Hisashi Otake

Lunar global shape and polar topography derived from Kaguya-LALT laser altimetry.

A global lunar topographic map with a spatial resolution of finer than 0.5 degree has been derived using data from the laser altimeter (LALT) on board the Japanese lunar explorer Selenological and Engineering Explorer (SELENE or Kaguya). In comparison with the previous Unified Lunar Control Network (ULCN 2005) model, the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers. Spherical harmonic analysis of global topographic data for the Moon, Earth, Mars, and Venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales. However, simple rigid support is suggested to dominate for the Moon, Venus, and Mars for smaller scales, which may indicate a drier lithosphere than on Earth, especially for the Moon and Venus.

The global distribution of pure anorthosite on the Moon

It has been thought that the lunar highland crust was formed by the crystallization and floatation of plagioclase from a global magma ocean, although the actual generation mechanisms are still debated. The composition of the lunar highland crust is therefore important for understanding the formation of such a magma ocean and the subsequent evolution of the Moon. The Multiband Imager on the Selenological and Engineering Explorer (SELENE) has a high spatial resolution of optimized spectral coverage, which should allow a clear view of the composition of the lunar crust. Here we report the global distribution of rocks of high plagioclase abundance (approaching 100 vol.%), using an unambiguous plagioclase absorption band recorded by the SELENE Multiband Imager. If the upper crust indeed consists of nearly 100 vol.% plagioclase, this is significantly higher than previous estimates of 82–92 vol.% (refs 2, 6, 7), providing a valuable constraint on models of lunar magma ocean evolution.

Simulation of space weathering of planet-forming materials: Nanosecond pulse laser irradiation and proton implantation on olivine and pyroxene samples

For the purpose of simulating the surface alteration process called “space weathering”, experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6–8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes. Depths of absorption bands do not change in the scaled spectra. The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra. FeO content of pyroxenes does not relate to the degree of reflectance change.

In-orbit calibration of the lunar magnetometer onboard SELENE (KAGUYA)

The high-sensitivity fluxgate Lunar MAGnetometer (LMAG) is mounted on SELENE (KAGUYA) to investigate the near-surface electromagnetic environment and the evolution of the Moon through magnetic field observation. To avoid possible electromagnetic interferences, a triaxial fluxgate sensor (MGF-S) is installed at the far end of a 12-m-long mast. It is critical for the accurate observation to monitor MGF-S alignment in orbit, and thus we have calibrated the sensor alignment by measuring the known magnetic fields generated by the sensor alignment monitor coil (SAM-C) wound onto the mast canister. In-orbit calibration of the MGF-S alignment was performed twice each revolution during the initial check-out phase of the satellite. It is concluded that there is no systematic difference in the sensor alignment between the day-side and night-side. Applying a new technique based on the Davis-Smith method to the observed magnetic field data when KAGUYA was exposed to the solar wind, a zero offset of each axis was quickly and stably determined every month. As a result, LMAG has been calibrated with an accuracy that is sufficient for detection of the lunar magnetic anomaly at an altitude of 100 km and for high-resolution electron reflectometry.

Scientific exploration of lunar surface using a rover in Japanese future lunar mission

Abstract A new lunar mission (SELENE-B) including a lander is now in consideration in Japan. The mission will follow up SELENE (SELenological and ENgineering Explorer, a global remote sensing mission of the moon in 2004). Scientific investigation plans using a rover are proposed: exploration of a crater central peak to discover subsurface materials and exploration of the polar region to discover the trapped ice. We have already developed a 5-wheel engineering-model rover, Micro5, which has a long manipulator with a camera on top. The rover can climb over 15cm steps and rocks by a new suspension system PEGASUS.

