MITSUBISHIELECTRIC

VOL. 86/JUN. 1999

Satellite Edition

Courtesy of NASDA

●Vol. 86/Jun. 1999 Mitsubishi Electric ADVANCE

A Quarterly Survey of New Products, Systems, and Technology

Satellite Edition

CONTENTS

TECHNICAL REPORTSOVERVIEWMitsubishi Electric’s Place in Space .................................................. 1by Hiroshi Kimura

Data Relay Test Satellites ................................................................... 2by Hiroyuki Ichino, Naoto Shikagawa and Keisuke Ozawa USERS, An Unmanned Space Experiment Recovery System ......... 5by Masao Sato and Tetsuo Yamaguchi

Space Radio Monitoring System ....................................................... 8by Yoshimasa Oh-hashi and Morio Higa

N-STAR Ka-Band Antenna ................................................................ 11by Takao Itanami, Kenji Ueno, Izuru Naito and Yuji Kobayashi

Adaptive Attitude Control of Spacecraft withMovable Antennas ............................................................................ 14by Katsuhiko Yamada and Shoji Yoshikawa

Digital Circuit Multiplication Equipment Based onIntelsat Specifications ..................................................................... 17by Nobuhiro Gencho and Mitsuhiro Takemoto

A Digital Satellite Newsgathering System ....................................... 20by Masamizu Hinata and Tatsuhiro Oba

TECHNICAL HIGHLIGHTSAutomatic Rendezvous and Docking Experiments ........................ 23by Hiroshi Koyama and Makoto Kunugi

A Very Small Aperture Terminal ....................................................... 25by Shuji Nishimura and Seiya Inoue

A Notebook-Size Satellite Terminal .................................................. 27by Katsumi Tsukamoto and Atsushi Manzaki

Our cover shows Engineering Test Satellite-VII(the pair facing each other, below) and a DataRelay Test Satellite (above). ETS-VII is intendedto acquire the basic technologies of rendezvousdocking and space robotics which are essentialto future space activities such as retrieval,resupply and exchange of equipment on orbit.In July and August 1998, it succeeded in theworld's first unmanned rendezvous docking.

Two DRTS satellites, which are to be launchedin 2000 and 2002, will make it possible for aground station to communicate with spacecraft(satellites and rockets) without the help ofother ground stations in most of their flightarea.

Shin Suzuki

Haruki NakamuraToshimasa UjiKeisuke UekiMasakazu OkuyamaYasuo KobayashiMasao HatayaHideki NakajimaMasashi HonjoTakashi NagamineHiroaki KawachiHiroshi KayashimaKouji IshikawaTsuneo TsuganeToshikazu SaitaAkira Inokuma

Sadanori Shimada

Masakazu OkuyamaCorporate Total Productivity Management& Environmental ProgramsMitsubishi Electric Corporation2-2-3 MarunouchiChiyoda-ku, Tokyo 100-8310, JapanFax 03-3218-2465

Yasuhiko KaseGlobal Strategic Planning Dept.Corporate Marketing GroupMitsubishi Electric Corporation2-2-3 MarunouchiChiyoda-ku, Tokyo 100-8310, JapanFax 03-3218-3455

Orders:Four issues: ¥6,000(postage and tax not included)Ohm-sha Co., Ltd.1 Kanda Nishiki-cho 3-chomeChiyoda-ku, Tokyo 101-0054, Japan

Editor-in-Chief

Editorial Inquiries

Mitsubishi Electric Advance is publishedquarterly (in March, June, September, andDecember) by Mitsubishi Electric Corporation.Copyright © 1999 by Mitsubishi ElectricCorporation; all rights reserved.Printed in Japan.

Editorial Advisors

Vol. 86 Feature Articles Editor

Product Inquiries

"Advance" to Become Online MagazineReaders are advised that the September, 1999,edition of Advance will be the last one to beprinted as a traditional magazine. From Decem-ber, Advance will continue to be available, as it isnow, at the Mitsubishi Electric global homepagewebsite (URL http://www.mitsubishielectric.com/ghp_japan/corporate_profile/advance/advance_index.html). It is hoped that the move toonline format will speed publication and enablereaders to print out only those articles of specialinterest to them.

MITSUBISHI ELECTRIC OVERSEAS NETWORK

TECHNICAL REPORTS

In recent years, American and European aerospace companies have beenundergoing a worldwide realignment that is concentrating them into a few,large enterprise groups. This process suggests that only those enterprises withwell-balanced technical, financial and sales strengths will survive to partici-pate in the development of the space industry in the 21st century.

In the Space Systems Division of Mitsubishi Electric, our strategy is basedon possession of powerful key technologies for satellite communication, earthobservation and aerospatial infrastructure, and taking full advantage of ourposition as an integrated electrical and electronic manufacturer. The strategyaims to achieve total vertical integration, enabling the company to offer ourcustomers one-stop shopping from the space segment itself through groundcontrol to the end user. Our efforts are specifically directed at supportingcustomers with the best, fastest and lowest cost services, and at configuringsystems with the flexibility to ensure complete satisfaction.

In 1998, the two ETS-VII satellites (Orihime and Hikoboshi) successfullyachieved the world’s first unmanned docking rendezvous, thus flight testing akey technology for the unmanned H-II transfer vehicles (HTVs) that will supplythe future International Space Station. A key technology for the next generationof communication satellites—the data relay test satellite (DRTS)—has com-pleted the protoflight model stage and they have now entered their finalacceptance tests.

The unmanned space experiment recovery system (USERS) has alreadycompleted customer design review, and represents significant progress towardsthe implementation of a low-cost recoverable system. Integration has alreadybegun in preparation for the launch of the ADEOS-II satellite in 2000. Orders forcommercial satellites include one from OPTUS, the Australian cable andwireless company, for the OPTUS-C1, a new type of communication satellite.

We are committed to working with our customers to conceive, propose andprovide the satellite systems for the 21st century.

*Hiroshi Kimura is General Manager of the Space Systems Division.

OverviewMitsubishi Electric’s Place in Space

by Hiroshi Kimura*

June 1999 · 1

TECHNICAL REPORTS

*Hiroyuki Ichino and Naoto Shikagawa are with the Kamakura Works and Keisuke Ozawa with NASDA.

Data Relay Test Satellites

by Hiroyuki Ichino, Naoto Shikagawa and Keisuke Ozawa*

NASDA plans to launch two data relay test satel-lites, DRTS-W in the year 2000 and DRTS-E in2002. The two medium-sized geostationary sat-ellites feature enhanced interorbit communica-tions support and control capabilities, and willform part of an experimental system to setup andtest future communication satellites.

The DRTS satellite system includes interorbitcommunication equipment (ICE) payload, a sat-ellite engineering bus consisting of eight sub-systems, technical data acquisition equipment,and monitoring camera equipment. All of theequipment is designed from the ground up to pro-vide a measure of redundancy. Table 1 lists themajor parameters and Fig. 1 shows the flight con-figuration of the satellite.

The DRTS has a number of design features thatwill increase the proportion of the satellite’s totalweight that can be devoted to its communica-tions equipment payload. In addition, the satel-lite has acquisition and tracking capabilitiesenhanced to support the high-accuracy require-ments of future interorbital communication sys-

Table 1 Major Specifications of DRTSPhysical dimensions

Satellite body 2.39 × 2.16 × 2.22m (x, y, z)

Interorbital link antenna 3.6m aperture diameter

Feeder link antenna 1.80m aperture diameter

Satellite with antennas 6.61 × 16.36 × 6.19m (x, y, z)and paddles deployed

Satellite mass

Prelaunch About 2,700kg

Dry weight About 1,270kg

Payload (ICE) About 310kg

Power generation capacity Better than 2,115W over mission life

Mission life 7 years

Attitude control Controlled-bias momentum system

Geostationary position

DRTS-W 90°E (tentative)

DRTS-E 170°W (tentative)

Solar paddle

Ka-band forward beacon antenna

Solar paddle

Telemetry, tracking and command S-band antenna 2

Telemetry, tracking and command S-bandantenna 1

Direction of flight Feeder link antenna

Coarse sun sensor head 1

Interorbital link antenna

Earth

Fine sun sensor head 1

Earth sensor assembly

X Y

Z

Fig. 1 DRTS configuration in orbit.

tems. The capacity of the return channel in theKa band interorbit communication equipment hasbeen boosted. The antenna aperture efficiency has

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TECHNICAL REPORTS

been increased to conduct experiments with morechannels and high data-rate transmission. Thetracking receiver features increased bandwidthand reduced noise.

The satellite bus design will incorporate tech-nologies from COMETS and other test satellitesto lower development costs wherever possible.Table 2 lists some of the main performance speci-fications of the satellite bus system.

Interorbit Communication EquipmentThe ICE subsystem is the satellite’s primarypayload. It consists of a Ka- and S-band interorbitantenna, five transponders and a Ka-bandfeederlink antenna.

NASDA will use the satellite to conduct ex-periments with a number of domestic satellites:the Advanced Earth Observing Satellite II(ADEOS-II), the Advanced Land Observing Satel-lite (ALOS), the Japanese Experimental Module(JEM), the Optical Interorbit CommunicationsEngineering Test Satellite (OICETS), the H-II

Table 2 Bus Subsystem SpecificationsTelemetry, tracking and command

S-band USB and Ka bands, data buses with central and remote-interface units

Electric power supply32~51.5V floating bus, two 50Ah NiH

2 batteries, digital sequential

shunt, better than 2,075W over mission life from solar paddles insunlight, better than 1,866W in shadow, better than 3,710W frombatteries in polar orbit

Solar paddle systemRigid ultralightweight panels, 2,115W power generation capacityover mission life, high-performance 100µm Si NRS/BSFphotovoltaic cells

Attitude control systemControlled-bias momentum system using adaptive algorithm withintegrated antenna control. Sensors include integrating gyroscope,earth sensor and coarse and fine sun sensors. Actuators includemomentum and balance wheels, and thrusters. Roll and pitch arewithin ±0.05° and yaw within ±0.15° in normal operating mode,varying within ±0.07° and ±0.20°, respectively during antennamovements or transient attitude control maneuvers. Roll and pitchare within 2° during apogee engine firing.

