From: "David M. Palmer" <dmpalmer@clark.net>
Newsgroups: sci.space.science
Subject: Re: Zero-g orientation
Date: Sat, 25 Mar 2000 10:22:49 -0500

In article <8bgorq$dpm$1@hercules.iupui.edu>, Chuck Stewart
<zapkitty@hotmail.com> wrote:

> (The kitty waves his tail trying to land on his feet... but in free
> fall there is no landing...)

Cats can change their orientation in zero gravity quite well, using the
sort of technique I am describing.

> I thought that a person in microgravity could change their
> orientation by moving their limbs.
>
> Not the fastest or most efficient way to do it, and near impossible
> in an EVA suit, but feasible in shirtsleeves.

True.  What you cannot do (ignoring air resistance etc.) is begin at a
dead stop, flail your limbs around for a while, and end up spinning
after you stop flailing.  You will end up in a dead stop, but you CAN
be in a different orientation.

As a simple to describe example: 'stand at attention' motionless in
space with your arms straight down at your sides.  Now windmill your
arms overhand, (moving your arms behind you, overhead, in front of you
down at your sides, repeat).  As your arms are spinning forwards, your
body spins slowly backwards.  Every time your arms go 360 degrees, your
body moves 20 degrees or so.  When you stop moving your arms, you will
be facing another direction, and once again motionless.

--
                        David Palmer
                        dmpalmer@clark.net
                        http://www.clark.net/pub/dmpalmer

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.science
Subject: Re: Zero-g orientation
Date: Sun, 26 Mar 2000 19:41:23 GMT

In article <954027894.2961.0.nnrp-06.9e98d142@news.demon.co.uk>,
Ian Stirling  <Inquisitor@I.am> wrote:
>If you can change your orientation, in vacuum (in a skinsuit), to any
>position, repeatedly, then you can spin yourself, and violate conservation
>of angular momentum.

Nope, not if the spin is only transient, and involves one part of the body
(the torso) turning one way as another (the limbs) turns another way.
Same principle as using reaction wheels to rotate a satellite.  When you
stop waving your arms (or whatever), you always end up with the same
angular momentum (vector) you started with -- zero if you were initially
motionless -- but you aren't necessarily facing the same way.

(There is also some possibility of changing angular momentum, a little,
by air drag.)
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)