Stochastic Approach to Spacecraft Thermal Control Subsystem

<div class="htmlview paragraph">The Columbus laboratory module, developed by Astrium Bremen as prime contractor and Alenia Spazio as co-prime, is the European contribution to the International Space Station (ISS) program and as such it will support, once in orbit, micro-gravity and space based research activities of the member states.</div> <div class="htmlview paragraph">Columbus Environmental Control System (ECS) employs an Environmental Control and Life Support System (ECLSS) providing atmosphere pressure, cabin ventilation and temperature humidity control inside the module in conjunction with an autonomous Active Thermal Control System (ATCS) that provides the heat collection capability. The ATCS, based on software controlled water loop, provides also the cooling capability for Payloads and Subsystem equipment. The ECS is completed with the Passive Thermal Control System based on software controlled shell heating system plus passive fixtures such as Multi-Layers Insulation (MLI) blankets.</div> <div class="htmlview paragraph">Generally, both, the Columbus ATCS as well as the ECLSS are qualified via simplified but representative tests and concluding analyses. Complete verification of the module thermal and environmental control design however, will be performed via analysis supported by ECS System Level Integrated Test as well as the predictions for flight.</div> <div class="htmlview paragraph">With respect to responsibility sharing, Alenia is responsible for all verification by test related to thermal/environmental aspects, i.e. Alenia will define the test requirements and cases to be performed via the establishment of a dedicated test specification. On the other side, definition and production of the test set-up as well as the performance of the test is assigned to the Columbus prime Astrium SI Bremen.</div> <div class="htmlview paragraph">In order to get confidence on the functional performance of the Columbus ECS and to validate the Integrated Overall Thermal Mathematical Model (IOTMM) on system level the module will be subjected to an Integrated System Test (IST).</div> <div class="htmlview paragraph">Purpose of the ECS IST is to provide the first verification of the thermal/environmental interrelation between the active cooling (ATCS) and environmental control system (ECLSS) hardware and software and to collect as much characteristic thermal data as possible for the validation of the flight configuration IOTMM. This test will represent the second and last test in series on the flight configuration of the Columbus module.</div> <div class="htmlview paragraph">Previous tests, for verification of the functional interfaces of the ATCS and ECLSS, have been performed already in the frame of the Electrical Test Model (ETM) utilization. However, this test did not provide information on environmental and thermal parameters of the system but rather on the functional interrelations of the relevant units of the subsystems. Presently, the subject test will be performed in the integration hall of Astrium SI Bremen (Class 100.000 clean room conditions) and the pressurized shell is planned to be covered by the flight multi-layer insulation only located beneath the meteoroid debris panels (MDPS) of the module. However, in order to get as much as possible characteristic data of the system not only the test cases have to be selected very carefully but also additional test supporting equipment (TSE) has to be evaluated.</div> <div class="htmlview paragraph">The present paper summarizes the efforts generated to establish the Environmental/Thermal test in the frame of the system level IST of the Columbus module, describes the interrelation aspects of the thermal/environmental subsystem verification by test and analysis and presents the derived methodologies and expected results.</div>

<div class="htmlview paragraph">The intensive endeavor of the human, to do research work and to test in the low earth orbit, results in complex orbital platforms. These space based platforms are either permanent or retrievable. This is the case of the European Retrievable Carrier (EURECA), a free-flying reusable platform that is launched and retrieved by the NSTS Orbiter. The first EURECA mission will be primarily a microgravity mission specifically for material processing and life science payloads.</div> <div class="htmlview paragraph">The thermal control system of EURECA has to ensure the correct environment for the carrier and the payload, throughout all mission phases, by means of passive and active means. The passive means consist of various multi-layer insulations, surface finishing, conducting straps. Electrical heaters work, in conjunction with the active cooling loop, to keep the spacecraft temperature at adequate level. The cooling loop consists of a single phase Freon 114 pumped loop, with two radiators in parallel. The possibility to accommodate different payload heat dissipations is ensured also by the capability of the system to bypass one of the two radiators.</div> <div class="htmlview paragraph">The degree of on-board autonomy required for EURECA, mainly due to the very short ground contact periods, necessitates a sophisticated control of the thermal functions performed by a dedicated on-board computer.</div> <div class="htmlview paragraph">The thermal control of EURECA is believed to be a good example of the System Thermal Control of today, which means a maximum of flexibility in the development, manufacturing and operation. This is required for the high density, complex structure, different mission profiles, considerations of retrieval capability, adaptation of future payloads and take over of non-thermal related tasks of today's spacecraft's.</div> <div class="htmlview paragraph">This paper deals both with the development and verification of the thermal control system design and with its operational aspects.</div> <div class="htmlview paragraph">In addition examples are given to show how the model development, the implementation of the different requirements and the design solutions are made, in case of problems not solvable by the affected subsystems alone, namely:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">Missing power interface for a payload in some mission cases</div> </li> <li class="list-item"> <div class="htmlview paragraph">Electronic design problem of the 20 N thruster chamber temperature monitoring</div> </li> <li class="list-item"> <div class="htmlview paragraph">High temperature of the battery due to specification problems</div> </li> <li class="list-item"> <div class="htmlview paragraph">Power shortage during operational phase</div> </li> </ul> </div> <div class="htmlview paragraph">The paper is completed by a critical review (lesson learned) of the performed System Thermal work, in which the authors give also some suggestions for improvements.</div>

<div class="section abstract"><div class="htmlview paragraph">Battery temperature is known to have a critical influence on overall battery pack performance, from electrochemical behavior, charge acceptance, power availability, trip efficiency, safety, reliability and life-cycle costs. Temperature monitoring is critical to ensure safe and reliable battery pack operation.</div><div class="htmlview paragraph">Monitoring of cell temperatures in battery packs allows for control and estimation algorithms that can ensure homogenous pack temperature distribution, prevent excessive pack temperature rise and even infer cell core temperature, potentially allowing to both predict and mitigate onset of thermal runaway.</div><div class="htmlview paragraph">The increasing need for improved accuracy requires inclusion of more detail in the modelling stage, leading inevitably to ever larger-scale, ever more complex dynamical systems. Simulations in such large-scale settings lead in turn to unmanageably large demands on computational resources, which is the main motivation for Model Order Reduction.</div><div class="htmlview paragraph">Model Order Reduction is focused on reducing the complexity of large-scale dynamical systems, while preserving their input-output behavior. Reduced models mimic the complex behavior of large-scale dynamical systems, and can be efficiently used for design, optimization and sensitivity analysis. The resulting reduced order model can be used to replace the original system as a component in a larger simulation or it might be used to develop a simpler and faster controller suitable for real time applications.</div><div class="htmlview paragraph">Three model order reduction techniques are compared. The first method, Balanced Truncation, assumes access to the high-fidelity model structure is available whilst the other two, Nyquist and neural network approximation, assume only input/output behavioral knowledge is available. The reduced order models are compared, in simulation, to a high-fidelity model of a battery pack in terms of simulation speed-up, model accuracy and property preservation. The applicability of each technique for real-time applications, particularly in the context of xEV (grid connected electric vehicle) thermal management, together with pros and cons of each method is discussed.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This report proposes a rheological model and a thermal analysis model for oil films, which transmit power through a variator, as a prediction method for the maximum traction coefficient, and then describes the application and verification of this method.</div><div class="htmlview paragraph">The rheological model expresses the conditions inside the contact ellipse using a combination of viscosity and plasticity.</div><div class="htmlview paragraph">The thermal analysis model for oil films was confirmed by comparison of previously obtained temperatures directly measured from the traction contact area of the four-roller experimental apparatus [<span class="xref">1</span>]. The measurement used a thin-film temperature sensor and the consistency between the calculated and measured values was verified in the estimation model by reflecting the precise thermal properties of the thin film. Most values were consistent with the calculated values for the middle plane local shear heating model inside the oil film. However, under some conditions, the values were closer to those calculated for homogeneous shear. Based on these results, this paper proposes a calculation method that combines both heating models within the contact ellipse.