GEM46 Motor Destruct Test

In an effort to better understand the properties of rocket noise, the statistical properties of noise data from various-sized solid propellant rocket motors. Time waveform data sampled at 204.8 kHz using 6.35 and 3.18 mm microphones were collected near motors with nozzle exit diameters ranging from 0.13 to 1.22 m. Non-Gaussian features of the data have been explored by calculating estimates of the probability density functions of the data and various statistical moments, including skewness and kurtosis. This has been carried out for both the pressure waveform and its first order time difference to better understand the formation of acoustic shocks within the noise. The analysis shows greater similarity between the statistics for the pressure than for the time derivative estimates.

In solid propellant rocket motors, the design of grain port geometry primarily dictates the motor ballistic performance. The flexibility offered by the spatial variation of the port shape on motor performance is often discounted due to the requirement of complex mandrel shapes along with their associated manufacturing issues coupled with propellant processing constraints. Literature data indicate improvement in motor volumetric loading and stability by planned distribution of burn surface area along motor length. This paper deals with the realization and testing of a subscale motor with central finocyl-based grain geometry. A novel method of casting complex grain shapes in solid rocket motors using the wax mandrel technique is discussed. The wax mandrel preparation, propellant casting procedure, and wax mandrel removal setup are elaborated. Static testing results of the subscale motor with central finocyl port geometry are also presented as proof-of-concept. This work has demonstrated the feasibility of realizing solid rocket motor grains using the wax mandrel technique, which further enables realization of complex grain designs necessary to meet various mission requirements.

Small, low-thrust, long-burn-time solid propellant rocket motors could provide propulsion for a new class of kilogram-scale, transonic, uncrewed aerial vehicles (UAVs). This paper investigates technological challenges of small, low-thrust solid rocket motors: slow-burn solid propellants, motors that have low thrust relative to their size (and thus have low chamber pressure), thermal protection for the motor case, and small nozzles that can withstand long burn times. Slow-burn propellants were developed using ammonium perchlorate and 0–20% oxamide (burn-rate suppressant), with burn rates of at 1 MPa. Using these propellants, a low-thrust motor successfully operated at a thrust/burn area ratio 10 times less than that of typical solid rocket motors. This kilogram-scale motor can provide 5–10 N of thrust for 1–3 min. An ablative thermal protection liner was tested in these firings, and a new ceramic-insulated nozzle was demonstrated. This paper shows that small, low-thrust solid motors are feasible and presents a baseline design for the integration of such a motor into a small UAV.

Summary form only given. Polymer Optical Fibers embedded in the propellant of Solid Rocket Motors are demonstrated for monitoring strains higher than 10%. A new architecture incorporating a closed-loop fiber is proposed and its theoretical behaviour is experimentally verified. The propulsion system of Solid Rocket Motors (SRM) is considered as the most critical system in a guided missile as it powers the missile with predetermined characteristics. A key issue for the safety and reliability of those SRM missiles and consequently for the effective and economic management of missiles' inventory is the efficient Structural Health Monitoring of the energetic propellant grain. This work proposes the use of photonic sensors [1,2] for SRMs' continuous SHM as the preferable solution in such environments, due to their electromagnetic interference immunity and inherent electrical and explosion safe characteristics. Polymer Optical Fibers embedded with excellent bonding characteristics to the propellant material of SRM are demonstrated as an efficient sensing platform. The use of POFs for SHM applications is considered as more robust in terms of installation and operational reliability compared to silica fibers where their fragility leads to a high rejection ratio (around 60%) of unsuccessful installations due to fiber breakage during handling and this ratio is prohibitive when installing fibers in highly expensive units such as SRMs. PMMA POFs used both as jacketed cables or unjacketed bare fibers, were successfully embedded into solid propellant materials and afterwards mechanically loaded in special tensile tests equipment. The experiments were realised with a simple optical setup of a high power LED of 1 mW at 650nm and a photodetector operating at linear regime. By using special primers an excellent bonding between fibers and propellant was achieved allowing thus efficient strain transfer from the energetic material and avoiding relative slipping [3]. Two different configurations were employed, one of axial longitudinal incorporation of the POF along the specimen and the other by incorporation of a fiber loop segment in the longitudinally embedded fiber. The applied strain in the specimen is transferred partially axially to the straight fiber sections while it also allows the geometrical deformation of the embedded loop from the circular to elliptical shape. This deformation results in change of local bend radii along the looped fiber inducing thus additional bend losses. The intrinsic elasticity of the POFs and also the macro-bend originated losses under strain provide monitoring capability for strain and stress much higher than 10%. Additionally resulted plastic deformation of POFs in excessively high strains, is proposed to serve as a data/event logger important for recording materials' stress history.

