Sugestão leituras

Comprei e li o “Space Weapons Earth Wars” em 2003 e penso (embora se tenham passado alguns anos) que o livro ainda é (demasiado?) actual.

Recomendo em particular o tema:

NATURAL METEOROIDS AS WEAPONS ( da pág 173 até á página 183 )

Chapter Three and Appendix B used the physics of meteoroids as a
starting point for developing an understanding of kinetic-energy
weapons delivered from space.

The discussions examined idealized meteoroids at sizes having effects that would be of tactical interest in conventional warfare. The impressive effects on earth of past large
meteoroids suggest the possibility that natural objects—earthcrossing
asteroids—could be used as weapons on a scale more suitable
for strategic deterrence, as are nuclear arsenals.

Such notables as Carl Sagan, in discussing means of preventing catastrophic natural
collisions, have expressed concern about the possibility of deliberately
deflecting an asteroid toward earth as a weapon (Harris et al., 1994; Sagan, 1994; Sagan and Ostro, 1994).

For nations that already have nuclear arsenals, asteroid weapons
might be of only academic interest.

Depending on the relative difficulty of acquiring a nuclear arsenal or equivalent weapons of mass destruction, the idea might be of more practical interest to other nations.

The decision process and motivations that might lead some nation to acquire such weapons were discussed in Chapter Six.

This appendix will review some of the practical issues in employing asteroids as weapons.

Já em 1997 (por exemplo) se abordava o tema neste livro: http://en.wikipedia.org/wiki/Titan_(Stephen_Baxter_novel)

Entretanto, agora, todo o texto pode ser obtido grátis online a partir do site da RAND:

http://www.rand.org/content/dam/rand/pubs/monograph_reports/2011/RAND_MR1209.pdf

Site: http://www.rand.org/pubs/monograph_reports/MR1209.html

Aproveito para citar um “fragmento” do texto:

WEAPON SUITABILITY

By the time very small meteoroids impact the ground, they have
slowed to several hundred or a few thousand miles per hour. These
meteoroids are too small for this discussion. Very large asteroids or
comets penetrate the atmosphere as if it were not there and strike
the ground with full force. At the larger end of this scale (diameter ≥1
km) are asteroids, whose effects are too great to be useful for strategic
deterrence. Threats of a mass extinction event are not likely to be
credible.

At the lower end of the scale are meteoroids large enough
to survive reentry to strike the ground; these represent the upper
bound of interest for strategic deterrence. Asteroids that can survive
to a low enough altitude to have blast effects represent the lower
bound.

Intermediate-size asteroids explode in the atmosphere. The altitude
at which such objects begin to explode is approximately determined
by equating the crushing strength of the material to the local atmospheric
density and the square of the instantaneous velocity. Asteroids
have median entry speeds of 13 to 17 km/sec (Chyba et al.,
1994). Iron asteroids that are only 10 m in diameter retain most of
this speed even in the lower atmosphere. Small iron meteorites have
crushing strengths of as much as 4,000 atmospheres. A statistical
analysis of the weakening due to fractures would suggest slightly
lower strengths for an object with a diameter of several meters to a
few tens of meters (Lewis, 1997, p. 380), with fragmentation beginning
at about 1 to 10 km. Substantial blast and heat effect could occur
on the ground below if the fragmentation takes place near the
lower limit of that range.

There were at least three demonstrations of the effects in the 20th
century alone (ordered from largest to smallest):

• Tunguska, Siberia, June 30, 1908. An asteroid weighing about
100,000 tons exploded at an altitude of between 2.5 and 9 km,
with a yield equivalent to 40 megatons of TNT (Vasilyev, 1996).
The blast felled trees over 2,500 km2 and burned 1,000 km2. Had
this explosion taken place over an urban area in Europe, it might
have produced 500,000 human casualties (Gallant, 1993).

• Sikhote-Alin mountains, Kamchatka Peninsula, 1947. An asteroid
estimated to have originally had a mass of less than 1,000
Natural Meteoroids as Weapons 175
tons fragmented at an altitude of around 5 km. The burst was
high but did produce some ground effects, and the explosive
yield was close to that of the Hiroshima and Nagasaki atomic
bombs. Over 30 tons of material have been recovered from this
event (Vasilyev, 1996).

• The Amazon, August 18, 1930. This smaller but still impressive
impact occurred in a remote region. This yield was about onetenth
that of Tunguska, and reports of the event have resurfaced
only in recent years (Schaefer 1998).

