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

-----------------
CCNet-LETTERS is the discussion forum of the Cambridge-Conference
Network. Contributions to the on-going debate about near-Earth objects,
the cosmic environment of our planet and how to deal with it are welcome.
The fully indexed archive of the CCNet, from February 1997 on,
can be found at http://abob.libs.uga.edu/bobk/cccmenu.html



CCCMENU CCC for 2000

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia.