Outbound Delta-V?

[zeppelinmage]

Okay, so while I plan my Jool mission, I'm using the wiki's Delta-V map. However, it only gives a single value for each body - the inbound values for intercept and orbit circularization. I know from my Mun and Minmus missions that outbound Delta-V is far less. For example, to go from LKO to Mun takes 800 (and another 200 to orbit), but to return to Kerbin takes only 200-250 from LMO.

Now, maybe I'm reading it completely wrong, but I suspect that in practice when I hop between Joolian moons I'll use a lot less delta-V. The question is... how much?

So, how do you plan the Delta-V for your Joolian missions?

The way I envision it right now:

- launch to Joolian intercept

- aerobrake around Jool

- circularize near Laythe

- Detach Laythe lander, send it on its way

- transfer to Tylo, detach Tylo lander, send it on its way

- transfer to Jool orbit near Tylo and detach multi-mission lander for Bop, Pol, Vall.

- Recover landers, return to Kerbin.

BTW, refueling isn't an option - I'm planning to bring everything I need. Right now the mothership has 11km/s, before the addition of landers.

[regex]

Right now the mothership has 11km/s, before the addition of landers.

Figure it out after landers. You should be able to get away with what you want to do with roughly, oh, 8km/s, especially with aerocapture. Probably less. I recently went to Vall and returned with a tug designed for Moho (some 9km/s with the payload, @11km/s without IIRC) and I had so much fuel I didn't know what to do with it. Of course, I was using drop-tanks and didn't bring my lander back, but I think 8km/s will be fine. If you're planning the Jool-5 challenge, I believe Kasuha will be along shortly with some advice for you.

[numerobis]

I've never found the maps to be useful; use a calculator such as http://alexmoon.github.io/ksp/

[regex]

I've never found the maps to be useful; use a calculator such as http://alexmoon.github.io/ksp/

They're pretty good for best-case estimates and figuring out lander delta-V, but yeah, a good pork-chop plot is so much better.

[Taki117]

I much prefer This dV map as it is much more accurate, but to get outbound dV you just add the totals from where you are to where you want to go. i.e if you are in LMO then you would add (Using the dV map I just posted) 230 to get to escape velocity, and then another 80 to get back to Kerbin. (Since you can aerobrake at Kerbin the rest is ignored) For a grand total of 310, but that's a maximum, I've never gone above 280.

[zeppelinmage]

Figure it out after landers. You should be able to get away with what you want to do with roughly, oh, 8km/s, especially with aerocapture. Probably less. I recently went to Vall and returned with a tug designed for Moho (some 9km/s with the payload, @11km/s without IIRC) and I had so much fuel I didn't know what to do with it. Of course, I was using drop-tanks and didn't bring my lander back, but I think 8km/s will be fine. If you're planning the Jool-5 challenge, I believe Kasuha will be along shortly with some advice for you.

Just adding my Laythe lander it dropped to 7.5 km/s. I need to redesign something, I think. (And that was a bare-minimum lift vehicle.)

And yeah, it's for Jool-5. Originally, it was just supposed to be just a universal interplanetary mothership... then I figured it needed a "shakedown" proving run... then, "If I can cover the Jool system I can go anywhere"... which brought my attention to Jool-5. My thought process.

[zeppelinmage]

I've never found the maps to be useful; use a calculator such as http://alexmoon.github.io/ksp/

I'll give this a shot. Thanks.

[Vanamonde]

As long as you are not passing through atmosphere at any point, the delta-V required for maneuvers should be symmetrical: trajectory A to trajectory B should cost exactly as much as going from trajectory B to trajectory A. That's why there is only one value between any two points on a delta-V chart; the direction is irrelevant. If you're seeing variation, it's most likely that you're not exactly re-tracing your path in reverse, or you've detached some payload mass along the way.

[SSSPutnik]

zeppelin, you need about 2-3000 or so to get to Jool from Kerbin orbit.

Once you get into Jool system, try to aerobrake so that your orbit is elliptical almost out to Tylo. Suggest aerobrake altitude about 120km or so. (F5 and F9 are your friend).

Adjust periapsis at next apoapsis so you no longer aerobrake.

After that, it depends on your landers, whether you use a tug etc once in-system.

Tylo will eat deltav even before you try to land. Getting to the little moons can be a pain too. It's almost impossible to avoid Vall and Laythe intercepts with this sort of orbit, but, you want good intercepts to save deltav. Don't take the first intercept without checking!

[Kasuha]

Regarding the calculator - use it with clear value for the destination orbit because you don't want the calculator to optimize for circularizing.

The same for maps - many of them assume you will circularize at certain Jool orbit first which is completely unnecessary.

Instead either aerobrake at Laythe or prepare a few gravity slingshots off Laythe/Tylo, these can slow you down and deliver you to your first target almost for free.

[Superfluous J]

The charts are guides, not lists of exact rules. You must understand what every number means and when and why it applies (and more importantly when and why it does NOT apply) in order to use them.

If you're flying by Tylo, you don't need to orbit Jool first. You don't need to orbit Tylo. You need to enter Jool's SOI and that's IT. You can aim a Tylo encounter from Kerbin's SOI with drops of fuel (If you have it, RCS works wonders). You can do it midway to Jool for a dozen Delta V. For all intents and purposes, it's the same cost as the cost to just get to Jool in the first place.

If you want to orbit Tylo, however, you need to basically get into orbit around Jool (Aerobraking can save dV but the good charts show you that) and then set your orbit to Tylo's and then finally circularlize. If you aim it right, you can do ALL of that in one huge burn, but that one huge burn will be roughly equivalent to the 3 or 4 burns you'd have to do to reach Jool orbit, encounter Tylo, and then enter Tylo orbit. Except of course for the Aerobraking.

It takes more dV to get to Mun than it does to come back not because it's inherently cheaper to return than it is to get somewhere. It's lower because you don't have to spend any fuel while landing thanks to Aerobraking at Kerbin. That dV still happens (else you'd hit the ground at 4km/s), it's just not because of fuel.

[theend3r]

Just adding my Laythe lander it dropped to 7.5 km/s. I need to redesign something, I think. (And that was a bare-minimum lift vehicle.)

And yeah, it's for Jool-5. Originally, it was just supposed to be just a universal interplanetary mothership... then I figured it needed a "shakedown" proving run... then, "If I can cover the Jool system I can go anywhere"... which brought my attention to Jool-5. My thought process.

Nothing can really calculate your dv automatically. Mechjeb shows my tug has 5000dv but it in fact has probably above 25000 without payload.

[Kasuha]

Nothing can really calculate your dv automatically. Mechjeb shows my tug has 5000dv but it in fact has probably above 25000 without payload.

dv without payload is only relevant if you're sending the ship without payload. Your tug has constant impulse, but dv generated by that impulse depends on how much weight do you carry.

[theend3r]

dv without payload is only relevant if you're sending the ship without payload. Your tug has constant impulse, but dv generated by that impulse depends on how much weight do you carry.

Obviously, both numbers were without payload. The point was that dv calculations have to be done by yourself or approximated.

[zeppelinmage]

Nothing can really calculate your dv automatically. Mechjeb shows my tug has 5000dv but it in fact has probably above 25000 without payload.

I use KER, and it is pretty accurate. I only need to hand-calculate when the display goes wonky after multiple re-arrangements with large pieces in the VAB. Or if I have non-standard staging.