Defending Planet Earth Near-Earth-Object Surveys and Hazard Mitigation Strategies (2010) / Chapter Skim
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5 Mitigation
5 Mitigation
Pages 66-88
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From page 66... ...
For larger events, changing the path of the hazardous object is the appropriate solution, although the method for changing the path varies depending on the amount of advance notice available and the mass of the hazardous object. For the largest events, from beyond global catastrophe to events that cause mass extinctions, there is no current technology capable of sufficiently changing the orbital path to avoid disaster.
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From page 67... ...
Civil defense and kinetic impactors are probably the closest to deployable but even these require additional study before they can be relied on. In all cases, the decision to initiate mitigation is a sociopolitical decision, not a technical decision.
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From page 68... ...
Characterization mission Slow-push orbit change (gravity tractor) Bilateral agreements Kinetic impact International agreements/cooperation Nuclear detonation No avoidance capability -- global devastation Table 5.2.eps
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From page 69... ...
Although civil defense is the most likely response to any impact hazard, the committee did not possess the expertise needed to address fully the political and economic aspects of even a small-asteroid impact. This issue requires additional study.
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From page 70... ...
While this apocalyptic possibility is extraordinarily unlikely to happen in the lifetime of anyone living now, traditional approaches to preparing for disaster would become irrelevant. Finding: Civil defense (evacuation, sheltering in place, providing emergency infrastructure)
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From page 71... ...
Assume that a 10-ton spacecraft is the maximum possible with current launch capability and that a 50-ton spacecraft might be possible with future heavy-lift launch vehicles (see later discussion and the accompanying Table 5.4)
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From page 72... ...
For long warning times (on the order of four decades) , one could spend somewhat less than a decade to design, build, and launch the spacecraft and travel to the NEO, then spend a decade thrusting, followed by somewhat more than two decades of
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From page 73... ...
, it is unrealistic to estimate limiting the sizes of NEOs in this niche. Applicability of Slow-Push-Pull Mitigation Techniques Unless a very long warning time before impact is available, the practical application of slow-push-pull tech niques is limited to NEOs that are predicted to pass through a keyhole and to small NEOs near the limit for which civil defense alone might be adequate.
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From page 74... ...
Don Quijote concept would reduce the uncertainties, especially for highimpact velocities and highly porous bodies, for which the uncertainties are largest. In addition, important questions will have to be addressed about the ability to hit a small NEO at high relative velocity; those considerations may limit the intercept velocities at which kinetic impacts can be effective.
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From page 75... ...
The 5-ton payloads are possible now, and the 50-ton-payload cases are based on the planned Ares cargo vehicle. Achievable intercept velocities will depend on the orbital parameters of the NEO and may be limited by targeting and intercept capabilities.
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From page 76... ...
Even a single impactor that could be launched within 6 months of discovery might change the orbit of a 100-meter-diameter NEO, the size that is near the upper limit for the use only of civil defense mitigation, with a warning time of only 1 to 2 years. Finding: Kinetic impactors are adequate to prevent impacts on Earth by moderate-sized NEOs (many hundreds of meters to 1 kilometer in diameter)
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From page 77... ...
A complete and adequate crushing model is necessary to determine the shock effects on a porous body. High-porosity dissipative surfaces lead to quantitatively similar uncertainties for both nuclear explosives and kinetic impactors, and an impactor mission to study asteroid structure would provide useful data for both approaches.
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From page 78... ...
This may be the only current means to prevent an impact by a large hazardous object (>500 meters in diameter) with a warning time under a decade or by a larger object (>1 kilometer in diameter)
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From page 79... ...
As the NEO size decreases and the required yield of the nuclear explosive drops below the tested regime, which extends down to about 0.1 kilotons, the kinetic impact approach will have to be used. Although the nuclear option provides considerable mitigation potential, for NEOs above some size the tested limits of nuclear explosives will become inadequate.
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From page 80... ...
The former is determined entirely by the available launch vehicles, whereas the latter is determined by the details of the orbit of the NEO. (Note, too, that the mass of the fuel required to provide the Earth-escape velocity and this additional velocity will come at the expense of payload mass.)
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From page 81... ...
In practice electric propulsion has been used primarily for rendezvous missions, for which it can provide both initial acceleration and subsequent deceleration to the rendezvous. The committee presents some sample trajectories to illustrate what is possible with today's launch vehiclesthat is, not including Ares V
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From page 82... ...
However, the key point is that intercept trajectories with reasonable flight times are feasible. A next-generation launch vehicle, such as Ares V, would make kinetic impacts feasible for some long-period comets.
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From page 83... ...
lift launch vehicles will considerably improve the situation. The development of advanced engines for in-space propulsion will considerably improve the capability of delivering rendezvous payloads (for characterization, to act as gravity tractors, or to emplace surface explosives)
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From page 84... ...
Toward the left edge of the figure, representing short warning times, one would likely be able to carry out nothing but civil defense, unless disruption was shown to be reliable; toward the right edge of the figure, representing long warning times, the uncertainty in the prediction might discourage action. Toward the right half of the figure, there would often be time to design, build, and launch a mitigation mission.
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From page 85... ...
Assured success includes being certain that the mitigation will not increase the hazard. This assurance is particularly important when one must initiate a mission to change the orbit of an NEO before the probability of impact approaches unity, which will often be the case, since an orbit change could then, in principle, divert a near-miss object onto an impact trajectory.
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From page 86... ...
Both the kinetic impact and gravity-tractor approaches require significant engineering study, but more basic knowledge is needed for the kinetic impactor. In cases of the late discovery of a hazardous NEO, the change in the NEO's orbit that must be made for it to miss Earth can be so large that the required impact energy is comparable to or greater than the energy to disrupt
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From page 87... ...
Recommendation: If Congress chooses to fund mitigation research at an appropriately high level, the first priority for a space mission in the mitigation area is an experimental test of a kinetic impactor along with a characterization, monitoring, and verification system, such as the Don Quijote mission that was previously considered, but not funded, by the European Space Agency. This mission would produce the most signifi cant advances in understanding and provide an ideal chance for international collaboration in a realistic mitigation scenario.
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From page 88... ...
2004. Catastrophic disruption of asteroids and family formation: A review of numerical simulations including both fragmentation and gravitational reaccumulation.
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