竹内 央

Asteroid 162173 Ryugu has numerous craters. The initial measurement of impact craters on Ryugu, by Sugita et al. (2019), is based on Hayabusa2 ONC images obtained during the first month after the arrival of Hayabusa2 in June 2018. Utilizing new images taken until February 2019, we constructed a global impact crater catalogue of Ryugu, which includes all craters larger than 20 m in diameter on the surface of Ryugu. As a result, we identified 77 craters on the surface of Ryugu. Ryugu shows variation in crater density which cannot be explained by the randomness of cratering; there are more craters at lower latitudes and fewer at higher latitudes, and fewer craters in the western bulge (160 degrees E - 290 degrees E) than in the region around the meridian (300 degrees E - 30 degrees E). This variation implies a complicated geologic history for Ryugu. It seems that the variation in crater density indicates that the equatorial ridge located in the western hemisphere is relatively young, while that located in the eastern hemisphere is a fossil structure formed during the short rotational period in the distant past.

Precise information of spacecraft position with respect to target body is of importance in terms of scientific interpretation of remote sensing data. In case of Hayabusa2, a sample return mission from asteroid Ryugu, such information is also necessary for landing site selection activity. We propose a quick method to improve the spacecraft trajectory when laser altimeter range measurements and a shape model are provided together with crude initial trajectory, spacecraft attitude information, and asteroid spin information. We compared topographic features contained in the altimeter data with those expressed by the reference shape model, and estimated long-period trajectory correction so that discrepancy between the two topographic profiles was minimized. The improved spacecraft positions are consistent with those determined by image-based stereophotoclinometry method within a few tens of meters. With such improved trajectory, the altimeter ranges can be converted to Ryugu's topographic profiles that are appropriate for geophysical interpretation. We present a geophysical application that invokes possibility of impact-induced formation of the Ryugu's western bulge.

This chapter presents an ongoing effort in preparing JAXA Uchinoura station support to the Artemis 1 mission, scheduled for launch in late 2020. The system involves three key participants: JAXA ground station at Uchinoura, the Deep Space Network (DSN) components at the Jet Propulsion Laboratory, California, and the Artemis 1 mission navigation at the NASA Johnson Space Center, Texas.Demonstration of Uchinoura station support to the future Artemis signal relies on the use of a low-cost, highly-portable software-defined radio (SDR) test equipment as well as the tracking of the Lunar Reconnaissance Orbiter (LRO) spacecraft. Using the SDR equipment, we validated the compatibility of signal format between the Artemis flight radio and the Uchinoura ground station without having to send the flight equipment to the station. By tracking an ongoing operational spacecraft such as LRO, we were able to calibrate the performance of the system in real operational conditions. The measured Doppler noise of 0.03 Hz (1-sigma), or 0.002 m/s range rate at S-band, for Uchinoura station is deemed suitable to the Artemis 1 mission navigation needs.This chapter also discusses the test equipment capability and its performance. In addition to being low cost, the equipment offers many advantages compared to the traditional full-scaled test signal simulator. Chief among them is portability making system easy to set up and transport, and the fidelity of the test signal that it captures from spacecraft flight equipment. Some of the lessons learned, such as internal frequency stability of the test signal, are also reflected.

© 2019 American Association for the Advancement of Science. All rights reserved. The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multicolor images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of ≤ 106 years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu's surface supports partial dehydration due to internal heating of the asteroid's parent body.

© 2019 American Association for the Advancement of Science. All rights reserved. The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018.We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.

© 2019, Univelt Inc. All rights reserved. This research investigates retrograde teardrop orbits (RTOs) about asteroids subject to strong solar radiation pressure. RTOs are closed orbits that are made periodic by introducing a deterministic impulsive delta-V within each period. This type of artificial periodic orbit provides high flexibility in orbit design compared with natural periodic orbits. RTOs are promising options for asteroid missions because of their stability and small delta-V values (on the order of 10 cm/s or less). This paper presents the dynamical theories of RTOs and possible applications for the Hayabusa2 mission.

