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[Marco Langbroek <marco.langbroek@xxxxxxxxxx>]

-------- Original Message --------
Subject:        ***SPAM*** NEO News (03/07/07) Planetary Defense Conference
Date:   Thu, 8 Mar 2007 22:06:22 -0800
From:   David Morrison <dmorrison@xxxxxxxxxxxx>
To:     David Morrison <dmorrison@xxxxxxxxxxxx>



NEO News (03/07/07) Planetary Defense Conference

The second triennial Planetary Defense Conference is being held this
week at George Washington University, Washington DC. The organizer is
Bill Ailor of the Aerospace Corporation, and 150 people are registered.
Following is a report of some highlights from the first two days
(dealing with NEA surveys and population, characterization, and
technologies for deflection), together with early press coverage.
Of special interest to the attendees is the long-awaited NASA NEO report
to Congress. Although the report had not been delivered, both Pete
Worden, Director of Ames Research Center, and Lindley Johnson of NASA
Headquarters discussed the study findings. The lead of the AP story
about the conference summarized:/ NASA officials say the space agency is
capable of finding almost every asteroid that might pose a devastating
threat to Earth, but because it lacks the money to do it, the job will
not get done./ On Monday we were told that the report would be submitted
this week, but by Wednesday it was clear that it had been delayed for
further editing at NASA Headquarters and/or OMB.

David Morrison

----------------------------------------

NEA Survey Status

Don Yeomans (JPL) and Al Harris (Planetary Science Institute) summarized
the results of the current Spaceguard Survey in separate reports. In
comparing their comments with previous "how are we doing" status
reports, note that the definition for 1-km asteroids in terms of the
observable brightness has changed, making direct comparison difficult.
With the new definition, there are fewer NEAs that meet the brightness
criterion for 1 km diameter (absolute magnitude H=17.75). With this
change, the current estimate for the population of >1km NEAs is 1000 +/-
50, and of PHAs (potentially hazardous asteroids) is 175 +/- 10. The
current survey completeness for both NEAs and PHAs is approximately 75%.

Why has the Spaceguard survey slowed in the past 2 years? It was always
known that the rate of discovery of new NEAs >1km would drop as the
survey nears completeness, but the observed drop is greater than
expected. Harris argues that this is a property of any asteroid survey,
which initially finds NEAs at a higher than expected rate by
preferentially discovering those in easy orbits, while later the rate
drops below the expected curve because the easy ones are already mostly
known. For this reason, it will always be difficult for a survey to meet
a 90% goal in a timely way. It might be more realistic to set the metric
at 80%, before the drop in efficiency reduces the expected rate of
return on these surveys.

Harris also estimated the reduction in statistical risk from present and
future surveys. He reported that the Spaceguard Survey has already
reduced the exposure (retiring the risk of impact by unknown NEAs) by
90%. Applying the same methodology to future surveys, he concludes that
the new ground-based surveys (Pan-STARRS-4 in Hawaii and LSST in Chile)
will likely be able to reduce the risk from smaller sub-kilometer NEAs
by 90% by 2020, even if they do not find 90% of all asteroids down to 140m.

Next Generation Surveys
Lindley Johnson (NASA HQ) summarized the conclusions of the current NASA
NEO Study, developed in response to the Congressional mandate. The study
team considered various combinations of ground-based surveys
(Pan-STARRS, LSST, and a separate NASA-dedicated LSST twin) and orbital
surveys (optical and infrared, from both near-Earth space and near the
orbit of Venus). To fully meet the Congressional mandate to find 90% of
the NEAs >140m by 2020 requires several instruments and may cost of
order $1 billion over the next 12 years, but finding 85%, or reducing
the risk exposure by 90%, may be possible with the currently-planned
ground-based systems at much lower cost to NASA. The uncertainty in the
NEA population down to 140 m exceeds the differences between different
survey strategies. NEO News will report more on these issues when the
NASA report is released.

