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PLANETARY ASTEROID DEFENSE STUDY
ASSESSING AND RESPONDING TO THE NATURAL SPACE DEBRIS
THREAT
by
Write a research paper on Planerary Asteroid Defense Study
Perry Monroe
April 00.ii
Disclaimer
The views expressed in this academic research paper are those of the authors and
do not reflect the official policy or position of the US Government or the Department of
Defense..iii
Preface
Interest in developing an asteroid defense system, intensified by the impact of
comet Shoemaker-Levy with Jupiter in 14, continues to grow by leaps and bounds.
Many major US publications such as Newsweek, Time, Ad Astra, Technology Review,
Nature and even The Economist have run extensive articles on the subject. However, the
interest goes well beyond the United States and the press. Russia, Italy, and Australia
have recently hosted conferences on the asteroid threat and the United Nations will host
one of its own in April of this year.
Because of public interest, and at the urging of scientists and astronomers, the US
Congress commissioned the Spaceguard survey to examine the asteroid threat. Though
no major decisions were made as a result of the survey (briefed in 1), all agreed that
the subject warranted continued discussion. In January of 16, a NASA sponsored
follow-on committee, headed by Dr. Eugene Shoemaker, will present recommendations
for asteroid defense to Congress. Most expect the Shoemaker Committee to recommend
an asteroid search program much like the one proposed in the original Spaceguard report.
While all of this is going on, it appears that the US military, specifically the Air
Force, has declined to participate in these surveys and the subsequent Congressional
briefs. The reluctance is somewhat understandable since scientists are just beginning to
understand and quantify the threat. Planetary Defense, if undertaken, would be a new
challenge, but one that clearly falls in the realm of military responsibility. The US Military
has organizations, equipment and talent that could be invaluable to an asteroid defense
program. We hope that this study will convince our leadership that the Air Force has both.iv
the capability and responsibility to participate in the defense of Earth (and our space
assets) from natural space debris.
We would like to express our sincere gratitude to the following people for their
assistance. We literally couldn’t have done it without them.
Of the multitude of people and agencies who have assisted us in the
preparation of this study, we owe special thanks to the Institute for
National Security Studies, Colorado Springs for seeing the potential in
our proposal and funding our research.
Dr. Peter Brown of the University of Western Ontario, Canada for
sharing his expertise and sound advice in the study of the meteor stream
threat. Peter went out of his way many times to help us find information
and make the contacts that made the paper possible.
Ellen Carey and Jean Gilbert of William Beaumont Hospital Medical
Library, Royal Oak, Michigan for their assistance in obtaining
documents pertaining to risk assessment.
David Morton, Hazard Center Library, University of Colorado-Boulder
for their hospitality and assistance in locating sources relating to
disaster planning. We are also indebted to the Hazard House for the long-term
use of many excellent references during our studies.
John Darrah, Chief Scientist, Sandy Sutherland, and Lt Col Shirley
Hamilton from Headquarters, Air Force Space Command for
providing materials, insight, and contacts to the numerous agencies
involved in asteroid research.
Lt Col Neil McCasland for providing a sanity check, playing devils
advocate and generally making us think. Our lengthy discussions helped
solidify many of the ideas expressed in the paper.
Bob and Patsy Hancock of Colorado Springs for making our trip
enjoyable and memorable (thanks for dinner, too).
Dr. Jack Hills of Los Alamos National Labs for his technical advice and
many tremendously useful papers on the subject.
Dr. Gregory Canavan of the Los Alamos National Labs for his advice
and technical expertise, as well as his insight into the asteroid community
and the preparation of the Spaceguard reports..v
Dr. William Wiesel, Dept of Astronautical Engineering, Air Force
Institute of Technology for taking time out of a busy schedule (even
canceling class) to discuss and advise on the project.
Maj Karl Johnson, our faculty research advisor for his incredible support
throughout the year. He kept our research flowing smoothly and relieved
us of many administrative burdens.
Most of all, we would like to thank our friends and families for motivating us when we
were beleaguered, and for bearing with us when we were gung-ho.
This research project would have been very difficult without the assistance and
encouragement of these individuals. However, the conclusions and recommendations, as
well as any errors, are entirely our own..vi
Table of Contents
Page
PREFACE....................................................................................................................... ii
LIST OF TABLES......................................................................................................... xi
LIST OF FIGURES ...................................................................................................... xii
LIST OF EQUATIONS ................................................................................................ xv
ABSTRACT................................................................................................................. xvi
CHAPTER 1 Introduction............................................................................................. 1
The Threat.................................................................................................................
Roles and Responsibilities of the United States Military Regarding NSD
Defense................................................................................................................
Notes......................................................................................................................... 4
CHAPTER Natural Space Debris ............................................................................... 5
Definition of Natural Space Debris (NSD................................................................... 5
Sources of Natural Space Debris................................................................................ 5
The Comets ......................................................................................................... 6
The Origin of Comets..................................................................................... 7
Types of Comets ............................................................................................ 8
Short-Period Comets......................................................................................
Long-Period Comets .................................................................................... 10
The Asteroids .................................................................................................... 11
Main Belt Asteroids ..................................................................................... 1
Extra-Belt Asteroids..................................................................................... 15
Earth-crossing Asteroids .............................................................................. 18
The AAAO Orbits........................................................................................ 0
Meteors and Meteor Streams ....................................................................... 6
The Natural Space Debris System A Summary.......................................................
Notes....................................................................................................................... 1
CHAPTER A Brief Overview of Impact Theory .......................................................
