Study On Structural Analyses And Optimizations For The Structural Test Article Of The AMS-02 Thermal Control System

With the development of aerospace technology, efficiency, economy and reliability are attached importance for the constructions of spacecrafts. The temperature of the components in a spacecraft must be kept within their different operational ranges but also stable over both time and volume. Hence, the Thermal Control System (TCS) of a spacecraft plays the key role on its running in the space. In this thesis, the methodology of structural analyses and optimizations for spacecrafts was provided according the study of the Structural Test Article (STA) of the Alpha Magnetic Spectrometer (AMS-02) Thermal Control System based on FEM. The dynamic analyses and the static analyses of the STA of the AMS-02 TCS were performed, and the optimizations of the STA structure for mass reduction were made. By the comparisons between the experiment results and the analyses results, the methodology in this thesis was proved to be effective. The main contents are as follows:The thermal control system of the AMS-02 includes two parts: the Flight Model (FM) and the STA. The FM of the TCS is the one that will be installed in the International Space Station (ISS), and the STA, which consists of the WAKE side STA and the RAM side STA, is used to illustrate the key technologies of design, structural analyses and structural test for the FM. In each side STA, the components include the main radiator, Tracker radiator, electronic boxes, brackets and links etc. To meet the validity of the STA in structural analyses and tests for the FM, the STA of the AMS-02 TCS was designed to ensure that its structure, size and physical properties are close to that of the FM. The comparisons of the physical properties between the designed STA the FM show that the mass, center of gravity and moment of the inertia etc. of the STA have small differences with that of the FM. The structural analyses, optimizations and tests can provide the accurate reference for the final design of the FM.Thermal modeling and simulations for the radiators and electronic boxes were carried out by applying the Crank-Nicholson implicit solution. Based on reducing the temperature gradient of the radiators and the mass of the TCS, the layout of the heat pipes in the radiators was optimized to solve the overheating issue of the electronic boxes. The non-operational and operational temperature dissipation for the TCS was calculated.The modal analyses of spacecrafts are the bases to judge whether their natural frequencies are apart from the natural frequencies of launch vehicles and the bases for their dynamic optimizations. The first eleven modes of the constrained RAM STA and WAKE STA and the mode shapes with effective mass greater than 5% of them were presented, and the modal frequencies of the STA and the FM were compared. The modal analyses show that the low rank modes of the STA are very close to that of the FM.Accordingly, the STA and the FM of the TCS have the consistent vibration characteristics. The low rank modes of the RAM side STA are similar to that of the WAKE side STA. The first mode shape of the RAM side and the WAKE side STA is the first bending on the bottom of the main radiators because the mass of the electronic boxes is big however the stiffness of their links is not enough. The second mode shape is the integral wiggle with local big amplitude on the bottom of the main radiators and the electronic boxes near the lower brackets. The third mode shape is the bending on the upper radiators and the electronic boxes. For these locations with big vibration amplitude, the thickness of the electronic box links should be increased. In addition, there are big deformations on the Tracker radiators because their stiffness is weak. From the fifth mode shape of the RAM side STA and the WAKE side STA, the vibration amplitudes decrease, and the vibration deformations just occur on the local positions of the radiators.The AMS-02 will experience complicated cases of launch, on-orbit and landing etc. Based on the results of the vibration coupling analysis between the ASM-02 and the launch vehicle and the results of the coupled load analysis in the launch case and landing case, the design load factors, which were equivalently represented by acceleration of gravity and angular acceleration along three coordinate axes in the AMS-02 coordinate system, were presented.The static analyses of the STA of the TCS were made by acting the design loads calculated in the load coupling analyses on the finite element models. The static analyses mainly consist of displacement analyses, strength analyses and stability analyses.The displacement analyses show that at launch case the maximum displacements of the RAM side STA and the WAKE side STA occur on the bottom of the main radiators near the lower brackets where the stiffness of the components is weak. The displacements of the other components in the STA are all less than the allowance displacement.Based on the forth theory of strength, the highest Von Mises stresses of the plate elements and solid elements and combined stresses of the bar elements for the key parts of the STA were calculated. The strength verifications of the parts of the STA were performed in terms of Margin of Safety (MoS). The STA parts, of which the values of MoS are negative, were redesigned and verified again.According to the verifications the Margin of Safety of the global buckling in the RAM side STA and the WAKE side STA are positive. That is to say, no global buckling problem occurs on the STA. According to the minimum principal stresses calculated by FEM and the allowance buckling stresses of the locations on the brackets, the Margin of Safety of the local buckling were calculated, and all the MoS are positive.In this thesis a verification method for the bolts in the STA was provided to check their safety. By applying the maximum tensile forces and shear forces acting on the bolts, the MoS of all type of bolts in the STA were calculated in terms of the verification procedure. The bolts with negative Margin of Safety were replaced by bolts with bigger strength. The verification results show that all the bolts are safety.After the STA of the TCS and other subassemblies of the AMS-02 were assembled together, the static tests were done to measure the displacements and the strains in the STA by acting the equivalent flight loads. The test results show that the design loads calculated by loads coupling analyses are accurate and the static analyses are effective.To provide the guidance for the design of the FM, the STA were optimized to reduce its mass. Based on Kuhn-Tucker criterion, the Lagrange function was formed and the iterative formula and the convergence condition for element thickness of the electronic box plates of the STA were deduced. To take the minimum mass as the objective function and the requirements of the displacements and strength as the constraint functions, the mass of the electronic box plates of the STA was optimized. The optimization procedure was developed based on the MSC.NASTRAN and Matlab. The procedure was convergent with 11 iterations on the RAM side STA and 12 iterations on the WAKE side STA, the mass of the electronic boxes on the RAM side STA was decreased from 61.37 kg to 52.64kg and the mass of the electronic boxes on the WAKE side STA was decreased from 72.06 kg to 62.58 kg. Similarly, the mass of the plates on the lower brackets were also optimized. Based on the MoS of the four mid brackets, the mass of them were also optimized with 1.88 kg reduction by the MSC.NASTRAN optimization procedure. Here the optimization objective function is the mass minimum and the constraint functions are the requirements of the strength, stability and displacement.In summary, the structure of the STA of the AMS-02 thermal control system was analyzed and optimized by FEM. The methodology applied in this thesis was proved to be effective by the comparison between the analysis results and the experimental results. The study in this thesis can not only meet the requirements of the structural analyses and optimization design for the STA of the AMS-02 TCS but also provide the methodology for the similar issues of other spacecrafts simultaneously.