岩田 隆浩

NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 mu m. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 mu m-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K (-85 degrees C), which enables to retaining sufficient sensitivity and noise level in the 3 mu m wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.

After the successful launch on the world first spacecraft, Sputnik 1 by the former Soviet Union in 1957, 58 years has passed. In 1960, Pioneer 5 of the United States escaped the Earth's gravity at the first time, and since then many interplanetary explorers had set to sail interplanetary. However, even in the present day, interplanetary voyages are not still easy. First, interplanetary missions require large amounts of delta-V, and second, the opportunity to get to the destination opens only every synodic period with the destination celestial body. For example, the synodic period with Mars is about 2 years, which means the opportunity to get to Mars opens every 2 years. For such circumstances, this paper proposes a new type of low-thrust orbit design method, "Interplanetary Parking Method" that realizes "anytime" launch of deep-space explorers. The proposed interplanetary parking method enables to make an Earth return orbit with an arbitrary time-of-flight connecting to the minimum energy transfer orbit to a destination. While the time-of-flight of the transfer orbit is fixed, the Earth return orbit with the arbitrary time-of-flight virtually eliminates the severe launch window constraint in interplanetary missions. As application of the proposed method, the paper demonstrates dual launch trajectory design of explorers to different destinations i.e., Mars and Venus. The proposed method will widen the scope of opportunity for interplanetary missions.

After the successful launch on the world first spacecraft, Sputnik 1 by the former Soviet Union in 1957, 58 years has passed. In 1960, Pioneer 5 of the United States escaped the Earth's gravity at the first time, and since then many interplanetary explorers had set to sail interplanetary. However, even in the present day, interplanetary voyages are not still easy. First, interplanetary missions require large amounts of delta-V, and second, the opportunity to get to the destination opens only every synodic period with the destination celestial body. For example, the synodic period with Mars is about 2 years, which means the opportunity to get to Mars opens every 2 years. For such circumstances, this paper proposes a new type of low-thrust orbit design method, "Interplanetary Parking Method" that realizes "anytime" launch of deep-space explorers. The proposed interplanetary parking method enables to make an Earth return orbit with an arbitrary time-of-flight connecting to the minimum energy transfer orbit to a destination. While the time-of-flight of the transfer orbit is fixed, the Earth return orbit with the arbitrary time-of-flight virtually eliminates the severe launch window constraint in interplanetary missions. As application of the proposed method, the paper demonstrates dual launch trajectory design of explorers to different destinations i.e., Mars and Venus. The proposed method will widen the scope of opportunity for interplanetary missions.

The correlation between the spatial patterns of surface Thorium (Th) abundance measured by SELENE GRS data and the crustal thickness from the GRAIL gravity field and LRO LOLA data is investigated in the lunar highland area. Our analysis reveals that there are several areas of local minima for Th abundance exhibiting similar values but different crustal thicknesses. To explain the result, we propose a two-stage scenario for crustal formation. In the first stage, plural thin plateaus form on the surface of the lunar magma ocean (LMO), which corresponds to the observed surface Th distribution. In the second stage, a global crust with dichotomy forms by solidification of the LMO under the plateaus.

<p>We are planning to explore the caverns through the skylight holes on the Moon and Mars. The holes and their associated subsurface caverns are among the most important future exploration targets. The importance of the lunar and Martian holes and their associated caverns is categorized from two aspects: (1) fresh materials are easily observed and sampled there, and (2) the subsurface caverns provide a safe, quiet environment. The expectation of lunar and Martian hole and cavern exploration is increasing in Japan. We name the project as UZUME (Unprecedented Zipangu (Japan) Underworld of the Moon Exploration) whose name is after a Japanese mythology. The ultimate purpose of the UZUME project is to investigate how to expand human activity and survival in space and on extraterrestrial bodies. </p>

