DV for Jool trip.

[Benji13]

I am trying to find a reliable source and I can't find one. Just how much DV would I require to do a return trip from all of jools moons? I don't plan on landing. Just orbiting each one. I currently have a ship with 10.2km/s but I can't get any more. If I need more, can anyone suggest some good designs (for 1.1)?

Edited August 30, 2016 by Benji13

[mhoram]

Regarding your first question head over to http://alexmoon.github.io/ksp/. This Webapp helps you with planning the needed Delta-V.

 

Regarding your second question there are two options:

1. reduce the mass of your payload
2. increase your fuel/engines or add additional stages

Here is a thread containing inspirations for creating Rockets with large amounts of Delta-V:

http://forum.kerbalspaceprogram.com/index.php?/topic/54529-022-0230-delta-v-maximization-challenge/

Also you can get advice on which engine to use in which situation in the following thread:

http://forum.kerbalspaceprogram.com/index.php?/topic/114995-web-111-optimal-engine-charts-interactive-webapp/

 

Edited August 30, 2016 by mhoram

[Streetwind]

You can't find a reliable source for this because... there isn't one. It's impossible to quantify.

The reason: while it's easy to calculate your dV requirements for going to one of Jool's moons and back to Kerbin using a dV map, all bets are off as soon as you start hopping moons. Depending on which timestamp you arrive at, how fast you arrive, the shape of the orbit you arrive in, which moon you chose as your first destination, the order in which you plan to visit the other moons, whether or not you are set up to aerobrake at Jool and/or Laythe, whether capturing into any orbit will do or a low orbit is required, and how long you're willing to wait between each of the legs of your tour, you're going to get significantly different numbers for the question "how much does it cost to visit all of Jool's moons". For example, you could pay as little as 150 m/s of dV to get gravity-assisted flybys (not orbit captures) of four of the five moons in sequence... or you could pay a thousand for the same if you were unlucky and/or set things up poorly.

This kind of thing is called "sensitive dependence on initial conditions", and it makes it impossible for anyone to tell you what you will experience.

You could put an upper bound on how much you need by pre-planning the sequence of your moon visits and then using an "intra-system" dV map for Jool to assume pure unassisted Hohmann transfers from one moon to the next. Unfortunately, while such a thing can easily be found for Jupiter's four Galilean moons IRL (see here in the lower right corner), I've never seen it done for Jool in KSP. It's no surprise either, since it's complicated, and few people use straight Hohmann transfers to go between the Joolian moons anyway. Though I suppose it may have academic value, so I'll just go and suggest it in the Community dV map thread...

Because I don't know enough about what you want to do exactly, I can suggest only one thing: make Bop or Pol your first destination, and carry an ISRU module (or lander) to refuel your Jool cruiser. A Jool transfer stage needs to carry around 3 km/s to complete the transfer burn and insert into orbit around one of Jool's moons without cutting it too close; if you refueled that stage, those 3 km/s will allow you to get a huge amount of work done and get quite familiar with the gravity assisted moon hopping procedures around Jool. And should it turn out to not be enough, you can always go back and refuel again. Same goes for heading back to Kerbin - refuel before you leave, and you won't have to lug the return fuel with you all the way. That should easily make up the mass penalty for the ISRU equipment.

Edited August 30, 2016 by Streetwind
Fixed the second link to actually link where it's supposed to link.

[Plusck]

I absolutely second Streetwind's advice: ISRU on Bop or Pol.

I'd add that you should enter Jool with a gravity assist from Tylo so that it sends you down into the system. If you get it right, for 0m/s cost at Tylo, Pe will be somewhere near Laythe/Vall and Ap will have you crossing Pol or Bop's orbit. The only expensive part of this process is circularising at Bop or Pol: I think Bop is more expensive at about 650 m/s or so doing it with this method (the only downside of Poll is you absolutely must avoid any visibly "creased" valleys when less than 2km from the terrain).

You could do a similar thing with a gravity assist from Laythe, but your resulting Pe will be very close to Jool itself and it'll be more expensive to circularise at the outer moons, unless you get more gravity assists from other moons like Vall or Tylo on the way there (and in this case, planning will be difficult).

So yes, if you have about 800-900m/s still in your tanks when you arrive in the Jool system, you can refuel and do it all.

However, if you don't want to land at all, you can bop around from moon to moon with very little effort - as long as you don't want to get into orbit. The standard delta-v maps give the amount needed to orbit each moon - less than double that total is all you need to get all of the moons done.

Edit: oops, sorry, the standard delta-v maps don't.  This one does, and gives lots of transfer options too. Since a highly elliptical orbit is basically just escape minus 1m/s, you just need the numbers to and from "escape" for each moon. Add in a couple of gravity assists and you really don't need much to do all that if you capture to Tylo or Laythe first. I'd definitely risk it with 4000m/s on arrival at the system (which appears to be what you will have).

Edited August 30, 2016 by Plusck

[Red Iron Crown]

I've found this dV map by jellycubes super helpful for planning moon-to-moon stuff in the Jool system:

It's old, but still accurate everywhere but the Laythe descent/ascent, which changed with new aero.

[John FX]

I went with 5KDv in orbit and it was fine although that craft had landers which it shed on the way which would have given me some more.

[GoSlash27]

Benji13,

It is possible (tedious but possible) to calculate a DV budget for such a trip, but you'd have to decide exactly what order you wish to do it in and exactly what orbits you want at each moon.
 It takes a lot of math, but it's fairly straightforward math.

You would use

1)vis-viva to calculate the excess velocity for the hohmann transfers,
2) Hyperbolic excess velocity to determine the DV of each burn
and
3) Gate orbit to determine the optimal orbit altitude for each leg of the trip.

I'm sure you wouldn't need anywhere near 10 km/s DV to do the whole thing.

HTHs,
-Slashy