LG-1997-02-450-HQ
ABOUT THE PICTURE
Astronauts are shown conducting experiments during the USML-2
mission. Catherine G. Coleman is busy at the Glovebox, which is a
small sealable box with gloves attached tor handling the
experiment inside. Fred Leslie is monitoring the Surface Tension
Driven Convection Experiment, which examines how surface tension
affects liquids.
USML MISSION SERIES
For the 1990s, NASA planned a series of missions that would
use the microgravity environment of the orbiting space shuttle as
a science laboratory. Many chemical and physical processes are
hidden by the force of Earth's gravity, but in microgravity, these
processes are revealed allowing scientists to observe them without
gravity's strong influence. The missions were fittingly named the
U.S. Microgravity Laboratory (USML) series.
To create a laboratory on the shuttle, NASA used Spacelab, which
is a module designed and built by the European Space Agency. The
module fits snugly inside the shuttle's cargo bay and is enclosed
and pressurized to provide a comfortable workspace for the
astronauts conducting the experiments.
Because there is no up or down in microgravity, racks to hold the
missions' experiment equipment were installed in Spacelab's
ceiling and floor as well as in its walls. The first USML mission,
USML-I, included 13 experiments and flew in June 1992. USML-2 had
17 experiments onboard and flew in November 1995. Both missions
were in orbit for about two weeks.
USML experiment results were recorded with a video camera and the
signals were sent to Earth. During USML-1, scientists on the
ground had to share the one video channel trom the Spacelab. For
USML-2, six video channels gave scientists more time to watch
experiments as they happened and to direct the astronauts
conducting their experiments.
USML-2 also had a live video uplink from the control center to the
shuttle so that astronauts watching a scientist perform a
procedure on the ground could then mimic that procedure in
space.
SCIENCE HIGHLIGHTS
BIOTECHNOLOGY: Proteins serve
many important functions in plants and animals, and viruses cause
diseases. Scientists use space-grown crystals to determine the
molecular structure of proteins and viruses. The crystals grow
larger in microgravity than they do on Earth, which gives
scientists better information about their structure. This
knowledge contributes to the design of disease-fighting drugs and
the engineering of plants with greater nutritional yield. More
than 1,500 crystals of proteins and viruses were grown during the
USML series.
COMBUSTION: On Earth, combustion, or
burning, depends on the flow of air around a flame. In
microgravity, that flow is nearly eliminated. Understanding how
the combustion process works in microgravity is important for
designing safe fuel systems tor space travel. On the USML
missions, scientists explored how candle flames extinguish, how
insulated wire smolders, and how drops of fuel burn in low
gravity.
FLUID PHYSICS: USML experiments
investigating fluids (liquids and gases) ranged from observing the
behavior of single drops of water to modeling the atmospheres of
planets. Microgravity provides scientists with a truer picture of
the influence of forces like surface tension, which is always
present but is often hidden by the stronger force of gravity.
MATERIALS SCIENCE: During the two
USML missions, a furnace was used to melt and cool various metals.
The metals form crystals as they solidify, and the structure of
the crystals determines the properties of the metal: whether it
will be hard, or brittle, or rust-resistant. On the shuttle, the
melted metals are not affected by flows caused by gravity. This
gives scientists greater control over the solidification process
and offers them clues for making better materials to improve
computers, infrared detectors (which can be used for observing the
Earth from space), and metal products such as cars and
airplanes.
WHAT IS MICROGRAVITY?
The force of Earth's gravity extends far into space. You would
have to travel 6.37 million kilometers (almost 17 times farther
away from the Earth than the Moon) to reach a point where the
strength of Earth's gravity is one-millionth of what it is on
Earth's surface. Why, then, do astronauts and objects float in the
space shuttle as if they were weightless? Weight is the force with
which a body is attracted to the Earth. If an object is falling
due only to the force of gravity, its apparent weight (that which
could be measured while in freefall) is nearly zero. Any object in
a state of freefall experiences microgravity, or near
weightlessness. An orbiting spacecraft is actually falling around
the Earth. The spacecraft's altitude and speed cause its fall to
match the curvature of the Earth, so that it never hits the Earth
but continually orbits the planet. All objects carried by an
orbiting spacecraft are also in a state of freefall.
To learn more, try these internet addresses:
http://microgravity.msad.hq.nasa.gov/
http://liftoff.msfc.nasa.gov/spacelab/usml2/welcome.html