Chapter 3
Planetary Defense System (cont Part B)

Command, Control, Communications, and Computers, and Intelligence Subsystems

The defense of the Earth-Moon system requires a global outlook, in spite of limitations in international cooperation. Leadership of a planetary defense program is a critical issue which must be established both nationally and globally. However some nations may possess the capability to unilaterally defend the planet, their own territory, or the territory of selected allies. This paper suggests a possible leadership framework. This section presents a command and control system based on that proposed framework. Command and control of a system of systems to detect and mitigate ECO threats poses many challenges-especially command relationships among international organizations.

Unilateral US Command Elements

By 2025 the United States could certainly possess the capability to defend the planet either through an expedient, ad hoc effort or through a deliberately planned, funded, and coordinated program. With either possibility the US could take the lead by default or by its own initiative. The proposed command structure will allow the United States to unilaterally lead and execute the effective detection and mitigation of an ECO threat (fig. 3-3).
 

Figure 3-3. Proposed Unilateral US Command Structure

The National Command Authority (NCA) would oversee the efforts of the primary players in the PDS and coordinate their activities. This coordination would take place through a new entity, the Planetary Defense Coordination Council (PDCC). The PDCC would in turn work with the European Space Agency and the Council of International Cooperation in the Study and Utilization of Outer Space-European Agencies with similar interests and capabilities. Although American private industry and academia are not subject to the strict command relationships of federal bureaucracies, during a time of global crisis they would likely adhere to the direction of the NCA-much in the same way they did during World War II--by banding together to combat a threat to all Americans and possibly to all other humanity.

International Command Elements

The alternate futures developed for the 2025 study pose varying degrees of global leadership; that is, the role of the United Nations varies greatly with the alternate future. This section assumes that the UN has no strict governmental authority-only its mandate over its member nations. This situation is similar to what exists in 1996. In that light, no nation has subjugated its sovereignty to the UN. So with respect to the world powers, the UN acts with little higher authority. There is no hierarchical structure. But regional organizations such as the European Union will have increased clout as some European nations will have banded together for increased influence. Other possibilities include regional alliances in other areas of the world, including Africa, Asia, and the Middle East. Countries in these areas may form coalitions to increase their political, economic, and military power.

Command Responsibilities-US Unilateral Action

With respect to planetary defense in 2025, there will be no official global government power to unilaterally organize, develop, deploy, and operate a planetary defense system. The planet will be forced to rely on voluntary cooperation of countries for defense against ECO impacts. But under the threat of such a catastrophe, the cooperation among nations to the decisions of the United Nations probably would run akin to the cooperation of American academia and private industry to decisions of the National Command Authority. An ECO could bring together and coalesce the nations of the world under one authority for the common good.

C4I for Detection Subsystems

Three entities would hold primary responsibility for detection of ECOs: international observatories (generally managed by academia in coordination with government), the US Air Force, and NASA. During normal times, these entities would conduct operations without requiring significant outside direction. Should an emergency posture be required due to a possible ECO impact, sites would coordinate their efforts under the direction of the US National Command Authority or UN as appropriate.

C4I for Mitigation Subsystems

Two US governmental departments would be responsible for mitigating an ECO threat: the Departments of Defense and Energy. Depending on the mitigation strategy, the NCA would direct either or both of these organizations to engage the ECO as described in the mitigation sections.

Research and Development

Research and development would fall into various realms. Specifically, the DOD and DOE would perform their own organic research but also contract out to academia and private industry for inputs. In addition, technological advances developed independent of the planetary defense initiative would be incorporated into the effort.

Exploration

Responsibility for physical exploration of space has fallen primarily into the lap of NASA and its association with academia. Manned occupation of space has been a responsibility primarily of NASA. Unmanned occupation of space has spread from NASA to the Department of Defense (and the National Reconnaissance Office) and rapidly to private industry (commercial satellites). There will be a growing trend towards the civilianization and privatization of space. But for the US unilateral defense of the planet, the federal government will continue to carry the lead for space exploration.

Exploitation

Private industry will retain its role as the primary exploiter of space. But governmental development of exploitation technologies will be critical. Moon-based manufacturing and mining for federally sponsored space occupation will fuel a growing trend of the private exploitation of space. Private industry will find uses for space resources or unoccupied expanses for its own use. These technologies will be directly applicable to the exploitation of ECOs. With the development of such technologies, ECOs will become attractive sources for minerals and other valuable resources.

