Shigemasa Ando

Simplified SRS Prediction Method for Pyroshock Source of V-band Clamp Separation Devices

[Abstract] V-band clamp separation device is commonly applied to the space engineering for releasing the connection of space payload from the launch vehicle. The release mechanism due to the pyroshock and modeling of the device is significant to predict the shock response spectrum (SRS), which is the transient dynamic load of the high frequency to the spacecraft. This paper proposes a simplified model to predict the pyroshock environment near the V-band clamp separation device. This model is based on a single degree of freedom system and calculates a free vibration after releasing, which is derived from the release mechanism of the device. Using the simple model, a simplified calculation method for the SRS interface specification is also proposed. Comparing simulation results with test ones, it is presented that this model will approximately predict the pyroshock response near the device. In addition, validation of the simplified SRS interface specification is also shown.

The Elucidation of Mechanism of Local Sound Pressure Increase Phenomenon

Payloads of satellite are exposed on the severe acoustic environment at the process of lift-off and supersonic zone of a launcher. This acoustic environment excites the payload in high pressure and broad frequency band of random acoustical excitation, which may cause serious damage to the structures or instruments of the spacecraft inside. Space instruments are designed and verified to the acoustic environment by ground reverberant acoustic chamber in order to specify random vibration level at component interface and to verify the payloads are working in function and the structure does not have structural damage. The present load sound pressure specification assumes that the sound pressure interior fairing is uniformly distributed. In spacecraft system acoustic tests, local pressure increase occurs in the narrow gap between spacecraft primal structure and components facing toward the fairing wall. This acoustical environment load to the components differs from that the components were tested alone and the flight acoustic environment may not be actually simulated in the ground testing. It is important to clarify the mechanism of sound pressure increase in the narrow gap in order to predict the level of sound pressure increase. In this study, we focus to the investigation of the mechanism by basic experiment including acoustic testing and vibration modal survey. It is clarified that the main reason of the phenomenon is dominated by the acoustic cavity on the appropriate boundary condition rather than structure vibration. And more, we predict the frequency at which the sound pressure increase at the narrow gap and compare analysis results with experiment results by using Boundary Element Method (BEM).Copyright

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.

Investigation of Spacecraft Vibration Subjected to Acoustic Sound Field of Fill Effect

Payloads are exposed to severe vibro-acoustic environments during rocket launches as shown in Figure 1-(a). At the same time, fill effect [1-3] occurs in the cavity, which is located in the clearance gap between the inner side of the fairing and the solar paddles of the spacecrafts (Figure 1-(b)). This phenomenon results in a maximum increase in sound pressure level (SPL) by approximately 10 dB [2] and causes the natural frequencies of the solar paddles to shift to the coupling modes as shown in Figure 2. These modes are derived from both the vibrational modes of acoustic sound in the cavity and the solar paddles of the spacecrafts. These coupling modes are different from each vibrational mode in vaco [4, 5]. At the same time, the accelerance level of the solar paddle on the structural vibration modes decreases by delta Hv due to the shifts in natural frequencies. The larger the size of the solar paddles, the lower the natural frequencies. It is important to consider this influence during the development of spacecrafts, because the shifts in natural frequencies can make the accelerance level decreased. However, recent researches on the fill effect focus on the increase of SPL by using FEM: Finite Element Method and BEM: Boundary Element Method. Despite the fact that the shifts in natural frequencies due to the fill effect cannot be neglected, more researches are being carried out on the problems of SPL than the problems of the shifts in natural frequencies.

Prediction of Upper Tolerance Limit of Acceleration Power Spectrum Density of Satellite Panel under Diffused Acoustic Field Excitation

Severe vibroacoustic random vibration is easily induced to satellite structure during the flight. Design specification of acoustically induced random vibration for satellite and equipment component is based on the acceleration power spectral density (PSD) at the mount interface. Ground acoustic test is conducted to verify the structural design and abnormal function of equipments. The response of a satellite structure under acoustic test can be predicted by Statistical Energy Analysis. In addition to the mean energy vibration level obtained by SEA, upper tolerance limit of vibration response in PSD needs to be predicted for conservative design purposes. This paper deals with the upper tolerance limit of PSD acceleration level of a satellite plate under high frequency diffused acoustic excitation. The upper tolerance limit is derived based on the statistical distribution of the vibroacoustic response together with the theoretical description of response variance. The upper tolerance limit for the acceleration PSD level obtained by Statistical Energy Analysis is compared with the experiment result. The result from the comparison shows that the upper tolerance limit presented in this paper yields good estimate of PSD upper tolerance level for conservative design. The effect of PSD estimation error in experiment on variance is also discussed.

Upper Bound of Vibration Response of Satellite Panel Under Diffused Acoustic Field Excitation

Severe random vibration is easily induced to satellite structure during the flight. Acoustic test at ground is applied to verify the structural design and abnormal function of equipment. An accurate prediction of acoustic induced vibration response of equipment, therefore, is critical for design purposes. Especially for a satellite exterior panel, it has been shown that two subsystem statistical energy analysis model composed of an acoustic chamber and a single panel will simplify the analyses approach and gives a satisfactory result. This paper derives two subsystem SEA model for the prediction of the exterior satellite panel and formulates the damping loss factor equation based on the experiment data. Moreover, the upper bound value of the two subsystem SEA model is presented for further simplification with which response is obtained without structural damping loss factor and radiation coupling loss factor. These two models were validated well by acoustic tests of eleven satellite honeycomb panels.

Sound Vibration Analysis at the Time of an Artificial Satellite Launch

In spacecraft system acoustic tests, one often sees local pressure increase in the narrow gap between spacecraft primal structures and components facing toward the fairing wall. This acoustical environment load to the components differs from that the components are tested alone and the flight acoustic environment may not be actually simulated in the ground testing. In this paper, in order to clarify the mechanism and evaluate this pressure increase, basic experiment including acoustic testing and vibration modal survey are employed. It is found that the main reason of the phenomenon is dominated by the acoustic cavity on the appropriate boundary condition rather than structure vibration. Boundary element method is used to analize the phenomenon and comparison of analysis and experiment results are carried out. The analytical and experimental results agree well. Furthermore, it is understood that the phenomenon of local sound pressure level increase is dominated by the acoustical standing wave mode (1, 1) which can be predicted by the presented methods.