Tomoaki Toda

We built a Ka-band dual-circular-polarization low-noise receiver for the Misasa 54 m parabola antenna in Misasa, Japan. The antenna is designed to be combined with a transmitter and receiver system at the X band (around 8 GHz) and simultaneously with a receiver system at the Ka band. The Ka band is the frequency band around 30 GHz, which is important for deep-space communications and radio astronomy. The receiver comprises some waveguide components including a feed horn, a circular polarizer, and low-noise amplifiers. The components are installed in a vacuum vessel and are cooled to 4 K with a Gifford-McMahon refrigerator, providing low-noise performance. The receiver is capable of simultaneously handling the left- and right-hand circular-polarization (LHCP and RHCP) channels. The receiver-noise temperature was measured to be T-RX similar or equal to 14 K in both the LHCP and RHCP channels. The system-noise temperature, including the antenna loss and atmospheric attenuation at the zenith, was measured to be T-sys = 36-37 K in both the LHCP and RHCP channels on a clear day in September at Misasa. When the receiver is used with the X-band transmitter, the system-noise temperature is maintained at T-sys similar or equal to 42 K in the RHCP channel. The degradation in the system-noise temperature is attributed to a frequency-selective reflector, which divides the signals in the X and Ka bands. There is no contamination from the transmitter to damage the receiver. The receiver has already been in use for deep-space communications and radio-astronomy observations. Our team in the radio-astronomy laboratory of ISAS/JAXA is responsible for the development of the receiver and the measurements of its performance.

A projectile accelerated by the Hayabusa2 Small Carry-on Impactor successfully produced an artificial impact crater with a final apparent diameter of 14.5 ± 0.8 m on the surface of the near-Earth asteroid 162173 Ryugu on April 5, 2019. At the time of cratering, Deployable Camera 3 took clear time-lapse images of the ejecta curtain, an assemblage of ejected particles forming a curtain-like structure emerging from the crater. Focusing on the optical depth of the ejecta curtain and comparing it with a theoretical model, we infer the size of the ejecta particles. As a result, the typical size of the ejecta particles is estimated to be several centimeters to decimeters, although it slightly depends on the assumed size distribution. Since the ejecta particles are expected to come from a depth down to ∼1 m, our result suggests that the subsurface layer of Ryugu is composed of relatively small particles compared to the uppermost layer on which we observe many meter-sized boulders. Our result also suggests a deficit of particles of less than ∼1 mm in the subsurface layer. These findings will play a key role in revealing the formation and surface evolution process of Ryugu and other small Solar System bodies.

The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2’s Small Carry-on Impactor. The impact produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu’s surface age.

©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 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.

© 2017 The Author(s). After the arrival of Akatsuki spacecraft of Japan Aerospace Exploration Agency at Venus in December 2015, the radio occultation experiment, termed RS (Radio Science), obtained 19 vertical profiles of the Venusian atmosphere by April 2017. An onboard ultra-stable oscillator is used to generate stable X-band downlink signals needed for the experiment. The quantities to be retrieved are the atmospheric pressure, the temperature, the sulfuric acid vapor mixing ratio, and the electron density. Temperature profiles were successfully obtained down to ~ 38 km altitude and show distinct atmospheric structures depending on the altitude. The overall structure is close to the previous observations, suggesting a remarkable stability of the thermal structure. Local time-dependent features are seen within and above the clouds, which is located around 48-70 km altitude. The H2SO4vapor density roughly follows the saturation curve at cloud heights, suggesting equilibrium with cloud particles. The ionospheric electron density profiles are also successfully retrieved, showing distinct local time dependence. Akatsuki RS mainly probes the low and middle latitude regions thanks to the near-equatorial orbit in contrast to the previous radio occultation experiments using polar orbiters. Studies based on combined analyses of RS and optical imaging data are ongoing.[Figure not available: see fulltext.]

