How much delta v is required to visit EVERY object in Kerbal system?

[cantab]

Aerospikes seem to be widely used, mainly because Eve's dense atmosphere means you're stuck at Kerbin sea level Isp until you pass about 10 kilometres.

Eve in any case is a considerable outlier. If you want a ship that can return from an Eve landing, you have to design it for the task. The same generally goes for Tylo, a Tylo landing and return needs more delta-V than a launch to LKO. Laythe also warrants special consideration, though you can probably get away with using a Moho lander with added parachutes if you're precise enough to come down on solid ground.

Edited May 5, 2014 by cantab

[Tortoise]

Take a look at some delta-v maps.

[Kasuha]

Delta-v maps, at least those available for KSP, are misleading. Oberth effect is usually only covered partially by them, usually assuming you travel from LKO using some relatively optimal transfer window. But on the way back, conditions may be very different. In general, you don't use the same dv on the way there and on the way back, even if you don't aerobrake. They also assume intercept speeds when trasferring from Kerbin SOI, not from other planets. And they don't cover gravity slingshots at all.

Yes, they're good for some initial estimates. But don't rely on them too much.

So 12, 000 delta v is enough to go to any planetary body in kerbal solar system and BACK to kerbin in 1 trip? Hmmm. Why is it when I look up other peoples craft, they have like 50 orange tanks with LV-N's sprinkled everywhere?

It takes a lot of fuel to move a lot of fuel around. Not everybody is using KER or MechJeb to calculate dv and prepare optimal ships, and many people just build huge craft because they can and they like them that way.

Not too long ago I have seen an Eeloo return mission consisting of one orange tank and one 1.25-m tank. My own mission to Eeloo used three and half Jumbos and the lander visited both poles and returned with extra fuel.

Also, huge fuel reserves and many engines don't actually mean more dv. Jumbo tank with one LV-N has the same dv as eight Jumbo tanks with eight LV-Ns.

Edited May 6, 2014 by Kasuha

[Streetwind]

One thing that makes things like the Grand Tour mission hard is the fact that a single rocket stage cannot have infinite dV. The reason is the fact that dV comes directly out of the mass fraction (the ratio between fuel and not fuel), and no matter how much fuel you add, that ratio will never even reach 1. You could add the entire universe's mass in terms of fuel and it would be functionally identical to a few hundred orange tanks due to diminishing returns.

Two things multiply the mass fraction in the rocket equation: the gravitational constant g0, which (as its name suggests) is a constant and thus never changes, and engine specific impulse - the one variable that's left to be changed. Therefore, the amount of dV you can fit into a single stage is directly proportional to your engine's Isp. In fact, it's been calculated that you can expect at most about 22 times your Isp in dV for a single stage, but that's already with massive diminishing returns, so I personally like to calculate with 20 times Isp.

If you're using LV-N's, that means going north of 16,000 to 17,000 dV is so impractical it may as well be impossible. With the 12,400 you already have, if they're all in a single stage, there's not much more room to improve.

The obvious solution is building a staged spacecraft, but that puts severe limits on reusability (it basically makes it a one-shot). Most Grand Tour vessels implement this in the form of dedicated landers for their target bodies. Since each of them only needs to land and return once, it doesn't need to be reusable, and the main mothership can probably get itself into orbit of all the relevant parent bodies within the LV-N's dV envelope. Of course, carrying landers for Eve, Tylo and all the other destinations at once and still pulling double digit dV makes for a truly gigantic vessel.

The other solution would be to migrate to higher Isp engines... which stock KSP only has one of. That said, with ion thrusters you could theoretically get some 85,000 to 90,000 dV out of a single stage.

Edited May 6, 2014 by Streetwind

[TeeGee]

One thing that makes things like the Grand Tour mission hard is the fact that a single rocket stage cannot have infinite dV. The reason is the fact that dV comes directly out of the mass fraction (the ratio between fuel and not fuel), and no matter how much fuel you add, that ratio will never even reach 1. You could add the entire universe's mass in terms of fuel and it would be functionally identical to a few hundred orange tanks due to diminishing returns.

