Posted on 01/23/2007 8:52:26 PM PST by John W
Mine it out so there won't even be a question of coming around to hit the planet.
Space travel is already open. Space development is not happening, and the Treaty is the sole and only reason there is no private devleopment of space resources right now.
Repeal the Treaty. Maybe private space development firms would then have a position available for you, but if you don't repeal the Treaty they certainly won't.
No doubt, probability calculations will be part of the threat assessment together with orbital mechanics. Hey, nobody said it would be easy! However, it's worth some effort because an extinction impact event on Earth would be very unpleasant, especially if mankind is snuffed out. :-)
I dunno, I'm probably absurdly ignorant about this subject - but. I guess my "but" is that I find it very difficult to figure how putting a mass into the trajectory of the threat asteroid, such that the threat is attracted to that mass enough to be pulled out of the threat trajectory, can possibly be more efficient than simply colliding with the threat asteroid. It seems to me that entraining the threat gravitationally is really, in principle, indistinguishable from colliding with colliding with it at a very low velocity.And if you in fact are colliding with the asteroid, you might as well burn your "sufficient mass" as fuel in your rocket and slam into the asteroid with that much greater momentum. It looks to me like ultimately the only issue is the net momentum of all the rocket combustion products before/during the collision. And that the "tractor" approach is simply a long-duration collision.
Bump for later reading
The idea of crashing a spacecraft into an asteroid to alter its trajectory is seductive because, at first thought, it appears to be a simple, predictable game of celestial billiards. In other words, if we hit the threat asteroid at point X with mass Y traveling at velocity Z then A, B, and C will result. They script variations of this all the time in the killer asteroid movies Hollywood produces, so it must be possible, right? It’s accomplished in a flash and everybody can breathe a sigh of relief and go on with their lives. Who wants to fret over a boring gravity tug on a killer asteroid that drags on for 20 years?
Unfortunately, the reality of the situation is very different. A solution in the collision scenario can be calculated with barely an acceptable degree of certainty only if we know beforehand the exact material composition of the threat asteroid in all regions and its mass distribution to a degree of certainty approaching what we know about a billiard ball. To obtain that scope and depth of knowledge about a small celestial object hurtling through space many millions of miles from Earth is essentially hopeless. Even if we had the requisite knowledge of the asteroid, the solution might show a sufficient mass for a collision scenario couldn’t be constructed and delivered from Earth in time.
A basic rule of killer asteroid wrangling has something in common with the ethical practice of medicine described in the Hippocratic Oath, i.e., “First, do no harm”. Since the precise consequences of a collision can’t be predicted or quantified to an acceptable degree of certainty, it’s wise to attempt to alter the trajectory of the asteroid without adding the risk of making the problem worse; especially if the result might be multiple asteroid fragments. The stakes would be too high to do otherwise if an approaching asteroid threatened Earth with an extinction impact event.
Use a nuke or an ion engine tug and a fission reactor for power. Problem solved.
Of course watching Greenpeace go into meltdown over nuclear reactors and weapons in space would be worth it as well.
WE'RE GONNA DIE!!1!
The best case performance of the thing would require that the engine thrust equals the amount of force to be exerted on the asteroid, but unless the distance between the craft and the asteroid is large or the craft uses a pair of engines firing at extremely shallow angles relative to the asteroid (which would be extremely inefficient) I would think the ejecta from the engines would push on the asteroid in such fashion as to work against the desired motion.
Agreed, but how about this?:
Replace the spacecraft with an equivalent inert mass. Tether the mass to a platform via a very long (~1000 kilometer) cable. Mount four, or better yet, six engines symmetrically on the platform so as to exert the necessary force keeping the inert mass at a constant distance from the asteroid. The angling of the engines can now easily be made shallow enough that their ejecta will miss the asteroid while providing a reasonably efficient thrust.
All of this technology is doable now (at admittedly enormous expense). In at most a few decades, it will be cheap enough for serious consideration.
No, no, no. Hoagland
knows all about this stuff and
Hoagland sez NASA
knows people who have
hyperdimensional craft
already zipping
around the system
tweaking comets and such stuff
to shock-and-awe us . . .
------------------------------------------
"...you would have sensed Isis (Sirius), the Goddess of the Nile, mother of Horus the Sun God, Consort of Osiris (Orion), rising from below at precisely 19.5°. This sacred tetrahedral latitude, symbolic of the magical power of the Gods themselves, has shown itself over and over in the history of the US space program. But what was Sirius doing marking the passage of a comet from the heart of Orion, the brother and husband of Isis herself?
