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davepamn davepamn
 

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 M¢25  Funded By Mahalo ? |  October 11, 2009 02:23 AM

How many inches will gravitational tethering move Apophis off course?

The popular idea for moving the asteroid Apophis is to use gravitational tethering. How many inches will gravitational tethering move the asteroid?
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phlogiston phlogiston
 
 October 12, 2009 01:08 AM
As far as I understand it, gravitational tethering is used to change the angle of the asteroid's trajectory. Therefore to ask how many inches the asteroid is moved is not quite the right question. This is because once the angle of trajectory is changed, even by a tiny bit, eventually the asteroid will be millions of miles from where it would have been. Given enough distance and time then theoretically the asteroid will be moved an infinite distance from it's original path. But practically it will never get infinitely far, only very very very far.

The technical challenge for tethering Apophis or any other near-Earth asteroid is that you have to interfere with it's trajectory sufficiently far from the earth in order to make a big enough change to be effective. The larger the spacecraft that is sent to tether with the asteroid and the longer it is near the asteroid the greater the angle of trajectory is changed.

I hope this helps.
Source(s):
http://cosmiclog.msnbc.msn.com/archive/2007/02/16/58617.aspx

Asker's Rating:
• I would like to know the optimum distance for deflection to work.


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davepamn davepamn
 
October 12, 2009 01:12 AM
Distance to interception is important. Distance, tethering, and angle change determine the final trajectory change

If the change in angle is a billioneth of a degree then the distance away from earth must be billions of miles away to make a difference. If the change in angle is 1 degree than a million miles will be more than sufficient to avoid impact with earth.

What is the perfect interception distance?

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phlogiston phlogiston
 
October 12, 2009 01:17 PM
You're right davepamn. I suppose that calculating the ideal distance is beyond me. I think the calculation would look something like this: Take the gravitational constant then you would have to know the weight of the spaceship used and use Newton's law to calculate the force exerted on the asteroid: F = GMm/rr where G is the gravitational constant M the mass of the asteroid, m the mass of the spaceship and r as the distance between the two. Then once the force is calculated you can calculate how much that force will effect the asteroid and thus you can determine the angle change per time period and then you will be able to calculate how long the tethering will have to be in place to produce the angle change needed.

Of course, the farther away that this all takes place the easier it will be to make the necessary change, but how far away interception should take place also depends on practical things like how far we can reasonably send a spaceship that we can maneuver properly and how long it will take to get there. These are things I don't know. Supposedly NASA has enough time to plan all this with Apophis, but there might be other near-Earth asteroids that we won't have the time needed to implement gravitational tethering.

Let me know if I'm off base with this.

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davepamn davepamn
 
October 12, 2009 02:20 PM
The problem is odds. The odds of impact are so low that the optimum deflection and interception point are not demonstrated.

The angular distortion must be in the billioneths of degrees or less because the gravitational pull of a space ship is required to solve the problem of impact.

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davepamn davepamn
 
October 12, 2009 02:23 PM
The sun pulls the moon a few inches each year out of orbit. A space ship in a parked position (optimum gravitational pull in the tethering process) may pull the asteroid millimeters off course, but over millions of miles affect the final trajectory to miss earth by miles. The question is how much money can be allocated to solve the problem.

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