If you have ever played with two toy magnets and tried to make one float over the other, you have done part of what TEMPUS will do, levitating a sample with a magnetic field.
The heart of TEMPUS
looks like a set of coils
you might use to heat coffee or tea at your desk. Actually, three coils
are used, one to emit radio waves that heat samples much like a microwave
oven, and two to generate an electromagnetic field that holds the sample
at dead center in the experiment chamber. Although TEMPUS, like the rest
of Spacelab, will be weightless, subtle motions can cause the specimen to
drift. TEMPUS generates the equivalent of a valley or null zone in the center
of the furnace. Moving the sample in any direction from center is like making
it roll up an increasingly steep hill. The diagram at right illustrates
the magnetic field lines produced by the TEMPUS apparatus. The closer the
lines, the stronger the field. The sample, repulsed by the field, will be
held away from the container sides.
Samples are the size of a gumball (left picture,
click for a larger image), about a third of an inch in diameter (7 to 8
mm). TEMPUS carries 22 samples on a lazy susan that rotates each sample
into position for a special probe to push it into the center of the coils.
Once there, the heater coil turns on and heats the specimen to as much as
2,500 deg. C.
Video cameras and heat sensors watch during experiments that rotate and oscillate the specimens. Analyzing how the specimens change shape - including how fast and how extensive those changes are - will yield basic information about the materials' properties.
One important measurement will come in a flash of
light (shown at left on a previous shuttle flight). Several experiments
will attempt to undercool the specimens. That is, they will be cooled below
their normal freezing point but still be liquid. This may sound odd, but
many materials can be undercooled if the sample is of high purity and nothing
disturbs it. Eventually, though, it will solidify. At that instant the molten
specimen gives off a flash of light as it surrenders the atoms and molecules
essentially stop moving and their energy of motion is converted into light.
Here is a 3 second video clip showing this phenomenon, from a previous shuttle
flight, in avi format
(480 KB) or quicktime
(540 KB).
Measuring where this recoalescence happens is one of the scientific objectives for TEMPUS.
The TEMPUS science team is looking forward to the MSL-1 experiments because of some problems they had on the IML-2 mission. Although the hardware performed mostly as planned, the coils had accidentally become misaligned and samples were pushed off center and into their cages which caused them too cool instantly. Enough valuable data were collected, though, to warrant a reflight.
TEMPUS is the acronym for electromagnetic processing under weightlessness in German (Tiegelfreies Elektromagnetisches Prozessieren Unter Schwerelosigkeit). The furnace was first flown on the second International Microgravity Laboratory (IML-2) mission in 1994.
The project scientist for TEMPUS is Dr. Egon Igry of the German Aerospace Agency. At Marshall, the U.S. project scientist is Dr. Jan Rogers.
Author: Dave
Dooling
Curator: Bryan Walls
NASA Official: John M. Horack