The solidification of the Lunar Magma Ocean (LMO) and formation of impact basins are important events that took place on the early Moon. The relative timing of these events, however, is poorly constrained. The aim of this study is to constrain the formation ages of old impact basins based on inferences of their thermal state. Most proposed basins formed before Pre-Nectarian (PN) 5 stage do not exhibit clear concentric features in either topography or gravity, suggesting substantial viscous lateral flow in the crust. Recent geodetic measurements reveal that the lunar crust is thinner than previously estimated, indicating that an extremely high crustal temperature is required for lateral flow to occur. In this study, we calculate lunar thermal evolution and viscoelastic deformation of basins and investigate the thermal state at the time of basin formation using recent crustal thickness models. We find that a Moho temperature 1300-1400. K at the time of basin formation is required for substantial viscous relaxation of topography to occur; the implied elastic thickness at the time of loading is <30. km. Such a high temperature can be maintained only for a short time (i.e., <50. Myr for most conditions) after solidification of the LMO or after mantle overturn if it took place; relaxed impact basins forming ≥150 Myr later than LMO solidification are unlikely. This result is in conflict with an intensive Late Heavy Bombardment (LHB) model, which assumes that most impact basins were formed at ~3.9. Ga, since it requires LMO solidification time much later than previous theoretical estimates. Either the LHB was moderate, or the majority of proposed early PN basins were not in fact formed by impacts.

The South Pole-Aitken (SPA) basin is the largest clearly recognized basin on the lunar surface. Determining the composition and structure of the SPA basin interior provides critical constraints on the deep crustal and/or mantle composition of the Moon and improves our understanding of large-basin-forming impact processes. Here we present a new mineralogical map of the SPA basin interior, based on high-spatial-resolution reflectance spectra using the SELENE (Kaguya) multiband imager, which is combined with topographic data in order to interpret the geologic context. The derived mineralogical map suggests extensive distribution of ejected low-Ca pyroxene-dominant mantle material with the presence of purest anorthosite crustal materials surrounding a possible melt pool of 0.26 to 0.33 of the basin diameter near the basin center, which is significantly smaller than that suggested by the crater-scaling law. The absence of clear evidence of lower crustal material is consistent with recent impact simulation results. Key Points Stratigraphy of the lunar mantle was revealed within the Moon's largest basin A smaller melt pool was suggested than that derived by the crater-scaling law Absence of clear evidence of lower crustal material is suggested by mineralogy ©2014. American Geophysical Union. All Rights Reserved.

Diverse geological characteristics found for the three major lunar provinces (i.e., the Feldspathic Highlands Terrane (FHT), the South Pole-Aitken Terrane (SPAT), and the Procerallum KREEP Terrane (PKT)) strongly suggest their distinctly different thermal histories. Quantitative differences among these provinces in their early thermal histories and crustal radioactive element concentrations, however, are highly unknown. One of the few observables that retain a record of the ancient lunar thermal structure is the viscoelastic state of impact basins. This study investigates the long-term evolution of basin structures using global lunar gravity field data obtained by Kaguya tracking and derives constraints for (1) the paleo-thermal state of impact basins and for (2) crustal column-averaged radioactive element concentrations for each province. Our calculation results indicate that impact basins in the central anorthositic region of the FHT (i.e., the FHT-An) require a very cold interior (dT dr ≤ 20 K km - 1 on the surface). This result strongly suggests that the deep portion of the thick farside highlands crust is highly depleted in radioactive elements (Th ≤ 0.5 ppm), indicating that the Th-rich SPA basin floor crust is clearly different from the lower crust underneath the FHT-An and cannot be accounted for by simple exposure of the lower crust. Our analysis also indicates that the observed basin structure allows as high as ∼ 6 ppm of column-averaged Th concentration in the crust inside the PKT. These results indicate that radioactive element concentrations deep in the crust probably vary greatly region by region, similarly to those observed on the surface. Key Points We investigate viscoelastic deformation of major lunar impact basins Constraints on the early thermal state vary greatly among geological provinces The thick lunar farside crust needs to be depleted in radioactive elements ©2013. American Geophysical Union. All Rights Reserved.

DESTINY which stands for "Demonstration and Experiment of Space Technology for INterplanetary voYage" is a mission candidate for the third mission of ISAS small science satellite series. DESTINY is launched by an Epsilon launch vehicle, JAXA's next-generation solid fuel rocket, and is firstly placed into a low elliptical orbit. It raises its altitude by the use of ion engine and reaches the Moon. Then, it is injected into transfer orbit for L 2 Halo orbit of the Sun-Earth system by using lunar gravity assist. On the way to L2 Halo orbit, DESTINY conducts demonstration and experiment on key advanced technology for future deep space missions. This paper presents the overview of DESTINY mission as well as its importance and significance in Japanese space science program.

