[Very thoroughly!] Design help?

[Artie]

Erm, hi.

I've made my first rocket that's achieved orbit, but it's very unreliable. Can someone look at the design and tell me what I'm doing wrong? What happens is, I usually reach sub-orbital, but I either run out of fuel, out of power, my second stage engine comes off (bracers have since been added), or I just can't complete the circle before I crash. Something that happens very often is my second stage spinning out of control after separation, that costs time to correct.

CRAFT file link (very slightly different to images - there is now only one antenna at the top, the I-beam and nosecone have been eliminated, and bracers added between the second stage fuel tank and engine).

Top-down view

Lower section

Middle section

Upper section

After launch

Second booster separation (Note: the boosters below separated well before this)

Second stage separation (where things go tits-up)

Edited June 16, 2013 by Artie

[legoheli]

You're over-engineering massively.

The reason your craft falls apart is that it's not a stable construction, for launching that small a satellite into orbit, you just need something like this, just with 1 meter parts:

This rocket takes that entire space station core into orbit with plenty of fuel to spare.

[peeri]

First, You don't need such many wings... actually do not use any wings or thrusters at all if you have gimbal in your engines.

second, rocket seems to be about 1 stage rocket... and it is quite difficult to reach orbit with that kind of rocket.

try to make many stages and dump the extra load away when it is possible.

[Artie]

Well, the idea was to make a generic heavy launcher, that could have anything at the top and have enough thrust to put it in orbit.

Thanks for the advice, though!

Erm, before I go, though, what exactly causes that spinning out of control at separation? From your comments, you think that the second stage doesn't have enough mass?

[Syhrus]

Another reason for the problems of spinning may be that you have too many wings on the ship. They tend to make things more unstable for the amount of control they give. Try to just launch it with a pair of canards at most, or even none at all. Also, if you're having trouble when you decouple those SBRs it may have to do with the chutes pulling them into the main rockets, which could explain the loss of control. I personally wouldn't bother with the chutes, seeing as you can't reuse parts yet...

To give you an idea of what sizes are possible, this craft is capable of reaching Duna:

It has no control surfaces, no RCS, and uses a Nuclear engine to power itself once in space. (I hate ion drives).

EDIT: I just realised it isn't even set up for asparagus staging either...

[Panichio]

I guess I can't add much more than what these two just did. Some sound advice here.

You need to play around with small, simple designs and learn about the behavior and capability of parts and part configurations. With the knowledge of performances from small test-designs, you can build a larger rocket that isn't over-engineered and doesn't have too little or too much fuel.

Good luck with future designs!

[starbork]

Yep -- you're lifting a LOT of gear up for no purpose other than lifting gear up :-)

My advice is this.

1. Keep your part count as low as you can -- e.g. ONE orange tank instead of TWO half-jumbos (same weight, same fuel count, more stable, less parts).

2. Lose the RCS systems -- pods and tanks -- for your orbital mission. I landed on the Mun long before I ever learned or added RCS systems.

3. Drop parts at stages if you can --an engine carried that is NOT thrusting is dead weight! Empty fuel tank is dead weight!

4. Use fewer engines and keep them burning as long as you can (drop tanks!).

5. Trust your ASAS, and only add wings and stabilizers as a last resort.

6. Fresh local ingredients, served simply and sensibly.

Look at legoheli's design. It is designed with the mission in mind. It is simple, it is (probably) quite stable in flight. You could simplify it even further and achieve the same orbital result.

Clear skies to you sir. Please keep us informed on your progress!

[Vanamonde]

Your ambition is impressive, but why not practice getting to orbit with small ships before trying to build an all-purpose jumbo launcher?

[Artie]

Thanks everyone!

I did get into orbit quite successfully using a rocket...based on legoheli's design.

It looks like this.

...

...

Shut up .