Mineo Suzuki

Comparison of Macro and Microtribological Property of Molybdenum Disulfide Film Exposed to LEO Space Environment

Macro- and microtribological properties of the MoS2 film exposed to atomic oxygen, ultraviolet rays and radiation both in low earth orbit (LEO) and in ground-based facility were evaluated relevance to micro/nano satellites. MoS2 samples are exposed to LEO space environment by the space environment exposure device experiment on international space station. Laser-detonation atomic oxygen beam source was used for atomic oxygen simulation on the ground. X-ray photoelectron spectroscopy and energy dispersive spectroscopy measurements suggested that electron beam and ultraviolet exposure did not affect chemical structure of MoS2 surfaces. However, atomic oxygen-exposed and flight samples showed surface oxidation. It was found that the macroscopic friction coefficient of the flight sample was similar to that of the control sample. In contrast, remarkable increase in friction coefficient in microscopic properties was observed.

Space Environment Effects on Materials at Different Positions and Operational Periods of ISS

A space materials exposure experiment was condcuted on the exterior of the Russian Service Module (SM) of the International Space Station (ISS) using the Micro‐Particles Capturer and Space Environment Exposure Device (MPAC&SEED) of the Japan Aerospace Exploration Agency (JAXA). Results reveal artificial environment effects such as sample contamination, attitude change effects on AO fluence, and shading effects of UV on ISS. The sample contamination was coming from ISS components. The particles attributed to micrometeoroids and/or debris captured by MPAC might originate from the ISS solar array. Another MPAC&SEED will be aboard the Exposure Facility of the Japanese Experiment Module, KIBO Exposure Facility (EF) on ISS. The JEM/MPAC&SEED is attached to the Space Environment Data Acquisition Equipment‐Attached Payload (SEDA‐AP) and is exposed to space. Actually, SEDA‐AP is a payload on EF to be launched by Space Shuttle flight 2J/A. In fact, SEDA‐AP has space environment monitors such as a high‐energy partic...

Comparison of Properties of Solid Lubricant Between Two Exposure Experiments Aboard the ISS

To evaluate the degradation of materials in low Earth orbit space environment, the Space Environment Exposure Device (SEED) experiments were carried out on the International Space Station. As part of these experiments, changes in the tribological properties of a molybdenum disulfide bonded film that is used as a solid lubricant, were evaluated. The results of friction tests in a vacuum and surface analysis by XPS were compared between two exposure experiments aboard the Service Module (SM) and the Japan Experimental Module (JEM). The investigations revealed silicon and fluorine contaminations in the JEM/SEED flight sample, but with a lower amount of silicon contamination than the SM/SEED flight sample. The JEM/SEED flight sample and ground-based tested samples showed lower friction coefficients than a reference sample at the beginning of the tests. The friction behavior of the JEM/SEED flight sample was similar to those of SM/SEED flight samples.

Microtribological Properties of Molybdenum Disulfide Bonded Film Exposed to Space Environment by SM/SEED Mission

Macroscopic and microtribological properties of MoS2 films exposed to atomic oxygen, ultraviolet rays and radiation both in low earth orbit (LEO) and in ground-based facility were evaluated. The MoS2 samples are exposed to LEO space environment in the Space Environment Exposure Device (SEED) experiment on International Space Station (ISS). Laser-detonation atomic oxygen beam source was used for atomic oxygen simulation on the ground. It was found that the macroscopic friction coefficient of the flight sample was similar to that of the control sample. In contrast, remarkable increase in friction coefficient in microscopic properties was observed.

Transfer Film Lubrication for Ceramic Pairs at a Temperature of 800°C and a Pressure of 1300 Pa

Tribological performance of two types of Si3 N4 pairs and one SiC pair was examined at a pressure of 1300 Pa and a temperature of 800°C. Prior to friction tests, a transfer film was formed from a self-lubricating composite in atmospheric environment. Test results showed that the transfer film acted effectively as a lubricant to prevent surface damage and lower friction for Si3 N4 pairs, but it was not effective for the SiC pair. This result confirms that transfer film lubrication is one of promising candidates of lubrication methods for re-usable space vehicles, in which operation at high temperature in low vacuum is required.Copyright

Effect of Aging on Wear Life of Sputtered MoS2 Films

Sputtered MoS2 films deposited on SUS440C stainless steel disks were stored in a desiccator or in a vacuum of 10−5 Pa to examine the effect of aging on their tribological performance. Five years’ storage in a desiccator (25%±5%RH, room temperature) elongated the wear life in a vacuum of sputtered MoS2 films in average by a factor of four. A sputtered MoS2 film stored in a vacuum for seven years showed tenfold increase in wear life when tested in a vacuum.Copyright