CCNet DIGEST, 24 September 1998

      Sir Arthur C Clarke

      Scott Manley <>

      Roy Tucker <>

      Leroy Ellenberger <>

      BBC Online News

      Andrew Yee <>


From Sir Arthur C Clarke

The first two novels about building Space Elevators were my THE FOUNTAINS OF
PARADISE and Charles Sheffield's THE WEB BETWEEN THE WORLDS (both 1979).
I suggested using Deimos for Mars but since then the literature has become so
extensive that I've not attempted to follow it - and the discovery of C60 nanotubes
has given the material necessary.

                     Sir Arthur Clarke     23 Sept 98


From Scott Manley <>

I've personally always been a big fan of the orbital tower/beanstalk/space
elevator concept but I think that Swift Tuttle is probably the worst possible
choice of anchor body.

Firstly it's in a high incluination orbit so the Delta V required is much
greater than that of many other objects which pass closer to earth. It's a
comet which meant that if it were in orbit it would be sublimating and
covering the Earth with vast amounts of dust wreaking climatological havok.
And of course it might end up disintegrating completely.

There are probably many more appropriate NEA's which are a Km or so across.

Actually constructing a space elevator is an interesting task in itself, the
cable has to be tapered correctly to accommodate the varying stresses along
the length and trying to grow the cable downwards from geostationary orbit
causes the cable to shear and start the tower rotating.

It is more than likely possible and would be a fantastic project, but at the
same time a rather delicate task.

And if the cable ever snapped the energy released would be equivalent to that
of a nuclear weapon.

Scott Manley (aka Szyzyg)
Armagh Observatory
Northern Ireland BT61 9DG


From Roy Tucker <>
* as posted on the MPML e-mail list <>

Hello Fellow Asteroid Chasers,

My attention was directed to this forum a couple of days ago. I'm delighted to
learn that there is a communications medium for those of us who have a passion for
small solar system bodies.  To acquaint you with my efforts, permit me to direct
your attention to my observatory web page at:
"". Since that was written, my
thinking about future instrumentation has changed. To stimulate discussion
about future search programs by the amateur community, I have been
encouraged to include an edited version of my proposal to the Planetary
Society for their NEO Grant Program.

                        P R O P O S A L

                        Roy A. Tucker

                        2 August 1998

The construction of a specialized instrument to find Near-Earth Objects is 
proposed. This instrument will consist of three 25 centimeter aperture f/5.5
Newtonian telescopes with identical CCD cameras at their foci. The cameras
will  be equipped with thinned, back-illuminated TK1024 imagers from Scientific
Imaging Technologies (Beaverton, Oregon). These devices are 1024x1024 arrays
with 24 micron pixels and will provide a field of view of one square degree
or 3.51 arcseconds per pixel. These telescopes will be mounted such that they
will be pointed at the same declination but separated in Right Ascension by about
fifteen minutes. Operated in time delay integration or scan mode, it would be
possible to search fifteen square degrees per hour to a limiting magnitude of
about 19.5 to 19.7. The search could continue uninterrupted and provide a
total coverage of about 145 square degrees for a ten hour night. Since the system
will operate every clear night of the month, including bright moonlit nights,
approximately four thousand square degrees per month may be searched.

The search for Near-Earth Objects requires the examination of large areas of sky
for faint moving objects. The highest priority targets, the Potentially Hazardous
Asteroids (PHA's), are considered to be those objects of absolute magnitude 22.0
(approximately 150 meters diameter) or larger. During favorable apparitions (close
to the earth and near the opposition region of the ecliptic) these objects may be
expected to be brighter than magnitude 19.5 for two or three weeks. During that
time a modest-sized telescope and sensitive CCD camera is capable of revealing
them. As examples, I have attached data describing the discovery apparitions of the
three Near-Earth Objects that I have discovered. All three of these objects were
brighter than nineteenth magnitude when they crossed the celestial equator and
would have been observable with the proposed instrumentation.

One of the usual methods of searching for moving objects such as asteroids
and comets involves operating a CCD camera in scan mode and imaging a strip
of sky (Gehrels, 1991). The telescope is then moved and the same region of sky
is imaged again. The images are then examined to see if anything has moved in
the time interval between them. To discriminate against cosmic ray events, a
third scan is often acquired, reducing the observing efficiency even further. By
using three identical telescope/camera combinations pointed at the same declination
but spread apart in Right Ascension, the search method is more efficiently
implemented and the need for a movable telescope mounting is eliminated.

The design will emphasize simplicity and reliability. A temperature-compensated
telescope structure will eliminate the need for routine focussing. Since the
telescopes will be mounted in a fixed orientation, the structure does not need  to
be stiffened to resist the flexures that would result from varying orientation. The
Newtonian optical configuration will involve only two reflections and minimal loss
of light.

