The Materials Science Laboratory supports microgravity research in the areas of solidification physics, measurement of thermo-physical properties of materials, and crystal growth. Therefore a number of different types of module inserts, exchangeable on orbit, are foreseen.
The MSL is installed in NASA's First Materials Science Research Rack (MSRR-1), in the US Laboratory Module of the ISS, called "Destiny". This rack is equipped with the Active Rack Isolation System (ARIS) which provides isolation from microgravity disturbances.
The Scientific Reference Module ( SRM ) of the exchangeable Furnace Insert Low Gradient Furnace will be placed at MUSC.
Low Gradient Furnace (LGF)
This is the first European furnace insert for MSL. It is developed to conduct experiments in the field of Bridgman crystal growth. The LGF consists of two heated cavities separated by an insulating, “adiabatic” zone. It can establish restricted, but well-controlled gradients between two stable temperature plateaux. Crystal growth is performed by translating the furnace over a stationary sample. Thermomechanical stresses in the grown crystal are minimised by keeping the solidified part of the sample in the heated cavity throughout processing. This insert can also be used for thermo-diffusion experiments, maintaining the furnace stationary, and using only the temperature gradient capability. Isothermal experiments can also be carried out utilising suitable sample/cartridge configurations.
LGF performance characteristics
The LGF consists of seven separately controlled heating zones. The heater elements are based on pyrolytic boron-nitride/pyrolitic graphite heater technology, with carbon composite diffusers to provide thermal uniformity. The LGF provides high-stability thermal control by sapphire optical fibre thermometers (OFT) and a high performance control algorithm. The achievable temperature gradients depend on cartridge design and on the sample’s thermal conductivity. An electromagnet provides for controlled stirring of the melt by a rotating magnetic field.
LGF technical data
A fundamental feature of MSL is its capability for on-orbit exchange of furnace inserts. In this way, the facility supports various materials processing techniques, with different thermal profiles. This also allows researchers the possibility to design new furnace inserts as scientific requirements evolve.
These are schematic examples of temperature profiles that can be implemented in MSL:
MSL is also reconfigurable for Experiment Cartridge instrumentation, and can accept experiment-dedicated diagnostics.
Experiments in MSL can only be performed subject to certain restrictions imposed by the manned-space environment, the ISS operations, and the facility itself. These are described in the section Scientific Utilisation of MSL.
MSL safety philosophy
MSL incorporates instrumentation to guarantee a safe working environment for the crew under all possible conditions and events. Hazards that may be anticipated include:
Overheating in the furnace insert is detected by various temperature sensors: in the heaters themselves, in the furnace insert’s cooling loop, and in the experiment cartridge. A hard-wired safety circuit, independent from the facility electronics, compares measured values to experiment-specific set points and switches off power to the furnace insert if a critical value is exceeded. The water-cooling system is designed to withstand possible temperature overshoots during the time between switch-off and actual cool-down; any damages shall be confined to the furnace insert, which can be exchanged.
Loss of cartridge integrity during processing is a hazard for toxic samples. These may release particles into the core facility and ultimately expose crew to toxic materials. Experiment cartridges containing toxic substances will therefore be required to include an amount of krypton tracer gas. Cartridge integrity is monitored by mass spectrometry analysis of the krypton peak for evacuated gases throughout processing. In case of ambiguous results, inspection of the cartridge through a glove-bag is anticipated. If a cartridge is believed to have leaked, the whole process chamber can be sealed off and transported to ground for decontamination.
Overheating in the electronics boxes due to malfunctioning components constitutes a fire hazard. All electronics boxes will therefore be equipped with temperature sensors. Anomalous temperatures will result in the immediate switch off of the facility. An alert signal will be issued to the crew.
Scientific utilisation of MSL
Once selected, and the appropriate contracts placed, the lead time for the development of an MSL experiment is expected to be 18–24 months. This time will be devoted to the design, construction, and qualification of a safe space experiment, and to the establishment of appropriate furnace processing parameters. In principle, the following split of responsibilities will be observed for the funding of MSL experiment hardware: ESA:
Investigators, with national agencies (also ESA for applications-oriented projects):
The International Space Station will be serviced every three months, and together with the subsequent operational period, this set of operations is called an increment. The interval between uploading of new experiment cartridges to MSL, and the return of the processed ones to ground, will consequently be (at least) three months. It is intended to run MSL experiment campaigns for the different furnace inserts. Several furnace inserts may be used within one increment, supporting different fields of research.
The execution of the space experiment itself starts with the astronaut loading the experiment cartridge into MSL. After evacuation of the process chamber, an Experiment Sequence is initiated; it consists of a number of process steps with pre-defined parameters (for instance heat-up, directional melting, homogenisation, pulling/directional solidification, quenching and cool-down). The transition from one step to another can either be time- or event-controlled. As a baseline, the Experiment Sequence is executed automatically from beginning to end, but MSL also provides the possibility to adjust process parameters and step sequences in real-time, through “telescience,” both from the ground and by the crew. Such actions, though, have to be verified as being safe before their execution. After processing, the cartridge is removed from the facility and stowed until it can be transported back to earth.