Koichi Shiratama

Acquisition, tracking, and pointing systems of OICETS for free space laser communications

Optical Inter-orbit Communications Engineering Test Satellite (OICETS) is under development by NASDA to verify the laser communications technology in space. The in-orbit experiment will be done by establishing inter-orbit communication between the OICETS and European geostationary satellite ARTEMIS in cooperation with ESA. These satellites will be launched in to the orbit in 2000. Laser communications system in space is a promising technology for future space activities, but it has many research matters. Acquisition tracking and pointing system of a laser terminal performs a prominent role to keep the laser communication. This paper describes the ATP system strategy of the laser terminal.

Performance evaluation of laser communication equipment onboard the ETS-VI satellite

Communications Research Laboratory (CRL) developed laser communication equipment (LCE) onboard the engineering test satellite VI(ETS-VI) and a ground system for establishment of basic technologies in optical intersatellite communications. The experiments using a ground-to-space laser link started on December 1994. In the paper, preliminary evaluation for the performance of LCE is presented based on a part of experimental data. Included in the paper are a brief description of operation and data acquisition system, acquisition, tracking and pointing subsystem performance, and communication subsystem performance.

The new tracking control system for Free-Space Optical Communications

The new tracking control system has been developed for Free-Space Optical Communications. It consists of the agile two-axis gimbals, the high performance fine-pointing-mechanism, the optical coarse acquisition sensor, and the optical fine tracking sensor. In the conventional tracking control systems, the two-axis gimbals is combined with the narrow range actuator for the fine pointing control, and it have the role of the coarse pointing control based on the GPS position and the body attitude. The each motion of the tracking mechanisms, therefore, is mutually disturbed by the individual control algorithms, and the obtained tracking accuracy is restricted by each motion. To improve the control performance of this two-stage type, the synchronized tracking-control system is proposed. The features of the system are the cooperative/predictive control using the each control/detective signals, and the improvement of the performance for disturbances, with the hollow-structured and rapid two-axis mirror gimbals. This control scheme is applied for the developed tracking control system, and makes it possible to achieve Free-Space Optical Communications. The paper shows the system configuration, the control algorithms and strategy for Free-Space Optical Communications, and the effect of the proposed control system by the several test results.1

Research and development of 40Gbps optical free space communication from satellite/airplane

This paper explains a plan of research and development of high speed optical communication technology for observed data transmission from satellites/airplanes. The amounts of data acquired on observation satellites or airplanes have become larger with the rapid improvements of resolutions of sensors. In order to transmit the vast amounts of data, a communication system that combines free space optical communication system and terrestrial optical networks is proposed. Particular communication protocol is planned to be developed to realize efficient and stable link quality under the special characteristics of free space optical link such as interruption by rain or cloud. Also digital coherent detection scheme is proposed to be implemented to the system to overcome the degradation by atmospheric scintillation. The plan includes the development of mobile onboard laser communication terminal and the demonstration experiments of the total system.

Point-ahead mechanism for ETS-VI optical ISL experiment

An offset feedback-type point-ahead method is described and its application to the Engineering Test Satellite VI (ETS-VI) laser communication equipment (LCE) is examined. The role in the method of a high-resolution mirror-deflection mechanism driven by a multilayered piezoelectric actuator is pointed out. The pointing resolution using the method is estimated to be less than 1 microrad at the output of the transmitting optics, which is sufficient of the LCE experiment.

Fine pointing mechanism using multi-layered piezo-electric actuator for optical ISL system

A new type of the fine pointing mechanism (FPM) was examined as part of the optical ISL studies conducted by NASDA. Compact piezo-electric mirror deflecting mechanism (MDM) , having a very high resolution (less than 3 irad) was fabricated, and the performance of the MDM was evaluated aiming for application in the ISL optical FPM. The fundamental performance of the fine pointing assembly (FPA) in optical ISL with the multi-layered piezo—electric MDM was confirmed sufficient for optical ISL having pointing error by disturbance (± 0.75 irad) and pointing angle (± 720 Mrad). It was confirmed that the examined FPM is suitable for the fine pointing of optical ISL, by combining appropriately designed optics and coarse pointing assembly (CPA) , through a preliminary system design.

