Engineering Test Satellite VIII Research Articles

Numerical investigations to suppress thermal deformation of the large deployable reflector during earth eclipse in space

ABSTRACTIn space, structures encounter various severe environments, including severe thermal conditions. The signal level of the radio wave from the Large Deployable Reflector (LDR) mounted on the Engineering Test Satellite-VIII (ETS-VIII) was observed to change during an Earth eclipse. This phenomenon was assumed to be caused by the thermal deformation of the LDR. Therefore, in this study, a means to suppress the thermal deformation is proposed and demonstrated by focusing on the internal force generated at the springs used to deploy the antenna. According to the numerical results obtained from finite element analyses, the thermal deformations at all apices that support the reflectors were suppressed at a high correction rate by adjusting the coefficients of thermal expansion in the structural members and by controlling spring forces differently in four areas depending on the distances from the constraint point.

Time-varying modal parameters identification of large flexible spacecraft using a recursive algorithm

In existing identification methods for on-orbit spacecraft, such as eigensystem realization algorithm (ERA) and subspace method identification (SMI), singular value decomposition (SVD) is used frequently to estimate the modal parameters. However, these identification methods are often used to process the linear time-invariant system, and there is a lower computation efficiency using the SVD when the system order of spacecraft is high. In this study, to improve the computational efficiency in identifying time-varying modal parameters of large spacecraft, a faster recursive algorithm called fast approximated power iteration (FAPI) is employed. This approach avoids the SVD and can be provided as an alternative spacecraft identification method, and the latest modal parameters obtained can be applied for updating the controller parameters timely (e.g. the self-adaptive control problem). In numerical simulations, two large flexible spacecraft models, the Engineering Test Satellite-VIII (ETS-VIII) and Soil Moisture Active/Passive (SMAP) satellite, are established. The identification results show that this recursive algorithm can obtain the time-varying modal parameters, and the computation time is reduced significantly.

Robust Two-Degrees-of-Freedom Attitude Controller Design and Flight Test Result for Engineering Test Satellite-VIII Spacecraft

This paper reports flight test results of robust attitude control for the Engineering Test Satellite VIII (ETS-VIII) spacecraft. The main mission of ETS-VIII is to support next-generation mobile digital communications, and for this purpose it is equipped with two large deployable antenna reflectors and a pair of large solar panels that rotate around the pitch axis. We have proposed and demonstrated several control methods for this spacecraft based on advanced control theories for linear parameter varying multi-input multi-output systems, and in this paper we focus on a two-degrees-of-freedom controller. We describe the controller design methods and present the results of on-orbit flight tests. The controller's superiority is demonstrated by comparing its performance with other controllers.

Synthesis of a linearly interpolated gain scheduling controller for large flexible spacecraft ETS-VIII

This paper illustrates a design procedure for a linearly interpolated gain scheduling controller for Engineering Test Satellite VIII (ETS-VIII) using its linear parameter-varying (LPV) model. The LPV model here consists of piecewise-linear functions of the paddle rotation angle and a norm-bounded perturbation. The main purpose of this research is to derive a simple structured scheduling law that can be easily implemented in a satellite onboard computer. The derived gain has only two grid points and is scheduled simply by linear interpolation, which is desirable from the standpoint of implementability. Moreover, since the synthesis condition is based on parameter-dependent Lyapunov functions, it gives less conservative results than existing methods. Simulation results are presented to show the effectiveness of the proposed synthesis.

Design and Flight Test Results of Robust Attitude Controller for the ETS-VIII Spacecraft

AbstractThis paper reports the flight test results of robust attitude controller for Engineering Test Satellite VIII (ETS-VIII) spacecraft. The main mission of ETS-VIII is to support next-generation mobile digital communications, and for this purpose it is equipped with two large deployable antenna reflectors and a pair of large solar paddles that rotate around the pitch axis. For the spacecraft, the authors have proposed and demonstrated several control methods based on the advanced control theories for the linear parameter varying multi-input multi-output system. The aim is to develop a baseline for future controller design technology for this class of satellite instead of existing classical PID control laws. This paper describes the on-orbit experiment results and compares these controllers performance.

