The Martian Dialogs - Continued

Posted by Bobba on Jun 06, 2002 at 13:39

Bobba said: ď..The issue is whether or not we can design a self-contained
zero maintenance reactor of a suitable small size and weight....Ē

Southern Man replies: What does it weigh? Was my estimate in error by more
than a couple of orders of magnitude?

I don't see why that really matters? We've literally got all the resources in the world to get it up our gravity well and down to the Martian surface. And itís not like weíre going to bring it back with us, right? But OK, how does 7.6 tons strike you? I happened to find this set of design drawings on the little bugger shows it to be far cooler (and tougher) than I originally guessed. It doesnít even require an external water source for cooling. The cool Martian breezes would more than suffice but...lets not lose sight of our goal to locate, melt, extract, and crack some H2O. By comparison, the Hubble Telescope was far more fragile and IIRC it was eight times the size (roughly 200 m^3 compared to our 24) and weighed 12 tons. Of course, that doesnít take into account the tanks well have to send as well. It might well require sending up the reactor first, then the tanks, and assembling the landing craft(?) at the space station.

Not hyperbole Ė real concern. You plan to make steam from
raw ground water in a well. That water contains more than just
hydrogen and oxygen. It would contain large quantities of every
element and molecule that dissolves in water. The steam that is
used in commercial steam turbines must be very clean to prevent
damaging the turbine blades. Your steam is going to be anything
but clean. And many of the elements in the crud make radioactive
isotopes when exposed to fast (or slow) neutrons.

Youíll forgive me if i think your concern is misplaced. But, luckily enough, given the Rapid-L design, quite moot, or at least essentially so. Still, the subject of secondary contamination due to neutron radiation is a matter of interest to me so Iíd appreciate any references you might have to qualify your claims. Even considering the dissolved minerals (which I admit not having considered previously), I just donít see the problem. Specifically, what types of isotopes do you think will be created and, more importantly, in what quantity?

So we need to accelerate the mother ship with 5e10 joules which
is also 5e10 watt-seconds. Going back a couple of messages you
proposed a 50KW net conversion to fuel from what I believe is a
very heavy reactor. So it takes 12 days to produce the net energy that
will be used to accelerate the mother ship from Mars orbit to Earth.
(Donít you just hate it when you finally get out the calculator and find
the numbers arenít exactly what you expected ;) )

Wow! Thatís all? I know thatís only part of the problem but itís still a lot less than I originally anticipated (in a calculatorless kinda way).

What is the energy release efficiency of hydrogen fuel?
How much does that much fuel weigh? Should be a simple
calculation from energy release of hydrogen-oxygen combustion
and momentum transfer. Donít have time this morning. Maybe tomorrow.

First, Iíd think that the liquefied fuel would weigh, by combined volume, exactly the same as an equal volume of water Ė 1 g/cm^3 Ė unless Iíve encountered some sort of unforeseen duh factor. As to the energy release efficiency, I have no idea and canít seem to find a simple explanation or answer on the net. I found something regarding this but couldnít really interpret it. Iím afraid that parts on you, should you feel obliged of course.

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