TOMIKI ATSUSHI

We have started development of small synthetic aperture radar (SAR) compatible to 100kg class small satellites with about 3m ground resolution and multi-polarization, aiming for constellation SAR observations. This technology enables us to realize high frequency SAR observations with only several hours observation interval. This paper desrcibes key technologies of this development such as deployable slot array antennas, waveguide feeder with a small gap at a deployment point, and GaN HEMT X band amplifier. Also we show an integration design result of this SAR system to 100kg class bus system.

We have started development of small synthetic aperture radar (SAR) compatible to 100kg class small satellites with about 3m ground resolution and multi-polarization, aiming for constellation SAR observations. This technology enables us to realize high frequency SAR observations with only several hours observation interval. This paper desrcibes key technologies of this development such as deployable slot array antennas, waveguide feeder with a small gap at a deployment point, and GaN HEMT X band amplifier. Also we show an integration design result of this SAR system to 100kg class bus system.

Recently small satellites play important roles in earth observations with medium resolution. This purpose requires a small earth station which is equipped with S band up/down satellite operation functions as well as with X band high data rate reception functions. We have developed a small earth station with a 3.8 m antenna and evaluated them with relatively low cost. This paper describes the cost-effective test method and the results.

Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is an infrared IR astronomical satellite to be launched in 2022. It is equipped with sensitive IR sensors, cooled down to 4.5K. It also consists of a high-power X-band transmitting antenna used for downlink to the earth. Since energy leakage should be stringently suppressed from the antenna to the IR sensors, it is necessary to evaluate electromagnetic shielding effectiveness (SE) of structural materials of the satellite, including carbon fiber reinforced plastics (CFRP), multi-layer insulator (MLI), and aluminium plates connected with rivets. The CFRP and MLI were found to yield SE equivalent to aluminium. The SE of the connected aluminium plates increased with decreasing spacings of the rivets. Chromate conversion coating, providing higher surface conductivity than anodized aluminium surface, also enhanced the SE.

Delta-DOR (Delta Differential One-way Ranging) is an application of VLBI (Very Long Baseline Interferometry) technique which enables very precise angular position measurements for deep space spacecrafts. The technique play an essential role in the critical events such as a planetary orbit insertion, landing, and gravity assist operations. International space agencies had been working for the improvement of the measurement accuracy of the Delta-DOR, and the current accuracy of the measurement reaches a-few nano radian level. In this lecture, the principle of the technique are described and several techniques that provides the better Delta-DOR accuracy are introduced. In particular a sweeping tone technique which aims at a reduction of phase ripple error in the ground station transmit line are described in detail. This newly developed technique will be used for an asteroid exploration mission PROCYON that will be launched in 2014 as a sub payload mission of the Hayabusa-2.

A high-speed downlink communication system is required to meet various applications for nano/small satellites. Therefore, it is essential to implement a transmitter with small weight and power in such satellites. Our recent research has focused on an efficient system with the compact transmitter incorporating a powerful error correction on ground station receiver. Generally, an operation at nonlinear region of RF power amplifier provides a RF power amplifier with high energy efficiency. However, an amplitude-phase modulation, which is an efficient scheme in term of frequency band, requires high linearity. GaN-HEMT SSPA, which has high efficiency and linearity, and Digital-pre-distortion can provide better answer. Also, I'm developing a new measurement method to evaluate Pas and transmitter systems. We will demonstrate a high-speed down link communication system in "Hodoyoshi-4" satellite.

JAXA has planned a light airplane ejected from a Mars orbiter for observing the residual magnetic fields near the surfaced and the exposed strata of Mars. An altimeter is indispensable to achieve the mission. It must be miniature and light weight to be equipped on the airplane flying in the thin atmosphere of Mars. For this propose, we have been developing an FM-CW radar for its accepted merits: easier signal processing and lower power consumption than a pulse radar. This paper presents the feasibility study of the radar and the results of ranging experiments using a breadboard model.

We have started development of small synthetic aperture radar (SAR) compatible to 100kg class small satellites with about 3m ground resolution and multi-polarization, aiming for constellation SAR observations. This paper describes key technologies of this development such as deployable slot array antennas, waveguide feeder with a small gap at a deployment point, and GaN HEMT X band amplifier. Also we show an integration design result of this SAR system to 100kg class bus system.

Recently small satellites start playing important roles in earth observation missions. It, however, is true that small satellites have drawbacks of sensor resolutions and down link data rate. As a solution to the latter drawback, we have developed novel communications system for 320 Mbps down link with 16QAM for small satellites with 50 kg class. We developed a new 2 W class GaN-HEMT X-band amplifier with high efficiency and small distortion, digital filter and pre-distortion processing with relatively low clock frequency in FPGAs. This paper describes our downlink system and evaluation result of the engineering model and the prototype model.