Mass Extinctions and the Geologic Record .............................................................. 5
Evidence of Periodic or Recurring Extinctions ......................................................... 6
Comet Showers ................................................................................................. 7
Problems Determining Periodicity-Potential Mechanisms..............................
Nemesis.................................................................................................. 40
Passage Through the Galactic Plane........................................................ 41.vii
Page
A Tenth Planet ....................................................................................... 4
Problems Determining Periodicity-Accuracy of Dating ................................. 4
Impact Signatures and the K/T Event ................................................................. 4
Summary ................................................................................................................. 47
Notes....................................................................................................................... 48
CHAPTER 4 Natural Space Debris Effects.................................................................. 50
Impact Energy ......................................................................................................... 51
Impact Effects ......................................................................................................... 56
Tunguska........................................................................................................... 56
Direct Impact Effects ......................................................................................... 5
Indirect Impact Effects....................................................................................... 60
Blast ............................................................................................................ 60
Tsunamis...................................................................................................... 64
Earthquakes ................................................................................................. 66
Global Impact Winter................................................................................... 67
Fires............................................................................................................. 6
Hypercanes .................................................................................................. 70
Electromagnetic Energy Generation and Electrophonics ............................... 71
The Effect of Meteor Storms and Meteoroid Impact on Space Vehicles ................... 75
Dust in the Stream ............................................................................................. 75
Debris Greater than 1 mm .................................................................................. 76
Summary of Effects ................................................................................................. 7
Notes....................................................................................................................... 80
CHAPTER 5 Natural Space Debris Clarifying Risk, Hazard and Threat..................... 8
Terms Defined......................................................................................................... 8
Hazard............................................................................................................... 8
Risk ................................................................................................................... 8
Threat................................................................................................................ 8
Conveying the Threat Message ................................................................................ 84
Historical Representations of the NSD Threat .................................................... 84
The Reasonableness Test.............................................................................. 85
Variations in Historical Risk Assessments..................................................... 87
Defining an Acceptable Level of Risk................................................................. 8
Action Thresholds ........................................................................................ 0
Summary ................................................................................................................. 1
Notes.......................................................................................................................
CHAPTER 6 The Natural Space Debris Threat ...........................................................
Estimating the Amount of Debris in Earth-crossing Orbits........................................ 4
Risk of Terrestrial Impact ........................................................................................ 8
In Search of an NSD Threat Model.......................................................................... .viii
Page
The Threat to Civilization ................................................................................ 10
Threat to Life................................................................................................... 10
Threat to Economy .......................................................................................... 104
An NSD Threat Model Summary........................................................................... 105
Satellites and the Meteor Storm Threat .................................................................. 108
Meteor Storms................................................................................................. 10
Meteor Streams ............................................................................................... 11
Summary The NSD Threat.................................................................................. 117
Notes..................................................................................................................... 10
CHAPTER 7 The NSD Detection and Discrimination Problem.................................. 1
Asteroid Detection and Discrimination................................................................... 14
Asteroid Detection Factors Optical Telescopes ................................................... 15
Magnitude ....................................................................................................... 16
Orbit Geometry and Phase Angle ..................................................................... 17
Distances ......................................................................................................... 1
Diameter.......................................................................................................... 10
Albedo............................................................................................................. 10
Reflection Phase Law....................................................................................... 11
Apparent Visual Magnitude.............................................................................. 14
Asteroid Detection Factors IR Telescopes........................................................... 15
Optical and IR System Comparison.................................................................. 16
RADAR Systems (Detection Discrimination) ..................................................... 17
Distinguishing Asteroids and Comets from Background Stars (Discrimination) ...... 1
Proper Motion ................................................................................................. 1
Parallax............................................................................................................ 14
Effects of Atmosphere on Ground-based Systems .................................................. 14
Atmospheric Effect on Apparent Visual Magnitude.......................................... 144
Atmospheric Effect on Resolving Power .......................................................... 145
Atmospheric Effect on IR and Radar Systems .................................................. 146
Key Instrument Design/Performance Factors.(Optical and IR Systems) .................. 146
Detection ......................................................................................................... 147
Discrimination.................................................................................................. 148
Summary ............................................................................................................... 151
Notes..................................................................................................................... 15
CHAPTER 8 Search Systems .................................................................................... 154
General System Objectives and Requirements ........................................................ 155
General System Requirements................................................................................ 160
Minimum Object Diameter of Interest .............................................................. 160
Survey Duration............................................................................................... 16
Optical System Requirements................................................................................. 165
Warning Time Indicator ................................................................................... 165.ix
Page
Simplified Warning Time Model....................................................................... 168
Coverage ......................................................................................................... 17
Impact Trip Wire Implications for Coverage............................................ 177
Minimum Detectable Proper Motion and Parallax............................................. 178
IR System Requirements........................................................................................ 180
IR Limiting Magnitude..................................................................................... 181
IR Resolution................................................................................................... 185
