get you to Duna or Eve.

Its also a good idea for Jool/Eeloo/Moho, as those burns need ~1km/second more than going to eve or Duna, so even with a perapsis out past minmus, you'll still have around a thousand m/s to burn.

Thats why to eject from the kerbin system to those destinations, I use Rhino engines and not LV-Ns

-Actually what I've got in career mode is a Rhino engine+ tanks + docking port Sr. + LF tanks and 2 LV-Ns.

The Rhine+ 2 nukes fire to put the payload on its interplanetary intercept trajectory, and then it detaches and burns retrograde to stay in Kerbin's SOI, and aerobrakes its apoapsis back down, at which point I transfer it to the Mun for refueling from the ISRU there (yea, I do ISRU mainly on Mun and not Minmus, because the transfers are faster and easier to setup)

[Melonfish]

By dark side I do mean i'm in LKO and burning prograde 90° so as to essentially be burning out of kerbin's orbit and into a lower heliocentric orbit, which is yes massively silly.

Not following you on a periapsis kick.

[Red Iron Crown]

Easy guide for where in orbit to do transfer burns (viewed from above, assuming an eastward orbit):

Fear my l33t MSPaint skills.

Periapsis kicking is splitting the burn up to make it more efficient, there's a tutorial linked in my signature about it.

[Snark]

In general, to take maximum advantage of Oberth effect you want to do all of your burn from low Kerbin orbit: one single big kick that sends you to your destination, with at most a small mid-course correction burn.

There are tools to help plan for that; my favorite is http://ksp.olex.biz. Just tell it where you're going from, where you're going to, and the altitude of your parking orbit at the source; it will tell you when, how much, and in what direction to burn.

Even without such a tool, though, you can just play around with the maneuver nodes. "Here I am in Kerbin orbit and I want to go to Duna"-- drag a node to get something that you think might work, see where the intersect markers are, and fiddle with it until you get an alignment. Note that one of the ways you can edit a maneuver node is to drag the node itself forward and backward along your trajectory, by grabbing the circle in the center. (Handy to know, and not all that discoverable. Was playing KSP for a year before I found out about that.)

The complicating factor to the "do all your burn in low orbit" strategy is if you have a very low-TWR ship (e.g. something massive and nuke-powered), because then your burn takes so long that you simply can't do it all in low orbit. There are three strategies there:

1. To heck with Oberth, just do a long burn. Conceptually simple, but it loses much of the Isp benefit from the nukes, and also makes maneuver planning harder.

2. Have an initial eject-from-orbit stage that uses something powerful to give you a kick. This is the strategy that KerikBalm mentions (using a Rhino for that initial wallop).

3. Periapsis kicking, as KerikBalm and Red Iron Crown mention. Don't eject in one burn: do a burn that boosts your apoapsis up a bit, coast back around to periapsis and do another burn, and repeat until you've gotten your apoapsis up to around the Mun's orbit or thereabouts. Then do a final big burn at periapsis to go on your way.

Edited October 19, 2015 by Snark

[Melonfish]

Brilliant cheers guys, i'm going to have a go at these tonight, I get the Idea behind raising the periapsis/apoapsis in increments and I like it, makes using Nukes much easier.

i'll post results