I have developed a relatively simple, economical camera design (Tucker, 1994)
providing low-noise readout and 16-bit digitization. I currently have two cameras,
one with a SITe TK512 and the other with a TK1024. I have operated these cameras on
my 14" aperture f/11 Schmidt-Cassegrain telescope and find that under my mildly
light polluted skies I can see as faint as magnitude 20.5 with a four minute
integration. When operating the TK1024 camera in scan mode, the  equivalent
integration time is 87 seconds at the celestial equator and the limiting magnitude
is 19.7. Using this instrumentation,  I have been engaged in a program of asteroid
astrometry since October of 1996. As the result of intentional search efforts, I
have discovered in the past year three Near Earth Objects: 1998 FG2, an Apollo
asteroid; and two Atens, 1997 MW1 and 1998 HE3.

Since I already have a second TK1024 imaging device and most of the parts for two
more cameras, I will only need to purchase a third imaging device, some
of the integrated circuits, and mechanical parts to provide the cameras for
this project. The telescopes will require the optics, mechanical structure, and an
enclosure to provide protection against the elements. A Pentium-class computer will
retrieve image data from the cameras and execute a search for moving objects. The
operation of the instrument will be highly automated and require little operator

In the event of the detection of an object requiring immediate follow-up, the
14-inch aperture, f/11 Schmidt-Cassegrain will be equipped with the TK512 camera.
The search instrument will not be required for any additional observations of that
object and may continue without interruption.

I should also like to point out that this system will not necessarily be limited to
dark nights. I was recently  able to astrometrically measure the Aten asteroid 1998
HE3 on the night of its closest approach while it was moving at a rate of 0.3
arcseconds per second, shining at a feeble 18th magnitude, AND only
64 degrees away from a FULL moon! Admittedly, the instrument's detection threshold
will suffer but it will be possible to continue automatic searching during the time
other operations are normally suspended.

Normally, the instrument will be pointed somewhere along the meridian, perhaps the
celestial equator, and would not see objects at heliocentric elongations of less
than about ninety degrees. A valuable experiment will involve pointing the
telescope array towards the east or west of the meridian to facilitate the
detection of objects at smaller heliocentric elongations.

If this experiment proves successful, it is my intention to build more such
instruments to provide additional coverage of the ecliptic region of the sky. Since
the motion of a Near Earth Object will almost certainly include a substantial
component of motion in declination, it would be possible to assure a high
likelihood of detection during the apparition of an object without complete
coverage of the ecliptic range of the meridian by spacing the coverage of  several
instruments equally between the northern and southern extremes of the ecliptic,
from +23.5 degrees to -23.5 degrees. If the object passes between the fields of
view of two instruments on one night, it may be detected the next night as it moves
north or south.  An additional experiment that I intend to attempt with this system
is to search for distant, slow-moving objects and transient events. By adding the
three images together it should be possible to penetrate another half magnitude
fainter to 20th magnitude or slightly better. Slow-moving objects and transient
events (variable stars, extragalactic  supernovae, optical components of gamma ray
bursters, etc.) will be detected by comparing images from different nights.


Gehrels, T. 1991, "Scanning with Charge-Coupled Devices", Space Science Reviews,
58: 347-375.

Tucker, R. A. 1994, "A Public Domain CCD Camera Design", Bulletin of the American
Astronomical Society, 185, #63.04


For what it's worth, it would be possible to build a single such
instrument for less than $25,000. Due to the economies of quantity
production, a number of such instruments could be built for substantially
less per unit. The instrument works like asteroid 'fly-paper'.

I invite your questions and discussion. Thank you.

- Roy Tucker


From Leroy Ellenberger <>

The CCNetDigest for 23 Sep contains an item on Alan Alford's ideas about Egyptian
religion based on an exploding planet and its consequences, a la Tom Van Flandern.
However, without even reading Alford's subject book and knowing Sitchin's dubious
influence on him, it is obvious to me how the Egyptian veneration of meteorites and
so forth (see G.A. Wainwright, Sky Religion in Egypt, 1938) can just as well
originate in the context of the Taurid Complex model where we have fragmentations
of a visible "large" body naively (in all likelihood) taken to be a "planet" by
Alford along with humongous fireball storms accompanied by meteorite falls, etc.
The ancients' awareness of the actual size of planets is a stretch, to put it
mildly. I'd bet Alford does  not even mention the Taurid Complex model or Clube &
Napier, which certainly has more going for it than any exploded planet theory, IMHO.



From BBC Online News

The Americans are having to pay more for the International Space

Yet again the American Government is to find more money to subsidise
the Russian space effort. Our science editor Dr David Whitehouse

The American space agency Nasa is to ask the US Government for
permission to buy an extra $660m worth of equipment and services from
the Russian Space Agency over the next four years.

