kukacos#119
Az atombomba deflekciós mechanizmusáról meg Appendix G.1.5 szó szerint azt meséli el, amit itt már egy ideje magyarázok:
Unlike a surface explosion, a nuclear standoff detonation does not use its energy to add impulse to the asteroid, but rather to vaporize some of the asteroid’s surface to produce the desired change in the NEO’s velocity. [30] [64]
By using a standoff detonation, the impulse absorbed will theoretically be less than the energy required to break up the asteroid, but sufficient to vaporize enough material to impart the necessary ΔV. For this mission, the spacecraft would be designed to detonate at a specific height above the object’s surface. The radiation produced by the explosion- X-rays, gamma rays, and neutrons - would bombard the surface, effectively vaporizing the surface layer. When material is vaporized and blown off an asteroid, an impulse is given to the asteroid due to conservation of momentum. Using this law and assuming the mass of the ejecta is very small compared with the mass of the asteroid, the amount of mass and average velocity of the ejecta needed to change the asteroid’s velocity by a certain ΔV can be calculated as [...] Using this relationship, one can see that by maximizing either the mass of the ejecta or its velocity, one can impart a greater momentum transfer to the asteroid.
The velocity of the gaseous ejecta is proportional to the square root of the temperature. [65] For this reason, it is better to have more mass vaporized to a relatively low temperature than little mass vaporized to a much higher pressure. To achieve this desired effect, an explosive custom made to emit mostly neutrons would be best for this scenario. Such devices have been designed and tested and are discussed in the Appendix P. Most fusion-based explosives produce the majority of their radiation as X-rays. Although X-rays can carry more energy then neutrons, they are able to penetrate the surface to a depth of roughly 10-50 microns depending on surface structure and material. [66] Neutron radiation has the ability to penetrate to a depth on the order of 10 cm, effectively
burning off more mass at a lower temperature and creating a higher-momentum transfer. Tailored neutron bombs have the ability to transfer roughly 10% of the blast energy into neutrons, which could vaporize the asteroid’s surface. [69]
To transfer the highest amount of momentum to the NEO, it is important to find the detonation height above the PHO’s surface. This allows the most mass to receive the most energy and to vaporize and exit with the necessary escape velocity. Reference [30] relates the momentum change, energy needed, and the optimum height of the explosion above the PHO.
Hivatkozások:
[30] Gennery, D.B., Deflecting Asteroids by means of Standoff Nuclear Explosions, AIAA 2004-1439, 2004 Planetary Defense Conference: Protecting Earth from Asteroids. February 2004.
[64] Barbee, B.W., Fowler, W.T., Davis, G.W., and Gaylor, D.E., Optimal Deflection of Hazardous Near-Earth Objects by Standoff Nuclear Detonation and NEO Mission Design, White Paper. NASA NEO Workshop, Vail, Colorado. June 2006.
[69] Holsapple, K., An Assessment of our Present Ability to Deflect Asteroid and Comets, AIAA 2004-1413, 2004 Planetary Defense Conference.