SpaceWire-based thermal-infrared imager system for asteroid sample return mission HAYABUSA2

Abstract A thermal-infrared (TIR) imager system is developed for HAYABUSA2, which is planned to be launched in 2014 and aims at sample-return from a C-class near-Earth asteroid 162173 (1999JU3) considered to contain organic or hydrated materials. The system consists of a TIR imager and digital electronics, which are used not only for the scientific investigation of physical properties of the asteroid surface, but also for the assessment of landing site selection and safe descent operation onto the asteroid surface with in situ measurement. TIR adopts an uncooled bolometer. Image operations such as multiple images summation, dark image subtraction, and the compensation of dead pixels are processed onboard. A processing module is connected to sensor interfaces through SpaceWire in order to provide deterministic processing time. Data compression is also provided to reduce the restriction of transmission time, which provides the equivalent compression ratio as JPEG2000 in 1 / 30 processing time in average. A high-speed data recorder is connected through SpaceWire in order to record TIR data in parallel with other sensor data. The modularity of SpaceWire enables us to use these as built devices for TIR and inherits the same design as the long-wavelength infrared imager developed for the Venus climate orbiter Akatsuki.

Subsurface Chemistry of the Imbrium Basin Inferred from Clementine UVVIS Spectroscopy

Since ejecta around an impact crater is excavated from a depth, its mineralogy and chemistry will provide us with information on the composition of the pre-impact subsurface. The depth from which crater ejecta were excavated was determined from laboratory experiments, field studies, and a simplified quantitative model (Z-model and the scaling law of ejection velocity). Based on the results of these studies, it is believed that surface material of an ejecta blanket between 1.1 and 1.5 radii from the crater was excavated from a depth of 0.13 to 0.15 radii. The following results were obtained from combining the surface and subsurface basalt distributions with crater-counting ages for the mare basalt, we obtained the following results: (1) The averages of TiO2 and FeO increased with time from the Imbrian to the Eratosthenian periods, which is represented by a continuous trend curve on the TiO2-FeO graph: (2) volcanic activities in Mare Imbrium drastically decreased and basalts changed from a low-Ti to high-Ti content around the transition of the Imbrian to Eratosthenian period: (3) basalts with less than 3 wt% TiO2 erupted in succession mainly in the Imbrian period.

Lunar mare volcanism: lateral heterogeneities in volcanic activity and relationship with crustal structure

Abstract Lunar mare basalts are spatially unevenly distributed, and their abundances differ between the nearside and farside of the Moon. Although mare asymmetry has been attributed to thickness variations in the low-density anorthositic crust, the eruptive mechanism of lunar magma remains unknown. In this study, we investigate the relationship between mare distribution and crustal thickness using geological and geophysical data obtained by the SELENE (Kaguya) and the Gravity Recovery and Interior Laboratory spacecraft, and quantitatively re-evaluate the influence of the anorthositic crust on magma eruption. We identify a lateral heterogeneity in the upper limit of crustal thickness that allows magma extrusion to the surface. In the Procellarum KREEP Terrane, where the surface abundances of heat-producing elements are extremely high, magmas can erupt in regions of crustal thickness below about 30 km. In contrast, magma eruptions are limited to regions of crustal thickness below about 20 km in other nearside regions, around 10 km in the South Pole–Aitken Basin and approximately 5 km in the farside Felspathic Highland Terrane. Such heterogeneity may result from lateral variations in magma production in the lunar mantle and/or crustal density.

The SpaceWire-based thermal infrared imager system for asteroid sample return mission HAYABUSA2

Thermal infrared imager system is developed for HAYABUSA2, which is planned to be launched in 2014 and aims at sample-return from a C class near-Earth asteroid 1999JU3 considered to contain organic or hydrated materials. The system consists of a thermal-infrared imager (TIR) and a digital electronics, which is used not only for the scientific investigation of physical properties of the asteroid surface, but also for the assessment of landing site selection and safe descent operation onto the asteroid surface with in situ measurement. Since round trip communication time between the asteroid and the Earth is more than thirty minutes, onboard automatic data processing function and high speed data recording capability are provided to exploit the limited downlink capacity which is up to 32kbps. TIR adopts an uncooled bolometer with 320 x 240 effective pixels. Image operations as multiple images summation, dark image subtraction, and the compensation of dead pixels are processed onboard. A processing module is connected to sensor interfaces through SpaceWire in order to provide deterministic processing time. Data compression is also provided to reduce restriction on storage capacity and operation time, which provides the equivalent compression ratio as JPEG2000 in 1/30 processing time in average. A high speed data recorder is also connected through SpaceWire in 50Mbps in order to record TIR data in parallel with other sensor data. The modularity of SpaceWire enables to use as built devices for TIR and inherits the same design as the long-wavelength infrared imager developed for the Venus climate orbiter Akatsuki.