Structural systemCentral cylinder system using CFRP monocoque shell and strutsweighing 185kg.

Thermal control systemCombined system using passive insulating laminate and an activesystem of heaters and heat pipes in the RF compartment andalong the satellite’s north and south surfaces.

Unified propulsion subsystemTwo-fluid 500N apogee-kick engine combined with 1 and 20N one-fluid gas jet thrusters, adjustable pressure blowdown, up to 973kgof N

2H

4 propellant, up to 640.8kg of mixed oxides of nitrogen 3%-

NO (MON-3), 200mN DC ion engine for stationkeeping.

Integrated hardware subsystemComponents include power distribution unit, power-dividerordnance controller, light-load mode units and heater controlelectronics. Also included are wire harnesses, RF cables,waveguides, separation switches, brackets, fasteners, andpyrotechnical products.

Transfer Vehicle (HTV), H-II Orbiting Plane X(HOPE-X) and H-IIA. NASDA is also planningexperiments with NASA and ESA.

Satellite Experiments InterfaceSatellite developers will be able to conduct ex-periments with their satellites’ ICE subsystemfrom the DRTS earth station that will be devel-oped as part of the project. Fig. 2 shows the feederand interorbit communication links that com-prise the network and its interfaces. Table 3describes the interorbital link. The DRTS earthstation will make some of its data interfacesavailable to satellite developers for systemscompatibility testing. Table 4 lists these inter-face functions.

ICE Functions and PerformanceThe ICE subsystem supports the following func-tions for data communications and acquisitionand tracking: S-band single access (SSA) forwardand return links, Ka-band single access (KSA)forward and return links, and Ka-band forwardbeacon links. Forward tests consist of transmit-ting data from the ground station to the DRTSand on to the target satellite. Return tests in-volve transmitting data from the target satel-lite to the DRTS and on to the ground station.SSA and KSA are coherent systems that linkphase synchronous pilot signals from the groundstation.

The DRTS can communicate with satelliteslocated within ten degrees of the earth’s center,which corresponds to altitudes up to 1,000km.

The system provides S- and Ka-band test sat-

Feeder link

Masuda tracking & communication

station

Ground control system

Tsukuba main

control center

Tsukuba second control center

Dummy satellite station

DRTS-E DRTS-W

Satellite-to-satellite link

Target satellite

Earth observation

center

Fig.2 DRTS experimental space network system.

June 1999 · 3

TECHNICAL REPORTS

ellite program tracking functions. The on-boardtracking receiver uses the KSA return data sig-nal to control the interorbital link antenna foracquiring and tracking the test satellite. Thereis also a scan and search program. The satellitewill forward a Ka-band beacon signal from theground to test a target satellite’s acquisition andtracking capabilities. The interorbital link an-tenna can also be controlled by manual groundcommands to point at angles up to 15 degreesfrom the earth’s center.

The satellite provides functions for tuning thefrequencies of the SSA and KSA links, both for-ward and return. The satellite can also storeten sets of acquisition and tracking programparameters on board, allowing it to conduct testsof multiple satellites.

The DRTS’ ICE subsystem has an enhancedversion of the technologies developed for thatof the COMETS satellites, and is designed toallow experiments with many kinds of satel-lites.

The interorbital link antenna gain and side-lobe performance have been boosted by modi-fying the antenna configuration and stay design.Errors related to thermal expansion of the an-tenna have been reduced.

The Ka-band transponders support a widerbandwidth and higher transmission power toincrease data capacity. The receiver features in-creased dynamic range, while phase noise inthe frequency synthesizer has been reduced.Feeder antennas for both DRTS-W and DRTS-Eare designed to allow changes to the orbitalposition. Pointing control is handled by the at-titude control system.

The slew and pull-in time for satellite acqui-sition have been shortened. Tracking can be

performed by manual pointing commands tosupport communications with satellites in vari-able orbits under 1,000km.

Detailed design of the DRTS systems has beencompleted, and production of protoflight modelDRTS-W is underway toward a launch in 2000. ❑

Table 4 Space Network Service CapabilitiesItem SSA link KSA link

Modulation

Forward UQPSK UQPSK, QPSK, BPSK

ReturnSQPN, SQPSK, SQPN, SQPSK,QPSK, BPSK, UQPSK QPSK, BPSK, UQPSK

Encoding and demodulation

Typically none used, andconvolutional encoding,

Forward Typically none used Viterbi decoding(R = 1/2, K = 7) withplans for JEM support

Convolutional encoding,Viterbi decoding (R=1/2,K=7) with plans for JEMsupport.

Convolutional encod- Reed-Solomon decodingReturn ing, Viterbi decoding (255, 223) with plans

(R = 1/2, K = 7) for ALOS support.Reed-Solomon decoding(255, 223) or none usedwith ADEOS-II support.

Data transfer rate

Forward 100bps~300kbps 100kbps~50Mbps

Return 100bps~6Mbps 100kbps~240Mbps

Transmission quality (BER)

1 × 10−6 or better underForward 1 × 10−6 or better 300kbps, 1 × 10−5 or

better over 300kbps

Return 1 × 10−5 or better 1 × 10−6 or better

Table 3 Communication Link Parameters for User SpacecraftItem SSA link KSA link

Frequency

Forward 2,025~2,110MHz (100kHz steps) 23.175~23.545GHz (1MHz steps)

Return 2,200~2,290MHz (100kHz steps) 25.450~27.500GHz (100kHz steps)

Forward beacon — 23.175~23.545GHz (1MHz steps)

Polarization Right or left Right or left(same for transmitter and receiver) (independent for transmitter and receiver)

Transmit EIRP (1dB steps)

Forward 38.0~46.0dBw 48.0~62.0dBw

Forward beacon — 30.5dBw (wide beam), 38.4dBw (narrow)~48.0dBw

G/T 8dB/K 27dB/K

Relay bandwidth

Forward 20~24MHz 50~60MHz

Return 13.5~16.5MHz 300~360MHz

Forward beacon — 10~12MHz

4 · Mitsubishi Electric ADVANCE

TECHNICAL REPORTS

*Masao Sato and Tetsuo Yamaguchi are with the Kamakura Works.

USERS, An Unmanned SpaceExperiment Recovery System

by Masao Sato and Tetsuo Yamaguchi*

June 1999 · 5

USERS is a reusable spacecraft being developedby Japan’s Ministry of International Trade andIndustry, the Organization for Development ofNew Energy and Industrial Technologies, andthe Institute for Unmanned Space ExperimentFree Flyer (USEF). USERS is intended to supportapplications of the space environment. Thespacecraft will consist of two major components,a reentry module (REM) and a service module(SEM). The REM will contain an electric furnacefor experimental production of superconduct-ing materials and will return to earth after theconclusion these experiments. The SEM willprovide electricity and other resources to theREM and will house its own experimental equip-ment. The SEM will be used to develop a multi-purpose compact satellite bus capable ofapplications in high, medium and low orbits.

The satellite bus will have the following de-sign features to support a wide range of applica-tions and low production costs. The satellite sizeand weight will be reduced by use of a software-intensive integrated control system that willlower reliance on special-purpose hardware.Mass-produced components will qualified inmission equipment and eventually incorporated

Tanegashima Space Center

USER Operation Center

Earth station for routine operation (Japan)

Overseas support earth station

Recovery ship

Launch

Launch vehicle separation

Solar paddle deployment

Engine firing to achieve REM mission orbit

REM/SEM separation

REM experiments

Continuing SEM mission

Engine firing to initiate reentry

Search plane

Unnecessary parts jettisoned

Parachute deployment Radio beacon activation

Engine firing to achieve REM mission orbit

Splashdown

into the satellite bus. Finally, project managementwill be simplified by adopting CALS technologies,reducing paper documentation, introducing 3DCAD systems, and automating test procedures.

USERS will be launched together with anothersatellite by a Japanese-developed H-IIA rocketfrom NASDA’s Tanegashima Space Center inwinter, 2000 and carried to an orbital altitude ofabout 500km. The REM will carry out its six-month mission then separate from SEM andreturn to earth while the SEM will continue anindependent two-and-a-half year mission (Fig.1). Mitsubishi Electric has been awarded theprimary development contract for the spacecraftsystem and is a supporting contractor for theoverall USERS system.

The USERS MissionsUSERS has two missions. The REM will carryunits for low-power experimental manufactureof superconducting materials in the space en-vironment and return these units and the mate-rials they contain to earth at the conclusion ofthe mission. Afterwards, the SEM will remainin orbit to conduct in-flight qualification test-ing of space equipment. SEM’s mission equip-

Fig. 1 USERS flight plan.

TECHNICAL REPORTS

6 · Mitsubishi Electric ADVANCE

ment is being designed to be developed cheaper,faster and better than typical custom-developedhardware. Five equipment designs will be se-lected from those proposed by the manufactur-ers participating in the USERS program.Mitsubishi Electric has proposed an advancedstar sensor system, which it is preparing to de-velop and test alongside the satellite bus sys-tems.

