Failing at anything past basic rocket design, can't escape the atmosphere :(

[zeritor]

I've tried various rockets like this: http://i.imgur.com/i6V20Ud.jpg

This is meant to be an attempt at getting a lander on Mun and back.

However, trying this design and even larger designs with more solid boosters and a bigger main engine has pretty much exactly the same results. I can only get the apoapsis of the orbit to be at about 60,000 with an orbit speed of barely 700, so as I try to change course to stretch out the periapsis I just end up with my motion vector point back towards Kerbin.

I can get a basic rocket into orbit just fine but any more advanced I seem to struggle with how to lift the extra weight!

[Epic DaVinci]

First of all, welcome to the forums.

Looking at your ship, it seems that once the SRB's are spent you dont really have much more than the one stage left, which is not enough.

Have a look at Asparagus staging + Srb's it can really help you get into orbit efficiently.

Also, have you got fuel lines running from the 4 mounted fuel tanks on the lander, into the main fuel tank? if not they are just dumb weights.

Click here, for a tutorial on Asparagus staging.

Edited April 28, 2013 by Epic DaVinci

[Nibb31]

If you haven't even managed to escape the atmosphere, don't try to go to the Mun. There are lots of intermediate steps that you are going to have to accomplish first.

First of all, you want to learn how to get to orbit. You need to nail down the basics of gravity turn, apoapsis, periapsis, orbital manoeuvers, inclination changes, and getting your ship back to the gound. There are tutorials on this.

My main suggestion is to read/watch some of the tutorials on this site and on YouTube.

As for your rocket, I'd say it is lacking at least one stage. Cut down that center stage, put a poodle on it, and use it as an upper stage. Add a large orange tank underneath it, with a mainsail. Drop the SRBs and use liquid engines instead. Read up on asparagus staging too.

[Specialist290]

Another handy thing to learn would be Tsiolkovsky's rocket equation, which lets you calculate the delta-v (potential change in velocity) of your rocket as a whole. These two pages explain the process in detail, but also in fairly simple terms. It takes a while if you do it all longhand, but it's handy to know the equations even if you let a plugin do the actual calculating for you just so you understand what's going on.

For reference, the delta-v target for getting into LKO is ~4,500 m/s.

[Vanamonde]

The rocket in your picture has enough thrust to carry a greater weight of fuel, so adding more fuel will allow it to go farther. But resist the temptation to add more engines, because as backwards as it seems to newbies (including me when I was a newbie), engines can actually hold you back. You want just as much thrust as necessary to lift the fuel you're carrying at about 1.5Gs of acceleration, and no more. Practice playing with those factors, and you will learn to greatly extend the range of your rockets.

[EndlessWaves]

However, trying this design and even larger designs with more solid boosters and a bigger main engine has pretty much exactly the same results.

Scaling up your rocket doesn't make it go any further.

So why do you get rockets of different sizes? Because the whole rocket scales up, including the payload. Bigger rockets can take heavier payloads the same distance as smaller rockets and their lighter payloads.

The efficiency factor that determines how far a rocket goes is largely the percentage of weight that's fuel. More fuel for the same weight makes you go further.

But the mass of your rocket is almost all fuel tanks anyway, how do you add more?

The key thing to do is actually not to add fuel, but to ensure you minimise your non-fuel weight at all times. In particular:

1. Use the smallest fuel tanks you can get your hands on. Down to the FL-T200 fuel tanks have identical proportions of fuel weight and dry weight (i.e. 4 quarter size tanks are identical to 1 full size tank). You get far better efficiency using small ones as you can jettison their dry mass much sooner rather than wasting fuel carrying a partially empty tank for a long time while burning all of the fuel in a large tank.

2. Staging fuel tanks good, staging engines bad. For a kerbin ascent you use all engines right from the start. You can drop excess ones but you should not be carrying engines you're not using. Any on the payload can have a fuel line run up to them so they only use fuel from the lower stages. Any engine you're carrying that isn't being used means you've had to fit another engine to lift it, so you've got twice the weight in engines that you need (and more fuel burned to lift this extra weight. On interplanetary trips where you may need fine control for landing or will be dipping back into an atmosphere the situation isn't as simple but it's a good rule of thumb.

