CCNet 71/2003 - 10 September 2003
"Today, we know an asteroid killed 90% of all living things - dinosaurs
and all kinds of other things. And that it was that asteroid that
actually stimulated our own evolution. I have never been in favor of
people dying out and a new world taking over. I would rather have
evolution based on dreamed possibilities. So I advocate the building
of telescopes, the prediction of collisions, and the deflection of
objects, such as asteroids."
(1) EDWARD TELLER (1908-2003) - FATHER OF PLANETARY DEFENCE
(2) EDWARD TELLER: THE NEED FOR EXPERIMENTS ON COMETS AND ASTEROIDS
(3) EDWARD TELLER (1908 - 2003)
(4) AN INTERVIEW WITH EDWARD TELLER:
(5) RE: "MUM'S THE WORD AS THE WORLD'S MEDIA FAIL TO RETRACT HYPED ASTEROID ALARM"
(6) THE FRUIT SALAD SCALE
(7) AND FINALLY: BRITISH HUMOUR AT ITS BEST....
(1) EDWARD TELLER (1908-2003). FATHER OF PLANETARY NEO DEFENCE
Benny Peiser <email@example.com>
Edward Teller, one the 20th century's most important and most controversial
scientist died yesterday, aged 95. He was the unsung hero of the free world
who was instrumental in the West's defeat of both Nazi Germany and Sowjet
Most people outside our small community do not know, however, that he was also
the spiritus rector of our planetary defence initiatives aimed at preventing
asteroid impacts to occur in the future. He was the main driving force behind
these activities in the US and a strong supporter of the Spaceguard project. He
was particularly successful in convincing the British Government to set up
a Task Force on Near Earth Objects.
With Teller, the NEO community has lost our most influencial voice and
scientific advisor to the White House.
In memory of his invaluable and unique contribution to the ideals of
universal freedom, international security and scientific progress,
I have attached a couple of papers and interviews. I would wellcome
any additional notes of remembrance by colleagues who have met and
worked with him over the years.
(2) EDWARD TELLER: THE NEED FOR EXPERIMENTS ON COMETS AND ASTEROIDS
Dr. Edward Teller
Lawrence Livermore National Laboratory
paper given at the Planetary Defense Workshop
Lawrence Livermore National Laboratory
May 22-26, 1995
First of all, I would like to thank Academician Khariton for his kind
words to all of us and tome especially. We are really sorry that he is
not with us. I am glad to see all the people who are here from China,
Japan, Italy, and very particularly from Russia.
Now, I would like to say a few things in a straightforward and very
serious manner. I believe we are here - in fact, we all know we are
here - to look into a situation that is unique in the size of the
trouble we are looking at and in the improbability of these big troubles.
For mathematicians, it is easy to multiply the two and to say that this
trouble is like other troubles because the product is the same. For
politicians who are trained to look carefully at what happens during
their terms of office and less carefully at everything beyond, the same
does not hold as for the mathematicians. And we, in turn, depend on the
politicians to make it possible for us-in the form of dollars, or
rubles, or anything else-to do what is needed to be done.
I think it is extremely important that we present a credible case so
we can go ahead. I would like to suggest a few points of view on how
to present the case that we are talking about-presenting it very
truthfully but emphasizing the things that ought to be emphasized.
Here is the situation that, in my mind, is a scandal, and I think people
can understand that it is a scandal: There is a probability of a few
percent in the next century of the arrival of a stony asteroid-not the
biggest possible but a fairly big one, approximately a hundred meters
in diameter. It delivers on impact maybe 100 megatons. It is a practical
certainty that, when and if such an object should bump into us, it will
come completely unannounced [remember, that paper was given in 1995, BP].
We won't have any indication of it. Yet such an object is apt, with a
fairly high probability, to do a lot of damage-for instance, cause a
tsunami if it falls into the ocean. Damage would be concentrated on the
shores region, where people like to aggregate. So the effect of the
asteroid and the pmple are attracted to the same meeting point-hence,
a lot of damage. Just in dollars it could be billions, and in lives it
might reach millions. Yet, no warning whatsoever.
