dietz@cs.rochester.edu (Paul Dietz) (04/01/89)
The apparent absence of major neutron emission and hot waste from the solid state fusion discovery raises the possibility of resurrecting nuclear rockets for launchers. I see two possibilities. The first is to use heat from a solid state fusion reactor to heat hydrogen, NERVA style. This would require that the power density be a couple of orders of magnitude higher than that claimed by Pons & Fleischmann. For on-orbit use the power density need not be as high. The second possibility is to use a smaller fusion reactor to preheat fuel and/or oxidizer before injection into a conventional chemical engine. This would increase the Isp beyond that possible with chemical fuels alone. For use in launchers, we'd want a fusion reactor that (1) can be shut down in seconds, (2) has high power density, and (3) operates at high temperature. (3) might mean we want a material with a higher melting point than palladium (hafnium, maybe?). Paul F. Dietz dietz@cs.rochester.edu
henry@utzoo.uucp (Henry Spencer) (04/02/89)
In article <1989Mar31.163051.5961@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: >The second possibility is to use a smaller fusion reactor to preheat >fuel and/or oxidizer before injection into a conventional chemical >engine. This would increase the Isp beyond that possible with >chemical fuels alone. I doubt the practicality of this. Existing oxyhydrogen rockets already run fuel-rich partly to *cool* the exhaust a bit (and thus reduce thermal dissociation of water into oxygen and hydrogen). It might help the less energetic fuels like hydrazine, but why bother? If the power densities stay low, the big use will probably be as a power source for electrical propulsion in space. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
dietz@cs.rochester.edu (Paul Dietz) (04/03/89)
henry@utzoo.uucp (Henry Spencer) writes: >>The second possibility is to use a smaller fusion reactor to preheat >>fuel and/or oxidizer before injection into a conventional chemical >>engine. > >I doubt the practicality of this. Existing oxyhydrogen rockets already >run fuel-rich partly to *cool* the exhaust a bit (and thus reduce thermal >dissociation of water into oxygen and hydrogen). So, a fusion preheated chemical rocket would be even more fuel rich. In the limit, no oxygen is used at all, and the system is a purely nuclear rocket. I can also imagine a nuclear scramrocket. A fusion NERVA rocket is used as a fuel injector into a supersonic airstream, which serves as a thrust augmentor. This might be a better use of a nuclear rocket, since peak power required is lower. >If the power densities >stay low, the big use will probably be as a power source for electrical >propulsion in space. I have a feelin that power densities can be increased markedly. For example, go to thinner pieces of Pd. If lithium is involved in the reaction, use purified Li6 (boosts the power density by a factor of 5). Boost the amount of deuterium in the lattice by upping the current density. Try DT instead of D. I've heard a report that the reaction doesn't work at high enough temperatures, though. Time to look for a better metal. Paul F. Dietz dietz@cs.rochester.edu
mmm@iconsys.UUCP (Mark Muhlestein) (04/03/89)
[ mention is made of use of fusion energy for launch ] Could someone comment on the use of cheap energy to power some kind of laser launch system? I remember reading somewhere about a design in which argon gas in the launch vehicle was heated by a (very large) ground-based laser system. Maybe some of the SDIO research may yet come in handy! -- Mark Muhlestein @ Icon International Inc. uunet!iconsys!mmm
stolfi@jumbo.dec.com (Jorge Stolfi) (04/03/89)
Most postings to this newsgroup seem to assume that the discovery of
cold fusion is a great boon to the exploration and colonization of
space. This does not seems obvious to me. From what I have read
so far, cold fusion may help space exploration only a litle,
and hamper space colonization quite a lot.
Let's assume that cold fusion will indeed turn out to be a source of
cheap energy, and not a mere laboratory curiosity. Still, it seems a
safe bet that it will take at least 5 to 10 years for cold fusion power
sources to become sufficiently efficient, practical, and reliabe to be
used in space. Even then, there is no indication that cold fusion will
be of any use as a first-stage propulsion system. At this point, the
only use for cold fusion in space that seems plausible enough is as a
source of electricity, which could perhaps be used by relatively
low-thrust ion motors. Note that energy is only a small fraction of
the cost of a launch, so cheap energy on the ground will not make space
launches much cheaper.
