Transient thermal parameters correlation of spacecraft thermal models against test results

There are always differences between the computer predicted temperatures of a spacecraft thermal model and the temperatures measured during the mandatory laboratory thermal tests. As a consequence, the model must be correlated before the spacecraft is launched to space, in order to identify the correct parameters that match the experimentally measured temperatures. A new technique is presented to identify the parameters, based on the minimization of the error of the transient equations which governs the heat transfer in the spacecraft. The steady state minimization was presented in a previous work, but the transient techniques presented hereafter enable a better and more extended identification of parameters despite the higher complexity of the computational problem. The use of a set of available subroutines (TOLMIN), which permits the constrained optimization of a general function, makes possible to ensure that the obtained parameters are non-negative, a requirement to have physical sense. The gradient function must be calculated for each problem, but this can be done automatically. Results show that for small and medium size transient Thermal Mathematical Models (TMM), a good correlation of thermal parameters can be achieved even if some of the nodes temperatures are not measured in the thermal tests.The findings presented in this paper are fruit of independent research. No financial assistance was received. I.G. wants to thank Dr. A. Usarraga for helping with a friendly environment where initial steps of this work were devised

Advances in automatic thermal model to test correlation in space industry

In space industry thermal models are an important tool to predict, analyze and understand the thermal behaviour of components, subsystems and whole spacecrafts. Most parameters of these models have a limited accuracy and consequently the models results are uncertain. In order to reduce this uncertainty to a required level the model parameters are adjusted (correlated) by fitting the model to test results obtained during thermo vacuum tests. This is often a difficult long lasting manual process. In order to perform these correlations automatically many different methods have been developed and analyzed. Two of these methods are analyzed regarding their requirements, efficiency and limitations. A genetic algorithm is compared to a method based on non-linear equations solving algorithms of the Broyden class.No sponsor

Performance of Gradient-Based Solutions versus Genetic Algorithms in the Correlation of Thermal Mathematical Models of Spacecrafts

The correlation of the thermal mathematical models (TMMs) of spacecrafts with the results of the thermal test is a demanding task in terms of time and effort. Theoretically, it can be automatized by means of optimization techniques, although this is a challenging task. Previous studies have shown the ability of genetic algorithms to perform this task in several cases, although some limitations have been detected. In addition, gradient-based methods, although also presenting some limitations, have provided good solutions in other technical fields. For this reason, the performance of genetic algorithms and gradient-based methods in the correlation of TMMs is discussed in this paper to compare the pros and cons of them. The case of study used in the comparison is a real space instrument flown on board the International Space Station

Transient thermal parameters correlation of spacecraft thermal models against test results

There are always differences between the computer predicted temperatures of a spacecraft thermal model and the temperatures measured during the mandatory laboratory thermal tests. As a consequence, the model must be correlated before the spacecraft is launched to space, in order to identify the correct parameters that match the experimentally measured temperatures. A new technique is presented to identify the parameters, based on the minimization of the error of the transient equations which governs the heat transfer in the spacecraft. The steady state minimization was pre-sented in a previous work, but the transient techniques presented hereafter enable a better and more extended identification of parameters despite the higher complexity of the computational problem. The use of a set of available subroutines (TOLMIN), which permits the constrained optimization of a general function, makes possible to ensure that the obtained parameters are non-negative, a requirement to have physical sense. The gradient function must be calculated for each problem, but this can be done automatically. Results show that for small and medium size transient Thermal Mathematical Models (TMM), a good corre-lation of thermal parameters can be achieved even if some of the nodes temperatures are not measured in the thermal tests

Influence of the Measurements Uncertainties in the Correlation of Spacecraft Thermal Models against Thermal Results

Ground thermal tests are always mandatory before any space mission is flown into space. The collected results of these tests are mainly temperatures of the different parts of the spacecraft (nodes) for different mission scenarios. The measured temperatures always show differences with the expected values coming from the computer thermal mathematical models. The origin of these differences is partially related to the inherent error coming from physical measurements. The thermal parameters that compose the computer thermal mathematical models must always be correlated with the results coming from tests. This paper studies, through three thermal models, the difficulties that are found in the correlation process when the measured temperatures reach a certain level of error. Thermal parameters become more difficult to be identified when the measurement error level increases. However, the temperature fields obtained with these poor thermal parameters are good enough for the mission thermal analysis. Several error levels, different load cases and correlation for steady-state and transient cases are studied to probe these findings

Direct Resistive Heating Simulation Tool for the Repair of Aerospace Structures through Composite Patches

Bonded composite patches are very appropriate for aircraft structural repair, showing very good properties when compared with traditional mechanical fastening of metal sheets. The curing process of the composite patch must be done “onsite” and a direct resistive heating method has been proposed. The heat produced by the electric current through the Joule effect when crossing the patch carbon fibre bundles has been modelled with a Finite Element Program code, developed for the electric current equation. The heat conduction equation has also been modelled in the program, as well as the kinetics of the curing reaction of the composite resin. The electric resistivity of the materials is function of the temperature, so a nonlinear coupled system has been developed. Therefore, a complete simulation tool able to study different configurations, current intensities, materials, etc. for the composite patches is presented. A study case has been run with the developed code and results have been compared with experimental values. Good agreement is found.This work was developed under the European Seventh FrameworkProgram, Theme7Transport, Project IAPETUS [GrantAgreementno.ACP7-GA-2008-234333]