What we need to rectify this situation is half a dozen arrays of charge
- coupled devices and appropriate (not very big) telescopes, amounting to
probably not much more than ten million dollars altogether. If such a
catastrophe should occur, afterwards we'll be able to point out on
existing pictures where the asteroid has approached, but we wouldn't know
it ahead of time because nobody would have looked at those pictures.
I shouldn't have said nobody; I should have said hardly anybody. And
actually, to find them would be extremely difficult. The CCDS can be
systematically trained to scream when there is something suspicious,
and in this way we could have information a week ahead of time. To my
mind, such action would correct a very large incompleteness in our
safety system. And I think that should be a very salable item.
So, we know ahead of time that something is coming. What do we do about
it? We would know ahead of time with sufficient accuracy, for instance,
what shorelines have to be evacuated. A week is not plenty of time, but
it is very considerably more than nothing.
I was interviewed today and the question was asked: Is the international
situation ripe for such action? I'm answering with every confidence:
It is. I have no doubt that if there is such a danger from outside, if
we know that people in certain spots will have to move to save their
lives and can't move to save their property, then it will be
psychologically not only a necessary thing but an easy thing to get
help from all over the world to whoever has to evacuate. I hope that
the same thing holds for all the other measures that we might be
willing and able to take in order to improve the situation, bwause
I certainly don't want to stop at the point of just saying "evacuate."
The next point that I feel is a real necessity is to know what more to
do. We have the power to reach out into space and to deliver what is
needed. But we don't know how the objwts behave that will arrive.
Very particulwly, we will know rather little about the actual object
that has been a mere spot on the best photographic plate and that has
grown for the last couple of days a little more to not very much more
than a bigger spot.
What do we do about it? I claim that the next thing we ought to do is
to gather knowledge about what can be done. What is the variety of things
that can be done? Such knowledge can be obtained in a number of different
ways. The one I prefer (and that all of us will not necessarily prefer)
is to make expenments - one or two or three per year - on objects that#
are getting close to the Earth, to the approximate distance of the Moon,
more or less one light-second away from the Earth. Whatever we do can
be observed from the Earth very easily. And to get out there is not
And what do we do there? Well, we can do a number of things. I would
recommend that, to begin with, we do the very simplest thing on which
we can agree: Put up sharp tungsten knives for the purpose of cutting up
the incoming object if it's of an appropriate size-something like
300 feet or 100 meters in diameter. Of such objects, approximately a
few approach in a year. We make experiments on them. Can every one of
them be sliced up sufficiently so that if the fragments fall on the
Earth, they will be burned up in the high atmosphere in a completely
harmless manner? This certainly can be found out by experiments on
objects that have already passed the Earth. I think such experiments
will contribute, to a considerable extent, to safety in the
one-percent-per-century case that such a danger might actually occur.
Now, if we find that the biggest or toughest of these objects will not
be completely sliced up, then, after we have become familiar with the
slicing up, we should take the big step-using a nuclear explosive.
If, for instance (which I think is a plausible situation), on a
300-meter-diameter object, we have succeeded in slicing up 20 meters
of the surface, we can then put a nuclear explosive close to the surface,
which will irradiate the rubble that we have atready created. This tends
to homogenize this rubble and push it one way, while, by reaction, the
remaining ninety percent of the material is pushed the other way.
The reaction on the main body will be very powerful, and there can
be no doubt that appropriate deflections can be arranged.
Objects a kilometer or more in diameter are apt to create worldwide
disaster. On the average, they are expected once in a million years.
We hope to discover them several months in advance. The use of nuclear
explosives as outlined might or might not suffice to deflect them. A more
radical method of using several nuclear explosives may be needed. We
might use them to create the rubble, and this maybe followed by one
big blast as mentioned above.
Or we might attempt to bore a hundred-meter-deep hole by successive
nuclear explosives and then blow up the object by one big, deeply
located explosion. Such methods cannot be relied upon without
experimentation on objects that have safely passed the Earth.