After the arrival of Akatsuki spacecraft of Japan Aerospace Exploration Agency at Venus in December 2015, the radio occultation experiment, termed RS (Radio Science), obtained 19 vertical profiles of the Venusian atmosphere by April 2017. An onboard ultra-stable oscillator is used to generate stable X-band downlink signals needed for the experiment. The quantities to be retrieved are the atmospheric pressure, the temperature, the sulfuric acid vapor mixing ratio, and the electron density. Temperature profiles were successfully obtained down to similar to 38 km altitude and show distinct atmospheric structures depending on the altitude. The overall structure is close to the previous observations, suggesting a remarkable stability of the thermal structure. Local time-dependent features are seen within and above the clouds, which is located around 48-70 km altitude. The H2SO4 vapor density roughly follows the saturation curve at cloud heights, suggesting equilibrium with cloud particles. The ionospheric electron density profiles are also successfully retrieved, showing distinct local time dependence. Akatsuki RS mainly probes the low and middle latitude regions thanks to the near-equatorial orbit in contrast to the previous radio occultation experiments using polar orbiters. Studies based on combined analyses of RS and optical imaging data are ongoing.

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.

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Japan's Venus Climate Orbiter Akatsuki was proposed to ISAS (Institute of Space and Astronautical Science) in 2001 as an interplanetary mission. We made 5 cameras with narrow-band filters to image Venus at different wavelengths to track the cloud and minor components distribution at different heights to study the Venusian atmospheric dynamics in 3 dimension. It was launched on May 21st, 2010 and reached Venus on December 7th, 2010. With the thrust by the orbital maneuver engine, Akatsuki tried to go into the westward equatorial orbit around Venus with the 30 hours' orbital period, however it failed by the malfunction of the propulsion system. Later the spacecraft has been orbiting the sun for 5 years. On December 7th, 2015 Akatsuki met Venus again after the orbit control and Akatsuki was put into the westward equatorial orbit whose apoapsis is about 0.44 million km and orbital period of 14 days. Its main target is to shed light on the mechanism of the fast atmospheric circulation of Venus. The systematic imaging sequence by Akatsuki is advantageous for detecting meteorological phenomena with various temporal and spatial scales. We have five photometric sensors as mission instruments for imaging, which are 1 m-infrared camera (IR1), 2 m-infrared camera (IR2), ultra-violet imager (UVI), long-wave infrared camera (LIR), and lightning and airglow camera (LAC). These photometers except LIR have changeable filters in the optics to image in certain wavelengths. Akatsuki's long elliptical orbit around Venus is suitable for obtaining cloud-tracked wind vectors over a wide area continuously from high altitudes. With the observation, the characterizations of the meridional circulation, mid-latitude jets, and various wave activities are anticipated. The technical issues of Venus orbit insertion in 2015 and the scientific new results will be given in this paper.

Radial variations of the amplitude and the energy flux of compressive waves in the solar corona were explored for the first time using a spacecraft radio occultation technique. By applying wavelet analysis to the frequency time series taken at heliocentric distances of 1.5-20.5 R-S (solar radii), quasi-periodic density disturbances were detected at almost all distances. The period ranges from 100 to 2000 s. The amplitude of the fractional density fluctuation increases with distance and reaches similar to 30% around 5 R-S, implying that nonlinearity of the wave field is potentially important. We further estimate the wave energy flux on the assumption that the observed periodical fluctuations are manifestations of acoustic waves. The energy flux increases with distance below similar to 6 R-S and seems to saturate above this height, suggesting that the acoustic waves do not propagate from the low corona but are generated in the extended corona, probably through nonlinear dissipation of Alfven waves. The compressive waves should eventually dissipate through shock generation to heat the corona.

Experimental evaluation of ultra wideband (UWB) wireless transmission was carried out with a view to replacing wired interface buses in spacecrafts. Application of wireless technologies within the spacecrafts could contribute to reduction in cable weight reduction in the cost of design, manufacture, and test more flexibility in layout of spacecraft subsystems and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed conductive enclosures, such as spacecrafts, restricts the link performance. Spatial distributions of UWB and narrowband propagation gains, delay spreads, and throughputs were measured with use of four different-sized shield boxes (simulated miniature satellites). Then UWB link throughput was experimentally evaluated in the boxes with use of connecting off-the-shelf MB-OFDM UWB devices. Increase in the inner volume of boxes resulted in higher UWB propagation gains, but wider delay spreads and hence lower link throughput.

