MESSAGE
| DATE | 2006-06-24 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] While NYLXS going off the air for a few days is not the end of the world....
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This just might be
http://www.airpower.maxwell.af.mil/airchronicles/apj/apj97/sum97/nici.html
Published Aerospace Power Journal - Summer 1997
DISTRIBUTION A: Approved for public release; distribution is unlimited.
PLANETARY DEFENSE Department of Defense Cost for the Detection,
Exploration, and Rendezvous Mission of Near-Earth Objects
LT COL ROSARIO NICI, USAF 1ST LT DOUGLAS KAUPA, USAF
EARTH IS ON a collision course! Micrometeorites regularly streak
into the atmosphere causing little more than a fiery flash. However,
larger near-Earth objects (NEO) can have a more dramatic effect on the
Earth. Recently scientists presented evidence in which an asteroid, at
least a mile in diameter, hit the ocean 35 million years ago southeast of
what is now Washington, D.C., shaping the Chesapeake Bay.1 Today such an
impact would cause devastation on a global scale. The mitigation of such
a natural disaster necessitates an international planetary defense. This
article provides a background of the threat of NEO-Earth impacts and
addresses planetary defense taskings and Department of Defense (DOD)
costs for the next 20 years as part of an international effort to detect
and learn more about NEOs. Background
A NEO is a natural object (asteroid, short- or long-period comet, or a
meteor stream) of any size that will come close to or cross Earth’s
orbit, or even impact the Earth. In the past 15 years, research on NEOs
has dramatically increased as astronomers and geologists realize the
Earth is nothing more than a billiard ball in a cosmic pool game. Our
world was struck in the past and will be struck in the future.
Craters on Earth do not last long due to weather and geological
erosion. Geologists have, however, pinpointed some very old craters. A NEO
slammed into Quebec 214 million years ago, leaving a 100-kilometer-wide
scar known as the Manicouagan Crater (fig. 1). In central Australia
70 million years later, another NEO created a 22-kilometer-diameter
crater (fig. 2). Evidence suggests the demise of the dinosaurs occurred
65 million years ago with the impact of an asteroid 10 kilometers in
diameter. Named the K/T event, the asteroid struck with the force of 100
million megatons of TNT, creating a crater 180 kilometers wide off the
coast of the Yucatan Peninsula in Mexico. Even North America was visited
by a NEO nearly 50,000 years ago, creating Arizona’s Meteor Crater
(fig. 3).2
Figure 1. Manicouagan Crater, Quebec
Figure 1. Manicouagan Crater, Quebec
Figure 2. Wolf Creek Crater, Australia
Figure 2. Wolf Creek Crater, Australia
Figure 3. Meteor Crater in Arizona
Figure 3. Meteor Crater in Arizona (Reprinted with permission of
University of Arizona Press from Tom Gehreis, ed., Hazards Due to
Comets and Asteroids [Tucson: University of Arizona Press, 1994],
430.)
Today there are 140 known impact sites on the Earth with many hundreds
awaiting verification.3 Figure 4 illustrates the major sites.
Figure 4. 140 Earth Impact Sites
Figure 4. 140 Earth Impact Sites (Reprinted with permission of
University of Arizona Press from Tom Gehreis, ed., Hazards Due to
Comets and Asteroids [Tucson: University of Arizona Press, 1994],
430.)
Earth, however, is not the only planet tormented by orbital debris. In
July 1994, Jupiter was struck by Comet Shoemaker-Levy 9. The comet passed
too close to the gas giant, breaking apart due to the immense gravity
and then scarring the planet in several locations shown in figure 5. If
even one of the kilometer-wide fragments had hit the Earth, the result
would have been catastrophic,4 as shown by the computer model in figure 6.