One final possibility should be considered. Of the hundred-meter
diameter objects, there are approximately a million. They could be
discovered, cataloged, and their orbits computed. If a huge,
hundred-kilometer object approaches and is apt to hit the Earth within
a year, then one of the hundred-meter objects is almost certain
to approach it to within approximately one Light-second before this
can happen. Careful deflection of this smaller object could steer it
into the path of the bigger one. The expected result would be to prevent
a collision with the Earth, which would be the ultimate catastrophe.
One must add that collision of a hundred-kilometer object with Earth
is not apt to be predicted even in a billion years.
I would like to conclude with emphasizing one obvious principle: We
scientists are not responsible and should not be responsible for
making decisions. But we scientists are uniquely and absolutely
responsible for giving information. We must provide the decision-makers
with the data. On the basis of this, they will have the best chance
to make the right decisions. That is the main reason why I say that
we must pursue and must be given the means to pursue the knowledge as
to when and how objects will arrive and the knowledge as to possible
ways to deal with them. The choice of how to deal with them can be
and should be delayed. If need be, it can be done and probably will
be done in the last moment. But knowledge - the firm knowledge, not
merely guesses on how asteroids will react but knowledge based on
experiments - should become available. That is our responsibility.
And I believe we should argue, in a carefully considered manner,
so that we can acquire, in the most efficient manner, as much of
the relevant knowledge as is possible.
I can add only two words: Good luck!
(3) EDWARD TELLER (1908 - 2003)
Edward Teller, a senior research fellow at the Hoover Institution since 1975, where he specialized in international and national policies concerning defense and energy, died Tuesday, September 9, 2003. He was 95.
Teller was most widely known for his significant contributions to the first demonstration of thermonuclear energy; in addition he added to the knowledge of quantum theory, molecular physics, and astrophysics. He served as a member of the General Advisory Committee of the U.S. Atomic Energy Commission from 1956 to 1958 and was chairman of the first Nuclear Reaction Safeguard Committee.
He had been concerned with civil defense since the early 1950s. He was a member of the Scientific Advisory Board of the U.S. Air Force, a member of the Advisory Board of the Federal Emergency Management Agency, and on the White House Science Council.
Teller received numerous honors, among them the Presidential Medal of Freedom, the Albert Einstein Award, the Enrico Fermi Award, the Harvey Prize from the Technion-Israel Institute, and the National Medal of Science.
He was a fellow of the American Physical Society and the American Nuclear Society and was a member of the National Academy of Sciences and the American Academy of Science.
His books include Memoirs: A Twentieth-Century Journey in Science and Politics (written with Judith Shoolery, 2001), Conversations on the Dark Secrets of Physics (Plenum Press, 1991), Better a Shield Than a Sword (Free Press, 1987), Pursuit of Simplicity (Pepperdine Press, 1980), and Energy from Heaven and Earth (W. H. Freeman, 1979).
He was director of the Lawrence Livermore Laboratory from 1958 to 1960, at which time he accepted a joint appointment as a professor of physics at the University of California and as associate director of the laboratory. He held these posts until his retirement in 1975. He continued as a consultant at the Lawrence Livermore National Laboratory.
From 1954 to 1958, he served as Associate Director at the new Lawrence Livermore Laboratory. He became a consultant to the laboratory in 1952.
In 1946, he became a professor of physics at the University of Chicago but returned to Los Alamos Scientific Laboratory in 1949.
In 1942, having served as a consultant to the Briggs committee, Teller joined the Manhattan Project. His efforts during the war years included work on the first nuclear reactor, theoretical calculations of the far-reaching effects of a fission explosion, and research on a potential fusion reaction.
In 1935, Teller and his wife came to the United States, where he held, until 1941, a professorship at George Washington University. The Tellers became U.S. citizens in 1941.
In 1934, under the auspices of the Jewish Rescue Committee, Teller served as a lecturer at the University of London. He spent two years as a research associate at the University of Goettingen, followed by a year as a Rockefeller fellow with Niels Bohr in Copenhagen.
Born in Budapest, Hungary, in 1908, he received his university training in Germany and completed his Ph.D. in physics under Werner Heisenberg in 1930 at the University of Leipzig.
(4) AN INTERVIEW WITH EDWARD TELLER:
When did you first realize that you were interested in your subject?
