August 25, 2005
Now Oh-bit, Oh-bit, Oh-bit
Posted by scott at August 25, 2005 09:52 AM
(Don't worry, there's only one person out there who's supposed to get the title.)
Slashdot's carryinig this update on developments in the private spacecraft industry. Virigin has announced its third generation spacecraft will be capable of Earth orbit. It now joins several other projects in vying for the fifty million dollar America's Space Prize for orbital flight.
Of course, announcing something is quite different from actually producing it. Orbital flight is supposedly much more difficult than the sub-orbital stuff that won the x-prize this year. Still, they've given themselves quite a bit of lead time, so who knows?
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HAHA!! thats how my dance teacher, Bonita said 'orbit' :).
and fah on the more difficult part. Just put a bigger rocket on the bugger. that'll get it orbiting.
Now, coming back in might be a bit difficult, but how hard can it be - just slow down and there goes the friction problem. maybe they could do with with big parachutes. kinda use them like sea anchors. alternatively, couldn't they go geosynchronous and then decend at roughly the same speed, thusly killing off friction?
(okay, I'm really not up on all of this space stuff. All I want is the Millenium Falcon parked in my garage so I can go jaunting around at my own free will. And blow stuff up with the laser cannons.)
Problem is, the nature of matter changes as you make things bigger. A structure that works fine at 1/1000 scale model will often collapse under its own weight at the actual size, even if made of materials that are a thousand times stronger.
My understanding is that, if you make a rocket too big, the weight of the fuel alone will prevent the rocket from reaching escape velocity, no matter how fast you burn it or how efficient your engine is. That's why rockets are made out of the lightest materials that can withstand the stresses of space flight... and even then, they have to disassemble themselves in mid-flight so the empty fuel tanks don't weigh them down.
Of course, I'm no rocket scientist either, and if I've been corrected about this before, please remind me, as I may have forgotten again.
You're talking about the "fuel fraction", and are basically correct, but with further implications. From various discussions I've read, one of the reasons space flight is so expensive and dangerous is because the chemical rockets we use aren't really all that powerful for the job they need to do. This forces the fuel fraction (the percentage of the weight of the craft that is, well, gas) to be up in the 90% range. In other words, the ENTIRE SPACECRAFT cannot make up more than around 10% of the total weight the engines have to lift, and that 10% must be able to withstand the complex and demanding environments spacecraft have to deal with. Hence launch vehicles that are incredibly expensive, fragile, and complex. When these factors are kept in mind, the Shuttle seems less a white elephant and more the miracle of engineering it really is.
Commercial aircraft typically have weight fractions in the 50-60% range, and if we were to figure out engines powerful enough to get spacecraft in that range that whole "Pan Am" sequence from 2001 suddenly becomes possible. Unfortunately there's nothing on the horizon promising that, so we've basically been waiting for materials science and engineering to produce stuff that performs in the 90th percentile that is comparatively affordable. Carbon composites are most of the answer, but in truth until we figure out some other way to get up there, spaceflight will probably remain in the realm of "the few and the brave" for some time to come.