Human Mars Mission Impossible?

"Sander Vesik" wrote in message ...
Ool wrote:

Solar collectors. You need mostly the heat, which you don't have to
produce electrically. And solar collectors you *can* make out of a
chunk of reflective raw metal by hammering it into shape. Photovolta-
ic cells are a different matter, agreed!

The problem is that you cannot make silicon in them or even purify it
once it has been made. So except for raw material for the substrate, they
are a dead end for photovoltaic cells.


There are other ways of creating electricity from solar power than
photovoltaic cells, though. If we have to use the thermal energy of
focused sunlight in order to drive certain reactive processes then
building similar devices with a sterling motor at its center for driv-
ing a generator may do the trick for providing the electricity needed
for electrolysis.

In order for that to work all you need is metal that's reflective
enough. It needn't be as pure as the silicon in photovoltaic cells.
It needn't even be silicon.

Yes, all that is thinking a little far ahead. It's tough to build an
industry in a vaccuum that can't support human beings, and rovers have
all sorts of problems with flash memory, and the like. Eventually the
vacuum and the natural cleanroom conditions up there might be a bonus,
though for making things like silicon wafers...

But let's concentrate on doing simple stuff first, that might pay for
the more complicated processes one day.


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Joe Strout wrote:
In article ,
Sander Vesik wrote:

LOX alone is not really a fuel - unles syou use it in a pressurised gas
engine which can redally work with any gas - you need to add something else,
and changces are very good that something else weights more than LOX.

No, it doesn't. Oxygen is far heavier than hydrogen (the most likely
fuel). For example, the SSME burns about 178 Kl/min of hydrogen and 64
Kl/min of oxygen. But LH2 masses 0.182 kg/l, whereas LOX is even
heavier than water, 1.19 kg/l. So each minute, the SSME needs 75600 kg
of LOX, but only 21100 kg of LH2.

I'm not at all convinced Lh2 is the obvious fuel. It has totaly attrocious
properties for a rocket fuel - it is not storable, it needs ultraspecial
handling, it canot be in thermal contact with almost anything (inc LOX),


In short, LOX is about 80% of the mass you need to make a rocket go.
Getting that in situ is an enourmous savings, even if we still had to
haul the LH2 up from Earth.

The "enormous savings" depend a lot of the flight / use rate and on how
much you spent on heavy equipment and its power supplies being lifted
from earth and being repaired on Moon. Either you have cheap access in
which case chances are good that Lunar LOX is nice but you don't necessarily
care about the extra complexity of rendezvous with the tanks coming
from Moon or alternaively you are getting small payback because lifting
the machinery and operating it was so damn expensive.


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Sander

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