Copyright © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Communication with spacecraft is essential to every space mission. However, when the estimation or control of the motion of a spacecraft cannot be performed precisely, it is extremely difficult to communicate with the spacecraft in real-time operations. To enable communication in this situation, this paper proposes an off-line signal-processing method to detect the weak signal transmitted from a spacecraft under poor communication conditions. This is achieved by the following process. First, the Doppler shift effect caused by the motion of the spacecraft is removed from the received signal. The signal power is then enhanced by integrating the signal spectrum over a long time period. Moreover, the estimated frequency model, which contains the Doppler shift information, can be used for orbit and attitude determination as well. A coarse-ranging technique based on the detected weak signal is then introduced as a method of improving the orbit-estimation accuracy. The validity and effectiveness of the proposed method are demonstrated by applying these algorithms to actual radio waves transmitted from the IKAROS.

©2018. American Geophysical Union. All Rights Reserved. Radio occultation (RO) is one of the most efficient techniques for studying fine vertical structures in planetary atmospheres. However, the geometrical optics (GO) method, which has been used for the analysis of RO data, suffers blurring by the finite width (Fresnel scale) of the radio ray and cannot decipher multipath propagation, which also prevents retrieval of fine structures. Here we apply Full Spectrum Inversion (FSI), which is one of the radio holographic methods, to RO data taken in Venus Express and Akatsuki missions to retrieve fine structures in Venus' cloud-level atmosphere. The temperature profiles obtained by FSI achieve vertical resolutions of ~150 m, which is much higher than the typical resolution of 400–700 m in GO, and resolve structures in multipath regions. Thin, near-neutral layers are found to be ubiquitous at cloud heights; we suggest here that those layers are caused by the mixing associated with the breaking of short-wavelength gravity waves. The wavenumber spectra of small-scale structures are consistent with the semiempirical spectrum of saturated gravity waves and show larger amplitudes at higher latitudes. Temperature profiles in the high latitudes frequently show a sharp temperature minimum near the cloud top, below which the vertical temperature gradient is near adiabat, implying that the sharp temperature minimum is created by adiabatic cooling associated with convective plumes that impinge on the overlying stable layer.

©2018. American Geophysical Union. All Rights Reserved. Temperature profiles of the Venus atmosphere obtained by the Akatsuki radio occultation measurements showed a prominent local time dependence above 65-km altitude at low latitudes equatorward of 35°. A zonal wavenumber 2 component is predominant in the temperature field, and its phase (i.e., isothermal) surfaces descend with local time, suggesting its downward phase propagation. A general circulation model (GCM) for the Venus atmosphere, AFES-Venus, reproduced the local time-dependent thermal structure qualitatively consistent with the radio occultation measurements. Based on a comparison between the radio occultation measurements and the GCM results, the observed zonal wavenumber 2 structure is attributed to the semidiurnal tide. Applying the dispersion relationship for internal gravity waves to the observed wave structure, the zonally averaged zonal wind speed at 75- to 85-km altitudes was found to be significantly smaller than that at the cloud top. The decrease of the zonal wind speed with altitude is attributed to the momentum deposition by the upwardly propagating semidiurnal tide excited in the cloud layer.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Hayabusa2 is a sample return mission to the C-type asteroid 162173 Ryugu. Hayabusa2 was launched by the Japan Aerospace Exploration Agency in December 2014 and will arrive at the asteroid vicinity in the summer of 2018. Hayabusa2 will explore Ryugu for 1.5 years and return to the Earth in winter 2020. The entire flight period of Hayabusa2 is divided into 4 phases; (i)EDVEGA (launch to Earth gravity assist), (ii) Transfer (Earth gravity assist to asteroid arrival), (iii) Asteroid Proximity, (iv) Return (asteroid to Earth reentry). Different operations are required in each phase. Especially in the asteroid proximity phase, there are many critical events such as low-altitude observation, touching down, rover deployment and crater forming. There are some difficult characteristics in performing these critical operations from ground; navigation and guidance in the submeter accuracy against the microgravity environment of Ryugu, 40 minutes round-trip light time due to the 3.6 billion kilometers distance between Hayabusa2 and the Earth. We have developed a ground operation system to clear the characteristics. This paper presents the ground operation systems overview for Asteroid Proximity Operation to realize high quality operation for mission success.