IR Coverage .................................................................................................... 185
IR Coverage Rate....................................................................................... 186
Radar System Requirements .................................................................................. 186
Wide Area Search ............................................................................................ 186
Tracking and Orbit Characterization................................................................. 186
System Architecture............................................................................................... 18
The Centralized Control and Coordination Center (CCCC) .............................. 10
Responsibility for NSD Search ................................................................... 11
Data Handling and Storage .................................................................................... 1
Meteor Storm Characterization System Requirements............................................ 15
Predicted Zenithal Hourly Rate and Storm Risk Factor..................................... 15
Minimum Meteor Storm Warning Time............................................................ 16
Survey of Optical Systems ..................................................................................... 16
Spaceguard Survey Network............................................................................ 17
Spacewatch...................................................................................................... 17
GEODSS......................................................................................................... 18
TOS................................................................................................................. 1
NASA Liquid-Mirror Telescopes ..................................................................... 0
LLNL Wide-Field-of-View Telescopes System ................................................ 0
Infrared (IR) Systems Survey................................................................................. 04
IRAS ............................................................................................................... 04
WIRE.............................................................................................................. 05
Radar Systems Survey ........................................................................................... 05
Search System Costs.............................................................................................. 06
General System Architecture............................................................................ 08
GEODSS/GUPS Based System........................................................................ 08
Combined NASA Liquid Mirror GEODSS/GUPS System............................. 0
Meteor Stream Characterization ............................................................................ 1
Conclusions ........................................................................................................... 14
Notes..................................................................................................................... 16
CHAPTER The Military’s Response to the Natural Space Debris Threat as a
Natural Disaster ........................................................................................1
Military Involvement in Disaster Response............................................................. 0
Doctrine Governing Military Support of Civil Authorities ...................................... 4
Employment of Military Forces in Domestic Disaster Relief ................................... 8.x
Page
Strategic Requirements .................................................................................... 8
Operational Requirements ................................................................................ 0
Preparing for Disaster Assistance Support.............................................................. 1
NSD as a Natural Disaster A Summary................................................................ 6
Notes..................................................................................................................... 7
CHAPTER 10 Threat Mitigation ............................................................................... 8
Mitigation to Reduce the Effects of the NSD Threat. ............................................. 8
Mitigation Measures .............................................................................................. 4
Planning........................................................................................................... 4
National Planning ....................................................................................... 44
International Planning................................................................................. 47
Preparedness.................................................................................................... 48
Warning and Alerting ................................................................................. 48
Training ..................................................................................................... 50
Defending Against the NSD Threat .................................................................. 51
Use of Existing Military Assets................................................................... 51
Threat Detection and Characterization Systems .......................................... 5
Protecting Life and Property from the NSD Threat..................................... 5
Mitigating the NSD Threat A Summary ............................................................... 58
Notes..................................................................................................................... 5
CHAPTER 11 Future Considerations ........................................................................ 61
Asteroid Mining..................................................................................................... 61
Extraterrestrial Artifacts ........................................................................................ 64
Notes..................................................................................................................... 67
CHAPTER 1 Recommendation Summary................................................................ 68
Recognize the Natural Space Debris Threat ........................................................... 61
Plan for the NSD Threat Now................................................................................ 6
Institute an Asteroid and Comet Search Program ................................................... 6
Recognize the Meteor Stream Threat..................................................................... 70
Characterize All Active Meteor Streams ................................................................ 71
Develop a Meteor Storm Warning Capability ......................................................... 7
Encourage Satellite Programs to Develop Meteor Storm Procedures ..................... 7.xi
List of Tables
Page
Table -1. Some Short-Period Comets and Their Orbital Periods............................... 8
Table -. Titius-Bode Sequence Predicted Planet at .8 AU from Sun ................... 1
Table -. Major Asteroid Families and Groups....................................................... 16
Table -4. Orbit Elements of Earth-crossing Asteroids For Which Families Are
Named.............................................................................................. 4
Table -5. Overlapping Definitions of Some Common Space Debris Terms ............. 6
Table -6. Some Well-known Meteor Showers and Their Parent Objects ................ 8
Table 5-1. Various Authors Have Put Forth Widely Differing Risk Assessments
Regarding Natural Space Debris ....................................................... 87
Table 6-1. Well Documented Meteor Storms Since 17....................................... 108
Table 6-. Estimated Probability of Space Network Meteoroid Collision ............ 115
Table 8-1. Asteroid and Comet Search System Key Requirements......................... 15
Table 8-. Warning Time Effect on Interception.................................................... 167
Table 8-. Meteor Stream Characterization and Storm Warning Factors................ 15
Table 8-4. Optical Search System Specifications.................................................... 01
Table 8-5. Military Radars..................................................................................... 06
Table 8-6. Detection Instrument Cost Estimates .................................................... 07
Table 8-7. Estimated Optical Search System Costs ................................................ 10
Table 8-8. IR, Radar and CCCC Costs .................................................................. 11
Table 8-. Estimated Cost of Complete Search System.......................................... 1
Table -1. Disaster Relief Organizations................................................................ 1
Table -. Emergency Support Function Assignment Matrix ................................. 7
Table 10-1. Issues Affecting NSD Defense Systems ................................................ 57.xii
List of Figures
Page
Figure -1. Artist Rendering of Comet With Tail ........................................................ 6
Figure -. Artist Rendering of a Fragmented Shoemaker-Levy Impacting
Jupiter .............................................................................................. 10
Figure -. Asteroid Ida (56 Km Long) and its Moon (1 Km Diameter) ................... 11
Figure -4. Relative Locations of Some Families and the Kirkwood Gaps................. 1
Figure -5. Artist Rendering of Asteroids Approaching a Planet ............................... 14
Figure -6. Location of Trojan Asteroids at L4 and L5 Lagrange Points ................... 17
Figure -7. 100 of the Largest Earth-crossing Asteroid Orbits Overlaid on
Earth’s Orbit..................................................................................... 18
Figure -8. Basic Elliptical Orbit Geometry .............................................................. 0
Figure -. Earth-crossing Obit with Inclination........................................................