DESTINY which stands for "Demonstration and Experiment of Space Technology for INterplanetary voYage" is a mission candidate for the third mission of ISAS small science satellite series. DESTINY is launched by an Epsilon launch vehicle, JAXA's next-generation solid fuel rocket, and is firstly placed into a low elliptical orbit. It raises its altitude by the use of ion engine and reaches the Moon. Then, it is injected into transfer orbit for L-2 Halo orbit of the Sun-Earth system by using lunar gravity assist. On the way to L-2 Halo orbit, DESTINY conducts demonstration and experiment on key advanced technology for future deep space missions. This paper presents the overview of DESTINY mission as well as its importance and significance in Japanese space science program.

This paper reports measurement results of the antenna phase patterns onboard flying spin satellites during the SELENE (KAGUYA) mission period, and shows monthly variations clearly for the first time. When an antenna is loaded on a spin satellite, due to the effects of the antenna phase patterns, periodical components with the spin frequency f s and higher order harmonics occur and influence Doppler measurements. Because Rstar and Vstar, two subsatellites of SELENE, have octagonal prismatic bodies, the 8th, 16th, and 24th harmonics are relatively stronger than the other ones in the 2-way and 4-way Doppler data. These three harmonics' amplitudes over the entire mission longer than one year clearly varied with a period of 27.32 days (one sidereal month). The antenna phase patterns were estimated using 1-26th harmonics, whose rms variations were also with a period of 27.32 days. From the 24th harmonic and the antenna phase patterns, the spin frequency variations of Rstar and Vstar over the entire mission were estimated with an accuracy of 10 -5 Hz. © 1965-2011 IEEE.

Measurements of lunar gravity and rotation are important because they provide information of the physical state of the lunar interior. Previously only passive LLR (Lunar Laser Ranging) using CCR (corner cube reflectors) has been applied for the detailed study of lunar librations, rotation variability. As for candidate instruments for SELENE-2 (forthcoming lunar landing mission by JAXA) and future lunar missions, we propose VLBI (inverse-VLBI and differential VLBI) for gravity measurement to constrain tidal Love number, LLR and ILOM (In-situ Lunar Orientation Measurement) for libration measurements.

Using 4-way Doppler tracking with relay satellite OKINA, KAGUYA obtained the first precise gravity field of the lunar farside. Multi-frequency differential Very Long Baseline Interferometry (VLBI) observation using OKINA and OUNA improved the accuracy of gravity, through precise determination of OKINA's orbit. The current gravity model is SGM100i involving VLBI data. Laser altimeter (LALT) on board KAGUYA obtained the first precise global topography of the Moon with range accuracy of 5m. The correlation of spherical harmonics coefficients between gravity and topography become higher than that of the previous model. Gravity signatures of far-side impact basins are mostly explained by topography except for the central high. Combined with topography data, we estimate Bouguer anomaly and the crustal thickness variation of the Moon.

Variations of Mars' rotation provide us information concerning both the interior structure and the surface mass redistribution of Mars. Precession and nutation of Mars mainly reveal the core-mantle subsystem, besides length-of-day variation and polar motion of Mars are generally referred to the atmosphere-cryosphere sub-system. As one of the missions of MELOS (Mars Exploration with Lander-Orbiter Synergy), we are proposing areodetic observations using space geodetic techniques including four-way Doppler measurement (FWDP) and inverse VLBI (IVLBI). FWDP is ranging rate measurement of target spacecraft via a relay spacecraft. Utilizing the heritage of four-way Doppler measurements by SELENE, we plan to track the MELOS Landers relayed by the MELOS Orbiter. We also introduce the new technology of IVLBI. In the framework of this technology, one ground radio telescope observes the phase-shift between mutually coherent signals on the orbiter and the landers. The estimated accuracy for the rotation obtained by IVLBI is better than 1 mas (milli-arc second) including the systematic phase noise. The measurements will provide the core radius estimation with the errors of less than 200 km by 50 weeks observations with two landers.