It is an effort to inject more cash into Russia ailing space industry
and ensure that vital components of the International Space Station are

Politicians in Washington are said to be annoyed at having to find yet
more cash for the Russian space effort but have added that it will cost
less than abandoning the space station altogether.

The first components of the station are due to be launched on a Russian
rocket in November but insiders expect it to be delayed.

Nasa has notified Congress and the White House budget office that it
wants to buy $60m worth of Russian spacecraft within the next two
weeks. Another $40m will be spent by the end of the year.

That $40m would be the first instalment of up to $150m a year that Nasa
wants to pay Russia over the next four years. That would cover about
half the annual Russian cost for the project.

But one Nasa official has said that they cannot be sure that Russia can
come up with the other half.

Recently Nasa's chief Dan Goldin said that the cost of the Russian
bailout plus modifications to the space shuttle fleet to compensate for
Russian equipment as well as other remedial measures are estimated at
about $1.2bn.

But he added that if Russia was not able to fulfil its space station
commitments it would cost at least $2bn. To date Nasa has paid Russia
more than $400m for goods and services, including the recently ended
series visits to the Russian space station Mir.

Copyright 1998, BBC


From Andrew Yee <>

Public Affairs Office
San Francisco State University
1600 Holloway Ave.
San Francisco, CA 94132

Contact: Wallace Ravven
Phone: (415) 338-6747

Sally Hall
University of Sussex, Great Britain
Phone: 011 44 1273 678384

Two more planets discovered beyond our solar system

San Francisco State University-based planet search has found nine of 12
extrasolar planets detected since 1995

SAN FRANCISCO, CA, September 24, 1998 -- Deploying the massive Keck
telescope in Hawaii in a new planet search, a team of astronomers has
detected two planets orbiting Sun-like stars, bringing to 12 the number of
distant worlds discovered beyond our solar system.

One of the new discoveries, a Jupiter-sized sphere that most likely appears
deep blue-violet, barely skims the outer reaches of its yellow star, passing
25 times closer to the star than the Earth's orbit of the Sun, and nine time
closer than Mercury's path around the Sun. Its close orbit allows it to
circle its star about every three days. In contrast, the other new planet
has a more Earth-like orbit. Its average distance from its star is nearly
the same as the Earth-Sun distance, the first planet discovered with such a
familiar distance. A year on this planet is 437 days.

"We had discovered planets that orbit much closer and much farther from
their stars than the Earth-Sun distance," said Geoffrey Marcy, University
Distinguished Professor of Science at San Francisco State University who,
along with Paul Butler of the Anglo-American Observatory, has discovered
nine of the dozen planets so far detected.

"We wondered if nature rarely puts planets at one Earth-Sun distance," Marcy
continued. "Now we know that such planets are not rare." Marcy also holds a
post as adjunct professor of astronomy at UC Berkeley.

A report on the planet with the small orbit (around star HD187123) has been
accepted by Publications of the Astronomical Society of the Pacific. The
paper on the planet with the more Earth-like orbit (around star HD210277)
will be submitted to the Astrophysical Journal Letters. Co-authors with
Marcy and Butler on both papers, and colleagues in the SF State-based
discovery team, are Steve Vogt, professor of astronomy at the University of
California, Santa Cruz, who developed the spectrometer needed for planet
detection; Debra Fischer, post-doctoral researcher with Marcy at SF State;
and Kevin Apps, an undergraduate at the University of Sussex.

Apps, a sophomore in physics and astrophysics at Sussex and an amateur
astronomer since the age of seven, is intensely interested in the likelihood
of planets around Sun-like stars. In 1997, he e-mailed Marcy and Butler,
asking if he could see their list of candidate stars in the new planet
search they were launching at the Keck Observatory in Mauna Kea, the world's
largest telescope for optical and infrared astronomy. Upon analyzing the
stars' temperature, luminosity, composition and other features using new
satellite data available on the Internet, Apps discovered that 30 of the
stars were actually not good candidates, and he offered to supply a list of
30 "solar ringers," as he calls them, in their place.

To his surprise, Marcy and Butler agreed to substitute 30 candidate stars
with Apps' 30 solar ringers. One of the newly discovered planets orbits a
star -- HD187123 -- from Apps' list.

"I don't think I can put into words how I feel about Geoff and Paul finding
a planet around one of my suggested targets," says Apps.

Marcy is quite impressed with the young amateur. "He used the latest
satellite data, sifted out the stars that would have the best likelihood of
harboring planets. He shows a fierce interest in this research. It's great
to have him as a colleague."

The two discoveries are among 430 candidates in the new planet search using
the Keck Observatory. The observations were made over 12 nights during the
last nine months, under the auspices of NASA and the University of

Marcy expects to discover "something like" two dozen Jupiter-sized planets
orbiting stars within one Earth-Sun distance. "That should happen within the
next three years if the law of averages applies," he says.

