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Holes Hold Water
Cages show new way to hold
liquids in space experiments
When you were a kid did you ever serve someone a drink in a dribble glass?
You know, with little holes that leak out on your "friend's" chin?
Well, it wouldn't dribble in space, and that may lead to a new way of holding
liquids in place for experiments in growing crystals in weightlessness.
"It's a whole new ball game in microgravity," said Dale Kornfeld,
a microgravity scientist with the Space Sciences Laboratory at Marshall
Space Flight Center in Huntsville, Ala.
"With space, we have to throw away all our experiences in one-gravity,"
added Basil Antar, a fluid dynamics professor at the University of Tennessee
Space Institute in nearby Tullahoma, Tenn.
Closeup
pictures show two of the cages tested by Kornfeld and Antar on the low-gravity KC-135 aircraft. All of the models -
including those with half-inch-wide meshes - performed as if they had solid
walls during tests.
Click on pictures for larger view.
The reason the dribble glass won't work in space is because
of surface tension, the same force that causes water to act like it has
a thin skin on the surface (and allows bugs to run across water without
sinking). Water forms drops - instead of spreading into a thin sheet - because
surface tension pulls the water together. Surface tension also makes water
cling to objects, which is why a window screen looks like a million tiny
lenses after a rainstorm or a drink rises slightly inside a straw - or the
drink dribbles down your friend's neck instead of dropping away.
Scientists from MSFC's Space Science Lab "fly
through the air with the greatest of ease" as they test the liquid
cages during weightless periods aboard the KC-135 airplane..
A window screen is one of several materials that Kornfeld
and Antar used in flight tests aboard NASA's
"Weightless Wonder." Their findings point the way to solving
problems that some scientists have had in growing crystals in space.
Like many scientific developments, they started with someone else's problem.
On the U.S. Microgravity Laboratory-1 mission (USML-1 on Columbia, STS-50;
June 25-July 9, 1992), payload specialist-astronaut Larry Delucas (a scientist
from the University of Alabama in Birmingham) kept getting bubbles in the
fluid for a crystal growth experiment he was running.
Kornfeld, NASA's 1984 Inventor of the Year, has spent more than 30 years
designing and testing microgravity experiments for space. He was working
as an Assistant Mission Scientist on USML-1 in Marshall's Payload Operations
Control Center when he noted the problem Delucas was having. Being an experimentalist,
he recruited Professor Antar, a theoretician who has worked with NASA for
more than 20 years on microgravity fluid problems, to help investigate the
problem after the flight.
What they found - and it took a high-speed movie camera working at 400 frames
per second - was that the needle Delucas was using accidentally whipped
open a small cavity in the water in microgravity and pulled in tiny air
bubbles.
Air bubbles have long been a problem in experiments to grow high-quality
crystals of proteins in space. Bubbles often get trapped in the corners
of growth chambers, or get stuck to the walls, and stay there - until the
experiment is under way, then the bubbles can wander and cause crystals
to grow where you don't want them. And sometimes the crystals grow on the
chamber walls where you don't want them.
So, Kornfeld and Antar expanded their experiments to look at the problems
of injecting bubble-free liquids into containers. They built plexiglass
cubes, 5.1 cm (2 in) on a side, and injected water and other fluids like
those used in protein crystallization. In one series of tests they sprayed
a water jet across the cube to hit the opposite wall and observe how it
stuck and spread across the wall. In others, they gently injected liquid
and watched as it formed a growing sphere held in place by surface tension.
And that led to a new idea. On his way home one day, Antar realized that
the liquid was showing them a better way to contain itself in space - a
container without walls!
"But, what you need is something to 'pin' the fluid in place,"
Kornfeld said.
Surface tension will hold the fluid together, but the fluid mass needs something
on which to pin itself. Antar's idea was to build a container out of as
little material as possible, a cage, that would act as an attach point for
surface tension.
Screens have been used in rocket propellant tanks to capture enough fuel
and oxidizer so they can restart rockets in orbit, but not to act as an
experiment "container."
Operating on a low budget -- they built their hardware for less than $10,000
- Kornfeld and Antar devised a series of cages
from chicken wire, window screen, fishing line, and hooked rug base. These
were suspended in plastic splash boxes (to keep the water from floating
out into the airplane) and water lines were attached to fill the cage during
the weightless period of the KC-135. High-speed film cameras captured everything
on 16mm film and showed that the idea worked just the way Antar and Kornfeld
thought it would.
When replayed in slow motion, you can see water ooze in like the water creature
in The Abyss, wobble around a bit, then latch onto the mesh as
soon as the surface touches solid. It sits there, seemingly breathing in
an out until the low-g period ends and everything drains out of the cage
as free fall ends.
Kornfeld said that the new design offers an innovative way to contain and
grow protein crystals in space. With their solutions caged in a mesh and
suspended inside a clear plastic splash and vapor container, scientists
could circulate air to change evaporation rates, or insert needles to remove
air bubbles or insert seed crystals.
Kornfeld and Antar plan additional experiments aboard the KC-135 using sound
waves and a mesh plunger as alternative means of driving out bubbles that
might get into the cage from the injection line.
But because the liquid still could be shaken out by quick movements, don't
look for astronauts to have coffee mugs built of chicken wire. Not even
as a dribble glass.
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Author: Dave
Dooling
Curator: Bryan Walls
NASA Official: John M. Horack
Closeup
pictures show two of the cages tested by Kornfeld and Antar on the low-gravity KC-135 aircraft. All of the models -
including those with half-inch-wide meshes - performed as if they had solid
walls during tests.