PLEASE NOTE:


*

CCNet 74/2001 -  1 June 2001
----------------------------


"We investigate the hypothesis that the so-called Late Heavy
Bombardment (LHB) of the Moon was triggered by the formation of Uranus and
Neptune. As Uranus and Neptune formed, which we assume occurred at the
epoch of the LHB, they scattered neighboring icy planetesimals throughout
the Solar System. Some of these objects hit the Moon. Our integrations show
that the Moon would have accreted about 6×10^21 g, if we assume that the
Uranus-Neptune region initially contained 5 times the current mass of
these planets in the form of small solid objects."
--Harold F. Levison et al., Icarus, 1 June 2001


"Eros was the subject of detailed study for over a year by the Near
Earth Asteroid Rendezvous (NEAR) spacecraft. The magnetometer on NEAR
failed to measure any sign of a global magnetic field for the
asteroid down to the limits of the instrument's sensitivity, 1-2
nanotesla. By comparison, the Earth's magnetic field is about 50,000
nanoteslas. "Eros is a remarkably unmagnetized body," said Mario
Acuna, team leader of the magnetic field experiment on NEAR. "It is
essentially a non-magnetic object." The lack of a magnetic field was
puzzling because spacecraft flybys of other asteroids, such as Gaspra and
Braille, had detected magnetic fields. In addition, most meteorites,
including those of the class most closely associated with Eros, are
also magnetic."
--Jeff Foust, Spaceflight Now, 31 May 2001


"It all sounds depressingly familiar. Humans have only been using
space for the past 50 years, yet we're already preparing to fight over it.
And having concluded that our present weapons are too messy, we're
building better ones. There's even the spectre of nuclear arms in space.
For rogue states, the threat of a nuclear detonation in orbit would be a
powerful bargaining chip. But maybe there's an upside. Space is a
long way off, and a war fought there by remote control would be all but
invisible and harmless to those on the ground. Way above your head,
right now, two nations could be settling their differences in space. You'd
never even need to know."
--James Oberg, New Scientist, 2 June 2001


(1) WHY DOESN'T EROS HAVE A MAGNETIC FIELD?
    Ron Baalke <baalke@jpl.nasa.gov>

(2) MANY ASTEROIDS TRAVEL IN PAIRS
    Space.com, 31 May 2001

(3) PLANETARY SOCIETY CALLS ON CHILDREN TO SUPPORT PLUTO CAMPAIGN
    The Planetary Society <tps@planetary.org>

(4) NASA'S RISK ASSESSMENT OF SAMPLE RETURN MISSIONS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(5) THE ASTEROID IDENTIFICATION PROBLEM IV
    Andrea Milani et al.

(6) SPECTRAL PROPERTIES OF NEAR-EARTH OBJECTS
    Richard P. Binzel et al.

(7) COULD THE LUNAR "LATE HEAVY BOMBARDMENT" HAVE BEEN TRIGGERED BY THE
FORMATION OF URANUS AND NEPTUNE?
    Harold F. Levison et al.

(8) AND FINALLY: THE HEAVENS AT WAR
    New Scientist, 2 June 2001

==============
(1) WHY DOESN'T EROS HAVE A MAGNETIC FIELD?

From Ron Baalke <baalke@jpl.nasa.gov>

From Spaceflight Now, 31 May 2001
http://www.spaceflightnow.com/news/n0105/31eros/

Why doesn't Eros have a magnetic field?
By Jeff Foust

BOSTON, Mass. - Scientists said this week that they may know the reason why
the asteroid Eros appears to lack a measurable magnetic field.

Two researchers told attendees of the American Geophysical Union's spring
meeting in Boston that Eros may contain a large number of tiny,
individually-magnetized bodies whose magnetic fields are randomly oriented,
effectively canceling each other out.

Eros was the subject of detailed study for over a year by the Near Earth
Asteroid Rendezvous (NEAR) spacecraft. The magnetometer on NEAR failed to
measure any sign of a global magnetic field for the asteroid down to the
limits of the instrument's sensitivity, 1-2 nanotesla. By comparison, the
Earth's magnetic field is about 50,000 nanoteslas.

