PLEASE NOTE:
*
LETTERS TO THE MODERATOR, 29 February 2000
------------------------------------------
(1) SUPPORT FOR GENERAL PETE WORDEN
Syuzo Isobe <isobesz@cc.nao.ac.jp>
(2) DEFENDING EARTH - FACTS & FICTION
Christian Gritzner <Christian.Gritzner@cargolifter.com>
(3) DEFENDING EARTH - FACTS & FICTION
Konrad Ebisch <kebisch@zycor.lgc.com>
(4) MANY IMPACTS - FEW CRATERS
Malcolm Miller <stellar2@actonline.com.au>
(5) MOON ORBITAL INCLINATION
Leonard Slack <lslack@wolfenet.com>
(6) MOON ORBITAL INCLINATION
Brian Marsden <brian@cfaps1.harvard.edu>
(7) INCLINATION OF THE MOON'S ORBIT
JEREMY TATUM <UNIVERSE@uvvm.UVic.CA>
(8) WHAT HAPPENED TO SATURN V?
Robert Clements <Robert.Clements@dva.gov.au>
(9) SATURN V BLUEPRINTS
Rich Godwin <GRSG@aol.com>
=================
(1) SUPPORT FOR GENERAL PETE WORDEN
From Syuzo Isobe <isobesz@cc.nao.ac.jp>
Dear Dr. Peiser:
According to S. Pete Worden, space missions are necessary to
study the
NEO problem instead of immediately developing asteroid mitigation
systems. This is the right approach, I feel, since we cannot get
100%
safety until all the PHAs have been detected. Some people argue
that
one or two space projects cost much more than all the necessary
ground
based NEO projects. This is true. The past IAU president,
Professor L.
Woltjer has estimated the annual cost of ground based and space
based
astronomy at 2000 million USDollar and 7000 million USDollar,
respectively (see L. Woltjer "Economic Consequences of the
Deterioration of the Astronomical Environment" in
Astronomical Society
of the Pacific Conference Series Volume 139 "Preserving the
Astronomical Windows", edited by Syuzo Isobe and Tomohiro
Hirayama.)
The matter is not only depending on the amount of money but also
on
what object and property we have to observe. Since we intend to
escape
from human disaster, we should obtain different types of data for
asteroid
character.
Yours sincererly,
Syuzo Isobe.
National Astronomical Observatory
2-21-1, Osawa, Mitaka, Tokyo 181, Japan
Tel: 81-422-34-3645, Fax: 81-422-34-3641
E-mail: isobesz@cc.nao.ac.jp
homepage http://neowg.mtk.neo.ac.jp/
==================
(2) DEFENDING EARTH - FACTS & FICTION
From Christian Gritzner <Christian.Gritzner@cargolifter.com>
Dear Benny,
this is my response to the statements of Robert Clements in the
CCNet
of February 28th on Defending Earth - Facts vs. Fiction.
The M2P2 propulsion system is a low thrust system which can be
used for
SMALL payloads while operating it for months. M2P2 seems to be a
great
propulsion system for small space probes, similar to electric
propulsion or solar sails - but it is just too weak for NEO
deflection.
A simple calculation will show this: the M2P2 system is capable
to
accelerate a 100 kg space probe within 3 months to a velocity of
some
80 km/s (which is far more than we can achieve using chemical
propulsion systems). A 1 km NEO roughly has a mass of some 10^12
kg
(which is 10^10 times more than the probe).
We assume that we would apply the same small M2P2 system to the
NEO for
10 years (which is 40 times more than 3 months), but the delta-V
that
we need to deflect the NEO away from the Earth by some 10 Earth
radii
is only about 1 cm/s (which is 8*10^6 times less).
When we multiply these 3 factors we find that deflecting a 1 km
NEO
needs a M2P2 system that is 2*10^5 times more powerful (and
heavier).... or has to run for aeons, or a mix of it, etc.
Such calculations for solar sails and electric propulsion show
similar
results, as I pointed out in my Thesis "Analysis of
alternative systems
for orbit alteration of near-Earth asteroids and comets" in
1996 (an
English translation was done by ESA and is available as a
technical
translation ESA-TT-1349 (1997).
The most powerful systems are nuclear explosives, but they suffer
from
the fact that they release their energy in a short event at very
high
forces that could disrupt the NEO producing many large and still
dangerous fragments. Impactors don't use nuclear explosives but
have
the same problem of possibly disrupting the NEO.
We still have to do much more research on NEO deflection in order
to be
successful one day! NEO discovery and tracking is the basis for
that
but what is it good for if we are not capable of deflecting a
possible
impactor in case of emergency?
Best wishes,
Christian
Dr.-Ing. Christian Gritzner
EUROSPACE Technische Entwicklungen GmbH
Lindenstr. 6
D-14467 Potsdam, germany
email: gritzner@eurospace.de
==================
(3) DEFENDING EARTH - FACTS & FICTION
From Konrad Ebisch <kebisch@zycor.lgc.com>
Dear Benny:
If your email makes me want to reply, then I guess it satisfies
its
purpose of making me think.
Here are some remarks on this latest one.
Melosh' proposal to wrap the planetoid in aluminum foil to
enhance
its reflectivity and thus the effect of sunlight pressure is
either
mistaken or misdescribed.