© 2017 The Author(s). We report results of a laser link experiment between a laser altimeter called light detection and ranging (LIDAR) aboard Hayabusa2 and ground-based satellite laser ranging stations conducted when the spacecraft was near the Earth before and after the gravity assist operation. Uplink laser pulses from a ground station were successfully detected at a distance of 6.6 million km, and the field of view direction of the receiving telescope of the LIDAR was determined in the spacecraft frame. The intensities of the received signals were measured, and the link budget from the ground to the LIDAR was confirmed. By detecting two successive pulses, the pulse intervals from the ground-based station were transferred to the LIDAR, and the clock frequency offset was thus successfully calibrated based on the pulse intervals. The laser link experiment, which includes alignment measurement of the telescopes, has proven to be an excellent method to confirm the performance of laser altimeters before they arrive at their target bodies, especially for deep space missions.[Figure not available: see fulltext.]

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The Consultative Committee for Space Data Systems (CCSDS) is an international organization supported by 39 space agencies and about 145 companies. CCSDS was formed in 1982 by the major space agencies of the world to provide a forum for solving common problems in the development and operations of space data systems. It has currently 137 active Publications for data and communications systems to promote interoperability and cross support among cooperating space agencies to reduce operations costs by sharing facilities and to reduce the cost to the various agencies of performing common data functions, by eliminating unjustified project-unique design and development. CCSDS also functions as an ISO Standards Committee, Technical Committee 20 Subcommmittee 13 (TC20=SC13), Space Data and Information Transfer Systems. In this capacity, CCSDS/ISO-TC20-SC13 represents 20 nations. In order to enable the next generation of spaceflight missions, CCSDS is aiming at technology evolution and innovation through the process of developing, validating, maintaining and promoting a body of unique space data systems standards, focusing on interoperability of space systems and cross-support between space organisations. In this paper we describe the different technical areas, its strategic goals and a general overview of the currently under development and future most innovative standards.

First Japanese probe orbiting Venus known as "AKATSUKI (Planet-C)", has been launched on May 21, 2010 on H-IIA booster from Tanegashima Space Center (TSC), Kagoshima, Japan. It arrived at Venus on December 7, 2010, but due to a malfunction of the thruster system, the Venus orbit insertion failed. Using the reaction control systems instead of the broken orbital maneuvering engine, the recovery maneuver was operated on December 7, 2015, and AKATSUKI was finally inserted into an orbit around Venus with a 0.36 million km apoapsis and a 10.5 day. It is described the strategy, analysis, and evaluation for the orbit determination to orbit Venus.

© Copyright (2017) by International Astronautical Federation All rights reserved. An asteroid explorer Hayabusa2 will arrive at the vicinity of C-typed asteroid 162173 Ryugu in the summer 2018 and start its asteroid proximity phase which consists of various descent operations including three touchdowns (TDs) aiming to obtain surface sample of the asteroid. During descent operations, guidance, navigation and control of lateral position of the spacecraft is basically executed by the command from the ground station under round trip time up to 40 minutes. This navigation scheme is called GCP-NAV (Ground Control Points Navigation). To increase reliability in each of the critical operations adopting GCP-NAV, Real-time Integrated Operation (RIO) trainings are planned during 2017, and a Hardware-in-the-Loop Simulator (HIL) is implemented to emulate the actual operational environment with the spacecraft behavior. This paper first presents the brief explanation of touchdown operation, then system configuration and major functions of HIL are described which enables the ground operator to perform closedloop descending operation training using unique GCP-NAV scheme. The validation results of the simulator obtained from actual operation training session are also reported. Finally, detail schedule of RIO training campaign is introduced.

We present the results of the simultaneous observation of giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2 GHz, we find that about 70% or more of the GRP spectra are consistent with single power laws and their spectral indices are distributed from -4 to -1. We also find that a significant number of GRPs have such. a. hard spectral index (approximately -1) that the fluence at 0.3 GHz is below the detection limit ("dim-hard" GRPs). Stacking light curves of such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the off-GRP light curve. Our samples show apparent correlations between the fluences and the spectral hardness, which indicates that more energetic GRPs tend to show softer spectra. Our comprehensive studies on the GRP spectra are useful materials to verify the GRP model of fast radio bursts in future observations.