Figure -10. Typical Earth-crossing Orbit of Atens Asteroid Family ........................... 4
Figure -11. Typical Earth-approaching Orbit of Amor Asteroid Family ..................... 5
Figure -1. Typical Earth-approaching Orbit of Apollo Asteroid Family.................... 5
Figure -1. Mass Extinctions in the Geologic Record................................................ 4
Figure -. Dots Show Approximate Position of Known Impact Sites ...................... 5
Figure -. Approximate Time Scale of Life on Earth According to Fossil
Record ............................................................................................. 6
Figure -4. Theoretical Occurrence of Comet Storms as Calculated by
Weissman Using Monte-Carlo Analysis of Random Star and
Molecular Cloud Passages ................................................................ 8
Figure -5. Photo of a 0.75mm Shocked Quartz Grain from K/T Boundary
Clay at Teapot Dome, Wyoming. Clearly Shows Two Sets of
Planar Deformations ......................................................................... 45
Figure 4-1. Impact Geometry.................................................................................... 51.xiii
Figure 4-. Aten Asteroid-Earth Impact Example ..................................................... 5
Figure 4-. Typical Meteorite Debris Field................................................................ 61
Figure 4-4. Simulation of a Bolide Passing Through the Atmosphere ........................ 6
Figure 4-5. Function of Hypercane ........................................................................... 71
Figure 4-6. Meteoroid Energy .................................................................................. 76
Figure 4-7. A Comparison of the Energy Content of Man-Made and Meteor
Stream Debris. Bullet Energy Too Low to Show On Graph ............. 77
Figure 4-8. Spectrum of Natural Space Debris Effects .............................................. 8
Figure 5-1. Threat is a Product of Hazard and Risk................................................... 84
Figure 5-. Variables Affecting Threat Determination............................................... 85
Figure 5-. There is a Relationship Between Risk and Efforts People are
Willing to Make to Reduce or Control the Risk................................. 8
Figure 6-1. Crater and Lava Flows on Moon ............................................................ 5
Figure 6-. Number of Earth Crossing Asteroids by Size .......................................... 7
Figure 6-. Typical Intervals Between Impacts ......................................................... 8
Figure 6-4. Elements of the NSD Threat Model...................................................... 100
Figure 6-5. The Threat to Human Life For Various Impactor Sizes......................... 104
Figure 6-6. Conceptual NSD Threat Model ............................................................ 106
Figure 6-7. Probability of Satellite Collision with Meteoroid ................................... 11
Figure 6-8. Risk of Satellite Being Struck By Meteor ............................................. 116
Figure 6-. Notional NSD Threat Spectrum............................................................ 11
Figure 7-1. General Detection and Discrimination Process for an Optical
System............................................................................................ 15
Figure 7-. Magnitude Scale................................................................................... 16
Figure 7-. Orbit Geometry and Phase Angles for a Typical Apollo Asteroid .......... 17
Figure 7-4. Orbit Geometry and Phase Angles for a Typical Aten Asteroid ............. 18.xiv
Figure 7-5. Light Path for Asteroid Observed From Earth....................................... 1
Figure 7-6. Phase Laws of Three Representative Asteroids ..................................... 1
Figure 7-7. Lunar Phase Law.................................................................................. 1
Figure 7-8. Collision With a Typical Aten Asteroid, Showing Small Proper
Motion ........................................................................................... 141
Figure 7-. Geocentric Parallax of an Asteroid Seen From Earth............................. 14
Figure 7-10. Change In Asteroid’s Apparent Visual Magnitude Due to
Atmospheric Extinction .................................................................. 144
Figure 7-11. Basic Functional Layout of a Typical Newtonian Telescope System...... 147
Figure 7-1. Factors Governing Detection................................................................ 14
Figure 7-1. Image Placement on CCD..................................................................... 150
Figure 8-1. Contributions of Optical, IR and Radar Systems to Search Mission
in Terms of General Search Areas................................................... 157
Figure 8-. Objects Outside of Our Detection Sphere Will Not Be Found Until
Their Orbits Carry Them Within Range of the Instruments.............. 16
Figure 8-. Discovery Completeness For 1 km and Larger Earth-crossing
Objects (Hypothetical Whole Sky Survey) ...................................... 164
Figure 8-4. Geometry of Orbits Used to Determine Warning Time Indicator,
Asteroid Orbit Intersects Earth Orbit at Aphelion............................ 168
Figure 8-5. Geometry of Orbits Used to Determine Maximum Warning Time
Indicator, Asteroid Orbits Intersects Earth Orbit at Perihelion......... 16
Figure 8-6. The Maximum Warning Time an Instrument Can Provide Depends
On Its Limiting Magnitude and Object Diameter ............................. 171
Figure 8-7. Realistic Maximum Warning Times....................................................... 17
Figure 8-8. Percent of Objects Found in a 5 Year, Monthly Survey Using
Dark Sky and Standard Search Areas.............................................. 17
Figure 8-. Orbit Geometry Used to Bound IR Limiting Magnitude
Requirements.................................................................................. 181
Figure 8-10. IR Magnitude of Object in Position #1.................................................. 18.xv
Figure 8-11. IR Magnitude of Object in Position #.................................................. 18
Figure 8-1. Smallest Visible Object for a Given Instrument Limiting Magnitude...... 18
Figure 8-1. Efficient Search System Architecture With Centralized Control
Coordination Center ....................................................................... 18
Figure 8-14. GEODSS Site ...................................................................................... 1
Figure -1. Strategic Decision Sequence................................................................. 0
Figure -. Operational Command Relationships ....................................................