"Eros is a remarkably unmagnetized body," said Mario Acuna, team leader of
the magnetic field experiment on NEAR. "It is essentially a non-magnetic
object."

The lack of a magnetic field was puzzling because spacecraft flybys of other
asteroids, such as Gaspra and Braille, had detected magnetic fields. In
addition, most meteorites, including those of the class most closely
associated with Eros, are also magnetic.

One possible explanation for the meteorites is that they have been
"contaminated" by the Earth's magnetic field, becoming magnetized only after
arriving at Earth. To test this, Gunther Kletetschka, a researcher with the
Catholic University of America and NASA's Goddard Space Flight Center,
exposed chondrules -- tiny droplets of primitive material embedded in the
meteorite -- to changes in temperature and magnetic fields similar to what a
meteorite might experience when arriving on Earth.

In about half of the cases Kletetschka found that the chondrules took on the
magnetization they were exposed to in the experiment. However, in the other
half of the cases there was no change in the chondrule's magnetism,
indicating that it has a strong remnant magnetism that likely existed since
the chondrule was formed billions of years ago, during the formation of the
solar system itself.

Since Eros is similar to the class of chondritic meteorites studied in the
lab, it likely contains a large number of magnetized chondrules. However,
Kletetschka argues that if the chondrules are randomly oriented, they will
effectively cancel each other's magnetic fields out, preventing a global
magnetic field from forming. This is seen to a limited degree in the lab,
where larger samples of chondritic meteorites appear to have weaker
magnetization than smaller ones as the randomizing effect begins to take
hold.

If true, this implies that Eros has not been modified since the formation of
the solar system in any way that would alter the magnetization of the
chondrules. "Eros is a very primitive object," said Acuna.

To confirm this, however, would require obtaining samples from the asteroid
itself, which is not likely to happen for the foreseeable future. Also
required, say scientists, are studies of other asteroids, including
follow-up studies of Gaspra and Braille to confirm that they have the
magnetic fields detected in previous flybys. 

© 2001 Pole Star Publications Ltd
 
===========
(2) MANY ASTEROIDS TRAVEL IN PAIRS

From Space.com, 31 May 2001
http://www.space.com/scienceastronomy/solarsystem/asteroid_pairs_010531_wg.html

By Andrew Bridges
AP Science Writer

LOS ANGELES (AP) -- Astronomers are discovering a bumper crop of binary
asteroids -- space rocks locked in an orbital dance with a partner.

The latest discovery was announced Wednesday, when radar images showed that
asteroid 1999 KW4 is actually two objects separated by about a mile,
something that had been suspected for the past year.

Radar images show a small moon just one-quarter of a mile across whipping
clockwise around a companion three times as large.

"Some day, people will go to a binary asteroid and what an interesting sky
they will see," said Steven Ostro of the National Aeronautics and Space
Administration's Jet Propulsion Laboratory.

The discovery boosts to roughly 10 the number of binary asteroids imaged by
radar since the spacecraft Galileo spotted the first, 243 Ida and its tiny
moon Dactyl. Another seven suspected pairs haven't been confirmed.

While the tally is still small, it is certain to grow as astronomers refine
the techniques used to spy the miniature planetary systems.

Observations of paired craters on the Earth and other bodies led astronomers
to suspect that binary asteroids existed.

On Earth, the craters -- all of equal age -- are too large and too far apart
to have been formed by a single asteroid breaking up in the atmosphere. The
odds of two asteroids hitting the Earth in the same location and at the same
time are slim -- unless they were paired before impact. But the first binary
asteroid was not seen until 1993, when Galileo spotted Ida and Dactyl while
en route to Jupiter.

Not all asteroid moons orbit asteroids. The two moons of Mars, Phobos and
Deimos, are probably asteroids captured in orbit by the planet's
gravitational tug.

Czech astronomer Petr Pravec said the study of near-Earth asteroids is
becoming more important -- especially if scientists are going to entertain
ways to defend the planet from potential asteroid impacts.

"If some of them are on a collision course with the Earth in the future, it
will be more difficult to divert them than if they were a single asteroid,"
Pravec said.

The asteroid pairs found so far share little more than diversity.

