Creating large, stable, non-laggy rockets for three-person lunar landing?

[ProbeIke]

So, I've hitting three main problems when making very large rockets, specifically for the 3-person moon mission. They are such:

1) Large numbers of fuel tanks/stages cause HEAVY lag on launch, and the beams to keep it stable are the main reason

2) Beams cause lag and fail to keep the ship stable, and oftentimes it simply explodes on the launch pad under its own weight

3) Keeping the ship from exploding at stage separation or on the pad, similar to item 2. I don't want to use mods right now, so I want to build a rocket with stock parks.

Here is the design I used yesterday for the one man capsule to the mun (My first EVAR mun mission)

And the design I'm trying to get to work.

Also, I don't want to decrease the rocket size since I want to bring extra fuel for the Minmus voyage. Does anyone have any tips/ideas for the design? Both use an onion-like configuration where all rockets fire at launch, and fuel pumps drive to the inner tanks making them full once the outer stages run out. Any ideas are open, I just want to get to the Mun again today. (And tomorrow Minmus)

[Nibb31]

Why so big ?

This will get you to the Mun and back and have fuel to spare:

[nhnifong]

You can get to the moon on much less than that and still get three kerbs there.

But to answer OPs questions, because huge rockets are fun.

The style of radial decoupler you are using is unnecessarily heavy.

one or two of the traditional 1 meter liquid engines would be lighter and more efficient than the 5 short 3m engines you have,

you have too many heavy legs.

The large decouplers are too heavy. Even though it looks stupid, the 1 meter decouplers are just as good and much lighter.

Allow your final stage to be very small and only have 1 tank.

connect side-mounted stack to their parents at the top and bottom with short struts. this is more important that connecting them to their siblings.

allow your radially mounted engines to drop in pairs 2-->1-->0<--1<--2.

don't look at the smoke while launching.

clear the KSP area of debris.

[Vanamonde]

The thing you are using for a lander is big enough to be the middle-stage of a lander-delivering rocket. You'll discover that while it takes a huge rocket to get to Mun, a lander can usually get all the way back by itself because it's not fighting Kerbin's atmosphere and gravity on the way out, and the atmo is actually helping (to decelerate) on the way back. I suspect most of your other problems arise from the requrement to make the rest of your ship proportional to that mega-lander. But also, you might try replacing the large, circular decouplers with small ones supported by struts, because in the current version of the game, there is a glitch and the large decouplers are much weaker than they're supposed to be.

(Just out of curiosity, what are the small landing legs on the capsule for?)

[Markus Reese]

For big rockets, I have little tidbits I like to pass along. They should help reduce the girth and in doing so, help with the rest.

First, nibb31's rocket might get there, but uses mod parts and I suspect a bit of the fuel bug. Where is the fun in exploiting bugs?

Second and foremost, reduce weight whenever you can. Remember that in lower g environments, you don't need as much thrust plus engines work more efficiently. From experience I can tell you that using for of the 2m half tanks with the efficency engines is overkill. I usually use the small booster ones radially mounted around the large core tank much like you already have in your single man lander. Possibly your mid engine, switch to the half tank instead of full tank. That would reduce alot of weight and help the launch considerably.

Third looks like you are already making use of. Fuel crossfeed. Try to avoid nonpowering engines whenever possible on launches. The outer ring of engines and their tanks should also feed towards your core orbital engines. Remember your engines are burning so much fuel per second so the faster you get to orbit, the more efficient your rocket will be. So while those outer ones timewise will run out of fuel sooner, they should, depending on weight balance, run out of fuel at a higher altitude which is really what is important. The outer tertiary ring and the secondary ring of engines if all firing together should do alot for your launch, but again, already looks like you are doing that.

Lastly is SRBs. Use those SRB engines on the ground to get that initial hit of velocity and into thinner atmosphere. I think if you removed that tertiary ring of tank and engines, replaced those with SRB it would be a considerable gain. Depending on when you are running out of fuel however, it might just need that initial speed boost at launch only.

With the large tanks, there really is no way around the struts, atm, the connections for the 2m parts are weak, so liberal struts are required. Also on the pad, try to use the launch stabilizers. Put them in your engines ignition stage so they launch the same time as the rocket stabilizers release.

[EndlessWaves]

Laggyness is caused by too many parts so sometimes it's sensible to accept a little more weight/less efficiency if it means fewer parts (1x large rocket rather than 5x aerospikes for example).

[EndlessWaves]

I would go for something like this:

It's capable of putting your 'lander' in a circular 75km kerbin orbit and runs pretty well. It's not the optimal design as I'm experimenting with modular ships so there are more struts then I'd like, and possibly a tank or two more than needed, but hopefully it can serve as a comparison.

Craft file: [ATTACH]33014[/ATTACH]

p.s. The lander may be missing a few bit like RCS but the overall plan is the same. I've only used four landing legs which will be enough for a low gravity landing on mun/minmus, the original 12 was probably sufficient to land the whole thing on kerbin with no engine assistance.

[lazarus2405]

Minimize the mass you have to deliver to Mün. The heavier your lander (and return stage) is, your launcher has to be exponentially bigger. Remember, to lift a larger payload you need more fuel, but then you have to lift that extra fuel, which itself requires more fuel...

Fun facts: In the real Apollo program, Grumman engineers went all-out to save weight on the lunar module. There were only two tiny windows because glass is heavy. Many non-structural areas were only a couple layers of mylar thick, which they then acid-cleaned to shave off grams of microscopic dirt. Some technicians signed and attached a paper note of good luck to Neil and Buzz to the arm of the external video camera on the Apollo 11 LM - and they even weighed the tape and paper!

[BruceJohnJennerLawso]

Launching even a basic 3-crew capsule with 1 large fuel tank & engine into orbit is incredibly hard, almost too hard, indicating a need for some parts tweaking in 0.17 or later. That being said, however, I have found one very stable way to accomplish it with a minimum of parts. Go on youtube and check out Scott Manleys video showing a complete minmus mission using only 8 parts or so. As you can see, that wont work in 0.16, due to the CM rescale, but try building the same idea (Command Module/SPS fuel tank/SPS engine/decoupler/3 Fuel Tanks/1st stage engine) with the big parts. Then add 3 of the 1m fuel tanks radially around the 1st stage base, add 1m engines on them, & crossfeed both ways, to and from the big 1st stage tank. Lastly add 3 large SRBs radially in the spaces between the small engines. Believe it or not, this design will get a 3-person CSM stack into orbit with at least 75% SPS fuel almost every time. The design sorta follows the Rocket science problem where a designer wants high-thrust, low ISP at launch, but needs lower-thrust, high ISP most of the time after Pitchover. The space shuttle took advantage of this by jettisoning its SRBs (high thrust, low ISP) before using up all fuel for the Liquid fueled main engines (lower thrust, higher ISP), but the KSP SRBs arent heavy enough to warrant a decoupler after burnout

[sjwt]

I have finally gotten off my ass and worked on a light weight Muner return vessel for 0.16...

I present Selena, named after the Greek Titaness of the moon!

Download at.. Selena MkI

For a tutorial in how to fly to the mun and back on the cheep, check this video out.. a little out of date, but thats how I got this there and back again!

http://www.youtube.com/watch?v=GzEEcNnBxqM#ws

Extra instructions..

This is rather close on the fuel, and my placement of the parachute did not help, when landing, you need to slowly burn the remaining of your fuel once you are bellow 1k and above 500 to get your speed down, or the parachute will be ripped off..

I would consider adding boosters to relieve some of the fuel.!