Figure -. Disaster Stages and Levels of Effort ..................................................... 4
Figure -4. Effort vs. Time for an NSD Disaster..................................................... 5
Figure 10-1. NSD Effect for Debris Less Than 56 Meters in Size.............................. 41
Figure 10-. Synergistic Effect of Multiple Mitigation Measures............................... 4
Figure 10-. Types of Joint Operation Planning ........................................................ 46.xvi
List of Equations
Formula Page
(1) .............................................................................................................................. 1
() .............................................................................................................................. 1
() .............................................................................................................................. 1
(4) .............................................................................................................................. 1
(5) .............................................................................................................................. 5
(6) .............................................................................................................................. 5
(7) .............................................................................................................................. 5
(8) .............................................................................................................................. 54
() .............................................................................................................................. 54
(10) .............................................................................................................................. 54
(11) .............................................................................................................................. 55
(1) .............................................................................................................................. 55
(1) .............................................................................................................................. 6
(14) .............................................................................................................................. 6
(15) .............................................................................................................................. 64
(16) .............................................................................................................................. 67
(17) .............................................................................................................................. 77
(18) .............................................................................................................................. 77
(1) ............................................................................................................................ 10
(0) ............................................................................................................................ 1
(1) ............................................................................................................................ 1
() ............................................................................................................................ 14
() ............................................................................................................................ 15
(4) ............................................................................................................................ 16
(5) ............................................................................................................................ 16
(6) ............................................................................................................................ 17
(7) ............................................................................................................................ 144
(8) ............................................................................................................................ 147
() ............................................................................................................................ 148
(0) ............................................................................................................................ 148
(1) ............................................................................................................................ 170
() ............................................................................................................................ 170
() ............................................................................................................................ 170
(4) ............................................................................................................................ 170
(5) ............................................................................................................................ 170
(6) ............................................................................................................................ 176.xvii
Abstract
The threat posed to Earth and Earth-orbiting spacecraft by natural space debris
(asteroids, comets and meteor streams) is examined in an effort to quantify the threat and
identify available, low cost mitigation measures. Our study found that the Earth resides in
a swarm of natural debris that consists of at least three families of asteroids (the Apollo,
Aten and Amor asteroids), several short-period comets and at least 11 active meteor
streams.
The results of recent studies regarding the risk of a significant asteroid or comet
impact on Earth are presented. Best estimates indicate the probability of a large impact
within the next century is about 1 chance in 10,000. Further, there is a much higher
probability of a smaller (Tunguska sized) impact sometime in the next century. The
myriad of potential impact effects are discussed in detail for various impactor sizes. The
threat that meteor storms pose to space-borne assets is also discussed. There has not been
a major meteor storm since 165, hence our modern space systems have never been
subjected to a severe storm. There is a very high probability that we will see an extremely
active storm from the Leonid stream around 17 November 1. We discuss the meteor
stream threat to our space systems (as an integrated network), and what we should do to
lessen the possibility of losing satellites in future meteor storms.
The natural space debris threat is real and mitigation measures should be
implemented. Before this can happen, the threat must be communicated. Problems
communicating the natural space debris threat are discussed using historical examples.
With these problems in mind, we offer suggestions to more clearly quantify and.xviii
communicate the threat to decision-makers in the future. The need for a better threat
model is discussed and the framework for an improved model is provided.
The need for an asteroid and comet search program is discussed, and basic search
system requirements are derived. Using these requirements, we evaluate the utility of
several existing and proposed systems. Then, the general architecture and approximate
cost of a suitable search program is presented. We estimate the program cost to be
$56.5M to $57M non-recurring, and $1.6M to $15.4M/yr for operations. A limited
search capability could be had for $1.5M to $0M non-recurring, and $10.6M/yr to
$1.4M/yr for operations. The need for meteor stream characterization and the
development of a storm warning capability is introduced, and a cost estimate presented.
To characterize all 11 active streams and develop a basic meteor storm warning capability
for our satellite programs will cost approximately $.M over eight years.
Given that the threat is real, we examine the roles and responsibilities of the US
military regarding the defense of Earth and our space assets from asteroids, comets and
meteor storms. Within the last 15 years, the military has responded to natural disasters
such as floods, hurricanes, earthquakes and volcanic eruptions. Based on existing policies,
and the historical role of the military in disaster response, we believe that the military has a
responsibility to address the natural space debris threat. Finally, several threat mitigation
measures are presented. Active measures such as the deflection or destruction of potential
impactors are briefly discussed. However, we recommend the search and planning
measures be given first priority. A summary of key recommendations is provided in the
final chapter..1
PLANETARY ASTEROID DEFENSE STUDY
ASSESSING AND RESPONDING TO THE NATURAL SPACE
DEBRIS THREAT
CHAPTER 1
Introduction
On 1 February 14 at 8 Universal Time, a piece of natural space debris
entered the Earth’s atmosphere just north of Kosrae island, off the coast of New Guinea.
Traveling at ~15 km/sec (,555 mph), it streaked across the sky toward the northwest
and exploded about 0 km above the sea, near the island of Tokelau, with a force of ~11
kilotons of TNT.
1
At its peak, the brightness exceeded magnitude -5 (similar to the
Sun).
The explosion triggered sensors on several US early warning satellites.
Fortunately, the blast occurred at high altitude and over a sparsely populated area; thus,
no damage was done.
On March 18, an asteroid about 800 meters (1/ mile) in diameter missed
Earth by about 6 hours.