© 2016 The Society of Instrument and Control Engineers - SICE. This paper presents the planning, flight results and lessons learned of flyby guidance experiments of interplanetary micro-spacecraft PROCYON. PROCYON is the world's first interplanetary micro-spacecraft and was launched on 3rd December, 2014. Orbital control of interplanetary micro-spacecraft is challenging because of severe restriction and lower reliability on spacecraft system. For guidance strategy of PROCYON, we have introduced an innovative guidance strategy by two-stage stochastic programming for thrust-direction-constrained problem. Although the flight experiment has many difficulties especially on navigation, the flight result shows that we successfully demonstrate that PROCYON has been guided to the target point with objective guidance accuracy, which is within 100[km] on B-plane at 3,000,000[km] distance from the Earth. These results contributes the future flyby navigation and guidance for interplanetary micro-spacecraft, which has severe constraints and lower reliability on spacecraft system.

© 2016 IEEE. PROCYON is a first full-scale, 50-kg-class probe featuring most of the key technologies for deep-space exploration. It was developed by the University of Tokyo and ISAS/JAXA and launched with Hayabusa 2 on 3 Dec 2014. PROCYON has a newly developed X-band telecommunication system fully compatible with the frequency range, up- and down-link turn-around ratio, modulation scheme, and DDOR tones following CCSDS-recommended standards, and it can establish X-band coherent two-way communication and ranging links with deep-space stations as larger deep-space probes have done. The total mass of the onboard telecommunication system is 7.3 kg excluding its RF coaxial harness, and total power consumption during two-way communication, 15 W of RF output power at SSPA, is 54.3 W. After launch, PROCYON's telecommunication system has been successfully working according to the system design. These achievements will provide core technologies for next-generation deep-space exploration by ultra-small probes.

<p>Mars EDL (entry, descent and landing) and surface exploration demonstration working group in Japan Aerospace Exploration Agency (JAXA) has assessed and discussed feasibility of a Martian rover mission to be launched in early 2020s. The primary objectives of this mission are to demonstrate technologies required for EDL and surface exploration of a massive planet with an atmosphere, to investigate Martian geochronology and to search for signs of lives, past or present, and to determine when the ocean was lost in the Martian history. The launch date is targeted in early 2020's in our study. In this paper, we investigate launch opportunities during 2020's and propose several launch windows considering some system requirements. Feasible interplanetary transfer trajectories from Earth to Mars are proposed. Assuming direct entry and following aerodynamic guidance in Martian atmosphere, we connected interplanetary and aerodynamic trajectories so as to land on an aimed point. Precision analysis of orbit determination at the entry and landing is also shown.</p>

© 2016 by CCSDS. The Consultative Committee for Space Data Systems (CCSDS) is an international organization supported by 39 space agencies and about 145 companies. CCSDS was formed in 1982 by the major space agencies of the world to provide a forum for solving common problems in the development and operations of space data systems. It has currently 137 active Publications for data and communications systems to promote interoperability and cross support among cooperating space agencies to reduce operations costs by sharing facilities and to reduce the cost to the various agencies of performing common data functions, by eliminating unjustified project-unique design and development. CCSDS also functions as an ISO Standards Committee, Technical Committee 20 Subcommmittee 13 (TC20=SC13), Space Data and Information Transfer Systems. In this capacity, CCSDS/ISOTC20- SC13 represents 20 nations. In order to enable the next generation of spaceflight missions, CCSDS is aiming at technology evolution and innovation through the process of developing, validating, maintaining and promoting a body of unique space data systems standards, focusing on interoperability of space systems and cross-support between space organisations. In this paper we describe the different technical areas, its strategic goals and a general overview of the currently under development and future most innovative standards

