Jool Rocket Suggestions

[GamerMitch]

So today, i was sorta proud of myself because I got a Jool Encounter and flyby.Problem was, I only got my PE down to about 580,000,000m...which you can't get much of a "Flyby" from that perspective.Here is the rocket I used to get there(no docking required).I used Mainsails for the outer liquid fuel boosters, and a skipper on the inside.I did not use Asparagus staging,just all the outer tanks feeding the inner one.After that,I have an FLT-800 w/ an LVT-45.On the outside is two FLT-400 tanks w/ two LVT-30 engines.Or vice versa. Anyway,After THAT,I have the probe core,an FLT-200 tank and one ant engine.One.ant.engine.And that got me to Jool,No joke.

And here was my best viewpoint.I had to circle Jool cause i was so far away.

The point is,How can I improve on this design while keeping the same"One rocket"idea?Post any suggestions you have Below.

Edited November 8, 2013 by GamerMitch

[Vanamonde]

More fuel, fewer engines. Once you're out of atmosphere, you can trade time for engine power. That is to say, burn fewer engines for longer. See how your upper stage has 3 engines? Dump the outer 2 and run their fuel lines to the middle one, then eject the tanks when they're empty. That's just one suggestion to give you the idea.

[Blue]

Unless you need lots of thrust fast (such as when you're inside an atmosphere) excess engines = excess weight = wasted thrust.

Also, once you've set yourself up with a transfer to Jool and are on your way out of Kerbin's sphere of influence, set up a manoeuvre node to adjust your Periapsis to be closer to Jool. This is what's called a mid-course correction. It usually uses very much less velocity-change than the initial departure burn, and can be on any angle. So try fiddling with the different controls on the manoeuvre node to see what results in getting the Periapsis lower. If you get the Periapsis less than 200,000 meters, you can aerocapture into orbit around Jool very easily. If your Periapsis disappears, this means unless you do another mid-course correction later, you're going to collide.

[700NitroXpress]

Here is what I used on my first flight to the Jool system using much of the same technique, only I had a live Kerbal in a lander pod. I did this as a test flight to see how many moons I could visit in the Jool system on my first try and possibly land on Lythe. This rocket uses jet engines to reach about 22,000 meters and then the main engine fires as the jets decouple. There's no asparagus staging in the outer engines so all of them burn out at the same time. Then I used the Ion engines to do all of my maneuvers and orbiting of Jool and Lythe. Just the two Ion engines shown on the craft below had enough power to move the craft well enough in physical time warp.

This is my first trip to Jool and the maneuver that put me on an intercept for Lythe. You can still see that I have lots of XenonGas left.

Here's a close Jool orbit that I achieved with the same craft.

Unfortunately I didn't manage to land it on Lythe, it crashed into the ocean because I didn't have enough rocket fuel to slow down and the parachute ripped off. But this design suits you purposes if you put a small probe core on the top and fly it unmanned.

[Kasuha]

Problem was, I only got my PE down to about 580,000,000m...

Difference between 580,000,000 and 580 m PA is in single units of m/s when doing the transfer burn. And in going down with time warp when crossing SOI boundaries. And in fine-tuning the trajectory a few times during the travel using RCS, if you really want to be precise. The rule is, do not follow the maneuver blindly when going on interplanetary travel. Maneuvers are very useful in telling you the general direction and dv, but for precise navigation you need to watch what the trajectory is really doing and issue corrections, the sooner the better.

[The Crispy F]

That is actually quite helpful - been playing for a while but I've not made Jools yet (vanilla set-up, no mods etc), but I also hadn't considered using jet engines at all. I'll have a bash at that tonight and see how far I get.

[SRV Ron]

The universal stock explorer, the LV-N Interplanetary Probe, has more then enough power to reach any planet or moon of the Kerbal system.

Orbiting Moho.

[DrMonte]

From my "Kerbal science lessons":

I've accidentally learned why NASA does not use Air braking. We know that it is really dangerous even in KSP.

When travelling to Jool I've accidentally "grabbed" Laythe in my path and this safely throwed me in to the Jool orbit without any additional dV or dangerous Airbraking.

[KerbMav]

Correct me if I am wrong, but this will only happen if you sling by the planets moon retrograde, meaning flying into its SOI while it is "coming at you" instead of "catching up" to it?

[Geschosskopf]

To the OP:

I think you're asking the wrong question. If the rocket got out as far as Jool, then there is no need to modify it. It works just fine. The problem you had was in not aiming it correctly so you got a crappy encounter. Probably because you didn't do enough tweaking of the trajectory while en route.

Understand that KSP's whole map and maneuver system was designed simply to get you to Mun. Both its ease of use and the accuracy of its representations of your future position fall off dramatically the further from Kerbin you go. Thus, you must accept that if you've just completed your ejection burn at Kerbin and see a Jool encounter that looks good, this is a lie. You can't simply warp out there without doing anything because you'll be WAY off when you get there.

It is therefore imperative to do 1 or more minor tweaks to your trajectory while en route. For nearby planets like Duna and Eve, you probably only need 1 tweak at about the 3/4 point of the trip. For everything else, 3 or 4 tweaks are usually necessary. When I go to Jool, I usually make tweaks at each 1/4 of the total trip out. I only try to get close to exactly what I want on the last one, but the others are necessary to stay in the ballpark so that the 4th tweak is still only a tweak instead of a major burn. And even then, you can't truly finalize your Pe with any planet until you're within its SOI.

[Monkeh]

2 very simple changes will work wonders I reckon.

First, get rid of that whacking great and heavy RCS tank. You don't seem to even have any RCS thrusters nor docking ports, it's pointless weight.

Change to nuke engines, or even engine, (singular), on the top stage. You've saved a nice bit of weight with the RCS gone and the higher ISP of those will get you very far once in orbit. Slower, granted, but suck up those long burns, concede to the lord of efficiency and you'll do fine.

The lower trust to weight of the nukes can actually be an advantage on the long burn out to Jool, you have more accuracy to land that closer periap.

[700NitroXpress]

That is actually quite helpful - been playing for a while but I've not made Jools yet (vanilla set-up, no mods etc), but I also hadn't considered using jet engines at all. I'll have a bash at that tonight and see how far I get.

Yeah, for lightweight stuff with one major attachment point it works pretty well. There are better ways to set it up, but for a test flight, that actually had a target destination, this worked perfectly. My actual ship that I used to do real missions to Jool is much larger and differently designed. I posted a thread about it in the space craft exchange called The Papa Dragon, check that out for other ideas. I also have a thread about different staging techniques in the questions area that might prove inspirational.