Thursday, July 27, 2017

GRAVITY TRACTOR–not yet Driving to an Asteroid Near You

Back in 2005 an interesting concept was tossed into the ring to protect us against that overdue asteroid. You know the one that’s going to either send us back to the dark ages or end it all mercifully. 

Well, to date it is still no more than a theoretical spacecraft that will theoretically assist us in deflecting an incoming asteroid if theoretically we see it coming.

What made me think of it was that the series SALVATION currently on TV as they tried to make use of it. (We have to wait and see what happens in the next installment, but I have my doubts. The first or second option in a movie/series so rarely works out!)

But what about the real gravity tractor – what’s the problem?

Easy, actually, the gravity tractor is (theoretically) able to tow an object (asteroid or other sort) by simply hanging out close by where its own gravitational pull then acts on it to push the object on a different trajectory. All this while maintaining a constant and stable trajectory of its own, one that neither runs into the asteroid nor forces the tractor to come out of its orbit.

Essentially, the gravity tractor tows an asteroid out of the way by hovering close by using its own slight gravitational pull to push an object into a different trajectory. The vehicle’s thruster would have to maintain a stable direction that they neither push the tractor into the asteroid nor do they cause the tractor to come out of orbit.

The idea for a gravity concept comes from a 2005 paper from NASA’s Johnson Space Center (written by Stanley Love & Edward Lu). Granted in theory the idea is a good one but there are also many limitations. 

First is the need to meet it far from Earth. If you wish to deflect an asteroid that is on an impact course than you need to change its trajectory; unfortunately any spacecraft we send out to greet it is not likely to have enough mass to have a major effect on the object. (Keep in mind that gravity is the curvature of space time due to mass/energy.) Therefore for any change in trajectory to make a real difference (i.e. the difference between hitting the Earth & well, not.) then it has to be sent out to meet the object when the object is truly far from us and since the likelihood of it being discovered is more alarming than one might think. With the large ones, not so difficult but this can’t be used for them (not enough mass) and with the little ones, not so much. Think of all the asteroids you hear about for the first time that perhaps are going to pass closer to the Earth then, well, the one that passed closer than ever to Earth the last time (usually not that much earlier.)

So, how many times could we hurry up in 2017 to keep an asteroid from hitting us in 2019? Umm, we can’t. Say we did see it and have the time; we don’t have anything that can get there that fast, at least not yet.

An asteroid on a trajectory to impact Earth could not be shot down in the last few minutes or even hours before impact.  No known weapon system could stop the mass because of the velocity at which it travels – an average of 12 miles per second. 

Sadly, it seems that the best technique to prevent the destruction of Earth from an asteroid is scenario-dependent. The velocity, size, make-up of the asteroid (or other object) and distance from us all become factors in the solution. But what about the NEOs (Near Earth Objects)?

Don’t be fooled by the name Near Earth Object. To qualify one only need be an object whose orbit brings one into proximity of Earth. It is considered ‘a solar system body’ and the definition of that is any NEO whose closest approach to the Sun is less than 1.3 astronomical units (120,806,516.91 miles or 194,477,231.858 kilometers).

A portion of the NEOs may be in orbits that are hard to reach unless we find them many years to decades in advance of impact – which NASA has a number of asteroids where they have mapped out their trajectory years in advance to make sure they are not on an eventual impact path.  There are many forms - some asteroids are no more than groupings of rubble, and thus rather difficult to “push on” without breaking them up further, others might be coherent monolithic bodies.  There are those that never make it to the surface of Earth thanks to our awesome atmosphere and so  emergency response planning would be the proper response.

So limits in our speed to travel out to meet the asteroid and limits in our ability to affect its trajectory if its mass is too high for our gravity tractor to influence, plus we have to locate the threat in time…We have a way to go to be fully Asteroid-proof, hopefully we get there in time!


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