The USERS SpacecraftTable 1 lists basic specifications of the USERSspacecraft and Fig. 2 illustrates the craft. The800kg SEM will be supporting its 100kg inter-nal payload as well as the 700kg REM (whichcarries 150kg of mission equipment.) SEM is

Launch By H-IIA rocket from Tanegashima Space Center in winter, 2000

REM recovery Ocean recovery near Ogasawara Islands six months after launch

Launch weight 1,500kg (SEM: 800kg, REM: 700kg, assuming 500km orbit)

Orbit Circular orbit, 500km altitude, 30.4° elevation

Mission life 6 months for coupled REM/SEM mission, 2.5 years for independent SEM mission

Microgravity environment Less than 10−5G in sun-facing mode

SEM

Payload Five types of equipment designed for high-performance fast and inexpensive development (100kgmax, 200W)

Structural thermal control system Central cylinder and panels with active thermal transport Integrated spacecraft control systemData processing CCSDS compliant packet command/packet telemetryData recorder 1GB semiconductor memoryAttitude control Sun-facing mode (±1°), earth-facing mode, inertial guidance (for REM separation maneuver)System management Power and heater control

Attitude and orbit control equipment Inertial reference unit, sun sensor, earth sensor, reaction wheel, magnetic torquer, GPS receiver

Communication systemCommands 4kbps USB systemTelemetry USB or high-speed S-band system (switchable), 256kbps max

Power system 50Ah nickel hydride battery, 2,450W solar paddles

Thrusters 1N and 23N single-fluid hydrazine engines, 126kg propellant

Environment measurement instruments Radiation counter and dosimeter

REM

Payload Superconducting materials experiment, reentry environment measurement (150kg, 600W total)Attitude control Dual-spin stabilizer with 50Nms momentum wheel and inertial referencePower system NiCd battery (charged prior to separation from SEM)Communication system S-band telemetry and command systemThermal protection Ablation systemRecovery system Parachute, GPS beacon, ARGOS transmitterSolid-fuel rockets Orbit separation (RBM, 1), spin (3), despin (3), tumble (1)Environment measurement instruments Microgravity meter

Earth sensorS-band antenna

REM

Fine sun sensor

Orbit control thruster

Attitude control thruster

SEM

Solar paddles

Fig. 2 An illustration of the USERS spacecraft.

Table 1 Major Specifications of the USERS Spacecraft and Mission

TECHNICAL REPORTS

June 1999 · 7

therefore supporting a total of 800kg of missionequipment, more than half of the spacecraft’sweight. SEM and REM will be mechanically andelectrically coupled at launch. Although USERSis intended for a circular orbit at an altitude ofabout 500km and an elevation of 30° , the choiceof orbits will be affected by the requirements ofits launch partner satellite. USERS will thereforecarry a single-liquid hydrazine thruster that willenable it to boost itself into its mission orbit.

Soon after REM separates from SEM, its or-bital separation motor will ignite to initiate re-entry. SEM will subsequently continue itsin-flight qualification mission. REM’s missionlife is six months; the SEM mission will last atotal of three years.

SEM will be supplying high-quality electricpower and other resources for REM’s supercon-ducting material tests. In addition to support-ing REM and assisting its reentry, SEM will beused to develop a standard bus for light (500~1,000kg) satellites to be used through the earlyyears of the new century. SEM’s control systemwill need to be able to reconfigure itself to adaptto the radically different orbital control dynam-ics, power management and thermal controlcharacteristics before and after REM separation.

The key to reducing the recurring costs forthe compact standard satellite bus is the intro-duction of an integrated spacecraft controller(ISC). The ISC combines the previously sepa-rate functions of data processing and attitudecontrol, and integrates power and thermal man-agement functions as well. Hardware size andweight is reduced by implementing functionsin software and reducing the usual multiplicityof interfaces to a bare minimum. This integra-tion will allow use of the same basic hardwaredesign in subsequent missions. Mission-specificchanges will be made primarily at the softwarelevel. Implementing functions at the softwarelevel has the added benefit of facilitating devel-opment of automatic test procedures.

The superconducting material experimentwill simultaneously require a high-current sup-ply for the furnace and a highly regulated low-power supply for control. To generate maximumpower, the spacecraft will adopt a sun-facing at-

titude that will maintain the solar paddles at90° to incident solar radiation. The paddles willbe fixed relative to the spacecraft to avoid theattitude disturbances associated with paddledrive operations. Attitude control will be imple-mented by a reaction wheel and magnetictorquer to maintain a stable microgravity envi-ronment on the order of 10−5G.

The SEM can also be operated in an earth-facingattitude control mode to support earth-observa-tion, measurement and communication missions.USERS is also designed to operate in earth-facingmode during orbital control maneuvers and dur-ing and following REM separation. In earth-facingmode, the solar paddle drive mechanism operatesto orient the solar paddles toward the sun, ensur-ing a supply of electrical power. Modifications tothe thermal control software to maintain appro-priate heat balance are all that is needed to adaptto these various orientations.

In addition to developing the new technologiesneeded to manage spacecraft separation and cap-sule recovery operations, USERS is providing avital test bed to lower the recurring costs ofspacecraft development. ❑

TECHNICAL REPORTS

Space Radio Monitoring System

by Yoshimasa Oh-hashi and Morio Higa*

*Yoshimasa Oh-hashi and Morio Higa are with the Kamakura Works.

The worldwide growth in satellite-based tele-communications and broadcasting is increas-ing the likelihood of radio interference insatellite-to-earth and satellite-to-satellitecommunications. This report describes a pro-posed space radio monitoring system that willmeasure satellite orbits while monitoring sat-ellite radio emissions.

Satellites are increasingly used to provide so-phisticated radio communication capabilitiesfor business and subscriber services. As satel-lites’ orbits and communication frequenciesget closer, the risk for interference increases.Japan’s Ministry of Posts and Telecommuni-cations (MPT) is developing satellite orbit andradio emissions monitoring facilities that willhelp prevent interference and support effec-tive use of satellite orbits and communicationfrequencies. The MPT is commissioning afixed monitoring station that will monitor theL, S, C, Ku and Ka bands used by geostation-ary satellites.

System ConfigurationFig. 1 illustrates the proposed system while Fig. 2shows a block diagram of the fixed monitoringstation. Two antennas arrays each consisting often elements will measure satellite orbits andmonitor radio emissions. One array will monitorthe L and S bands, the other the C, Ku and Ka

Geostationary satellite

Monitoring antenna for C, Ku and Ka bands

Monitoring antenna for L and S bands

3.2m 2.6m

LEO satellite

Central office

Fixed monitoring

station Monitoring vehicle Monitoring

equipment for LEO satellite

Fig. 1 Configuration of space radio monitoringsystem.

ANTENNA ARRAY FOR L AND S BANDS

Azimuth rotation

Azimuth rotation

Elevationrotation

Elevationrotation

Drive unit

Drive unit

ANTENNA ARRAY FOR C, Ku AND Ka BANDS

Control desk

L, S BAND RECEIVER

Receiver 1

Receiver 2

Receiver 10

ADC

ADC

ADC

Receiver 1

Receiver 2

Receiver 10

ADC

ADC

ADC

DBF Beam combiner Time-frequency spectral analysis

C, Ku, Ka BAND RECEIVER

Signal processor

Outputs

1. DOA 2. Power flux density 3. Polarization 4. Signal copy

Fig. 2 Block diagram of a fixed monitoring station.

KeyDBF Digital beam-forming

8 · Mitsubishi Electric ADVANCE

TECHNICAL REPORTS

bands. Fig. 3 shows the configuration of the an-tenna array. The signals from each of the elementsare individually amplified, frequency convertedand passed through an ADC in preparation for thesignal processor. The signal processor will employan extended version of the ESPRIT algorithm (es-timation of signal parameters via rotational in-variance techniques)[1] to determine direction ofarrival (DOA), power flux density and polariza-tion of incident satellite radio signals, and to copysignals.

Features

HIGH RESOLUTION DIRECTION DETERMINATION.The extended ESPRIT algorithm enables themonitoring station to precisely and instanta-neously determine satellite azimuth and eleva-tion from received radio signals, despite theantennas’ relatively small aperture.

DISTINGUISHING BETWEEN MULTIPLE SATELLITES.When two or more satellites are in the antenna’sfield of view, the extended ESPRIT algorithm eas-ily distinguishes and locates the satellites, whichis not possible using the monopulse or step-trackmethods. Resolution is higher than the multiplesignal classification (MUSIC) algorithm[2] while thecomputing cost is much lower.

WIDE FIELD OF VIEW. By using the extendedESPRIT algorithm with multiple small-apertureantenna elements, the system achieves a widerfield of view than is possible using previous tech-nology with a large-aperture antenna.

COPYING MULTIPLE SIGNALS. An eigenspace pro-jection algorithm[3] makes it possible to extractindividual signals when multiple radio sourcesare within the antenna’s field of view.

SUPPRESSION OF FALSE DOAS. The antenna ele-ments’ aperture must be larger than the satel-lite transmission wavelength in order to receiveweak signals, however the present of gratinglobes can lead to computation of spurious DOAs.An original angle diversity reception system sup-presses these false DOAs.