4
If it had hit, the impact would have released energy equivalent to
about 40,000 Megatons of TNT or ,000 hydrogen bombs.
On 8 December 1, another asteroid, named Toutatis missed hitting the Earth by
about lunar distances.
5
Toutatis is nearly 4 km in diameter (.5 miles), more than twice
the size required to create a global catastrophe.
6
Its impact would release more energy
than all the nuclear weapons in existence, about million megatons..
These are just a few examples of the risks we face each day from Natural Space
Debris (NSD). While the probability of a large asteroid like Toutatis hitting us is relatively
low, it may not be as low as we have traditionally believed.
The Threat
In 18 the US Congress commissioned NASA to study the threat posed by Earth-orbit
crossing debris and investigate means of mitigating that threat. Christened the
“Spaceguard” study, a team of over one hundred of the top US and international scientists
participated. Their conclusion was that natural space debris does present a real (though
not eminent) threat to Earth and that some reasonable effort should be made to find,
catalog and track Earth-orbit crossing objects.
7
Further, they found that, if a large
asteroid were on a collision course with Earth, we now have the technology to deflect or
destroy it and prevent catastrophe.
Since the publication of the Spaceguard Survey report in 1, much work has
been done by scientists around the world to further define the risks presented by NSD. In
the following pages we will present our assessment of the risk based on the most current
data available and what should be done about it. We intend to assess the results of the
Spaceguard Survey and to use additional new information to better understand the threat
posed by NSD and investigate tools that the military, particularly the Air Force, may have
available to counter the threat.
Roles and Responsibilities of the United States Military Regarding NSD Defense
The US military’s role in providing domestic disaster relief is not a new one, but it
is indeed an ever-changing one. In the past, military assistance was simply welcomed;.
today it is expected. Further, there is growing pressure at all levels of government to
ensure designated agencies provide the necessary assistance and relief in a timely manner.
Our paper will discuss how evolving policy, doctrine and detailed preparedness planning
have all contributed to improving the military’s response to domestic emergencies. We
will also discuss several challenges and concerns that the military must address in order to
plan for, and respond to, a disaster resulting from an asteroid impact.
Our premise is that the hazard posed by natural space debris is much like that of
any other natural hazard. The military, particularly the Air Force, can’t afford to ignore
natural space debris and its potential for causing serious damage. In the last decade,
military units participated in relief operations stemming from volcanic eruptions,
earthquakes, hurricanes and floods. It seems only logical that national leaders and the
public will continue to look to the military for help in times of disaster. Thus, it follows
that the military must assume some degree of responsibility for NSD defense.
The necessity of planning for a domestic disaster resulting from natural space
debris has apparently never been seriously considered within the Air Force. The defense
of Earth from asteroid impact has, in the past, been considered both expensive and
unnecessary. Recent events, such as those presented above, combined with new data and
theories regarding the nature of the NSD threat, give reason to re-examine these issues.
Notes
1
“Satellites Detect Record Meteor,” Sky Telescope 11 (June 14).
Ibid.
Ibid..4
4
George E. Brown Jr., Chairman, House of Representatives, Committee on
Science, Space and Technology. “The Threat of Large Earth-Orbit Crossing Asteroids,”
Hearings before the House Sub-committee on Space on Results of Spaceguard Study. 4
March 1.
5
Corey S. Powell, “Asteroid Hunters,” Scientific American 4-40 (April 1).
6
Clark Chapman and David Morrison, “Impacts on the Earth by Asteroids and
Comets Assessing the Hazard,” Nature 67 5 (6 January 14).
7
David Morrison, Chairman of Asteroid Detection Workshop (Spaceguard
Study), NASA Ames Research Center. “Statement Given House of Representatives,
Committee on Science, Space and Technology, before the House Sub-committee on
Space. 4 March 1..5
CHAPTER
Natural Space Debris
Definition of Natural Space Debris (NSD)
Natural space debris, for the purposes of our discussion, consists of all naturally
occurring solid matter orbiting the Sun whose orbits intersect or share that of the Earth
from time to time, or might do so in the future. Thus, we are specifically excluding man-made
debris (i.e. objects orbiting the Earth or Sun placed in orbit by man). We are also
excluding natural debris in permanent orbit around the Earth since most of it is relatively
small and the quantity is fairly constant. While the Spaceguard study focused on objects
greater than 1 km in diameter, our discussions will include objects of all sizes; from the
smallest grain of sand to the 10 km diameter planet-busters.
1
Sources of Natural Space Debris
There are two major sources of natural space debris asteroids and comets. Both
are considered to be left-over material from the formation of the planets in our solar
system. Occasionally, these objects are perturbed by chaotic interaction with gravitational
fields of the Sun and planets into paths that cross Earth’s orbit.
Comets and asteroids are
not always very different. Both can occupy the same types of orbits as illustrated by the
fact that some of the Earth-crossing asteroids are actually burnt-out comets.
The primary
differences have to do with their composition and origins. As you’ll see in the following
discussion these differences have an effect on the detection problem..6
The Comets. A comet, unlike an asteroid, contains a large quantity of various
ices. Common ices would include materials such as water, methane, ammonia, carbon
dioxide, hydrogen and nitrogen.
4
The ices act as a glue to hold the comet together; thus
comets are often thought of as dirty snowballs containing a mixture of rock and metals all
held together in a frozen mass. As such they would be physically more fragile than an
asteroid made of solid rock (which is important if you want to deflect one). As they orbit
the Sun and the ices boil away, the core of the comet will be weakened. Over time, it will
lose all of its ices leaving only rock or metal. Because of this process, comets are
responsible for two magnificent astronomical displays the comet with its tail as seen in
Figure -1, and some well-known annual meteor showers.
