From: kjenks@gothamcity.jsc.nasa.gov
Subject: Re: Micro-g in KC-135
Originator: kjenks@gothamcity
Keywords: microgravity
Organization: NASA/JSC/GM2, Space Shuttle Program Office
Date: Mon, 14 Dec 1992 17:36:35 GMT

1st:
>In article <1gfti1INNaqj@rave.larc.nasa.gov> claudio@nmsb.larc.nasa.gov (Claudio Egalon) writes:
>>What causes the microgravity in the KC-135 [...] ?

2nd:
In article <Bz7v1M.6DC@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) replied:
>You don't "cancel" the gravitational acceleration, you fall with it.  The
>KC-135 flies the exact trajectory that it would follow if it were falling
>free in a vacuum.
>
>That trajectory isn't exactly a parabola; it is in fact a segment of an
>elliptical orbit (one that intersects the Earth's surface).  It's very
>close to being a parabola.  It would *be* a parabola if the Earth were
>flat and gravity did not diminish with altitude.

3rd:
Henry's correct.  Our KC-135 "Zero Gravity Trainer" follows a
trajectory which causes all of the objects inside the aircraft to fall
at the same speed as the aircraft itself.  Since there is some air
resistance, the pilot does apply some power, and he keeps an eye on the
G-meter in the cockpit.

The KC-135 flight starts off at Ellington Field a few miles north of
JSC.  The experimenters (and the experimental test subjects) stay in
their seats at the rear of the plane until the plane gets out over the
Gulf of Mexico, at which time the people get up and set up their
experiments.  The airplane flies about 40 parabolas, with about 2
minutes of 1.8 G, then 30 seconds of (nearly) zero G, then 2 minutes of
1.8 G, etc.  There are longer gaps (at 1 G) between some of the
parabolas as the pilot navigates and/or steers around weather.

What surprised me about the KC-135 was that the gravity was so
variable.  It was nowhere near MICROgravity; it was closer to 0 G +/-
0.1 G.  During the periods of low gravity, everything in the padded
cargo/experiment area floats about and drifts around as the
accelleration vectors shift due to bumpy air, wind gusts, etc.  There
is very little variation in accelleration along the plane's X-axis
(tail to nose) and Y-axis (left/right), but there are variations in the
Z-axis (up/down).   If you are strapped down with an experiment in your
lap (as I was), your experiment will float "up" and "down."  However,
if you and your experiment are both floating, you'll stay together.

At the end of the set of parabolas, the aircraft makes a broad swing
around and flies back to Ellington.  During this time, those
experimenters who are still able to function stow their equipment and
make their way back to the seats where the rest of us are recovering.

On the flights I was on, there was quite a variety of experiments,
including an improved treadmill, an excercize bike, a test of a foot
restraint system, a fluid dynamics experiment, some tests of the Space
Station food service equipment (paper plates don't cut it), and my
Portable Aerodynamic Work Surface (PAWS) experiment.  On my third
flight, there were some new astronauts undergoing zero-G
familiarization training.

On my first two flights, I barfed.  Quite a lot on the first flight,
and only once (on the downside of parabola 35) on the second flight.
I had no trouble on the third flight, and we went to Pe-Te's Barbeque
for Cajun food after we landed.  I was doped to the gills on Scop-Dex,
a mixture of scopalamine and dexadrine.  

GIF available upon request.  (Blech.)

-- Ken Jenks, NASA/JSC/GM2, Space Shuttle Program Office
      kjenks@gothamcity.jsc.nasa.gov  (713) 483-4368

     "We choose to go to the moon not because it is easy,
      but because it is fun." 
	-- John F. Kennedy, as [mis]quoted by 
             Scott Brigham, scotbri@rosemount.com,
             in alt.folklore.urban
Newsgroups: sci.space