Or, “You don’t know what you’re talking about Snarky Boy.” that came from this and this.
That may be, after all I’m not a rocket scientist. However, I do have some experience scaling things, and while I might not know the correct rocket terminology, I think I’m correct when I stipulate that chemical rockets will never lift enough mass off the Earth to allow a meaningful human presence in space.
The Saturn V, the biggest thing we’ve ever launched (just go with me here) weighed in at 6,699,000 lbs, or 3,350 tons, and managed to put a measly 100,000 lbs (50 tons) into lunar orbit.
So lets pretend we want to build a classic L5 space colony. How big does it have to be?
Well, I don’t know, but the Empire State Building weighs 365,000 tons and it’s only about a thousand feet tall. Some of the L5 colony designs are several miles long. But for the sake of argument, lets start small.
The Snarky L5 habitat will weigh 500,000 tons. I suspect that’s too small but you’ll see it doesn’t matter for the sake of this thought experiment.
The Saturn 5 could lift 50 tons into Lunar orbit. L5 is comparable to lunar orbit for our purposes so let’s start building Saturn Vs to launch material and start building the Snarky Space Colony.
We’ll need 10,000 Saturn Vs. (NASA only ever launched 12, so we might have a problem or two.)
If we launched one a day, we’d be done in 28 years. How likely is that?
Lets wave a magic wand and double the payload to L5.
That’s now 5,000 magical rockets.
Double it again. The rocket gods have blessed us with a magical chemical rocket drive that can put 200 tons of payload at L5. (I’ll leave it to the real rocket scientists to explain how unlikely that really is.)
That’s 2,500 super magical rockets.
For one colony.
Oh. Did you want more than one colony?
How about supplies and such?
Oh, you cry foul… That’s cheating to insist on L5. Build it closer, like in Low Earth Orbit.
OK, lets see, the Saturn V could put 130 tons into LEO. It doesn’t help much. The biggest step is getting the mass off Earth in the first place.
It’s just not going to happen with chemical rockets.
On the other hand, General Atomics figured they could launch a 400 meter diameter, 8,000,000 ton (Yes, that’s 8 million tons) payload at once. And not just to Earth Orbit, but anywhere you wanted it.
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I apologize for my colleagues’ rudeness, but they are mostly correct. The problems with chemical rockets have nothing to do with scaling. We don’t know how to make cheap small ones, either.
The mass of a pressure vessel scales linearly with volume. Aerodynamics favors larger vehicles, and larger launch vehicles tend to cost less per pound than smaller ones. There’s no reason in principle why you couldn’t build a rocket as large as a supertanker and launch it from water as Robert Truax (Seadragon) and Jim Akkerman (Advent) proposed. But you’d never find enough customers at $5000/lb. to fill your manifest. The problem is that all launch vehicles, large and small, are prohibitively expensive for commercial manned spaceflight.
However, you may be correct about having struck a nerve. Here are a couple of dirty little aerospace engineering secrets:
1. Nobody really knows why rockets are so expensive.
2. Nobody will admit that they don’t know.
Rand Simberg claims that it’s because of economies of scale, but I’m not persuaded. I prefer Maxwell Hunter’s “lack of intact abort capability” explanation.
You have an economics background. I would be delighted to hear your reaction to my Launch Cost Rant (a discussion of 19 different explanations I’ve heard):
http://home.earthlink.net/~peter.a.taylor/launch.htm
Once you get into low Earth orbit, I agree that large vehicles need something better than chemical rockets. But for Earth launch, if we don’t know why chemical rockets are so expensive, how do we know that something else is going to be better?
Peter Taylor
Economically speaking, I think there is one main reason rockets are so expensive, although everything on your list (except for the first three) contributes to the problem.
Economies of scale in rocket production and operation.
Historically, rockets have been one off builds. One offs can’t use the economies of scale that an industrial production line brings to cost savings. Since World War II even airplanes haven’t been built in true assembly line quantities. A few hundred or even a few thousand built won’t drive the price down much. You have to build tens of thousands or even millions. Then the true economies of scale kick in.
Think of cars. If your car had to be built one at a time, and the factory only made a few hundred a year from all custom parts, it would cost millions of dollars. Sure enough, if you look at Formula 1 cars, those are the prices they deal with.
Anything built as a one off will be orders of magnitude more expensive than the product of an assembly line. Prototypes of everything from cars to electronics are hundreds of times more expensive than the final product. I used to work for a company that designed microchips, and the chips they made to test designs were incredibly expensive because the production runs were so small. When they finalized the design, they shipped it off to one of the big fabs and the chips were made for pennies a piece.
I mentioned airplane production in WWII. The US built over 300,000 airplanes from 1939 to 1945, and on assembly lines like cars. I think that if we made that many rockets in six or seven years, they’d be pretty cheap.
Notice that I’m talking about economies of scale in building the rockets, not in launches. Operational economies of scale have more to do with manpower costs than anything else. Imagine NASA trying to launch a rocket every day of the year. Epic Fail.
One off production methods equal expensive. Sometimes there’s nothing you can do about it. Dams and tall buildings are one offs too, and incredibly expensive, but the expense is amortized through constant use over decades. A new 737 costs around $50 million (Boeing made 5700 as of 2008, an average of 142 a year. Still not what I consider production line quantities.), but an airline will fly it full, at least a couple of times a day, every day for years. A Boeing 777 is estimated at $187 – $250 million yet airlines are buying them because they know they can amortize the costs over thousands of flights. If you could do that with the space shuttle, you’d amortize the $1.7 billion cost of the Endeavor pretty quick, but it would be impossible to fly that pig twice a day, every day for years. Instead we get estimates of $1.3 billion per launch over the life of the program for the space shuttle.
If we get to the point where we can build a rocket that can be launched thousands of times with minimal turn around expense and low operational manpower requirements then they’ll approach airliner economies of scale in operation. On the other hand, if we can build hundreds of thousands of them, the cost per rocket would be lower and we wouldn’t have to worry about amortizing the costs over long term operation.
Frankly I don’t see hundreds of thousands of rockets being built. So the best bet is to come up with a robust design that can hold up with minimal maintenance for thousands of flights.
So I’ll throw it back to you, as an aerospace stress analyst, is it possible to build an airframe and engine system for a rocket that can hold up for the thousands of flights required to amortize it’s costs down to levels comparable with those of airline operations? I think your point about intact abort capability falls in there somewhere.
(My bet is no, but I’d love to be wrong.)