Pairs like 90 Antiope are nearly twins, each 50 miles or so across. Some,
like 2000 DP107, are also of about equal size, but just hundreds of feet in
diameter. Others are far more lopsided, like the case of 87 Sylvia, which at
176 miles across dwarfs its moon, just 5 percent as large.

Collisions may have formed many of the binary asteroids, meaning each little
moon is, literally, a chip off the old block. In other cases, passing close
to Earth may have pulled off material, dumping it into a mini-orbit.

In the case of 1999 KW4, the objects may be the remnants of an extinct
comet. Orbital observations will allow astronomers to determine the mass,
density, composition and porosity of each member of the pair.

"That tells us an awful lot about these things without having to go there,"
said Bill Merline, a senior research scientist at the Southwest Research
Institute in Boulder, Colo., who has discovered three binary asteroids.

Copyright 2001, AP

=======
(3) PLANETARY SOCIETY CALLS ON CHILDREN TO SUPPORT PLUTO CAMPAIGN

From The Planetary Society <tps@planetary.org>

NEWS RELEASE

The Planetary Society
65 N. Catalina Avenue, Pasadena, CA 91106-2301 (626) 793-5100 Fax (626)
793-5528
E-mail: tps@planetary.org  Web: http://planetary.org

For Immediate Release: May 31, 2001
Contact: Susan Lendroth

Planetary Society Launches Campaign For New Pluto Generation

"Wouldn't it be cool to go to Pluto?" asks a new Planetary Society web site
that helps kids let Congress know what they think about sending a spacecraft
to visit the last planet in our solar system.

The Planetary Society has been campaigning for a Pluto mission ever since
work on NASA's Pluto-Kuiper Express mission stopped in fall 2000. Now the
Society invites young people to express their views about exploring Pluto.

"Pluto is cool -- actually very cold," notes Bill Nye the Science Guy, a
member of The Planetary Society's Board of Directors. "But there is a lot
about it we don't know, and that is why we should go now. Kids today will be
coming of age and reaping the benefits of our new knowledge when a
spacecraft reaches Pluto."

The Planetary Society wants to introduce Pluto to the generation that will
be supplying future planetary scientists. Even if NASA funds a new Pluto
mission to launch in 2004, the soonest the spacecraft could reach Pluto is
2012. Some of the kids sending messages to Congress today could be part of
that mission science team in the future.

The Society has not forgotten the grown-ups either. It continues its
long-running web campaign where Pluto supporters can log in to send messages
to Congress. It has also turned up the heat by asking its 100,000 members to
write to Congress on postcards included in the latest Planetary
Report, the Society's bimonthly magazine. A different campaign last year
elicited 10,000 post cards in support of a Pluto mission.

That strong response helped convince Congress to ask NASA to keep the option
of a Pluto mission alive. In December, 2000, NASA issued an Announcement of
Opportunity for principal investigators and institutions to submit proposals
for a new mission to Pluto. NASA is now evaluating those
proposals.

The reason it is urgent to send a mission to Pluto now rather than later is
that some scientists believe the thin atmosphere of Pluto will freeze to the
surface as the planet moves in its orbit further from the Sun. We'd then
have to wait over 200 years for the next thaw to occur some time
around 2230. The longer a mission is delayed, the more likely it will be
that we will lose the opportunity to study Pluto's atmosphere.

Nye added, "Pluto is a planet, and the things we learn there will help us
better understand and take care of our home world here."

Children and adults can log on to The Planetary Society's website at
http://planetary.org to send their messages directly to Congress.

-o0o-

THE PLANETARY SOCIETY:
Carl Sagan, Bruce Murray and Louis Friedman founded The Planetary Society in
1980 to advance the exploration of the solar system and to continue the
search for extraterrestrial life. With 100,000 members in over 140
countries, the Society is the largest space interest group in the world.

CONTACT INFORMATION:
For more information about The Planetary Society, contact Susan Lendroth at
(626) 793-5100 ext 237 or by e-mail at susan.lendroth@planetary.org.