The combustion instabilities in solid rocket motor (SRM) are abiding predicament since their inception seven decades ago. The availability of large amount of energy in SRM combustion in comparison to small amount required to generate the combustion instabilities ensue the likely occurrence of the problem. This entails the SRM combustion instability prediction. This paper deals with the prediction of acoustic longitudinal mode linear combustion instabilities in 3D grain SRM. The stability history of SRM is predicted during motor burn time. This necessitates the performance (pressure/thrust) analysis. The FEA based solver is employed for the acoustic analysis of the grain port cavity as the grain burns. This is followed by determination of propellant response function. The computer code developed using approximate stability analysis results based on spatial and temporal averaging of the equations of two phase flow is used to predict the stability history. The results are presented and discussed for various longitudinal acoustic modes of SRM. The study evinces the decrease in stability margin with time and increase with mode number.

During the whole life cycle of solid rocket motor (SRM), shell damage and propellant interface debonding will occur, which will destroy the structural integrity of SRM. Therefore, it is necessary to monitor the SRM health status, and the existing nondestructive testing technology and the designed optical fiber sensor cannot meet the monitoring requirements. In order to solve this problem, this paper uses femtosecond laser direct writing technology to write high contrast short femtosecond grating array. A new packaging method is proposed to enable the sensor array to measure 9000 με. It solves the grating chirp phenomenon caused by stress concentration in the SRM, and breaks through the key technology of fiber optic sensor implantation in the SRM. The shell pressure test and strain monitoring inside the SRM during long-term storage are realized. For the first time, the experiments of tearing and shearing specimens were simulated. Compared with the results of computed tomography, it proves the accuracy and progressiveness of implantable optical fiber sensing technology. Combined with theory and experiment, the problem of SRM life cycle health monitoring is solved.

High-speed motion analysis system could record images up to 12,000fps and analyzed with the image processing system. The system stored data and images directly in electronic memory convenient for managing and analyzing. The high-speed motion analysis system and the X-ray radiography system were established the high-speed real-time X-ray radiography system, which could diagnose and measure the dynamic and high-speed process in opaque. The image processing software was developed for improve quality of the original image for acquiring more precise information. The typical applications of high-speed motion analysis system on solid rocket motor (SRM) were introduced in the paper. The research of anomalous combustion of solid propellant grain with defects, real-time measurement experiment of insulator eroding, explosion incision process of motor, structure and wave character of plume during the process of ignition and flameout, measurement of end burning of solid propellant, measurement of flame front and compatibility between airplane and missile during the missile launching were carried out using high-speed motion analysis system. The significative results were achieved through the research. Aim at application of high-speed motion analysis system on solid rocket motor, the key problem, such as motor vibrancy, electrical source instability, geometry aberrance, and yawp disturbance, which damaged the image quality, was solved. The image processing software was developed which improved the capability of measuring the characteristic of image. The experimental results showed that the system was a powerful facility to study instantaneous and high-speed process in solid rocket motor. With the development of the image processing technique, the capability of high-speed motion analysis system was enhanced.

Polymeric composites are widely used in aerospace. One such important use of polymeric composites is the filament-wound composite case for the Solid Rocket Motor (SRM). Environmental conditions expected during flight and other phases of the SRM’s life cycle affect its performance. The performance of SRM, in turn, depends primarily on the composite case and propellant grain. In this study, the performance evaluation of SRM with the composite case is carried out for different environmental conditions. These cases are designed to sustain very high pressure and temperature environments generated due to the combustion of propellant grains and are intended to perform adequately at any time during their service life. The performance evaluation test matrix is formulated considering various expected dynamic and thermal conditions. The small SRM with a composite case is subjected to planned tests as per the matrix, followed by static tests. The pressure versus time data is plotted for all test conditions. The ballistic parameters result of the virgin (without subjecting it to any test) small SRM is considered as a reference for comparative studies with the rest of all other test conditions results. All the ballistic performance test results are also analysed with respect to the pressure-time curve for mission bounds. The analysis of experimental test results reveals that various environmental dynamic conditions like random vibration, acceleration and shock, do not affect the composite case and the ballistic performance of a small SRM. The effect of grain temperature on ballistic performance is also found as expected.

