豊田 裕之

深宇宙探査技術実証機デスティニー・プラス（DESTINY PLUS(＋)）は，理工一体でふたご座流星群母天体である小惑星(3200) Phaethonの高速フライバイ観測に挑む計画である．2025年度の打ち上げを目指し，現在開発を進めると共に，目標天体Phaethonの地上観測を継続的に行っている．本連載では，DESTINY+の計画概要，目指すサイエンス，プロジェクト化の経緯，搭載観測装置，地上観測，地上研究や他の探査計画との連携，サイエンス推進に係る活動などを紹介していく．

Abstract This paper discusses the hypervelocity impacts of micrometeoroids and orbital debris (MMODs) on inverted metamorphic triple-junction (IMM3J) and perovskite solar cells, which are much thinner than conventional triple-junction (3J) solar cells. We experimentally found that IMM3J solar cells can suffer from short-circuit faults due to hypervelocity impacts of MMODs unlike conventional 3J cells, and determined the projectile diameters and velocities that could cause them using a model proposed by Burt. No short-circuit mode was identified in perovskite solar cells, but they had open-circuit faults several days after the hypervelocity impact experiment, which are possibly attributed to the decomposition of the perovskite crystal by moisture in the air due to the broken seal.

A 6U CubeSat “OMOTENASHI” was developed to be the world's smallest moon lander. It was launched by NASA's SLS Artemis-1 on November 16, 2022. However, because of the spacecraft anomaly, the battery was depleted and the communication with the spacecraft had been lost. After we gave up the moon landing experiment, we have been conducting a search and rescue operation till September 2023. But it was unsuccessful, unfortunately. In this article, the mission objective, the spacecraft design, the planed mission scenario, and the in-orbit operation results are presented. Additionally, lessons learned from the development and the in-orbit operation are presented.

Organo-halide perovskite solar cells (PSCs) are lightweight and low cost, and they offer high power conversion efficiencies. PSCs have proven to be useful in terrestrial applications. In addition, they are particularly attractive for space applications because they can offer a higher radiation tolerance than GaAs and Si solar cells. This paper evaluates the damage coefficient for minority-carrier diffusion length K-L of perovskite crystals after 1 MeV electron irradiation by time-resolved photoluminescence measurements to investigate the reason for their high radiation tolerance. Results show that perovskite crystals have a lower damage coefficient K-L than that of InP crystals with a high radiation tolerance. On the other hand, first-principles calculations indicate that the displacement energy of perovskite crystals is as low as that of Si, which does not have a high radiation tolerance. The present results suggest that the annealing effect occurs for PSCs at room temperature.

© 2020 COSPAR This paper reports on the manufacturing and evaluation of a solar power sail membrane prototype for the OKEANOS project. The in-house prototype was built by the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. Mechanical and electrical evaluation tests were conducted. The membrane, thin-film solar cells, reflectivity control devices were good condition after the manufacturing and handling. The improvements in the manufacturing process and design were found. The manufacturing process and design were fundamentally established. After the prototype, improvement plans for the manufacturing process and design were tried. We have a prospect of manufacturing the flight model sail and continue to the development.

Copyright © 2020 by the International Astronautical Federation (IAF). All rights reserved. A 6U CubeSat “OMOTENASHI” will be the world's smallest moon lander which is launched by NASA SLS Artemis-1. Because of its severe mass and size limitation, it will adopt semi-hard landing scheme. That is, OMOTENASHI is decelerated from orbital velocity to less than 50 m/s by a small solid rocket motor and shock absorption mechanism has been developed to withstand the high-speed impact. Ultra small communication system (X-band and P-band) is also developed. It observes radiation environment of Earth and moon region with portable dosimeters. This paper shows the mission outline, the design, and the development results of OMOTENASHI.