The Planetary Society
65 N. Catalina Ave.
Pasadena, CA 91106-2301
Tel:  (626) 793-5100
Fax:  (626) 793-5528
E-Mail:  tps@planetary.org

==========
(4) NASA'S RISK ASSESSMENT OF SAMPLE RETURN MISSIONS

From Andrew Yee <ayee@nova.astro.utoronto.ca>

From Boston Globe, 30 May 2001
[ http://www.boston.com/dailyglobe2/150/nation/mars_rocks_seen_coming_before_means_to_handle_the_+.shtml ]

Wednesday, May 30, 2001

Mars rocks seen coming before means to handle them

Samples, Earth feared in danger of contamination

By David L. Chandler, Boston Globe Staff, chandler@globe.com

If NASA goes ahead with plans to bring Martian rocks back to Earth early
next decade, Earth would barely have enough time to get ready.

No lab has yet been built that could adequately handle an alien soil sample,
and such a facility is years away, according to a report released yesterday.

A robotic mission to fetch Mars rocks was initially planned to return
samples by 2008. But a federally appointed research panel warned yesterday
that the facility necessary to quarantine Mars rocks will take at least a
decade to design and build.

The facility needed to protect Earth from even the remote possibility of a
dangerous organism in the Mars sample, and to protect the sample itself from
contamination, will require "a sample-receiving quarantine and research
facility unlike any other in existence," said John Wood, chair of a panel of
the National Academy of Sciences that prepared the report, which was
released yesterday at a meeting of the American Geophysical Union being held
this week at the Hynes convention center.

The new facility, the report said, would have to combine the protections
afforded by the highest level of biological containment facilities, called
BSL-4, with the protection from outside contamination afforded by "clean
rooms" used to process microchips. BSL-4, which stands for biological safety
level 4, is used to handle deadly pathogens like the Ebola virus.

John Rummel, NASA's planetary protection officer, is responsible for
protecting Earth from any alien organisms. Rummel, also responsible for
protecting alien organisms from Earth contaminants, said in an interview
yesterday that he was pleased with the report and plans to "adopt some or
all" of its recommendations.

But Rummel added that he is not sure the report went far enough. Any Mars
sample containing clear signs of life, the report says, would require "a
very elaborate plan of handling, curation and study," areas the panel did
not attempt to discuss in detail.

If a sample shows signs of life, said Rummel, the level of excitement and
interest among scientists and the public will be too intense to accommodate
the delays involved in a new round of research and planning. Well before the
samples come back to Earth, he said, NASA should have in place "a plan of
what you do if you do find life."

Wood, a senior scientist at the Harvard-Smithsonian Center for Astrophysics,
said that "if the sample really, truly seemed to have life in it, it would
become a question of such towering importance that the resources available
to investigate it would become much larger."

"We would need to completely rethink the situation in that case," he said.

The new report concentrates primarily on what it calls a more likely
scenario: that whatever is found in the samples from Mars will be unclear,
with signs that point to the possibility of living organisms, but no clear
proof. In that case, it suggests that samples could be thoroughly sterilized
so that some tiny parts of the alien rock or soil could be sent out for
study in much less restrictive laboratories.

Inside BSL-4 facilities, researchers must work inside cumbersome "space
suits" that severely limit what they can do, with heavy gloves that restrict
their ability to manipulate the material.

It was the ongoing saga of a meteorite from Mars, which NASA researchers
announced in 1996 contained evidence of possible fossilized Martian
microbes, that guided the panel's recommendation for the release of
sterilized samples for research, Wood said. Five years after the initial
report, the question of whether the meteorite contains signs of past life or
not remains unresolved and contentious.

Rummel said he thinks there should also be some additional tests for the
presence of life, beyond those recommended by the panel, before the samples
are presumed to be safe. The panel called for tests that assume all life
will operate on the same principles as Earth life, he said, and it is too
soon to make such an assumption.

"We ought to do some studies that don't depend on us knowing anything," he
said. But overall, he said, "the spirit of the report is right on." When it
comes to handling Martian samples, he said, "we should take our time to do
it right."

© Copyright 2001 Globe Newspaper Company.