First, light energy from the sun will strike a "white"
planetoid and
be reflected back into space. Thus the planetoid gets its
incoming
momentum, plus -1 times its outgoing momentum. Light energy from
the
sun will strike a "black" planetoid, be absorbed, and
emitted back
into space as infrared. Thus the planetoid gets its incoming
momentum, plus -1 times its outgoing momentum. Six of one, half
dozen
of another.
Second, a big rock does not intercept enough sunlight to have
more
than a negligible effect on its orbit. Its mass to surface area
ratio
is just too big. This is fine for micron-size dust grains, but
even a
pea-sized meteoroid seems to follow its comet's orbit just fine
until
we see the pretty meteor as it happens into out atmosphere.
A sail
to deflect a planetoid will have to be very much larger, in area,
than the planetoid.
Perhaps we should go back to the nuclear explosion idea? We
may
worry that such an explosion might fragment the body, but recent
observation shows that Eros withstood an impact sufficient to
generate a 5 km crater.
"AND FINALLY: ISRAELITES SUE GOD FOR BREACH OF COVENANT
....."
Is this a change in the focus of your newsletters?
MODERATOR'S NOTE: No, it's just a gentle and witty reminder that
we, the
chosen primate, have to take our fate into our own hands &
brains :-)
=======================
(4) MANY IMPACTS - FEW CRATERS
From Malcolm Miller <stellar2@actonline.com.au>
Dear Benny,
I was very glad to see Juan Zapata-Arauco's note about the
inclination
of the Moon's orbit. While the error was apparent to any
astronomer, I
had to point out to a student that the figure should be five
degrees
and not 23, which probably confused the equator-ecliptic angle
with
that of the lunar orbit and Earth's equator.
Roberto Gorelli needs a good editor, but his paper is very
interesting.
So many impacts, so few craters, is a new concept that should
start
many people thinking.
Keep up the good work. One day soon I hope to be inspired
again to
render in verse some aspect of the impact environment!
Malcolm Miller
=======================
(5) MOON ORBITAL INCLINATION
From Leonard Slack <lslack@wolfenet.com>
People keep getting the facts on the Moon's orbital inclination
confused. The Moon's orbit is quite unique. Unlike most moons in
the
solar system the Earth'e Moon has an orbit that is inclined with
respect
to the Ecliptic (the Earth's orbital plane and apparent position
of the
Sun throughout the year) and not the Earth's equator. This allows
for
frequent solar eclipses. The Ecliptic is inclined with
respect to the
Earth's equator by about 23 degrees which is the axial tilt of
the
Earth.
In many ways one can think of the Moon orbiting the Sun (but
gravitationally bound to the Earth) with an inclinaion of
approximately 5 degrees with respect to the Earth's orbit.
The
Moon's orbit pressesses about the ecliptic in an 18.6 year
period.
If the Moon's orbit were inclined with respect to the Earth's
equator
then one might find the Moon near the Orion Nebula every 18
years.
Clearly this never happens since the Moon stays near the Ecliptic
=====================
(6) MOON'S ORBITAL INCLINATION
From Brian Marsden <brian@cfaps1.harvard.edu>
Dear Benny,
RE- Juan Zapata-Arauco's remark, Govert
Schilling was quite
correct: the moon's orbital inclination with respect to the
equator
currently averages 23.4 degrees. The 5-degree inclination refers
to the
ecliptic.
Regards
Brian
=====================
(7) INCLINATION OF THE MOON'S ORBIT
From JEREMY TATUM <UNIVERSE@uvvm.UVic.CA>
This morning's peisergram arrived in the very nick of time! In
just
under an hour, I am due to teach a lecture on the Moon to my
Solar
System class, and I was going to teach them that the orbit of the
Moon
is inclined between 18.5 and 28.5 degrees to the Earth's equator,
averaging 23.5 degrees, and that it is inclined to the ecliptic
at five
degrees. Thank goodness the peisergram arrived in time to set me
straight. I'll change my lecture notes accordingly.
Jeremy Tatum
=======================
(8) WHAT HAPPENED TO SATURN V?
From Robert Clements <Robert.Clements@dva.gov.au>
Wasn't everything re: the Saturn V program intentionally
destroyed as
part of the financial winding up of the program?
Can't generate the references off the top of my head; but my
understanding is that the White House insisted on it (presumably
using
the excuse that they preventing the technology from falling into
the
wrong hands) as a requirement for final payout on construction
contracts. Some of the technology - which included two pretty
much
ready-to-fly mission units, intended for the cancelled Apollo 18
& 19 -
was salvaged for Skylab & a Saturn V lies in state outside of
Kennedy;
but the rest....
All the best,
Robert Clements <Robert.Clements@dva.gov.au>
========================
(9) SATURN V BLUEPRINTS
From Rich Godwin <GRSG@aol.com>
Dear Benny
In response to the Saturn V blueprints. They were ordered
destroyed by
the US Congress back in 1969. However I happen to know where
there is a
complete copy, kept safe, just in case.
However even though they built the first ones in about 6 years,
NASA
says that now with our wonderful technology it would take us over
ten
years. Wonder how long it would take us to build a pyramid now??
Rich Godwin
The Watch
-----------------
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The fully indexed archive of the CCNet, from February 1997 on,
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