The Radio Science experiment (RS) in the Akatsuki mission of JAXA aims to determine the vertical structure of the Venus atmosphere, thereby complementing the imaging observations by onboard instruments. The physical quantities to be retrieved are the vertical distributions of the atmospheric temperature, the electron density, the H2SO4 vapor density, and small-scale density fluctuations. The uniqueness of Akatsuki RS as compared to the previous radio occultation experiments at Venus is that low latitudes can be probed many times thanks to the near-equatorial orbit. Systematic sampling in the equatorial region provides an opportunity to observe the propagation of planetary-scale waves that might contribute to the maintenance of the super-rotation via eddy momentum transport. Covering the subsolar region is essential to the understanding of cloud dynamics. Frequent sampling in the subsolar electron density also helps the understanding of ionosphere dynamics. Another unique feature of Akatsuki RS is quasi-simultaneous observations with multi-band cameras dedicated to meteorological study; the locations probed by RS are observed by the cameras a short time before or after the occultations. An ultra-stable oscillator provides a stable reference frequency which is needed to generate the X-band downlink signal used for RS.

The effect of the phase patterns of antennas onboard flying spin satellites on the Doppler measurements is reported. Phase patterns mean that there are deviations in wave fronts from perfect sphericity, expressed as a function of the angular position around the antenna. We analyzed what effect the phase patterns of dipole and patch antennas onboard two flying spin satellites, Rstar and Vstar, used in the Japanese lunar mission, SELENE (KAGUYA), had on 2-way and 4-way Doppler measurements, and detected higher harmonics in the spin frequency up to an order of 26 in the Doppler frequency. We developed a low-pass filter (LPF) using a Kaiser window, with the optimal parameters empirically determined, to remove the influence of phase patterns and to precisely conserve information on the lunar gravity field. We processed the 2-way and 4-way Doppler data of SELENE by using LPF. After using LPF, a high degree of accuracy of about 0.001 Hz was achieved for the 2-way Doppler measurements, and signals that reflected the gravity field on the far side of the Moon were first detected from the 4-way Doppler data. We also suggested a method for estimating the phase response of satellite antennas using the Doppler frequency variations. In order to estimate the Doppler frequency variation, a filtering technique was adopted to extract the harmonics of interest in the residual signal, from which the antenna phase pattern was derived.

Measurements of physical and free librations of lunar rotation are important because they provide information of the physical state of the lunar interior. For example, we can discuss if the lunar core is molten from the amplitudes of libration terms. Previously only passive LLR (Lunar Laser Ranging) using CCR (corner cube reflectors) has been applied for the detailed study of lunar librations. As for candidate instruments for SELENE-II (forthcoming lunar landing mission by JAXA), we propose detailed measurements of lunar rotation by ILOM (In-situ Lunar Orientation Measurement) and IVLBI (Inverse-VLBI) in addition to LLR.

On the basis of the gravity model of the Moon developed by SELENE (Kaguya), we propose new classification and compensation mechanism of lunar impact basins. Impact basins on lunar far side and limb are classified into Type I and II basins depending on the magnitude of central gravity high in free-air and Bouguer gravity anomalies. Among previously known gravity anomalies, most typical mascons are referred as primary mascon basins. Topographic depression and rim of both Type I and II basins show good correlation between topography and free-air gravity anomaly suggesting elastic support of lunar lithosphere. Central gravity high of Type I basin is inferred to be a result of mantle uplift at the time of basin formation, and is elastically supported, too. On the other hand, free-air anomalies at the center of Type II basins are lower than Bouguer anomalies indicating brittle deformation of the basins. Topographic depression and rim of primary mascon basins on near side of the Moon show little to no free-air gravity anomalies. This indicates a result of elastic relaxation that occurred probably after eruption of mare basalts. Plateau-like signature of gravity anomalies of primary mascon basins implies viscous relaxation at crust-mantle boundary beneath the basins and significant heat (or volatile) transport by basaltic magma.

The electron density profiles above the lunar surface are being observed by the radio occupation technique during the mission using the Vstar and Rstar sub-satellites. In addition to a traditional technique which uses one orbiter, we are conducting another method which uses two orbiters with the second one being used to measure the terrestrial ionosphere contribution. Previous radio occultation measurements have indicated the existence of an ionosphere with densities of up to 1000 cm-3 above the dayside lunar surface. These densities are difficult to explain theoretically when the removal of plasma by the solar wind is considered, and thus the generation mechanism of the lunar ionosphere is a major issue, with even the validity of previous observations still under debate. The SELENE radio science experiment will establish the morphology of the lunar ionosphere and will reveal its relationship with various conditions to provide possible clues to the mechanism.

