RE: JetPacks vs. AirCars

Robert J. Bradbury (
Sun, 22 Aug 1999 22:16:21 -0700 (PDT)

On Sun, 22 Aug 1999, Billy Brown wrote:

> Well, it really runs on sunlight in that case.

Obviously you cannot power a vehicle on a fuel in a low energy state. Water is a low energy state unless you have an even lower energy state compund to convert it into. Methane is a low energy state in an atmosphere without any free oxygen.

Yes, ultimately everything runs on free energy inputs (e.g. sunlight, radioactive decay, gravitational contraction, etc.) to provide the energy for chemical reactions.

In our environment you have to use sunlight to drive water "uphill", so you have hydrogen to oxidize to release energy. So, yes, everything really is powered by sunlight (except that small percentage of things powered by leftover power from radiation and/or gravitational contraction leading to plate tectonics and/or the release of energy from molten materials.

The result would be a car
> that has to spend several hours recharging for every hour of use, which
> would make it impractical as a consumer device. Not everyone needs to be
> able to run the car 8 hours per day, but we all want to know we can do so
> when we need to.

I've gone about a year without ever having to drive a vehicle for more than an hour. Your use of a vehicles capacity depends on the requirement for that capacity. Most people don't buy a means of trasporatation because it can travel 8 hours without refueling.

> > The problem isn't with the science, it is with the unflexible
> > manufacturing infrastructure.
> That seems a bit unfair. Economical production of internal combustion
> engines was possible quite a while ago. Economical production of solar
> power collectors and fuel cells is a bit iffy even now, and certainly was
> not possible as recently as the 70s. High-speed recharging of electric
> vehicles is still problematic, as is storing hydrogen.
> I'm not sure how one would calculate the hypothetical 'volume production'
> cost of such a vehicle with any precision. However, it seems clear that
> there are still technical hurdles that need to be overcome before such
> production will be practical, and it is not at all clear that the overall
> production cost would be lower.

The "rule-of-thumb", which I will admit is very gross, is that every time the quantity manufacutured "doubles", the cost declines by a factor of two.

It would be a worthwhile exercise to explore this prediction in such diverse areas as floopy disk drives, microprocessors and solar cells. My gut level "feeling" is that there is some truth in the statement, though it may vary from industry to industry.