"attenberger stan%d.mfenet"@LLL-MFE.ARPA (03/07/86)
Concerning Mike Knudsen's claim that you will never see
fusion reactors in space due to their large size: "Conventional"
designs for tokamak reactors call for doughnut shaped plasmas about
eight meters across. Energy conversion devices, shielding,
stabilizing structures, and peripheral equipment take up more space,
but I don't think that you can justify the statement that the
smallest possible reactor may not fit in the Astrodome. Alternate
designs such as "spherical tokamaks" would be more compact,
possibly about 2.4 meters across. That would probably fit
in your office, including the vacuum vessel. Of course, the
peripherals would still occupy several offices.
Barring a major breakthrough, I don't see fusion being used
as a power source for a rocket. But how about as a power
plant for an orbiting industrial lab? You would have free vacuum,
reduced shielding and structure requirements... I don't know of
anyone who is actually working on fusion reactors for space (let's
do it on the ground please, first) but I wouldn't rule out their
possible use in space.
disclaimer: the above personal opinion should not be construed
to be a statement of the ORNL Fusion Energy Division.KFL@MC.LCS.MIT.EDU ("Keith F. Lynch") (03/08/86)
One could make a better argument that since all known fusion reactors are so large, none will ever exist EXCEPT in space. (They are called stars). Presumably, once someone manages to build a controlled fusion reactor on Earth, someone will manage to make it smaller and smaller... It wasn't that long ago that 'everyone knew' that computers were too large to be launched into space! ...Keith
dietz@SLB-DOLL.CSNET (Paul Dietz) (03/10/86)
Uses for fusion reactors in space seem limited. Both fusion and solar power plants are essentially machines for converting capital into energy (fuel cost is low); solar-thermal collectors can be simple and lightweight (and therefore cheap) and don't become radioactive. Inertial fusion reactors might make good rockets. Magnetic fusion reactors won't make good rockets; although they have good Isp their power/mass ratio is limited by the need to radiate waste heat deposited in the reactor structure. In inertial confinement fusion rockets the exploding pellet debris will carry away much of the heat, and the reaction chamber can be designed to let most of the neutrons escape to space.
MCGRATH%OZ.AI.MIT.EDU@XX.LCS.MIT.EDU ("Jim McGrath") (03/11/86)
Barring a major breakthrough, I don't see fusion being used as a
power source for a rocket. But how about as a power plant for an
orbiting industrial lab? You would have free vacuum, reduced
shielding and structure requirements...
Actually, you could still use fusion for a rocket even if the reactor
was gigantic. In this case you would have to broadcast the power via
microwaves (or another portion of the EM spectrum) from a large
orbiting reactor to a receiver on the rocket. Note that this works
best when both are in vacuum. For launches from earth you could
employ the energy from the fusion reactor more directly (e.g. have it
power lasers for a laser launching system). For launching from the
moon and such, use it to power a mass driver.
Jim
-------bzs@bu-cs.UUCP (Barry Shein) (03/15/86)
>Inertial fusion reactors might make good rockets. Magnetic fusion >reactors won't make good rockets; although they have good Isp their >power/mass ratio is limited by the need to radiate waste heat >deposited in the reactor structure. In inertial confinement fusion >rockets the exploding pellet debris will carry away much of the heat, >and the reaction chamber can be designed to let most of the neutrons >escape to space. Being as I was the one who brought up using fusion instead of fission in space I thought I would clarify that what I had in mind was an onboard power source, not a rocket propellant, although this turn of the discussion is interesting. -Barry Shein, Boston University