On the other hand, cheap energy on the Earth means there won't be any
need for solar power satellites (SPS). Now, SPSes are the only
large-scale space operation that is not obviously an economical
nonsense. Without SPSes, space colonies would lose their main raison
d'etre; and without space colonies, there is hardly any reason to
consider lunar and asteroid mining. (By the way, cheaper energy would
make possible to exploit many low-grade ore bodies that now are
uneconomial, so mining the asteroids for the Earth market would make
even less sense that it does now.)
To summarize, I bet that in the foreseeable future cold fusion may turn
out to be of some use *in* space, but it will not make going *to* space
any easier. In fact, if it is successful, it will make the
colonization of space a lot harder to sell.
Jorge Stolfi @ DEC Systems Research Center
stolfi@src.dec.com, ...!decwrl!stolfi
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``My dear listeners,'' he went on, ``if we are to believe certain
narrow-minded people --- and what else can we call them? --- humanity
is confined within a circle of Popilius from which there is no escape,
condemned to vegetate in this globe, never able to venture into
interplanetary space! That is not so! We are going to the moon, we
shall go to the planets, we shall travel to the stars just as today
we go from Liverpool to New York, easily, rapidly, surely, and the
oceans of space will be crosed like the seas of the moon!''
--Verne, _From the Earth to the Moon_ (1865)
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DISCLAIMER: Opinions are just opinions.henry@utzoo.uucp (Henry Spencer) (04/04/89)
In article <351@iconsys.UUCP> mmm@iconsys.UUCP (Mark Muhlestein) writes: >Could someone comment on the use of cheap energy to power some kind >of laser launch system? ... Energy is not the major bottleneck in laser-launch systems, unless you want to launch seriously big payloads in one lump. Beam-directing optics are probably the biggest challenge. >Maybe some of the SDIO research may yet come in handy! The US laser-launcher research program is indeed relying on SDI to build big lasers and figure out how to point them; they're working on the other engineering problems of the scheme. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
jeff@censor.UUCP (Jeff Hunter) (04/05/89)
In article <13667@jumbo.dec.com>, stolfi@jumbo.dec.com (Jorge Stolfi) writes: > Most postings to this newsgroup seem to assume that the discovery of > cold fusion is a great boon to the exploration and colonization of > space. This does not seems obvious to me. From what I have read > so far, cold fusion may help space exploration only a litle, > and hamper space colonization quite a lot. > ... > Note that energy is only a small fraction of > the cost of a launch, so cheap energy on the ground will not make space > launches much cheaper. Some rocket designer who's name escapes me noticed the same thing and proposed the Big Dumb Booster (BDB). The theory is that if the cost of the rocket structure is much greater than the fuel, then making the structure cheaper (and therefore heavier) will easily offset the additional cost in fuel to lift it. Using fuel costs of two years ago he figured that it would be much cheaper to make huge boosters out of sheet steel (?) with last generation rockets than the current practice of using ultra-thin aluminum shells with every-last-drop-performance motors. Anything that drops the cost of LOx and liquid hydrogen just makes this approach more attractive. I realize that there's more cost than just the rocket & fuel, but the BDB should have it's uses. -- ___ __ __ {utzoo,lsuc}!censor!jeff (416-595-2705) / / /) / ) -- my opinions -- -/ _ -/- /- No one born with a mouth and a need is innocent. (__/ (/_/ _/_ Greg Bear
jwm@stdb.jhuapl.edu (Jim Meritt) (04/05/89)
In article <1989Mar31.163051.5961@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: }The apparent absence of major neutron emission and hot waste from the }solid state fusion discovery raises the possibility of resurrecting }nuclear rockets for launchers. } }For use in launchers, we'd want a fusion reactor that (1) can be shut }down in seconds, Paul, the CURRENT launchers cannot be shut down in seconds. Why put restrictions on something that are not currently met? (solid-fuel boosters turn 'on' fine, but 'off' is a b*tch!) Disclaimer: "It's mine! All mine!!!" - D. Duck