Re: [Phys-l] Rocket Hovering and Conservation of Momentum

[Michael Porter <listmoe@gmail.com>]

On Jul 24, 2006, at 12:56 PM, Marc "Zeke" Kossover wrote:
> ...The gas gets negative momentum and the rocket
> gets positive momentum due to conservation of momentum, but
> the rocket is pulling on the planet -- the planet doesn't
> just pull on the rocket but the rocket also pulls on the
> planet! Though the distance between the rocket and the
> planet doesn't increase, the rocket and planet, together,
> get some velocity in the positive direction...

Marc, you might be interested in the following:

A Gravitational Tractor for Towing Asteroids
Edward T. Lu and Stanley G. Love
NASA Johnson Space Center
We present a concept for a spacecraft that can controllably alter the  
trajectory of
an Earth threatening asteroid using gravity as a towline.  The  
spacecraft hovers
near the asteroid with thrusters angled outward so the exhaust does  
not impinge
on the surface.  This deflection method is insensitive to the  
structure, surface
properties, and rotation state of the asteroid.

<http://www.b612foundation.org/papers/tractor.pdf>


---
Michael Porter
Colonel By Secondary School
Ottawa, Ontario, Canada