-Z- (Z@Gundam.Com)
Sat, 28 Aug 1999 13:56:44 -0700


We got into the discussion of megatonnage yield of a colony drop after
someone raised the question of the comparative impact of a colony and an
asteroid, per such recent films as Deep Impact.

Besides the fact that the colonies are hollow and, except for a cubic
kilometer of docking block at either end, consist mostly of compressed air
within a skin of titanium-reinforced concrete, there's another factor to
consider.

Earth's atmosphere.

In Deep Impact, the big rock punches into the Earth at a near-right angle
at about 45 times the speed of sound (15.24 km/sec = 55,000 kph = 50,000
ft/sec = 34,100 mph) and crosses the 80 km (50 miles) or so of atmosphere
in a little under five seconds, producing a nice, crisp annular shock wave.

But, with the possible exception of the Dublin colony drop in ZZ, that's
not what happens in Gundam.

In the Operation British drop, the colony re-enters at no more than Mach 33
(11 km/sec = 39,500 kph = 36,000 ft/sec = 24,545 mph) at a near-tangent
angle. The final northwesterly course may be determined by drawing a Great
Circle through Jaburu (which I've tentatively placed at 5S x 63W) and
Sydney (34S x 151E), a distance of some 25,000 km (15,500 miles), ripping
laterally through the atmosphere the entire time (a little over half an hour).

Never mind "impact winter" from particulates and water vapor blown into the
stratosphere by the impact -- the aerial shockwave must've been tremendous
and spawned cyclonic "aftershocks" all around the globe!

And raised the air temperature a few degrees. (Talk about global warming!)

And left a trail of ionization that would've beget the mother of all
electrical storms.

Ditto the Operation Stardust drop, albeit less so. The colony only
transited the atmosphere from Jaburu (5S x 63W) to a point a few hundred
kilometers north of Oakley KS (40N x 101W) -- a Great Circle distance of
about 5,000 km (3,100 miles) and an "air time" of about 15 minutes.

This discounts the "air time" prior to passing over the primary target.
Since all of the colonies begin in a roughly equatorial orbit and must be
deflected into a nearly polar orbit to achieve the observed trajectories,
there's no way to know whether they re-entered over Argentina, Antarctica,
Africa or Asia and thus no way to determine total atmospheric transit time.

But the "climactic changes" attributed to the colony drops may have less to
do with the impact than with the atmospheric disruptions that occurred
during the drop itself!

-Z-

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