Steel

Yep, rocketry is in fact that hot http://www.braeunig.us/space/comb-OE.htm

Also just FYI an ethanol/oxygen combustion temperature will be in excess of 3000K. Solid rocket motors are more difficult to tell because the propellant absorbs most of the heat for most of the flight.

No as hot. Also regarding launching rockets in the US. I've just had a brief skim of the FAA website and to launch anything with more than 125g of propellant you need to get permission from the FAA for the launch, launch further than a quarter of the maximum expected flight altitude away from any other persons or property and be under the supervision of an adult (i.e. over 18) who takes responsibility for the whole project.

While Charlie Duke is undoubtedly a cool guy, he almost certainly couldn't build a rocket anywhere near as well as he could fly one

So a lot of these have been answered above, but on the subject of gimaballing, it's a really complex thing to try and do. Trying to keep the engine bell attached and not melted if it's part of the combustion chamber will be hard enough, gimballing not only add problems in that department but also numerous extra points of failure as well as having to add a large and well insulated hydraulics system to you rocket. In terms of control you're better off going with fin stabilisation and some clever flight planning. The JAXA mission I mentioned earlier has NO ACTIVE GUIDANCE (i.e no movable fins, no gimbal, no thrust vectoring) onboard, it just uses spin stabilisation and pressesion about it's long axis to get into orbit For liquid rockets, you're looking at combustion temperature ranges in the 1000s of degrees, far above the melting point of almost any metal (unless you're willing to splash out on some horrendously expensive high temperature alloys of titanium or similar (all dependent on your choice of proppellant) your choice to keep the nozzle from melting are to make it out of an ablative material (essentially like a heat shield), to cool it by pumping fuel or some other fluid through the engine bell (hugely complex and potentially very dangerous if not designed properly), or to fire the engine for such a short time that the nozzle doesn't overheat. The thrust you need is entirely dependent on your weight at launch, but you're looking at kN ranges. I have no idea how you would go about using a turbopump rocket engine without 10s, if not 100s of engineers, so you'd be far far far far far better off with a pressure fed system (emptying a tank of inert gas forces propellants into the engine, rather than a horrendously complex piece of turbomachinary moving at over 100,000 RPM)

Nope, he said he wanted a liquid first stage and solid upper stage!

These last two posts have it exactly: There's never one, perfect design. There is always more than one way to meet a design brief. The design that Scaled Composites have come up with satisfies their brief, and does it while drawing upon their existing expertise. Yes it could be changed as @Northstar1989 has said, but if the design already fits within all their targets, why bother? Let's put it this way, in an alternate universe where the designers have designed the carrier with all the changes that have been talked about in this thread, there would probably be a discussion on an internet forum about how they should have used straight wings instead of swept ones and how they could have only used 6 engines rather than all 8.

We don't even use the metric system properly, we still use miles for speeds and distances (despite the fact that very few people under 30 or so could actually tell you how far a mile is) As for football... anyone who want to see my thoughts on that one can click the spoiler below, I'm not going to clutter up a thread on Planet 9 with it Anyway, so from what I can see of this new Planet 9 stuff, theres a little more evidence of it's existence from some people who are looking really hard to signs, but there's still nothing anywhere near concrete?

In Europe (though strangely not here in the UK) and probably some other places too they use decimal points to denote thousands and commas to donate decimals

I doubt there's anything as concrete as a proof. The issue I guess is the fact that the system is chaotic, so it's hard to know how a small change will affect the outcome until you actually try it and see. This is a large part of the reason long range space missions use weeks of supercomputer time for trajectory analysis.

These look great for anyone who wants to get a bit deeper into the theory. Delft is an excellent technical university (just see their FSAE team or their amateur rocketry program)

Yeah, what efficiency are we talking about here?

If you're genuinely serious about wanting to do high-performance amateur rocketry, the way I'd suggest going is this (ideally with some help/guidance from people who have done this stuff before): 1. Build and test a small-scale engine. Follow the thread below exactly, build a small rocket engine and get to grips with the complexities involved. 2. Scale the engine up. Build bigger and bigger engines, one step at a time. Bearing in mind that if your end goal is the first ever amateur launch to orbit, you're going to have to single handedly develop the largest and most powerful amateur rocket engine ever, so just keep scaling it up. 3. Once you have an engine that works, then you can start to think about making a rocket to go with it. By all means use melted down drinks cans to make the our skin, but for structural components, tanks e.t.c (components where small flaws in your manufacturing process will be catastrophic) i'd use material made for industry.

Wrong. You do not. KSP does not furnish you with the tools to design and build an orbital rocket.

This is real hazardous.

Yeah, echoing what others have said above, without wanting to crush ambitions, I think you might want to take some time to think about this. For a start, only one amateur team has ever reached space (i.e above 100 km), and it took a team of around 30 people (some with a lifetime of experience building amateur rockets) to design and build the rocket. The smallest rocket that has ever tried to reach orbit is the one that the Japanese space agency attempted to launch last week. Bearing in mind that that was made by JAXA (a large antional space agency), it had no active guidance and was all solid motors - they didn't even consider liquid propulsion. It also stands almost 10 metres tall and half a metre wide. In rocketry, safety is everything. I don't care who you are or where you live, if you have lax attitudes towards safety you will put people in danger and you will get shut down.

Ok, so how are you planning to get hold of and store cryogenic oxygen?

What oxidiser are you planning to use along with the ethanol? Also are you planning to actively cool this engine, as most fuel/oxidiser combinations burn a lot hotter than the melting point of aluminium alloys?

Ok. Are you planning to build the engine, plumbing, pressure vessels e.t.c from scratch too?

Yes, but do you have a way to accurately measure and control the composition of the alloy you've attempting to make? Ok, sensible choice! Which oxidiser?

Yes, I'm aware that the alloy exists, I'm just saying you'd probably struggle to make it in a workshop by melting down drinks cans. The other question I had was what sort of fuel you would use for this?

Ok, what are you trying to tell me?

Amongst many other things, I think you may find this particularly difficult if you have no way of accurately monitoring or controlling the composition of the metal. Drinks cans are not 100% aluminum and don't have a standardised composition, so you could large amounts of steel in them in some places, no steel in other places e.t.c. Also, I'm not sure there are many shops that have equipment that can deal with getting copper up to it's melting point (almost 1400 K)

It is true. I've done the integrals and, as weird as it sounds, it is true. If you don't fancy doing it yourself, see below: https://en.m.wikipedia.org/wiki/Shell_theorem

Or, as is more likely, that they do not want to fly at the engine's top speed.