Design and Fabrication of a Phase Change Material Heat Storage Device for the Thermal Control of Electronics Components of Space Applications

In this paper, the design and validation of a heat storage device based on phase change materials are presented, with the focus on improving the thermal control of micro-satellites. The main objective of the development is to provide a system that is able to keep electronics within safe temperature ranges during the operation of manoeuvres, while reducing mass and volume in comparison to other thermal control techniques. Due to the low thermal conductivity of phase change materials, the conductivity of the device as a whole is one of the major challenges of the development. This issue has been solved by means of the use of a lattice of aluminium fins. The thermal behaviour of the proposed solution is assessed with numerical simulation tools, and the results prove that the developed phase change material-based thermal control technique is able to provide the suitable integrated thermal management of micro-satellites. Fabrication challenges found in the project are also explained. Numerical results are validated through a testing stage. The predicted temperature profiles are in good agreement with experimental data and inside the range foreseen for the heat storage device.This work was supported by the Spanish Ministry of Economy and Competitiveness through the financial support given to the project “Soluciones térmicas para componentes espaciales basadas en materiales con cambio de fase” (ref: AYA2010-18663)

Design and Fabrication of a Phase Change Material Heat Storage Device for the Thermal Control of Electronics Components of Space Applications

In this paper, the design and validation of a heat storage device based on phase change materials are presented, with the focus on improving the thermal control of micro-satellites. The main objective of the development is to provide a system that is able to keep electronics within safe temperature ranges during the operation of manoeuvres, while reducing mass and volume in comparison to other thermal control techniques. Due to the low thermal conductivity of phase change materials, the conductivity of the device as a whole is one of the major challenges of the development. This issue has been solved by means of the use of a lattice of aluminium fins. The thermal behaviour of the proposed solution is assessed with numerical simulation tools, and the results prove that the developed phase change material-based thermal control technique is able to provide the suitable integrated thermal management of micro-satellites. Fabrication challenges found in the project are also explained. Numerical results are validated through a testing stage. The predicted temperature profiles are in good agreement with experimental data and inside the range foreseen for the heat storage device.This work was supported by the Spanish Ministry of Economy and Competitiveness through the financial support given to the project “Soluciones térmicas para componentes espaciales basadas en materiales con cambio de fase” (ref: AYA2010-18663)

Metamodels’ Development for High Pressure Die Casting of Aluminum Alloy

Simulation is a very useful tool in the design of the part and process conditions of high pressure die casting (HPDC), due to the intrinsic complexity of this manufacturing process. Usually, physics-based models solved by finite element or finite volume methods are used, but their main drawback is the long calculation time. In order to apply optimization strategies in the design process or to implement online predictive systems, faster models are required. One solution is the use of surrogate models, also called metamodels or grey-box models. The novelty of the work presented here lies in the development of several metamodels for the HPDC process. These metamodels are based on a gradient boosting regressor technique and derived from a physics-based finite element model. The results show that the developed metamodels are able to predict with high accuracy the secondary dendrite arm spacing (SDAS) of the cast parts and, with good accuracy, the misrun risk and the shrinkage level. Results obtained in the predictions of microporosity and macroporosity, eutectic percentage, and grain density were less accurate. The metamodels were very fast (less than 1 s); therefore, they can be used for optimization activities or be integrated into online prediction systems for the HPDC industry. The case study corresponds to several parts of aluminum cast alloys, used in the automotive industry, manufactured by high-pressure die casting in a multicavity mold.This work was supported by projects OASIS and SMAPRO. The OASIS project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No 814581. The SMAPRO project has received funding from the Basque Government under the ELKARTEK Program (KK-2017/00021)

Lamellar Spacing Modelling for LPBF Aluminum Parts

The high cooling rates reached during metal additive manufacturing (MAM) generate microstructures very different from those obtained by other conventional manufacturing methods. Therefore, research about the modeling of this type of microstructure is of great interest to the MAM community. In this work, the prediction of the lamellar spacing of an AlSi10Mg sample manufactured by laser powder bed fusion (LPBF), is presented. A multiscale approach is used, combining a CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) model to predict the material properties, with a macroscale model of the sample manufacturing and with a microscale model to predict the microstructure. The manufacturing and metallographic characterization of the sample is also included. The results prove that the multiscale strategy followed is a valid approximation to simulate this type of manufacturing process. In addition, it is shown that the use of a generic simulation software focused on metal casting processes can be useful in predicting the lamellar spacing of the microstructure manufactured by LPBF. Finally, the relationship between the cooling rate and the resulting lamellar spacing has been established for this AlSi10Mg under the specific manufacturing conditions considered.This work was supported by the ICME project, which has received funding from the Basque Government under the ELKARTEK Program (KK-2021/00022)