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The Iowa Joint Experiment in Microgravity Solidification was an experiment designed to study metal-matrix composites in a microgravity environment. It flew in the cargo bay of the space shuttle Endeavor (STS69) attached to the cross bay carrier of the Wake Shield experiment. IJEMS was composed of four experiments of identical construction, with varying run time parameters. Of the four experiments, one ran perfectly, two had mechanical failures, and one did not run long enough. Even with those faults, it was a grand success for the mostly student engineers from Iowa State University.



Experiment
IJEMS was a set of four experiments designed to study metal-matrix composites in a microgravity environment. Each experiment had an identical mechanical construction which consisted of a complex crucible with five thermocouples inserted at various points along it's length, and three foil heaters, two of which were wrapped along it's length, and the third was fastened to the base.

Experiment Crucible


The crucible was designed to minimize the volume of the tin-cadmium ingot it enclosed. Five thermocouples protruded into the crucible A spring loaded piston forced the melted ingot into the smallest volume.

The tin-cadmium ingot contained nickel particulates which were used to measure the solidification behavior of the ingot.

Each experiment ran with a custom heating and cooling profile. Although slightly different compared to each other, the profiles all heated the ingot to the melting point, and allowed the ingot to cool while maintaining a temperature gradient between the endpoint thermocouples.

IJEMS Components and Construction
IJEMS had the following major systems:


 * Physical structure
 * Power conditioning equipment, and distribution
 * Process control / data acquisition equipment and software
 * Component stabilization
 * Experiment Crucible

Physical Structure
The physical structure, a Smartcan, was an airtight vessel with electrical interfaces to the external environment. Internally the smartcan was subdivided into four quadrants. Each quadrant wall served as a mounting point for one experiment, and in some cases other equipment and cabling.

Power Conditioning Equipment, and Distribution
Power was supplied unfiltered at 28V with a maximum of 20A. Unfiltered power was cabled to two distinct circuits. Circuit 1 was filtered and converted to various voltages to drive the electronics. Circuit 2 was cabled to Solid State Relays which through software control would drive the heaters in each experiment.

Process control / data acquisition equipment and software
The system was comprised of the following components:
 * 33Mhz 486SLC based single board computer with 2MB RAM, 3MB of flash storage, and running DOS.
 * 1 digital I/O board
 * 2 A/D converter boards
 * 1 four slot backplane
 * 1 Solid state relay array.
 * 2 screw terminals

The system was run on a 33Mhz 486SLC based single board computer provided by Toronto MicroElectronics. The computer was configured with 2MB of RAM, and 3MB of flash which was presented as a hard drive to the DOS operating system.

The process control was a closed loop system comprised of thermocouples, heaters, and Solid State Relays to control power to the heaters, and software to drive the entire system.

For each experiment module, the software would enable all three heaters causing the ingot to melt. Once melted, the two wrap heaters would be turned off, while the base heater remained on. Heating only one end caused a temperature gradient through the length of the ingot.

Component Stabilization
IJEMS was required to withstand various vibration and shake tests, each of which was representative of the ascent, and descent conditions expected in the shuttle cargo bay. Most components were fastened directly to the smartcan structure. However some components required additional support, or locking.
 * Copper circuit board stiffening plates
 * Heat conducting epoxy coated electronics
 * Silicone coated screws terminals
 * zip ties wrapped cable bundles





Pre-flight testing

 * IJEMS was housed within a smartcan for which the volume of air was replaced with 1/2 ATM of dry nitrogen. Some electrical components are susceptible to damage caused by vacuum conditions. Of particular concern were electrolytic capacitors. An assortment of capacitors were tested at various vacuums conditions and none failed during the testing. These were assumed to be representative of the components incorporated into IJEMS.


 * IJEMS was required to survive various shake and vibration testing including 9G vibrations testing.

Flight results

 * Several thermocouples were positioned throughout the smartcan. The resulting data is illustrated in the following graphs. The data shows temperatures that fell outside the warranted operating range of many of the system components.