Technology ElementsFigs. 4 and 5 show numerical simulation resultsfor DOA estimations of the extended ESPRITalgorithm for signals in the L and Ku bands. Fig.4 assumes the following conditions:

Frequency L band (1.525GHz)Antenna element diam. 0.65mAntenna element C/N −15 ~ 0dBFirst signal source 0° azimuth,

0° elevationSecond signal source 7° azimuth,

0° elevationArray manifold error for each elementwithin a 3dB beamwidthAmplitude error 1.6% (0.07dB)Phase error 1.3°

In Fig. 5, the conditions are:

Frequency Ku band (17.7GHz)Antenna element diam. 0.8mFirst signal source 0° azimuth,

0° elevationSecond signal source 0.4° azimuth,

0° elevationArray manifold error as above

Fig. 3 Triangular array of ten antenna elements.

June 1999 · 9

a

TECHNICAL REPORTS

References[1]Y. Oh-hashi, “High-Performance Space Monitoring System with

Small Antennas Using Superresolution Algorithms,” in Proc.International Space Radio Monitoring Workshop sponsored byJapan’s Ministry of Posts and Telecommunications, Tokyo, Japan,Nov. 1998.

[2]R.O. Schmidt, “Multiple Emitter Location and Signal ParameterEstimation,” IEEE Trans. on AP, vol. AP-34, no.3, March 1986.

[3]Y. Oh-hashi, M. Higa, T. Matsui, T. Seo, H. Yanagisawa, and M.Tachiki, “A Method of Forming Null Beams for Arbitrary ArrayAntennas,” in Proc. IEICE Spring Nat. Conv., vol.B, p.B-142, 1996.

-15 -10 -5 00.001

0.01

0.1

1

10

Extended ESPRIT (first signal source)

Extended ESPRIT (second signal source)

Monopulse (first signal source)

Sta

nd

ard

dev

iatio

n (

de

gre

es)

C/N ratio (dB)

Fig. 4 Comparison of extended ESPRIT andmonopulse DOA estimation forf = 1.525GHz.

-15 -10 -5 00.0001

0.001

0.01

0.1

1

Extended ESPRIT (first signal source)

Extended ESPRIT (second signal source)

Monopulse (first signal source)

Sta

nd

ard

dev

iatio

n (

de

gre

es)

C/N ratio (dB)

Fig. 5 Comparison of extended ESPRIT andmonopulse DOA estimation forf = 17.7GHz.

The broken lines in Figs. 4 and 5 show the DOAestimation using the monopulse method withthe first signal source. The model assumes theantenna aperture shown by the broken line inFig. 3. The extended ESPRIT algorithm can per-form multiple simultaneous DOA estimation,resolving signal sources with accuracy superiorto the monopulse method.

The proposed monitoring station will combine theversatility of array antennas with a superior signal-processing algorithm to identify the DOA of sig-nals from satellites. The MPT is considering theuse of these capabilities to minimize the risk ofradio interference disrupting satellite communi-cations. ❑

10 · Mitsubishi Electric ADVANCE

TECHNICAL REPORTS

N-STAR Ka-Band Antenna

by Takao Itanami, Kenji Ueno, Izuru Naito and Yuji Kobayashi*

*Takao Itanami is with NTT Service Integration Laboratories, Kenji Ueno is with Advanced Space Communications ResearchLaboratory, Izuru Naito is with Information Technology R&D Center and Yuji Kobayashi is with Kamakura Works.

N-STAR[1] designates a series of Japanese domes-tic communications satellites of the NTTGroup, Japan’s privatized telephone and tele-graph utility. They are multi-functional, provid-ing S-, C-, Ku- and Ka-band services. Of thevarious antennas installed on them, this articlesummarizes the Ka-band antenna, which wasdeveloped by Mitsubishi Electric to be used forboth multibeams and shaped beams in commonfor uplink (30GHz) and downlink (20GHz) bands.

Antenna ConfigurationThe Ka-band antenna is shown under test in Fig.1. It is an array-fed offset Gregorian type with2.2m-diameter aperture. A subreflector and feedarrays consisting of pyramidal horns are accom-modated in a tower. This tower has a windowthat provides a path for the beams between themain reflector and the subreflector.

The major specifications of this antenna areshown in Table 1. It is multi-functional, gener-ating multibeams and shaped beams simulta-neously. The multibeams cover the whole ofJapan (including the southernmost islands ofOkinawa) with eight beams in the uplink band(30GHz) and three beams in the downlink band(20GHz). The shaped beams cover the Japanesemainland, that is, the four main islands ofHonshu, Kyushu, Shikoku and Hokkaido withone beam each in uplink and downlink bands.Adequate sidelobe isolation between uplinkmultibeams is achieved for frequency reuse be-tween every fourth beam, e.g., between the firstand the fifth, the second and sixth, etc. There isno frequency reuse in downlink multibeams.Table 2 shows the frequency allocation for eachbeam of this antenna and Fig. 2 illustrates themultibeam coverage for uplinks.

In order to generate the variety of beams de-scribed, a curved frequency selective reflector(FSR) is employed as the subreflector to allowspace diplexing for separate feeds between up-link and downlink beams. The subreflector isshown in Fig. 3, and the space-diplexing func-tion it provides is illustrated in Fig.4. Thesubreflector has a double-wall construction con-sisting of the front curved FSR and the rear solid

reflector. The front reflector consists of some16,000 resonant elements photo-etched on thesurface so as to be transparent to 30GHz-banduplink signals and to reflect 20GHz-band down-

Fig. 1 The Ka-Band Antenna Under Test.

June 1999 · 11

Table 1 Major specifications of the Ka-bandantenna

Uplink Downlink

Multibeam Shaped Multibeam Shaped

No. of beams 8 1 3 1

Frequency 30GHz band 20GHz band

Polarization LH circular RH circular

Antenna type 2.2m-diam. offset Gregorian

Table 2 Frequency allocation of Ka-band antennaUplink (30GHz band)

BeamMultibeam

Shaped#1 #2 #3 #4 #5 #6 #7 #8

Freq. f1 f2 f3 f4 f1 f2 f3 f4 27.0~28.2GHz

28.3~30.4GHz

Downlink (20GHz band)

BeamMultibeam

Shaped#1 #2 #3

Freq.f5 f6 f7 17.8~18.4GHz

18.5~20.1GHz

TECHNICAL REPORTS

Fig. 5 Feed Array and BFN for Uplink (30GHzband).

link signals. The quasi-periodic disposition ofelements on the curved surface is made by thenovel method developed.[2] Double-ring resonantelements with reduced polarization dependencyare adopted for circular polarization applicationsin the Ka band. The curved front FSR and solidrear reflector are connected with ribs around thereflectors. The curved surfaces on the FSR andrear reflector are both ellipsoidal. One focus ofeach surface is common to the focus of the pa-raboloidal main reflector and the other foci ofthe front and rear reflectors are displaced fromone another. This configuration allows for sepa-ration between uplink and downlink feed arrays.

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Curved FSR

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for uplink (30GHz)

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Fig. 4 Schematic Showing How the Double-WallSubreflector (FSR and solid) Achieves theSpace Diplexing Function.

Feed Arrays and Beam-Forming NetworksThe feed array and beam-forming network (BFN)for uplink are shown in Fig.5. Those for down-load are similarly configured. The uplink feedarray consists of 26 pyramidal horns and thedownlink feed array of 14 pyramidal horns. Eachhorn is excited via waveguide BFNs. Both of the

12 · Mitsubishi Electric ADVANCE

Fig. 3 The Subreflector Assembly.

TECHNICAL REPORTS

feed arrays for uplink and downlink are used incommon for multibeams and shaped beams. Theuplink feed array generates eight multibeams(two folded-frequency reuse) and one shapedbeam, and the downlink feed array generatesthree multibeams (with no frequency reuse) andone shaped beam.

The block diagram of the BFNs for uplink isshown in Fig. 6. That for downlink is similar.BFNs are divided into two categories; those for

multibeams and those for shaped beams. Theformer distribute signals to multiple horns foreach multibeam, with some horns used in com-mon by adjacent multibeams in order to pro-vide continuous coverage of the whole land areaof Japan. Common-use horns use multi-modeBFNs.[3] The multi-mode BFNs consist of hybridsand phase shifters, and have multiple input/output ports. Amplitude and phase at the out-put ports correspond to the input port selectedand are determined by the parameters of thehybrids and phase shifters. The amplitude andphase values cannot be independently controlledfor each input port. Therefore, unlike conven-tional BFNs, the BFNs for multi-mode multi-beam connections must be designed specificallyfor each multibeam. A novel simultaneous de-sign technique has been developed and appliedto the BFNs for multibeams to achieve the ap-propriate horn-excitation coefficients.

The BFNs for shaped beams distribute signalsto the midpoint of the BFNs for multibeams viadiplexers. These shaped-beam BFNs are designedto achieve the desired amplitude and phase atthe output ports connected to the diplexers. Thedesired amplitude and phase for the appropriatehorn-excitation coefficients for shaped beamsare derived by simulation. The simulation isrigorously performed using equivalent-circuitmodels corresponding to the hardware of theBFNs for multibeams and diplexers.

A number of novel techniques have contributedto the development of these flexible and effi-cient Ka-band antennas, which serve to providereliable and continuous coverage of the entireland area of the Japanese archipelago. ❑

References[1]Nakagawa, K., Minomo, M., Tanaka, M., Itanimi, T. : N-STAR:

Communication satellite for Japanese domestic use, 14th AIAAInternational Communications Satellite Systems Conference, AIAA-94-1078-CP, pp.1129-1134 (1994).

[2]Itanami, T., Ueno, K., Honma, S., Noguchi, T., Makino, S., Ishida,O.: Arrangement methods of the resonators on a curved FSR, 1991Autumn Nat. Conv. Rec. IEICE, B-25 (1991) (in Japanese).

