[amsat-bb] Gravity Gradient?

skristof at etczone.com skristof at etczone.com
Thu Aug 25 00:03:16 UTC 2016


A quote:"The mass on the end of the dumbbell closest to the center of
the earth is attracted to it by a force that we denote F. The force on
the other mass we will denote f. Even if these masses are equal it is
easy to see that force F will be larger than f. " 

The article goes on to say that the torque produced will keep the closer
end pointed towards Earth. This paper actually starts with the
assumption that the two end masses are the same, then goes on to say
that it will still work even if the masses are different.

So, I'm siding with Bob. 

Full disclosure: I'm not a professional, but I do teach physics. 

Steve AI9IN 

On 2016-08-24 18:11, Robert Bruninga wrote:

> My understanding of Gravity Gradient is that a small spacecraft with a long
> boom and tip mass will align in an UP/Down attitude.  But it is bi-stable
> so either end can be  up and be stable.
> What about a small satellite with TWO booms (dipole wires) in opposite
> directions with small tip masses, it will be just as stable as before but I
> may even get by with half the mass on each end.  More or less.  When I mean
> "stable" I mean roughly up down, anything within +/- 40 degrees is still a
> vertical HF antenna....  Besides faraday rotation will rotate the received
> pattern every whichaway anyway.
> I disagree with an opinion I have received that says "gravity gradient"
> wont work with dual opposite end tip masses.  Says one has to be bigger and
> it cannot be in the middle.  I disagree.
> Any professionals have an opinion?
> Bob, Wb4aPR
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