Orbital Evolution

Paul Chodas and Steve Chesley, both of JPL, presented papers examining
the way impact probabilities are computed and how our knowledge evolves
over time as new observations (either optical or radar) are added to the
calculations. This is a complicated problem, and for asteroids that come
very close, we must expect a period of months, or even years, before we
can say for certain whether a NEA will hit or miss. Chesley pointed out
in particular that the calculated probability of impact for a NEA that
is coming close to the Earth is likely to rise initially with the
addition of new data, before it falls rather suddenly to zero. These are
not errors or false alarms, but rather an aspect of calculating impact
probabilities that we will need to live with.

NEA Properties

Rick Binzel (MIT) reported on the classification and characterization of
NEAs from remote (telescopic) observations, noting that this
astronomical approach is the first line of defense against NEAs. In
particular, the spectral matching to meteorites is an effective tool for
physical and chemical characterization of NEAs.

Steve Ostro's paper on radar imaging showed several recent successes,
some of which have been discussed recently in NEO News. A major concern
throughout the first two days of the conference was the pending closure
by NSF of the unique Arecibo radar telescope. This facility has been an
invaluable tool for understanding NEAs, and many speakers expressed
dismay at its expected demise. One attendee proposed that NASA should
not contribute "one thin dime" toward the LSST until NSF reinstates
funding for the Arecibo radar.

The results of the Hayabusa mission to Itokawa, also reported previously
in NEO News, were enthusiastically received. These represent our best
information on any sub-kilometer NEA, and we look forward to future
Japanese NEA missions.

Characterization Missions
Erik Asphaug (UC Santa Cruz) described the challenge of probing the
interior structure of small NEAs and discussed the value of radar
tomography. David Morrison (NASA Ames) presented a paper discussing the
role of future NEA characterization missions. The missions being planned
or studied include NEAT (NASA Ames), a mission from Ball Aerospace, Deep
Interior (UC Santa Cruz), OSIRIS (U Arizona), Don Quixote (ESA) and
future Japanese missions. All of these spacecraft plan either rendezvous
or landing on the NEA; flybys are not very useful for such small
targets. Major issues surround the proper programmatic role of such
missions. Obviously, if and when an asteroid is found on a collision
course, there will be a major effort to characterize it in detail. But
meanwhile what do we need to know, and with what urgency? Is it possible
to plan for deflection technologies without learning more first about
the physical and chemical and dynamical nature of the small NEAs?

Deflection Technology

This meeting included substantial advances in defining the options to
deflect a small NEA if and when one is detected on a collision course
with Earth, using ballistic impact, nuclear explosive, or gravity tractor.

Ed Luu (NASA JSC) discussed controlled deflection using the gravity
tractor, a technique that allows precise measurement of the asteroid
orbit before and during deflection. Even with small spacecraft (of order
one ton mass), the gravity tractor works for many NEAs up to 200m, and
it is most effective where there are close Earth flybys to amplify the
applied orbit changes. The consensus was that a gravity tractor was the
appropriate first defense mission approach, in part because it did not
require a precursor mission.
Kinetic impactors were presented by Jesse Koenig (SpaceDev). He used
simulations involving all known PHAs to show that kinetic impacts using
current large launch vehicles can deflect most sub-km NEAs through a
combination of direct momentum transfer and cratering, given several
decades of warning. In this approach, we need only a high-speed
intercept, not a rendezvous. Koenig argued that ballistic impacts are
simple, cheap, fast, and require no new technology; however, the orbital
change is uncontrolled. Primary questions concern the response of the
asteroid including the possibility of catastrophic disruption. For
smaller asteroids, the energy of even a modest kinetic impact exceeds
the gravitational binding energy of the asteroid. Others noted that for
these asteroids, the challenge of hitting the NEA target was much
greater than it had been for the Deep Impact comt mission because the
targets are so much smaller.