We will discuss wireless technologies with emphasis on spacecraft proximity links. The proximity in space covers a link distance from several meters to thousands kilometers. Various telecommunication schemes have been designed for and applied to spacecraft for the proximity links. Those wireless links usually offers line-of-sight ranging and velocity measurement capability, too. It is important to know that their specification is not simply determined by themselves. Within strict constraints on onboard resource allocations like mass, power, and dimensions, the systematic point of view considering a total spacecraft system is also necessary. We will introduce SCOPE mission in this paper, as an example to take a look at the process of such a systematic optimization. It will help you to understand a mission-oriented development of space technologies. In recent years, in addition to inter-spacecraft wireless technologies, intra-spacecraft ones have been within a scope of practical applications. We will also discuss them to remove wire harness within a spacecraft, especially on their purpose and effectiveness, and their future applications.

Radio scintillation observations have been unable to probe flow speeds in the low corona where the scattering of radio waves is exceedingly strong. Here we estimate outflow speeds continuously from the vicinity of the Sun to the outer corona (heliocentric distances of 1.5-20.5 solar radii) by applying the strong scattering theory to radio scintillations for the first time, using the Akatsuki spacecraft as the radio source. Small, nonzero outflow speeds were observed over a wide latitudinal range in the quiet-Sun low corona, suggesting that the supply of plasma from closed loops to the solar wind occurs over an extended area. The existence of power-law density fluctuations down to the scale of 100 m was suggested, which is indicative of well-developed turbulence which can play a key role in heating the corona. At higher altitudes, a rapid acceleration typical of radial open fields is observed, and the temperatures derived from the speed profile show a distinct maximum in the outer corona. This study opened up a possibility of observing detailed flow structures near the Sun from a vast amount of existing interplanetary scintillation data.

BepiColombo is the joint Mercury exploration program between JAXA (Japan Aerospace Exploration Agency) and ESA (European Space Agency). MMO (Mercury Magnetospheric Orbiter) is JAXA's satellite in this program. She requires a telecommunication system that survives a harsh heat environment surrounding Mercury. She will stay in a polar orbit circulating Mercury for a year for continuous observations of Mercury magnetosphere. MMO has an X-band telecommunication system. We newly developed a high gain antenna for the use of her daily operations and wider field of view antennas for critical events. They are ones directly exposed to a high temperature environment of Mercury. The remains of the telecommunication system such as a transponder and a power amplifier were selected from the heritage of our past deep space missions. These instruments are placed inside MMO where a milder environment is expected than the outside. The total telecommunication system has been designed so that it should work through the MMO mission lifetime from the launch in 2016 to the end of the mission in 2025 including an extra year of extension. The system has experienced thermal environmental tests and proved its excellent resistivity to predicted environments. We will discuss these technologies incorporated in MMO and her telecommunication system design. (C) 2013 IAA. Published by Elsevier Ltd. All rights reserved.

Experimental evaluation of ultra wideband (UWB) wireless transmission was carried out with a view to replacing wired interface buses in spacecrafts. Application of wireless technologies within the spacecrafts could contribute to reduction in cable weight; reduction in the cost of design, manufacture, and test; more flexibility in layout of spacecraft subsystems; and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed conductive enclosures, such as spacecrafts, restricts the link performance. Spatial distributions of UWB and narrowband propagation gains, delay spreads, and throughputs were measured with use of four different-sized shield boxes (simulated miniature satellites). Then UWB link throughput was experimentally evaluated in the boxes with use of connecting off-the-shelf MB-OFDM UWB devices. Increase in the inner volume of boxes resulted in higher UWB propagation gains, but wider delay spreads and hence lower link throughput.

This paper describes measurement and characterization of radio propagation and transmission-particularly of ultra wideband (UWB) signals-within spacecrafts with a view to partly replacing on-board data buses with wireless connections. Adaption of wireless technologies within spacecraft could contribute to reduction of cable weight and resulting launching costs, and more reliable connections at rotary, moving, and sliding joints. This paper presents measurements and characteristics of radio propagation and transmission and addresses the effects of apertures perforated on the outer surface of satellites on the UWB propagation and transmission for low-and high-band UWB within a shield box. Channel responses, spatial distributions of UWB and narrowband propagation gains, delay spreads, and throughputs were derived from measurements. On the effects of apertures, the larger total area of apertures resulted in lower UWB propagation gains, shorter delay spreads, and (slightly) higher link throughput. The propagation study was followed up with experimental evaluation of UWB link throughput within a simulated spacecraft. Commercially off-the-shelf UWB devices were used in the experiments of ultra wideband technology to facilitate a high data rate (e.g. maximum of 400 Mb/s per node attained with SpaceWire, equaling the standards of a wired onboard data bus) and to reduce the fading margin. © 2013 IEEE.