When I was maybe five years old, maybe not yet five years old, it is one of my earliest memories. I was supposed to go to sleep and didn't, and I invented a game. I was trying to find out how many seconds in an hour, or in a day, or in a year. And that, of course, obviously, I did it in my head. Quite naturally, I got different answers in my head every time I did it. And that made the game more interesting. I don't know how unique it is; I don't know how many other children did that, but I played with numbers.
I was taught German and Hungarian at the same time. The earliest words I remember are a mixture of the two. My mother spoke German much better than Hungarian. My father's German was quite poor. His legal books, of course, were Hungarian. The literary books in our house were German.
I am sure I must have been awfully confused about what all these people talked about, using different sounds for the same objects. I did not catch on! The one thing with which I felt familiar, were numbers. There, at least, was something that hung together.
My father had an older friend who was a retired mathematics professor. His name was Leopold Klug, and he is probably the man who had the greatest influence on my life. He was a retired mathematics professor, and he got me a book. Algebra by Leonhard Euler. I was ten years old. The problems that came up were too difficult for me to solve, but not too difficult to understand. Klug gave me that book and I read it. It was my favorite book. Klug was the first grown-up whom I met who loved what he
Who did not get tired. He even enjoyed explaining things to me. That, I think, is when I made up my mind very firmly that I wanted to do something that I really did want to do.
Not for anyone else's sake, not for what it might lead to, but because of my inherent interest in the subject. I knew one other exception in the whole world to the rule that grown-ups were unhappy.
My mother played the piano beautifully. She really wanted to be a concert pianist and she really wanted me to become a concert pianist, as a kid. Practicing (piano) was much too hard. Multiplying numbers was not.
My interest in mathematics was soon discouraged. It so happened that we had a very good math teacher, who was a Communist. I remember having learned from him something that I never forget: the rule of nines. A simple point: you add up the numerals in a number, and if the original number was divisible by nine, then the sum of the figures also is. For instance, you take a number like 243. Two and four and three is nine. Therefore, 243 must be divisible by nine. Actually it is nine times 27. The rule is interesting because its so simple. What was really interesting is to us ten year-olds is that our math teacher proved it. The proof is not terribly difficult, but it was one of the first simple and not quite obvious mathematical proofs that I encountered. That actually was a little before I read Euler's Algebra.
Then the Communists took over for a few months in Hungary, and our math teacher talked about some very strange things which I can't say I liked. After communism ended he was replaced as a teacher by a Fascist. The new teacher was less interested in mathematics, but interested in how to write equations so that the writing should be easily legible. I think my writing improved slightly, but my school mathematics vanished. I blame him only in part, because a real interest should not have been stopped that easily. I got interested in reading fantastic stories like Jules Verne, and I got interested even more in reading about technology.
After a few years, I also got interested in the lectures on physics. I had started to read Einstein's relativity, and did not quite understand what it was all about. I went to the teacher and he asked me to bring him the book. I brought it to him and I didn't see the book again for a year. When I passed the final examination, the teacher gave the book back, and said, "All right, now you can read it." This time I read it and I did understand it.
In our teaching system, we consider mathematics and science as exact. It is so, it is proven, it is indisputable. All of it is true. But this misses the point. The interesting thing in the "exact" sciences is what is not yet known, what is in doubt. That element of doubt, of contradiction, which actually occurs as science changes from century to century, should be reproduced in every student's mind. I think, as a matter of fact, it is being reproduced in every good student's mind.
FULL INTERVIEW at http://www.achievement.org/autodoc/page/tel0int-1
=========== LETTERS ==========
(5) RE: "MUM'S THE WORD AS THE WORLD'S MEDIA FAIL TO RETRACT HYPED ASTEROID ALARM"
Paul Sutherland <firstname.lastname@example.org>
> Not a single of Britain's national papers or media outlets
> (with the sole exception of 7 lines in today's Daily Telegraph) has...
Actually this is not correct, Benny. The Sun also reported the same day (Sept 4)
that the asteroid would miss as soon as the Press Association report was received.
(It arrived too late for the first edition which may be the one you monitored).
