Satellites are subjected to pyrotechnic shocks caused by actuating the pyrotechnic separation devices during various missions such as separation from the launch vehicle and deployment of the solar panel. Pyroshock rarely damages structural members, but it may cause damage to mounted electronic equipment, which can lead to mission failures. In order to protect electronic equipment from pyroshock, shock propagation characteristics need to be identified. This paper proposes a compact pyroshock simulator that can be used to identify the pyroshock propagation characteristics at various locations of a structure. A small resonant fixture and high air pressure are used to make the simulator compact in size. A diaphragm breech design is also introduced to achieve high-bursting pressure and increase the repeatability of the simulator. The developed simulator can produce the pyroshock environment with repeatability in the shock propagation path, and also the pyroshock environment can be changed by using different resonant fixtures. The developed simulator can be used for the experimental characterization of the pyroshock propagation over various structures.
Pyrotechnic separation devices have been widely used for the separation events of space systems because of their advantages in high energy per unit volume and high reliability, among others. The actuation of the pyrotechnic devices generates a localized, large pyroshock on the surrounding structures. Pyroshock rarely damages structures, but the high-frequency components of the shock motions propagating to the structure can cause malfunction or failure of mounted electronic equipment such as relay chatter, circuit shortage due to the breakage of lead wires, and dislodging of contaminants [
Most pyroshock testing of qualifying sensitive equipment involves shock testing using pyrotechnic or nonpyrotechnic devices. Testing using pyrotechnic devices can simulate the near-field environment, but they have safety problems and require trial and error for repeatability [
(a) Tunable resonant bar setup and SRS [
To study the characteristics of shock propagation over space structures, the simulator must be used at various positions of the structure and must have repeatability at a shock path to a measurement location from a shock source. In order to design a compact simulator without using pyrotechnic devices, a high-pressure air release device and a cylindrical resonant fixture are used. For the high-pressure air release device, a new method is applied by improving the double diaphragm breech method [
The high-frequency excitation in a short duration, which is typical characteristics of a pyroshock, can be simulated by the sudden release of energy, such as a projectile’s impact on the structure [
The wrap-around breech method [
The conceptual design of the pyroshock simulator.
Cross section and dimensions of the simulator.
The solenoid valve STH32C-15-4-T-H.
Specification of the solenoid valve.
Descriptions | Specification |
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Fluid | Air, water, oil, and steam |
Operating | Normal closed |
Port size | Rc(PT) 1/2 inch |
Orifice size | 14.5 mm |
Response cycle | Max 80 ms |
When the diaphragm bursts, the compressed air acting on the back of the diaphragm accelerates the projectile. The impact speed of the projectile is predicted by using a simple gas gun model, as shown in Figure
Schematic drawing of a simple one-stage gas gun.
The motion equation of the projectile accelerated by the pressure of the chamber can be expressed as follows:
The major factor affecting the repeatability of the simulator is the bursting shape and bursting pressure of the diaphragm. The pressure applied to the projectile depends on the bursting shape of the diaphragm. The ANSYS software is used to expect the bursting pressure and the bursting shape of the diaphragm. The diaphragm is analyzed until it is burst by increasing pressure.
First, the geometry adjacent to the diaphragm is modeled to minimize the analysis time. The shape of the diaphragm is a circular plate with a diameter of 26 mm and thickness of 0.1 mm. As shown in Figure
Geometric model and the meshing result of the diaphragm, the barrel, and the chamber.
After that, mesh modeling of the three parts is conducted. For accurate results and fast computational time, mesh modeling is important in ANSYS explicit because the time interval is determined by the Courant–Friedrichs–Lewy (CFL) condition [
The material of the diaphragm is modeled as stainless steel 304. The material properties define the density and linear state equations and failure theory to predict the bursting of the diaphragm. Plastic strain failure and bilinear strength model are used to simulate plastic and failure behavior. The plastic strain is defined as 0.7. The material properties of stainless steel 304 are summarized in Table
Material properties of stainless steel 304.
Stainless steel 304 | ||
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Property | Value | Unit |
Density | 7,900 | kg/m3 |
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Linear EOS | ||
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Bulk modulus | 166.7 | GPa |
Reference temperature | 295 | K |
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Bilinear strength | ||
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Shear modulus | 86 | GPa |
Yield stress | 2.15 | MPa |
Tangent modulus | 1.0 | GPa |
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Failure model | ||
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Plastic strain | 0.7 |
A fixed boundary condition is applied to the bottom of the barrel, and a constant pressing load of 500 N is applied perpendicular to the upper part of the chamber to fix the diaphragm. The pressure boundary condition is defined as a ramp pressure of 200 bar during 10 ms at the upper surface of the diaphragm as shown in Figure
Boundary conditions on the analysis model.
An asymmetric bursting shape may result in a nonuniform pressure distribution to the projectile, and then, the simulator performance may be low. In order to prevent this phenomenon, a Y-shape indentation on the center of the diaphragm is considered so that the diaphragm bursts in the center. The depth of the indentation is modeled as 0.03 mm. The analysis results reveal that the indented diaphragm bursts from the center, not from the edge of the diaphragm (Figure
Bursting shape of the indented diaphragm.
The frequency at which the slope changes the shock response spectrum is called the knee frequency, which corresponds to the dominant frequency of the pyroshock environment [
To make the size of the simulator compact and generate a point-source shock on the test object structure, the shape of the resonant fixture is designed as a cylindrical shape with various numbers of design variables, as shown in Figure
Shape and design parameters of the resonant fixture.
To understand the response of the resonant fixture, the device with a resonant fixture can be modeled as a three-degree-of-freedom (DOF) system, as shown in Figure
3-DOF model for the assembly of the chamber, the barrel, and the resonator.
