Ever growing number of space systems raises a question about their safety and longevity. Over time, the complex space environment influences structural materials and electronics affecting mission objectives and performance. In order to determine the effect of space environment on spacecraft’s structural condition, material properties and structural interfaces need to be assessed in space. Hence, it is suggested that active non-destructive measurements are employed to provide structural health information to the spacecraft’s operator. Electro-mechanical impedance method is a promising approach to SHM of space structures due to its use of small unobtrusive piezoelectric sensors and lightweight hardware. In laboratory settings, this method typically utilizes bulky and heavy instruments, but for mid-frequency bands, a small and lightweight impedance measurement circuit could be built. A miniaturized impedance measurement analyzer was designed and built for applications requiring very small hardware mass. The development was driven by the intention to utilize the miniaturized analyzer for SHM of space structures in orbit. The impedance analyzer was designed and built from off-the-shelf components to enable impedance measurements in lower kHz frequency band. It was used to measure the impedance of a payload structure resembling a fixed plate. The aim of this measurement was to demonstrate data acquisition and storage by the miniaturized impedance logger and to compare its performance to laboratory scale instruments. The paper further discusses the effect of space environment on structures, describes and validates an analytical model for a fixed-fixed rectangular plate and provides analysis of the potential influence of thermal variation and radiation in space on electro-mechanical impedance signature.
KEYWORDS: Piezoelectric thin film actuators, Sensors, Structural health monitoring, Finite element methods, Mathematical modeling, Data modeling, Data communications, Semiconducting wafers, Aluminum, Algorithm development, Data storage
Structural Health Monitoring (SHM) systems are proposed as a method to reduce cost and improve flight safety by monitoring environmental and vehicle conditions during space travel. For this experiment, a real-time SHM data acquisition system was designed, developed and implemented as an addition to a flight recorder on a suborbital spaceflight. The flight recorder, provided by a commercial partner, Immortal Data Incorporated, collects flight information and distributes it to several units for improved data survivability. The aim of this flight experiment was to demonstrate real time data acquisition and storage by the flight recorder and the integration of the SHM experiment into the flight recording process. The parameters of the flight environment were acquired using various sensors in the payload. The SHM experiment used a small cantilevered beam with attached piezoelectric sensor and utilized a miniaturized Canary impedance analyzer to collect the electro-mechanical impedance signatures of the beam in the particular frequency range. The Canary unit was designed to collect electro-mechanical impedance data, store it on a SD card, process stored data in real time and communicate diagnostic data features to the flight recorder during flight. An algorithm was developed to extract a small set of diagnostic features (impedance peak amplitudes and frequencies) from raw impedance data and communicate this data set to the flight recorder. The paper discusses development of the SHM experiment for a suborbital flight, describes and validates the associated analytical model for impedance signature and provides analysis of the post flight electro-mechanical impedance data. The results obtained in the sub-orbital flight experiment indicate the utility of SHM for space vehicles.
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