Same beam very long baseline interferometry (VLBI) observations of the two subsatellites of SELENE (KAGUYA) are demonstrated for purpose of the precise gravimetry of the Moon. Same beam VLBI contributes a great deal to cancel out the tropospheric and ionospheric delays and to determine the absolute value of the cycle ambiguity by using the multifrequency VLBI method. As a result, the differential phase delay of the X-band signal is estimated within an error of below 1 ps. This accuracy is more than 1 order of magnitude smaller than former VLBI results. The preliminary results for the orbit determination of the subsatellites show a decrease of the orbit error from a few hundreds of meters to around 10 m when the differential phase delay data are added to the conventional range and Doppler data. These results reveal the possibility of precise gravimetry.

The farside gravity field of the Moon is improved from the tracking data of the Selenological and Engineering Explorer (SELENE) via a relay subsatellite. The new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside. Several basins have large central gravity highs, likely due to super-isostatic, dynamic uplift of the mantle. Other basins with highs are associated with mare fill, implying basalt eruption facilitated by developed faults. Basin topography and mantle uplift on the farside are supported by a rigid lithosphere, whereas basins on the nearside deformed substantially with eruption. Variable styles of compensation on the near- and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered.

SELENE (Selenological and Engineering Explorer) is a Japan's lunar probe which was launched and injected into the lunar polar orbit in 2007. The Main Orbiter of SELENE named Kaguya has separated the Relay Satellite: Rstar (Okina). We have executed four-way Doppler measurements which determined the orbit of Kaguya aviating above the lunar far side. The ground station up-links ranging signals, and the relay satellite transponder on Rstar (RSAT-1) relays the carrier waves to Kaguya. Then the transponder on Kaguya (RSAT-2) receives the signals and returns to Rstar, and down-linked to UDSC. Three of four receivers through four-way links acquires signals and tracks Doppler frequency shift with phased lock loops. For that purpose, the receivers should be locked sequentially under the condition of large Doppler shift due to mutual velocities of three moving bodies. The receivers were designed in consideration of the above condition and system operability. Eventually, our system has realized the first case to track two fully moving links between the lunar orbiters and carried out Doppler measurements. Results of the orbit determinations for Kaguya above the lunar far side have shown the anomaly distributions of the gravity fields which could be scarcely found by the conventional two-way RARR methods. ©2009 IEEE.

The Japanese lunar mission, SELENE (Kaguya) consists of a main satellite and two small satellites, Rstar and Vstar. In same-beam VLBI observations of Rstar and Vstar, phase fluctuations caused by atmosphere, ionosphere and instruments were reduced to a low level of 1-2 deg, and the differential phase delay between Rstar and Vstar was obtained with a very low error of 2 pico-seconds. We corrected the long-term atmospheric and ionospheric delays by using GPS techniques and analyzed other possible influence such as phase-frequency characteristic of the receivers and phase variation in the main beam of telescopes. We performed orbit determination for Rstar and Vstar, the accuracy was much improved from a few tens meters when using only Doppler and range data, to a level of about 10 m when same-beam VLBI data are also used. In addition, the lunar gravity field model was also improved by combing VLBI data. ©2009 IEEE.

The Japanese lunar mission, SELENE (Kaguya) consists of a Main satellite and two small satellites, Rstar and Vstar. In S-band same-beam VLBI observations of Rstar and Vstar, phase fluctuations caused by the atmosphere, ionosphere and instruments were reduced to a low level of ldeg ∼ 2 deg, and the S-band differential phase delay between Rstar and Vstar was obtained with an error of 1 pico-second. We corrected the long-time atmospheric and ionospheric delays by using GPS techniques. According to the VLBI observation results up to February 2008, we changed the VLBI observation method that the telescope tracked the midpoint of Rstar and Vstar even if when the separation angle is as large as 0.56 deg. From March 2008, the chances for S-band same-beam VLBI observations are thus much increased and more data were obtained for orbit determination and estimating the global lunar gravity field model. We performed orbit determination for Rstar and Vstar, the accuracy was improved from a few tens meters when only using Doppler and range data, to a level of about 10 m when S-band same-beam VLBI data are also used.