Figure 5. Impact Scars on Jupiter
Figure 5. Impact Scars on Jupiter
Meteor streams occur when the Earth passes through the orbital path
of debris left behind by comets. The debris can range in size from a
centimeter to a millimeter in diameter. Though these streams pose no
threat to humans on the surface, satellites and space stations may be
impacted, degrading their solar arrays or damaging optical sensors.5
Figure 6. Simulation of Shoemaker-Levy 9's projected impact on Earth
Figure 6. Simulation of Shoemaker-Levy 9's projected impact on Earth
Some NEOs nearly reach the Earth’s surface. From 1975 to 1992, nuclear
detonation detecting satellites recorded 136 atmospheric blasts in the
megatons-of-TNT range.6 NEOs can also cause damage to the Earth without
reaching the surface.7 In 1908, an asteroid or comet exploded in the
atmosphere near Tunguska, Siberia. Though no crater formed, the shock wave
from the exploding body devastated 2,000 square kilometers of forest.8
If this NEO had reentered a few hours later, it could have destroyed
Moscow with a force one thousand times greater than the Hiroshima and
Nagasaki atomic detonations.9
In 1992, a brilliant asteroid streaked through the night sky in Peekskill,
New York, during several high school football games. This event was
caught on a camcorder at one of the games, and the asteroid damaged
a car.10 The Tunguska blast area is twice as big as New York City and
three times as large as Washington, D.C.
Luckily, not all NEO “near hits†cause damage, but they do illustrate
the fact the Earth is not immune to their destructive effects. Recorded
on a videocamera in 1972, an asteroid grazed Earth’s atmosphere
near Wyoming’s Grand Teton Mountains and skipped back out into space
(fig. 7).
Figure 7. An Asteroid skips through the atmosphere, only one of many
"near hits" recorded.
Figure 7. An Asteroid skips through the atmosphere, only one of many
"near hits" recorded.
In 1989, astronomers discovered an asteroid labeled 1989FC after its
closest approach to Earth. This illustrates a disturbing fact. Currently
only astronomers on shoestring, academic budgets are trying to locate and
track NEOs, making estimates of NEO populations very imprecise. Through
the end of 1992, 163 NEOs had been detected and catalogued, representing
only 5 percent of the estimated 2,000 to 5,000 NEOs larger than one
kilometer.11 Scientists believe a Tunguska event will occur every
century and a kiloton (K/T) event every 25–26 million years based on
the density of impact craters on the moon.12
Illustrated in figure 8 is the equivalent yield in megatons of TNT based
on a NEO with a density of 3 grams/centimeters (CM3) and a velocity of
20 kilometers per second (km/sec). The shaded area to the left represents
the NEO size that will burn up or explode in the atmosphere, though blast
effects like Tunguska still could produce damage to the surface. Near
the one-kilometer size, NEOs could produce global consequences, though
there is some uncertainty in the threshold size required as shown in
the dashed vertical lines.
Figure 8. Average Impact Interval Versus Size
Figure 8. Average Impact Interval Versus Size (Reprinted with
permission of Nature Magazine from Clark R. Chapman and David
C. Morrison, “Impacts on the Earth by Asteroids and Comets:
Assessing the Hazard,†Nature 367 [6 January 1994]: 37.)
Global disasters will result if a large (1-km) NEO impacts the Earth,
perhaps killing as much as 25 percent of the human population.13 This
is largely due to the indirect effect of the impact. A land impact
produces fires and earthquakes, while an ocean impact produces tsunamis
measuring several hundred meters in height, and perhaps even hypercanes,
which are runaway hurricanes that inject large amounts of sea water and
aerosols into the atmosphere, causing major global climate changes.14
Both will have blast effects flattening nearby structures with the
possibility of a global winter emerging. Global winters are when large
amounts of ash and dust enter the atmosphere, blocking sunlight from
reaching photosynthesizing plants. Crops will die and world starvation
may result. Also, worldwide temperatures would plummet for months,
perhaps years.15
Scientists have compared mass extinctions with major impact craters
found on Earth and discovered a striking comparison as seen in figure
9.16 The K/T event could have begun the demise of the dinosaur era. The
Manicouagan Crater in Quebec may have also helped to end the Triassic
Era by throwing tons of sky-darkening dust into the air.17
Scientists have compared mass extinctions with major impact craters
found on Earth and discovered a striking comparison as seen in figure
9.16 The K/T event could have begun the demise of the dinosaur era. The
Manicouagan Crater in Quebec may have also helped to end the Triassic
Era by throwing tons of sky-darkening dust into the air.17
Figure 9. Mass Extinctions in Geological Record
Figure 9. Mass Extinctions in Geological Record (Reprinted with
permission of Plenum Press from C.R. Chapman and David C. Morrison,
Cosmic Catastrophes [New York: Plenum Press, 1989])
If a NEO impacted the Earth today, what would the estimates of fatalities
be? Should we even be concerned? Figure 10 portrays projected fatalities
per event. The dash line represents an ocean impact while the solid line
portrays a land impact.