[it was indeed the morning editions of the British papers I checked, BP].
My own comment piece, printed the previous day alongside the original news
story, had said that this was likely to be the case.
DON'T PANIC SAYS SUN SPACEMAN
The Sun, 3 September 2003
By Paul Sutherland
WE have been here before. Other space rocks have been discovered on a collision
course with Earth - only for the all-clear to sound when closer monitoring
showed they would whizz by. The chances are that asteroid 2003 QQ 47 will
do the same. So are astronomers guilty of scaremongering? Absolutely not.
Countless asteroids travel the spaceways. Enough cross our orbit for there
to be a significant threat. We need a network of telescopes to discover them
earlier. Big impacts are rare. But somewhere out there is an asteroid with
the Earth's name on it. It is not a matter of if - but when.
MODERATOR'S NOTE: For readers not aquainted with the British media, The Sun newspaper
in Britain's biggest selling paper with 12 million people reading it everyday.
It most certainly doesn't need any asteroid scares to increase its circulation!
Famous for it's page three topless models (who at times can be seen to assess
the risk of heavenly bodies), it's by far Britain's most popular newspaper.
It says something about its quality that its science correspondent and long-time
CCNet subscriber got the QQ47 (non-)story spot on, right from the start! BP
(6) THE FRUIT SALAD SCALE
Konrad Ebisch <email@example.com>
Dear Benny Peiser,
It has always seemed to me that the Torino scale is based on two estimates. (1) How
likely is that rock to hit us? (2) How much damage will it do if it hits us? Mixing
two very different things into just one number can be a confusing over-simplification.
Apples times Oranges = [fruit salad ?]
(7) AND FINALLY: BRITISH HUMOUR AT ITS BEST....
The Sun, 6 September 2003
"Whenever they tell us that an asteroid is on a collision course with Earth,
you can be absolutely certain it will miss. Because when they do eventually
find one that's coming to kill everyone, you can be assured you won't be told."
--Jeremy ('Top Grear') Clarkson, The Sun, 6 September 2003
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Sent: 10 September 2003 16:51
NASA RELEASES NEAR-EARTH OBJECT SEARCH REPORT
"The Team recommends that the search system be constructed to produce a catalog that is 90% complete for potentially hazardous objects (PHOs) larger than 140 meters."
--NASA NEO SEARCH REPORT, September 2003
NASA NEO Program, 10 September 2003
NASA has released a technical report on potential future search efforts for near-Earth objects after a year of analysis by scientists working on this issue. This Science Definition Team was chartered to study what should be done to find near-Earth objects less than 1 kilometer in size. While impacts by these smaller objects would not be expected to cause global devastation, impacts on land and the tsunamis resulting from ocean impacts could still cause massive regional damage and still pose a significant long-term hazard.
In 1998 NASA commenced its part of the "Spaceguard" effort, with the goal of discovering and tracking over 90% of the near-Earth objects larger than one kilometer by the end of 2008. An Earth impact by one of these relatively large objects would be expected to have global consequences and, over time scales of a few million years, they present the greatest impact hazard to Earth. Approximately 60% of the estimated 1,000 to 1,200 large near-Earth objects have already been discovered, about 45% since NASA efforts started, and each of the five NASA-supported search facilities continue to improve their performance, so there has been good progress toward eliminating the risk of any large, undetected impactor.
To understand the next steps to discovering the population of potentially hazardous asteroids and comets whose orbits can bring them into the Earth's neighborhood, NASA turned to this Science Definition Team of 12 scientists. The Team, chaired by Dr. Grant Stokes of the MIT Lincoln Laboratory, was asked to study the feasibility of extending the search effort to the far more numerous, perhaps hundreds of thousands, of near-Earth objects whose diameters are less than one kilometer.
NASA considers the Science Definition Team's findings to be preliminary, and a much more in-depth program definition, refining objectives and estimating costs, would need to be conducted prior to any decision to continue Spaceguard projects beyond the current effort to 2008.
The link below will allow a download of the complete Science Definition Team report (pdf format) and the Executive Summary of this report follows.