Command Relationships/Connectivity

Command relationships and connectivity among units within the PDS subsystems have unique requirements to consider. The detection systems operated by USAF, academia (observatories), and NASA will all be tied into Space Command headquarters rapidly providing information on ECOs. These detection systems then cross check each other to determine the accuracy of the observation and its resulting prediction.

Detection groups share information on asteroids in a centralized database, storing asteroid orbit, composition, and proximity data. Private industry would then be able to determine which bodies to seek and potentially exploit.

For the mitigation systems, connectivity is not as complicated as for the detection systems. Commander in Chief, US Space Command, would posses the responsibility to engage ECOs under direction from the NCA. From a military planning standpoint, commander-in-chief, United States Space Command would periodically perform a deliberate planning process to establish a plan to engage a ECO. The CINC's cosmic area of responsibility possesses few threats other than ECOs, and prudence dictates establishment of an operations plan to defend against potential ECO impacts. This plan would include the mitigation options described later.

Communications

Communication among the players who study the potential threat that ECOs pose is growing. In 1996 the detection system is loosely and informally integrated through the Internet. The earth's sentries scan small portions of the skies at a time and deposit their data on the Internet for other sentries to verify. Their techniques are rather basic and heavily dependent on computing power. An appropriate analogy here is the air defense network employed by the British during the Battle of Britain. Many observers deployed along the coast of the English Channel scanned the skies for formations of German planes and, once detecting them, identified their size and composition. These forward observers relayed their information to the centralized command centers where their information would be integrated into the big picture with radar and other observations.73 So those who scan space for ECOs would benefit greatly from an improved communication network.

In 2025 the communication links among observatories will be well-meshed to cross feed and up-channel ECO data. Speed of data transfer is not a critical technology, and current capabilities are adequate to perform this function. But the integration of this information is what is lacking in 1996. Currently no person or agency officially possesses the chartered job to collect, analyze, and disseminate all ECO data. In 2025 a system to collect and analyze the data provided by the observatories will be essential. This becomes less of a technology issue than a functional, command and control issue. In 2025 that responsibility could fall on CINCUSSPACECOM.

Communications between command facilities and space vehicles may greatly benefit from technological advances. The concept describing faster-than-light communications (currently thought to be beyond current understanding of physics) is one which would benefit, though is not necessary for, mitigation systems that must physically intercept the ECO.74 Instantaneous communications between the earth and the space vehicle would facilitate endgame decision making-where and how to engage the ECO, for example. Not having to enlarge the space vehicle with computer hardware containing preprogrammed or automated engagement phase capabilities will allow larger payloads, faster engagement speeds, and farther engagement distances. The faster-than-light communications concept hinges on a concept of the conservation of quantum properties. If the sender alters the quantum properties of his transmitter, the receiver instantaneously is altered to compensate for the change in quantum properties.

Additionally, very high rate (gigabyte per second) communications for data relay would greatly benefit deep space control of intercept vehicles. Combined, these two concepts of high-speed and high-rate communications could have far-reaching effects.

Computers

Probably the biggest area in which great strides can be made is in the computer processing of observation data. The degree volume of space scanned is limited by scan resolution and processing capability. Faster computers coupled to more capable telescopic devices allow larger sky volumes to be searched for ECOs. Comparing new scans with archive scans at resolutions required for early detection of ECOs requires rapid database management tools and sophisticated analysis programs. In 1996 the shift from photographic to digitized techniques is almost complete. By 2025 the expansion of archive data and advances towards finer scan resolutions will make detection of ECOs far more complete and accurate.

Improved computing capabilities is also important in the astrometry realm. Astrometry currently relies upon optical and radar for the follow-up tracking that permits refinement of the orbit necessary to identify an ECO. With better orbit-calculating models that account for orbit perturbations induced by planetary gravity (e.g., by Jupiter) and with better computing power (e.g., more significant digits), orbits can be predicted more accurately and farther into the future than with current systems. The orbital chaos contributed by Jupiter's gravitational pull to the mechanical calculations can be minimized by better modeling and greater computational power. Also, in 2025 we anticipate a combination of ground- and space-based remote sensing devices for astrometric calculations. On the ground there likely would be optical (telescope) and radar devices; in the air there would likely be optical (Hubble-like) telescopes, radar, radio array, infrared, LIDAR, and LADAR sensors.