But a second goal of the planet search is to discover Jupiters much farther
out from their stars -- "like five Earth-Sun distances: the signposts of solar
systems like ours," Marcy adds. "Make no mistake about it," he says. "What
we're all about is discovering (planets) where evolution might have gotten a
toehold. Jupiter-sized planets at a greater distance from their star would
suggest a solar system that could host a rocky Earth-like planet. And if it
should turn out that out of more than 400 stars, none has a Jupiter orbiting
at five Earth-Sun distances, that would be a frightening reality. It might
be the first sign that Earth is truly unusual and so life may be rare."

The planets were discovered by detecting a characteristic wobble in the
motion of the star, a wobble caused by the gravitational effect of the
planet orbiting the star. The detection was made using the HIRES
spectrometer built by Steven Vogt and deployed on the Keck telescope.

HD 187123, the star with the close orbiting planet, is a near twin of the
Sun. This star is 154 light years (48 parsecs) away in the constellation
Cygnus (the Swan). The star has the same size, mass, temperature and
luminosity as the Sun, but is richer in heavy elements such as iron. Almost
all planets found to date orbit stars that are at least as rich in heavy
elements as the Sun. This trend toward heavy elements, Marcy says, may be a
clue about how planets form.

The planet is closer to its host star than any planet found before. It
orbits only 0.042 AU away from its sun. (An AU is the Earth-Sun distance).
Indeed, it orbits only four stellar diameters from the surface of the star
HD187123. Its period is 3.097 days.

HD210277, the star with the planet that has the Earth-like orbit, is slightly
bigger than the Sun. It is 68 light years (21 parsecs) away, in the direction
of the constellation Aquarius. The planet has an average orbital distance
barely greater (15 percent) than that of the Earth's. Until now, the
extrasolar planet that had been closest to an orbit the size of Earth's was
16 Cygni B, with an average distance 70 percent greater than Earth's. The
planet is about the size of Jupiter.

The technical paper and graphs on the discovery of HD187123 can be viewed

Further information on the planet search is available at:

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CCNet DEBATE, 24 September 1998


From James Oberg <>

I thought this might be of interest to your newsgroup, please feel free to
circulate it anywhere.


Planetary climate modification and the US Space Command --
As-Yet Unrecognized Missions in the post-2025 time frame

Futures Focus Day
Symposium sponsored by
Commander-in-Chief, US Space Command
Colorado Springs, Colorado
July 23, 1998

By the year 2025, I predict that we will have a list -- a short list, perhaps
-- of asteroids whose orbits take them on 'collision courses' with Earth. To
within an statistically significant degree, their future paths will intersect
our planet.

There was brief anxiety earlier this year about the mile-wide asteroid
1997-XF-11, when initial calculations showed it passing about 30,000 miles
plus or minus a hundred thousand miles from Earth in 2028. But this media
panic faded abruptly when older photographs showed its earlier positions,
which allowed a recalculation to be made that showed the 'close approach' was
an artifact of insufficiently accurate observations. But the preliminary
prediction -- which never claimed more than a 1 in a 1000 chance of impact,
despite how the news media hyped it -- is a foretaste of things to come when
astronomers catalog more and more of the candidate impactors.

We already know what we're going to do about it. It's not just Hollywood and
its blockbuster summer movies, or Dr. Teller and his plan to find a new
mission for the US's nuclear arsenal. There is a remarkable national consensus
of what the right thing to do is. 

When we watch these movies, there is no doubt in the audience's minds that
artificially saving the Earth by interfering with a natural process is the
correct, ethical, and practical thing to do. There were no "Friends of the
Asteroid" picketing Cape Canaveral to protest more filthy human interference
in the affairs of Mother Nature. There was no moral ambiguity in the action

The Universe threatens us. We resist.

What I want to address today is not merely the asteroid-deflection idea, which
is certainly an extreme case, but the entire spectrum of deliberate human
intervention in Earth's biosphere. We must as a society discover a strategy of
responding to the many unintentional but global impacts of human industrial
activity. An activist, interventionist approach to artificially repairing
damage and threats to Earth's biosphere --  both accidentally man-made and
randomly natural in origin -- is, I predict, going to be one of the most
intense ideological and philosophical conflicts of the next century. And
governments -- as well as their operational elements which would be tasked in
carrying out these projects -- will be at the focus of this controversy.

The current ecological consensus centers on merely reducing human influences
on climate. This relies on two unspoken assumptions. First, that Earth's
biosphere has powerful self-governing stabilization and healing capacities.
And second, that it is human activity which is the main threat to the
stability of planetary climate.