The most visible difference between an asteroid and a comet is the tail. As a
comet approaches the Sun, solar radiation vaporizes the ices on the surface of the nucleus,
forming a luminous cloud around the nucleus called the coma which blends into the tail.
Source David Irizarry.
Figure -1. Artist Rendering of Comet With Tail.7
The tail always points away from the Sun since it is made up of vaporized material being
blown away from the nucleus by the solar wind. The length and brightness of the tail can
vary considerably since the ablation rate of the comet material varies with the composition
of the nucleus, distance from the Sun and orientation of the nucleus. As the comet passes
perihelion (closest approach to the Sun) it loses a lot of its ices and gravitational forces
will severely stress the nucleus. Eventually, due to loss of the ices, the comet will break
up, or it will lose so much material that it will no longer be capable of generating a bright
tail.
It’s the slow disintegration of a comet that produces many of our annual meteor
showers. As the ices in the nucleus warm and subsequently vaporize, they leave behind
the rock which is itself eventually ejected from the surface. Therefore, in the path of a
comet, clouds of debris begin to form. Over time, debris can become distributed (albeit
unevenly) around the orbit.
5
This effect is extremely important since these clouds of
debris form the streams that are the source for at least some of our annual meteor
showers. Streams will be discussed in more detail later.
The Origin of the Comets. The origin of comets is unknown. No one
has ever seen or irrefutably proven the existence of a single source of new cometary
debris; however, it seems certain a source does exist. Short-period comets can not survive
more than a few tens-of-thousands of years before the Sun boils away their ices. Thus, a
supply of comets must exist someplace in deep space where the Sun can not destroy them.
The most accepted theory today proposes the existence of a cloud of icy debris at the very
edge of the Sun’s gravitational influence. At this great distance, the accretion process that
created the planets some 4,800 million years ago did not happen. Material in the outer.8
reaches of the solar system combined with leftover debris ejected by the planets to form a
spherical cloud of debris around the solar system called the Oort cloud, which consists of
somewhere between 10
1
and 10
14
potential comets. Occasionally, for reasons not yet
fully understood, debris from this cloud (comets) are sent sunward where they may
eventually hit one of the planets.
Types of Comets. Comets are classified as either long, intermediate or
short period, where period is defined as the time it takes the comet to orbit the Sun.
Cometary orbits are often different than those of the asteroids. They are usually highly
elliptical and are often inclined at large angles to the orbit plane of the planets. The
significance is that, unlike the asteroids, comets could approach the Earth from almost any
direction and at very high velocity. Therefore, to find them you would have to
continuously survey the entire sky.
Table -1. Some Short-Period Comets and Their Orbital Periods
Comet Name Period
(years)
Encke .0
Schwassman-Wachmann 5.5
Giacobini-Zinner 6.5
Halley 76.0
Swift-Tuttle 11.60
Source Comets and Meteor Streams, Vol ,
Porter.
Short-period Comets. To simplify our discussion, we will combine the
traditional short and intermediate period comets into the category of Short-period comets.
Though called short-period comets, periods range from only a few years up to 00
hundred years. The number of short-period comets in our solar system is unknown but is.
believed to be on the order of 15,000 with a diameter greater than 100 meters.
6
The
number of these that are Earth-crossing is estimated to be about 10-0% of all short-period
comets or about ,000.
7
Unfortunately, only a small portion of these have been
discovered and have known orbits.
While the orbits of short-period comets are more stable than many in the long-period
class, their orbits are still subject to perturbations by the planets and collisions with
other minor solar system objects. Comet Shoemaker-Levy is a prime example of the
drastic orbit changes that can occur when a comet has a close encounter with one of the
planets. Some time ago, Shoemaker-Levy was captured by Jupiter where it orbited in a
highly elliptical orbit until 8 July 1 when Jupiter’s tidal forces tore it apart.
8
One orbit
later, on 16 July 14, pieces of the fragmented comet began colliding with Jupiter
sending fireballs rising out of Jupiter’s atmosphere and leaving dark scars that were visible
from small Earth-based telescopes.
A similar impact on Earth would be disastrous.
Source David A. Seal, Paul W. Chodas and Donald K. Yeomans of JPL.
Figure -. Artist Rendering of a Fragmented Shoemaker-Levy Impacting
Jupiter.10
Long-period Comets. Long-period comets consist of all comets with a
period greater than 00 years. As with the short-period comets, the number of long-period
comets is not known. Its likely that there are literally trillions in the solar system,
waiting in the Oort cloud. Approximately 700 are known to have passed through the
inner solar system and about half of them had Earth-crossing orbits.
10
The total
population of long-period comets is hard to characterize for two reasons. First, its
difficult to find and catalog them. Comets are most visible when they are close to the Sun.
The long-period comets will spend most of their time in deep space where very little Sun
light will reach them. Thus, most of the population is far enough out in space that we
can’t see them. Secondly, the orbits will be greatly affected by the outer planets,
especially Jupiter. For example, comet 110 I has a calculated period of ,10,000
Source NASA, Galileo Photo.
Figure -. Asteroid Ida (56 Km Long) and its Moon
(1 km Diameter).11
years.