Finally, as the database of main belt asteroids grows, data management becomes critical. Keeping track of hundreds of thousands of asteroids and comets calls for improved computing power, faster processing, and larger memory. Fortunately, this power appears to be achievable in time.

As chip technology improves, memory capacity surpasses the 1 gigabyte threshold, providing an enormous capacity to store huge amounts of data. But along with these advances, the chips and their ability to perform becomes more susceptible to space radiation. Space vehicles using these advanced chips will require hardening from cosmic radiation.75

Intelligence

Much intelligence is required regarding NEOs, but relatively little is presently known. This intelligence becomes vitally important to decide which mitigation system(s) can best be used against them and to predict the probability of mitigation success.

Specific intelligence necessary for all NEOs includes, but is not limited to, individual physical shape, size, mass, structure, surface and interior material compositions, brittleness, terrain, velocity, and inherent motion (e.g. spinning or wobbling). Specific intelligence necessary for targeted ECOs includes the aforementioned properties and particular weak points and maybe landing sites.

Several satellites have been used to perform NEO flybys, either as primary or secondary missions. Much data has been obtained; however, there is much more to be gained. The recently launched Near Earth Asteroid Rendezvous (NEAR) satellite will rendezvous with an asteroid to characterize its physical and geological properties (elemental and mineralogical composition, density, shape, spin state, interior structure, and surface morphology).76 Other planned satellite missions include Clementine II; a comet rendezvous mission by ROSETTA--a European Space Agency program; Imaging of Near Earth Objects (INEO)--an NEO flyby mission by the German Center of Applied Space Technology and Microgravity; and a yet-to-be-named near-earth asteroid rendezvous mission by the Japanese Institute of Space and Astronomical Science (ISAS).

Clementine II is a congressionally directed technology demonstration satellite designed to test state-of-the-art sensors, components, and subsystems in the deep-space environment. Presently, the directed baseline mission is to fly by three near-earth asteroids (NEA) in quick succession. Several hours prior to the NEA flyby, a small (less than 20 kilograms) probe will be released from the mothership and directed to intercept the asteroid using onboard autonomous navigation techniques.77

The planned ISAS satellite will map the surface and hover within one foot of an asteroid.78 These and other missions are of critical importance if our mitigation systems are to be designed to work effectively. Other missions are suggested by various authors.79

C4I Summary

Table 5 summarizes the technical hurdles that must be overcome to implement the ideas outlined in this section effectively. Overall, there are few showstoppers that prevent the implementation of a workable C4I planetary defense subsystem. Cost of the C4I subsystem is relatively low. Current systems and capabilities are nearly sufficient to perform the mission.

Table 5 - C4I Subsystem Characteristics

System
 Tech
 ECO Scenario

Application*
 Risk Level
 Problems
 Maintenance
 
C2 for Detection Systems
 Now to 2025+
 1,2,3,4
 Low
 Large volume of sky to scan.
 Low-Med
 
C2 for Mitigation Systems
 Now to 2025+
 1,2,3,4
 Low
 High-speed intercept of ECO
 Low-Med
 
High-Speed, High- Memory Computers
 Now to 2025+
 1,2,3,4
 Low
 Requires precise calculation of ECO orbits
 Low-Med
 
Communicat-ions
 Now
 1,2,3,4
 Low
 Relatively few
 Low-Med
 
Intelligence- gathering sensors,

systems
 Now to 2025+
 1,2,3,4
 Low
 Requires detailed knowledge of ECO properties
 Low-Med
 

* ECO Scenarios 1-4 are described in Table 3.
 