[3]Patenaude, E., Amyotte, E., Ilott, P., Menard, F., Gupta, S., Mok, C.:MSAT L band antenna subsystems, 14th AIAA InternationalCommunications Satellite Systems Conference, AIAA-94-0984-CP,pp.449-567 (1994).

June 1999 · 13

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Fig. 6 Block Diagram of BFN for Uplink (30GHzband).

TECHNICAL REPORTS

Adaptive Attitude Control ofSpacecraft with Movable Antennas

by Katsuhiko Yamada and Shoji Yoshikawa*

*Katsuhiko Yamada and Shoji Yoshikawa are with the Advanced Technology R&D Center.

Studies on adaptive attitude control are under-way to minimize satellite attitude disturbanceassociated with movement of large antenna as-semblies. Parameter estimation accuracy hasbeen improved by supplementing conventionalattitude control laws with a simple online pa-rameter estimation law. This enables a satelliteantenna assembly to be moved rapidly whilemaintaining the satellite in a precise attitude.

Recent observation and data-relay satellites arebeing fitted with large movable antenna assem-blies for interorbit (i.e. satellite-to-satellite) com-munications (Fig. 1). The action of a motordriving the antenna assembly to a new positioncreates a counter-torque that tends to rotate thesatellite body, and the momentum of this rota-tion must be canceled through the operation ofthe satellite’s thrusters and wheels driven by afeed-forward control loop. By using a momen-tum equation to calculate the effect of the an-tenna movement, the wheels can be drivensimultaneously to cancel the unintended mo-mentum. This method reduces attitude fluctua-tions without raising the feedback gain of theattitude-control system. A problem with this ap-proach is that compensation is calculated by anumerical model of the momentum equationso the torque errors resulting from inaccuraciesin the model are not canceled and tend to accu-mulate. The adaptive attitude control systempresented here overcomes these problems offeed-forward control systems. Under this method,model errors are identified and measured by theattitude fluctuations that result and this infor-mation is used to compensate for model errors.

We will now examine the control system de-sign and give examples of numerical simulation.

The following equation expresses the conser-vation of the system’s angular momentum,which include components of the satellite andmomentum. Note that the while the parameterestimation rule is operating the thrusters areproviding no external force so that angular mo-mentum remains constant.

Mθθθθθ..... + mφφφφφ

..... + w = 0 ................................... (Eq. 1)

Movable antenna

Fig. 1 Model of satellite with a large movableantenna.

θθθθθ, φφφφφ and w are vectors representing the satelliteattitude angle, the angle of antenna displace-ment and the wheels’ angular momentum, re-spectively. M and m are the mass matrices for θθθθθand φ φ φ φ φ and mφφφφφ

..... is the angular momentum term

created by the antenna movement, and expressesthe satellite attitude fluctuation at satellite at-titude angle θθθθθ. We can express mφφφφφ

..... from the an-

tenna rotation angle and antenna rotation speed,making it possible to separate constant param-eters:

mφφφφφ..... = Yααααα ........................................................................................................................................................................................................................................... (Eq. 2)

Y is a matrix describing the antenna angle andangular velocity, and is known from the antennarotation command. ααααα is a vector depending onthe satellite and antenna mass, the position ofthe center of mass, and the moment of inertia.ααααα is not always known, but may be treated as aconstant. The basic principle of online param-eter estimation is using the linear relationshipbetween the angular momentum of the attitudedisturbance and ααααα, a vector with unknown pa-rameters. By simple inference, the estimatedvalue for ααααα can be brought to converge on thetrue value.

14 · Mitsubishi Electric ADVANCE

TECHNICAL REPORTS

If ααααα ̂ is the initial estimate for ααααα, we can writethe following attitude control law:

w = −YYYYYααααα ̂ + KP θ θ θ θ θ +++++ KI ξ , ξ ξ , ξ ξ , ξ ξ , ξ ξ , ξ ===== ∫ θθθθθdt ............(Eq. 3)

where w is the angular momentum commandvalue, and KP and KI are the control gain. This isa classical proportional and differential controllaw (proportional and integral with respect tothe wheel momentum) with a feed-forward con-trol law added. Implementing local feedback onthe wheel allows momentum commands to begiven. Deriving w from Eq. 3, then pseudo dif-ferentiation gives us the wheel torque commands.In either case, the wheel achieves an angularmomentum almost exactly as specified. Con-sidering the change of ααααα̂ over time, we add thefollowing parameter estimation law.

ααααα ̂ . = −PY PY PY PY PY Τθθθθθ ........................................... (Eq. 4)

where P is a symmetric positive definite esti-mated gain matrix. This parameter estimationlaw is taken from adaptive control laws forground-based manipulators, but in a simplifiedform because it is based on the conservation ofangular momentum expressed in Eq. 1. Theadaptive attitude control law we are proposinghere is a conventional attitude control law withthe parameter estimation law of Eq. 4. The sta-bility of this control law can be established bythe Lyapunov function, showing that the atti-tude angle converges to zero. By adding a simpleparameter estimation law (Eq. 4) to a conven-tional attitude control law with feed forward(Eq. 3), the attitude control error approaches zeroeven when an estimation error occurs. Analyz-ing the behavior of the approach of the param-eter estimation value ααααα̂ , we can show that ααααα̂approaches the true value of ααααα..

Fig. 2 shows a block diagram of the controlsystem. Except for the point where the param-eter estimation law causes ααααα ̂ to fluctuate, be-havior is similar to conventional attitude controlsystems. The ααααα ̂ used in the parameter estima-tion law need not include all the components ofααααα, and in fact, it is better to choose only the

Fig. 2 Block diagram of adaptive attitude controlsystem.

most influential components. As for the othercomponents, by using an initial estimate, theparameter estimation law (Eq. 4) is simplified.When the parameter estimation law has beenused to estimate the parameters, even return-ing to a conventional attitude control law, theunknown parameters approach the true values,

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Fig. 3 Attitude variation during first, fourth andseventh antenna drive operations. Theinitial values of the estimated parametersare 80% of the true parameter value.

June 1999 · 15

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o o

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^

TECHNICAL REPORTS

and the attitude control precision improvementremains. That is, estimating online parametersat the start of antenna operation results in im-proved attitude control precision when the an-tenna is operated.

We will now describe the simulation of a sat-ellite with a movable antenna as shown in Fig.1 that was conducted to verify the adaptive sat-ellite attitude control law. The antenna wasmoved 20° back and forth and this cycle wasrepeated to determine the cumulative effect onsatellite attitude error. Fig. 3 shows the effect ofantenna movements on satellite attitude fluc-tuations on the 1st, 4th and 7th movement whenthe initial value of the estimated parameter ααααα ̂ is80% of the true value ααααα. As the antenna is movedmore times, the estimate accuracy increases, sothat even fast antenna movements can be ab-sorbed by wheel movements, leading to highattitude precision.

Because the bandwidth of the attitude controlis narrow due to structural flexibility, attitudeerror increases during the antenna motion, dis-turbing the stability required for effective com-munications. This problem is heightened assatellites are fitted with large, movable antennaassemblies that apply torques to the satelliteswhen they are moved. By feeding attitude errorsback into the control equation to improve pa-rameter estimation, it becomes possible to ef-fectively damp these disturbances. ❑

16 · Mitsubishi Electric ADVANCE

TECHNICAL REPORTS

*Nobuhiro Gencho and Mitsuhiro Takemoto are with the Communication Systems Center.

Digital Circuit Multiplication EquipmentBased on Intelsat Specifications

by Nobuhiro Gencho and Mitsuhiro Takemoto*

Mitsubishi Electric has developed Model DX-5000 digital circuit multiplication equipment(DCME) based on the Intelsat IESS-501 Revi-sion 3 specifications. Field tests for the equip-ment were completed and commercial deliveriesbegan in May 1995.

DCME uses three essential techniques: digitalspeech interpolation, ADPCM and fax demodu-lation and transmission technologies. DCMEis generally installed between an internationalswitching center (ISC) exchange and a satelliteearth station transceiver (Fig. 1).

IESS-501 Revision 3 was drafted by Intelsatto ensure compatibility among DCME equip-ment from differing manufacturers, and thecorporation's Model DX-5000 (Fig. 2) is fullycompliant with its provisions. This article in-troduces the DX-5000 DCME and the results ofits field testing.

Product FeaturesThe DX-5000 achieves a gain of five by com-bining digital speech interpolation (DSI) tech-nique with an ITU-T G.726 compliant ADPCMcodec. The statistics for typical telephone con-versations show that speech is present on each

transmission line for only about 40% of the time.DSI operation dynamically connects the activetrunk channels with the available bearer chan-nels to achieve a multiplication factor, known asthe DSI gain, of about 2.5.

ISC ISC

Trunk

DCMEDX-5000

DCMEDX-5000

BearerIDR or

TDMA

IDR or

TDMA

Satellite link

or cable link

Fig. 1 Single destination topology.

Fig. 2 Model DX-5000.

June 1999 · 17

TECHNICAL REPORTS

The number of fax modems accommodatedcan be expanded up to 128 depending on theactual percentage of facsimiles in the traffic.

The DX-5000 has self-diagnostic functions.The customer can execute self-checking of faxmodems and ADPCM codecs, and provides fortransmission tests using bearer loopback. Asingle OMC console supports up to 80 DCMEsystems to collect alarm/event data, manage-ment statistical data and monitoring data.

Fig. 3 Multiple clique topology.

Fig. 4 Multiple destination topology.