This paper reports the design, fabrication, and testing of a reversible thermal panel breadboard model (RTP-BEM). RTP is a flexible, re-deployable radiator that autonomously controls the temperature of a heat source. It promotes heat dissipation by deploying the radiator surface when the heat source is at a high temperature. Conversely, in a cold case, heat dissipation is conserved by stowing the radiator surface. Herein, deployment/stowing and thermal vacuum tests were conducted herein to evaluate the validity of the design, and model correlations were conducted via thermal analysis. The RTP-BBM comprises high thermal conductivity graphite sheets as the flexible fin, and shape-memory alloys (SMA) as a temperature sensitive passive actuator. The deployment/stowing test was conducted in a thermal constant bath, confirming that the fin was deployed and stowed according to the SMA temperature. However, temperature hysteresis of up to + 60 degrees C was confirmed between heating and cooling cycles. In the thermal vacuum test, power step and power cycle tests were conducted. Results showed that the fin deployed and stowed according to the temperature of the onboard equipment while autonomously regulating the temperature. Additionally, the thermal analysis model correlated with the experimental results, showing good agreement within +/- 6 degrees C.

Lead halide perovskite single layers with three grain sizes are subjected to proton-beam irradiation in order to assess the durability and radiation tolerance of perovskite solar cells (PSCs) against space radiation. Proton-beam irradiation is chosen because proton beams significantly affect solar cell performance in the space environment. We evaluate the effects of proton beams by focusing on the grain structure, crystal structure, and carrier lifetime of a perovskite single layer by using scanning electron microscopy, X-ray diffraction, photoluminescence (PL) spectra, and time-resolved PL (TRPL). The results show that proton irradiation does not significantly affect the grain structure and crystal structure of perovskite layer; the TRPL results show that the carrier lifetime inside the grain is constant up to a fluence of 1 x 10(14) p(+)/cm(2) and decreases significantly at a fluence of 1 x 10(15) p(+)/cm(2). Proton-beam radiation tolerance of the grain inside the perovskite layer is dominant in the radiation tolerance of PSCs.

We found that the solar panel output current of JAXA's Venus explorer Akatsuki is below values expected from percentage of shadow during penumbras. We also found that a similar phenomenon occurs in JAXA's Van Allen radiation belts explorer Arase during Earth shadow penumbra. However, during a Lunar shadow penumbra, solar panel output current decreased in proportion to percentage of shadow. We consider that sunlight attenuated by the planetary atmosphere caused this decrease in current. As in the transit spectroscopy technique, planetary atmospheres could be characterized by trends in solar panel output current.

The exploration of energization and radiation in geospace (ERG) satellite, nicknamed "Arase," is the second satellite in a series of small scientific satellites created by the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency. It was launched on December 20, 2016, by the Epsilon launch vehicle. The purpose of the ERG project is to investigate how high-energy (over MeV) electrons in the radiation belts surrounding Earth are generated and lost by monitoring the interactions between plasma waves and electrically charged particles. To measure these physical processes in situ, the ERG satellite traverses the heart of the radiation belts. The orbit of the ERG is highly elliptical and varies due to the perturbation force: the apogee altitude is approximately 32,200-32,300 km, and the perigee altitude is 340-440 km. In this study, we introduce the scientific background for this project and four major challenges that need to be addressed to effectively carry out this scientific mission with a small satellite: (1) dealing with harsh environmental conditions in orbit and electromagnetic compatibility issues, (2) spin attitude stabilization and avoiding excitation of the libration by flexible structures, (3) attaining an appropriate balance between the mission requirements and the limited resources of the small satellite, and (4) the adaptation and use of a flexible standardized bus. In this context, we describe the development process and the flight operations for the satellite, which is currently working as designed and obtaining excellent data in its mission.

© Copyright 2017 by the International Astronautical Federation (IAF). All rights reserved. DESTINY+ (Demonstration and Experiment of Space Technology for Interplanetary Voyage, Phaethon Flyby and Dust Science) is a candidate of ISAS Epsilon class small program. The mission of DESTINY+ is to validate key technologies for our future deep space exploration. DESTINY+ will demonstrate the high performance electric propelled vehicle technology and execute the flyby exploration of asteroid 3200 Phaethon. DESTINY+ starts its voyage from a low elliptic orbit, spirals up the orbits, fly-by the Moon, escapes from the Earth, and depart for the asteroid 3200 Phaethon. It will detect and analyze interplanetary and interstellar dust particles during deep space cruise. This paper will introduce an overview of the DESTINY+ mission.

