PLEASE NOTE:
*
CCNet DEBATE, 6 October 1998
----------------------------
(1) DUBIOUS DANGERS OF ASTEROID DEFLECTION
James D Perry <AJDPerry@aol.com>
(2) URGENCY OF PLANETARY DEFENSE SHOULD BE ASSESSED AFTER
SPACEGUARD SURVEY
Jens Kieffer-Olsen <dstdba@post4.tele.dk>
(3) TRANSFER OF RADIATION AT ASTEROIDAL SURFACES IN RELATION TO
THEIR
ORBIT DEFLECTION
S. Yabushita, KYOTO UNIVERSITY
(4) ORGANIC METEOROIDS
Jiri Borovicka <borovic@sunkl.asu.cas.cz>
===============
(1) DUBIOUS DANGERS OF ASTEROID DEFLECTION
From James D Perry <AJDPerry@aol.com>
Dear Benny,
Sagan and Ostro argue that an asteroid deflection system could be
used
irresponsibly to crash asteroids into the earth. I do not
agree with
the Space Command counterargument that the Sagan/Ostro thesis is
unsound due to "operational issues in navigation, targeting,
guidance
and control." On the other hand, I believe Sagan and
Ostro's fears are
wildly exaggerated. I particularly disagree that "it is hard
to imagine
guarantees against eventual misuse of an asteroid deflection
system
commensurate with the dangers such a system poses" (Nature,
8/7/94, p.
501). My reasons are as follows:
(1) Crashing an asteroid into the earth would most likely be the
act of
a madman, since it is hard to make the case that any nation could
"benefit" from a global catastrophe. (Sagan and Ostro
conspicuously
fail to articulate a convincing motive for asteroid deflection
towards
the earth as an act of national policy.) However, the act of a
madman
would be the easiest action to prevent. The long experience of
the
United States military with the command and control of nuclear
forces
would be highly relevant here, especially since nuclear weapons
would
have to be used to deflect an asteroid. For example, the
"two man rule"
(a requirement that at least two persons act in concert in
dealing with
nuclear weapons), Permissive Action Links, locks with
"limited try"
codes, and various other institutional checks and balances would
all be
used. Command and control could be highly centralized, because
there
would presumably be more than adequate warning time, and there
would be
no enemy attacking the command and control system.
(2) The nations most likely to finance, install, and operate an
asteroid deflection system (the United States, Japan, and the
Western
European countries) are precisely the nations who could be
trusted NOT
to crash an asteroid into the planet, because they have the most
to
lose from global catastrophe. These countries are highly unlikely
to
start an aggressive war, least of all by means of asteroid
collision.
(If the asteroid deflection system were put in place by (say)
North
Korea, Iran, and Libya, then there might be more cause for
concern.) A
system built and operated by the US, Japan, and Western Europe is
unlikely to be hijacked by any single one of these nations, and
it is
hard to believe that all of them would agree to deflect an
asteroid
towards some other country. If "we all live on the same
planet, we all
breathe the same air" -- then what would anyone have to gain
by
a collision?
(3) Asteroids, even ones of less than "global
catastrophe" size, have
much less military utility than nuclear weapons. Asteroids
are
inherently unwieldy. There is no guarantee that they would be
available
when needed (as are ICBMs), and it is doubtful that the asteroid
deflection system could achieve the accuracy of an ICBM (in the
hundreds of feet). An asteroid might even cause more
environmental
damage than a nuclear weapon, because the trend in nuclear
weapons is
towards smaller and "cleaner" (less radioactive)
weapons delivered with
high accuracy. In short, why choose asteroids as weapons when
nuclear-armed ICBMs are far more reliable and effective?
I see no reason why an asteroid deflection system could not be
constructed which would provide adequate security against madmen,
and
adequate safeguards to ensure that asteroids were only deflected
away
from (and never towards) the earth.
James D. Perry
====================
(2) URGENCY OF PLANETARY DEFENSE SHOULD BE ASSESSED AFTER
SPACEGUARD SURVEY
From Jens Kieffer-Olsen <dstdba@post4.tele.dk>
Pardon me for interjecting, but it is clearly inevitable that in
the
LONG run the planetary defense effort must lie within Defense
Dept regi
due to the nuclear issue involved.