Several network operations are supported: apoint-to-point configuration (Fig. 1) a multipleclique configuration (Fig. 3) and a multiple des-tination configuration (Fig. 4).

The DX-5000 supports N:1 redundancy con-figuration; up to seven DCME terminals can bebacked up by one redundant DCME terminaland are automatically switchable.

The G.726 ADPCM codec dynamically matchesthe transmission rate to the line load, with a

18 · Mitsubishi Electric ADVANCE

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C A C B

TECHNICAL REPORTS

maximum rate of 16kbps. The DX-5000 can de-modulate and remodulate modem signals up toV.17/14.4kbps for GIII standard facsimile trans-mission.

Table 1 lists the major specifications, whichare derived from IESS-501 Revision 3, ITU-TG.763 and G.766.

Field Testing ResultsTesting began in March 1993 at the IntelsatTechnical Laboratory in the United States.Drafted by Intelsat, the test program included143 items covering transmission of fax, toneand voice signals and other items to establishinteroperability with other manufacturers’DCME systems. All test items were completedby the March 1996 deadline, then field testingwas conducted pairing the Mitsubishi DCMEwith equipment from the Israeli manufacturerECI. The following paragraphs describe fieldtests conducted in May 1996 over a Canada-to-

Sweden link under Intelsat guidance.The tests were conducted over a 2.048Mbps

IDR network system with two Mitsubishi Elec-tric DX-5000 DCME units installed in Swedenand two DTX-360 units from ECI installed inCanada.

The tests were divided into three phases: con-firming proper equipment operation by eachmanufacturer’s engineers, performance mea-surements over the satellite link, and finallylive traffic tests over the link.

In the initial operational tests, simulated tonesignals, simulated 9.6kbps voice-band data sig-nals or simulated voice signals were sent overthe trunk and statistical data were monitoredat the OMC console. In fax transmission tests,two types of fax simulator and some real faxmachines which supported actual V.17/14.4kbps and V.29/9.6kbps transmission wereused. V.34/28.8kbps modems were also tested,and the the modem signal was transmitted atthe 19.2kbps data rate.

In the next stage of testing, simulated voice,simulated voice-band data and fax signals weretransmitted simultaneously and statistical datawere analyzed to check for problems.

In the final stage of testing, engineers fromIntelsat and Sweden’s Telia Corporation veri-fied that the DCME equipment functioned prop-erly when carrying actual signal traffic. Thesetests found no interoperability problems.

Advanced functionality such as variable-ratecodecs and dynamic speech interpolation im-prove the efficiency of Mitsubishi DX-5000DCME equipment, maximizing utilization ofsatellite communications capacity. ❑

Table 1 Model DX-5000 SpecificationsInterfaces 2.048Mbps CEPT, 1.544Mpbs T1

Operation modesSingle destination mode, multiple cliquemode up to two destinations, multipledestination mode up to four destinations

No. of trunk channels Up to 216 channels per trunk, up to 102.048Mbps trunks or 10 1.544Mbps trunks

No. of bearer channels Up to 31 2.048Mbps channels or 241.544Mbps channels

No. of voice bearer channels2.048Mbps bearer 122 channels max, including 61 overload

channels1.544Mbps bearer 94 channels max, including 47 overload

channels

DSI processing 5/4/3/2 bit mode operation

Channel usage 16/24/32/40kbps DSI, 32/40kbps DNI orconfiguration 64kbps clear channel

Signaling ITU-T Nos. 5, 6, 7, R1, R2

Q.50 functions ITU-T Q.50 Annex A, B

Data transfer Rates up to 9600bps guaranteed through40kbps ADPCM coding

Demodulated fax data Up to 128 sets

Fax demodulation signalType ITU-T T.30 standard protocol,

GIII facsimile signalData rates

V.17 7,200, 9,600, 12,000 and 14,400bpsV.29 7,200 and 9,600bpsV.27 2,400 and 4,800bpsV.21 300bps

ADPCM codec ITU-T G.726

Rack dimensions 2,100 x 650 x 450mm (H x W x D)

Power consumption 300W

DX-5000 panel 445 x 552 x 370mm (H x W x D)

DX-5000 weight 60kg

June 1999 · 19

TECHNICAL REPORTS

*Masamizu Hinata and Tatsuhiro Oba are with the Communication Systems Center.

A Digital SatelliteNewsgathering System

by Masamizu Hinata and Tatsuhiro Oba*

20 · Mitsubishi Electric ADVANCE

MPEG2-based digital video technologies are be-ing incorporated into satellite newsgathering(SNG) systems to lower broadcasters’ sound andvideo signal transmission costs. Mitsubishi Elec-tric has recently developed eight-phase digitalphase-shift keying (PSK) modulation technologiesand video bandwidth compression technologiesthat enable a single satellite transponder to carryfour video channels—double the two-channel ca-pacity of the previously used analog FM modula-tion system—while boosting video image quality.In addition, a demand assignment multiple access(DAMA) system has been developed to use excesstransponder capacity for emergency communica-tions. All data transmissions, including order wiresignals, have been converted to digital form.

Commercial domestic satellite communicationservices began in Japan in 1989 with the launch ofprivate-sector communication satellites. Satellitelinks were soon employed for broadcast networkSNG systems, which benefit from the wide band-width, wide area coverage, minimal transmissiondelay and immunity to ground disturbances thatdistinguish satellite communications from terres-trial networks. The transmission costs of thesefirst-generation SNG systems were high becausethe two-channel-per-transponder capacity avail-able with the analog FM modulation system meantthat a busy broadcast network would need morethan one transponder to serve the needs of bothnewsgathering and relaying program content be-tween stations. The development of eight-phase

∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗

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Main station to all affiliate stations

Affiliate station to main station

*Note: Asterisks (∗) indicate satellite telephone system (DAMA)

Main station to single affiliate station

Fig. 1 The FSAT transponder frequency allocation.

KeyMCPC Multichannel per carrierPTT Press to talkPL Private line

TECHNICAL REPORTS

June 1999 · 21

PSK modulation systems ameliorates this prob-lem by halving the bandwidth requirement forvideo and audio signal transmission.

Mitsubishi Electric’s digital video codec,which is responsible for this increased capacity,uses discrete cosine transform (DCT) movementprediction to achieve high coding efficiency. Twotypes of modulation are supported. QPSK modu-lation with two levels of error correction (con-volutional coding with Viterbi decoding andReed-Solomon coding/decoding) provides ro-bustness and a lower operation rate for use inrain or other adverse conditions. Eight-phasePSK modulation is available to support higheroperation rates permitting high-quality imagesto be carried at half the transmission cost perchannel.

Network ConfigurationMitsubishi Electric is working with Fuji Televi-sion, which serves as the main network hub,

along with Kansai Television and other affili-ated broadcasters to build FSAT, a digital net-work that will eventually link 26 stations. Thenetwork will use multiple flexibly configuredchannels that will reduce transmission costs.Increased rate of operation and reduced cross-channel interference will improve picture qual-ity, while data scrambling will protect thesesignals against unauthorized reception. Theequipment size is being reduced to save spacein mobile satellite trucks.

The channel configuration and picture qual-ity goals are realized by the frequency alloca-tion scheme illustrated in Fig. 1. The systemoperates in a two-channel EX-NORMAL mode,and in a four-channel NORMAL/SNG mode.

Video CodecThe video encoder includes digital audio andvideo coding units that compress the signalbandwidth. The compressed digital signal is then

Scram-bling

Interleav-ing

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Digital serial video(SMPTE259M)*

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Order wire

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Fig. 2 Block diagram of Model VX-3000E video encoder equipment.

KeyPSI Program-specific informationPES Packetized elementary streamTS Transport streamVBL Vertical blanking line* Asterisk indicates optional equipment

TECHNICAL REPORTS

1GHz IF signal

Down converter

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demodulator

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decoderDe-

interleavingQPSK

demodulatorViterbi

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packetized, forming what is called a packetizedelementary stream (PES). The video blankingline signal is separated and multiplexed withthe order wire signal. The PES and order wiresignals are then multiplexed to form a transportstream (TS). The transport stream is thenscrambled for privacy and energy distributionpurposes, and Reed-Solomon coding is applied.After interleaving, convolutional coding is usedfor QPSK modulation and Trellis coding foreight-phase PSK. Finally, digital modulation isperformed in an orthogonal modulator, yielding a140MHz intermediate frequency (IF) signal out-put.

The video decoder performs frequency con-version on the received 1GHz IF signal followedby demodulation by coherent detection. Viterbidecoding is used for QPSK signals and TCMdecoding for eight-phase PSK in a reversal of thecoding process to recover and separate the origi-nal video, audio and order-wire signals.

Fig. 2 shows a block diagram of video encoderModel VX-3000E and Fig. 3 a block diagram of

video decoder Model VX-3000D. The basic fea-tures of this equipment are as follows: MPEG2compliance, four- and eight-phase operatingmodes, various transmission modes, digitalvideo interface functions, order wire support,net queue signals multiplexed with verticalblanking line signals, and signal scramblingsupport.

The digital SNG system described here has beenimplemented, tested, and found to reduce cross-channel interference to levels well below thatof previous analog FM, boosting picture qualityeven while transmitting four video channels. Atthe same time, the ability to transmit four chan-nels per transponder has halved signal transmis-sion costs. The authors would like to thank FujiTelevision and its affiliates for cooperation thathas been instrumental in assembling the FSATnetwork. ❑

KeyPSI Program-specific informationPES Packetized elementary streamTS Transport streamVBL Vertical blanking line* Asterisk indicates optional equipment

Fig. 3 Block diagram of Model VX-3000D video decoder equipment.