AKATSUKI is the Japanese Venus Climate Orbiter that was designed to investigate the climate system of Venus. The orbiter was launched on May 21, 2010, and it reached Venus on December 7, 2010. Thrust was applied by the orbital maneuver engine in an attempt to put AKATSUKI into a westward equatorial orbit around Venus with a 30-h orbital period. However, this operation failed because of a malfunction in the propulsion system. After this failure, the spacecraft orbited the Sun for 5 years. On December 7, 2015, AKATSUKI once again approached Venus and the Venus orbit insertion was successful, whereby a westward equatorial orbit with apoapsis of similar to 440,000 km and orbital period of 14 days was initiated. Now that AKATSUKI's long journey to Venus has ended, it will provide scientific data on the Venusian climate system for two or more years. For the purpose of both decreasing the apoapsis altitude and avoiding a long eclipse during the orbit, a trim maneuver was performed at the first periapsis. The apoapsis altitude is now similar to 360,000 km with a periapsis altitude of 1000-8000 km, and the period is 10 days and 12 h. In this paper, we describe the details of the Venus orbit insertion-revenge 1 (VOI-R1) and the new orbit, the expected scientific information to be obtained at this orbit, and the Venus images captured by the onboard 1-mu m infrared camera, ultraviolet imager, and long-wave infrared camera 2 h after the successful initiation of the VOI-R1.

We have shown the effectiveness of polarized photoluminescence imaging for analyzing the structural and spectroscopic properties of small-angle grain boundaries (SA-GBs) in multicrystalline Si. The dislocation-related deep-level emission band at approximately 0.79 eV at room temperature was found to be polarized, whereas the band-edge emission did not show the polarization effect. The anisotropy of the 0.79 eV band was classified into two groups depending on the tilt and twist characteristics of SA-GBs determined by the electron backscatter diffraction measurement.

This paper presents analysis results for the onorbit performance of a solar array paddle of the X-ray astronomy satellite Suzaku. The current generated by the solar array was decreasing significantly for approximate one year after mid-2011. We estimated the degradation of the output by simulating the on-orbit environment according to the JPL prediction method. The analysis results indicate that the on-orbit degradation of the solar array paddle is greater than the predicted performance degradation in a space environment. We determined that the difference between the on-orbit data and the analysis results could be attributed to either an increase in cell temperature or radiation degradation due to solar flares.

Emcore has been performing High Intensity High Temperature (HIHT) tests on covered, interconnected cell (CIC) assemblies. End-of-life performance of spacecraft solar panels depends to a great extent on changes in the optical properties of the CICs' coverglass adhesive during the mission. An important change in silicone coverglass adhesives is observed as degradation of short wavelength transmission, often called "darkening" or "yellowing". This is understood to be driven by exposure to high intensity UV and by exposure to elevated temperature. Solar panels on the Solar Probe Plus (SPP) spacecraft will be exposed to both high UV irradiance and elevated temperature over the course of a long mission. This paper reports on the thermal-mechanical design work performed and planned by Emcore in order to test CICs designed for SPP under these extreme conditions. Three types of thermal test designs are presented: conduction/convection with a single fixed temperature, thermal radiation with multiple fixed temperatures, and thermal radiation with a variable single temperature. We present some detail from predictive thermal models used in the test designs along with temperature data measured during the test runs.

We demonstrated high-speed imaging of photoluminescence (PL) and electroluminescence (EL) for not only band-to-band but also multiple deep-level emissions in a multicrystalline Si solar cell. We used a cooled In GaAs camera with a photosensitive range of 900 - 1700 nm equipped with band-pass filters for the selective detection of various deep-levele missions. The exposure time for imaging was only 1 - 10 seconds. Comparisons of the present PL images with the microscopic PL mappings confirmed for us that essentially the same luminescence patterns were obtained. © (2012) Trans Tech Publications, Switzerland.

