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[LoSboccacc]

Remembe the asas uses the point of your nose as input vector direction if your rocket bends its control will be... Suboptimal.

Also check out wing attachment because not all surfaces will produce the expected result when placed on rotational simmetry.

Static surfaces on the bottom should provide enough force within the atmosphere to keep your nose upright, but remember that you will need to turn at sone point to get in orbit so don't overdo it, I once did a rocket so stable I could not turn ot anyway 

[Chattox]

Argh, can anyone give me some tips for rocket building? Where should I be trying to get my centre of mass/thrust to be? I'm sucking hard at this, out of all my tries on the Mun, I only landed 3 times, only survived one of those 3, and had no fuel to get back.

[alexandertnt]

Argh, can anyone give me some tips for rocket building? Where should I be trying to get my centre of mass/thrust to be? I'm sucking hard at this, out of all my tries on the Mun, I only landed 3 times, only survived one of those 3, and had no fuel to get back.

For the center of mass, im not sure where it should be along the Z axis (up/down, my guess is higher is better) but along the X/Y axis, it should be in the center (the symmetry tool is increadibly useful for this). Same with the thrust. The more center-ness it is, the more straight the rocket will go (and further down from the center of mass along the Z axis will help too.)

Post your rocket as an image, it will be easier to identify issues.

[sneakey pete]

Just make sure they are both along the centreline, basically

[Sean Mirrsen]

Center of mass and center of thrust position don't matter much. What you need is the thrust vector to be pointing through the CoM. That's all there is.

General tips: the less drag on the nose, the better. Don't put wings or control surfaces on the nose. Use only as many engines as it takes to lift all your fuel. Even if all you can get is 1m/s acceleration on the launchpad out of just the engines, it'll work. Strap some solid boosters on to get yourself up to speed in that case. Remember, a simple rocket will usually work better than a complicated one. Don't overdo the staging. Remember: ASAS is a control unit, you only ever need one of it. Don't forget to use the thrust vectoring engines - larger ones don't give you a choice in the matter (they all vector), but the smaller ones, while less effective, are still vital, especially if you rely on Aerospikes too much. Don't shun the air-breathers for vertical-launch rockets. It may seem silly, but they are ridiculously effective boosters for smaller rockets. They'll save you tons of fuel just by bringing you those 15km up so your other engines can work more efficiently.

That's all the tips I can remember off the top of my head.

Also, the pendulum rocket fallacy assumes just the thrust position difference. In practice, a nose-engine rocket would be top-heavy, with the fuel tanks in the back forming an aerodynamic foil that gets lighter as the rocket burns fuel. In addition, it'd allow to jettison fuel tanks as they empty, for when the benefit of the stabilizing "tail" is less than the efficiency gained by losing its mass.

[ank]

Also, the pendulum rocket fallacy assumes just the thrust position difference. In practice, a nose-engine rocket would be top-heavy, with the fuel tanks in the back forming an aerodynamic foil that gets lighter as the rocket burns fuel. In addition, it'd allow to jettison fuel tanks as they empty, for when the benefit of the stabilizing "tail" is less than the efficiency gained by losing its mass.

I've been thinking about using the separator boosters to make a reverse rocket, with the landing stage just above the engines, and fuel tanks on top of it all. It's will then use the separators to blow the fuel tanks away from the top....
It's gonna be awesome!


There is one more thing to consider with centre of mass and thrust, above having a stable rocket:
Structural integrity. Clearly having most of the mass close to the thrust will reduce overall stress to the craft. Allowing for less struts, and therefore less lag and weight.
This is also one of the reasons why a good craft is cone shaped, besides aerodynamics.

[LoSboccacc]

An important thing is the lateral stress if you stage your rocket inside in:

If your outer layer produces struts and your inner layer engines are off, you are all weight plus inertial mass ob the outer layer struts. This is what makes more stable cross feeding fuel toward the inner layer and using the internal layer engine too.

Also, if you accellerate too much, however, the nose stage inertial mass will crush the stage separator.

[Aptus]

I think I have finally managed to create my Mun-Lander. Now I will just have to practice using it and I am good to go. I'm using mostly stock parts except for a set of nose cones and booster rockets with built in detachers. For the last stage I wanted to use a nuclear engine for fuel efficiency but I had issues with the landing gear not being long enough to reach below the engine so I am using a non-stock part that seems to be comparable statswise to the nuke engine but shorter.
By popular demand I am only using one ASAS unit now :p



Stage 1: The four fuel tanks sitting on detachers feed the main engine for take off and as far up as it goes.

Stage 2: Detach the four radial fuel tanks, turn off the main engine and activate the four booster rockets. I have to turn off the main engine here or I noticed the acceleration becomes too great and the lower part cruises on through the upper part causing everything to go boom.

Stage 3: Detach the booster rockets and use the main engine to get on a trajectory for the Mun.

Stage 4: Lander stage using the small engine to correct the course and decellerate for Mun landing. Hopefully this engine will then be enough to get off the mun as well.


I did just notice now that I forgot to add ladders to the lander so that will have to be fixed as well :p

So the rocket and lander are good to go, now I just have to practice actually HITTING that damn ball of cheese.

EDIT: Whoops I had set the booster rockets to the same stage as the decoupling of the main engine which lead to some premature shenanigans. Atleast I got to test my lander on kerbin from near orbit, I managed to straighten it out from a quite severe spin and reduce the falling speed to about 60m/s which was well within what the parachute could handle so silver lining and all that.

EDITEDIT: One feature I do really want though is the ability to dump fuel. As in not just by decoupling the fuel tank but actually emptying out the fuel from it. Would make me less nervous when landing on Kerbin if I could drain any left over fuel from the tank first :p

[Sean Mirrsen]

Okay, I have engineered myself a new ship.

Spoiler (click to show/hide)

Any bets on how the launch will go?

[sluissa]

It's just a guess, but I don't believe you have enough engine.

[Graknorke]

Destructively?
I'd say that's the word I'm looking for. Will that even fit on the launch pad?

[Sean Mirrsen]

It's just a guess, but I don't believe you have enough engine.

Well, that's one rare guess there that's both right and wrong. It has enough engine to fly, by far. But I fail at using the NERVAs to establish orbit. The previous modification got to a fairly sizeable orbit (somewhere beyond 2K Km apogee) on just the main thrusters, so I wanted to use NERVAs to take it a little further. I guess I'll need to use the main thrusters to establish an orbit first, huh?

[Aptus]

Quick question: I've seen it mentioned a few times here but what is NERVA?

[andrea]

the new low thrust high ( vacuum) efficency nuclear rocket that was introduced in latest version.

[sluissa]

NERVA Nuclear Engine for Rocket Vehicle Applications

Essentially you have a core of nuclear material which is very hot and you pump very cold, compressed fluid(usually liquid hydrogen) over it. The fluid heats up, turns into a gas, and expands out the back of the nozzle giving you thrust. The benefit to this is that you give up having to carry weighty oxidizer for the fuel. It's not perfectly emulated in the game, but essentially it gives you the same benefit.