From: jeff davis (jrd1415@yahoo.com)
Date: Mon Oct 22 2001 - 23:39:58 MDT
--- Doug Jones <djones@xcor.com>,
on Sun Oct 21 2001 - 15:03:54 MDT wrote:
< snip all kinds of terrific, detailed, on point,
scrumptious rocket scientist stuff. Yummm! >
Thanks a bunch Doug.
How sweet it is that this list has a genuine,
certified, card-carrying rocket scientist ready to
respond to that sudden emergency. You know, that
unquenchable nerd-boy jones for a fix of the real
stuff: pure, hard-core spaceflight info with that
savory high-signal flavor.
Ain't the extropian lifestyle grand!
Oh, and thanks also to Doug's faithful indian
companion Zenmaster Spike-plip-plip-the-ant-man Jones.
(Thanks as well to Robert, Gene, Adrian, Mike, et al)
---------------
Plaudits taken care of, on to substance.
There were some comments about micrometeorite damage.
Recently, there was an event in the news about a
Russian-launched, US space society, inflation-deployed
scaled-down version of a solar sail. As I understand
it this item was to be deployed and held open by a
circumferential inflated tube. I've also heard of
other designs using straight tubes in a spoke-like
arrangement. IMO these are all worthy approaches.
The inflation concept does require that we deal with
the micrometeorite puncture deflation issue, but I
don't see it as a difficult problem, solvable, as
someone mentioned, by the injection of expansion foam
that then hardens, ie, styrofoam or a
whatever-is-more-appropriate-for-the-conditions
alternative.
(As I understand it, some foams are "blown", which I
take to mean mixed under pressure with the inflation
agent and then extruded from high pressure to low,
where the agent expands, and with it the foam. CFC's
in liquid form and nitrogen are two of the expansion
agents I've heard of. Then there seem to be foams
which chemically generate the gas which then expands
the mixture, much as bread rises due to the generation
of CO2 by the on-board yeast.)
Obviously, such a foam would be transported to the
building site in compact liquid form. Does anyone
have an idea of how little expansion agent one might
get away with when expanding into the ultimate low
pressure environment of the vacuum of space?
So hardened foams don't deflate.
The backing for a solar reflector is just one--a
somewhat mundane one IMO--of many possible space-based
applications of foam. (I recommend a thread dedicated
to Building Materials and Methods in Space, with The
Uses of Foam in Space as a subthread.) Prior threads
for example, have dealt with the problem posed by
space junk. A large foam sphere, or a suitably thick
layer of cladding around a space "station" might prove
an effective debris collector/shielding. Impacting
bodies would easily penetrate a thin but tough
skin--to minimize fragmentation near the
surface--making a small hole, then gradually
decelerate through layers of increasing density.
Junk checks in but it doesn't check out!
Micrometeorite damage to the reflector: I agree, as
someone mentioned, that it would seem non-critical
since it would effect, IMO, with the possible
exception of grazing impacts, a virtually
imperceptible fraction of the total reflective
surface.
The issue of degradation due to atomic oxygen seems
inherently connected to a location in low earth orbit.
As Gene observes, leo is primarily useful as a place
to pass through on your way to somewhere you really
want to go, someplace, anyplace, higher up. So it's
"Up and away", and away from atomic oxygen.
On stabilization. Maybe spin stabilization is not the
way to go, but the conserved nature of that angular
momentum vector has a track record, and really appeals
to me. How to keep such a system pointed at the sun,
and compensate for deflections due to external forces:
solar(and terrestrial, lunar, stellar, and cosmic)
radiation pressure, solar wind, magnetic fields, and
space "dust"? (Forget atmospheric drag--see previous
paragraph). First, regarding the disturbing forces:
they will be small to begin with, but--in the case of
a solar reflector--the resultant forces for solar
wind, and radiation pressure should act through the
center of rotation, reducing the rotational
disturbance from these two sources to near zero. This
leaves only very small unbalanced disturbances to be
compensated for--unless we're talking ultra-humongus
mega dish. To compensate for disturbances and
maintain accurate orientation, I would propose a set
of small, light, high-speed flywheels. Since, over
the course of one revolution around the sun, the
angular momentum vector must be caused to rotate 360
degrees, the net change ends up being zero. The
flywheels just suck up the angular momentum in one
half of the cycle and return it during the other half.
To whatever extent the rotational disturbances also
tend to average out over the period of one revolution,
torquing first one way and then the other, then, for
these disturbances as well, the flywheels, will cycle,
loading up in one half of a rotational period and
unloading in the other half. If they ever do reach
the limit of their capacity, then they can be
jettisoned along with their cargo of "waste" momentum,
and replaced with a new "empty" set of flywheels. (I
read up on flywheels recently and recall two
applications for use in space. Energy storage as an
alternative to battery use, and orientation
stabilization as an alternative to reaction jets.
Beyond that, I freely admit, I may be talking out my
asteroid.)
Finally, a suggestion regarding the gun launch
concept. Get past the Babylon gun. It's just a
starting point. I suggest a longer tube for more
velocity and/or lower g forces, located in the ocean
for easy building and maneuvering--think of the butt
end in the depths of the Marianas trench. This gives
you a ten mile length at an inclination of 45 degrees.
That's all I have time for for now.
Best, Jeff Davis
"Everything's hard till you know how to do it."
Ray Charles
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