Two things multiply the mass fraction in the rocket equation: the gravitational constant g0, which (as its name suggests) is a constant and thus never changes, and engine specific impulse - the one variable that's left to be changed. Therefore, the amount of dV you can fit into a single stage is directly proportional to your engine's Isp. In fact, it's been calculated that you can expect at most about 22 times your Isp in dV for a single stage, but that's already with massive diminishing returns, so I personally like to calculate with 20 times Isp.

If you're using LV-N's, that means going north of 16,000 to 17,000 dV is so impractical it may as well be impossible. With the 12,400 you already have, if they're all in a single stage, there's not much more room to improve.

The obvious solution is building a staged spacecraft, but that puts severe limits on reusability (it basically makes it a one-shot). Most Grand Tour vessels implement this in the form of dedicated landers for their target bodies. Since each of them only needs to land and return once, it doesn't need to be reusable, and the main mothership can probably get itself into orbit of all the relevant parent bodies within the LV-N's dV envelope. Of course, carrying landers for Eve, Tylo and all the other destinations at once and still pulling double digit dV makes for a truly gigantic vessel.

The other solution would be to migrate to higher Isp engines... which stock KSP only has one of. That said, with ion thrusters you could theoretically get some 85,000 to 90,000 dV out of a single stage.

Yup, this is what I just realized today when I was trying to design my craft to perform better than 14,000 delta v, u just can't do it.

My mothership conundrum continues because using ion engines for interplanetary mothership is beyond ridiculous.... let me try it out and see if I can pull it off.

What thrust to weight ratio should I be aiming for in an interplanetary craft? 0.22? 0.11?

So here is what I am going to do... build the interplanetary mothership and send her ahead of my lander(s). Park her into orbit and wait. Then launch my lander with just enough delta v to make a one way trip to the planet I am aiming for. Meet up with the mother ship and refuel with JUST enough to get down and back up in 1 stage. Leave the lander in orbit (with a little fuel) and return home with my mothership.

Edited May 6, 2014 by TeeGee

[cantab]

Drop tanks are a viable alternative to full staging. You won't gain quite so much since you're not ditching engine mass, only tank mass, but it's still enough to go beyond what a single stage can do, and it makes it practical to use again by simply docking another set of drop tanks.

[TeeGee]

Drop tanks are a viable alternative to full staging. You won't gain quite so much since you're not ditching engine mass, only tank mass, but it's still enough to go beyond what a single stage can do, and it makes it practical to use again by simply docking another set of drop tanks.

Yeah I've been exploring that idea, how much delta v can we squeeze out of our ships if we do that?

Also, should I be using RCS or reaction wheels to orient my craft? Im not seeing much of a reason to use RCS given that it eats away at my delta v the more monoprop I add to the ship.

I've re-designed my craft slightly and now it has 14,000 delta v, one stage, no manned pods, no rcs, and 5 reaction wheels. It's thrust to weight ratio is about 0.14.

Is that a bad thrust to weight? I'm not very happy with it myself.

[TeeGee]

Solution to my delta v problem, launch refuel stations to every planet first, then use a high delta v lander to travel to each world on the way to my target. I've already built a 7,500 delta v lander that has a greater than 1 thrust to weight ratio for most of the planetary bodies, just travel from world to world and refuel along the way.

After my tankers are getting low on fuel, return them back to kerbin for a refuel then send them back out again.

For my eve mission, build a staged lander and launch it from LKO (completely intact) to eve orbit, refuel it, land it with parachutes, then launch and stage the craft along the way to make orbit again.

[cantab]

Unless you have something exceptionally unwieldy or specifically want to eschew them, use reaction wheels for orientation. RCS is invaluable for docking, useful for fine course corrections (though a good alternative is to drop the thrust limiter on the main engine), and serviceable for orbital manouvering and as a sort of emergency fuel reserve.

[Red Iron Crown]

I've been kicking around the idea of putting a single ion drive on either end of a big interplanetary ship, just for course corrections. The power requirements aren't as ominous in a big ship where the mass of Gigantor panels is almost negligible, and the low thrust is actually beneficial for precision reasons.