============
* ABSTACTS *
=============

(5) THE ASTEROID IDENTIFICATION PROBLEM IV

Andrea Milani*, Maria Eugenia Sansaturio, Steven R. Chesley: The Asteroid
Identification Problem IV: Attributions. Icarus, Vol. 151, No. 2, June 1,
2001, pp. 150-159 
 
Existing archives of asteroid observations contain many objects with very
short observed arcs. In this paper we present a method that we have used
with considerable success to attribute these short arc "discoveries" to
other objects with better defined orbits. The method consists of a
three-stage filtering process whereby several billion possible
attribution/orbit pairs are systematically analyzed with more and more exact
algorithms, at each stage rejecting improbable cases. The first stage
compares an attributable, by definition a synthetic observation
representative of all the observations over a short arc, with the predicted
observation for each available orbit. The second stage compares the proposed
attributable observations with predicted positions from the known orbit
using conventional linear covariance techniques, considering both the
position and motion on the celestial sphere. In the final filter we attempt
to compute a best-fitting orbit by differential corrections using the
combined dataset. With this algorithm we have found 1675 attributions in
approximately one year of operations, in addition to 902 identifications
found with another algorithm. We discuss the lessons learned from this
one-year experiment and the possibilities of further improvement and
automation of the procedure. Copyright 2001 Academic Press.

*Dipartimento di Matematica, Universitą di Pisa, Via Buonarroti 2, Pisa,
56127, Italy, milani@dm.unipi.it

© Harcourt, Inc.

===========
(6) SPECTRAL PROPERTIES OF NEAR-EARTH OBJECTS

Richard P. Binzel*,  Alan W. Harris,  Schelte J. Bus,  Thomas H. Burbine:
Spectral Properties of Near-Earth Objects: Palomar and IRTF Results for 48
Objects Including Spacecraft Targets (9969) Braille and (10302) 1989 ML.
Icarus, Vol. 151, No. 2, June 1, 2001, pp. 139-149

We present results of visible wavelength spectroscopic measurements for 48
near-Earth objects (NEOs) obtained with the 5-m telescope at Palomar
Mountain Observatory during 1998, 1999, and early 2000. The compositional
interpretations for 15 of these objects have been enhanced by the addition
of near-infrared spectra obtained with the NASA Infrared Telescope Facility.
One-third of our sampled objects fall in the Sq and Q classes and resemble
ordinary chondrite meteorites. Overall our sample shows a clear transition
between S-type and Q-type compositional classes over visible and
near-infrared wavelengths. Taken together these results point toward an
abundance of near-Earth asteroids capable of providing sources for ordinary
chondrite meteorites. Our sampling strategy favors targeting the smallest
observable objects and we report results for the 15-m diameter object 1998
BT13, the smallest spectroscopically measured NEO to date. NEOs show a
greater spectral diversity than main-belt asteroids, and our small sample
includes objects falling in the rare categories of K, L, O, and V classes.
The K-class object 1999 JD6 is found to match CV chondrite meteorites.
Potential spacecraft targets received top priority for observation, with the
ordinary chondrite-like composition of (9969) Braille being reported prior
to the Deep Space-1 encounter. The relatively accessible asteroid (10302)
1989 ML displays a neutral spectrum that may be interpreted as a
shock-darkened ordinary chondrite. Copyright 2001 Academic Press.

*Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts
Institute of Technology, Cambridge, Massachusetts, 02139, rpb@mit.edu

© Harcourt, Inc.

===========
(7) COULD THE LUNAR "LATE HEAVY BOMBARDMENT" HAVE BEEN TRIGGERED BY THE
FORMATION OF URANUS AND NEPTUNE?

Harold F. Levison*, Luke Dones*, Clark R. Chapman*, S. Alan Stern*, Martin
J. Duncan,  Kevin Zahnle: Could the Lunar "Late Heavy Bombardment" Have Been
Triggered by the Formation of Uranus and Neptune? Icarus, Vol. 151, No. 2,
June 1, 2001, pp. 286-306

