Will the government save us?

The Mitigation Approach:

The only way of preventing a large comet or asteroid from striking Earth on a short notice would be to use a nuclear device. That is the only means to generate enough energy to counter this threat. Two mitigation approaches have been proposed: (1) interior nuclear detonation that would explode the object into smaller fragments, (2) stand-off nuclear detonation that would deflect or nudge the object out of the way without fragmentation. Several experts believe that a fractured comet or asteroid poses more danger than a whole comet or asteroid because multiple impacts from several smaller fragments could generate greater damage to the Earth than a single impact from the entire mass. To avoid the danger of fracturing the comet, the nuclear device would need to be detonated about 2.5 miles from the comet’s surface.⁸ According to Johndale Solem, a mathematical physicist at Los Alamos; this distance would offer optimal nudging with the least chance of splintering.

The approach for mitigating the threat posed by a comet is different than the threat posed by an asteroid. A comet and an asteroid vary significantly in composition. I feel that we may be making a fatal mistake by not seriously considering the fragmentation approach. Different mitigation approaches should be considered individually for these two different types of threats. Whereas it has been suggested that an asteroid be deflected by a standoff nuclear explosion that gently pushed the asteroid off-coarse without fracturing; in the case of a comet, the goal may be the opposite. Comets develop a dark crust that acts like a heat shield protecting the volatile ices in the nucleus from the rays of the sun. By vaporizing this shield, the comet will become vulnerable to the effects of the volatile outgassing, which will produce great jets that will erratically alter the comet’s trajectory. By fracturing and increasing the surface area of the exposed volatile gases, the sun may magnify the effects of the nuclear weapon on the comet trajectory.

In my opinion, the optimal mitigation approach for a large comet is a below surface detonation. The logic is as follows:

* A comet is composed of a high percentage of various ices. Under the energy of the sun’s heat or the heat of a nuclear bomb, these ices will change into a gaseous state that can work like a jet engine thrusting a comet into a different trajectory. To put this point in context, the NASA Solar and Heliospheric Observatory (SOHO), observed over 10,000 tons of water vapor per hour pouring off Hyakutake’s comet nucleus.²³ I believe that fracturing the comet into several pieces is a strong approach because it will maximize the surface area of exposed ices to the effect of solar radiation.

* When comparing a standoff detonation, a surface detonation, and a subsurface detonation; the latter provides the greatest effective force and places the most thermal energy into the comet.

* I believe that a swarm of comet fragments will begin to order themselves into a structure similar to a string of pearls (i.e. Shoemaker-Levy 9 comet fragments). This is a natural structure. As the lead fragment outgases, the dust and vapors will impact trailing fragments causing the structure to separate into a line over time. This structure will permit subsequent attacks from nuclear missiles. Further fragmentation of the leading comet fragment will bombard the string of pearls.

* The fragments of the Shoemaker-Levy 9 comet hit Jupiter like bullets from a Gatling gun. The size of Earth is significantly smaller than Jupiter and the gravitational field exerted by Earth is significantly less than that of Jupiter. I believe that spreading out this line of pearls through an ordered attack might produce the following result.

Action	Result on Collision with Earth
Without any engagement	One very large BANG
First Missile	7 Fragments: Bang, Bang, Bang, Bang, Miss, Miss, Miss
Second Missile	7 Fragments: Gone, Bang, Bang, Miss, Miss, Miss, Miss
Third Missile	7 Fragments: Gone, Gone, Miss, Miss, Miss, Miss, Miss

The Ideal Missile:

The ideal missile for delivering a nuclear payload to an incoming comet or asteroid doesn’t exist. I do not believe that it is even on the drawing board. The ideal missile will be hybrid, blending elements of a strategic nuclear missile technology and spacecraft technology. The missile will need to achieve speeds of 100,000 miles per hour. The ideal missile will require the development of a new type of rocket motor, for example the Variable Specific Impulse Magnetoplasma Rocket (VASMR). To achieve these velocities, the missile will need to be launched from space in order to minimize the influence of gravity. After achieving velocity, the missile will deploy solar panel arrays for power. The ideal missile will have mid-coarse guidance controlled from Earth and final intercept terminal guidance and control within the missile.

* For a stand-off detonation, the missile will require a very precise proximity fuze that will control the trigger on the detonation. This level of control, approximately 1 mile, with a missile/comet closing velocity of 200,000 miles per hour, means the detection & trigger must be accurate to +/- 2.5 microseconds.

* For a subsurface detonation, the missile will require an impact detonator - a device that uses the force of the impact to drive the Uranium core together to generate a nuclear explosion and protects the core for a sufficient period of time to allow the nuclear reaction to occur. In general, the nuclear missile with a closing velocity of 200,000 miles per hour will vaporize upon impact with the comet. The impact detonator will need a hardened shell that will survive for a few microseconds. During this time, the shell will drive deep within the comet. The shell construction might take a layered design, such as found in the reinforced carbon-carbon tiles used on the space shuttle. It might be composed of layers; similar to the construction used in tank armor, such as glass sandwiched between layers of depleted uranium.

The Present Technology Missile:

If we were forced to deal with the threat of an incoming comet today, our only choice would be to modify an existing spacecraft to engage this threat with a stand-off nuclear detonation. There are two significant drawbacks to this approach.

* The speed of an incoming comet is approximately 100,000 miles per hour. The speed of a convention spacecraft is around 10,000 miles per hour. The further we intercept the comet away from Earth, the greater we will be able to affect its trajectory. Refer to the Figure 1. If the comet is engaged when it is first detected at approximately 186 million miles from Earth, the intercept between an Ideal and a Present Technology Missile is very significant.

* Current missile technology using pre-trigger on intercept is about 5,000 miles per hour. The present technology missile will have a closing velocity on the comet of approximately 110,000 miles per hour. At this speed, if the spacecraft should strike the comet, the spacecraft along with the warhead will be vaporized. If the pre-trigger is off by a few microseconds, the energy imparted to the comet will be weak and ineffectual.

When Will the Government Act:

Presently, despite the threat, governmental bodies are not funding any asteroid intercept systems. Governmental bodies are only providing very limited funding for asteroid searches and cataloging potentially threatening asteroids.¹⁵

Three international treaties which the United States are signatories to: the 1963 Limited Test Ban Treaty, the 1967 Outer Space Treaty, and the Anti-Ballistic Missile Treaty forbid the use of nuclear weapons in space. I don’t believe that the U.S. government or any other government would pursue developing such a weapon until an actual impact threat is identified. We would probably use up valuable time arguing whether an impact will really occur because different experts will have different predictions. (This is called the denial stage.) When we do decide to react, we will probably put all our resources and talent to bear on the problem. We will use off-the-shelf equipment, modified for this mission. Time will limit testing, critical failure mode will remain undetected, and the risk of failure will be substantial. We will probably launch multiply weapons at the incoming comet. But because of the short reaction time, the lack of proper testing, the use of non-ideal missiles, we will probably fail.

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