Asteroid Deflection

Oct 21, 2019
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Asteroid Deflection

The average distance between asteroids in the Asteroid Belt is 600,000 miles.

In order to deflect a threatening asteroid by the right amount in the right direction, would require very accurate information, not only about its present course, but about its future course. I don’t think we have the ability to accurately predict the course of any asteroid or comet 10 or 20 years down the road. There are perhaps dozens or hundreds of bodies that may have a gravitational influence upon a given asteroid during that journey. If we begin deflecting it, that may introduce even more unknowns into the equation. IIRC, we currently must make occasional course corrections on our interplanetary spacecraft to compensate for the effects of unknown gravitational perturbations.

It might be possible, in our ignorance, to actually deflect what would otherwise have been a harmless close pass into a collision with Earth.

Before undertaking the task of deflecting asteroids, I think we must first implement a system of detectors far enough out to give us a little extra lead time, but not so far out that we would be beyond them. I’d say that about 1.4AU should be about right. Since virtually all threats would be at or near the orbital plane, I suggest perhaps a dozen detectors equally spaced out at about 1.4AU. That would also be a good location from which to launch interceptors.

Unless and until we can accurately predict the course of an asteroid or comet some 10-20 years ahead of time, we may be stuck with more forceful, and faster methods of asteroid deflection than gravitational tugs.

I see no advantage to performing a trajectory correction maneuver at perihelion. The further from coincidence that an evasive maneuver is performed, the smaller the input of energy required. Many asteroids are “piles of rock” conglomerates, loosely held together by a very weak gravitational bond. It would take very little to shatter one of those rock piles, and the result could be deadly. Therefore, the “orion” concept would be not only impractical, but potentially dangerous.

While that is true, there may be an overriding consideration. Depending on the orbit of the asteroid, the difference in orbital velocity between perihelion and aphelion may only be 15%. While this may give you the most “bang for your buck” (% deviation) at that point (perihelion), it won't necessarily provide the most total deviation to the orbit. IOW, if you back up halfway around the orbit and apply the deviation force there, at aphelion, by the time the asteroid has reach perihelion, it will already have deviated (over the course of 1/2 orbit), more than the same amount of force could deviate the orbit at perihelion.

Example. 3361 Orpheus with an orbit of q=.819, Q=1.60 a=1.21 P=1.33
That gives us an orbit of 7.5995AU or 706,754,674.5 miles.

Suppose we impart a deviation (perpendicular to the orbital plane) of .1 degrees at aphelion. By the time the orbit reached perihelion, it would already be deflected by 610,865 miles, IF it was a straight line. Orbital mechanics doesn't work that way. The actual deviation would be 305,432.5 miles in the opposite direction at perihelion. Still, that would be a big head start on deflection, compared to beginning the same deflection at perihelion. The 15% or so that you gained by deflecting at perihelion, would be overshadowed by the overall deflection started at aphelion.
 
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MMohammed

Assistant Community Manager
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Oct 10, 2019
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So, essentially, there is no viable method nor any use in detecting the course of any asteroid that is, say, decades away?
 
Oct 21, 2019
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So, essentially, there is no viable method nor any use in detecting the course of any asteroid that is, say, decades away?
Not that I am aware of. Perhaps someone here has more information on that.
One rather low-tech solution might be to attach transponders to suspect asteroids, making it easier to keep accurate track of them. It would also make tracking their exact orbit more precise. That would be very low risk and relatively inexpensive. It might be possible to send a spacecraft on a long mission, passing near many different asteroids and shooting transponders into them from a distance. If a given tagged asteroid exhibits a trajectory that will intercept Earth, then a mission could be launched to intercept it at a point in its orbit where it is furthest from Earth, requiring less force to make it miss Earth. The transponder would also make it possible to determine if the deflection was enough, and in the right direction.
 
Feb 18, 2020
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Hi

I would say the answer depends totally on the size of the asteroid (or comet).
You have a total size spectrum between any too large to deal with (RUN ifpossible) and any too small to worry about. Within that band I believe there is a chance time permitting to adopt one of the suggested methods such as deflection.

I congratulate Mental Avenger on an excellent exposition but would add one small point. Whilst I totally agree with him regarding destruction possibly producing multiple hazards, there is one possibility of breaking an object already close to the harm/no harm boundary where the pieces would each be too small to cause serious damage.

Cat :)
 

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