XPost: sci.space.policy
From: henry@spsystems.net
In article <3c6b9c1e.0401231956.4e2d9287@posting.google.com>,
Ross A. Finlayson wrote:
>I'm wondering about "lava tubes on the moon". I guess I was under the
>impression that besides Earth only Jupiter's moon Io had active
>volcanic activity, and I was thinking Luna was a cold chunk of rock.
Nowadays, probably. But there is no question that it had extensive
volcanic activity early in its history; indeed, there are geochemical
hints that much of its surface was molten at one point.
>Lava tubes, miles long underground caverns similar to lava tubes on
>Earth, where higher temperature magma flowed out and left behind open
>space, would probably be among the major geologic reasons for their to
>be caverns on the moon with the lack of running water. I just had
>never heard of their existence before yesterday, and don't know of any
>on the moon itself.
Hadley Rille, which Apollo 15 landed beside, is almost certainly a
collapsed lava tube. (Lunar lava tubes can be *big*.) A few halfway-
intact ones have been spotted in images taken by orbiters. Some of them
show up as "dashed lines" -- the roof has fallen in on some parts but not
other parts, which might be very convenient for getting into them.
>I think there should be shortly ten or fifteen satellites about the
>moon, these would be necessary for a variety of surface operations. I
>may be wrong, the moon has no appreciable atmosphere, thus no
>ionosphere and only line-of-sight radio communications. A satellite
>array would be critical in providing global (?) coverage of
>communications availability to surface operations.
Indeed, there's no ionosphere, so radio is line of sight or nearly so.
But you don't need a whole bunch of satellites. One near the Earth-Moon
L1 point, and another in a "halo orbit" near the L2 point, will suffice
initially. (Later on, it may be better to have larger numbers in lower
orbits, to reduce transmitter power and speed-of-light delays, but that
can wait.) The L1 satellite, in fact, can be postponed for a while in
favor of using Earth stations for that role.
>I always why there weren't more air-boosted launches, an aerodynamic
>launch plane flies a hundred thousand feet high and the launch vehicle
>separates and boosts to orbit from high in the sky.
It's a rare aircraft that can fly at 100kft. Half to a third of that is
more typical. Air launch does have advantages, mostly for thinner air
(neither the speed nor the altitude per se is very significant), but it
also limits your rocket's mass to what your aircraft can carry, and even
for a 747 that's fairly limited.
>I was reading about the Shuttle-C for cargo and saving the liquid fuel
>tanks in holding orbits, I think that's a good idea. What prevents
>the addition of new modules to the ISS, Freedom, the International
>Space Station, every year? What's so great about the ISS's orbit that
>it is there?
The limitation on adding new modules is the cost of building them and
launching them. The orbit is a rather complex compromise involving
reachability from launch sites, minimum air drag, and maximum payload
for launches.
>About mapping the lunar surface and within it, I wonder if ground
>penetrating radar instruments would be any good, for example for
>discovering lava tubes.
Yes. This was done experimentally from lunar orbit on Apollo 17, although
data analysis was difficult (then) and I'm not sure how much was learned.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. | henry@spsystems.net
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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