Figure 10. Estimated Fatalities Per Event
Figure 10. Estimated Fatalities Per Event (Reprinted with permission
of Nature Magazine from Chapman and Morrison, “Impacts on the
Earth by Asteroids and Comets: Assessing the Hazard,†Nature 367
[6 January 1994]: 37).
In figure 10, we see the curved line representing increased fatalities
with increased NEO size, yet the time scale on the left indicates longer
times between larger NEO asteroid diameters. In other words, small
NEOs near 50 meters in diameter impact the Earth much more frequently
than larger ones. However, small NEOs could produce another Tunguska
blast. Therefore, one needs to understand the probability of death by
any size NEO. The relative probability of death by an asteroid impact
is shown in table 1.
Table 1 Probability of Death by an Asteroid
Source: "Impacts on the Earth by Asteroids and Comets: Assessing the
Hazard," Nature 367 (6 January 1994): 39.
How does one arrive at a number of 1 in 25,000? Scientists estimate
there are 500,000 years per global devastating impact, as shown by the
horizontal line in figure 10. The probability of a strike in any one year
is 1 in 500,000 assuming the strikes are completely at random. Assuming
25 percent of the world’s population could die as a result, the risk
of death is 1 in 4. Thus, in any one year per person, the risk of death
is approximately 1 in 2,000,000. Over a 75-year lifetime, the risk is
nearly one in 25,000.18 Please realize that the probability of a NEO
impacting the Earth and causing global disasters is very slim, yet the
consequences if one did impact would leave us with this estimated risk of
death. Furthermore, you are probably wondering when the last person was
killed by a NEO. Referring back to the Tunguska blast, the expedition
that researched the blast found trees, reindeer, teepees, and nomadic
artifacts partly incinerated.19 It is still unknown if anyone did die.
By now you are thinking we’re predicting that the sky is falling. We are
not trying to scare the reader into spending billions of dollars to save
the Earth. Rather, we ask for money to be spent wisely on assessing the
threat, learning more about NEOs, and tracking and cataloguing NEOs. No
NEO is currently predicted to hit the Earth. Yet someday there will be
one, as the probability is finite. So who will take a leading role?
The US government, through the DOD, is obligated to protect the lives
and safety of its citizens.20 Further, the US may use its armed forces,
under the hierarchy of interests, for cases of strict humanitarian
concern.21 Thus, responding to the NEO threat could be seen to fall
under this policy.
In the past few years, several different organizations in addition to
DOD began to assess the NEO threat. Astronomers working at colleges have
discovered NEOs by several methods, such as by using telescopes equipped
with cameras to photograph small sections of the sky at two different
times nearly an hour apart. The astronomers then compare the two photos to
observe if any smudge or streaks occurred, thus representing a NEO passing
by the Earth. However, it is very tedious and time consuming to peer at
photographs with a microscope looking for such movement. Furthermore,
if a streak does appear, the astronomers must first check to see if
the streak is not a satellite flying overhead or a known asteroid or
comet. Another method is to use charge-coupled devices (CCD) detector
telescopes.22 This method utilizes computers to analyze electronic
photographs for any streaks that occur that are not previously known,
such as satellites or NEOs that have not already been detected. The CCD
method is much quicker, though more expensive. Altogether, this is only
a limited search due to the astronomers’ restricted academic budgets.