In Figure
The main variables of the resonant fixture are the diameter (
Dimensions of the resonators.
Resonator type | Type 1 | Type 2 |
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Natural frequency (Hz) | 6600 | 1100 |
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40 | 40 |
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73 | 110 |
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20 | 20 |
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6.5 | 9.75 |
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3 | 8.8 |
Mode shape of the resonators in the axial direction: (a) type 1 and (b) type 2.
In order to assume the barrel and the chamber as one lumped mass, it should have a natural frequency sufficiently higher than that of the resonator. Using ANSYS modal analysis, the axial natural frequency of the chamber-barrel assembly is found to be 21900 Hz (Figure
Mode shape of the chamber-barrel assembly in the axial direction (21900 Hz).
In order to evaluate the characteristic of the device, a pretest is performed. The test configuration is shown in Figure
Configuration of the experiment setup.
The clamped simple plate for pyroshock propagation experiment.
The pyroshock is measured with an acceleration signal. The accelerometer can be saturated beyond the measurement range of the accelerometer sensor, and it may be damaged due to the accelerometer resonance when the accelerometer is located near the shock source. Therefore, an accelerometer with a built-in mechanical filter should be selected so that the sensor inside the accelerometer is not damaged [
Specifications of the accelerometer and signal conditioner.
Accelerometer (PCB 350B03) | |
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Sensitivity |
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Measurement range | ±10,000 G peak |
Frequency range (±1 dB) | 0.4 to 10,000 Hz |
Frequency range (−3 dB) | 0.2 to 25,000 Hz |
Mechanical filter resonant frequency | 23,000 Hz |
Resonant frequency | More than 100,000 Hz |
Nonlinearity (per 10 kg) | Less than 2% |
Transverse sensitivity | Less than 7% |
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Signal conditioner (NI PXI3-6366) | |
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Sample rate (single channel maximum) | 2.00 MS/s |
Number of channels | 8, differential |
ADC resolution | 16 bits |
Input coupling | DC |
Input range | ±10 V |
Maximum working voltage for all analog inputs | ±11 V |
Bandwidth | 1 MHz |
Slew rate | 20 V/ |
In the preliminary experiment, the projectile and the barrel made of aluminum alloy and stainless steel 304 are plastically deformed. The deformation of the barrel and projectile affects the impact duration so that the repeatability of the test results can be worse. Therefore, stainless steel 630, which has a higher yield strength than aluminum alloy and stainless steel 304, is selected. The material properties of stainless steel 630 are summarized in Table
Material properties of stainless steel 630 used in the projectile and the barrel.
Stainless steel 630 | |||
Condition | Density (kg/m3) | Tensile strength (MPa) | Yield strength 0.2% proof (MPa) |
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H900 (projectile) | 7750 | 1310 | 1170 |
H1150 (barrel) | 7750 | 930 | 725 |
The experiments are carried out under the same conditions to evaluate the repeatability of the simulator in the pyroshock propagation path. The experiment is performed three times under the same conditions. The thickness of the diaphragm is 0.1 mm, and the resonant fixture is not used. The similarities of the measured acceleration time histories and calculated shock response spectrum (SRS) from the acceleration time histories are compared. The SRS is the most commonly used method to quantify pyroshock. The SRS means the maximum value of response for each natural frequency by applying shock excitation to the base of a system consisting of a single degree-of-freedom (SDOF) system with independent natural frequencies [
If the test results are inside this criterion, they can be regarded as the same shock environment. In this study, the results are evaluated in the frequency range between 100 Hz and 10,000 Hz.
In the results of the experiment, the bursting pressure of the diaphragm is almost similar to the three experiments, as shown in Figure
Pressure graph of the chamber.
Bursting shape of the diaphragm. (a) Initial, (b) Exp. 1, (c) Exp. 2, (d) Exp. 3.
The acceleration time histories during 20 ms and acceleration SRS at 30 mm, 150 mm, and 350 mm points are shown in Figures
Acceleration time history (a) at 30 mm, (b) at 150 mm, and (c) at 350 mm from shock source.
Acceleration SRS (a) at 30 mm, (b) at 150 mm, and (c) at 350 mm from shock source.
The effect of the resonant fixture, which is designed to obtain the different shock environment, is evaluated. The first natural frequencies of two resonant fixtures are designed as 6,600 Hz (resonator type 1) and 1,100 Hz (resonator type 2), respectively. Two resonant fixtures are made of stainless steel 304. The shock simulation experiment is performed three times for each resonant fixture. Figure
Acceleration SRS of the pyroshock simulator using resonator 1 and resonator 2 (a) at 30 mm, (b) at 150 mm, and (c) at 350 mm from shock source.
This paper proposes a compact point-source pyroshock simulator without explosive devices for the pyroshock propagation test. The developed simulator is much more compact than other pyroshock simulators and has repeatability on a shock path from the shock source. For the pyroshock test, the pyroshock measurement instruments were prepared and repeated tests were performed to evaluate the feasibility of the pyroshock propagation test. In order to design the pyroshock simulator in a compact size and applicable on various positions of real structures, the high-pressure air release mechanism consisting of the air tank, the solenoid valve, and the indented diaphragm was built. To increase the repeatability of the simulator, the diaphragm was designed to burst in the same shape at a certain pressure by indenting a Y-shape on the center. The effect of the indentation on the diaphragm was analyzed using explicit analysis. To simulate various pyroshock environments, the knee frequency should be adjustable. The knee frequency of the generated pyroshock can be easily changed by using the resonator with different natural frequencies.
Data presented herein are not freely shareable because this research is a classified program of the funding institution.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This work was supported by the Global Surveillance Research Center (GSRC) program funded by the Defense Acquisition Program Administration (DAPA) and Agency for Defense Development (ADD).