</div><div class="htmlview paragraph">In addition, the variator in a continuously variable transmission (CVT) was verified for the first time by using a test box to take direct temperature measurements from the transmission contact area in the CVT. This test verified the precision of the thermal analysis model, including the spin motion.</div><div class="htmlview paragraph">Finally, the maximum traction coefficient was estimated using these calculation models and compared with measured values.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Modern automotive powertrains are increasingly adopting engine downsizing and down speeding to meet stringent emission regulations and improving fuel efficiency However, these changes result in higher torsional vibrations excitation amplitudes and NVH (Noise, Vibration, and Harshness) refinement more challenging. With growing customer expectations for premium driving experiences conventional clutch is no longer sufficient. To meet the NVH performance targets of the vehicle Dual Mass Flywheels (DMFs) are used</div><div class="htmlview paragraph">In DMF due to lower stiffness and inertia separation there is a greater advantage on torsional filtration in normal drive and idle condition. But the torsional resonance frequency of the connected DMF is lower than the idle RPM. Engine startup is a key drawback with DMF equipped vehicles. The proper tuning of starter motor performance & DMF stiffness is required to cross the resonance zone faster otherwise it will lead to DMF to stay in the resonance zone for a longer time leading to structural failure over the period.</div><div class="htmlview paragraph">In this paper we focus on DMF resonance crossing during engine startup condition in the 3 Cylinder Gasoline application. Test measurement is done to capture the startability behavior of DMF. AMESIM 1D simulation model is developed to reproduce the DMF resonance behavior and relative displacement between Primary and secondary flywheel is simulated. Optimization of DMF Spring stiffness between stages are proposed based on correlated simulation model. With the new design of DMF, the startability of the vehicle has improved & also the DMF displacement is reduced within the design limit. This evaluation method gives quick assessment on startability improvement in DMF equipped vehicles.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In recent years, emission regulations have been getting increasingly strict. In the development of engines that comply with these regulations, in-cylinder pressure plays a fundamental role, as it is necessary to analyze combustion characteristics and control combustion-related parameters. The analysis of in-cylinder pressure data enables the modelling of exhaust emissions in which characteristic temperature can be derived from the in-cylinder pressure, and the pressure can be used for other investigations, such as optimizing efficiency and emissions through controlling combustion.</div><div class="htmlview paragraph">Therefore, a piezoelectric pressure sensor to measure in-cylinder pressure is an essential element in the engine research field. However, it is difficult to practice the installation of this pressure sensor on all engines and on-road vehicles owing to cost issues. Therefore, there have been several studies aiming to estimate the in-cylinder pressure using only the data available from the Engine Control Unit (ECU) without an additional pressure sensor.</div><div class="htmlview paragraph">An in-cylinder pressure prediction model for conventional light-duty diesel engines had been established by authors and described in this paper. First, the pressure during the compression stroke was estimated using a variable polytropic index. Next, the Wiebe function was applied to describe pressure during pilot and main combustion. This prediction of the in-cylinder pressure was established for real-time estimation.</div><div class="htmlview paragraph">The complete pressure prediction model consists of subordinate models, where physical phenomena are simplified for the real-time application of the model. The accuracy of the submodels has a direct influence on the error in the parent model the pressure prediction. Therefore, sensitivity analysis was conducted in this study to verify the effect of the submodels, including the polytropic index model, ignition delay model, heat loss model and combustion duration model, on the entire pressure prediction model. This study will contribute to establishing a more accurate pressure prediction through sensitivity analysis and will be useful to many studies that require in-cylinder pressure information.</div></div>