In 1990, the American Institute of Aeronautics and Astronautics (AIAA)
issued a position paper concerning the threat of NEOs after Apollo
asteroid 1989FC made the closest approach to the Earth ever detected.23
Stimulated by this AIAA paper, Congress recognized the impact hazard of
NEOs and in 1991 asked the National Aeronautics and Space Administration
(NASA) to convene a detection and interception workshop. The Subcommittee
on Space of the Committee on Science, Space, and Technology, US House of
Representatives, received the summaries and held hearings on the threat
of large Earth-orbit-crossing asteroids on 24 March 1993.24 Ironically,
Shoemaker-Levy 9 was discovered about this time. Due to the impending
impact on Jupiter, Congress directed NASA to develop a program and
a budget estimate for cataloging NEOs in 10 years.25 NASA’s report
encourages collaboration of the international community and the US Air
Force.26 However, Congress only asked NASA to give a cost estimate,
and currently NASA has no plans to spend new money on tracking NEOs.27
The military has also written about the NEO threat. Air University’s
Spacecast 2020 reported on the Air Force’s future and looked at the NEO
threat in “Preparing for Planetary Defense.â€28 Research was conducted
at Air Command and Staff College on the same topic.29 The chief of staff
of the Air Force tasked Air Force Space Command to accomplish a mission
area assessment for defense of Planet Earth, which should be finished in
fiscal year 1997.30 Thus, to date there has been some attention given
to the NEO threat. However, the authors believe in order to accurately
assess the threat, we need to follow several taskings as elaborated in
the next section. Taskings
A planetary defense should include everything that could mitigate a
NEO-Earth collision. What does one need to know or do before one can
mitigate the damaging effects of a NEO collision with the Earth? Should
any of these tasks be accomplished concurrently? The following list of
tasks answers the previous two questions.
Coordination is required to systematically cover the sky. Several
astronomers from around the world are surveying the sky, although
not in a joint effort. Who will do confirmations and follow-up orbit
determination? Can we use the Air Force’s tracking systems to help
detect NEOs?
Detection is required. What should be the limiting NEO size detected? How
fast should this occur, within 10 or 20 years? The requirement for
timely completion of detection affects the decision concerning sky
coverage versus limiting NEO size and magnitude. What are the sources
of NEOs? Should we detect possible NEOs, ones that are currently not
near Earth’s orbit but that might become ones? Furthermore, how often
should we recheck previously scanned areas?
Science covers the material characterization of the object. What does one
need to know about the object in order to mitigate any damage effects? Can
one simulate NEO composition on Earth and “test†these NEOs? Can we
deflect the orbital paths of NEOs or is destroying NEOs and suffering
the remnants impacting the Earth the only option?
Figure 11. Exploration of a NEO in the Future
Figure 11. Exploration of a NEO in the Future
Exploration of NEOs may be a means to combine the requirement to
rendezvous with a NEO for scientific study while providing the orbital
dynamics know-how for destruction or deflection. Missions to NEOs will
prove helpful in planetary defense.
Destruction and Deflection may be the only ways to prevent damage to the
Earth. Operation concepts and options should be planned and practiced
before they are required to be used to avoid a catastrophe.
Harvesting is a spin-off of deflection. Would Earth be lucky if an NEO
was approaching? Could a NEO be “captured†into Earth orbit and then
mined to provide resources in space?
Warning of the “Big One†is only good if the outcome (global
devastation) is avoidable. Warning of “small†NEOs may save
countless lives and prevent destruction due to tsunamis, forest fires,
and earthquakes. Also, warning to prepare for a meteor stream may save
valuable space assets. Cost
Currently planetary defense is not itemized in the DOD budget. As
with any organization, priorities set the budget. The apprehension
from those not in DOD may be that any planetary defense could be just
another excuse for an arms race since the cold war is over. The reality
from the congressional perspective is that the money for any efforts
specifically itemized for planetary defense should come out of DOD’s
current budget.31
Given that the funding is from DOD, support should be given to those
academic research programs that are currently conducting NEO detection,
research, and technology development and to the Air Force Space Command,
which has spent over $100 million on the technology to improve the current
space surveillance mission of the ground based electrical-optical
deep space system (GEODSS). Space Command’s relentless efforts
of quality and continuous improvement should be lauded. Not only is
there an improvement in the accuracy of detecting man-made debris in
Earth orbit, but also the enhanced tracking of NEOs for a planetary
defense is now feasible. Clearly, the humanitarian search for NEOs
would be a hallmark for efforts to transform military assets into
civilian endeavors. Furthermore, current improvements in the GEODSS
can be utilized to improve environment, weather, and remote sensing, as
well as to create smaller, faster, more intelligent hardware. However,
tracking NEOs is not the only solution for protection. We need to learn
more about NEOs and be prepared to avoid a future collision.
