[ExI] powersats

[Keith Henson]

On Fri, Mar 28, 2008 at 4:44 AM, Bryan Bishop <kanzure at gmail.com> wrote:
> On Friday 28 March 2008, Keith Henson wrote:
>  > Brian, this is just getting the physics wrong.  Long ago there might
>  > have been an excuse, but not with the net.  It is impossible to get
>  > oxygen to the liquid state with pressure alone, the critical
>  > temperature is about -118.6 deg C.  And people do make it cheap, less
>  > than 25 cents a liter.
>
>  It was my understanding that the gas laws still apply.
>  http://en.wikipedia.org/wiki/Gas_laws
>
>  PV = nRT (the *ideal* gas law)

The laws don't apply when there is a change of phase.  Steam, water
and ice don't obey the same laws.

>  > Fueling the rockets with electrolytic hydrogen is the only reasonable
>  > approach for a really large capacity lift, so while you still have to
>  > make it into a liquid, it come off as a no cost byproduct of making
>  > hydrogen.
>
>  Maybe the same fractional distillation method can be used to get H?

No.  The energy hog is splitting water.  That yields a nearly pure
stream of H2.  It's not nearly as energy expensive to make H2 into a
liquid as it is to make the gas from water.  I could put numbers on
it, but why don't you and I will verify your numbers.

This level of knowledge was common by or even before high school some
50 years ago, at least among the proto nerds I hung out with.  I
strongly suggest that all those who want to contribute here on
technical matters of this kind need to come up to that level by taking
chemistry or reading up on chemistry and thermodynamics.  Otherwise
the noise to signal ratio gets out of hand.

Best wishes,

Keith