[capi3101]

Got nothing to add that everybody else hasn't said. Those SRBs ain't going to get you very far and then your main tank doesn't have enough fuel to get you the rest of the way. Your lander looks beefy enough to hit the Mun. I'd suggest replacing the SRB outriggers with two F-800 tanks and an LV-30 each, and set an external fuel duct to run from them to the center engine. Use all five engines at liftoff; that Mainsail in the center should get you the rest of the way. If it doesn't, add a third can of gas. If there isn't enough thrust, increase the number of outriggers to six and consider using the larger radial decoupler.

And listen to EndlessWaves; his advice is liable to be better than mine.

[zeritor]

Wow guys, thanks for all the advice! There's so many helpful people here, obviously I can't reply properly to you all.

Thanks for the nice welcome. I have read all your posts and been trying various changes. I've not had the sucess I was originally after but that's possibly because I was aiming too high

The SRBs were just so I could turn my ship easier in space, as previously I could barely shift my ships rotation due to its size.

I managed to get a rocket into orbit by staging my fuel differently, however each fuel tank had an engine and I was out of fuel once I actually reached space. So after reading some of your posts, I'm going to aim for a more central thrust supplied by various stages of fuel so I an jettison the dead weight.

The main problem I have now is once I'm in space, what design should I have? Will I have decoupled the old larger thruster for a smaller design? I tried that but ran out of fuel whilst stabilising the orbit.

[falofonos]

As vanamonde said, anything over 1.5g acceleration is mostly wasted fuel. The first 20km of ascent you're fighting both the highest gravity and the highest drag. Keeping the acceleration down during that phase is mainly to keep your rocket below terminal velocity to make a small reduction to fuel wasted on overcoming drag however.... If you are comfortable creating a monster you can create a pancake of SRBs around your payload and just force the thing to 100km altitude through sheer brute force. Your Kerbals may be experiencing 10g on the way up but they're resilient fellows.

A rough estimate with stock aerodynamic model and terrible rockets I make says that to get any payload to orbit I am going to be burning roughly 3 to 6 times its mass in fuel (depending on how many rocket motors are involved).

Once you have established a stable orbit above the atmosphere with your fueled mission section getting to land on the Mun is relatively easy.

A minor thing but I would change the staging so that the parachutes are in stage 0 and the Munar ascent rocket is a separate stage. That lander may need more than one parachute to safely land on Kerbal if you're looking to have it land in one piece.

[capi3101]

I built a lander that looks almost exactly like yours as one of my first designs (I'd put up the .craft file but the forum's been stupid since it got nuked). Trying to remember my design - I think it was what I suggested to you earlier: a set of six outriggers with F-800s/LV-30s, with external fuel ducts attached to the central tank (which used an LV-45). That gave me sufficient fuel to get in orbit and get out to the Mun before decoupling completely from the ascent stages; I usually didn't jettison that part of the stack until after I'd made the initial descent burn for the Mun. If you've got one of those dinky engines (LV-900?) on the lander and 4 F-200 fuel tanks on the lander, you've definitely got enough fuel there to get down to the Mun and return safely.

A word of caution: first time you try to land on the Mun, you will botch it. Probably badly. Like death badly. To avoid death, send a Probodobodyne OKTO with 4 PB-NUKs in place of the command pod; same weight as a Mk-I Command Pod, same functionality, no kerbals.

Except yours had the big command pod, didn't it? Okay, first tweak: swap that out...

Second tweak, you should consider using the LT-1 instead of LT-2 landing legs. You'll save weight and they should still support what you've got.

Just took another look at my lander design; I had put the big RT-20 SRBS on the bottom of my LV-30s/LV-45 with stack decouplers. Big no-no there, of course, but it was one of my earliest designs. I do recall it gave me like 700 extra m/s of delta-V...

Edited April 29, 2013 by capi3101

[Laphtiya]

A word of caution: first time you try to land on the Mun, you will botch it. Probably badly. Like death badly. To avoid death, send a Probodobodyne OKTO with 4 PB-NUKs in place of the command pod; same weight as a Mk-I Command Pod, same functionality, no kerbals.

This is actually really good advice, I built an Apollo style mission with command module and MunLander but I attached a small Probe on the top of the Lander below the docking port. This way I could take a fully fuelled mission with all parts I wanted but I could land without risking Kerbals and simulate a return flight so I could tweek my designs. Later I added a rover but I moved the probe to the base of the lander which gets left behind do I can always revisit the landing sited for happy memories (plus control the rovers as drones now).