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NASA Science News for January 24, 2003

The G's in the Machine
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Zero-g is a myth. Even in orbit, spacecraft experience tiny
accelerations called "microgravity" that scientists monitor using a
device named SAMS. 

January 24, 2003:  Anyone who says there's no sound in space has never 
actually been there. 

In the near-vacuum of open space, of course, "nobody can hear you
scream," as the sci-fi thriller Alien famously put it. But onboard the 
space shuttle and the International Space Station (ISS), life is
filled with activity and sounds. 

Some come from the pervasive plumbing, wiring, and mechanical hardware 
that fills every corner and cranny. If you were aboard, you'd hear 
air-circulation fans whirring, electric motors humming, pumps 
switching on and off--constant reminders that you're living in the 
bowels of a giant machine, switched "on."

Others come from the people themselves: an astronaut chugs-away on a
spring-mounted exercise bike to prevent muscle atrophy; crew members
move around, talk, bump into things, work with clanking metal tools;
tinny-sounding music plays from little speakers to keep the crew's
spirits up amid their gray, metallic surroundings. 

All these little sounds lend a kind of machine "personality" to the
spacecraft--like the distinctive feel of your own car. To astronauts
the hubbub is familiar, comforting, better by far than dead silence.
But to scientists with experiments onboard, the sounds are a sign of
something possibly unwelcome. Every clank, hum and buzz corresponds to 
a tiny jolting acceleration. 

"They are the "g's in the machine."
----------------------------------
Experiments are done in space (more often than not) to escape
acceleration. On Earth objects are accelerated downward at a rate of
9.8 m/s2 or 1-g ("one gee"). That constant pull is responsible for
effects such as convection and sedimentation that can complicate
chemistry and physics experiments--effects that scientists would like
to leave behind on Earth. Yet after all the trouble of going to space
to get away from big g, the space shuttle and the ISS are filled with
little g's of their own. 

Is that a problem?

"Not usually," answers John Charles, the chief scientist for shuttle
mission STS-107. Most of these vibrations are vanishingly small--less
than one-millionth the acceleration of gravity here on the ground.
(Hence the term "microgravity;" the prefix "micro" means
one-millionth.) But sometimes, he says, occasional jolts and ill-timed 
vibrations can upset the most delicate experiments.

For example, "combustion experiments really don't like thruster
firings." Charles explains: Flames in space do something odd. Instead
of forming the familiar teardrop shape of candle flames on Earth, they 
contract into little balls, which float around and burn using almost 
no fuel. Scientists suspect these flame balls hold the secrets to 
leaner burning auto engines. The problem is, flame balls are delicate. 
A gentle bump is enough to knock one out. 

The mission that Charles leads, STS-107--a 16-day flight of the
shuttle Columbia, has 80+ science experiments on board. Three of them
involve flames and combustion. 

One called SOFBALL (short for "Structure of Flame Balls at Low Lewis
number") will ignite some of these flame balls in a special chamber
where scientists can experiment with them and measure their
properties. The shuttle's thrusters will be turned off to avoid
sending the floating balls careening into the walls of their chamber.
But what if a flame ball winks out anyway? Did scientists just learn
something new about flame balls? Or was it one of those g's in the
machine? 

"This is why we have SAMS--the Space Acceleration Measurement System," 
continues Charles. SAMS is a sensitive accelerometer that monitors 
vibrations and other small accelerations. "SAMS picks up everything," 
he says. People coughing. Things bouncing off walls. A knob gently 
twisted. "The device is so sensitive," he notes, "that thruster 
firings can overwhelm it." 

SAMS was developed for space research missions by a group of engineers 
and scientists at the Glenn Research Center. "When NASA started doing 
microgravity experiments onboard the shuttle, we realized that we 
would have to measure the vibratory g-levels," says Thomas Kacpura of 
ZIN Technologies, Inc., a contractor who works on SAMS. "Otherwise how 
would you know if a blip in your data was real or not?"

SAMS sensors have flown before on 22 shuttle missions, on the Mir
space station, and one is permanently mounted in the Destiny lab
module of the International Space Station. "It's indispensable for
space research," adds Charles.

On the shuttle Columbia (STS-107), SAMS is located near the SOFBALL
experiment, which is inside the SPACEHAB module in the middle of the
shuttle's cargo bay. Data from SAMS are transmitted directly to Earth
where researchers can monitor the microgravity environment in
near-real time and make decisions accordingly. If the shuttle is still 
vibrating after a thruster firing, for instance, they might wait a 
while before igniting their flame balls. SOFBALL isn't the only 
experiment that will benefit because SAMS can detect vibrations
throughout the ship. Its record of micro-accelerations will be like a
communal well--all are free to draw from the well as needed. 

So astronauts can go ahead and ride their exercise bikes, cough, turn
knobs ... even scream if they feel like it. SAMS won't neutralize
those vibrations, but it lets researchers keep track of them. And that 
sounds like good science. 

Editor's note: Not all of the g's in the machine make noise. Tune in
next week for a follow-up story, "Gravity's Last Laugh," which will
explain some other slow and silent accelerations onboard the shuttle
that researchers are monitoring using a device called OARE. 

Credits & Contacts
Author: Patrick L. Barry: Dr. Tony Phillips
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Steve Roy

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