The Result of SELENE (KAGUYA) Development and Operation~!2009-06-28~!2009-08-10~!2009-10-01~!

Japan’s first large lunar explorer was launched by the H-IIA rocket on September 14, 2007 and had been in observation operation from December 21, 2007 to June 11, 2009(JST). This explorer named “KAGUYA (SELENE: SELenological and Engineering Explorer)” has been keenly anticipated by many countries as it represents the largest lunar exploration project of the post-Apollo program. The lunar missions that have been conducted so far have gathered a large amount of information on the Moon, but the mystery surrounding its origin and evolution remains unsolved. KAGUYA investigate the entire moon in order to obtain information on its elemental and mineralogical distribution, its geography, its surface and subsurface structure, the remnants of its magnetic field and its gravity field using the scientific observation instruments. The results are expected to lead to a better overall understanding of the Moon’s origin and evolution. Further, the environment around the Moon including plasma, the electromagnetic field and high-energy particles will also be observed. The data obtained in this way is of great scientific value and is also important information in the possibility of utilizing the Moon in the future. This paper describes the highlight of KAGUYA development and operation with some newly developed engineering achievements including a separation mechanism of sub-satellites from main orbiter as well as the latest scientific accomplishment of KAGUYA. Keyword: SELENE, KAGUYA, H-IIA, JAXA, moon, origin and evolution, ground system, GIS, YouTube, WMS, EPO. KAGUYA SATELLITE SYSTEM OVERVIEW KAGUYA consists of a main orbiter at about 100km altitude and two sub-satellites (Relay Satellite named “OKINA” and VRAD Satellite named “OUNA”) in lunar polar orbit. The main orbiter is also called as KAGUYA. The main orbiter weight at the launch is about 2.9 tons and the size of its main body is 2.1m 2.1m 4.8m. This satellite is 3 axis stabilized and the panel (+Z panel) on which mission *Address correspondence to this author at the SELENE Project, Japan Aerospace Exploration Agency, Tsukuba, 305-8505, Japan; E-mail: sobue.shinichi@jaxa.jp instruments heads are installed is pointed to the gravity center of the Moon. About 3.5 kilo watt is the maximum power produced by a solar paddle. The surface of the KAGUYA is covered with the black color conductive MLI (multi-layer thermal insulators) for conductivity requirement of plasma observation instrument (PACE). The on-orbit configuration of the Main Orbiter is shown in Fig. (1) [1-3]. KAGUYA MISSION PROFILE The Lunar transfer orbit which contributes to reduction of mission risk via two phasing loops around the Earth was adopted. KAGUYA was inserted into a polar elliptical orbit at a perilune altitude of 100 km of lunar. The two subThe Result of SELENE (KAGUYA) Development and Operation Recent Patents on Space Technology, 2009, Volume 1 13 satellites (OKINA and OUNA) were separated from the main orbiter at an apolune of 2,400 km and 800 km respectively. Finally the main orbiter reached the circular orbit at about 100 km altitude and the inclination of polar circular orbit is 90 deg. The apolune altitude of OKINA is determined to measure the gravity field anomaly on the far side of the Moon through relaying the Main orbiter s-band signal effectively. The apolune altitude of OUNA is selected for the low order gravity model coefficient measurements using radio sources on the OKINA and OUNA by VLBI method. When OKINA and OUNA separating from the main orbiter, the spin rotation power were added. This subsatellite separation mechanism which gives the rotational and the translational force simultaneously was originally developed for JAXA’s micro-lab satellite. To consider power generation, octagonal prism shape was selected for subsatellites. All faces of satellite are covered with the solar cells, and each sell produces about 70 watt powers. KAGUYA mission profile is shown in Fig. (2). OKINA was impacted to the far side of the Moon on February 11, 2009 and gravity anomaly observation at the far side of the Moon was successful completed. Fig. (1). The on-orbit configuration of the main orbiter. Lift off Separation from H -IIA Rate Dumping Solar Array Paddle Deployment Sun/Star Capture, High Gain Antenna Deployment Altitude Control of Perigee Lunar Elliptical Orbit Insertion Altitude of Perilune about 100 km