22 · Mitsubishi Electric ADVANCE

TECHNICAL HIGHLIGHTS

Automatic Rendezvous and DockingExperiments

by Hiroshi Koyama and Makoto Kunugi*

*Hiroshi Koyama and Makoto Kunugi are with the Kamakura Works.

The world’s first successful ren-dezvous and docking between un-manned spacecraft was achieved onJuly 7, 1998, between two ETS-VIIsatellites. Thrustering problems thatarose during a second experiment amonth later were eventually re-solved and a second docking achievedon August 27.

The two ETS-VII satellites—Ori-hime the target and Hikoboshi thechaser—were launched in Novem-ber 1997 aboard an H-II rocket, andorbited while coupled together at analtitude of 550km.

Working under Japan’s NationalSpace Development Agency(NASDA), Mitsubishi Electric over-saw development of the rendezvousand docking system and the groundoperation system and continues towork with NASDA on preparationsand operations support for ongoing

Relative position

Relative position

Position held

X

Z

Y

Time(s)

Time(s)

Rel

ativ

e at

titud

e (d

eg)

Rel

ativ

e at

titud

e (d

eg)

Position held

Position held Roll

Pitch

Yaw

on-orbit experiments. The naviga-tion, guidance and control systemwas researched, designed and testedby Mitsubishi Electric. The com-pany conducted closed loop tests ofthe assembled hardware and soft-ware and other ground-based test-ing to qualify the systems for flight.

Once the satellites were in orbit,the company also tested the rendez-vous-related functions of the navi-gation, guidance and control systemprior to the first on-orbit docking at-tempt.

The first test was designed toevaluate the on-orbit performanceof the docking and separation sys-tems and the navigation, guidanceand control systems at separationsunder 2m. On July 7 at 7:09am, op-erators using a special control con-sole at the Tsukuba Space Centersent a command to Hikoboshi todecouple and push the two space-

craft apart at a rate of about 2cm/s.After separation, an image sensoraboard chaser Hikoboshi extractedinformation about the relative posi-tion and attitude of the satellites.This information was used by a con-trol system that simultaneouslymanages the relative position andattitude of the satellites—six axesin all—to maintain a constant rela-tive attitude and position. A separa-tion of about 2m was sustained forabout 15 minutes. Then a commandfrom the ground was sent to initiatea final approach using a rendezvouscontrol function in which the chasersatellite squares to the target satel-lite prior to docking. Hikoboshi ap-proached Orihime at about 1cm/s,captured the target’s docking mecha-nism and completed docking at7:33am.

Fig. 1 shows the relative attitudeand position data (six axes) for the

Fig. 1 Docking position and attitude data plotted with respect to time.

June 1999 · 23

TECHNICAL HIGHLIGHTS

experiments. Fig. 2 shows a photoof the docked condition. The upperpart of the docking mechanism be-longs to Orihime, the lower part toHikoboshi.

The second rendezvous and dock-ing experiment was conducted at aseparation of 500m to evaluate thein-flight performance of the naviga-tion, guidance and control functions.The satellites separated on August7 at 2:46am. The satellites werehalted at the distance of 2m as inthe previous test, and a chaser satel-lite pointing system using a laser-based rendezvous radar wasswitched on. After control switch-ing, a command from the groundwas to send Hikoboshi back at aspeed of 10cm/s to a distance of520m. Fig. 3 shows a photograph ofOrihime taken from Hikoboshi af-ter separation. After confirming thatHikoboshi had stopped at 520m,ground control sent a command toapproach Orihime. Ordinarily,Hikoboshi’s control system ensuresthat the satellite faces Orihime, butan attitude control problem aroseduring the final approach forcing thesystem to enter a fail-safe mode de-signed to minimize risk of a colli-sion. Engineers on the grounddetermined that a momentary fail-ure of Hikoboshi’s propulsion sys-tem was responsible. Various thrustlevels were tried in an attempt towork around the irregularity but theattitude control problems continuedand the docking attempt was even-tually aborted.

These problems were eventuallyovercome by developing new dock-ing software that minimized reli-ance on the problem thruster. Alsoincorporated into the program werehalt and resume functions that re-spond to a thruster problem by halt-ing the approach, reestablishingattitude control, and then continu-ing the approach. The next dockingattempt, conducted at 10:43pm onAugust 27, succeeded.

The mission featured extensivesafety functions and utilization of aGPS-based relative navigation sys-tem for trajectory control that is the

first of its kind. The satellites’ ren-dezvous capabilities exceeded ex-pectations, important flight data wasgained and invaluable lessonslearned. A study on the irregulari-ties that occurred is continuing andthe results will be reflected in fu-ture rendezvous and docking sys-tems.

NASDA has contracted with Mitsu-bishi Electric to develop technolo-gies for the H-II transfer vehicle(HTV) that Japan is developing to de-liver resources to the International

Space Station planned for launch in2002. The supply spacecraft will userendezvous and docking technolo-gies based on the experiments des-cribed here. ❑

Fig. 3 A photo of Orihime from Hikoboshi (courtesy of NASDA).

Fig. 2 A photo of the docked condition (courtesy of NASDA).

Docking surface, Orihime

Dockingmechanism

Docking surface, Hikoboshi

Earth

24 · Mitsubishi Electric ADVANCE

TECHNICAL HIGHLIGHTS

A Very Small Aperture Terminal

by Shuji Nishimura and Seiya Inoue*

*Shuji Nishimura and Seiya Inoue are with the Communication Systems Center.

Mitsubishi Electric has de-veloped a 30kg portable VSAT ter-minal that is easy to transport andset up, and supports voice, facsimileand data transmission. Weighingless than 4kg, the system’s indoorunit is compact and easily trans-ported.

The terminal consists of a 75cm off-set parabola antenna, an outdoorunit and an indoor unit. Fig. 1 showsa photo of the system and Fig. 2 ablock diagram. Table 1 lists the gen-eral specifications, Table 2 givesdetails of the indoor unit. The an-tenna, the antenna tripod and thesupport for the outdoor unit sepa-rate to facilitate transport and canbe assembled without tools. Eachpiece weighs under 10kg.

The outdoor unit consists of twofunctional blocks. The high-powerconverter (HPC) receives an inter-mediate frequency (IF) signal fortransmission from the indoor unit,performs frequency conversion,amplifies the signal and delivers itto the antenna. The low-noise blockconverter (LNB) passes signals re-ceived by the antenna from a satel-

lite through a low-noise amplifierand extracts the IF signal.

The indoor unit has a voice inter-face unit, a microprocessor that con-trols the system and modulator anddemodulator circuits. It is fitted withconnectors for a telephone handset,fax machine or synchronous or asyn-

75cm antenna

ODU

OMT

HPC

LNB

Transmit cable (IF signal, reference signals, power and

monitoring-and-control signals)

Receive cable (IF signal)

Mod

ulat

or a

nd

dem

odul

ator

Baseband signal processor (DSP)

Microprocessor

Voice interface

IDU

Terminal equipment (typically a voice

handset, fax or modem)

KeyODU Outdoor unit HPC High-power converter OMT Ortho-mode transducerLNB Low-noise block converter IDU Indoor unit

Fig. 2 A block diagram.

chronous modem. The outdoor unitand indoor unit are connected bytwo coaxial cables, one for transmit-ted signals, the other for receivedsignals. The transmission cable alsocarries power for the outdoor unit,reference signals and monitoringand control signals.

Fig. 1 The complete VSAT terminal.

June 1999 · 25

TECHNICAL HIGHLIGHTS

FeaturesThe weight of the indoor unit hasbeen reduced, bringing the termi-nal’s total weight to under 30kg. Theterminal supports voice, facsimileand data communications. A secondchannel can be easily added to sup-port simultaneous voice/fax orvoice/data communications. Theterminal is easily adapted to bothdemand assignment multiple access(DAMA) and preassignment mul-tiple access (PAMA) line manage-ment protocols. Power for thesystem is supplied to the indoor unit:

either a 12V car battery or an ACadapter plugged into a 100VAC sup-ply may be used, with battery powerpermitting mobile or emergency use.

The Indoor UnitTable 2 lists the major specificationsof the indoor unit. The transmittercircuitry takes a voice-band signalfrom a handset, facsimile or modem,encodes the signal using quadratureshift phase keying (QPSK) modula-tion, and passes it to the outdoorunit. The receiver circuitry convertsthe frequency of the IF signal fromthe outdoor unit, applies coherentdetection and extracts a basebandsignal that is processed to demodu-late the original voice signal. Vol-ume and weight have both beenreduced by a factor of four comparedwith the company’s previous prod-ucts. Weighing just 4kg, the unit iscompact and lightweight, throughuse of direct modulation, a DSPbaseband signal processor and sim-plified construction. A direct digi-tal synthesizer using a phase-lockedloop permits small IF frequencysteps with low phase noise. Voiceencoding by ITU-TG.728-compliant16kbps low-delay code-excited lin-ear prediction (LD-CELP) providesa narrow-bandwidth voice signal foreffective bandwidth utilization. Thesystem can also be switched to32kbps adaptive differential pulse-code modulation (ADPCM) forcompatibility with the company’sprevious terminals.

Baseband Signal ProcessorThe transmitter receives a voice sig-nal from the voice interface, super-imposes control signals received fromthe microprocessor and scramblesthe result in one-frame units. Con-volutional encoding is performed,

followed by unique word multiplex-ing and Nyquist filtering. The signalis then delivered to the modulator.