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. This paper describes the earth swing-by operation of Hayabusa2. Hayabusa2 is a Japanese interplanetary probe launched on December 3, 2014 to visit asteroid "Ryugu". It is a sample return mission like Hayabusa, but the spectrum type of the target asteroid is different from Itokawa, Hayabusa's target body. Itokawa is S-type asteroid but Ryugu is C-type asteroid. C-type asteroids are believed to contain more organic matter and hydrated mineral. Hayabusa2 is scheduled to reach Ryugu in the middle of 2018 and will perform an asteroid proximity operation for 1.5 years. Three touch downs for collecting the asteroids sample and one 2m class-crater generation by a kinetic impact are planned during the asteroid proximity operation. The collected sample will be brought back to the Earth by the re-entry capsule in 2020. Hayabusa2 is equipped with a high-specific ion engine system to enable the round-trip mission. The ion engine system can provide larger than 2 km/s delta-V with very small amount of xenon propellant. First one year after launch is an interplanetary cruise phase called EDVEGA (Electric Delta-V Earth Gravity Assist) phase. The transfer orbit to the asteroid is connected with the EDVEGA orbit by the Earth swing-by. After the launch, several ion engine commission operations have been successfully conducted and three long-term ion engine maneuvers were also conducted to direct the spacecraft onto the Earth swing-by corridor. The last two months before the swing-by was the precise navigation / guidance phase to the Earth swing-by. During this phase, trajectory correction maneuvers by the chemical reaction control system (RCS) were conducted. As a result, Hayabusa2 successfully performed the Earth swing-by on December 3, 2015 and it is now on its target orbit to the asteroid. This paper describes how the guidance / navigation operations were conducted around the Earth swing-by. A lot of science observation were also performed during this phase. This paper also shows the result of the science observations.

Delta-DOR (Delta Differential One-way Ranging)とは,長基線電波干渉計技術を用いて深宇宙探査機の軌道を精密に決定する手法であり,探査機の惑星への軌道投入や着陸時・スイングバイ時など,高精度な軌道決定が求められる局面では必須の技術である.世界の宇宙機関の間で高精度化のための取り組みが続けられており,現在では数ナノラディアン程度の角分解能(IAU先で数百m程度の位置精度)が得られるようになっている.本講演ではDelta-DOR技術の概略を解説すると共に, Delta-DORの精度向上のための手法を解説する.はやぶさ2への相乗りを目指して開発が進められている小型小惑星探査機PROCYONでは, DORトーン信号をスイープさせる事により受信局伝送路内の位相特性の不均一性に起因する誤差の低減を目指すという,世界初の手法が試みられる予定であるため,その詳細について特に詳しく解説する.

This paper reports on very-long-baseline interferometry observations of the radio-loud broad absorption line (BAL) quasar J1020+4320 at 1.7, 2.3, 6.7, and 8.4 GHz using the Japanese VLBI network (JVN) and European VLBI network (EVN). The radio morphology is compact with a size of -10 pc. The convex radio spectrum has been stable over the last decade; an observed peak frequency of 3.2 GHz is equivalent to 9.5 GHz in the rest frame, suggesting an age on the order of -100 years as a radio source, according to an observed correlation between the linear size and the peak frequency of compact steep spectrum (CSS) and giga-hertz peaked spectrum (GPS) radio sources. A low-frequency radio excess suggests a relic of past jet activity. J1020+4320 may be one of the quasars with recurrent and short-lived jet activity during a BAL-outflowing phase. © 2013. Astronomical Society of Japan.

本稿は,世界初のソーラー電力セイル実証機IKAROSが打ち上げられてからおよそ2年間という期間に実証された,ソーラーセイルの誘導・航法に関する成果をまとめたものである.世界初となるソーラーセイルの軌道上での実際の航法・誘導において,光圧加速度・光圧トルクのその類稀なる大きさから,一般的な手法だけでは評価しきれない点が少なからず存在し,そのため,IKAROSの誘導・航法技術に関しては,いくつかの工夫がなされた.ここでは,航法技術に関して,セイルによって発生する光圧加速度を精密に計測するための推定法,及び評価結果を,また,誘導技術に関しては,光圧トルクによって発生する姿勢のドリフト運動を考慮した誘導法,及びその評価結果について紹介する.また,航法技術に関連して,IKAROSに搭載されたDDOR用のトーン生成器によって得られたデータの評価結果についても紹介する.