Pre-launch instrument characterization results and in-orbit verification plan of GCOM-C/SGLI

The Global Change Observation Mission (GCOM) aims to establish and demonstrate a global, long-term satelliteobserving system to measure essential geophysical parameters to facilitate understanding the global water circulation and climate change, and eventually contribute to improving future climate projection through a collaborative framework with climate model institutions. GCOM consists of two polar orbiting satellite observing systems, GCOM-W (Water) and GCOM-C (Climate). The first satellite, GCOM-W with Advance Microwave Radiometer -2 (AMSR-2), was already launched in 2012 and has been observing continuously. The follower satellite, GCOM-C with Second Generation Global Imager (SGLI), will be launched in Japanese fiscal year 2017. SGLI enables a new generation of operational moderate resolution-imaging capabilities following the legacy of the GLI on ADEOS-II (Advanced Earth Observing Satellite-II) satellite. The SGLI empowers surface and atmospheric measurements related to the carbon cycle and radiation budget, with two radiometers of Visible and Near Infrared Radiometer (VNR) and Infrared Scanning Radiometer (IRS) which perform a wide-band (380nm-12μm) optical observation not only with as wide as 1150-1400km FOV (field of view) but also with as high as 250-500m resolution. Also, polarization and along-track slant view observation are quite characteristic of SGLI, providing the sensor data records for more than 28 standard products and 23 research products including clouds, aerosols, ocean color, vegetation, snow and ice, and other applications. Sensor instrument proto-flight tests including optical characterization tests such as radiometric and geometric were completed, and satellite system proto-flight tests have finished including thermal vacuum, vibration and acoustic test. In this paper, the pre-launch phase instrument characterization of SGLI flight model and status of GCOM-C satellite system flight model along with the overview of them will be described. Especially we focus on the pre-launch geometric and radiometric performance test results, in-orbit calibration activities and methodologies: VNRs on-board calibrator, IRSs on-board calibrator and calibration maneuver, and in-orbit verification plan during a commissioning phase lasting approximately 3 months.

Design and breadboarding activities of the second-generation Global imager (SGLI) on GCOM-C

The Global Change Observation Mission (GCOM) is the next generation earth observation project of Japan Aerospace Exploration Agency (JAXA). GCOM concept will take over the Advanced Earth Observing Satellite-II (ADEOS-II) and develop into long-term monitoring of global climate change. The GCOM observing system consists of two series of medium size satellites: GCOM-W (Water) and GCOM-C (Climate). The Second-generation Global Imager (SGLI) on GCOM-C is a multi-band imaging radiometer with 19 spectral bands in the wavelength range of near-UV to thermal infrared. SGLI will provide high-accuracy measurements of Ocean, Atmosphere, Land and Cryosphere. These data will be utilized for studies to understand the global climate change, especially human activity influence on earth environments. SGLI is a suite of two radiometers called Visible and Near Infrared Radiometer (VNR) and Infrared Scanner (IRS). VNR is a pushbroom-type radiometer with 13 spectral bands in 380nm to 865nm range. While having quite wide swath (1150km), instantaneous field of view (IFOV) of most bands is set to 250m comparing to GLI’s 1km requirement. Unique observation function of the VNR is along-track ±45deg tilting and polarization observation for 670nm and 865nm bands mainly to improve aerosol retrieval accuracy. IRS is a wiskbroom-type infrared radiometer that has 6 bands in 1μm to 12μm range. Swath and IFOV are 1400km and 250m to 1km, respectively. This paper describes design and breadboarding activities of the SGLI instrument.

Proto Flight Model (PFM) development status of visible and near-infrared radiometer (VNR) on the Second-generation Global Imager (SGLI)

The Second-generation Global Imager (SGLI) is a mission instrument on the Global Change Observation Mission-Climate (GCOM-C) satellite. The SGLI includes two radiometers, the Visible and Near Infrared Radiometer (VNR) and Infrared Scanning Radiometer (IRS). The VNR is a multi-band optical imaging radiometer observing at wavelength range from 380 nm to 868.5 nm, including non-polarization and polarization observation. The test of the instruments consisting of VNR-SRU (Scanning Radiometer Unit) PFM (Proto-Flight model) has been finished, and the VNR-SRU PFM is under the phase of assembly and test. This paper describes the test result of the VNR-SRU PFM.

Development and pre-launch test status of Second Generation Global Imager (SGLI)

Global Change Observation Mission (GCOM) consists of two series of satellites, GCOM-W (Water) and GCOM-C (Climate) for long-term monitoring of earth environment. Second-generation Global Imager (SGLI), the onboard mission instrument of GCOM-C, is the wide FOV multi-spectral optical radiometer in the wavelength range of near-UV to thermal infrared. SGLI consists of two sensor units, Visible and Near Infrared Radiometer (SGLI-VNR) and Infrared Scanning Radiometer (SGLI-IRS). SGLI will provide high accuracy measurements of Ocean, Atmosphere, Land and Cryosphere. Manufacturing and sensor system integration of SGLI flight models were completed. The sensor system proto-flight tests (PFTs) are on-going including optical characterization tests such as radiometric tests using an integrating sphere and geometric and MTF tests using a collimator. This paper describes development and pre-launch test status of SGLI flight model. Especially we focus on the pre-launch radiometric performances such as the spectral response characteristics and signal to noise ratio.