starship-design: Heat design limits

[Ben Franchuk <bfranchuk@jetnet.ab.ca>]

Johnny Thunderbird wrote:
 

> Current designs
> > such as VASIMR rely on extremely high density magnetic fields in the
> > nozzle to keep the plasma from coming into contact with the nozzle,
> > but radiated energy is still a problem. At these performance levels,
> > radiated heat absorption is greater then what we are currently dealing
> > with in CHEMICAL rocket engines. If the plasma were to be permitted to
> > contact the nozzle it would melt practically instantly.

This brings up a interesting point... Heat generated buy propulsion
systems. Heat in space is transmitted by radiation only and that is lousy
at low heat levels. < 100C. Chemical/fission nuclear engines can carry some
heat with in the exiting material but what is the size level limits for
deep space craft do to the size of the radiators for energy production
and trust?


> 
> The thermal considerations of an electric arc are pretty plain, you have to
> keep stuff away from it you don't want vaporized. Propulsion engineering
> like we're doing here has to take this factor into account among the first
> things.
> 

> > VASIMR is a much more low tech concept that is capable of providing
> > the same performance and is "tunable". There is currently research
> > ongoing that is similar to your concept in that it is still a "throw
> > the nuclear something out the back and detonate it" approach, but it
> > is using antimatter as the activation, not an accelerator. This
> > concept provides many orders of magnitude increase in performance, but
> > is still far short of interstellar capability.

I think antimatter would easier to produce in space...
Cheap solar power and vacuum for the antimatter generators.

>I design things to be
> built with the most plentiful and abundant materials, to raise the
> probability they will really be constructed sometime.

 That is a good way to design things.
 
 The jet of our ship is composed partly of a proton beam. We have ionized
> neutral hydrogen to get those protons, to feed into our linac. But we have
> to shed an equal number of electrons, so our ship will remain in charge
> balance. A cathode fires those electrons on a trajectory which nearly grazes
> the proton beam at an angle, and those electrons will orbit the proton beam
> in a helical path, by their electrostatic attraction to its positive charge.
> So we have spiraling electrons, but as moving charges, spiraling electrons
> are a solenoid, they are a magnet. We have built a magnetic field which
> confines our jet, for some arbitrary distance back along our jet. Now we
> have something to tune, now we can start to optimize our conditions to make
> the most of our fusion. We have no coils to melt, no wires to burn, but we
> have a magnet which is not sensitive to temperature, not affected in the
> least by radiant heat. We have a magnet which is as strong as we want to
> make it, and is as long as we want to make it, and is directly coupled to
> the inertial environment of the ship, stiff as a steel beam. That's where
> your fusion belongs.

Where does the energy for the linac come from? What about loses with the
proton beam being slowed down by fusion debris and the fact that only a
small amount of fusion power is converted into thrust because you have no
nozzle.  (fusion)<45 degrees angle>[ship thrust shield] this is 45/360
or 1/8 thrust used for propulsion.

> Johnny Thunderbird

-- 
"We do not inherit our time on this planet from our parents...
 We borrow it from our children."
"Ancient Logic" http://www.jetnet.ab.ca/users/bfranchuk/al/index.html