Ultra wideband (UWB) propagation was measured and characterized within spacecrafts, with a view to partly replacing onboard data buses with wireless connections. Adaptation of wireless technologies in spacecrafts could contribute to: reduction of cable weight (and launching cost as a result), more flexibility in layout of spacecraft subsystems, and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed metal enclosures, such as spacecrafts, restricts the transmission performance. To realize the above benefits, multipath propagation affecting the transmission performance must be scrutinized. 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. In this present paper, UWB channels within a small scientific satellite was measured and statistically analyzed, based on a modified Saleh-Valenzuela (SV) model [2], which modeled indoor UWB propagation channels. The modified SV model is based on a cluster concept of rays. The clusters, as well as the multipath components within a cluster, arrive according to Poisson processes with different rates. The received power of both the cluster and the rays within a cluster decays exponentially.

We have started development of small synthetic aperture radar (SAR) compatible to 100kg class small satellites with about 3m ground resolution and multi-polarization, aiming for constellation SAR observations. This technology enables us to realize high frequency SAR observations with only several hours observation interval. This paper describes key technologies of this development such as deployable slot array antennas, waveguide feeder with a small gap at a deployment point, and GaN HEMT X band amplifier. Also we show an integration design result of this SAR system to 100kg class bus system.

JAXA has the Satellite AIS demonstration experiment named SPAISE1 (SPace based AIS Experimentl) which is installed in Small demonstration Satellite 4 (SDS-4). We are now executing reception performance experiment from 30/May. Experimental studies on the delay characteristics of signal propagation must be conducted in order to achieve improved reception rate in the signal interference area. We have analyzed the detected AIS signals for measuring the SPAISE propagation delay profile with the replica signal in the 160 MHz band. This paper presents the results of the SPAISE propagation analysis.

We have made a conceptual design of a long-distance wireless power transmission (WPT) experiment using a small scientific satellite, which is developed by ISAS/JAXA. The purposes of the WPT experiments are to demonstrate a precise directional control of microwave beam, which includes the direct detection of rectenna sites, and to clarify the propagation characteristics of intense microwaves in the plasma of the ionosphere. The sub-recurrent orbit at an altitude of 370 km is a prime candidate. Typical microwave power radiated from the transmission antenna with frequency of 5 GHz band is around 2kW. This level of microwave power injection will generate a power density above 1,000 W/m^2 within 40 m in the ionosphere. The onboard instrument that consists of plasma probes and wave receiver can measure effects of interaction between high power microwaves and plasma in ionosphere. The ground system is designed to evaluate the microwave beam characteristics such as the radiation pattern and microwave power. Wireless power transmission efficiency from space to the ground will be evaluated by analyses of the results of space demonstration experiments.

Recently small satellites start playing important roles in earth observation missions. It, however, is true that small satellites have drawbacks of sensor resolutions and down link data rate. As a solution to the latter drawback, we have developed novel communications system for 320 Mbps down link with 16QAM for small satellites with 50 kg class. We developed a new 2 W class GaN-HEMT X-band amplifier with high efficiency and small distortion, digital filter and pre-distortion processing with relatively low clock frequency in FPGAs. This paper describes the transmitter design and evaluation result of the engineering model.

Japan has decided to launch the second sample return mission "Hayabusa-2" to the Near Earth asteroid 1999JU3 in 2014. The predecessor spacecraft "Hayabusa" made a great success when it returned to the Earth in June 2010 with a capsule containing some particles obtained around the S-type asteroid "Itokawa." The authors installed a tiny hopping rover called "MINERVA" into Hayabusa spacecraft. The rover was deployed at the vicinity of the asteroid in 2005, but failed to make a surface exploration since the human operator on the ground made a critical failure in deploying the rover. The second spacecraft also involves a plan to have a tiny rover system which will make a surface exploration over the 1km-sized asteroid. With the past experience in developing a rover, the authors are again working to install some rover packages to Hayabusa-2. The total concept is the same but this time multiple rovers are considered. Many of the aspects of the mother spacecraft come from the heritage of the previous explorer which was build using the technologies more than ten years ago. But the rover system is a completely brand-new one, based on the lessons learned from the previous rover system. Since the target asteroid parameters are different from the previous target, the rover design has to be made from the beginning. We also face to the another technically challenging matters arisen from the point of the distance from the Sun as well as the surface cruel temperature of low-albedo body. This paper describes the system configuration of the rover system currently designed and developed for the launch in 2014.