The Science Definition Team members include:
Dr. Grant H. Stokes (Chair) MIT Lincoln Laboratory
Dr. Donald K. Yeomans (Vice-Chair) Jet Propulsion Laboratory/Caltech
Dr. William F. Bottke, Jr. Southwest Research Institute
Dr. Steven R. Chesley Jet Propulsion Laboratory/Caltech
Jenifer B. Evans MIT Lincoln Laboratory
Dr. Robert E. Gold Johns Hopkins University, Applied Physics Laboratory
Dr. Alan W. Harris Space Science Institute
Dr. David Jewitt University of Hawaii
Col. T.S. Kelso USAF/AFSPC
Dr. Robert S. McMillan Spacewatch, University of Arizona
Dr. Timothy B. Spahr Smithsonian Astrophysical Observatory
Dr./Brig. Gen. S. Peter Worden USAF/SMC
Ex Officio Members
Dr. Thomas H. Morgan NASA Headquarters
Lt. Col. Lindley N. Johnson
(USAF, ret.) NASA Headquarters
Don E. Avery NASA Langley Research Center
Sherry L. Pervan SAIC
Michael S. Copeland SAIC
Dr. Monica M. Doyle SAIC
Study to Determine the Feasibility of Extending the Search for Near-Earth Objects to Smaller Limiting Diameters
Report of the Near-Earth Object Science Definition Team
August 22, 2003
Prepared at the Request of
National Aeronautics and Space Administration
Office of Space Science
Solar System Exploration Division
Full 166-page report available here as a PDF document:
A Study to Determine the Feasibility of Extending the Search for Near-Earth Objects to Smaller Limiting Diameters
In recent years, there has been an increasing appreciation for the hazards posed by near-Earth objects (NEOs), those asteroids and periodic comets (both active and inactive) whose motions can bring them into the Earth's neighborhood. In August of 2002, NASA chartered a Science Definition Team to study the feasibility of extending the search for near-Earth objects to smaller limiting diameters. The formation of the team was motivated by the good progress being made toward achieving the so-called Spaceguard goal of discovering 90% of all near-Earth objects (NEOs) with diameters greater than 1 km by the end of 2008. This raised the question of what, if anything, should be done with respect to the much more numerous smaller, but still potentially dangerous, objects. The team was tasked with providing recommendations to NASA as well as the answers to the following 7 specific questions:
What are the smallest objects for which the search should be optimized?
Should comets be included in any way in the survey?
What is technically possible?
How would the expanded search be done?
What would it cost?
How long would the search take?
Is there a transition size above which one catalogs all the objects, and below which the design is simply to provide warning?
The Science Definition Team membership was composed of experts in the fields of asteroid and comet search, including the Principal Investigators of two major asteroid search efforts, experts in orbital dynamics, NEO population estimation, ground-based and space-based astronomical optical systems and the manager of the NASA NEO Program Office. In addition, the Department of Defense (DoD) community provided members to explore potential synergy with military technology or applications.
The Team approached the task using a cost/benefit methodology whereby the following analysis processes were completed:
Population estimation - An estimate of the population of near-Earth objects (NEOs), including their sizes, albedos and orbit distributions, was generated using the best methods in the current literature. We estimate a population of about 1100 near-Earth objects larger than 1 km, leading to an impact frequency of about one in half a million years. To the lower limit of an object's atmospheric penetration (between 50 and 100 m diameter), we estimate about half a million NEOs, with an impact frequency of about one in a thousand years.
Collision hazard - The damage and casualties resulting from a collision with members of the hazardous population were estimated, including direct damage from land impact, as well as the amplification of damage caused by tsunami and global effects. The capture cross-section of the Earth was then used to estimate a collision rate and thus a yearly average hazard from NEO collisions as a function of their diameter. We find that damage from smaller land impacts below the threshold for global climatic effects is peaked at sizes on the scale of the Tunguska air blast event of 1908 (50-100 m diameter). For the local damage due to ocean impacts (and the associated tsunami), the damage reaches a maximum for impacts from objects at about 200 m in diameter; smaller ones do not reach the surface at cosmic speed and energy.