<div class="htmlview paragraph">In the course of establishing a thermal mathematical model of the pressurized volumes of the HERMES Spaceplane, it was found that the flow field in these volume strongly influences the overall thermal behaviour of the ACS (Atmosphere Control Section).</div> <div class="htmlview paragraph">The analysis of the flow field was carried out to get more detailed information about the heat transfer between the walls and the air inside the Spaceplane. Furthermore, the effects of gravity and mixing of return air from other volumes were studied.</div> <div class="htmlview paragraph">The analysis was carried out with the PHOENICS Software Package, specially developed for fluiddynamic simulations.</div> <div class="htmlview paragraph">The results gained by use of a two dimensional flow field indicate that gravity effects are neglectible due to the relatively high air velocities of the forced convection prevailing during all mission phases. Free convection does not contribute to the air movement.</div> <div class="htmlview paragraph">With a three dimensional flow field model the mixing effects were studied. It will be shown that the return air from the capsule does not seriously affect the flow field in the cabin, if air outlets and diffusore are placed correctly.</div> <div class="htmlview paragraph">A slightly varied 3-d model was used to determine the heat transfer coefficient between the walls and the air. Exact values will be determined when the final configuration of the cabin interior will be fixed.</div>

<div class="htmlview paragraph">The aim of this paper is to present the Hermes Thermal Control Concept which constitutes the reference baseline for the phase 2 of the Hermes program.</div> <div class="htmlview paragraph">The technical solutions based on active and passive means, are dictated by a variety of requirements including temperature and heat flux limits, mass & power minimization, availability of space for accommodation of TCS devices.</div> <div class="htmlview paragraph">Furthermore thecomplex mission profile (including atmospheric flight and several modes of operation o002d;orbit) and the configuration of the space-vehicle, require the adoption of a particularly flexible thermal control.</div> <div class="htmlview paragraph">The <b>ATCS (Active Thermal Control Section)</b> is based on a dual loop concept, using both water and Freon R114 cooling loops for heat collection from the various sources, heat transportation and heat rejection through dedicated devices.</div> <div class="htmlview paragraph">The main heat sources to be considered are those extracted from the cabin air loop, the electronics, the power generation items (fuel cells and lithium batteries) and the environmental loads during ascent and re-entry.</div> <div class="htmlview paragraph">The major heat rejection devices are the Ground Support Equipment Heat Exchangers (on ground, before launch and after landing), the Ammonia Boilers during ascent or re-entry (low altitude), the Hermes Radiators on orbit, the Water Evaporators during ascent and re-entry (high altitudes) and to complement the radiator rejection capability.</div> <div class="htmlview paragraph">The <b>PTCS (Passive Thermal Control Section)</b> relies on different concepts of insulations together with a system of temperature sensors and heaters, to control the thermal excursions of the space-plane components and structural parts, within the specified limits.</div> <div class="htmlview paragraph">Thermal insulation blankets (foams, thermal control coatings, multi layer insulations) involve an extensive material research and testing activity, since they are subjected to quite different conditions: vacuum, atmospheric, internal, external and very different level of temperatures depending on the location.</div> <div class="htmlview paragraph">The present design of the Thermal Control Subsystem is oriented to the minimization of mass and power budgets and to respect the quantitative and qualitative safety and reliability requirements.</div>

<div class="section abstract"><div class="htmlview paragraph">The electrification of mobility is a major inflection point for reducing greenhouse gas emissions and air pollutants from the transportation sector. In this context, the Li-ion battery is currently the technology shared by automakers to provide the energy storage needed to deploy electrified vehicles.</div><div class="htmlview paragraph">However, Li-ion batteries can undergo incidents with dramatic consequences, referred to as thermal runaway (TR). This can result from abnormal conditions: excessive temperature, mechanical deformation, electrical overcharge, internal short circuit. TR is characterized by a violent reaction, that is, difficult to control and can release hazardous gases. This issue is today a crucial safety concern that strongly impacts the design and the battery management strategies.</div><div class="htmlview paragraph">The objective of this study is to contribute to the understanding of the phenomena by focusing on the variability of the battery cell (BC) TR induced by thermal initiation. The commercial BC used is an 21700 cylindrical LG M50LT with state-of-the art active materials: NMC811 for the positive electrode and silicon graphite composite for the negative electrode.</div><div class="htmlview paragraph">The variability of the TR phenomenon is analyzed experimentally using two different devices: the first is Accelerating Rate Calorimeter (an ARC) with the specific Heat Wait and Search protocol and, the second, is a high-pressure/high-temperature vessel, based on constant heating ramps, using specific instrumentation with optical access to visualize the combustion phases.</div><div class="htmlview paragraph">The variability of the TR phenomenon is subsequently examined through essential key parameters as cell self-heating onset, venting event and accelerated TR temperature.