The EML payload consists of a Gas Supply Module, a Levitation Power Supply and Water Pump Module, the Experiment Module, and the Experiment Controller Module. The modular design of the payload allows the replacement of entire modules or components making EML a flexible payload – allowing for maintenance and upgrades.
The operation of the payload is mostly automatic – only requiring the crew members to set up the facility, perform regular maintenance and insert/remove sample cartridges. Experiment runs are executed automatically based on parameters loaded by controllers on the ground. For the experiment run, live telemetry and video is needed to allow intervention from the ground in case of instabilities or other issues. For that, the payload provides a rapid reaction time to abort an experiment run on ground command.
Finally, sample dampening can be used to mechanically dampen oscillations in a sample by moving the sample holder closer to the sample.
EML can accommodate up to 18 samples, each 5 to 8 mm in size. The samples are facilitated in individual sample holders that are installed in a carousel inside the sample chamber that allows the selection of a sample that is then transferred from the storage position to the RF coil for an experiment run and back to the holder when the experiment finished to return to Earth. Sample holders developed for EML include a cup-type and cage design with slit openings for sample observation. The holders consists of ceramics with high thermal stability and no interaction with the electromagnetic field. Silicon nitride is used for the cup holders while tungsten-rhenium is used for the cage.
The experiment is designed for an easy installation and removal of the sample chamber that allows the processed samples to be returned to Earth while new sample chambers can be flown up on different cargo vehicles.
The camera can operate at a frame rate of up to 200 fps at a field of view of 8x8mm and a 280x280 pixel resolution. Resolution increases at the expense of frame rate, settings of 150Hz and 352x352 pixels, 50Hz and 704x704 pixels, and 15Hz and 1280x1024 pixels can be selected for the different experiment and maintenance runs.
The radial camera system observes the sample through an 8mm gap in the RF coil also using a series of exchangeable mirrors. The system operates in a recalesence mode and oscillating drop mode using a bifocal lens that images a constant field of view on two different detectors. Imaging at 30,000 frames per second allows the camera to capture the progressing solidification front on a sample providing a sufficient resolution that is increased in the oscillating drop mode at the expense of frame rate to visualize surface oscillations and thermal expansion of the sample. The camera includes an 8GB ring memory to record the video at high speed before being transferred to the payload memory and finally to the ground. HSC has a 800 by 600 pixel CMOS detector achieving a resolution of 250 by 250 pixels at 30kHz and 600 by 600 pixels at 8.5kHz. The radial camera also provides thermal radiation mapping by displaying temperature distribution across the sample in false color as part of ground processing.
Another diagnostics tool is the RF coil system itself that is used to record frequency, voltage and current of the oscillating circuits at high time-resolution to provide electrical conductivity and inductivity measurements of the sample since the RF coils and sample act as a transformer with the sample being the dampening element. Knowing the geometry of the coils and measuring the given properties allows the calculation of conductivity and inductivity.
Data processing and payload commanding is accomplished with the Experiment Control Module that collects the various data streams from the payload at frequencies of 1 to 100Hz and transfers it in real time to the Drawer Rack using the Express Rack Data Protocol. Video is acquired separately by two systems for the two cameras. The axial video feed is processed in real time to deliver two data formats – uncompressed video that is stored in the mass memory for post-experiment downlink and a compressed video for downlink in real time for monitoring by ground controllers. The radial camera transfers acquired video from its own ring memory to the mass memory for downlink to the ground.
Aboard ATV-5, cartridges with samples for six different studies using the EML are being delivered to ISS.
The Coolcop experiment will study the mixing properties of copper and cobalt metals in zero-G since the two metals are known for their bad mixing characteristics on Earth. Studying surface tension during the experiment runs may provide valuable data for the improvement of casting processes on Earth.