"Good question.
"It has been suggested that a "Hyperdimensional" vehicle - essentially a flying saucer - could fly out to the asteroid belt or beyond and casually nudge up against a rock, then gently push it into a precise orbit of virtually any configuration. Such technology is implicit in the "HyperD" model - and could explain just how Hale-Bopp was able to reach its closest point to Earth at exactly the same moment as a major Lunar Eclipse - creating the most amazing celestial spectacle of the the last 1,000 years."
[OH MY GOD! THEY KILLED SOHO!]
This would seem like an improvement on the concept, especially since the "inert mass" need not be of terrestrial origin. In addition to improving rocket efficiencies, this approach would also allow the mass to be much closer to the asteroid (indeed, I should think that having it land on the surface would probably not pose any particular problem).
I'm still unconvinced, though, of the practicality of getting any useful amount of mass into the right place to do any good. Gravity is a pretty weak force, after all, so the mass in question would have to be pretty incredibly big to do anything.
Unfortunately, the reality of the situation is very different. A solution in the collision scenario can be calculated with barely an acceptable degree of certainty only if we know beforehand the exact material composition of the threat asteroid in all regions and its mass distribution to a degree of certainty approaching what we know about a billiard ball.
I confess that in advocating direct impact I was taking for granted that the collision would be perfectly elastic and that the target would stay in one piece. And it seems to me that, unless the target is actually an accretion of dust, those assumptions should be sound. They could be made more so by detonating explosives on board the rocket to shred it into small fragments a moment before impact.It is of course true that as the mass of a distant asteroid would not be known a priori, the extent of the effect of a given impulse on the velocity of the target would also not be known a priori.
Thank your for your erudite explanation of the problem.
I seem to remember watching a show about this and the problem was if the asteroid was a "rubble pile" type, then what would happen is that it would come apart and be 50 asteroids instead of one.
This would seem like an improvement on the concept, especially since the "inert mass" need not be of terrestrial origin. In addition to improving rocket efficiencies, this approach would also allow the mass to be much closer to the asteroid (indeed, I should think that having it land on the surface would probably not pose any particular problem).
I had not thought it through as far as that, but remember, the asteroid may be tumbling in its path, in which case at least some separation between it and the inert mass will be necessary.
I'm still unconvinced, though, of the practicality of getting any useful amount of mass into the right place to do any good. Gravity is a pretty weak force, after all, so the mass in question would have to be pretty incredibly big to do anything.
I had intended to post the following response:
"Not necessarily, because it wouldn't have to do much. Remember, we're talking here about an asteroid whose 'appointment with Earth' is many years, maybe even decades in the future. In such a case, even a very tiny change in its trajectory will result in a large change in its position at the critical moment. Even a very small gravitational acceleration, if applied continuously for long enough can amount to a substantial alteration in its velocity.
"At the kind of velocities we are discussing (~ 5 X 104 m/sec), a lateral acceleration of one micron/sec2 applied continuously for a period of 107 seconds (which is less than four months) will result in a lateral modification to the asteroid's velocity of 10 meters per second. Over a period of several years, such a change results in a very large change in the ultimate position of the asteroid."
However, I then actually tried some figures, and came up with this:
"Assume an asteroid of density 5000 Kg/m (i.e. a stony body, about five times as dense as water), of size equivalent to a sphere 1000 meters in diameter. Such a body would have a mass of approximately 2.6 X 1012 Kg. The force necessary to cause an acceleration of one micron/sec2 would thus be 2.6 X 106 Newtons. Further assume a distance between the centers of gravity of the inert mass and the asteroid to be one kilometer.
"Plugging these figures into Newton's Law of Gravitation ( F = M1M2G / d2) yields a mass of approximately 1.5 X 1010 Kg, or about 15 million tonnes."
Clearly, we can improve upon this mass both by bringing the bodies closer together (although the radius of the asteroid will limit this), and by applying an even smaller acceleration. However, it does not seem to me that it is possible to get the mass much below one million tonnes and still achieve the desired deflection. Furthermore, engines capable of exerting a force of that magnitude for a period of months do not currently exist.
Under the circumstances, I think you're right: It's a nice idea, but beyond the capabilities of our technology for at least the next several decades.
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