Chapter 3
Planetary Defense System (cont Part C)

Mitigation Subsystems

Potential mitigation subsystems are as numerous as there are science fiction novels, ranging from near-current capability to the near impossible. Mitigation subsystems typically fall into two categories--those that destroy the ECO to the point where it is no longer a hazard and those that deflect the ECO such that it would not impact the EMS. Primary factors affecting the suitability of the mitigation subsystem are the distance at which engagement with the ECO is desired, shape, size, composition, and inherent motion (e.g., spin) of the ECO. (Note: These "primary factors" will be mentioned several times in our discussion.) Popular potential mitigation subsystems addressed by current literature include, but are certainly not limited to, rocket propulsion systems; rockets with chemical, nuclear, or antimatter warheads; kinetic energy systems; high-energy lasers; microwave energy systems; mass drivers/reaction engines; solar sails; and solar collectors as shown in figure 3-4.
 

Legend: a. Rocket Propulsion; b. Rocket-Delivered Chemical/Nuclear/Antimatter Warheads; c. Kinetic Energy; d. Directed Energy; e. Mass Driver; f. Solar Sail

Figure 3-4. Potential Mitigation Subsystems

In addition, we propose several new ideas, including biological/chemical/mechanical ECO eaters, supermagnetic field generators, force shields, tractor beams and gravity manipulation (fig. 3-5).
 

Legend: a. Biological, Chemical, Mechanical ECO Eaters; b. Supermagnetic Field Generators; c. Force Shields; d. Tractor Beams; e. Gravity Manipulation

Figure 3-5. New Potential Mitigation Subsystems

Table 6 summarizes the aforementioned mitigation systems according to technology, ECO scenario applicability, risk, potential problems, required maintenance, and cost. Evaluations are provided by the authors based on their limited knowledge of the potential systems at the present time, similar evaluations provided in various literature, and likely availability by 2025.80 Costs do not reflect added cost to transfer systems into space (other than rocket-based systems) or manned operations to assemble or operate systems in space unless otherwise noted. Maintenance requirements and estimated cost for some systems are not provided because they are too far beyond current technologies to provide this data.

Rocket propulsion systems could be employed directly to guide an ECO out of its EMS-crossing orbit. Further, many of the subsequently discussed defense systems require delivery to or near the ECO and thus would require a space lift system to get them there. A variety of propulsion systems including, but not limited to, chemical, nuclear, antimatter, laser pulse detonators, ion-electricity, spark gun, super orion, DHe3 fusion drivers, and magnetohydrodynamics have been proposed by various authors.81 These systems range from current capability to possible capability by 2025. (It is not the intent of this paper to discuss the variety of propulsion systems in detail, as they are a topic of many other studies.) The main problem with the direct method would involve attaching the rockets to the ECO. Range is a relatively simple scale-up problem for existing propulsion systems or a change to advanced propulsion systems. Intercept capability has been improved for missile systems recently primarily due to research in strategic defense initiative (SDI) and theater missile defense (TMD). Safety issues for launching larger rockets and some of the advanced propulsion systems must be considered. Development costs are estimated to range from $5 to $20 billion.82

Table 6- ECO Mitigation Systems

System
 Tech
 ECO Scenario
Application*
 Risk Level
 Problems
 Maintenance
 Cost in Billion
(dollars)
 
Propulsion
 Now to
2025+
 1,2,3,4
 Low-High
 Safety
 Low-High
 5-20
 
Nuclear/
Chemical/
Antimatter
Explosives
 Now/
Now/
2025+
 1,2,3,4
 Medium/
Low/
High
 Space Treaties,
ECO Breakup/
Efficiency, Storage
 Low/
Low/
High
 1+
1+
10+
 
Kinetic
Energy
 Now
 1,2,3,4
 High
 Long lead,
ECO Breakup
 Low
 10+
 
Laser
 2005
 1,2,3
 Low
 ABM Treaty, High
power
requirements
 Medium
 10-20
 
Microwaves
 2015
 1,2,3
 Low
 System size, power
requirements
 High
 20+
 
Mass Driver/
Reaction
Engine
 2015
 1,2
 Low
 May requrie
Manned assembly
 Medium
 5+
 
Solar Sails
 2025
 1,2,3
 Low
 May require
Manned assembly
 Medium
 1+
 
Solar
Collectors
 2025
 1,2,3
 Low
 May require
Manned assembly
 Medium
 5+
 
ECO Eaters
 2025
 1,2
 Low
 Slow. Quantities
required
 None
 1+
 
Magnetic
Field
 2025+
 1,2,3
 Low
 High-power
requirements
 TBD
 TBD
 
Force Shield
 2020
 1,2,3,4
 Low
 Environmental
effects
 Low
 TBD
 
Tractor Beam
 2025+
 1,2,3,4
 Low
 Undeveloped
technology
 TBD
 TBD
 
Gravity
Manipulator
 2025+
 1,2
 Low
 Undeveloped
technology
 TBD
 TBD
 

* ECO Scenarios 1-4 are described in Table 3.