Over the next 20 years, NEO detection, exploration, and rendezvous
missions need to take place. In a recent Air Command and Staff College
study, Larry D. Bell and others provided an excellent in-depth look at
search systems, their advantages and disadvantages, a system architecture,
and cost.32 Detection includes searching for NEOs, maintaining a NEO
catalog, estimating populations of NEOs, and recurring operations
and support. Exploration consists of determining the NEO origins,
understanding how their orbits change due to the planets or collisions,
and resolving the composition and density of NEOs. Are they solid or
rubble objects orbiting together? Flybys or ground-based research will
be the vanguards. Missions like Galileo, Clementine 1 and 2, NASA’s
near-Earth asteroid rendezvous (NEAR) system, and use of the Arecibo and
Goldstone radar systems will increase our knowledge of NEOs. Finally,
rendezvous missions practice the meeting of NEOs beyond the Earth’s
orbit, testing methods to deflect or destroy an NEO. These are the
practice, small-scale mitigation missions in case we need to perturb or
destroy a NEO months or even years before an Earth collision occurs. The
science missions may require observations from Earth or flybys of the
target, whereas rendezvous missions require the interceptor to orbit the
target NEO. The bottom line is that the estimated cost for a planetary
defense is near $14 million per year for detection, $23 million per
year for exploration, and $75 million per year for rendezvous missions
averaged over the next 20 years. Figure 12 reflects the breakdown of the
budget each year if we begin today. These estimated costs were finalized
with comments from Mr Nick Fuhrman, science advisor to the Committee
on Science, US House of Representatives, and Dr. Bill Tedeschi of the
Sandia National Laboratory.
A limited mitigation system that would cost approximately $1 billion over
three years is not included above.33 A different estimate sets costs
at $120 to $150 million per year for two mitigation missions to either
destroy or deflect non-Earth impacting NEOs over a 10-year period.34
The United States will perhaps need an impact scare to push Congress to
approve a mitigation program because any system with the capability to
deflect or destroy NEOs might be viewed as a weapon.
Figure 12. Projected Cost for a Potential Planetary Defense Effort
Figure 12. Projected Cost for a Potential Planetary Defense Effort
The cost of the detection mission also includes the installation of an
infrared sensor in the year 2003 to supplement the optical system. The
exploration costs are portrayed as three distinct missions launched
during the years 2002, 2007, and 2013. These missions could be easily
slipped forward or backward depending on what is detected and what NEO is
of interest. The rendezvous missions of 2008 and 2017 should be used to
develop the operations concepts and procedures for a mitigation mission.
Summary
Assessing the NEO threat would be a small cost for insurance, whereas
an impact would cost billions of lives and trillions of dollars. While
there is no reason to fear NEOs daily, there is a finite probability
another NEO will collide with the Earth.
We have the technology to track and predict NEO-Earth impacts and the
possibility of preventing a catastrophic natural disaster. Other species
are extinct because they could not protect themselves. We must not be
the next. Therefore, it is imperative that we use our knowledge and
technology to assess the NEO threat by addressing the seven tasks and
invest in the detection, exploration and rendezvous missions.
Figure 13. An Earth Impact, a Natural Disaster We Can Avoid
Figure 13. An Earth Impact, a Natural Disaster We Can Avoid Notes
1. Justin Gillis, “Bay Meteor Theory Appears Rock Solid,†Washington
Post, 12 September 1995.
2. Steel, Duncan, Rogue Asteroids and Doomsday Comets (New York: John
Wiley and Sons, Inc., 1995), 148.
3. Ibid, 90.
4. John R. Spencer and Jacqueline Mitton, The Great Comet Crash: Impact of
Comet Shoemaker-Levy 9 on Jupiter (New York: Cambridge University Press,
1995), 106.
5. Bill Yenne, The Atlas of the Solar System (New York: Bison Books,
1987), 174–75.