A use of ultra wideband (UWB) technology within spacecrafts has been proposed with a view to partially replacing wired interface buses with wireless connections. Adoption of wireless technologies within the spacecrafts could contribute to reduction in cable weight (and launching cost as a result), reduction in the cost of manufacture, more flexibility in layout of spacecraft subsystems, and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed conductive enclosures, such as spacecrafts, restricts the link performance. In this paper, UWB and narrowband propagation were measured in a UWB frequency band (from 3.1 to 10.6 GHz, the full-band UWB approved in the United States) within a small spacecrafts and a shield box of the same size. While narrowband propagation resulted in considerable spatial variations in propagation gain due to interferences caused by multipath environments, UWB yielded none. This implies that the UWB systems have an advantage over narrowband from a viewpoint of reducing fading margins. Throughputs exceeding 80Mb/s were obtained by means of commercially-available UWB devices in the spacecraft. Path gains and throughputs were also measured for various antenna settings and polarizations. Polarization configurations were found to produce almost no effect on average power delay profiles and substantially small effects on the throughputs. Significantly long delay spreads and thus limited link performance are caused by a conductive enclosure (the shield box) without apertures on the surfaces. Even in such an environment, it was found that delay spreads can be suppressed by partially paneling a radio absorber on the inner surfaces. More than 96Mb/s throughputs were attained when the absorber panel covered typically 4% of the total inner surface area. Copyright © 2013 The Institute of Electronics.

Dual (X and Ka) band downlink operation is demanded scientific satellite missions, to facilitate much higher data rate and to increase the available radio channels. A combinations of a corrugated horn (for X band) and a disk-on-rod antenna (for Ka band) have used as a primary feed for a satellite-borne dual-band reflector antenna, but its volume was not satisfactorily small. The anothers proposed a combination of a sequential four-element array of rectangular microstrip antennas fed with L-shape probes for X band and a four-element array of helical antennas for Ka-band, to realize a small-volume, light-weight circular-polarized primary radiator. This paper reports the performances-VSWR, XPD, and radiation patterns of a prototype radiator.

Ultra wideband (UWB) technology has been expected to communicate in very high data rates by wireless within closed environments, such as spacecrafts. With a view to replacing onboard wired interface buses by wireless connection, UWB and narrowband propagation were measured in a UWB frequency band (from 3.1 to 10.6 GHz) within a small spacecraft. While narrowband propagation resulted in considerable spatial variations in path gain due to interferences caused by multipaths, UWB yielded nearly no fading. This suggests that the UWB systems have an advantage over narrowband from a viewpoint of reducing fading margins. Propagation gains were measured with full-, low-, and high-band UWBs, and narrowband (20 MHz bandwidth) for various antenna settings and polarization configurations for transmission and reception. Polarization configurations were found to produce almost no effect on average power delay profiles. Throughputs were also measured with a WiMedia UWB device. More than 85-Mb/s throughputs were observed for all antenna settings and propagation configurations.

Ka-band communications is one of the most important technologies for increasing the amount of data acquired in deep space missions. As a first step toward developing this technology, a Ka-band extender was attached to an existing X-band transponder. The Ka-band extender can generate Ka-band signals from the transponder's signals. The extender is designed so as to reuse design elements of the X-band transponder. This approach ensures reliability of the extender without additional qualification, lowers production costs, and allows for flexibility in the Ka-band extender configuration. For instance, the minimum configuration is a simple upconverter, which is realized by sharing circuits to the greatest extent possible with the transponder. The extender is compatible with the Ka-band specifications in Consultative Committee for Space Data Systems standards. Properties such as a flexible coherent ratio, high-speed analog and digital modulation, and ultralow phase noise for radio science missions are provided. Here, a breadboard model of the Ka-band extender was evaluated in experiments. The Allan variance of the Ka-band output signal was less than 1 × 10^-12 (at 1 s), 1 × 10^-13 (at 10 s), and 1 × 10^-14 (at >100 s) when an external reference signal was used. The Allan variance degradation and phase noise degradation, which were caused by the internal phase locked loop or frequency translation loop, were also measured. The measured phase noise degradation was about 25 dB from the theoretical value.