In order to coordinate the many design parameters of the solid rocket motor (SRM) grain to get a better performance. A structure optimization method based on variation sketch and genetic optimization algorithm is proposed. Then by choosing a slotted-tube grain as the example, corresponding structure parameters optimization processes show the efficiency and convenience of this advanced structure optimization method. The objective function of SRM internal ballistics curves are converged after about 500 generations' evolution. The SRM internal ballistics curves comparison with initial one and optimized one also shows that the fluctuation range of the internal ballistics curve is reduced from about 20% to 8%. This is helpful to reduce the negative weight of SRM and improve its performance. It proves the accuracy of this grain design and optimization method.

Taylor-Culick flow is of importance on the interior ballistics of solid rocket motor (SRM). The combustion of solid fuel results in the motion of the wall boundary of the flow. Therefore, the understanding of Culick-like flow with a regressing wall plays a significant role in the study of SRM. However, the complex geometry of real fuel surface of SRM leads to considerable difficulty on the analysis and numerical simulation. In this paper, Navier Stokes equations coupled with Level-set equation are resolved to mimic the flows inside the combustion chamber with grain regression of the propellant. The four typical geometrical structure which corresponds to classical propellant grain shapes are simulated. The results demonstrate that the different geometrical structure in associate with flow direction could significantly affect the flow inside the combustion chamber. Besides flow turning could be substantially changed based on different geometrical configuration, isolated vortex could also be introduced under the influence of different injection schemes. Considering both flow turning and vortex play an important role in the combustion instability of the SRM, the geometrical design of grain should be taken additional care except for the traditional requirement of thrust.

The first step experimental researches about embedded fiber Bragg grating (FBG) sensors network for health monitor of solid rocket motors (SRM) were presented in this thesis. In the experiment, the FBG sensors networks were embedded in composites plane with simulative delamination and scale SRM models. The results of the plane bend test indicated that damage could be identified by detecting concentration strain field, and the results of the scale SRM shells internal hydraulic pressure test indicated that the complex strain and deformation could be monitored by the sensors network, leading to the possibility to develop FBG sensors network systems for composites SRM health monitor. These researches will extend missile weapons reliability and safety in serving lifetime, enhance maintenance procedures to maximize serving time and improve reliability.

The influence of solid rocket motor retro-burns on the space debris environment

EXPERIMENTAL VERIFICATION OF DYNAMIC STABILITY OF VERTICAL CANTILEVERED COLUMNS SUBJECTED TO A SUB-TANGENTIAL FORCE

Thermoacoustic instability is a persistent problem frequently observed in various types of combustors, resulting in damaging consequences. However, our understanding of the dynamics in industrial combustors undergoing thermoacoustic instability, particularly in solid rocket motors, still remains limited. Data-driven precursors for thermoacoustic instability in such systems are also unknown. In this study, we use recurrence network measures and spectral entropy to characterize the dynamics of pressure data obtained from a full-scale solid rocket motor transitioning to thermoacoustic instability and design data-driven precursors for thermoacoustic instability. We show the scale-free nature of combustion noise and that the dynamical transition from combustion noise to thermoacoustic instability can be detected using two complex network measures: the average path length and average betweenness centrality. We calculate the spectral entropy in the frequency domain and find it more sensitive to detecting the dynamical transition and computationally cheap, which is promising for flexible use as a new precursor in thermoacoustic instability prediction. Our work highlights the feasibility of employing complex network measures and spectral entropy for precursors in solid rocket motors, paving a new path for using data-driven measures to early warning of thermoacoustic instability in solid rocket motors.

Black powder is commonly used for ignition of propellants in solid rocket motor. However, the condensed products of black powder will affect the size accuracy of condensed combustion products during the combustion of solid rocket motor. To solve this situation, a “clean” ignition technology, laser-induced ignition, was used to replace the traditional method of ignition. Besides, the ignition performance of aluminized composite propellant and agglomeration/combustion processes of aluminum particle were investigated. Moreover, it was discussed that the application prospects of laser-induced ignition technology in solid rocket motor from the perspective of particle size, especially the condensed combustion products size distribution generated during pressurization. Therefore, an experimental system for the investigation of ignition and agglomeration /combustion processes was developed using the laser-induced ignition and visualization techniques was presented. Furthermore, the properties of condensed combustion products were discussed in this review, and it found the multimodal nature of the condensed combustion products size distribution function. The investigation in this paper showed that the application of laser-induced ignition techniques, instead of the use of ignition composition, prove useful to avoid the plume pollution during pressurization. It is also found that the aluminum powder is more different to ignite than aluminized propellants and rough surface of propellants is easier to ignite. The work also provides a technical basis for the subsequent application of laser-induced ignition technology to solid rocket motors.