I believe that both assumptions are highly questionable, at best. And
furthermore, I believe that the most promising option has hardly even been
mentioned yet. It involves deliberate artificial application of energy  and
material to intentionally force large-scale, even global, climate changes.

This new strategy will be based on scientific discoveries made in large part
from space vehicles, and when implemented, will depend in large part on
monitoring and manipulation from space vehicles. So every government entity
which depends on space will be unavoidably involved.

Furthermore, considering the scale of the forces to be applied, and the
reliably required, those US government entities with the greatest power and
reliability will likely form the implementing teams. As we shall see from
examples, purely scientific research groups do not appear to have the proper
mindset to be trusted with the task. That leaves agencies such as NOAA, NASA,
and the armed forces -- particularly the latter. When the country looks for a
team with the capability and the integrity to be trusted with these tasks, it
will have a very short list of candidates, and the US Space Command will be
near the top of that list whether it seeks the mission or not.

I argue that the current strategy of "hands off the Earth" is a naive,
superficial, and ultimately doomed approach, driven more by political ideology
and internalized guilt-trips than by practical engineering. Here's why I think
it's the wrong approach.

Human civilization is still enormously brittle, dependent on crop growth and
other economic activities -- such as transportation -- that are very sensitive
to climate fluctuations. Biosphere characteristics such as storms, wind and
rainfall patterns, ocean levels, atmospheric transparency, and -- yes! --
outside influences such as solar variability and "falling rocks"  have in the
past made civilizations prosper, and doomed them. We are not yet that
economically secure that such changes wouldn't have equivalent impacts on our
civilization as well.

And it's not just a matter of a temporary retreat from modern capabilities,
perhaps a fallback to eighteenth century technology that could later be made
up again. Our worldwide developing civilization has eaten up all the easily
accessible resources -- the near-surface oil, the easily reachable rich ores,
the biological reservoirs of fish, game and timber. A future less
technogically capable society would be unable to reach the oil and ores we now
harvest. It would not be able, no matter how detailed the preserved blueprints
and technical drawings, to reach and surpass where we are now.

So the "enemy" is not merely unintentional human pollution and land ravaging,
no matter how visible and how graphic may be those and other anti-biosphere
effects. The enemy is also Mother Nature with her wind and rain patterns, her
biological interactions (including epidemics), her geologic threats, and even
her asteroids.

Thus I believe that the ethic will arise -- hesitently at first, then
overcoming fierce emotional and philosophical opposition -- that people will
step in and interfere on purpose with natural processes.

I suggest an analogy with personal physical health. As a first step,
certainly, do no harm. Avoid poisons and dangerous activities. Exercise and
eat right. But we all realize that this is only "Part 1" of a 2-part strategy
for health.

The second part is the activitist, interventionist phase. Vaccinate against
possible outside infections. Surgically intervene to overcome systemic
weaknesses or to forestall localized failures. Provide mechanical augmentation
of degraded senses and muscles. Respond to external trauma with appropriate
levels of care and repair.

This is how people stay healthy. And by analogy, it is how a planet should
stay healthy.

By adding in the second phase of this philosophy to the care of Earth, we can
begin to see technological solutions to technological AND natural problems. We
can begin to see effective, affordable defenses against threats. And in the
more distant future -- the subject of a subsequent talk -- we can glimpse
desired engineered improvements to this planet, and ultimately to others as

Bluntly -- do we know enough now to take this kind of planetary
responsibility? Can we guarantee that human meddling in climate won't have
unintentional, deleterious effects? No, we don't know enough, and no, we can
make no such guarantees.

But that is no more reason to avoid the strategy than the sad history of
centuries of medical blunderings toward knowledge is a reason not to make use
of modern medical science.  The initial ignorance and misconceptions of
medical workers were often more of a threat to patients than were the original
ailments. But to a statistically significant degree we've passed through that
prologue into the dawn of the age of effective medical science.

To refrain from taking actions in defense of Earth's biosphere, using the fear
of our ignorance as an excuse, is -- I argue -- an abdication of our
responsibility to our planet and to our nation and to our children.

Here's the Hollywood version: high-risk remedies are called for in the face of
high-impact dangers. In such extreme situations, there is no moral ambiguity,
no doubt about the "whether we should", only a debate about "which method is

Now, Hollywood and popular culture isn't always so explicit in accepting this
theme. Look at 'Jurassic Park', where the Jeff Goldblum character, the chaos
mathematician Dr. Malcolm, argues against the morality of resurrecting
dinosaurs. Malcolm argues that "dinosaurs had their chance" but that "nature
selected them out" based on some inadequacy of their species. We are hubristic
and foolhardy to argue with the verdict of nature, Malcolm -- and millions of
like-minded people -- insist.