We investigate the hypothesis that the so-called Late Heavy Bombardment
(LHB) of the Moon was triggered by the formation of Uranus and Neptune. As
Uranus and Neptune formed, which we assume occurred at the epoch of the LHB,
they scattered neighboring icy planetesimals throughout the Solar System.
Some of these objects hit the Moon. Our integrations show that the Moon
would have accreted about 6×1021 g, if we assume that the Uranus-Neptune
region initially contained 5 times the current mass of these planets in the
form of small solid objects. In addition, Mars would have accumulated
~6×1022 g of icy material, which could have supplied its putative early
massive atmosphere. However, Earth would likely have accreted only ~7×1022 g
of water, or ~5% of its oceans, through the mechanisms studied here. The
numerical experiment that we have performed on the behavior of
Uranus-Neptune planetesimals shows very good agreement with current
constraints on the LHB. The influx of Uranus-Neptune planetesimals onto the
Moon could have lasted for a time as short as 10 or 20 million years. The
dynamical transport of the Uranus-Neptune planetesimals during this process
would have caused Jupiter and Saturn to migrate. This migration, in turn,
would have destabilized objects in the jovian Trojan swarms and the asteroid
belt. Thus, not only would Uranus and Neptune planetesimals have struck the
Moon, but asteroids would have as well. We find that the Trojan asteroids of
Jupiter could not have contributed a large percentage of material to the
LHB, but the asteroid belt could, in principle, have contributed to, or even
dominated, the LHB. Although this model appears to explain the LHB well, it
requires that fully formed Uranus and Neptune not appear in the
trans-saturnian region until some 700 million years after the formation of
the Earth. Copyright 2001 Academic Press.

*Space Studies Department, Southwest Research Institute, Boulder, Colorado,
80302, hal@gort.boulder.swri.edu

© Harcourt, Inc.

============
(8) AND FINALLY: THE HEAVENS AT WAR

From New Scientist, 2 June 2001
http://www.newscientist.co.uk/features/features.jsp?id=ns22931
 
The final frontier is set to become a battleground. How will the superpowers
fight it out for space supremacy, asks James Oberg

IN A remote valley in New Mexico's Manzano Mountains, the US is tooling up
for war. Here, in a four-storey building with walls more than a metre thick,
it runs a secret particle-beam project. The weapons it's developing will
never be used on Earth because they only work in a vacuum. But that's no
problem--the idea is to fire them in space.

Once, space was empty and there was nothing there worth fighting for. Now
it's teeming with valuable equipment and tensions are mounting. The US
believes a war in space is a virtual certainty--just last month defence
secretary Donald Rumsfeld announced plans for upgrading its military
presence there. Russia and China are also preparing for combat. And while
there are no offensive weapons in orbit today, there's nothing to stop
nations from putting them there tomorrow. True, particle beams and other
sophisticated weapons are at least a decade away. But some space weapons are
so simple that dozens of nations are already capable of building them.

Military strategists have been thinking about orbital combat since the
launch of Sputnik 1 in 1957. For the first few years of the space race,
their ideas were hopelessly impractical and neither side sent weapons into
space--although cosmonauts carried handguns in case of an emergency landing
on enemy soil. But soon they began to design, build and test various pieces
of anti-satellite (ASAT) weaponry. The US focused on guided missiles,
launched from the air and designed to ram the target directly. The Soviets
preferred "killer satellites"--orbiting spacecraft armed with shrapnel
charges that could disable enemy craft. Both sides also dabbled in nuclear
warheads. All were decommissioned without being fired in anger.

The end of the cold war killed off most of the systems, but the threat of
space war hasn't gone away. In fact, it's worse than ever. Occupation of
space is no longer a two-sided affair. Any government, private
organisation--or terrorist group--can buy off-the-shelf satellites and
launch them for a few million dollars apiece. Space has become valuable
territory, both commercially and strategically. Many nations rely on it for
intelligence, and space is teeming with privately owned communications
satellites. Taken together these have enormous potential to cause offence.
No nation likes to be spied on, and some governments see TV satellites as a
weapon of cultural aggression against which defensive measures are
justified. Some time soon, someone will be tempted to have a pop.

Analysts agree that the first move will probably be a ground-based
electronic assault on a satellite. Some say this kind of attack has already
happened. A British military communications satellite was reportedly
kidnapped and driven off course by hackers, though officials denied it.
Nation states have also been getting in on the act. The pro-government Saudi
newspaper Al-Watan has been running a series of articles on communications
satellites, in which it accuses broadcasters of spreading "political
sedition". The newspaper advocates silencing the offending satellites. And
the government of Nauru has accused its neighbour Indonesia of jamming a
commercial satellite in orbit over its territory. Indonesia denies the
charge.