This paper summarizes the guidance, navigation and control of the world&rsquo;s first solar power sail IKAROS. During the 1.5 years of its interplanetary flight, IKAROS has carried out the guidance, navigation and control experiments using the large solar radiation force generated by its 200 m2 solar sail. Since solar radiation pressure is the main controllable force for a solar sail, its modeling is the key factor for a successful guidance. A precise solar radiation pressure modeling for this spinning solar sail has been performed in order to support the navigation and guidance using the large membrane. Due to the complexity of the sail surface and shape, the refinement of the SRP model is done after the deployment in space with radiometric measurements. This solar sail navigation is also supported by the precise delta-DOR (Differential One-way Range) measurements. These in-flight demonstrations with IKAROS enable the future deep space exploration with solar sailing technique.

"Akatsuki" mission has been launched on May 21, 2010 on an H-IIA booster from Tanegashima Space Center (TSC), Kagoshima, Japan, and arrived at Venus on December 6, 2010, without trouble, after cruising interplanetary approximately seven months. In this paper, the orbit determination result, the estimation strategy, and experiences during the period from the launch through the VOI (Venus Orbit Insertion) phase are discussed.

This paper describes a modeling of attitude dynamics of spinning solar sail spacecraft under influence of solar radiation pressure (SRP). This method is verified and actually exploited in the attitude and trajectory guidance operation of Japanese interplanetary solar sail demonstration spacecraft IKAROS. IKAROS shows a unique attitude behavior due to strong SRP effect. This paper introduces a new generalized dynamics model called Generalized Spinning Sail Model (GSSM), which clearly explains physics behind the observed phenomena with only three parameters. Precise understanding of attitude dynamics through the GSSM led to 6 months of world first interplanetary trajectory guidance of solar sail-craft toward Venus. The GSSM also contributed to realize a zero-fuel spin axis maintenance for most of the flight path before the Venus flyby. In this paper, an overview of IKAROS attitude and trajectory control operation in the cruising phase, derivation of the proposed model and its implementation to the actual IKAROS operation are shown.

We are planning to construct a VLBI system in the Andes dedicated only to the detection of the event horizon of the SgrA* black hole.

IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is the world's first spacecraft to successfully demonstrate solar-sail technology in interplanetary space. The spacecraft is made of square shape of very thin membrane, whose diagonal dimension is 20m. By changing its attitude toward Sun, radiation pressure of solar photons can be used as propulsive force of the spacecraft. To determine the orbit under the continuous big influence of the nongravitational perturbative force (i.e. solar radiation pressure), Very Long Baseline Interferometry (VLBI) observation is effective because sky plane position of the spacecraft can be directly and instantaneously measured by VLBI observables without (or with less dependence on) a priori assumption for solar radiation pressure model. In order to effectively perform VLBI measurements, a signal generator of Differential One-way Range (DOR) tones, which consist of multiple tones whose spanning bandwidth is about 28MHz, was developed and installed to the spacecraft. A digital backend system for the ground stations which has maximum output performance of 4-Gbps had also developed to sample wideband DOR tones. A total number of 24 international VLBI experiments were carried out by using totally 15 antennas among 8 agencies during July and August in 2010. As a result of initial analysis, measurement accuracy of VLBI delay was confirmed to be 50 pico second level, which is 20 times improved precision compared to the JAXA's conventional deep space spacecraft such as Hayabusa and Akatsuki. © 2011 IEEE.

This paper investigates the solar sail modeling and its estimation approach of solar power sail spacecraft IKAROS. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop before the launch. In this paper, a practical analysis of estimating the solar sail force model from radiometric tracking data is investigated. This is demonstrated by orbit determination including parameter estimation of generalized sail model.

This paper investigates the solar sail modeling and its estimation approach of solar power sail spacecraft IKAROS. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop before the launch. In this paper, the spinning solar sail model is introduced considering the deformation of the sail. A practical analysis of estimating the solar sail force model from radiometric tracking data is investigated. The solar sail model estimation using the real tracking data is also demonstrated. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

This paper investigates the solar sail modeling and its estimation approach of solar power sail spacecraft IKAROS. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop before the launch. In this paper, a practical analysis of estimating the solar sail force model from radiometric tracking data is investigated. This is demonstrated by orbit determination including parameter estimation of generalized sail model.

This study investigates the trajectory analysis of small solar sail demonstration spacecraft IKAROS considering the uncertainty of solar radiation pressure. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop on the ground. In this paper, a practical analysis of estimating the solar sail force model from Doppler and range observable is investigated. This is demonstrated by orbit determination including parameter estimation of solar sail model. Some examples are described to investigate better parameters to estimate the solar sail force model.

