Methods for the Deflection of Threatening Asteroids: Some Problems, Theoretical Considerations and a Few Myths.
Holsapple, Keith
University of Washington

The methods suggested for the deflection of a potentially hazardous asteroid or comet has remained relatively static some time now. Most are based on the idea that a small change in its linear momentum along its flight path would suffice to either slow it down or speed it up so as to avoid the possible intersection of its trajectory with that of the Earth; although some still contemplate "vaporizing it" or "blowing it up" with explosives or other energy sources.
In this talk I will discuss various approaches, note their possible flaws, present some simple theoretical considerations and discuss some misconceptions occurring in the literature.
The momentum alteration approaches group into two categories: the slow-steady approaches and the rapid impulsive approaches: "slow-steady pushes" and "whacks".
Most slow-steady approaches are based on ejecting matter from the surface for months or years.
An attached rocket propulsion device would use rocket fuel carried to the body; a mass driver mechanically launches material from the surface; laser beams and reflected solar beams would eject vaporized material from the surface. Other methods use photons: a solar sail with an attachment uses the reflection of photons from the sun and the alteration of the surface reflectivity might beneficially enhance the Yarkowsky thermal photon effect. The gravity tractor idea uses propulsive devices but without attachment: a large spacecraft that uses its propulsive devices to slowly pull the asteroid using only the mutual gravitational force.
The fast impulsive methods include direct impact with a spacecraft, a cloud of dust or steam in the path of the asteroid, an impulsive ejection of vaporized surface material created by a nearby explosion, or an impulsive ejection of solid surface material by a surface or buried explosion.
Many questions arise about these methods. Some of the most significant questions involve technical issues of controllability, attachment, robustness and redundancy. In turn those technical uncertainties spawn serious social and political issues about alternative uses, liability, and government responsibilities.
This talk will attempt to outline the features, unanswered questions and misunderstandings about the various approaches. For now, for our amusement, I quote one statement in the literature: "Disintegration would be required because deflection is not possible in space."