A fine structure on the higher energy side of donor--acceptor (DA) pair luminescence at 4.2 K has been analyzed in compensated Si involving P donors and B acceptors. We calculated the density distribution of DA pairs against photon energy from the number of pairs as a function of the transition energy of respective pairs. A close agreement was obtained between the density curve and the observed spectral structure using the generally accepted values of energy gap and P donor and B acceptor ionization energies. This allows us to conclude that the structure is due to discrete DA pair recombination.

The Japan Aerospace Exploration Agency has been developing the Mercury Magnetospheric Orbiter (MMO), which is Japanese part of the BepiColombo mission. During its mission around Mercury, the spacecraft will be exposed to high solar irradiance of up to 11 suns, with an estimated maximum solar panel temperature of 230°C. In such an environment, solar cells are required to operate under high intensity and high temperature (HIHT) conditions. Therefore, it is necessary to evaluate the durability of solar cells to meet the power requirements throughout the mission life. We conducted a continuous operation test under HIHT conditions to examine the validity of the solar array configuration, using the interior planetary thermal vacuum chamber. Our HIHT tests clarified the following facts: (i) Transparency of the coverglass and the performance of the solar cells do not degrade and (ii) transparency of the DC93-500 adhesive in the top cell response region degrades mainly due to ultraviolet exposure at high temperatures. We decided to use AR0213 coverglass (from JDSU) with a thickness of 300 μm, which have a longer cut-on wavelength in ultraviolet region. With this configuration, the predicted decrease in Pmax due to the HIHT environment is 17.3% and that due to radiation effects is 11.0% Our new design will offer the available power at EOL of 394.2 W, which is 46.7 W greater than the required power. © 2010 IEEE.

Results of our study of effects of high-light-intensity and high-temperature conditions (HIHT) on the output performance of an InGaP/GaAs/Ge triple-junction solar cell are described herein. The HIHT conditions are adjusted for spacecraft environments expected for a Venus mission (Planet-C) and a Mercury mission (MMO) to be undertaken by the Japan Aerospace Exploration Agency (JAXA). Measurements of currentvoltage characteristics under high light intensity for a wide range of cell temperatures exhibit a kinked pattern at 0 current at +200°C. The thermal cycle test results for bare cells with a wide temperature range show no output performance degradation. Continuous operation tests of 3J cells under HIHT conditions reveal gradual current output degradation, implying that solar panel design should address decreased output specifically.

The lithium-ion battery has a high energy density, which satisfies the demand of lightening the power system for the space craft. We are developing a lithium-ion battery for a Venus probe "PLANET-C" of JAXA based on the technology for "Hayabusa", which is world's first spacecraft carrying a lithium-ion battery. We have developed 23.5 Ah class engineering model cells, and have confirmed the capacity deterioration is enough small by conducting operational simulation tests. We have successively manufactured prototype model (PM) cells, which achieved an energy density of 107 Wh/kg. The PM cells have passed a overcharge test, a short circuit test, and a mechanical environmental test with no failure.

The Institute of Space and Astronautical Science of JAXA is planning a Venus climate orbiter "PLANET-C", which will be launched in 2010. This paper describes development of solar array paddles of the spacecraft. The solar array paddles must operate under highintensity illumination of 2 suns and at high temperatures up to +172°C for two Earth years. We conducted tests of two kinds to qualify the solar array paddles. One is a thermal cycling test over a temperature range of -160°C to +172°C. Although some structural damage resulted from the thermal shock at an early stage of the test, the causes were eventually resolved. The other kind of test was a continuous operation test under high-intensity illumination and high-temperature conditions. A slight decrease in the generated current was revealed by this test. The predicted generated power at the end of the mission remains greater than the requirement, although the cause is under investigation now.

Both an experimental observation and a numerical modeling of streamer development in SF6-N2 gas mixtures are performed and the results are compared with each other. By using a steep-front square high voltage in the measurements, it is possible to keep the constant condition of the electric field during the streamer development. Minimum sparkover voltage and streamer velocities obtained from the numerical modeling show good agreement with those from the experimental observation, and the change in the streamer velocity against the gas mixture ratio shows a similar tendency. © 2005, The Institute of Electrical Engineers of Japan. All rights reserved.