Temperature and power supply of two sub satellites of SELENE (Kaguya), Rstar and Vstar, are controlled either by automatically or by commands from a ground tracking station, and their conditions are judged from related telemetries such as voltage, current and temperature of the batteries. After two sub satellites were separated from the main orbiter of SELENE, first test operations of all the instruments onboard the two sub satellites were carried out in the initial check-out for six days, and the electric power system such as solar arrays and batteries were confirmed to have enough power to supply for all the instruments. It was also confirmed that temperatures of all the instruments were controlled in the range of designed value. Throughout the nominal mission period from the beginning of November in 2007 to the end of October in 2008, there was no serious problem in the temperature control system and the electric power system even in an eclipse of the moon, and it was clarified that Rstar and Vstar were capable of producing more power than expected from detailed analysis of the telemetry data obtained during the eclipse. As the result, we could increase chances of 4-Way Doppler measurements and VLBI measurements by several tens of percents, and could obtain a better gravity anomaly map of the lunar far side.

Lunar gravimetry on the far side is one of the most important missions in SELENE. A stable frequency transmitted from a ground station is relayed to Main Orbiter by Rstar, and-Main Orbiter returns back the signal to Rstar. Then the signal is changed to X-band in Rstar, and transmitted to the ground station. This measurement is called 4way Doppler method. When the 4way Doppler measurement is performed successfully, the Rstar receives the signal from the ground station and transmits a different frequency signal synchronized with the received signal to Main Orbiter by using a PLL. In this case, the PLL is in "Locked" status. Main Orbiter also relays the signal by the same way. Usually the status of "Locked" or "Unlocked" is sent to the ground station as telemetry information to confirm the completion of the 4way link. However, the ground station is not able to get the telemetry information from Main Orbiter on real time, because the orbiter is on the far side during 4way Doppler measurements. The new methods have been proposed to know the status of the PLL from variations of the Doppler rate and/or frequency shift of the received signal itself on the ground station. They were applied to actual operations of SELENE and were very useful.

SELENE Main Orbiter (KAGUYA) has separated two small sub-satellites (1) the Relay Satellite "OKINA (Rstar)", and (2) the VLBI Radio Satellite "OUNA (Vstar)". These sub-satellites started to perform 4-way Doppler measurements using Relay Satellite Transponder (RSAT) and multi-frequency phase-delay differential VLBI using VLBI Radio Sources (VRAD) for lunar gravity mapping. We have developed the frequency conversion system, multi frequency S/X-band vertical dipole antenna, and light weighted S-band patch antenna to perform these missions. Simple structured release mechanism has also been developed and confirmed its performance by ground test and orbital demonstration using micro-Lab Sat. Initial check out were executed and properties of satellite bus equipments, onboard mission instruments, and observation systems including ground stations were evaluated. Electric power and thermal control subsystems have shown that they conduct as designed and inspected in the ground tests. The release mechanisms have given the spin which can maintain the stability of the satellite attitudes. Communication functions of mission instruments conform to the link budgets. These results suggest that OKINA and OUNA have enough performances to produce efficient data by RSAT/VRAD gravity observations.

SELENE (Kaguya), which was successfully launched on Sep. 14, 2007, consists of the main orbiter, and two small free-flying sub-satellites, called Rstar (OKINA) and Vstar (OUNA). We use multi-frequency VLBI to measure the angular distance between the two sub-satellite radio sources Okina and Ouna in order to improve the accuracy of the low degree gravitational harmonics and the gravity field near the limb. The observations are made at three frequencies in S-band, (2212, 2218 and 2287 MHz), and one in X-band, (8456MHz) with carrier waves. The Japanese domestic VLBI network, VERA, will conduct VLBI observations for the whole mission period of one year. In addition, we will conduct two periods of international observations, each one month in duration, which will also include the international stations, Shanghai, Urumqi, Hobart, and Wettzell. We have succeeded in making VLBI observations of Okina/Ouna with VERA and the international network, and have also succeeded in correlating of signals from Okina/Ouna. We obtained phase delays with an accuracy of several pico-seconds in S-band.

SELENE Main Orbiter (KAGUYA) has separated two small sub-satellite (1) the Relay Satellite "Rstar (OKINA)", and (2) the VLBI Radio Satellite "Vstar (OUNA)". These sub-satellites started to perform 4-way Doppler measurements using Relay Satellite Transponder (RSAT) and multi frequency differential VLBI using VLBI Radio Sources (VRAD) for selenodesy. Initial check out was executed and properties of satellite bus equipments, onboard mission instruments, and observation systems including ground stations were evaluated. Electric power and thermal control subsystems have shown that they conduct as designed and inspected in the ground tests. The release mechanisms have given the spin which can maintain the stability of the satellite attitudes. Communication functions of mission instruments conform to the link budgets. These results suggest that Rstar and Vstar have enough performances to produce efficient selenodetic data by RSAT/VRAD observations.