Nonsense. Malcolm's assessment is wrong. We know why the dinosaurs died out.
It was because they didn't have a space program. More specifically, they
didn't have a NASA and a Space Command with the powers that  ours soon will

Many of the themes of 'asteroid defense' coincide with themes of intimate
concern to the US Space Command. Perhaps the most pressing one is
surveillance, the ability to know what is happenng out there. Ideally, one
should know what is happening soon enough to take effective countermeasures.

For a future asteroid impact, given our current level of insight into the
situation in space, the expected warning time before impact will be zero.
Well, say, five or six seconds, since there will be a bright flash that a few
people will notice before being pulverized.

Programs now in preliminary stages will be able to catalog more and more of
the "Near Earth Objects" to smaller and smaller sizes, providing in most cases
longer and longer advance notice of impact hazards -- but not for a few
decades  yet.

Among all the dangers that nature has dished out for Earth, there's a silver
lining to the asteroid impact threat. The most likely objects to hit Earth are
in orbits that repeatedly pass close enough to Earth to be spotted, tracked,
and catalogued far in advance. Their orbital inclinations are close -- ten or
twenty degrees off, at most -- and their orbital periods are within a factor
of two of Earth's.

These objects constitute 99% or more of the impact threat, because the
eccentric comets and deep-space interlopers -- while they exist -- usually
have only one shot at Earth as they pass through the inner solar system. In
contrast, these "NEO's" keep making passes again and again and again  UNTIL
they hit, or are flung clear by a very close approach.

The bigger objects -- the ten kilometer rocks -- are the dinosaur killers, the
millions of megatons of explosive force. They are pretty well all catalogued
and all look safe on a time scale of tens of millions of years.

The one-kilometer rocks, like 1997 XF 11 and a few thousand others, are the
continent-killers, the thousand megaton exploders. About 130 of them have been
catalogued, and NASA hopes to discover 90% of the rest over the next decade.

The 100-meter objects are the kind that made the 20-megaton Tunguska impact
over Siberia in 1908. These are the city-busters, and we should expect them
every few decades -- every century perhaps. There are hundreds of thousands of
these out there and very, very few have ever been detected visually.

Even smaller objects hit more frequently, as you would expect. In 1965, a tens
of kilotons mid-air blast over Revelstoke, Canada, scattered black dust across
miles of new-fallen snow. A similar-sized object barely missed Earth, but
entered our atmosphere and streaked across the Rockies -- not far from
Colorado Springs -- and was videotaped by vacationers. Just a few years ago, a
100-kiloton-sized midair explosion over the western Pacific was startling
enough that President Clinton was awakened to be informed of it -- it might
have been somebody's nuclear weapons test. More will occur, and not merely
over arctic waste, mountains, and open ocean.

There was worldwide near-panic in 1979 when Skylab fell back to Earth, and
there has been understandable world concern about the safe disposal of the
hundred-ton Mir space station, as it nears the end of its useful life. Russia
has promised to steer it into the empty South Pacific when it crashes to
Earth. Meanwhile, unnoticed and unwarned, several  mini-asteroids  as massive
as Mir or Skylab fall to Earth randomly every year. So perhaps this
illustrates how public attention is somehow misdirected towards manmade
threats while correspinding natural threats are entirely overlooked.

In discussing what can be done about such threats, we come across a number of
conceptual problems with the purely academic approach. It turns out that the
operational skills possessed by NASA and the US Space Command  are much more
easily and reliably applied to this asteroid problem than are the theoretical
skills of the scientific and intellectual community.

For example, Dr. Carl Sagan and some of his colleagues suggested that it was
statistically more dangerous to build an asteroid defense system than simply
to wait for the impacts. Their argument was based on the thesis that a system-
in-being could under some circumstances be abused by "a madman" to
deliberately divert otherwise-harmless objects toward an Earth impact.
Although admittedly unlikely, this manmade danger was deemed MORE likely than
the original natural threat of asteroid impact.

But this view is erroneous. The concern fails to account for operational
issues in navigation, targeting, guidance and control, issues which real-world
spaceflight operators deal with on a daily basis. By assuming that a space
rendezvous -- bringing two objects into contact -- is merely an inverse
process of avoidance -- guaranteeing that two objects do NOT come into
contact, this concern is unrealistic.

The "avoidance" maneuver is already in the reportory of spaceflight operators
today, in low Earth orbit. If the predicted path of a piece of space debris
comes "close enough" (defined in the dimensions of the avoidance zone around
the shuttle), the shuttle makes a small orbital adjustment to take it (and the
zone centered on it) away from the predicted path of the candidate impactor.