</div><div class="htmlview paragraph">Finally, a calibrated and validated TR model for the BC studied allows the observed phenomena to investigating by confronting the experimental results with a sensitivity analysis of the model.</div><div class="htmlview paragraph">The results allow to highlight the interest of considering the variability of the TR phenomenon by thermal initiation for numerical calibration.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Crash tests of vehicles by striking deformable barriers are specified by Government programs such as FMVSS 214, FMVSS 301 and the Side Impact New Car Assessment Program (SINCAP). Such tests result in both crash partners absorbing crush energy and moving after separation. Compared with studying fixed rigid barrier crash tests, the analysis of the energy-absorbing behavior of the vehicle side (or rear) structure is much more involved. Described in this paper is a methodology by which analysts can use such crash tests to determine the side structure stiffness characteristics for the specific struck vehicle. Such vehicle-specific information allows the calculation of the crush energy for the particular side-struck vehicle during an actual collision – a key step in the reconstruction of that crash.</div><div class="htmlview paragraph">Based on fundamental principles of physics and engineering, this methodology provides transparency in the calculation of side structure stiffness parameters for the particular vehicle of interest. Additionally, sample calculations are presented. Utilizing widely available computational tools and publicly available test data, the method was applied to a representative sample of recent-model vehicles.</div><div class="htmlview paragraph">The results of this study show that variability in side structure stiffness from vehicle to vehicle appears to be real – not an artifact of computational method or data uncertainty – and not necessarily related to vehicle size or weight, for example. Independent tests of comparable vehicles, while few in number, produce remarkably similar stiffness results.</div><div class="htmlview paragraph">Supported by sensitivity analyses, various simplifications are presented that in most cases will allow a good approximation to more rigorously-derived results.</div></div>

<div class="section abstract"><div class="htmlview paragraph">With an objective of improving the range as well as other safety and comfort aspects, thermal management becomes increasingly important in the development of electrified vehicles both at the component as well as system level. The considerable increase in complexity of the thermal management system and its tighter interactions with the complete vehicle is driving an increasing trend towards system simulation compared to expensive testing.</div><div class="htmlview paragraph">At the system level, different sub-systems interact with each other at varying extents. An example of one such strong interaction is between the coolant and AC circuits using battery chillers. Thermal management system simulation models must be capable of simulating such interactive systems.</div><div class="htmlview paragraph">At the component level, ensuring the efficacy of the several components used in these intricately linked systems becomes increasingly important. An accurate prediction of temperature distribution inside the battery pack is essential to avoid damaging situations such as thermal runaway. An integrated approach of 1D-flow inside the cooling plates combined with 3D-thermal analysis of battery cells and cooling plates in GT-SUITE is described in this study.</div><div class="htmlview paragraph">Also, a new predictive electrochemical and thermal battery models to analyze and optimize both component and system level behavior is described. This allows selection of cell chemistry and design in addition to providing heat rejection values for design of the cooling system. Aging predictions at both the cycle and calendar time scales are described that consider effects of varying environmental and operating conditions.</div><div class="htmlview paragraph">After the e-powertrain, the HVAC compressor is the largest consumer of electrical energy. For optimizing compressor power consumption without compromising on human thermal comfort attention is focused on localized cooling inside the cabin. This paper outlines an integrated co-simulation approach, that allows an investigation of the trade-off between passenger comfort and driving range, or to develop smart controls of the HVAC system.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This study focuses on enhancing energy efficiency in electric vehicle (EV) thermal management systems through the development and optimization of control logic.</div><div class="htmlview paragraph">A full vehicle thermal management system (VTMS) was modeled using GT-Suite software, incorporating subsystems such as the high voltage battery (HVB), Electric powertrain (EPT), and an 8-zone cabin. Thermal models were validated with experimental data to ensure accurate representation of key dynamics, including coolant to cell heat transfer, cell-to-ambient heat dissipation, and internal heat generation.</div><div class="htmlview paragraph">Control strategies were devised for Active Grille Shutter (AGS) and radiator fan operations, targeting both cabin cooling and EPT thermal regulation. Energy consumption was optimized by balancing aerodynamic drag, fan power, and compressor power across various driving conditions. A novel series cooling logic was also developed to improve HVB thermal management during mild ambient conditions.</div><div class="htmlview paragraph">Simulation results demonstrate significant energy savings while maintaining desired thermal performance, showcasing a systematic approach to sustainable EV thermal management</div></div>