In the very long baseline interferometry (VLBI) radio sources mission of selenological and engineering explorer, the differential phase delay between the Rstar and Vstar sub-satellites is obtained by using the multifrequency VLBI method during the switching VLBI observation period. The cycle ambiguity is successfully determined and the differential phase delay is estimated within an error of 7 picoseconds. The RMS error is somewhat larger than that for the case of same-beam VLBI because fluctuations of propagation delays whose periods are shorter than the switching interval cannot be canceled out between Rstar and Vstar. However, the differential phase delay during the switching VLBI period is sufficiently accurate and, together with Doppler and range measurements, can be a useful means for precisely determining satellite orbits and precisely estimating the lunar gravity field.

The electron density profiles above the lunar surface will be observed by the radio occultation technique during the SELENE mission using the Vstar sub-satellite. Previous radio occultation observations have indicated the existence of an ionosphere with densities of up to 1000 cm(-3) above the dayside lunar surface. The measured densities are difficult to explain theoretically when the removal of plasma by the solar wind is considered, and thus the generation mechanism of the lunar ionosphere is a major issue, with even the validity of previous observations still under debate. The SELENE radio science experiment will establish the morphology of the lunar ionosphere and will reveal its relationship with various physical conditions to provide possible clues to the mechanism.

In the JAXA's long-term vision, "JAXA 2025" at last March, the importance of exploration and utilization of the Moon is clearly identified as one of the major goals for the next two decades. The assigned long-term goal of the Moon exploration is the sound technology development for the lunar base after 2025. In this presentation, we will introduce the summary of this JAXA vision related to the Moon exploration, describe the interim result of the voluntary 60 days study team for the concrete plan of this JAXA's Moon exploration vision, and present quick report of some technological examination. © 2006 Elsevier Ltd. All rights reserved.

一年後のSELENE打ち上げを前に，プロジェクトチームではサイエンス小研究会を開催し，月の科学に関する統合サイエンスの進め方について議論を重ねてきた．広範囲な地球・惑星科学研究者に対して「月の科学」と「SELENEデータ利用」を呼びかけるために，本講演では小研究会でのこれまでの議論をまとめて報告する．これまでの小研究会での議論にもとづき，(1) 海のテクトニクス，(2) 地殻の形成，(3) 極域探査，(4) 多重リング盆地オリエンタールの地下構造，という4つのテーマを選定してプロジェクトチームでは研究計画を作成している．

In the JAXA's long term vision in March 2004, the exploration and utilization of the Moon for human lunar base is clearly identified as one of the JAXA's main goals for the next two decades. For this Moon goal, the ELR (Eternal Light Region) is going to be recognized as the major target for Japanese first Moon landing. In this paper, we will introduce the ELR, our expectations, topics of ELR exploration, and several PSR exploration concepts as the neighborhood of ELR.

In Japan’s lunar mission called SELENE (SELenological and ENgineering Explorer), detailed measurements of the lunar gravity field will be made by using two methods. The first is the differential VLBI measurement with two sub-satellites, and the second is the four-way Doppler measurement by using a sub-satellite which relays radio waves from the main lunar orbiter. The lunar far-side gravity field will be directly measured for the first time by using the second method, which will give us new information about the inner structure of the Moon. For the four-way Doppler measurement, the confirmation of the link establishment is an important issue because there is no telemetry relay from the main satellite to the sub-satellite in SELENE. The instruments are now under development, and a compatibility test of the instruments to the ground antenna station was carried out in March 2003. We have applied recently proposed algorithms for the confirmation of the link establishment and confirmed that they work successfully for data obtained during this test. The accuracy of the 2- and 4-way Doppler measurement are also measured and confirmed to be the expected level.

In the JAXA's long term vision, "JAXA 2025" at last March, the importance of exploration and utilization of the Moon is clearly identified as one of the major goals for the next two decades. The assigned long term goal of the moon exploration is the sound technology development for the Lunar Base after 2025. In this presentation, we will introduce the summary of this JAXA vision related to the moon exploration, describe the interim result of the voluntary 60 days study team for the concrete plan of this JAXA's moon exploration vision, and present quick report of some technological examination.