Rendezvous is also routine in low Earth orbit, but it is a far different
process than merely reversing the avoidance maneuver. As the active vehicle
nears the target it receives more and more precise relative position data
(navigation), which it converts into desired course corrections (targeting),
which converts into required rocket burns (guidance), and which it then
performs -- to the required level of precision -- using onboard rockets

As the range and time-to-contact drops, so does the size of the uncertainty
zone around the target, where the chaser is aiming. At the same time, the
effect of rocket maneuvers on miss distance also drops rapidly -- they have
less time to propagate and grow.  Unless the approach is flown very precisely,
the predicted miss distance can easily drift outside the "uncertainty zone" to
such a great distance that the active vehicle's rockets simply cannot bring
the aim point back onto the target fast enough. In other words,  there is not
enough "control authority" in the system. And the active vehicle flies past
the target. The rendezvous fails.

For the proposed asteroid-deflection schemes of the next several decades at
least, their control accuracy is far too poor to perform a "rendezvous", a
deliberate collision, with Earth. Such systems would be fully effective in
diverting dangerous asteroids, but would be physically unable to do the
opposite, bring them into contact with Earth. As a threat for misuse, they
would panic only those who don't understand real space operations.

Sagan however was not off base in raising the question about deliberately
steering asteroids closer to Earth, because at some future point there will be
excellent reasons to want to do this. Starting with the smallest trackable
objects -- the 100-meter rocks -- it's plausible later in the next century to
bring some of them back into high-earth orbit for mining. They contain
commercially attractive amounts of metals and water, especially in competition
with the cost of such materials brought up from Earth. And at a range of
several hundred thousand kilometers from Earth, missing an orbital aim point
by tens of thousands of kilometers will not matter.

And perhaps these asteroids' greatest resource -- one which military space
planners half a century from now should be very interested in -- is simply the
slag and dirt left over from mining. This material would provide shielding --
against impacts, against radiation, against visual inspection -- for
otherwise-vulnerable space-based systems. Such mini-Gibralters in high orbit
could become the literal "high ground" that space strategists have so far
sought in vain.

Here's another example where today's experienced space operators already have
a better grasp on required mid-century environmental modification operations.
The obvious response to an approaching asteroid is to "deflect" it sideways to
miss Earth. This is the mode for an approaching tomahawk in "The Last of the
Mohicans", sure.  But this "common sense" idea fails to appreciate the
unearthly nature of out-of-plane dynamics in space.

Assuming a long-enough lead time, the last kind of impulse you would ever want
to impart to an asteroid is perpendicular to its motion. This would merely
make it wobble in its orbit, but it would for the most part still arrive at
future points close to the original predictions.

Instead, the impulse should be directed ALONG its flight path -- slowing it
down (from in front) or speeding it up (from behind) would work equally well.
This would alter the energy of the orbit and cause it to arrive at predicted
future intersection points at a different time. When it got there, the fast-
moving Earth wouldn't be there -- and the impact would be avoided.

But try and explain this to someone unfamiliar with orbital operations. Tell
them that in order to make it miss Earth, you want to SPEED UP the approaching
asteroid, and see the reaction!

The US Defense Department may still be discussing for decades whether or not
it wants to get involved in this business -- and in the end, the assignment
may be dropped in its lap whatever its own desires may be. But already there
have been very practical DoD interests in asteroids, and one of them is the
probe Clementine-2.

Although Clementine-2 was line-item-vetoed last year by President Clinton,
apparently on the advice of policy wonks that it might be misinterpreted as a
space weaponization scheme that might upset the Russians, the recent Supreme
Court decision overturning the constitutionality of the whole line-item-veto
idea may allow the project to resume. It was always a good idea from the DoD's
point of view -- test an autonomous microsatellite sensors and controllers --
but it is also very good idea from an asteroid deflection point of view, since
it addresses the key unknown about asteroids, what is their internal structure
and how would they respond to external forces (such as the US Space Command!).

Not long ago, astronomers thought of asteroids as rocks, perhaps rubble
covered, but still mainly single bodies. But evidence has accumulated that
asteroids are rubble piles all the way through, loosely bound together by what
is generously called "gravity" (escape velocity is 11,000 meters per second on
Earth but less than 1 meter per second on a typical small asteroid). The
Shoemaker-Levy object was torn apart by a close brush with Jupiter in 1992 so
when it fell back onto Jupiter two years later it was a string of smaller
objects. Crater chains on the moons of Jupiter, on Earth's moon, and on Earth
itself also point to the gravity-induced disintegration of many asteroids
prior to impact. Asteroids which rotate fast enough to fling pieces clear are
extremely rare -- only two are known -- which suggests that these are the rare
single-rock objects.

What this means is that big impulses -- say, from another asteroid collision
or from a nuclear detonation -- would more likely disperse the material than
deflect it. Pushing an asteroid has been likened to clearing a landslide off a
road, rather than rolling a rock.

So other techniques -- gentle pushes over long periods -- may prove to be
required. There are plenty of such ideas. None of them will prove workable, I
predict, but the second and third generation ideas will turn out to be quite
feasible. And information from a reborn Clementine-2 may powerfully augment
new astronomical discoveries.

