X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
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>>Even to place a 20 kg payload in orbit would be quite a trick. The only
>>laser technology capable of sufficient power is the gas dynamic laser.
>
>Nonsense. Outfits like Avco will happily build you a CO2 laser of the
>required size, if you're willing to pay for it. (Well, it will be a bank
>of lasers rather than a single tube, but the net effect will be the same.)
>There is some small risk involved, since it will be an unprecedentedly
>large laser, but for a 20kg system it's felt to be a reasonably understood
>scaling of existing lasers.
>
>>... It would take at least 100 times
>>as much fuel to power such a laser as would be required by a chemical
>>rocket to launch the same payload.
>
>The economics of the matter have been studied; they look feasible. CO2
>lasers run on electrical power, not chemical fuels. The amount of power
>needed for a 20kg system is hefty, but not to the point of needing to
>build your own power plant.
>
The only *single* tube technology currently understood that can generate
the required power is a flourine gas dynamic laser. CO2 lasers have
horrible efficiencies and terrible cooling problems. Most others are
even worse. Getting a laser system to approach 10% efficiency is very
difficult. When you have to throw away over 90% of your input energy
as waste heat before you even start beaming energy through the dense
atmosphere, you've got real problems.
Even with a gas dynamic laser where the reactants pass through only once,
the cooling problem is severe but tractable, much like a conventional
rocket engine. Then you have to look at the problem of beaming energy
through the lower atmosphere to your spacecraft. Very high power laser beams,
even long wave IR beams, heat the atmosphere through which they pass to a
superheated plasma. That plasma then becomes a very good absorber of optical
energy further heating the gas and causing rapid expansion or "blooming" that
sharply defocuses the beam. Suddenly, you aren't delivering much energy to
your spacecraft anymore.
>>... Like the chimera of controlled nuclear fusion, they are
>>unlikely to deliver any useful results even after hundreds of billions
>>of dollars and decades of effort are expended on them.
>
>My my, aren't we negative today? :-) These systems are somewhat speculative,
>but we'd know a whole lot more about how practical they are if we spent, say,
>a few hundred million on building and testing prototypes. The 20kg laser
>launcher, win or lose, would not cost billions.
Both the laser fusion people and the SDI folks have been playing with the
problem for a while now without taking money from the space program. I
think we should let them play a while longer before funding a system that
wouldn't put much useful payload in orbit.
>>small clever rockets like Pegasus, and eventually, direct to orbit
>>aerospace planes are much more likely to be sucessful at delivering
>>payloads to orbit economically and in a realistic timeframe.
>
>Ah, direct-to-orbit aerospace planes. As Gary Hudson put it, roughly,
>"this thing is a cross between the Concorde and the Shuttle and you
>think it's going to be cheap and on schedule?".
I think that SSTO is realistically 50 years away from routine operation.
It requires a much better grasp of SCRAMJET technology and hypersonic
lifting bodies than we have at present. An interm step, advocated by
Von Braun and the original shuttle designers, of a flyback first stage
is closer to current technology. Rather than their design, however, I
envision a very large scale version of the launch system used by Pegasus.
A conventional aircraft designed to carry an orbiter to a 40,000 or 50,000
foot starting point. Most of the fuel of a conventional rocket is expended
gaining those first eight miles. It's surely more efficient to take advantage
of aerodynamic lift and air breathing engines during this early phase of
spaceflight.
Gary
------------------------------
Date: 16 Apr 91 12:44:15 GMT
From: pasteur!agate!bionet!uwm.edu!zaphod.mps.ohio-state.edu!mips!pacbell.com!iggy.GW.Vitalink.COM!widener!hela!aws@ucbvax.Berkeley.EDU (Allen W. Sherzer)
Subject: Re: comsat cancellations and lawsuits
In article <21541@crg5.UUCP> szabo@crg5.UUCP (Nick Szabo) writes:
>* NASA does not care about their customers.
Agreed. The US today would have had 95% of the launch market instead of
about 40% if NASA operations people cared about providing good service.
>Other examples include... the removal of microgravity scientists out of
>the Fred plan when they asked for politically unpopular design changes they
>require for their work.
Actually, this was a pretty gutsy move by NASA. Freedom would have long term
utility as a life science lab but not much as a microgravity facility. The
appropriations people in Congress however wanted microgravity done first.
NASA is telling the people who sign the checks to go to hell which is not
