Skylights

George: Here are some random thoughts on glass windows.

Automobile front windshields have a multilayered approach to preventing
complete window blowout. But the middle section seems to be some type of
polymer, something not very viable for the High Frontier.

In the dim memory of my childhood, I recall that my elementary school had
first floor windows that were glass, but within the glass was chicken
wire. Somehow there was a process of making glass with wire mesh
completely contained within the glass. As kids, we would play baseball
by throwing the ball against the wall of the school, and these first floor
windows were presumably some protection against errant pitches.

In the intervening years, those elementary school windows were replaced by
more modern plexiglass windows. But perhaps this older technique of
reinforcing glass with metal mesh might again prove useful on the High
Frontier for preventing loose tools from causing complete window blowouts.
Both glass and metal would seem to be in good supply on the High
Frontier. Viewed from far away, the metal mesh within the window would
not be esthetically disruptive.

Ron
******

Gturner6PPC@...
10/31/01 01:44 PM
Please respond to spacesettlers

To: spacesettlers@yahoogroups.com
cc:
Subject: [spacesettlers] Skylights

Hi all,

I was thinking about the construction of the skylights, which are
a prominent feature in current designs. I think they may present a
significant cost problem, since even on earth thick plates of
annealed glass, of any serious thickness, are very expensive.
Amateur telescope makers are very aware of this, and haven't found a
way around it. Then there is the additional problem of sealing each
window, and making sure the seal and mount doesn't place it under
undo stress. Large panes would have to be pretty thick, with the
edges manufactured to precise tolerances. The mount can't introduce
significant bending stresses, must seal completely across a wide
temperature range (Can't have the windows all start leaking during
the first eclipse), and be quickly replaced in case of rupture. For
more on the paranoid design of pressure windows, check out
http://www.psubs.org
(And you thought WE were crazy...) Anyway, a sealed viewport is not
a trivial thing, apparently.

Lexan is also expensive, would probably have to be shipped from
earth, and in submersibles is always replaced every ten years. But
submersibles don't have to face incredible amounts of UV light, which
damages most plastics.

So I've been thinking of fiber optic sunflowers, which minimizes the
design problems, or an even simpler idea of using standard
photovoltaics powering the new sulfur bulbs, which have beautiful
spectra and are extremely long lasting and efficient, as seen here
http://www.fusionlighting.com/sulfur.htm
http://www.neon-lighting.com/fiberOptic-intro.htm

Sure, it's a design cop-out, but it might be more likely to survive
the budget and design review processes, at least for a small, initial
station. Either of the fiber optic sunflowers, or the standard
electrical lighting methods, would avoid the complexities of windows
and mirror geometries that dominate current station designs.

I also worry about the impact resistance of windows against large
dropped tools. Since the station's floor is rotating at least at 200
miles per hour, an astronaut at the hub, who lets something large
drift away, could create disaster. It's an extra problem when the
design of a large window must withstand a 200 mph impact, with
whatever large object might get loose. Although the torus and
cylinder windows will take the impact at a very oblique angle, we
still would have to worry about a tool ricocheting off another part
of the structure, and into a window.

I think T.A. Heppenheimer didn't think about these accidents, as he
was focused on the odds of meteor impacts. In his 1977 book, the
second paragraph on page 157 discusses the unlikeliness of
significant meteoroid impact, he says

"Anything heavier than a few hundred pounds would produce severe
damage when striking the colony, about the same effect as setting off
a fair-size bomb in the World Trade Center. However, even
meteoroids as small as a pound would be rare and much less of a
problem than airliners crashing into backyards on Earth."

Well, now we know that these odds, though small, are not
insignificant.

P.S. How did he know?!!!

Best Regards,

George Turner