Suppression of Thermal Deformation of the Large Deployable Reflector

Space structures encounter various special environments in space. One of these environments is severe thermal condition. Difference of temperature of space structures during day-time and night-time is about 200 kelvin. These severe thermal conditions cause thermal deformation of the structures. In fact, we observed the signal level of radio wave from the LDR (Large Deployable Reflector) of the ETS-VIII (Engineering Test Satellite -VIII) changing during the Earth eclipse. This phenomenon may be caused by thermal deformation of the LDR. This thermal deformation is a key issue to maintain the accuracy of communication beams reflected by the space antenna. Analysis of thermal deformation of the LDR is carried out, and a new suppression scheme for thermal deformation is proposed in this paper.

Field Measurement on Simple Vehicle-Mounted Antenna System Using a Geostationary Satellite

This paper presents a field measurement of a simple antenna system mounted on a vehicle by utilizing a geostationary test satellite called Engineering Test Satellite VIII (ETS-VIII). Our developed antenna system is compact, lightweight, and promising for low-cost production. The antenna system is constructed by a 16-cm patch array antenna, which has simple satellite tracking that is controlled by a control unit as the vehicle's bearing is updated from a navigation system in real time. A Global Positioning System (GPS) module is utilized for the navigation system to provide accurate information of the vehicle's position and bearing during traveling. A control unit is provided as antenna-beam control and measured-data acquisition. We thoroughly examine the developed system in field measurements under open field areas and blockage areas in order to evaluate the propagation characteristics caused by utility poles, pedestrian overpasses, and vegetation-covered roads. In this measurement, the received signal power and the average bit error rate (BER) are simultaneously retrieved. Steadily received levels and average BER are satisfactorily attained during satellite tracking in open field areas. Moreover, the fade characteristics and average BER performance are also investigated during signal blockage. The results show that different environments give different degrees of attenuation, which affects the BER performance in terms of fade depth. Ultimately, our proposed antenna system can contribute to the design of future cost-effective mobile satellite communications.

On-Orbit Experiment Results of Robust Symmetric Attitude Controller for ETS-VIII Spacecraft

AbstractThis paper reports results of an on-orbit experiment using Engineering Test Satellite VIII (ETS-VIII) spacecraft. The ETS-VIII was launched into geostationary orbit by the Japan Aerospace Exploration Agency in December 18 2006. The main mission is to support next-generation mobile digital communications, and for this purpose it is equipped with two large deployable antenna reflectors and a pair of large solar paddles that rotate around the pitch axis. For the spacecraft, the authors have proposed several control methods by applying advanced control theories for the linear parameter varying multi-input multi-output system. Among them, this paper describes the results using two degrees-of-freedom control system based on symmetric feedback control.

Design and implementation of robust symmetric attitude controller for ETS-VIII spacecraft

To meet increasing mission requirements, communication satellites are being equipped with large flexible antenna reflectors and solar paddles. A typical such satellite, the Engineering Test Satellite VIII (ETS-VIII) spacecraft, was launched into geostationary orbit by the Japan Aerospace Exploration Agency (JAXA) in December 2006. The main mission of ETS-VIII is to support next-generation mobile digital communications, and for this purpose it is equipped with two large deployable antenna reflectors and a pair of large solar paddles that rotate around the pitch axis. The authors are planning to perform on-orbit attitude control experiments using ETS-VIII at the end of its mission life, aiming to develop a baseline for future controller design for this class of satellite using advanced control theories. This paper proposes two degrees-of-freedom control based on robust direct velocity and displacement feedback as a candidate controller technology. The spacecraft modeling and controller synthesis methods are discussed, and a controller implementation for an on-orbit control experiment is presented with simulation results.

In-orbit deployment characteristics of large deployable antenna reflector onboard Engineering Test Satellite VIII

This paper describes design, ground testing, an in-orbit experiment, and a novel in-orbit operation for large deployable antenna reflectors (LDRs). Two LDRs (TX-LDR for transmitting and RX-LDR for receiving) are installed on Engineering Test Satellite VIII (ETS-VIII). The reflector design features that the antenna reflector whose aperture is 13 m in diameter (the mechanical dimension is 19 m × 17 m ) consists of 14 basic modules, and each basic module consists of a gold-plated molybdenum mesh, a system of cables, and a deployable frame structures. Several ground tests had been performed using a modular nature to advantage. Prior to the launch of ETS-VIII, we performed an in-orbit deployment experiment using LDREX-2 which consists of seven half-scale modules of LDR, to confirm evaluation accuracy. The LDREX-2 was launched by ARIANE 5 launch vehicle as a piggy-back payload. Deployment characteristics were measured to evaluate the accuracy of analytical prediction obtained by ground deployment testing. ETS-VIII was launched by H-IIA launch vehicle on 18 December 2006. After the successful injection into Geo Synchronous Orbit, the RX-LDR and the TX-LDR were successfully deployed on December 25th and 26th, respectively. We confirmed adequacy of the proposed design and ground verification methodology.

