Re: Propellantless propulsion system

From: Perplexed in Peoria (jimmenegay_at_sbcglobal.net)
Date: 01/22/05 

To: sci-space-tech@moderators.isc.org
Date: Sat, 22 Jan 2005 03:09:08 GMT

"John Smith" <user@example.net> wrote in message news:Fl4Id.10188$mo2.764470@news.xtra.co.nz...
> James Nicoll wrote:
> > Although the idea of being able to convert angular
> > momentum into linear with actually throwing stuff is an old
> > one in space: didn't both Tsiolkovsky _and_ Oberth briefly
> > toy with that before seeing the obvious problem?
>
> As a bit of whimsy - how about two long thin contra-rotating masses,
> with an electric motor at the pivot point that makes them contra-rotate.
> (Motor is powered by sun.) Two chopsticks spinning against each other.
> ...

More whimsy, but with a serious point: 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, whereas the toilet paper itself can be recovered and reused!
Or, if your toilet paper roll was large enough, you have just
deployed a space elevator!!!

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? (It took me a long time to figure this one out. Dooooh!)

More seriously, since linear momentum is conserved, wouldn't the
escaping cardboard tube have to have greater velocity than the
original vertical velocity of tube plus paper? Mass has decreased,
Right?

In any case, I suspect that variants of this idea may be useful
in the future for "propellantless propulsion" in future commerce
between space stations in solar orbit. The advantage over
rockets is that you are not throwing away volatiles: the "propellant"
mass can be recovered and reused.

Relevant Pages

  • Re: The failure in university administration
    ... paper also dispenses the toilet paper. ... went to that room and took a roll back to their toilet. ... Only an employee of the department ... Non-authorized employees had to fill out a supplies requisition form ...
    (alt.usage.english)
  • Re: Totally OT: Toilet roll use
    ... I never put the paper on the roll because O T likes to grab it and run. ... Have awakened many mornings to the frontroom decorated in toilet paper. ... Do you scrunch or fold your toilet paper? ... Two people said they thought most Europeans fold and most Americans ...
    (rec.pets.cats.anecdotes)
  • Re: Totally OT: Toilet roll use
    ... Do you scrunch or fold your toilet paper? ... Pine Cone neatly unrolls the paper and drapes it over his offerings. ... There is a good reason the tp isn't on the roll in there. ... My very thrifty mother made my older sisters reroll the toilet paper ...
    (rec.pets.cats.anecdotes)
  • Re: Propellantless propulsion system
    ... Set the roll rotating. ... > release some clamps so that it is unfurling the toilet paper. ...
    (sci.space.tech)