Japanese deep space missions have been developed based on Usuda Deep Space Center 64m station (UDSC64). Thus, it is the onboard telecommunication subsystem that determines deep space link capabilities of Japanese deep space spacecraft. Beginning by introducing the current performance of Japanese deep space telecommunications based on our Venus mission, AKATSUKI, we will briefly review those of our past deep space missions by comparing them with ones of NASA. Finally, we will discuss the technologies under development for our future missions and the future prospects of Japanese deep space telecommunications.

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.

In this paper, we present a sequentially rotated array antenna with a rectangular patch MSA fed by an L-probe. Since it's important to decrease couplings between patch elements in order to suppress the cross-polarization level, rectangular patches with aspect ratio of k are adopted. We investigate the cross-polarization level of the sequential array and discuss the relationship between the cross-polarization level and the mutual coupling. As a result, the bandwdith of the antenna element is obtained 14.6% when its VSWR is less than 1.5, and the directivity and cross-polarization level of a 4-patch sequential array are 10.8 dBic and 1.7 dBic, respectively, where k=0.6 and the patch spacing of d=0.5 wave length. These characteristics are 5.6 dB and 5.8 dB better than the corresponding values of a square patch sequential array antenna.

The application of Ka band to deep space communication is attractive. It makes profit of either higher bit rate or more compact system depending on what we prefer for our system. We also have tried to introduce Ka band technology to our deep space activities since the beginning of the 21st century. But a decade was needed till the missions actively take the Ka band benefits in their proposal. They are also active to construct a new deep space ground station for Ka band. We will discuss our onboard and ground station system for Ka band that we have prepared for this decade. Among them we will take up a Ka band coherent transmitter attached to the exiting X band transponder and a blueprint of our future Ka band ground station. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

PLANET-C (PLC) is the mission of Japan Aerospace Exploration Agency (JAXA) for Venus exploration. It is a successor of HAYABUSA in the history of Japanese deep space missions and is expected to be the first Japanese planetary orbiter. The spacecraft will be launched in the summer of 2010 from Tanegashima Space Center. The mission has demanded new onboard telecommunication instruments. Among them are X-band digital transponder, high gain flat antenna, and low gain wider field of view antenna. Through their developments, new technologies such as deep space regenerative ranging adapted for JAXA ground stations have been successfully incorporated into the PLC system. They are now raedy for their first space-borne demonstration. We will discuss these telecommunication technologies newly introduced for the PLC mission.

Ultra wideband (UWB) propagation was measured and characterized within spacecrafts, with a view to partly replacing onboard data buses with wireless connections. Spatial distributions of UWB and narrowband propagation in frequency (from 3.1 to 10.6 GHz) and time domains were measured with a microwave vector network analyzer. While narrowband resulted in a number of dead spots (deep fading points) within the conductive enclosures, UWB yielded none. This implies the UWB systems have an advantage over narrowband ones from the viewpoint of reducing fading margins. It was also found that delay spreads can be suppressed by partially panelling a radio absorber on the inner surfaces to facilitate high data rate transmission. © 2009 IEEE.

PLANET-C, the spacecraft for Venus exploration developed in Japan Aerospace Exploration Agency (JAXA) is under careful construction for the coming launch in the summer of 2010. It is expected to be the first Japanese orbiter other than Earth and Moon. Some new onboard communication instruments to encourage PLANET-C ambitious missions have been developed since 2001. Among them are X-band digital transponder, slot array high gain flat antenna, and low gain wide field of view lens antenna, and X-band power amplifier. New technologies such as deep space regenerative ranging have been introduced and customized so as to fit the JAXA style. They are now successfully operated through the ground tests of PLANET-C and ready for flight qualification. The qualified products will be catalogued as standard components in deep space activities of JAXA for the next decade.