Space VLBI (very long baseline interferometry) mission, ASTRO-G, will be launched in 2013 by Japan Aerospace Exploration Agency (JAXA). ASTRO-G is a follow-on mission of HALCA (VSOP) mission in 1990s, which was the world first space VLBI mission. ASTRO-G will consists of a huge synthetic aperture with diameter of 35,000 Km together with radio antennas in the ground. They will achieve the world highest angular resolution imaging by means of 43 GHz observation. This paper describes the advanced key technologies of ASTRO-G such as the 9 m deployable antenna with very accurate surface, the fast rest - to - rest attitude maneuver, and the precision orbit determination above NAVSTAR's orbits. These advance technologies lead ASTRO-G mission to the astronomical observation with the world highest angular resolution.

The solar sailing spacecraft is one of the promising propulsion systems for the future deep space exploration mission. Japan Aerospace Exploration Agency (JAXA) has been studying the spin solar sail spacecraft which has a squared-shape type solar sail. One of the most significant objective to control the satellite orbit of the spacecraft is to estimate the thrust force induced by the photon, namely to establish the acceleration model before the launch. In a view point to use this model in orbit, the calibration of the acceleration model and evaluation of the dynamics on orbit are also important issue. This paper presents the way to construct the acceleration model of the Solar Radiation Pressure (SRP) on ground, and the calibration and evaluation strategy for this model by using the on-orbit data.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. Recent Japanese e-VLBI activities are reported in this paper. Offline data transfer though the network has been regularly performed for geodetic VLBI experiments. Besides these offline transfers, real-Time eVLBI experiments for ultra-rapid UT1 measurements have been performed among Onsala, Metsähovi, Tsukuba, and Kashima stations in a pilot project. In the field of astronomy, a real-Time e-VLBI demonstration session organized by the ATNF in 2008 was the first occasion for Kashima to transmit VLBI data obtained by the K5 system to a foreign correlator in real-Time. The global e-VLBI observation session organized by JIVE for the opening event of International Year of Astronomy in January 2009 was the first participation for a Japanese station in a global real-Time e-VLBI session. Overview of the K5 DAS systems (K5/VSSP, and K5/VSI) used for the e-VLBI is described. Optically linked e-VLBI observations with domestic VLBI stations have been conducted by the NAOJ. Also the NAOJ has developed a high speed VLBI data sender/reciver equipment named VOA-200 and a high speed hardware correlator (2Gbps × 6 baselines). A test observation of 8 Gbps real-Time VLBI was successfully achieved by using the VOA-200 and the hardware correlator in 2008.

We are planning to construct a sub-mm VLBI system at Andes only dedicated to the detection of event horizon of SgrA*black hole. Using two of fixed large spherical dishes and a mobile small station, we sample sufficient u-v coverage, aim to image and detect the event horizon of SgrA *.

ASTRO-G for the VSOP-2 project is a radio telescope satellite for a next-generation space very-long-baseline interferometry (VLBI) following HALCA for the VSOP project. It will be launched in 2012. We present the overview of ASTRO-G observing systems and available observing modes.

Precise orbit determination (POD) is a key factor to enable phase referencing observations with Astro-G. A POD accuracy of 30 cm is required for efficient X-band phase referencing observations, accuracy of 6 cm for K-band observations, and accuracy of 3 cm for Q-band observations. For the POD, Astro-G will be equipped with a GPS/Galileo receiver and a SLR (Satellite Laser Ranging) retroreflector array. Four POD antennas will be equipped on four sides of the satellite body, to cover all directions. The SLR will be used as a complement to the GPS at middle-to-high altitude. Because the refroreflector array should always face to the Earth direction, it will be set up on the Ka-link antenna gimbal. The most significant perturbing force for the Astro-G is solar radiation pressure (SRP). The reflectivity of each surface component should be preliminary measured in detail to model the SRP. The estimated achievable POD accuracy at apogee is 10 similar to 30 cm in nominal case. Phase referencing observations in K- or Q-band can be performed if the enough amount of SLR tracking data can be obtained at high altitudes.