Search technology - Broad ranges of technology and search systems were evaluated to determine their effectiveness when used to search large areas of the sky for hazardous objects. These systems include ground-based and space-based optical and infrared systems across the currently credible range of optics and detector sizes. Telescope apertures of 1, 2, 4, and 8 meters were considered for ground-based search systems along with space-based telescopes of 0.5, 1, and 2 meter apertures. Various geographic placements of ground-based systems were studied as were space-based telescopes in low-Earth orbit (LEO) and in solar obits at the Lagrange point beyond Earth and at a point that trailed the planet Venus.
Search simulation - A detailed simulation was conducted for each candidate search system, and for combinations of search systems working together, to determine the effectiveness of the various approaches in cataloging members of the hazardous object population. The simulations were accomplished by using a NEO survey simulator derived from a heritage within the DoD, which takes into account a broad range of "real-world" effects that affect the productivity of search systems, such as weather, sky brightness, zodiacal background, etc. Search system cost - The cost of building and operating the search systems described herein was estimated by a cost team from SAIC. The cost team employed existing and accepted NASA models to develop the costs for space-based systems. They developed the ground-based system cost estimates by analogy with existing systems.
Cost/benefit analysis - The cost of constructing and operating potential survey systems was compared with the benefit of reducing the risk of an unanticipated object collision by generating a catalog of potentially hazardous objects (PHOs). PHOs, a subset of the near-Earth objects, closely approach Earth's orbit to within 0.05 AU (7.5 million kilometers). PHO collisions capable of causing damage occur infrequently, but the threat is large enough that, when averaged over time, the anticipated yearly average of impact-produced damage is significant. Thus, while developing a catalog of all the potentially hazardous objects does not actually eliminate the hazard of impact, it does provide a clear risk reduction benefit by providing awareness of potential short- and long-term threats. The nominal yearly average remaining, or residual, risk in 2008 associated with PHO impact is estimated by the Team to be approximately 300 casualties worldwide, plus the attendant property damage and destruction. About 17% of the risk is attributed to regional damage from smaller land impacts, 53% to water impacts and the ensuing tsunamis, and 30% to the risk of global climatic disruption caused by large impacts, i.e. the risk that is expected to remain after the completion of the current Spaceguard effort in 2008. For land impacts and all impacts causing global effects, the consequences are in terms of casualties, whereas for sub-kilometer PHOs causing tsunamis, the "casualties" are a proxy for property damage. According to the cost/benefit assessment done for this report, the benefits associated with eliminating these risks justify substantial investment in PHO search systems.
PHO Search Goals and Feasibility
The Team evaluated the capability and performance of a large number of ground-based and space-based sensor systems in the context of the cost/benefit analysis. Based on this analysis, the Team recommends that the next generation search system be constructed to eliminate 90% of the risk posed by collisions with sub-kilometer diameter PHOs. Such a system would also eliminate essentially all of the global risk remaining after the Spaceguard efforts are complete in 2008. The implementation of this recommendation will result in a substantial reduction in risk to a total of less than 30 casualties per year plus attendant property damage and destruction. A number of search system approaches identified by the Team could be employed to reach this recommended goal, all of which have highly favorable cost/benefit characteristics. The final choice of sensors will depend on factors such as the time allotted to accomplish the search and the available investment (see Figures 9.3 and 9.4).
Answers to Questions Stated in Team Charter
What are the smallest objects for which the search should be optimized?
The Team recommends that the search system be constructed to produce a catalog that is 90% complete for potentially hazardous objects (PHOs) larger than 140 meters.
Should comets be included in any way in the survey? The Team's analysis indicates that the frequency with which long-period comets (of any size) closely approach the Earth is roughly one-hundredth the frequency with which asteroids closely approach the Earth and that the fraction of the total risk represented by comets is approximately 1%. The relatively small risk fraction, combined with the difficulty of generating a catalog of comets, leads the Team to the conclusion that, at least for the next generation of NEO surveys, the limited resources available for near-Earth object searches would be better spent on finding and cataloging Earth- threatening near-Earth asteroids and short-period comets. A NEO search system would naturally provide an advance warning of at least months for most threatening long-period comets.