Jamming a satellite hardly constitutes an act of war, but a more aggressive
approach is technically possible and also desirable--the threat of physical
damage has always been a useful negotiating tool. The trouble is there's
little to stop threats from escalating into violence. Just like the high
seas, space is a region beyond national sovereignty. While we have treaties
banning weapons of mass destruction in orbit, international law has nothing
to say about ordinary space weaponry.

What's more, the fact that space-based technologies are vulnerable to attack
hasn't gone unnoticed. As one Chinese newspaper commented in July last year:
"For countries that could never win a war by using tanks and planes,
attacking the US space system may be an irresistible choice."

The US certainly expects that to happen. Last year a special commission on
the military aspects of space concluded that a conflict in space was "a
virtual certainty". And during the intelligence community's annual "world
threat" briefing in February, the heads of both the CIA and the Defense
Intelligence Agency openly voiced their concerns about an attack in space.
DIA director Thomas Wilson warned that several foreign governments were
experimenting with space weapons. He named China and Russia as the biggest
threats and predicted that by 2015, they would be capable of blowing big
holes in the US space programme.

In January the US even held a war game based in space. The scenario was set
in 2018 and involved an enemy state attacking US satellites that were
supporting a military operation on the ground. The results are classified,
but the military made its conclusions clear: without more funding for space
defence, the US faces a Pearl Harbour in orbit.

Independent experts believe there are no weapons in space at the moment,
apart from a gun in the Russian emergency kit on the International Space
Station. There's also very little on the ground that could do harm in space.
But the technologies to make highly destructive weapons already exist or are
in development.
 
The simplest way to attack a satellite is with weapons launched from the
ground. That's the principle behind the "poor man's ASAT" (see Diagram). The
idea is to use a small missile to deposit a cloud of sand, ball bearings and
other hard objects in the path of an oncoming satellite. The target's own
velocity provides the impact energy. It's unreliable, but it poses a
credible threat. A dozen countries without space capabilities could build
such a system, although none claim to have done so yet.

But there are problems with ground-based weaponry. You can only strike while
the target is in range and it takes time for your missile to climb into
orbit. That gives the satellite time to take evasive action. For this
reason, some strategists want to arm the satellites themselves.

One approach is "parasite satellites"--orbiting limpet bombs that attach
themselves to enemy craft for detonation at a later date. The Chinese say
they can do this already, though the claim is hard to verify. A simpler
method is to disable your enemy with a high-speed projectile. In other
words, shoot at it. This was tried in 1974 when the Soviet Union launched
Salyut 3, the first crewed military reconnaissance outpost in orbit. In
anticipation of an attack by the US, the Soviets mounted a modified machine
gun on the satellite so they could greet any hostile approach with a hail of
bullets. The attack never came. Salyut 3 proved to be a white elephant and
was quickly decommissioned, although not without a shot being fired. After
the two-man crew had left, the ground crew fired a few rounds by remote
control. It must have been quite a sight.

Shooting projectiles is a standard way of doing combat on Earth, but in
space it's a little different. For one thing, there's no atmosphere or
gravity, so the projectile behaves strangely. In low-Earth orbit, most of
your bullets would eventually hit the atmosphere and burn up, though some
would settle into a stable orbit. Some of these orbits would intercept
yours, so you'd have be careful not to shoot yourself down. The rules of
engagement are also completely different. Satellites circle the planet at
high speeds, which makes it difficult to take on an enemy craft in a dog
fight.

The simplest way to manoeuvre to within shooting distance is to intercept
the satellite "in plane". In other words, approach it from behind in a lower
and faster orbit and then boost yourself into its path. From the target's
point of view, an attack craft would close in from behind and below, and the
final few hundred metres of approach would be almost a straight line.

At this moment a burst of cannon fire would be lethal. The impact would
cause a shock wave in the satellite's structure, pulverising its electronic
equipment, shattering the glass in viewports and solar panels, and cracking
open pressurised propellant tubes. A hit to a compartment containing oxygen
could start a fire and incinerate the contents. But in the vacuum of space
there would be no billowing Star Wars explosions or shock rings, just an
eerie silence and tumbling, twinkling space confetti.