The receiver takes the basebandsignal from the demodulator and per-forms quasicoherent detection withsoft decisions to recover the encodeddata. Unique word detection is usedto establish a frame-synchronous ref-erence that is used in subsequentViterbi decoding and descrambling todeliver voice and control signals.

Modulator and DemodulatorThe transmitter employs QPSK, adirect modulation method, in the1GHz band. The receiver performs asingle frequency conversion to ex-tract the IF signal. The signal for oneIF channel is selected and passedthrough an AGC to equalize the sig-nal level. Detection is performed bythe demodulator IC to recover thebaseband signal.

Continued advancement in circuitintegration combined with otherpower and weight-saving innova-tions have made this VSAT termi-nal power-efficient and easilytransportable. ❑

Table 1 Main SpecificationsCarrier frequency range

Transmit 14 ~14.5GHz

Receive 12.25 ~12.75GHzIntermediate frequency range

Transmit 977~1,053MHz, 25kHz stepsReceive 950~1,450MHz, 25kHz steps

Antenna 75cm offset parabola

Transmit gainBetter than 38.7dBi at14.25GHz

Receive gainBetter than 37.6dBi at12.50GHz

Polarization Linear, V/H or H/V

Weight Under 17kgOutdoor unit

Transmit satura-1 or 2 watts tion power

Receive noise170K max at 25°C temperature

Weight Under 8kg

Indoor unitModulation

QPSK method

Voice coding16kbps LD-CELP or32kbps ADPCM

Frequency25kHz step size

Input power85~132VAC, 47~63Hz or10~16VDC

Power dissipation 50W

Dimensions 330 x 263 x 86mmWeight Under 4kg

Operating environment

Wind Operates under gusts to 20m/sTemperature, antenna & −30 ~ +45°C outdoor unit

Temperature,0 ~ +40°C indoor unit

Table 2 Indoor Unit SpecificationsModulation method QPSK

Transmission rate 35kbps or 70kbps

Voice coding16kbps LD-CELP or32kbps ADPCM

Forward errorConvolutional coding

correctionR = 1/2 K = 7 with 3-bitsoft-decision Viterbi decoding

Bit error rate 1 x 10−6 at Eb/No = 5.9dBMultiple access

DAMA or PAMAprotocolUser interface

Voice 2- or 4-wire

Fax G3 up to 9,600bps

Synchronous data16kbps or 32kbps,RS232C or RS422

Asynchronous data1,200~14,400bps,28,800bps, RS232C

26 · Mitsubishi Electric ADVANCE

TECHNICAL HIGHLIGHTS

A Notebook-Size Satellite Terminal

by Katsumi Tsukamoto and Atsushi Manzaki

*Katsumi Tsukamoto and Atsushi Manzaki are with the Communication Systems Center.

Mitsubishi Electric has sup-plied terminal equipment for theMSAT mobile satellite communi-cation system since 1995, when thegeostationary satellite based servicewas inaugurated by American Mo-bile Satellite Corporation and TMICommunications. Mitsubishi Elec-tric has previously supplied vehicle-mounted, transportable, marine andfixed-station MSAT terminals andhas now developed OmniQuest, anotebook-size portable MSAT ter-minal. The OmniQuest terminalhas a volume of about three litersand a weight of 2.4kg, approxi-mately one fifth the volume andweight of the corporation’s previouscompact terminal equipment.

As with the corporation’s previ-ous MSAT terminals, OmniQuestsupports voice, data, facsimile anddispatch radio services. The batteryoperating time, a key parameter ofportable equipment, is one hour ofcontinuous transmission or eighthours on standby. This report de-

Data/fax

Antenna

RF UNIT

Power amplifier

Diplexer

Low-noise amplifier

TRANSCEIVER UNIT

CONVERTER BOARD

Modulator

Frequency synthesizer

Down converter

DAC

TCXO

ADC

DIGITAL BOARD

LSI

DSP

CPU

PCM codec Voice

Main unit

Handset

Antenna

Cradle

Fig. 1 The OmniQuest satellite terminal.

Fig. 2 A block diagram of the OmniQuest terminal.

KeyTCXO Temperature Compensated Crystal Osillator

scribes the size reductions achievedthrough technical advances includ-ing a thin antenna, compact RF anddigital signal processing circuitryand reduced power consumption.Compact dimensions and light

weight make the product suitablefor personal as well as business use.

Fig. 1 shows an illustration of theterminal and Fig. 2 a block diagram.When the terminal is used, a lidcontaining the antenna is opened

June 1999 · 27

TECHNICAL HIGHLIGHTS

and faced toward the satellite. Thebattery is an internally mountednickel metal hydride type. The ter-minal unit contains a transceiverunit and an RF unit. The transceiverunit includes a converter board anda digital circuitry board. The trans-ceiver unit is removable, and anoptional mobile transceiver unit canbe used for vehicle applications withan optional vehicle-mounted an-tenna. Table 1 lists the major specifi-cations of the OmniQuest terminal.

When the terminal is used totransmit voice, the signal from thehandset is digitized by a PCM codecand coded as a 6.4kbps audio signalby a DSP using an improved multi-band excitation algorithm. The sig-nal is then converted to the frameformat required for the satellite link,a digital filter performs waveformcorrection, and circuitry on the con-verter board performs direct QPSKmodulation. Finally, the QPSK sig-nal is applied to a power amplifierand the amplified signal passedthrough the diplexer to the antennafor transmission to the satellite. Aremovable connector linking the

Table 1 Major SpecificationsTransmit frequency 1,626.5~1,660.5MHz

Receive frequency 1,525.0~1,559.0MHzPolarization Right-hand circular

EIRP 13dBwG/T −14.6dB/KChannel separation 6kHz

Frequency step size 500HzModulation rate 3.375 kilobaud

Modulation QPSK

Error correctionConvolution coding withK=7 and R 1/2 or R 3/4;Viterbi decoding

Voice codecImproved multibandexcitation, 6.4kbps

Data portAsynchronous,2,400 or 4,800bps

Standby time 8 hours

Table 2 Comparison of Terminal EquipmentParameters OmniQuest ST150A

Weight 2.4kg 13.0kgDimensions 285 x 210 x 50mm (main unit) 356 x 356 x 108mm

Volume 3,000cc (main unit) 13,680ccG/T −14.6dB/K −12dB/KEIRP 13dBw 13dBw

Standby time 8 hours 8hoursBattery 3,100mAh nickel metal hydride 12,000mAh lead acid

diplexer to the antenna allows anexternal antenna to be used.

Received signals are amplified ina low-noise amplifier and convertedto an IF signal in two steps by cir-cuitry on the converter board, thendigitized by an ADC. The digital IFsignal is converted to a basebandsignal, and filtering is performed.The DSP has functions for demodu-lating and deframing this digital sig-nal and for decoding the voice signal.Multisymbol delayed detection andmaximum likelihood sequence es-timation techniques are used indemodulation for optimum perfor-mance under Rice fading.

When the terminal is in standbymode, it monitors a control signalfrom the satellite. This signal isconvolutional coded with a con-straint length of 7. The signal is de-modulated by soft Viterbi decoding.

The frequency synthesizer achievesa combination of high-speed perfor-mance and extremely small 500Hzstep size through using direct digi-tal synthesis techniques with twophase-locked loops.

Table 2 compares the perfor-mance of the OmniQuest termi-nal with the corporation’s ST150Aterminal equipment. OmniQuestoffers comparable performancewith 22% of the volume and 18%of the weight in a triumph of min-iaturization.

The OmniQuest terminal equip-ment represents a dramatic reduc-tion in the size and weight ofsatellite terminals, achieving a five-fold improvement over the cor-poration’s previous product. Omni-Quest marks a significant steptoward a future generation of hand-held satellite terminals. ❑

28 · Mitsubishi Electric ADVANCE

Country Address TelephoneU.S.A. Mitsubishi Electric America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500

Mitsubishi Electric America, Inc. Sunnyvale Office 1050 East Arques Avenue, Sunnyvale, California 94086 408-731-3973Mitsubishi Electronics America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500Mitsubishi Consumer Electronics America, Inc. 9351, Jeronimo Road, Irvine, California 92618 949-465-6000Mitsubishi Semiconductor America, Inc. Three Diamond Lane, Durham, North Carolina 27704 919-479-3333Mitsubishi Electric Power Products Inc. 512 Keystone Drive, Warrendale, Pennsylvania 15086 724-772-2555Mitsubishi Electric Automotive America, Inc. 4773 Bethany Road, Mason, Ohio 45040 513-398-2220Astronet Corporation 3805 Crestwood Parkway Suite 400 Duluth, Georgia 30096 770-638-2000Powerex, Inc. Hills Street, Youngwood, Pennsylvania 15697 724-925-7272Mitsubishi Electric Inf ormation Technology Center America , Inc. 201 Broadway, Cambridge, Massachusetts 02139 617-621-7500

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U.K. Mitsubishi Electric U.K. Ltd. Livingston Factory Houston Industrial Estate, Livingston, West Lothian, EH54 5DJ, Scotland 1506-437444Apricot Computers Ltd. 3500 Parkside, Birmingham Business Park, Birmingham, B37 7YS, England 121-717-7171Mitsubishi Electric Europe B.V. Corporate Office Centre Point (18th Floor), 103 New Oxford Street, London, WC1A 1EB 171-379-7160

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Pudong New Area, ShanghaiMitsubishi Electric (China) Co., Ltd. Guangzhou Office Room No. 1221-4, Garden Tower, Garden Hotel, 368, Huanshi Dong Lu, 20-8385-7797