What is technically possible? Current technology offers asteroid detection and cataloging capabilities several orders of magnitude better than the presently operating systems. NEO search performance is generally not driven by technology, but rather resources. This report outlines a variety of search system examples, spanning a factor of about 100 in search discovery rate, all of which are possible using current technology. Some of these systems, when operated over a period of 7-20 years, would generate a catalog that is 90% complete for NEOs larger than 140 meters (see Figure 9-4).
How would the expanded search be done? From a cost/benefit point-of-view, there are a number of attractive options for executing an expanded search that would vastly reduce the risk posed by potentially hazardous object impacts. The Team identified a series of specific groundbased, space-based and mixed ground- and space-based systems that could accomplish the next generation search. The choice of specific systems will depend on the time allowed for the search and the resources available.
What would it cost? For a search period no longer than 20 years, the Team identified several systems that would eliminate, at varying rates, 90% of the risk for sub-kilometer NEOs, with costs ranging between $236 million and $397 million. All of these systems have risk reduction benefits which greatly exceed the costs of system acquisition and operation.
How long would the search take? A period of 7-20 years is sufficient to generate a catalog 90% complete to 140-meter diameter, which will eliminate 90% of the risk for sub-kilometer NEOs. The specific interval depends on the choice of search technology and the investment allocated.
Is there a transition size above which one catalogs all the objects, and below which the design is simply to provide warning? The Team concluded that, given sufficient time and resources, a search system could be constructed to completely catalog hazardous objects with sizes down to the limit where air blasts would be expected (about 50 meters in diameter). Below this limit, there is relatively little direct damage caused by the object. Over the 7-20 year interval (starting in 2008) during which the next generation search would be undertaken, the Team suggests that cataloging is the preferred approach down to approximately the 140-meter diameter level and that the search systems would naturally provide an impact warning of 60-90% for objects as small as those capable of producing significant air blasts.
Science Definition Team Recommendations
The Team makes three specific recommendations to NASA as a result of the analysis effort:
Recommendation 1 - Future goals related to searching for potential Earth-impacting objects should be stated explicitly in terms of the statistical risk eliminated (or characterized) and should be firmly based on cost/benefit analyses.
This recommendation recognizes that searching for potential Earth impacting objects is of interest primarily to eliminate the statistical risk associated with the hazard of impacts. The "average" rate of destruction due to impacts is large enough to be of great concern; however, the event rate is low. Thus, a search to determine if there are potentially hazardous objects (PHOs) likely to impact the Earth within the next few hundred years is prudent. Such a search should be executed in a way that eliminates the maximum amount of statistical risk per dollar of investment.
Recommendation 2 - Develop and operate a NEO search program with the goal of discovering and cataloging the potentially hazardous population sufficiently well to eliminate 90% of the risk due to sub-kilometer objects.
The above goal is sufficient to reduce the average casualty rate from about 300 per year to less than 30 per year. Any such search would find essentially all of the larger objects remaining undiscovered after 2008, thus eliminating the global risk from these larger objects. Over a period of 7-20 years, there are a number of system approaches that are capable of meeting this search metric with quite good cost/benefit ratios.
Recommendation 3 - Release a NASA Announcement of Opportunity (AO) to allow system implementers to recommend a specific approach to satisfy the goal stated in Recommendation 2.
Based upon our analysis, the Team is convinced that there are a number of credible, current technology/system approaches that can satisfy the goal stated in Recommendation 2. The various approaches will have different characteristics with respect to the expense and time required to meet the goal. The Team relied on engineering judgment and system simulations to assess the expected capabilities of the various systems and approaches considered. While the Team considers the analysis results to be well-grounded by current operational experience, and thus, a reasonable estimate of expected performance, the Team did not conduct analysis at the detailed system design level for any of the systems considered. The next natural step in the process of considering a follow-on to the current Spaceguard program would be to issue a NASA Announcement of Opportunity (AO) as a vehicle for collecting search system estimates of cost, schedule and the most effective approaches for satisfying the recommended goal. The AO should be specific with respect to NASA's position on the trade between cost and time to completion of the goal.
CCCMENU CCC for 2003