Rockets employing chemical (conventional) or nuclear warheads already exist. They fall short, however, in terms of range, megatonnage of yield, and ECO intercept capability. Many scientists believe that nuclear weapons systems are currently the only feasible method for planetary defense for most situations, and much analysis and research has gone into the subject. Depending on the primary factors, the rocket(s) would be launched to deflect the ECO that it would not impact the earth or to fracture the ECO into sufficiently small pieces. The rockets may be earth- or space-based. Actual employment of the weapon system would involve either a single or multiple proximal burst(s), surface burst(s) or subsurface burst(s). In general, in the deflection mode, proximal bursts minimize the potential danger of fragmentation of the ECO but at a penalty of greater required yield when compared to surface or subsurface bursts. Surface bursts could be used to deflect or destroy the ECO. Subsurface bursts would be used only to fragment the ECO. Table 7 lists the required nuclear explosive yields necessary to perturb the velocity of various size asteroids by 1 centimeter per second (sufficient time if a decade is available to achieve deflection), or, in the case of subsurface bursts, to fragment the asteroid into pieces less than 10 meters in diameter, as estimated by T. J. Ahrens and A. W. Harris.83

V.A. Simonenko et al. estimate a 1 MEGATON nuclear charge detonated on the surface can deflect a 300 meter 'astral assailant' if it is engaged at a distance about equal to the earth's orbital radius.84 Roderick Hyde et al. estimate that hundreds of gigatons of energy will be required to deflect an asteroid of 10 kilometers by about 10 meters a second at a time greater than two week's distance from earth.85

Table 7 - Nuclear Charges Required for Various Asteroid Employment Scenarios

Asteroid
Size
 Proximal
Burst (with
radiative
efficiency of
0.3-0.03)
 Surface
(with
radiative
nuclear
charges*)
 Subsurface
(optimally
buried charges)
 Subsurface -
soft rock
(optimally buried
charges)
 Subsurface -
hard rock
(optimally buried
charges)
 
0.1 km
 0.1-1 kt
 500 kg
 800 kg
 1 kt
 3 kt
 
1 km
 100 kt-1 mt
 90 kt
 22 kt
 1 mt
 3 mt
 
10 km
 100 mt-1 gt
 200 mt
 0.6 gt
 1 gt
 3 gt
 

* Based on extreme extrapolation of the effect of gravity on gravity dependent cratering.

Other scientists have done similar work.86 Table 8 provides necessary payload mass to be delivered for required nuclear yields.87 Note that we have extrapolated the mass required for 1,000 megaton yield.

Table 8 - Yield Versus Mass for Nuclear Explosive Devices

Yield
 Mass
 
1 mt
 0.5 ton
 
10 mt
 3-4 ton
 
100 mt
 20-25 ton
 
1000 mt (1 gt)
 120-150 ton
 

Additional megatonnage is a relatively simple scale-up problem. Safety concerns exist. Though improbable, any accident with a nuclear weapon of the size to be used, particularly during launch, obviously could be catastrophic. Technically, developing and deploying such a nuclear system is possible now at an estimated cost of $1+ billion.88 Use of antimatter or other warheads, such as the proposed concept of a high-explosive driven particle beam warhead, is technologically not likely to be available until beyond 2025.89 Estimated costs for antimatter warhead systems exceed $10 billion.90

