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On Tuesday 23 October 2007 23:57, Eric Lavigne wrote:
> > It's not reasonable to expect rockets to run as cheaply as airplanes:
>
> The claim was not that the total cost would be similar to airplanes,
> but that fuel would make up a similar portion (1/3 to 1/2) of the
> total cost. Thus $10 worth of fuel per pound of payload translates
> into between $20 and $30 of total cost per pound of payload. Your
> arguments which follow all suggest a higher fuel consumption but
> provide no indication that costs other than fuel should make up a
> larger portion of the total cost.

The claim is backed up by no evidence whatsoever. Just a dubious analogy to 
airplanes. They also say it is a rough order of magnitude claim, meaning that 
they think the cost is under $100 of fuel per pound delivered to orbit. And 
since you brought up the aircraft industry, it probably suffers from more 
regulation and licensing requirements than any other, but that doesn't seem 
to be keeping people from flying. The claim that most of the cost of a $30 
million launch is due to regulations and politics just defies common sense. 
What it is due to is the high cost of engineers and skilled technicians.

You can find lots of web sites which calculate that a gallon of gasoline has 
more than enough energy to put a one pound payload in orbit. That's a physics 
student answer. The engineering answer is that to get the pound of payload in 
orbit, you have to include fuel and oxidizer tanks, an engine (more likely 
two or three), and some sort of guidance system. In other words, it takes 
tens or hundreds of pounds of support to lift that one pound payload into 
orbit. All of those tanks, engines, and structural members weigh far more 
than the payload itself, and they all have to be lifted at least part of the 
way (the reason for multi-stage rockets is that you can dump some of the 
excess weight and reduce the fuel requirement to something significantly less 
than infinity).

The huge amount of fuel required is also in part because you are pushing the 
rocket at high speed through the lower atmosphere -- wind resistance 
increases as the cube of velocity. That's one of many reasons recent efforts 
toward a low-cost space transport system have launched from airplanes or 
balloons. It also has the advantage of requiring much less in the way of 
ground facilities.

The Pegasus launch system (the first privately developed launch vehicle) uses 
this strategy but still costs $30M per launch with a payload capacity of 443 
kg. Not nearly the bargain that SpaceX expects to provide when they become 
operational. And the Pegasus vehicle weighs 18,500 kg (almost 90% fuel), more 
than 40 times the weight of the payload it carries to orbit, not counting the 
110,000 kg aircraft that carries it to altitude.

Yes, some day space flight will be cheap, comparable to air transport. But 
that will not be because someone got rid of all the regulations, lawyers, and 
politics. It will be because some rich people were willing to spend an 
obscene amount of their own money to pay for an obscenely priced service 
until the economies of scale (and experience) bring the cost down to 
something more people can afford. Some people are already paying the Russians 
around $20M each to fly to the space station. When SpaceX offers them the 
opportunity to fly to a private hotel in space for the same price, they will 
have customers. And then the cost will drop to $10M, then $1M, then $100K, 
etc.  Almost all modern technologies have been developed the same way: early 
international telephone calls cost $10/minute at a time when $10 was a week's 
pay for a secretary. They had customers. The first cell phones cost $3/minute 
when a secretary got $5/hour. They had plenty of customers. The first 
commercial airliners... well I don't know what they cost, but it was rich 
people flying in them.  They each became affordable because enough rich 
people bought the service to keep it in business long enough to pay off 
development costs and gain enough experience to become efficient enough that 
the average person could afford it. If you want to kill the future of cheap 
space transport, then increase taxes on the rich, or increase taxes on the 
profits made by investing in space flight (we call those "capital gains 
taxes").

- Bob