<div class="htmlview paragraph">Crash severity is quantified by the change in velocity experienced by a vehicle during an impact along with the time duration over which that change in velocity occurs. Since the values of the input parameters for calculating the change in velocity are not known exactly, there is uncertainty associated with the calculated change in velocity. Accurate evaluation of the crash severity will, therefore, include analysis of the effect that uncertainties in the values of the input parameters have on the calculated change in velocity. Monte Carlo simulation, a statistical technique, enables the reconstructionist to evaluate the effect of uncertainty on the analysis of crash severity.</div> <div class="htmlview paragraph">Use of the Monte Carlo simulation technique is beneficial since a reconstructionist can enter a range of values for each input parameter. A probability distribution can be assigned to the range of values, which indicates the likelihood that any value in that range corresponds to the actual value of the parameter. The simulation generates thousands of possible combinations of the input parameters selected from the specified ranges, monitors the results of the combinations and analyzes them statistically. Application of the Monte Carlo technique is intended to improve the legitimacy of crash severity analysis by helping the reconstructionist consider a wide range of possible solutions within the bounds of the imperfect data and report statistically meaningful ranges for the change in velocity.</div> <div class="htmlview paragraph">This paper demonstrates the application of the Monte Carlo technique to impact severity analysis using a derived two-dimensional, rigid body, momentum-based impact model. Thorough guidance is given to aid the reconstructionist in integrating the momentum model with the Monte Carlo simulation technique and this method is illustrated with a case study. Since the impact model employs restitution constraints in the normal and tangential directions, the effect of uncertainty in formulating appropriate ranges for the values of the restitution coefficients is discussed.</div>

<div class="section abstract"><div class="htmlview paragraph">In the view point of driving safety, the crosswind sensitivity of a vehicle becomes more important, as the driving speed in highway gets higher in these days. The sensitivity of a vehicle to crosswind depends on many factors, including the design of the suspension and aerodynamics of the body, etc. However, the knowledge about this phenomenon has still to be improved, in order to develop vehicle with optimum characteristics for crosswind stability.</div><div class="htmlview paragraph">In this research, the physics behind the sensitivity of a vehicle is discussed in detail through various kinds of virtual test using computer aided engineering (CAE) simulation scheme. In the first, a reliable simulation model for vehicle, driver, wind generator and interactions among them is built. This simulation model is verified by comparison with test results of real vehicle. Then, the sensitivity analysis is carried out to find out the most influential design parameters. Finally, an automated design optimization process is carried out based on sensitivity analysis results by connecting virtual test environment to process integration & design optimization (PIDO) tool.</div><div class="htmlview paragraph">With this procedure, both deep understanding of interaction among vehicle, driver and crosswind, and optimized set of design parameter to make a vehicle robust against the disturbance by crosswind can be achieved.</div></div>

<div class="htmlview paragraph">The results are presented of a thermal balance test performed at subsystem level on the thermal model of EURECA (EUropean REtricvable CArrier) in the ESTEC LSS Vacuum Chamber.</div> <div class="htmlview paragraph">The test article, thermally representative of the most relevant items of the flight unit, was equipped both with “passive” thermal control hardware (MLI blankets, heaters) and “active” thermal control hardware (fluid loop, cold plates, radiators).</div> <div class="htmlview paragraph">This test consisted of several phases with different functioning conditions. Solar lamps and heated plates were used to reproduce solar, albedo and IR fluxes.</div> <div class="htmlview paragraph">The analysis of the test results confirmed the adequacy of the thermal control design, in particular, of the key items of the fluid loop and MLI, while an extensive correlation campaign validated the thermal mathematical model.</div>