The victorious craft would then have to avoid the wreckage. Shooting down a
satellite isn't like shooting down an aeroplane, where the engine or wings
are so badly damaged that it falls out of the sky. Dead satellites continue
to circle the Earth. The same goes for bits of shrapnel.

Debris isn't just a short-term problem. It can stay in orbit for years.
Soviet ASAT tests in the late 1960s left behind a dozen clouds of metallic
shards which are still a hazard today. The fragments are too small to track
and too numerous to dodge, so all space vehicles have to be armoured against
them.

For this reason, the US is reluctant to start shooting at things in orbit.
After the recent war game, General Ralph Eberhart, commander-in-chief of US
Space Command, told reporters he considered it a last-ditch option. But
that's not to say space war has been ruled out. In the next couple of
decades, projectiles are likely to be replaced by electromagnetic cannons,
lasers and particle beams--high-tech weaponry capable of inflicting damage
without creating debris.

Electromagnetic cannons are well developed (New Scientist, 1 July 2000, p
20) and are probably closest to being deployed in space. They fire intense
bursts of radio waves at their target, jamming or destroying its
electronics. At close range, they could permanently cripple a satellite's
circuitry. At greater distances their power may only be enough to
temporarily paralyse circuits.

Prototype cannons have already been built and tested. The two main types are
the high-power microwave (HPM) system and the ultra-wide-band (UWB) system.
HPM weapons fire a narrow and powerful beam of high-frequency radiation
which can pierce a satellite's armour and fry its circuitry. The UWB beam is
more of a scattergun weapon, with a broad beam and wide frequency range
designed to knock out any electronic equipment in the vicinity.

Laser weapons dump large amounts of energy onto the satellite's surface,
causing violent thermal expansion and setting up shock waves that tear
components from the interior walls. People who've seen the damage inflicted
by laser weapons say the effect is like a shotgun blast at point-blank
range. So far lasers have only been used for rangefinding and guidance, but
prototype weapons exist. And if President Bush goes ahead with his plan to
revive "Star Wars", they could be in space very soon.

For the past 15 years, the US military has been experimenting with lasers at
a test facility in White Sands, New Mexico. This is the home of MIRACL (the
mid-infrared advanced chemical laser), a powerful deuterium fluoride laser
built about 20 years ago for ships, then transferred to White Sands in the
mid-1980s to study its anti-satellite capabilities. In October 1997, MIRACL
was test fired into space. Although not powerful enough to vaporise a
satellite, most experts believe that MIRACL could disable optical equipment
and damage solar arrays and other delicate structures. There are some
problems with atmospheric interference, but putting the laser into orbit
would solve those.

Particle-beam weapons inflict damage in a similar way. They emit beams of
particles, perhaps hydrogen or deuterium ions, at near-light speed. Details
remain sketchy, but the principle is essentially the same as in an
ion-propulsion system (New Scientist, 21 November 1998, p 22). A working
particle beam is believed to have been on board the mysterious Soviet
"battlestar" Polyus-Skif, which was launched in May 1987 but crashed during
take-off. Polyus-Skif also carried a prototype laser for destroying
satellites. In the US, research on particle-beam weapons continues at the
High Energy Research and Technology Facility on Kirtland Air Force Base, New
Mexico.

It all sounds depressingly familiar. Humans have only been using space for
the past 50 years, yet we're already preparing to fight over it. And having
concluded that our present weapons are too messy, we're building better
ones. There's even the spectre of nuclear arms in space. For rogue states,
the threat of a nuclear detonation in orbit would be a powerful bargaining
chip.

But maybe there's an upside. Space is a long way off, and a war fought there
by remote control would be all but invisible and harmless to those on the
ground. Way above your head, right now, two nations could be settling their
differences in space. You'd never even need to know.

James Oberg is a space writer and a former space flight engineer based in
Houston, Texas. His new book, Space Power Theory, can be downloaded at
http://www.jamesoberg.com/books/spt/spt.html 

From New Scientist magazine, 02 June 2001.

© Copyright New Scientist, RBI Limited 2001

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