Deflections by nuclear explosions were discussed by David Dearborn
(Livermore Lab). Deflection is based either on surface heating by
absorption of neutrons from a stand-off explosion, or by cratering with
a surface explosion. Nuclear blasts might also be used to disrupt and
disperse sub-km NEAs if warning time is short. The nuclear option
delivers the greatest energy per unit mass, but the resulting effects
are not well controlled. While it is technically attractive, several
speakers on the final day of the meeting noted the strong opposition to
be expected from other nations and therefore recommended that any
nuclear option should be a defense of last resort.

Keith Holsapple (U Washington) discussed the results predicted for
kinetic impacts. He expects most small NEAs to be rubble piles, based on
frequency of impacts of their parent bodies in the main asteroid belt.
The effectiveness of all the deflection techniques except the gravity
tractor depends on asteroid interior structure. One major issue is
momentum multiplication: because of cratering, the transmitted momentum
is larger than the impacting momentum by factors of several (up to ten).
Even when impact energy is greater than gravitational binding energy,
the target will not disperse unless there is some efficient way of
distributing the energy throughout the target. Normally, we expect only
a small fraction of the mass to achieve escape velocity.

==================

NASA SAYS CAN FIND MOST KILLER ASTEROIDS BY 2020 BUT LACKS THE MONEY

International Herald Tribune, 5 March 2007
The Associated Press

WASHINGTON: NASA officials say the space agency is capable of finding
almost every asteroid that might pose a devastating threat to Earth, but
because it lacks the money to do it, the job will not get done.

The cost to find at least 90 percent of the 20,000 potentially hazardous
asteroids and comets by 2020 would be about $1 billion, according to a
report NASA will release later this week. The report was previewed
Monday at a Planetary Defense Conference in Washington.

Congress asked NASA in 2005 to come up with a plan to track most killer
asteroids and propose how to deflect the potentially catastrophic ones.
"We know what to do; we just don't have the money," said Simon Worden,
director of NASA's Ames Research Center. . . .

The agency already is tracking larger objects, at least [1 km] in
diameter, which could wipe out most life on Earth, much like what is
theorized to have happened to dinosaurs 65 million years ago. Even that
search, which has spotted 769 asteroids and comets - none on a course to
hit Earth - is behind schedule. It is supposed to be completed by the
end of next year.

NASA needs to do more to locate other smaller, but still potentially
dangerous space bodies. While an Italian observatory is doing some work,
the United States is the only government with an asteroid-tracking
program, NASA said.

One solution would be to build a new ground telescope solely for the
asteroid hunt, and piggyback that use with other agencies' telescopes
for a total of $800 million. Another would be to launch a space infrared
telescope that could do the job faster for $1.1 billion, but NASA
program scientist Lindley Johnson said NASA and the White House called
both those choices too costly. A cheaper option would be simply to
piggyback on other agencies' telescopes, a cost of about $300 million,
also rejected, Johnson said. "The decision of the agency is we just
can't do anything about it right now," he added.

Earth got a scare in 2004, when initial readings suggested an 885-foot
asteroid called 99942 Apophis seemed to have had a chance of hitting
Earth in 2029. But more observations showed that would not happen.
Scientists say there is 1 chance in 45,000 that it could hit in 2036.
They think it would be most likely strike the Pacific Ocean, which would
cause a tsunami on the U.S. West Coast the size of the devastating 2004
Indian Ocean wave.

John Logsdon, space policy director at George Washington University,
said a stepped-up search for such asteroids is needed. "You can't
deflect them if you can't find them," Logsdon said. "And we can't find
things that can cause massive damage."


--

+++++++++++++++++++++++++++++++++++++++++++

NEO News (now in its thirteenth year of distribution) is an informal
compilation of news and opinion dealing with Near Earth Objects (NEOs)
and their impacts. These opinions are the responsibility of the
individual authors and do not represent the positions of NASA, the
International Astronomical Union, or any other organization. To
subscribe (or unsubscribe) contact dmorrison@xxxxxxxxxxxxx For
additional information, please see the website
http://impact.arc.nasa.gov. If anyone wishes to copy or redistribute
original material from these notes, fully or in part, please include
this disclaimer.




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