Re: Propellantless propulsion system

From: Paul E. Black (p.black_at_acm.org)
Date: 01/24/05 

To: sci-space-tech@moderators.isc.org
Date: Mon, 24 Jan 2005 12:57:02 -0500

On Sat, 22 Jan 2005 03:09:08 +0000, Perplexed in Peoria wrote:
> "John Smith" <user@example.net> wrote in message
> news:Fl4Id.10188$mo2.764470@news.xtra.co.nz...
> ... Consider a propellantless launch
> system consisting of a huge roll of toilet paper. Set the roll rotating.
> Set it rolling with a large horizontal velocity. Let it roll up a ramp of
> increasing slope so that it is now moving vertically. At this point,
> release some clamps so that it is unfurling the toilet paper. The toilet
> paper is released gradually as our "spacecraft" climbs, until at last we
> have only the innermost cardboard tube thrown out of the earth's
> gravitational field, ...
>
> But here is the hidden point in this whimsy. Since angular momentum is
> conserved as the roll unwinds, it must be the case that the ultimate
> escaping cardboard tube is rotating faster than the original roll
> consisting of tube and paper. The moment of inertia has decreased, Right?

Consider the *** about to be unfurled. Just before it is unfurled,
it is moving very fast. After, it is stationary. As described the
rest of the stationary paper stops it. So no energy is transferred to
the spinning roll.

Now if you had a motor and wheel attached to the roll that pushed
against the unfurling ***, the momentum could be transferred. Of
course, this just describes a rocket with a mechanical feed and a
toilet paper exhaust.

-paul- 

-- 
Paul E. Black (p.black@acm.org)