Re: Cheap Access to Space
- From: kT <cosmic@xxxxxxxxxxxx>
- Date: Mon, 17 Dec 2007 20:31:08 -0600
John Schilling wrote:
On Sun, 16 Dec 2007 13:46:00 +0100, "Jim Relsh" <jrelish@xxxxxxxxx> wrote:
<wrschlanger@xxxxxxxxx> wrote in message news:a4a31ddd-0ed9-457a-8f95-4b9c82001804@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxThere has been lots of interest in Scramjets because of their
potential to lower the cost of access to space, or Single Stage to
Orbit as a means of lowering cost of access to space.
I personally believe we won't see cheap (as in: every ordinary Joe can go into space for the price of an expensive airplane ticket) access to space for hundreds of years. Why? Because no matter how you view it we're still using good-old fashioned momentum-transfer technology where we spit out something in one direction and we and the rocket move in the other. Rocket technology is and will most likely continue to be the easiest and best way to get into space but due to the size and explosiveness of these vehicles it will remain something of a hazardous experience making it impossible to launch millions of people into space.
"Size and explosiveness of the vehicles"?
The typical rocket-powered space launch vehicle has a dry weight rather
less than that of a typical jet airliner. Even the Space Shuttle only
comes in at 282 tons with the ET and RSRMs, comparable to a 747-400 or
an A-380, and the Shuttle is the behemoth of the launcher world. An
Atlas 552 comes in at 48 tons dry, which is less than a 737 or A-310.
The gross weight is rather more, but not hugely so and in any event
that's all fuel. Fuel is cheap; even a shuttle's worth of fuel should
only cost ~$3.2 million, which divided by the hypothetical capacity of
an all-passenger shuttle would only come to $40K/ticket. A bit more
than the usual airline ticket, but plausible for an Ordinary Joe's
once-in-a-lifetime dream vacation, and again the Shuttle is a bloated
monstrosity even by today's standards so that's an upper limit.
Related to this, the ammount of payload you can deliver to orbit per
ton of vehicle is rather less than a jet airliner can manage. But again, not by so much as to make tickets impossibly expensive.
As for explosiveness, well, OK, the Shuttle does have those pesky solid
rocket motors. So look at a no-solids Atlas. There's seventy-five tons
of kerosene in there. I'd wager you have flown on airplanes with more
than seventy-five tons of kerosene on board, without fear of perishing
in a sudden, random explosion. It's true that the rocket also has a
whole lot of liquid oxygen, but liquid oxygen isn't explosive or even
incendiary unless it has fuel to match, and if your fuel supply is
seventy-five tons of kerosene that's plenty for a vehicle-immolating
fireball just with ordinary air as your oxidizer.
So how is it that seventy-five tons of kerosene is somehow inherently
more explosive in a rocket vehicle than it is in a jet?
If a rocket crashes, it will probably "explode". Big-ass fireball, at
very least. But the same tends to be true of jet airplanes, and in either case the explosion is almost always A: the result, not the cause,
of the crash, and B: irrelevant because the vehicle and payload were
already lost on account of being smashed into the ground at high speed
or something like that.
Rocket-powered space launch vehicles are not terribly large and they are
not terribly "explosive". They are, at present, very expensive and very
unreliable, but that's not the same thing. And more importantly, the
cost and the unreliability are in no way intrinsic to rocket propulsion.
One of the benefits of hydrogen is that you don't need any escape motors, just a blast shield, and well designed seat and vehicle.
The hydrogen fireball will blow you right out of it, and then blow itself out. The hydrogen core stage itself is a great kick motor.
One less thing to worry about!
.
- References:
- Cheap Access to Space
- From: wrschlanger
- Re: Cheap Access to Space
- From: Jim Relsh
- Re: Cheap Access to Space
- From: John Schilling
- Cheap Access to Space
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