joema - 24/3/2007 3:16 AM
Olga - 23/3/2007 4:40 PMA stand-off detonation is absolutely ineffective because of lacking an air blast in space – the base of sticking factor. A stand-off detonation is very effective -- the immediate X-ray and neutron burst simply vaporizes a thin layer of material from the asteroid surface which propulsively nudges the body in the opposite direction, without fragmenting it.
If you insist I’ll try to give more arguments.
At first let’s consider a high altitude thermonuclear explosion. Utilization of a thermonuclear explosion for defense from hazardous space objects was suggested for the first time in Hyde R. A., 1984. Cosmic bombardment. - Special report UCID-20062, Lawrence Livermore Nat. Lab. Resulted from the thermonuclear explosion decay products, X-ray and gamma-radiation and a neutron flux arrange an air-blast. The main role belongs to the neutron flux (Hammerling P., Remo Y. L., 1992. NEO Interaction with X-ray and neutron radiation. - In: IW-92, p. 186.), which gets at a depth of 20 cm under a surface of an object at a density of ?=2g/cm3 and average atom weight of a substance equal to 25. A part of substance will be “blown-off” (here is a source of origin English terms “blow-off” and “stand-off” for this type of thermonuclear explosions) and a space object will get an additional impulse.
At an optimal height of explosion over a surface (Ahrens Th. J., 1992. Deflection and fragmentation of Near-Earth- As-teroids. - IW-92, pp. 89-111) equal to
h=D((v2 - 1)/2)˜0.2D
0.3 of its surface will undergo radiation. For all that explosion energy equal to f=0.28 gets to the surface. A share of explosion energy transmitted to a neutron radiation is equal to e=0.32. For all that a velocity of a blown-up particle is equal to v =feW/CP, where W is a power of thermonuclear explosion in kilotons; CP = 2 km/s – is a velocity of spreading a neutron blast wave, and a velocity v is directed orthogonally to the object’s surface. At accepted values v = 44 m/c for each of kiloton of the charge. A reduction of v for a direction of object’s motion gives vr =0.7 v = 31 m/c for each of 1 kt of the charge (for D = 100 m a drift speed is 5.3 cm/s).
As a result the object with a mass M will get a velocity DV (m/s) equal to
where W in kt, D in m, in g/sm, M in g.
The consequence is that by explosion equal to 300 kt you will give to a “medium” in his density asteroid with a diameter of 1 km increase of velocity about 2-3 cm/s.
Variants of stand-off and immediately surface explosions give similar results in a diapason up to 20 mt. I will save you your calculations of different variants. You can use an average value of 106
(t m/s)/Mt. For the rest be so kind as to calculate yourself. If you meet any difficulties I can provide you with diagrams for explosions of various power and asteroids of various dimensions, just to save you from a necessity to use sources like http://en.wikipedia.org
or kids’ encyclopedias.
As for ICBM I consider the format of this forum is not appropriate to give lectures on space ballistic and etc. It requires some time to invent a situation with a dangerous space object where this carrier would be useful and when it would be worthy to use it (heavy space types of it for instance 3C has better chances). And if you care a little about consequences for ecology after ICBM utilization then it’s better to forget about military toys all together.
Here is a typical, even optimistic case: a long-period comet-type object from a remote area of the Solar system is discovered. The core’s diameter is about 8 km. An inclination to ecliptic’s plane is 65 degrees. A direction of revolution round the Sun is reverse to the Earth revolution at its orbit. A velocity relative to the Sun while crossing an Earth orbit is about 30 km/s. Time to a possible collision is 6 months (we were lucky). Estimations of collision’s probability are 60% (after 10 days of observation). After three months from discovering the comet became active, a trajectory is corrected; the core’s decay is predicted for one large (90% of mass) and few small fragments. Estimations of collision’s probability become higher up to 90% (after 90 days of observation).
Is there anything incredible? Now let’s suggest NASA use Titan. Can you guess where they will advice you to allocate it? I can’t use rude words here, but you can ask me via private mail. Or do you hope that we will need to deflect only those objects which will be “comfortable” to deflect? May be you would ask asteroids to be polite and check with us their trajectories and dimensions in advance?