Re: EV2?



Pat Flannery wrote:


Rick Jones wrote:
sufficient current to drive a car at any useful velocity.

Or acceleration I suspect :)
http://en.wikipedia.org/wiki/Voyager_program suggests that at their
peak the RTGs were generating something like 470 Watts of power, and
are presently down in the 290s. Not sure what the Amps are, didn't
look that closely.
I couldn't easily find kW ratings on the motor/batteries for the EV1,
but:

http://en.wikipedia.org/wiki/Chevy_Volt

says that the electric motor is 111 kW with the charging moter rated
at 53 kW.

I've no idea if the wattage of an RTG is directly proportional to its
mass - seems like a decent first guess - this link:

http://www.fas.org/nuke/space/bennett0706.pdf

suggests the RTGs on Voyager were 37.69 kg, so if it is a linear
relationship to mass it suggests that to get to the 53 W of the Chevy
Volt's charging engine it would be (53/0.470) * 37.69 or ~4250 kg or
~9350 lbs. Double that if you want to match the electric motor rather
than the charging engine. I'm fully ready for my peanut gallery
assumptions to be torn to shreds :)
There's a different approach one could use to it though.
The RTG uses the heat of the isotope to heat the hot side of a thermocouple with the cold side being the radiator panels sticking out into space around its exterior.
This works fine in vacuum, although total electrical power output is low.
If the isotopes were heating _air_, then the heated air could be used to drive some sort of electrical generator - like a Sterling cycle system or steam generator - with the isotopes replacing the heat source that would be normally be supplied by solar heating or combustion.
The advantages of such a system over a classical nuclear reactor for generating heat would be that the radiation generated by it would be primarily Alpha Particles, which are very easy to shield against (radiation from the system could be blocked by a thin sheet of cardboard, or even by a couple of inches of air).
The disadvantage would be cost of manufacturing...to get enough heat to drive a car via this system would require a _lot_ of isotopes by weight, and since they have to be either made in a breeder reactor or extracted from spent fuel rods from a reactor, any benefits in their long half life for power production over that of gasoline, straight electric, or fuel cells quickly vanish.
Turning out a isotope-powered car that can run for fifty years on a single nuclear battery doesn't make sense if that isotopic power supply costs over a million dollars to make, as today it easily would.
Even if you could get it made at a lower cost, the total weight of isotopes needed to replace all motors on cars, trucks, and trains throughout the world would imply a world running entirely on nuclear fission electrical power generated by breeder reactors, and when you kick things up to that level the radioactive ores are going to run out in fairly short order.
The best short-term solution (beyond hybrids or alcohol generated by fermenting switchgrass) might be fuel cells converting hydrocarbons into hydrogen and carbon; the long-term solution almost _has_to be pure stored electrical power.
We should be throwing lots of money at room-temperature (or at least at fairly high temperature) superconductors, as if we can get a superconducting battery/capacitor to work, we've solved around half of the problems with transport in the future.
And speaking of which - if you can stick enough electrical power into one of those things, and seal it in vacuum bottle, there's no reason that it can't run a refrigeration system to keep its temperature down in the superconducting range at pretty low total power expenditure, even with today's technology.

Pat

Why can't you use the 'loose electrons' in plutonium as electron flow in a battery in place of lithium or other chemicals.



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