Extended Operation and Modification of 20 mN Class Xenon Ion Engine

To extend the application of the 20 mN class xenon ion engine which was used for north-south station keeping of a geosynchronous satellite--the engineering test satellite-VIII-, the ion thruster's thrust throttling performance was evaluated. The candidate target application is aerodynamic drag compensation of a super-low-altitude earth observation spacecraft. Performance test results show that the thruster, which passed through 12,000 h life test, exhibited a thrust throttling performance from 6 mN to 28 mN, although the thruster showed performance degradation from its initial performance before the life test. A power processing control unit is under development to meet the thrust throttling performance.

Realization of Simple Antenna System Using ETS-VIII Satellite for Land Vehicle Communications

This paper presents a realization of a simple antenna system for land vehicle satellite communication that is tested in experiments conducted on the Engineering Test Satellite-VIII (ETS-VIII). The developed antenna system which was mounted onto a vehicle roof is compact, light weight with simple satellite-tracking operation. In order to realize compact antennas, an onboard-power divider and switching circuit for antenna feeding control are mounted under the array antenna. A Global Positioning System (GPS) module is used to provide accurate information on the vehicle's position and bearing during travelling. A personal computer (PC) is used as the control unit and data logger, which was specifically designed for this application, allow the switching circuit control as well as the retrieving of the received power levels and error rate. The field tests reported in this paper mainly address the tracking performance of the proposed antenna system. Satisfactory results were obtained. Good received power levels and bit error rate (BER) for tracking the ETS-VIII satellite were confirmed. Furthermore, in order to grasp the environmental factors that impact the quality of land vehicle communications, we carefully captured data at obstacles such as buildings, foliages, utility poles and highway overpasses. The results showed blockage and shadowing was confirmed. Additionally, when the antenna was tested at the inclined-road for simple propagation characteristics in elevation direction, stable reception of the satellite signals was realized.

Simple Switched-Beam Array Antenna System for Mobile Satellite Communications

This paper presents a simple antenna system for land vehicle communication aimed at Engineering Test Satellite-VIII (ETS-VIII) applications. The developed antenna system which designed for mounting in a vehicle is compact, light weight and offers simple satellite-tracking operation. This system uses a microstrip patch array antenna, which includes onboard-power divider and switching circuit for antenna feeding control, due to its low profile. A Global Positioning System (GPS) receiver is constructed to provide accurate information on the vehicle's position and bearing during traveling. The personal computer (PC) interfaces as the control unit and data acquisition, which were specifically designed for this application, allow the switching circuit control as well as the retrieving of the received power levels. In this research, the antenna system was firstly examined in an anechoic chamber for S parameter, axial ratio, and radiation characteristics. Satisfactory characteristics were obtained. As for beam-tracking of antenna, it was examined in the anechoic chamber with the gain above 5dBic and the axial ratio below 3dB. Moreover, good received power levels for tracking the ETS-VIII satellite in outdoor measurement, were confirmed.

On-Orbit System Identification Experiments of the Engineering Test Satellite-VIII

This paper presents the results of on-orbit system identification of the Engineering Test Satellite-VIII (ETS-VIII), which was launched by the H-IIA Launch Vehicle No. 11 in December 2006. On-orbit system identification experiments were performed using data acquired during normal operations in the initial check-out phase, such as station acquisition and wheel unloading. The satellite's unconstrained modes were identified using attitude rates and data from accelerometers located on the main body, solar array paddles and large deployable antenna reflectors at various solar array paddle angles. In addition, the constrained modal parameters of the solar array paddles and large deployable antenna reflectors were estimated for comparison with the analytical model.

System Identification Using Impulse Response Including Initial States

This paper presents a new algorithm for a single-input single-output (SISO) system identification including non-zero initial states response in the time domain using impulse response. Eigensystem Realization Algorithm (ERA) realizes a SISO system with zero initial states, therefore we modify the method and first estimate system matrix and initial states using free decay response. In the process, system matrix is obtained by the singular value decomposition as same manner as ERA, and initial state values are refined by recursive least square iteration. Next, deducting initial states effect from the measured impulse response data, we reconstruct ideal impulse response, then identify the input and output matrices using another recursive least square iteration in the time domain analysis. Numerical simulations are performed to verify the new algorithm. Results of examples clarify the validity of the new identification scheme. Finally, we apply the new algorithm to an actual on-orbit data of Engineering Test Satellite-VIII (ETS-VIII) in orbital control mode (OCM), which was launched in December, 2006 and injected into geosynchronous orbit, for the system identification.