Kinetic energy systems would use the mass and velocity of a projectile to either shatter the ECO into smaller pieces or redirect its path. Projectiles must be of sufficient energy and size to do the job. Projectiles would be a rocket, rocket-powered object, or, as a bizarre twist, even another asteroid. The major problem associated with this system is the relatively large mass of projectile required to be propelled at the ECO. Heavy spacelift systems would be required. Figure 3-6 describes the capability of 1-, 10-, and 100-meter-diameter projectiles.91 According to J. C. Solem and C. M. Snell, kinetic energy deflection is practical only for ECOs of 100 m or less in diameter for the case of terminal intercept of less than one orbital period warning; furthermore, it may be an effective method for ocean diversion of rocky asteroids smaller than 70 meters in diameter if the interceptor encounters the ECO at a distance of greater than 1/30 AU.92 Ahrens and Harris agree that it is feasible to deflect 100 meter ECOs by way of direct impact.93 Another variation of the kinetic energy solution would be to use a system of small penetrators, arranged in lattice fashion, and placed in the path of the ECO which would use the kinetic energy of the ECO against itself.94 Costs of kinetic energy systems are estimated to exceed $10 billion.95 At first glance, high-energy lasers would appear to be a feasible defense system against ECOs, especially prior to 2025, at the current rate of laser development. Laser systems, however, are currently limited by extreme size, expense, and atmospheric beam divergence.96 A sufficient ground-based or space-based laser would offer the shortest response times to the ECO threat.
 

(Note: The three lines represent impacts by projectiles of 100, 10, and 1 meters in diameter and show how large an asteroid may be deflected from a collision with the earth as a function of the time elapsed between the impact on the asteroid and the predicted collision with earth)

Figure 3-6. Capability of Kinetic Energy Deflectors

A laser deflection system based near the Earth or Moon is well suited to the deflection of small bodies (100-200 meters in diameter) which are more difficult to detect at large distances from Earth.97 Employment depends on the primary factors, especially the composition of the ECO, but regardless of composition, the laser would have to either cut the ECO into smaller pieces, heat it up until it explodes from internal pressure, melt it, or deflect it by imparting impulse energy on it. The latter option appears to be the most feasible. The required power for a system capable to accomplish such feats may be well beyond current capability, especially at the ranges at which the system must work if the system is earth-based. B. P. Shafer et al. estimate that an earth-based laser beam output necessary to match the energy of a 1 megaton nuclear blast (deflection mode) is roughly 1 gigajoule(s) for an uninterrupted period of 12 days, neglecting beam losses.98 Such a laser would require relatively enormous optics, but innovative large optics technologies are currently being investigated, such as 20+ meter thin film mirrors and other techniques. New technology phase conjugation correctors, shorter wavelengths, more accurate pointing and tracking techniques will also increase the feasibility of such systems.99 Longer radiation times or a more powerful laser would be required to account for beam losses. Space-based systems may reduce required optics size and beam losses and thus the power required, but these advantages may be offset by the cost associated with delivering and maintaining such systems in space. Development costs for an earth- or space-based system are estimated to range from $10 to $20 billion.100

Microwave energy systems are similar to lasers in that they are also directed energy systems. Phased array antennas would be used to focus microwave beams which would then deflect the ECO by, depending on the composition of the ECO, heating the surface or subsurface, resulting in reaction to the resultant expanding vapor plumes. Narrow band systems have a long way to go to achieve power required, but introduction of new materials is expected to improve high-voltage performance, cathode emission, and pulse lengths.101 Ultra-wide band (UWB) class systems with greater power capability are current technology, but the energy flux delivered is not concentrated enough. A UWB source capable of delivering 25 gigawatts (gW) of peak power has been demonstrated, a 100 gW pulser will be demonstrated within the year, and a terawatt machine is on the drawing board.102 The likely limiting factor of these systems is the massive antenna arrays that would be required. To focus microwaves on a spot 100 meters in radius at a distance of only .003 AU requires a phased array 160 kilometers in diameter. The total radiated power would require 10 gW for energy fluxes on the asteroid to reach 106 Wm-2, which would lead to sufficient deflection.103 To deflect ECOs greater than 100-200 meters in diameter, the system would likely have to be space-based. Estimated development costs exceed $20 billion.104

A mass driver and reaction engine requires interfacing with the ECO in such a manner that it can be anchored to the surface. Reaction mass must be removed from the ECO then propelled into space in the required direction, resulting in a propulsive effect in the opposite direction. Since the thrust to be developed is proportional to the mass removal rate and the ejection velocity, a power plant able to provide sufficient energy (estimated at 300m/s) is required; a nuclear plant or a solar energy plant would suffice.105 Figure 3-7 depicts the capability of a mass driver using a solar energy plant operating at a realistic 10 percent efficiency with solar collectors of 1 and 10 kilometers in diameter at a distance of 1 AU from the ECO.106 This system is favorable for ECOs at greater distances, which allow for greater time to influence. The mass driver system itself is within current technology. The long pole in this system appears to be the ability to rendezvous with the ECO, attaching the mass driver and ejecting the mass in the desired direction. This would be especially difficult if the ECO has an unstable surface or any inherent motion such as a spin. Manned installation and operation may be required. Estimated development costs exceed $5 billion.107
 