Smaller asteroids produce no more damage than the psychological
effect on the viewing population (although demonstrating the capability
of delivering an asteroid to earth precisely and on schedule
would have high deterrence value).

On October 9, 1997, a fireball was observed from Santa Fe to El Paso, where it finally exploded at a height of 36 km and released energy estimated to be equivalent to
about 500 tons of TNT (Schiff, 1997).

Assuming a stone asteroid— since no meteorites were recovered—the diameter was estimated to be 2 m and the mass 20 tons. Similar events happen a few times each
year. This one was notable because the meteoroid exploded high
over a major population center.

Much-more-energetic events have occurred recently. What was reportedly
the brightest fireball to be seen by a satellite resulted from a
explosion on February 1, 1994, 20 km over a remote area of the western
Pacific Ocean; the yield was estimated at 11 to 110 kilotons. The
object responsible was probably a stony meteoroid with a diameter
of 7 to 15 m (Satellites Detect Record Meteor, 1994). If the El Paso
object had been this size, the ground effects would have been very
minor, but the population of El Paso would have had much more to
talk about.

In 1996, a large asteroid designated “1996 JA1” approached earth—
453,000 km at closest. This is slightly more than the distance to the
moon, but some asteroids have been observed passing within a fraction
of the earth-moon distance. This particular asteroid is distinctive
because it was observed only four days before its closest
approach and is believed to have had a diameter over 100 m. The
impact of such an object would produce a ground or near-ground explosion
equivalent to a 100-megaton weapon.

Pág 176 Space Weapons, Earth Wars

In summary, the suitability of weapon effect depends on the combination
of size and materials. Precise control of the effects in an impact
area would be very challenging. An object large enough to cause
a big explosion would generally have a high enough β to suffer only
minor angular changes in its trajectory due to atmospheric effects.
But even for such objects, precisely predicting the extent of destruction
would require understanding their internal composition, including
possible internal fracture statistics or heterogeneity, to predict
the altitude of breakup and the extent of blast effects from the
breakup. The breakup of the Brenham stony-iron meteorite, for example,
produced some specimens that are essentially iron metal and
others that are mixtures of iron and olivine, a variety of stone.

LOGISTICS

Availability

Two well known groups of asteroids—the Atens and the Apollos—
currently cross earth’s orbit, and each originates in the main asteroid
belt between Jupiter and Mars. Astronomers have discovered 190
that are over 1 km in diameter and estimate that there are 900.

In addition, the 1,500 Amor asteroids are believed to be very large nearearth
objects that could pose significant future danger, having the
potential for global destruction.

Among the smaller, potentially useful objects may be over 1 million
asteroids over 30 m in diameter that cross the earth’s orbit
(Rabinowitz et al., 1994; Shoemaker et al., 1995).

The objects among them that are important for this discussion have diameters ranging
from a few tens of meters to a few hundred meters, depending on whether they are stone or iron and on the effect desired.

The relevant questions here are:

• Can we reasonably expect to find enough of them?

• Do they pass near enough to the earth to be deflected enough for
accurate collisions with the earth?

• Can this be done quickly enough?

• Can we expect to find them whenever necessary?

…..

SUMMARY

With some patience, waiting perhaps a month or two, suitable
asteroids could be routinely found that would produce weapon
effects equivalent to nuclear weapons with yields ranging from tens
of kilotons to many megatons. With some effort, they could be
diverted to weapon using technology (and extensive supporting
infrastructure) similar to that for exploiting lunar materials,
generating solar power with satellites, or defending against asteroids.

However, at best, it would take months after a decision to use one as
a weapon to reach the desired conclusion.

Because much cheaper, more responsive weapons of mass destruction are readily available, this one is likely to remain safely in the realm of science fiction.

Tendo em conta tudo o que os “seres humanos” já provaram que são capazes de fazer, a nível de crueldade para com os seus semelhantes, eu leio com uma certa preocupação a frase ” likely to remain safely in the realm of science fiction” pois os argumentos contra o seu uso são “argumentos racionais” e o comportamento humano nem sempre é suficientemente razoável, minimamente lógico ou sequer racional…

Penso que a frase de que “com um grande poder vem (sempre?) uma grande responsabilidade” se aplica particularmente bem á tecnologia espacial, neste caso…