Development and Operation of Engineering Test Satellite-VIII (KIKU-8)

Development and Operation of Engineering Test Satellite-VIII (KIKU-8)

Circularly Polarized Rounded-Off Triangular Microstrip Line Array Antenna

SUMMARY The Japan Aerospace Exploration Agency (JAXA) plans to launch a geostationary satellite called Engineering Test Satellite VIII (ETS-VIII) in FY 2006. In this paper, a microstrip line array antenna, which has a very simple structure, is introduced to radiate a circularly polarized wave aiming at ETS-VIII applications. This antenna consists of a triangular conducting line with its vertexes rounded off, located above a ground plane, with a gap on one of its side to produce a circular polarization. The proposed antenna is analyzed by numerical simulations for a single element as well as for a three elements array configuration and the possibility of beam-switching in the azimuth space is experimentally confirmed in the latter case. It is found that by properly feeding the elements constituting the array antenna, for an elevation angle El = 48 ◦ in Tokyo area, three beams are created in the conical-cut direction with a minimum gain more than 6.6 dBic and an axial ratio less than 3 dB.

Circularly polarised equilateral triangular patch antenna for mobile satellite communications

A left-handed circularly polarised (LHCP) triangular patch antenna is developed to support the next generation of mobile satellite communications using Engineering Test Satellite VIII (ETS-VIII). The targeted minimum gain of the antenna is set to 5 dBic for applications of a hundred kbps data transfer with an axial ratio less than 3 dB for circular polarisation. A dual-proximity-coupled equilateral triangular patch antenna is proposed and simulated by the method of moments (MoM) for finite and infinite ground plane models to investigate the ground plane effect. Then measurements of the fabricated antenna are performed to confirm the simulation results. The measurement results show that the frequency characteristics of the fabricated antenna is 0.2% shifted to the higher frequency, and the maximum gain is 0.45 dB lower than the result of the finite ground plane model. Additionally, the simulation results show the ground plane size influences the antenna characteristics, especially the gain and axial ratio of the developed antenna.

Dual-band circularly polarized equilateral triangular-patch array antenna for mobile satellite communications

The Japan Aerospace Exploration Agency will launch the Engineering Test Satellite VIII (ETS-VIII) in 2006 to support the next generation of mobile satellite communications covering the area of Japan (beam coverage El=38/spl deg/ to 58/spl deg/). In this paper, a satellite-tracking left-handed circularly polarized triangular-patch array antenna is developed for ground applications. The targeted minimum gain of the antenna is set to 5 dBic at the central elevation angle (El=48/spl deg/), in the Tokyo area, for applications using data transfer of around a hundred kbps. The antenna is composed of three equilateral triangular patches for both reception and transmission units operating at 2.50 and 2.65 GHz frequency bands, respectively. The antenna was simulated by method of moments (MoM) analysis, and measurement of the fabricated antenna was performed to confirm the simulation results. The measurement results show that the frequency characteristics and the 5-dBic gain coverage in the conical-cut plane of the fabricated antenna satisfy the specifications for ETS-VIII. A prototype of the proposed antenna system is employed in outdoor experiments using a pseudosatellite and shows good performance from El=38/spl deg/ to 58/spl deg/.

Development of Time Comparison Equipment for ETS-VIII Satellite

Engineering Test Satellite VIII (ETS-VIII) is planning to be launched in 2005 for fundamental studies on satellite positioning technologies and is the one first to have installed a highly precise cesium clock in Japan. To measure the clock offset between the satellite and the TCE earth station, Time Comparison Equipment (TCE) has been developed by NICT. The TCE will be used to measure both code and carrier phases and this system will improve two-way time and frequency transfer. This equipment makes it possible to compare two clocks with high precision. Moreover, TCE and TCE earth stations have abilities to remove the delay caused by terrestrial ionosphere and that between the receivers and transmitters. We estimated measurement precision in code and carrier phases. Furthermore, from the examinations using TCE-EM (Engineering Model), we confirmed that TCE is able to measure the clock phases with a subnanosecond precision by code phase observation and a precision of a few picoseconds by carrier phase observation. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 61–71, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20385