We present the results of our recent experiments for physicochemical processes of hydrogen such as tunneling reaction and surface diffusion on amorphous solid water at low temperatures as low as 10 K, which are closely related to chemical evolution on cosmic ice dust in a very cold region of space, so-called molecular cloud.
The cathode-less electron cyclotron resonance ion engines propelled the Hayabusa asteroid explorer, launched in May 2003, which is focused on demonstrating the technology necessary for a sample return from an asteroid, using electric propulsion, optical navigation, material sampling in a zero gravity field, and direct re-entry from a heliocentric orbit. It rendezvoused with the asteroid Itokawa after a two-year deep space flight using the ion engines in 2005 and accomplished a round trip space mission between Earth and an asteroid in 2010. For the deep space odyssey between Earth and the asteroid, the ion engines served the total accumulated operational time 39637 hour･unit, the powered spaceflight in 25590 hours. Hayabusa and microwave discharge ion engines pioneered the space exploration and will bring us further deep space. This paper also report recent topics in space technology associated with the surface science.
Thermal control is one of the most important issues in designing a spacecraft. A light, reliable, and inexpensive thermal-control device is strongly demanded. We have developed a new thermal-control device, Smart Radiation Device (SRD), based on a metal-insulator transition of (La, Sr) MnO3 perovskite-structure oxides. The emittance property of the device changes significantly at the transition temperature near room temperature; high at high temperatures whereas low at low temperatures. Thus, the device automatically controls the emmisive heat transfer from the spacecraft without the need for any mechanical parts and electrical power. The practical validity of the device was demonstrated in the recent flight of a spacecraft “HAYABUSA”. The developed oxide-thin-film radiator also greatly reduces the weight and production cost of the thermal control devices.
We have devoted the past 25 years to the development of the Comprehensive Analytical System for Terrestrial and Extraterrestrial Materials (CASTEM), an exclusive laboratory for materials science. CASTEM facilities allow for the determination of elemental and isotopic abundances of geochemically significant elements in multi-scale ranges. CASTEM research targets are not limited to lithic rocks. We have successfully analyzed a variety of materials including human tissue. Utilizing CASTEM, we conducted the “initial analysis” of grains collected from the outermost surface of the asteroid Itokawa that were subsequently returned to Earth by the Hayabusa spacecraft. These analyses involved processing the grains, describing surface morphology, and the determination of elemental and isotopic abundances. The history of the asteroid was unveiled through comprehensive geochemical examinations of the microscopic grains suggesting a physically hostile environment at the asteroid's surface. Our results reveal that impact processes play a central role in the long-term evolution of planetary bodies in the solar system.
The review reported the microgravity experiments performed using space shuttle, drop tower and Chinese recovery satellite. In addition, the experimental plan for microgravity experiment in the International space station was introduced. From the space shuttle experiment, it was found that the space-grown sample with free melt surface was almost spherical and Marangoni convection enhanced the melt mixing. Whereas the melt mixing without free melt surface was controlled by diffusion. Formation of spherical projections on the surface of InGaSb was in-situ observed using a high speed CCD camera in the drop experiment. Microgravity studies on the dissolution and crystallization of InxGa1-xSb was carried out having the sandwich combination of GaSb(111)A/InSb/GaSb(111)B using the Chinese recoverable satellite. It was demonstrated clearly that the shape of the solid/liquid interface and composition profiles in the solution was significantly affected by gravity.
The requirements on space mission duration have continued to increase and tribology is the key technology for extending life of space mechanisms. This paper describes adhesion experiment, which is the most fundamental wear mechanism in vacuum, and lubrication technology focused on fluid lubricants (oil or grease). It is also shown that two oil-lubricated space mechanisms, a reaction wheel and a strain wave gearing, operate with a small quantity of lubricant. Basic study using a laboratory friction tester showed that the lubrication lifetime with a small quantity of fluid lubricants under high vacuum become short when the lubricant quantity is small. This is possibly due to the insufficient resupply of the lubricant from the surrounding due to the viscosity increase. The occurrence of oxidative polymerization under high vacuum catalyzed by a nascent surface is suggested.