Effect of Atomic Oxygen Exposure on Surface Resistivity Change of Spacecraft Insulator Material

Spacecraft surface charging can lead to arcing and a loss of electricity generation capability in solar panels or even loss of a satellite. The charging problem may be further aggravated by atomic oxygen (AO) exposure in Low Earth orbits, which modifies the surface of materials like polyimide, Teflon, anti-reflective coatings, cover glass etc, used on satellite surfaces, affecting materials properties, such as resistivity, secondary electron emissivity and photo emission, which govern the charging behavior. These properties are crucial input parameters for spacecraft charging analysis. To study the AO exposure effect on charging governing properties, an atomic oxygen exposure facility based on laser detonation of oxygen was built. The facility produces AO with a peak velocity value around 10-12km/s and a higher flux than that existing in orbit. After exposing the polyimide test material to the equivalent of 10 years of AO fluence at an altitude of 700-800 km, surface charging properties like surface resistivity and volume resistivity were measured. The measurement was performed in a vacuum using the charge storage decay method at room temperature, which is considered the most appropriate for measuring resistivity for space applications. The results show that the surface resistivity increases and the volume resistivity remains almost the same for the AO exposure fluence of 5.4×1018 atoms cm-2

Development of Electron-emitting Film for Spacecraft Charging Mitigation

Prevention of spacecraft charging and discharging has become increasingly important as geostationary Earth-orbit satellites employ higher bus voltages. There are numerous mitigation techniques against spacecraft charging, including electron emission from the spacecraft chassis. A new electron emission device operating in a completely passive manner has been developed, which uses the field enhancement at the triple junction where the interface of metal and insulator is exposed to space. It has been named electron-emitting film for spacecraft charging mitigation (ELF’S CHARM). Microetching was applied to polyimide-copper laminated film to manufacture a laboratory prototype. This prototype ELF maintains the emission current at the steady state from the triple junctions instead of leading to arcing. The electric field at the triple junction is macroscopically enhanced by charging the polyimide film and microscopically by dielectric impurities on the copper surface. The laboratory experiments confirmed a stable current emission from 10 to 100μA for 4 hr from a 5-mm square sample having a 500-μm microetching pattern. Recently, the endurance of this ELF design has been confirmed by 100 hr of accumulated emission testing

Effects of Energetic Electron and Proton Irradiation on Electron Emission Yield of Polyimide Induced by Electron and Photon

As the electron emission yield induced by electron and photon plays a key role in surface potential of spacecraft materials, the ground based degradations including 500 keV electron and 50 keV proton irradiation with 4 different fluences were conducted for the polyimide film separately. Based on the developed measuring systems, thecomparative measurements of total electron emission yield and photoelectron emission yield were carried out for the virgin and degraded polyimide samples respectively. The total electron emission yield and photoelectron emission yield tended to have different variation tendency after high energy electron and proton irradiation. The Monte-Carlo analysis software Casino and SRIM were used to analysis the distribution and stopping power of electron and proton respectively. According to the measurement results and analysis, the free radicals caused by irradiation was considered to be the main effect for polyimide films, which can primarily reveal the degradation mechanism of energetic electron and proton on the emission yield of polyimide.The 29th International Symposium on Space Technology and Science (29th ISTS), June 2-9, 2013, Nagoya, Aich

ATF6α/β-mediated adjustment of ER chaperone levels is essential for development of the notochord in medaka fish.

ATF6α and ATF6β are membrane-bound transcription factors activated by regulated intramembrane proteolysis in response to endoplasmic reticulum (ER) stress to induce various ER quality control proteins. ATF6α- and ATF6β single-knockout mice develop normally, but ATF6α/β double knockout causes embryonic lethality, the reason for which is unknown. Here we show in medaka fish that ATF6α is primarily responsible for transcriptional induction of the major ER chaperone BiP and that ATF6α/β double knockout, but not ATF6α- or ATF6β single knockout, causes embryonic lethality, as in mice. Analyses of ER stress reporters reveal that ER stress occurs physiologically during medaka early embryonic development, particularly in the brain, otic vesicle, and notochord, resulting in ATF6α- and ATF6β-mediated induction of BiP, and that knockdown of the α1 chain of type VIII collagen reduces such ER stress. The absence of transcriptional induction of several ER chaperones in ATF6α/β double knockout causes more profound ER stress and impaired notochord development, which is partially rescued by overexpression of BiP. Thus ATF6α/β-mediated adjustment of chaperone levels to increased demands in the ER is essential for development of the notochord, which synthesizes and secretes large amounts of extracellular matrix proteins to serve as the body axis before formation of the vertebra

Evaluation of electron-emitting film for spacecraft charging mitigation (ELFs charm)

To protect the satellite from the accidents due to spacecraft charging, Kyushu Institute of Technology (Kyutech) is developing a device called ELFs-Charm, which stands for ELectron-emitting Film for Spacecraft CHARging Mitigation. ELFs-Charm was mounted on HORYU-II, which was launched to a Polar Earth Orbit in May 2012. From the orbital data, the emitter’s soundness and working principles were confirmed. As a next step, we are considering the practical operation for mitigation of spacecraft charging. The present emission level was not enough to increase the satellite potential. Theoretically, if the emitter can emit more electrons than the incoming electrons, it can increase the satellite potential during the sub-storm. We focus our efforts on improving two parameters. One is the potential difference of the emitter surface. Another one is the threshold voltage of electron emission. A potential difference of the emitter surface depends on the insulator charging capacity due to the secondary electron emissions with each energy gap between the satellite potential and the primary electron energy. The threshold voltage depends on the shape of emitter. We can improve the ELFs-charm emission performance by measurement of these two parameters in ONERA Space Environment vacuum chamber and Kyutech Space Environment chamber. In this paper, we describe the two parameters of several samples and how the performance was improved.The 31st International Symposium on Space Technology and Science (31st ISTS), June 3-9, 2017, Matsuyama, Japa

Ancient Jomon genome sequence analysis sheds light on migration patterns of early East Asian populations

Anatomically modern humans reached East Asia more than 40,000 years ago. However, key questions still remain unanswered with regard to the route(s) and the number of wave(s) in the dispersal into East Eurasia. Ancient genomes at the edge of the region may elucidate a more detailed picture of the peopling of East Eurasia. Here, we analyze the whole-genome sequence of a 2,500-year-old individual (IK002) from the main-island of Japan that is characterized with a typical Jomon culture. The phylogenetic analyses support multiple waves of migration, with IK002 forming a basal lineage to the East and Northeast Asian genomes examined, likely representing some of the earliest-wave migrants who went north from Southeast Asia to East Asia. Furthermore, IK002 shows strong genetic affinity with the indigenous Taiwan aborigines, which may support a coastal route of the Jomon-ancestry migration. This study highlights the power of ancient genomics to provide new insights into the complex history of human migration into East Eurasia