This report presents a preliminary study of the radar altimeter for an airplane cruising in the Mars' atmosphere. Furthermore it presents the states of BBM (Bread Board Model) development and a plan for an experiment using the Mars-like terrestrial ground.

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.

A high-speed downlink communication system is required to meet different applications for nano/small satellites. Therefore, it is essential to implement a power- and weight-limited transmitter in such satellites. Our recent research has focused on an efficient system with the limited transmitter incorporating a powerful ground station receiver. Generally, an operation at nonlinear region provides a RF power amplifier with high energy efficiency. However, an amplitude-phase modulation, which is an efficient scheme in term of frequency band, requires high linearity. Digital pre-distortion on the transmitter is known as a powerful complementary nonlinearity of power amplifier. We are developing pre-distortion scheme for nano/small satellite transmitter. And we developed a new measurement method to evaluate the transmitter system. We will report the results of evaluation of the new transmitter engineering model. The results indicate that the new PA performances are suitable for multi-level modulation high-speed downlink system with pre-distortion such as 16-QAM system. Therefore, the power amplifier with high efficiency can be implemented.

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 (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. This paper addresses the effects of apertures perforated on the outer surface of satellites on the UWB propagation and transmission for low-(4.2-4.8GHz) and high-band (7.4-7.9GHz) UWB. The larger total area of apertures resulted in lower UWB propagation gains, shorter delay spreads, and (slightly) higher link throughput.

This research proposes an X-band high efficiency onboard SSPA for deep space missions by focusing on GaN HEMT whose remarkable material properties, such as high thermal conductivity, wide band gap, and high breakdown voltage, are suitable for high power and high efficiency applications. To develop a high efficiency onboard SSPA is one of the great issues when we consider some missions toward Mars, Jupiter, and much farther planets because of the requirements of both ultra-long distance communication and low power consumption. In this paper, results of preliminary design and evaluations of some trial productions using COTS device will be shown.

A high-speed downlink communication system is required to meet different applications for nano/small satellites. Therefore, it is essential to implement a power- and weight-limited transmitter in such satellites. Our recent research has focused on an efficient system with the limited transmitter incorporating a powerful ground station receiver. To overcome signal distortion at the cost of some limitations of the transmitter, an SCCC turbo equalization system equipped with nonlinear distortion compensation techniques in the receiver has been developed. However, digital predistortion on the transmitter is known as a powerful complementary nonlinearity of power amplifier. We are developing predistortion scheme for nano satellite transmitter. We evaluate performances of the new GaN-HEMT power amplifier. The results indicate that the new PA performances are suitable for multi-level modulation high-speed downlink system with predistortion such as 16-QAM system.Therefore, the power amplifier with high efficiency can be implemented

In Recent year, small satellites have been developed by universities and companies to investigate Earth environment. High-speed downlink communication system for small satellites is required to realize different kind of applications. We have developing the system which is optimized to reduce a load of transmitter and signal distortion caused by the transmitter. To achieve a low power consumption and high-speed communication, optimum pre-distortion must be selected. This paper shows that the method can be determined by a index related with received symbols mean power and symbol distances.

The more technologies advance, the higher mission achievements are demanded in small satellite missions. In this study, we have been developing an S-band transponder for small satellites of Category-A missions (such as the lunar orbiter, halo orbiter and Lagrange point missions). It has dimensions of 110×110×90 mm^3, weighs about 1kg, consumes less than 10W, and use of COT devices. In this paper, we will discuss the RF property that obtained phase noise of PCM (NRZ-L)-PSK/PM, error vector magnitude of BPSK and QPSK, bit error rate of the PCM (NRZ-L)-PSK/PM, and spectrum of each moderation mode (PCM (NRZ-L)-PSK/PM, PCM (Biφ-L)-PM, BPSK, QPSK) on our new transponder.

A high-speed downlink communication system is required to meet different applications for nano/small satellites. Therefore, it is essential to implement a power- and weight-limited transmitter in such satellites. Our recent research has focused on an efficient system adopting CCSDS 131.0-R signaling formats with the limited transmitter incorporating a powerful ground station receiver. To overcome signal distortion at the cost of some limitations of the transmitter, an SCCC turbo equalization system equipped with nonlinear distortion compensation techniques in the receiver has been developed. We simulate the system using practical distortion models to determine the performances of BER and synchronization.

High reliability S-band communication and X-band communication for fast mission data transmission are both required for many satellite users. But for small satellite users, it is difficult to use both the S-band and the X-band transponder in order to limitation of on-borad power, area, mass and so on. By these current conditions, we start concept study of the multi-band transponder for category-A region.