11
Little credence should be placed in calculations of such an orbit since before it
can return to the inner solar system (assuming that it will return) it is likely that its orbit
will be perturbed. In fact, it will probably be difficult to recognize 110 I if it reappears
since its orbit may be changed so much that it would be indistinguishable from a new
comet. There are potentially many thousands of comets within the solar system with such
long periods that we will never be able to say with confidence that we know where they all
are. If only a fraction of these are Earth-crossing they could pose a significant risk.
The Asteroids. There are three very general groups of asteroids that need to be
addressed planet-crossing, main belt and extra-belt asteroids. Of these, the planet-crossing
bodies are of greatest concern since they frequently cross Earth’s orbit; thus they
offer the greatest probability of impact. The main belt and extra-belt bodies do not pose
an immanent threat since they stay well beyond Earth’s orbit; however, the chaotic
gravitational interaction between the planets and the asteroids may perturb them into
Earth-crossing orbits sometime in the future.
1
Table -. Titius-Bode Sequence Predicted Planet at .8 AU from Sun
Planet Series Titius Series
Value
Distance
From Sun in
AU
Mercury 0 0.4 0.
Venus 0.7 0.7
Earth 6 1.0 1.00
Mars 1 1.6 1.5
------- 4 .8 -------
Jupiter 48 5. 5.0
Saturn 6 .6 .54
Source Cosmic Impact, John K. Davies.1
Main Belt Asteroids. In 177, a German professor named Johann Daniel
Titius found an interesting mathematical relation between the sequence of numbers 0, ,
6, 1, 4, 48, 6 and the orbits of the planets.
1
Notice that in this series each number is
double the previous one (except for the second). If the number 4 is added to each number
in the series the resulting new series gives the ratios of the distances of the planets from
the Sun. If you define the distance from the Earth to the Sun as 1 Astronomical Unit
(AU) and divide by 10 the series gives the distance of each planet from the Sun in AU.
The series is nearly perfect for all planets through Uranus. The significance of this is that
Titius, and later a German Astronomer named Johann Bode, noticed that planets existed at
each of the predicted locations except .8 AU. The discovery of Uranus in 1781 by
William Herschel at almost exactly the orbit predicted by the Titius Series (mean orbital
distance from the Sun 1.6 AU) started a search for the missing planet at .8 AU.
1 4 6
Semi-Major Axis (AU)
Earth Jupiter
41 7. 1 5 7 1 5 4 11 Jovian Resonances
Atens
Apollos
Amors
Hungarias
Phocaea
Koronis
Trojans
Cybeles
Centarl Main Belt
Hildas
Kirkwood Gaps are Areas
Between Families at Resonance
Points. Not a Complete List.
Figure -4. Relative Locations of Some Families and the Kirkwood
Gaps.1
In 1801 an Italian astronomer Giuseppe Piazza accidentally discovered Ceres at
.77 AU. The search for the missing planet would probably have ended there; however
another astronomer named Heinrich Olbers found another object in the same area. The
object was named Pallas; the second body in a region that has come to be known as the
asteroid belt. For reasons that are still not clearly understood the region between Mars
and Jupiter contains many planetesimals rather than a single planet. The most accepted
explanation is that the gravitational field of Jupiter created a disturbance that prevented
the debris from coming together to form a planet.
14
Further study has shown that the belt itself isn’t just a random collection of
objects. There’s a definite structure which was discovered by Daniel Kirkwood in 1857.
He showed that, within the belt, there were no asteroids with an orbital period equal to an
even fraction of Jupiter’s period.
15
He explained this by saying that all objects in the belt
receive a gravitational “tug” by Jupiter. For most of the objects, this tug occurs at
different places in their orbits so the effects cancel out. For those with a period equal to a
fraction of Jupiter’s orbit, they receive the tug at the same place each time; so, these
objects will eventually be ejected into a new orbit. Thus, the Kirkwood gaps represent
unstable regions referred to as resonances. Any object in or very near one of these
regions is will be ejected by Jupiter. A small disturbance, such as a collision by another
asteroid, could perturb such an object enough to send it into a new orbit possibly ejecting
it from the main belt entirely. This is at least a small part of a larger process which is
apparently resupplying the Earth-crossing asteroid complex.
16
Extra-Belt Asteroids. In 118, K. Hirayama put forth the theory that
clumpings of asteroids are related in that they could have formed as a result of the.14
breakup of a larger parent body by catastrophic collision.
17
He called these clusters of
asteroids families. A partial listing of these families and their approximate semi-major
orbit axes is shown in Table -. There is much discussion about the nature of asteroid
families, their boundaries and the membership of certain objects.
18
For the purposes of
this paper we use the term very loosely to refer to existing clusters of asteroids in similar
orbits in order to convey the general distribution of asteroids in the solar system rather
than their origins in terms of parent bodies. In other words, we do not claim that the
objects in a particular family all came from the break-up of a single larger object. They
only have similar orbits. As can be seen from Table -, asteroids are not limited to the
main belt. There are families of asteroids outside the main belt as well as a few that can
cross Earth orbit.
Source Artist, Joe Legeckis.
Figure -5. Artist Rendering of Asteroids
Approaching a Planet.15
Table -. Major Asteroid Families and Groups
Major
Asteroid
Orbital
Families and
Groups
Location Approximate
Semi-Major
Axis of Orbit
(AU)
Earth
Crossing
Orbit At
Present ?
Atens These asteroids orbit inside
Earth’s Orbit. Their
aphelion distance is
approximately 1 AU.
1.0 Yes
Apollos These asteroids have
aphelion’s in the asteroid
belt (though there are
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