The Doctor (dr_nebula) wrote in snobss,
The Doctor

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Swing your partner..

In today's New Scientist, I'm intrigued by this on a gravitational tractor. What is being proposed that instead of deflecting an errant asteroid/comet via nuclear weapons (as in the movie "Deep Impact"), a massive satellite (> 20 metric tons) would "lurk 50 meters" from its target for about a year to 'change its velocity enough to knock it off course". This idea has been applauded in the community as the "most innovative' and 'simple' means of deflection.


No grappling hooks and just sit and 'lurk'?


Being 'teh doctor', I sat down and did a few simple calculations:

Whereas: The average asteroid has a density of 2.0g/cm^3 = 2 x 10^6 g/m^3, or 2 metric tons (2000kg).

Assuming a spherical body (more likely it will be a rough cylinder) of 200 meters in diameter:

Volume of a sphere = 4/3 x Pi x radius^3, r = 100m

= 4.2 x 10^6 meters cubed, or ~ 8.4 x 10^6 metric tons.

A 20 ton 'gravitational tractor' probe will be outmassed by 420,000 times. The probe should not go into orbit as both objects would revolve around a common balance point called the barycenter - sort of like an elephant and a small mouse on a teeter-totter. *g* Or, in other words - this deflection would be negligible.

Nope - it would have to stay close to the target and slowly change its orbit by very small changes in the thrust direction. It would need to be applied continuously - which would require an ion propulsion system. This would be quite tricky to pull off to say the least.

But being a man of action - I'd recommend a modified solution. Being this damned close - slowly touch down a small device on the surface and NUKE the bastard. (or liberal use of velcro and duct tape..)

Certainly more bang for the buck.

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