From: Doug Jones (random@qnet.com)
Date: Wed Dec 08 1999 - 19:58:23 MST
"Robert J. Bradbury" wrote:
>
> On Wed, 8 Dec 1999, Brian D Williams wrote:
> > The notion of "Cheap Power from space" has been thoroughly
> > discredited, see Robert Zubrins "Entering Space" for details.
> >
>
> I strongly doubt that Zubrin understands either self-replication
> or nanotechnology sufficiently to *discredit* "Cheap Power from
> Space". All he can possibly do is point out that using current
> technologies it isn't going to be "cheap".
Entirely true, especially since *peak* power can be sold to the utilities
at higher prices- simple earthbased photovoltaic without storage is very
closee to being profitable even now, while O'Neill-type space systems would
require huge risky investments with poor ROI.
> I mean really now,
> quoting Zubrin as a source on this list? For heaven's sake
> this man wants to *colonize* something at the bottom of a
> gravity well. That means you are going to have to pay
> through the nose every time you want to go someplace else
> or ship something. Give me exclusivity on the Mars to Earth
> FedEx route and I'll show you a rich man.
Actually, with direct entry into the Mars atmosphere, Mars is easier to get
to than the moon, in terms of delta-V. Granted, you need a larger crew
vehicle for the longer mission duration, but if it's a colonization
mission, you need the living quarters anyway. It has advantages for
near-term colonization in that volatiles can certainly be extracted from
the atmosphere. As for Mars to Earth transportation, the propulsion can be
supplied by a single stage *pressure fed* LOX-methane rocket, about the
dumbest of dumb boosters.
> The idea of "colonizing" a planet has been discredited since
> O'Neill showed it was entirely unnecessary. I think Greg
> is right, that the Mars folks are a bunch of romantic
> idealists in love with their pipe dreams.
A dispassionate examination of the detailed trades seems not to favor
either approach. I've been a senior assoiciate of SSI *and* a Mars
Undergrounder, so I've looked at both pretty closely, and it seems a wash.
> Since you have to have a completely sealed environment anyway
> (otherwise your atmosphere leaks out) you are never going to
> lose any H2O. So you can get buy with a lot less than you
> need in an Earth based environment. With colonization you
> are going to need power, lots of it, and for that the moon
> is better.
Habitats leak, and badly. Current state of the art, given the trades
between fabrication costs, mass per unit volume, etc, yield habitats with
nearly 1%/day overboard leakage. Every joint, hatch, power feedthrough,
and window mount _leaks_, and substantial amounts of makeup gases and water
will be needed.
Power is the weakness of Mars bases, volatiles *and* power (2 week nights)
are both a problem for lunar bases. An appropriate asteroid may allow good
access to sunlight for power as well as containing adequate volatiles, but
if the delta-V requiremenat are low, the launch windows are rare, a
catch-22 of the synodic period.
Thus:
Attribute Moon Mars NEO
Launch window Daily 22 months 2+ years
Flight time 3 days 9 months 3-6 months
Stay time indefinite 16 months years at minimum
Volatiles Polar ice/concrete Atmosphere Chondrites?
Delta-V from LEO 6 km/s 3.5 km/s 3.5 to 6 km/s
Delta-V return 2.5 km/s 6 km/s 0.5 to 2 km/s
Sunlight 1350 W/m2 470-690 W/m2 <1350 W/m2
Nights 350 hr 12 hr avoidable
The tradeoffs are not immediately obvious. I think the moon's south pole
might be best *if* volatiles can be extracted, since it would have frequent
launch windows, short travel times, and reliable power (if only in limited
geographical locations). While the delta-V for landing is high, the short
trip time allows use of high performance cryo stages.
Without lunar volatiles, I feel Mars would be a better choice, and random
NEOs might have advantages at particular times, but at the cost of very
long manned missions.
> > >You're still dead if there's a decompression. You still leak stuff
> > >outside and have to continuously replace it. But you cannot launch
> > >anything with a mass driver from the surface, with the possible
> > >exception of the top of Olympus Mons.
>
> Eugene, I don't think thats accurate. If you've got calculations
> I'd like to see them. NASA is studying mass drivers to assist
> launching on Earth, so I would think they have to work on Mars.
> The question comes down to whether the friction limits launch
> speed to sub-orbital rates, in which case you need rocket assists.
You don't need mass drivers on Mars- a skyhook lowered from Phobos can
troll through the upper atmosphere at about mach 1 (250 m/s in cold CO2),
with a good taper ratio. Indeed, Phobos & Deimos are wonderful resources
for O'Neill development in the Mars system, far better than our own moon.
> > >Mars should be a second
> > >step. If you have the Moon, Mars is easy. Not vice versa. And you
> > >can't do both, it's too expensive.
>
> If you did self-replication here on Earth first, you could do them
> both very quickly and very cheaply...
Yeah, if we had some ham, we could have ham & eggs, if we had some eggs...
-- Doug Jones Rocket Plumber, XCOR Aerospace http://www.xcor-aerospace.com
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