Before separate funding can commence - and eventually exceed the
NASA
budget - it is, however, desirable that the civilian space
programme has
stabilized around the ISS.
If planetary defense and a manned mission to Mars are mutually
exclusive
projects competing for the same funds over the next 50 years, the
winning
agenda will depend on the urgency of the former project, which
can only be
determined after having completed the job of mapping at least 90%
of Near
Earth Objects larger than 1km.
Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
====================
(3) TRANSFER OF RADIATION AT ASTEROIDAL SURFACES IN RELATION TO
THEIR
ORBIT DEFLECTION
S. Yabushita: On the transfer of radiation at asteroidal surfaces
in
relation to their orbit deflection - II. MONTHLY NOTICES OF THE
ROYAL
ASTRONOMICAL SOCIETY, 1998, Vol.299, No.1, pp.244-248
KYOTO UNIVERSITY, DEPT APPL MATH & PHYS, KYOTO 606, JAPAN
The efficiency of absorption of X-rays generated by a nuclear
explosion
at the surface of an asteroid, estimated earlier, is used to
calculate
the explosion yield needed to deflect the orbit of an asteroid.
Following the work of Ahrens & Harris, it is shown that a
recoil
velocity of 1 cm s(-1) is required to deflect an asteroid from a
collision course with the Earth, and the necessary yield of
explosion
energy is estimated. If it is assumed that the scaling law
between the
energy and the diameter of the resulting crater, obtained from
experiments carried out on the Earth, remains valid on the
asteroid
surface, where gravity is much weaker, an explosion energy of 8
and 800
megaton (Mton) equivalent of TNT would be required for asteroids
of
diameter 1 and 10 km respectively. If, on the other hand, the
crater
diameter is proportional to a certain power of the gravity g, the
power
being determined from a dimension analysis, 130 kton and 12 Mton
would
be required to endow asteroids of diameters 1 and 10 km with the
required velocity, respectively. The result indicates that in
order to
estimate the required explosion energy, a better understanding of
cratering under gravity much weaker than on the Earth would be
required. Copyright 1998, Institute for Scientific Information
Inc.
========================
(4) ORGANIC METEOROIDS
From Jiri Borovicka <borovic@sunkl.asu.cas.cz>
> Duncan Steel, an astronomer with Spaceguard Australia in
Adelaide,
> has thrown another variable into the equation. If his model
of the
> chemical composition of the Leonid meteors is correct,
attempts to
> observe the approaching meteors may detect only a few per
cent of
> them.
Dear Sirs,
I have not read Duncan Steel's article yet, but from what I know
about
the meteor spectra I would say the following:
Yes, most of the luminosity of meteors in the visual light comes
from
the lines of sodium, magnesium, iron and other inorganic
elements. So,
hypothetical meteoroids composed only from the organic material
would
certainly produce fainter meteors than "normal"
meteoroids of the same
mass. On the other hand, I doubt that the organic meteors would
be
completely invisible, especially if they were so fast as Leonids
(71
km/s). This is because:
- Organic material can produce radiation of molecules like
CN, C_2, CH, OH.
- Fast meteors induce the atmosphere to radiate. Although
bright lines of nitrogen and oxygen lie in the
near-infrared,
there are bright visible nitrogen bands.
- Even faint fast meteors often exhibit trains of duration
of about 1 second produced by the forbidden oxygen line
at 5577 A of atmospheric origin.
As far as I know, no spectra corresponding to organic meteoroids
were
reported up to now, although they may have been simply discarded
as
"poor spectra". I agree that such meteoroids may exist
and may
be more abundant in fresh cometary ejecta. The more reason to do
a
careful faint meteor spectroscopy during the forthcoming Leonid
outburst. Although this may be too late for the satellites. But
as for
the number of meteoroids, I am not so optimistic (sorry,
skeptical).
Jiri Borovicka, Ondrejov Observatory
borovic@asu.cas.cz