(Note: The mass driver is categorized by the diameter of a solar collector (at 1 AU) needed to supply operating power at 10 percent overall efficiency. The lines for 1 and 10 km diameter circular collectors show that modest-size systems may be capable of diverting asteroids in the 1 to 10 kilometer range.)

Figure 3-7. Capability of Mass Drivers

Solar sails would be employed in a manner similar to a sail on a sailboat or a paraglider using solar radiation as "wind." The required sail sizes are enormous even to deflect relatively small ECOs (fig. 3-8).108 Further, solar sails would have to be attached to the ECO, and manned assembly likely would be required. Though this system probably has the lowest risk and would be the most environmentally friendly, the space construction effort is likely beyond our capability for at least several decades or more. The estimated cost for developing solar sails is $1-2 billion.109
 

(Note: The three lines are for different solar sail diameters. Even small asteroids require enormous solar sails (10 - 1,000 km in diameter) which, along with the technical difficulty of tethering them to the asteroid, makes such a deflection system look very unfavorable.)

Figure 3-8. Capability of Solar Sails

Solar collectors would use solar sails as a solar energy collector, focus light onto the surface of the ECO with a secondary mirror, and generate thrust on the ECO from the vaporization of the ECO. It is estimated that a solar collector of 1 kilometer in diameter could deflect ECOs up to 3.4 km if continuously operated for a year.110 Figure 3-9 summarizes the capabilities of solar collectors.111 Solar collectors suffer from similar problems as the solar sail system, though also require additional hardware. Manned assembly and operation also would likely be required. Costs for development of the system are estimated to exceed $5 billion.112
 

(Note: This plot shows the diameter of the asteroid (or comet) that can be deflected as a function of the time before impact. The pairs of solid and dashed lines are for silicate and icy bodies, respectively, that can be deflected by either 1 km or 10 km diameter solar collectors. The heavy dotted curve with representative points is for the nuclear stand-off scenario employing a 0.1 gt neutron bomb with an [optimistic] assumed conversion of 0.3 into neutron energy.)

Figure 3-9. Asteroid deflection capabilities of solar collectors versus nuclear weapons.

Biological/chemical/mechanical ECO eaters, as the name suggests, would "eat" ECOs.113 Since this would likely be a slow process, all primary factors must be considered, but the composition of the ECO is most important, as these systems would only work on particular compositions. Biological/chemical/mechanical eaters would have to digest or react with the ECO material in such a manner to produce primarily a gas which would result in a net loss of mass of the ECO, or to fracture the ECO into smaller pieces, or to make the ECO more susceptible to destruction by the earth's atmosphere. The mechanical eater would have to fracture the ECO or to make the ECO more susceptible to destruction by the earth's atmosphere. These types of systems may have more success on comets, which are known to contain large amounts of ice. Stony/metallic asteroids would be more difficult to attack but not impossible. The biological and chemical agents are not envisioned to be exotic, and some related research has been done for other purposes. A related, though more unlikely proposed concept, is a chemical morphing system, which would change the physical characteristics of material.114 These systems would have to be deposited on the surface of an ECO in sufficient quantities to have an effect on them. This would probably require heavy spacelift system with the chemical/biological agent as the payload/warhead. The mechanical systems may have to be more complex. Self- replicating mechanical systems have been envisioned.115 There may be safety issues associated with accidental release of potentially toxic or otherwise dangerous biological/chemical eaters. Cost estimates are unavailable.

Supermagnetic field generators could be effective against iron containing ECOs, though ineffective against comets. In its simplest terms, this system would be a magnet in space activated to attract or repel an ECO out of its orbit. The system could be based on the moon, or it could be a stand-alone satellite system or even deployed on a "captured" asteroid. Potential electromagnetic interference with earth-based electrical systems or satellites systems and environmental damage on the earth may further reduce the utility of such a system close to earth. The required power and likely bulk of such a system make it unrealistic at the present time. Heavy space lift may be required. No research was discovered regarding such a system. The idea is presented for further investigation. Estimated costs are unavailable.