Once the concept of asteroid deflection becomes widely accepted, in both
practical and philosophical terms, we can move on to much more interesting and
much more likely biosphere engineering projects. For many of them, the
connection with the future US Space Command is going to be unavoidably

By the way: If there's one class of modern intellectuals who do not find the
idea of deliberate environmental modification to be incredible, it's the
international lawyers and diplomats. There already is a treaty -- the
Convention on the Prohibition of Military or Any Other Hostile Use of
Environmental Modification Techniques -- which was signed in 1977 and ratified
in 1980. It defines "environmental modification techniques" to be "any
technique for changing -- through the deliberate manipulation of natural
processes -- the dynamics, composition or structure of the Earth, including
its biota, lithosphere, hydrosphere and atmosphere, or of outer space." But
all that is forbidden is doing this in order to create "widespread, long-
lasting or severe effects as the means of destruction, damage, or injury." So
peaceful uses are explicitly allowed.

The US Air Force's last major involvement with climate engineering was Project
Stormfury, a quarter century ago. Attempts were made to steer hurricanes by
preferential cloud seeding, to increase localized rainfall and heating. This
was supposed to lead to alteration of the 'steering currents' which naturally
and randomly direct a storm's motion. Results were ambiguous, except for the
discovery that once you "touch" a hurricane, everybody blames you for where it
eventually goes (of course, those living in areas the storm avoids do NOT come
out to thank you). That's another reason for governments to do this -- so you
won't be sued for damages. In any case, future projects to steer hurricanes --
or at least, mitigate their wind speeds when they do reach populated areas --
are only a matter of getting up the nerve to try it.

Equally daunting in a political sense is the question of earthquake control
and the "geologic engineering" involved. The problem is not the slippage of
tectonic plates, but their stickiness. They grab and hold as tension builds up
(tension perhaps measurable in terms of magnetic field distortions observed by
very high altitude sensor arrays), then break free all at once. Geologists
have long known that near-surface fault lines can be "greased" or "fixed" by
artificially varying the amount of water in the rock, and it has been proposed
that known fault lines be massaged by fixing two end points and then
deliberately slipping the inside region. This would allow a constant and low-
force release of the energies. But for deeper faults lines, who in the
government is going to suggest taking action to deliberately trigger an
earthquake -- even though such an effort, at a predetermined time, would be
far safer and probably much less damaging than simply waiting for it to happen
at random? Here again it is not the science and technology but the politics
and philosophy that stand in the way.

Global warming depends on many factors, of which greenhouse gases are only one
component. The degree of cloudiness -- and hence, heat reflection -- is a
factor subject to manipulation by high-flying aircraft. The degree of surface
absorption of heat depends on ground albedo, which in turn can be controlled
by area-wide plant cover -- another factor already being manipulated in semi-
desert lands. And eventually the amount of solar energy falling on Earth's
atmosphere could  be modulated the same way we vary the heat coming into our
cars and homes -- setting up blinds and shades.

Proposals to modulate solar insolation -- incoming energy -- from space have
been discussed since the 1920s. Counting on the kinds of projects likely to
get his government's financial backing, German space pioneer Hermann Oberth
suggested using mirrors to concentrate sunlight to ignite forests in enemy
territories, as Archimedes is said to have done with soldiers' shields to
ignite the sails of an attacking Roman fleet. Less belligerently, Krafft
Ehricke later worked out a sequence of peaceful terrestrial applications for
very large space reflectors he called "lunettas" and (bigger) "solettas". NASA
made some studies of its own, and their were even DoD studies in the 1960s to
see if the Ho Chi Minh trail could be illuminated from space.

Five years ago, the first small "space mirror" was tested by the Russians --
they used a 20-meter diameter disk called "Znamya", held taut by spin, to
reflect sunlight onto the Earth below. A follow-up test of a 25-meter mirror
was planned for this November but has now been indefinitely postponed due to
budget problems in the retreat from Mir. It could easily be rescheduled for an
early mission to the International Space Station.

The biggest objections to the Russian space mirror project came from amateur
astronomers, who prefer a night sky. But there were also environmentalist
attacks on the proposed follow-on brighter project. Newspapers were full of
accusations that space mirrors could upset the breeding habits of endangered
species or could melt the Arctic ice pack.

Those accusations and objections are just a tiny foretaste of the kind of
emotional clash that will be caused by any future proposals for artificial
environmental modification. But in closing, I want to stress that this concept
-- an activist, interventionist approach to maintaining our planet's health --
is going to slowly gain ground in coming years. And when the time comes to
actually perform experiments and ultimately operational activities of this
sort, it is going to be NASA and the US Space Command that will be intimately

CCCMENU CCC for 1998