Is bigger better

[Nomial_Control]

Is bigger rockets with lots of fuel and lots of thrust better, or smaller rockets with smaller fuel and smaller thrust Bette?

[Xannari Ferrows]

It depends on what you want to do with it. Big rockets with high specific impulse engines can get you more Delta-V, but small craft with a low mass to fuel ratio can get you decent Delta-V, and generally costs less.

[Vanamonde]

It's not so much the absolute numbers as the proportion payload to fuel to engine efficiency that determine rocket performance. Look in the tutorials section of the forum for explanations of "delta-V."

[Lord Aurelius]

The best rocket is just as big as it needs to be and no bigger. In other words, when you reach orbit you should have very little extra fuel left (at most enough to deorbit the upper stage).

As for thrust, you want a lot of thrust in the lower stages to get the rocket up to speed until you've done your gravity turn (this is what SRBs are for), at which point you just need enough thrust to keep pushing out the apoapsis so you don't fall back into the atmosphere. The exact numbers will vary based on the specific rocket/payload and ascent profile, but that's generally how it works.

[Lego8_bit]

basicly building a big rocket is cool and all but in reality it depends on where your going and if your coming back.(if you want to come back that is >)

[Nomial_Control]

Thx everyone

[Shpaget]

Aurelius is onto something.

If you can fly a perfect trajectory (with no fumbling around) and do the intended mission with no fuel left, you've made an optimal rocket.

Generally speaking, you want the engines to be as light as possible, but with as high ISP as possible. However, to reach orbit you need high thrust engines since you don't have the time to wait for ions to push you over the period of several hours. You'll be reentering in matter of minutes.

High thrust is also needed for lift off, since you want to spend as little time as possible fighting gravity and pointing up. The trouble is that high thrust engines usually don't have a particularly good ISP. You need to find the balance, which is not hard if you use a mod such as KER which automatically calculates your thrust to weight ratio, burn time for the given amount of fuel, dv, etc..

Having that information, you can try different configuration. Small fuel tank with small, weak, but high ISP engine, or larger tank with more powerful, but less efficient engine.

Unfortunately, the problems don't stop there. Let's assume that a larger tank with larger engine is more suitable for the final stage. You now have to make all the lower stages larger too. This means that for a small increase in payload (or final stage), your previously smallish rocket has now grown to be a monstrosity.

I, like probably everybody else (right?), build the rockets in reverse, starting with the last stage. After building the payload (for example a probe with all the stuff it needs to accomplish the mission) I try to figure out the minimal dv required and try out different fuel tank/engine combinations to achieve that dv, while keeping the total mass as low as possible, while still keeping an eye at TWR if I need the probe to land somewhere. Overengineering is a sure way for a rocket to fail. Moar boosters!! applies only for the first stage.

[Frank_G]

Bigger might be better... but efficient is always best.

And welcome to the forums Nomial_Control!

[Just Jim]

OK, I have an example where bigger isn't better, my space station shuttles. I have stations in orbit of Kerbin, the Mun, and Minmus, and I experimented with several designs for a shuttle that could ferry crew and tourists from one station to another.

At first I built them big, like this one:

But later I made a smaller shuttle that proved much more efficient:

The second shuttle is only half the weight and fuel of the first, but has more efficient Nuke Engines, and can get to Minmus and back with almost 50% more fuel left than the bigger shuttle. Plus it's easier to dock a smaller ship.... IMO.

So in this case, smaller is definitely better.