Star Trekian force shields are a figment of our imagination, but if perfected they would be the ideal system against ECOs. We currently have a pseudo force shield for the earth-our atmosphere-effective enough to repel or destroy ECOs up to about 50 m (stony asteroids) and 100 meters (comets) in diameter.116 We are concerned with ECOs of larger size. Perhaps temporarily augmenting our atmosphere by changing its characteristics or extending it out further would enable us to mitigate larger ECOs. (Once again the concept of chemical morphing may apply.) Ionizing a path in the atmosphere to an asteroid may induce destructive lightning strikes, though the effects are debatable. If we can cause holes in the ozone, we ought to be able to do similar things in reverse. Potential effects on the earth's environment would be of great concern. No dedicated research was discovered for such a system. The ideas are presented for further investigation. Development costs are unknown.

A tractor beam is a system common in science fiction stories, but an equivalent system may not have to be limited to fiction. The similar system would create a vacuum greater than that of space or implosion rather than explosion to move the ECO out of its orbit. No research was discovered regarding such a system. In general, it is beyond the present understanding of physics. The idea is presented for further investigation. Estimated costs are unavailable.

Similar to a tractor beam is a gravity manipulator. If we can manipulate, or somehow take advantage of the gravity of the Earth, the Moon, or other celestial bodies such as black holes (with enormous gravitational fields), we can perhaps affect the orbit of an ECO.117 A captured asteroid of sufficient mass could be steered to a position where its gravitational pull could be used against ECOs. No research was discovered regarding such a system. In general, it is beyond the present understanding of physics. The idea is presented for further investigation. Estimated costs are unavailable.

Concept of Operations-A Three-Tier System

To defend the EMS from ECOs, our concept of operations proposes a three-tier PDS to be deployed by 2025. The far tier would be forward deployed in or above the asteroid belt, the midtier deployed somewhere between the asteroid belt and the EMS, and the near tier deployed within the EMS (Earth, Moon, or space-based). Each tier would have overlapping ranges and capabilities. Such a system would allow us to mitigate all four ECO scenarios. Further, with such a system, we would have maximum warning times, the ability to intervene at the earliest possible times, and, in some cases, the ability to reengage the ECO should the far and/or mid tier(s) fail. Finally, such a system would take advantage of the best available subsystems for each tier. Table 9 summarizes our proposed three-tier PDS based on expected development of technologies at the times of expected deployment. Figure 3-10 provides a notional picture of the three-tier proposal. As time goes on and technologies expand, new systems undoubtedly will be more effective and less costly and may replace the recommended systems. Figure 3-11 is a proposed research, development, and deployment timeline for a three-tier PDS.

Table 9 - Three-Tier PDS

Tier
 Deploymnet Zone
 Detection
Subsystem(s)
 C4I
Subsystem(s)
 Mitigation
Subsystem(s)
 
Near
 Within EMS
 EMS-based optics,
radar, and infrared
 Primarily conventional
Earth-based
 EMS-based rockets
with nuclear warheads
 
Mid
 Between EMS &
Jupiter Asteriod Belt
 Space-based
optics, radar, radio
array, infrared &
LADAR
 Conventional Earth
and space-based
 Space-based kinetic
energy systems
 
Far
 Within or around the
Main Asteroid Belt
between Mars and
Jupiter
 Space-based miniature
remote sensing
satellite constellations
 Conventional Earth
and space-based &
forward-deployed
comm relay satellites
 Space-based laser
systems
 

Each tier would be developed sequentially from near to far, with the detection systems developed and deployed first, in parallel with and followed by C4I systems and in parallel with and followed by mitigation systems.
 

Figure 3-10. Proposed Three-Tier PDS

Such a timeline allows us to detect potential ECOs and verify the need for mitigation systems prior to their deployment. Further, such a system would allow us to be protected from all ECO scenarios at the earliest possible time with the near tier, while allowing the technological advances and cost reductions to allow us to deploy the more challenging mid and far tiers in the future.
 

Figure 3-11. Proposed three-tier PDS research, development, and deployment timelines.