I can get to Laythe, but what about the other moons?

[Epthelyn]

After taking a short break from KSP I came back to build a rocket finally capable of reaching one of the Joolian moons (other than Laythe) and landing on it rather than crashing into it at several kilometers per second due to lack of fuel. Unfortunately I failed to achieve what I set out to do and yet another Kerbal is taking an endless holiday by the sea.

View including the top section:

Lower 'lifting' section:

Staging Order:

1) 8 mainsails fire together, asparagus staging on the outer tanks

2) Reach near-orbit with the central tanks (approximately half the fuel left by the time the periapsis is up to 100km)

3) Drop the rest of the orange tanks, and fire the 8 LV-T30s to finish circularisation

4) Burn out Kerbin's SoI using the T30s (Leaves 5-10 seconds at full burn worth of fuel left in the tanks)

5) Drop the T30s and use 4 LV-Ns to reach Jool, circularise and burn to wherever (in this case Laythe unless it's a suicide mission)

6) Drop the LV-Ns and use the LV-909 and smaller fuel tank to land/crash/splash-down

The images don't show the asparagus staging because I took them before I made that modification and forgot to take new screenshots (). However, it doesn't actually appear to make much difference to the range of the rocket, and certainly doesn't make enough difference to land without an atmosphere.

Any ideas? The "MOAR BOOSTERS" approach just made it fall apart on the launchpad

[capi3101]

You could try boosting up a seperate transfer stage, dock that to a fueling module and then dock all that to your lander before you head out that way. I might also suggest a rocket with a higher Isp than the LV-909 on the lander...an Aerospike, perhaps (you haven't got anything under the lander engine anyway). It'd have more thrust than you'd need for a landing, sure, but you'd get more delta-V out of the engine; perhaps enough to actually land. Only other thing I would suggest is adding another set of fuel tanks to the LV-Ns. And more struts if it falls apart on you.

I'm sure someone around here will tell you that you should be using all your engines from the get go...

[saik0]

You could try boosting up a seperate transfer stage, dock that to a fueling module and then dock all that to your lander before you head out that way. I might also suggest a rocket with a higher Isp than the LV-909 on the lander...an Aerospike, perhaps (you haven't got anything under the lander engine anyway). It'd have more thrust than you'd need for a landing, sure, but you'd get more delta-V out of the engine; perhaps enough to actually land. Only other thing I would suggest is adding another set of fuel tanks to the LV-Ns. And more struts if it falls apart on you.

I'm sure someone around here will tell you that you should be using all your engines from the get go...

The 909 has the best ISP of all the stock chemical rockets, its also 1/3 the mass of the aerospike and is stackable. If you really wanted to pack light and conserve fuel you could use a lander with an LV-N on all the bodies except Tylo and lug around a big tank for the transfers, leaving it in orbit for the landings.

[capi3101]

Well, the Aerospike has a comparable Isp in vacuum; it's Isp is superior to the LV-909 in atmosphere and it can produce more thrust. That may be a consideration depending on the intended target. Just saying.

[Temstar]

I'm sure someone around here will tell you that you should be using all your engines from the get go...

You should be using all your engines from the get go.

No seriously, the idea of asparagus staging is you never carry engines as dead weight during the ascent, or in other words you have so few engines (and thus so little dead weight) that you NEED all your engines to fire for the rocket to get into orbit correctly. This save on weight can get pretty huge.

Now let's look specifically at your ship for inefficiencies that's holding you back:

1) 8 mainsails fire together, asparagus staging on the outer tanks

Too much thrust, you don't need so much thrust for a rocket that size. Your TWR at lift off should be around 1.7

2) Reach near-orbit with the central tanks (approximately half the fuel left by the time the periapsis is up to 100km)

3) Drop the rest of the orange tanks, and fire the 8 LV-T30s to finish circularisation

You're wasting an astonishing amount of delta-V if you drop 12000L of fuel. Remember the less fuel you have in the tank, the more bang you get out of the remaining fuel as the rocket get lighter. That second half of the fuel in that stage will probably be 70% of the total delta-V of that stage

4) Burn out Kerbin's SoI using the T30s (Leaves 5-10 seconds at full burn worth of fuel left in the tanks)

5) Drop the T30s and use 4 LV-Ns to reach Jool, circularise and burn to wherever (in this case Laythe unless it's a suicide mission)

the 8 LV-T30 engine is again a source of inefficiency. Circularising and interplanetary transfer are both low TWR manoeuvres so you should use the same set of LV-N engine for them. That last 5-10 second of burn out of eight LV-T30 engine in a near empty stage is a HUGE amount of delta-V (probably 1000m/s or more) that you're throwing away. You're better off deleting the LV-T30 stage all together and just use the LV-N stage to circularise. And since now you have a smaller payload to orbit your booster underneath can be a lot smaller too.

As for Laythe landing, since it has a pretty dense atmosphere you're better off using parachutes for most of your deceleration down. You only need a little bit of thrust before touch down to cushion the landing and since it's a such small burn, you're better off holding onto your LV-N and use them for this retroburn too.

TLDR: LESS BOOSTERS

[CalculusWarrior]

Less boosters?!? Jeb would be ashamed! But seriously, that's good advice, it seems to me like you are missing out on a lot of central space in your design. The most stable place to put an engine is in the centre, as you won't have to worry about structural failures* and flipping out of control if an engine breaks off on the other side. I would suggest putting a fuel tank below your lander's engine and putting the LV-Ns radially off that. Then, you could put your boost stage below that same fuel tank, and you will find that the entire rocket is a lot more structurally sound.

*not guaranteed, if you have too high a TWR, you will find that your rocket will compress together and attempt to become an accordion, and you will not go to space today.

EDIT: Here's a picture of what I'm talking about:

Edited May 3, 2013 by CalculusWarrior

[Epthelyn]

You're wasting an astonishing amount of delta-V if you drop 12000L of fuel.

Dropping fuel? No. That's dropping the 4 sets of double stacked orange tanks when empty.

As for Laythe landing, since it has a pretty dense atmosphere you're better off using parachutes for most of your deceleration down. You only need a little bit of thrust before touch down to cushion the landing and since it's a such small burn, you're better off holding onto your LV-N and use them for this retroburn too.

This is why I always fall back on Laythe; it's easy to land there. Landing on the land not so much

As for the '8 mainsails is too much', well, using the just the outer 4 provides the rocket with enough lift to leave the ground but not enough to allow me to throttle back to a point where the engines won't explode after 20-30 seconds.

Modifications to make either way. Thanks for the suggestions.

[Temstar]

using the just the outer 4 provides the rocket with enough lift to leave the ground but not enough to allow me to throttle back to a point where the engines won't explode after 20-30 seconds.

Oh that, the trick is to stick a grey tank between an orange tank and the mainsail. Once you've done that you can fire the mainsail at full throttle as much as you want and they won't overheat.

Have a look at this rocket for example:

Edited May 3, 2013 by Temstar