Satoru Ozawa

ALOS-Next/TanDEM-L: A highly innovative SAR mission for global observation of dynamic processes on the earth's surface

ALOS-Next/Tandem-L is a proposal for a highly innovative L-band SAR satellite mission for the global observation of dynamic processes on the Earths surface with hitherto unparalleled quality and resolution. It is based on a collaboration between DLR and JAXA which started with a pre-phase A study in 2013 and is currently undergoing a phase A study. Thanks to the novel imaging techniques and the vast recording capacity with up to 8 Tbytes/day, it will provide vital information for solving pressing scientific questions in the biosphere, geosphere, cryosphere, and hydrosphere. By this, the new L-band SAR mission will make an essential contribution for a better understanding of the Earth system and its dynamics. ALOS-Next/Tandem-L will, moreover, open new opportunities for risk analysis, disaster management and environmental monitoring by employing especially designed acquisition modes and techniques in combination with a reconfigurable tandem satellite configuration and an L-band SAR instrument with advanced digital beamforming techniques.

Concept Design of 15m class Light Weight Deployable Antenna Reflector for L-band SAR Application

In recent years, Japan Aerospace Exploration Agency (JAXA) has been researched and developed next generation SAR satellites. For the next generation SAR program, combination of a digital beam forming technique and a large reflector is required to satisfy the performance requests, wide swath and high resolution. For this purpose, 15 meter class L-band large deployable reflector concept design study was conducted. As a result, lighter reflector design concept is established. Deployment analysis and cable network equilibrium analysis by using flexible multi-body dynamics simulation software are conducted to confirm the design feasibility. In addition, assurance method of surface accuracy is studied. The error factors of the surface accuracy measurement due to gravity are identified and guidelines for accuracy assurance in manufacturing phase was obtained.

Tri-Fold Deployable Reflector for Communication Satellites

JAXA, Japan Aerospace Exploration Agency, is now developing tri-fold deployable reflectors. The reflector can be made to be up to 28m in diameter. The weight density is less than half its predecessor, the large deployable reflector mounted on the Engineering Test Satellite VIII. This concept can be applied to realize an over 50m reflector by constructing modular reflector in which the tri-fold reflector is one of the segmented modules. The trifold reflector is made from the tri-fold deployable truss and the reflector surface. The trifold deployable truss is composed of three four-sided links with joints and can be stowed as a collapsible umbrella. As a stand-alone, the reflector can take on an octagonal shape. For the modular reflector, the segmented module is hexagonal. The feasibility and design of tri-fold deployable reflectors have been confirmed and improved through structural analyses. The analyses are performed with JAXA’s FEM analyzer “Origami/ETS.” The prototype of trifold reflector has been developed and is now undergoing testing. From the result of tri-fold truss deployment test it is confirmed that JAXA’s FEM Analyzer can estimate the mechanical behavior of hardware within 10% error. Afterwards the reflector will be tested and evaluated in the deployment, hold and release, vibration, and surface accuracy measurement tests.

Lightweight Design of 30m Class Large Deployable Reflector for Communication Satellites

JAXA, Japan Aerospace Exploration Agency, is now developing 30m class lightweight large deployable reflectors. The reflectors are made from seven tri-fold deployable truss modules. The tri-fold deployable truss is composed of three four-sided links with joints and can be stowed as collapsible umbrella. Each segmented module has six tri-foldable ribs so that it shapes hexagonal reflector. The seven modules form a large deployable reflector whose size is 30m in aperture. Since the ribs of tri-fold deployable truss is relatively longer than that of single-fold deployable truss, which was used for the Engineering Test Satellite VIII and successfully deployed in orbit in 2006, the weight is reduced from the previous design. The feasibility and design of tri-fold deployable truss have been being confirmed and improved through structural analyses. The analyses are performed with JAXA FEM analyzer “Origami/ETS.” After this, it is planned to verify and modify the design of reflector with the experiments of prototype models.

Spaceborne synthetic aperture radar signal processing using FPGAs

Synthetic Aperture Radar (SAR) imagery requires image reproduction through successive signal processing of received data before browsing images and extracting information. The received signal data records of the ALOS-2/PALSAR-2 are stored in the onboard mission data storage and transmitted to the ground. In order to compensate the storage usage and the capacity of transmission data through the mission date communication networks, the operation duty of the PALSAR-2 is limited. This balance strongly relies on the network availability. The observation operations of the present spaceborne SAR systems are rigorously planned by simulating the mission data balance, given conflicting user demands. This problem should be solved such that we do not have to compromise the operations and the potential of the next-generation spaceborne SAR systems. One of the solutions is to compress the SAR data through onboard image reproduction and information extraction from the reproduced images. This is also beneficial for fast delivery of information products and event-driven observations by constellation. The Emergence Studio (Sōhatsu kōbō in Japanese) with Japan Aerospace Exploration Agency is developing evaluation models of FPGA-based signal processing system for onboard SAR image reproduction. The model, namely, “Fast L1 Processor (FLIP)” developed in 2016 can reproduce a 10m-resolution single look complex image (Level 1.1) from ALOS/PALSAR raw signal data (Level 1.0). The processing speed of the FLIP at 200 MHz results in twice faster than CPU-based computing at 3.7 GHz. The image processed by the FLIP is no way inferior to the image processed with 32-bit computing in MATLAB.

Experimental verification of a control law for the position and attitude of two objects using multiple coils

This article presents a method for relative position and attitude control for reconfigurable space structures using magnetic force with a multi-dipole system. This technology can be applied to the docking phases of space structures that can restructure themselves by assembling basic structural units. The focus of this research is on current control of dipoles, which produces strong nonlinear magnetic forces, and on the development of a method to control a strong nonlinear electromagnetic system. In a previous study, the feasibility of using this method to perform relative position and attitude control was investigated by conducting a series of three-dimensional simulations of position and attitude control. In this study, experimental verification of the control method is conducted to determine whether magnetic forces can be used to correct position and attitude simultaneously. The good agreement obtained between the simulation results and the experimental results confirms the effectiveness of our proposed method.

Development of corotational formulated FEM for application to 30m class large deployable reflector

JAXA, Japan Aerospace Exploration Agency, is now developing a corotational formulated finite element analysis method and its software Origami/ETS for the development of 30m class large deployable reflectors. For the reason that the deployable reflector is composed of beams, cables and mesh, this analysis method is generalized for finite elements with multiple nodes, which are commonly used in linear finite element analyses. The large displacement and rotation are taken into account by the corotational formulation. The tangent stiffness matrix for finite elements with multiple nodes is obtained as follows; the geometric stiffness matrix of two node elements is derived by taking variation of the elements corotational matrix from the virtual work of finite elements with large displacement; similarly the geometric stiffness matrix for three node elements is derived; as the extension of two and three node element theories, the geometric stiffness matrix for multiple node elements is derived; with the geometric stiffness matrix for multiple node elements, the tangent stiffness matrix is obtained. The analysis method is applied for the deployment analysis and static structural analysis of the 30m class large deployable reflector. In the deployment analysis, it is confirmed that this method stably analyzes the deployment motion from the deployment configuration to the stowed configuration of the reflector. In the static analysis, it is confirmed that the mesh structure is analyzed successfully. The 30m class large deployable reflector is now still being developed and is about to undergo several tests with its prototypes. This analysis method will be used in the tests and verifications of the reflector.