6. Adam Erlich, “Detection of Meteoroid Impacts by Optical Sensors in
Earth Orbit,†in Tom Gehrels, ed., Hazards Due to Comets and Asteroids
(Tucson: University of Arizona Press, 1994).
7. Larry D. Bell, William Bender, and Michael Carey, “Planetary
Asteroid Defense Study: Assessing and Responding to the Natural Space
Debris Threat,†research paper ACSC/DR/225/95-04 (Maxwell AFB, Ala.:
Air Command and Staff College, 1995), 71–74.
8. Voyage through the Universe: Comets, Asteroids, and Meteorites (New
York: Time-Life Books, Inc., 1990), 106.
9. Jefferey L. Holt, Lindley N. Johnson, and Greg Williams, “Preparing
for Planetary Defense: Detection and Interception of Asteroids on
Collision Course with Earth,†research paper (Maxwell AFB, Ala.:
Air Command and Staff College, 1994), 7.
10. Steel, 175.
11. Holt, Johnson, and Williams, 2.
12. Ibid., 3.
13. Steel, 50–53.
14. Bell, Bender, and Carey, 59–74.
15. Steel, 55–73.
16. Clark R. Chapman and David C. Morrison, Cosmic Catastrophes (New York:
Plenum Press, 1989).
17. Bell, Bender, and Carey, 33–37.
18. Chapman and Morrison, 39.
19. Steel, 173–75.
20. Secretary of Defense William J. Perry, Annual Report to the President
and the Congress (Washington, D.C.: US Government Printing Office,
February 1995), 1.
21. Ibid., 15.
22. Eleanor F. Helin, “A Brief History of NEO Discovery,†The NEO
News 1, no. 2.
23. “Dealing with the Threat of an Asteroid Striking the Earth,â€
American Institute of Aeronautics and Astronautics, Washington D.C.,
April 1990.
24. House, The Threat of Large Earth-Orbit Crossing Asteroids: Hearing
before the Committee on Science, Space, and Technology, 103d Cong.,
1st sess., 24 March 1993.
25. H.R. Report 103-654, accompanying H.R. 4489, The National Aeronautics
and Space Administration Authorization and Space Policy Act, 1995.
26. Eugene M. Shoemaker et al., “Report of Near-Earth Objects Survey
Working Group,†NASA Solar System Exploration Division, Office of
Space Science, Washington, D.C., June 1995.
27. National Aeronautics and Space Administration, “Report of the
Near-Earth Objects Survey Working Group,†presented to the Committee
on Science, House of Representatives, June 1995, preface to the Honorable
Robert Walker.
28. Holt, Johnson, and Williams.
29. Bell, Bender, and Carey.
30. John Darrah, AFSPC/CN, “AFSPC Inputs to the Third Near Earth Object
(NEO) Search Committee Meeting,†presentation, 13 January 1995.
31. Nick Fuhrman, professional staff member, Eric R. Sterner, professional
staff member, Richard M. Obermann, science advisor, Committee on Science,
Subcommittee on Space and Aeronautics, US House of Representatives,
private communication with the authors, 12 September 1995.
32. Bell, Bender, and Carey, chapter 7.
33. Bill Tedeschi, scientist, Sandia National Laboratory, private
communication with the authors, 13 September 1995.
34. Maj Lindley N. Johnson, private communication with the authors,
15 December 1995.
Contributors
1Lt Douglas F. Kaupa (USAFA) is currently completing navigator
training. He was the 1991 recipient of the Millennium Scholarship from
the Planetary Society. Previous assignments include research assistant
in the Department of Astronautics at the US Air Force Academy.
Lt Col Rossario Nici (USAFA; MS, PhD, University of Colorado) is currently
assigned to the Department of Astronautics at the USAF Academy. Previous
assignments include flying tours in KC-135, and TG-7A aircraft and a
tour as an instructor and assistant professor in astronautics at the
USAF Academy. He is a grad-uate of the Squadron Officer School and Air
Command and Staff College.
Disclaimer
The conclusions and opinions expressed in this document are those of the
author cultivated in the freedom of expression, academic environment
of Air University. They do not reflect the official position of the
U.S. Government, Department of Defense, the United States Air Force or
the Air University.
--
__________________________
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