Design of a Sublimator Driven Coldplate Development Unit

<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="htmlview paragraph">The increasing need for higher electrical power levels for military and scientific space purposes has spurred development of energy conversion systems with higher efficiencies than the traditional solar array. Numerous nuclear options are currently under development. These fuels eliminate the need for large deployable solar arrays or concentrators, allow unrestricted pointing and maneuvering, and are inherently less susceptible to natural and threat environments; they are the only viable energy source for outer planetary exploration. Fission reactors are the most desirable nuclear source for electric power levels above 10 kW. Radioisotope sources have been used in conjunction with thermoelectrics up to 1 kWe for planetary exploration. However, for radioisotope systems in the 1 to 10 kWe range, a much higher conversion efficiency is required. For over 15 years, NASA and the Department of Energy (DOE) have been developing closed cycle turbo-alternator (dynamic) power conversion systems for space use. The Air Force and DOE are jointly developing such a system under the Dynamic Isotope Power System (DIPS) program.</div> <div class="htmlview paragraph">Two closed dynamic cycles are being evaluated for use as part of the DIPS system. They are the Closed Brayton Cycle (CBC) which uses an inert (single phase) gas as the working fluid. The other system is the Organic Rankine Cycle (ORC) which utilizes the phase change properties of the working fluid. Each has a significantly different effect on the design of a radiative heat rejection system, primarily because of the temperature variation of the CBC single phase heat rejection versus the nearly constant temperature two-phase (condensing) ORC heat rejection. The heat rejection system plays an important role, since the power conversion efficiency is strongly dependent on the heat rejection temperature. The lower the rejection temperature, the higher the efficiency. However, the radiator area requirement increases as the rejection temperature is reduced. On a weight optimization basis both systems are comparable, however, the ORC system requires more radiator area for the same cycle efficiency. With the design requirement that the radiator be mounted around the circumference of the vehicle, available area is limited. Therefore, the heat rejection system design may not be a clear-cut weight optimization but rather a matter of area reduction at minimum penalty to efficiency and weight.</div> <div class="htmlview paragraph">The paper presents the results of an optimization study performed on the heat rejection system for a space based ORC power system using an isotope heat source. The radiator sizing depends on the heat rejection temperature, radiator configuration, and radiator properties such as the fin effectiveness, emissivity, and absorptivity. The optimization analysis to evaluate the effect of each of these parameters on the system weight and area is presented.</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">A porous plate sublimator (based on an existing Lunar Module LM-209 design) is baselined as a heat rejection device for the X-38 vehicle due to its simplicity, reliability, and flight readiness. The sublimator is a passive device used for rejecting heat to the vacuum of space by sublimating water to obtain efficient heat rejection in excess of 1,000 Btu/lb of water. It is ideally suited for the X-38/CRV mission as it requires no active control, has no moving parts, has 100% water usage efficiency, and is a well-proven technology.</div><div class="htmlview paragraph">Two sublimators have been built and tested for the X-38 program, one of which will fly on the NASA V-201 space flight demonstrator vehicle in 2001. The units satisfied all X-38 requirements with margin and have demonstrated excellent performance. Minor design changes were made to the LM-209 design for improved manufacturability and parts obsolescence.</div><div class="htmlview paragraph">This paper presents sublimator performance, including ground test data at both CRV and off-design conditions and also contains a discussion on sublimator integration into the vehicle. Sublimator operation at ambient pressure while boiling a sea-level evaporant (such as HCFC-124) is also discussed as it could enable expanded CRV ECLSS system capability during the post-landing phase of the mission.</div></div>

Objective. The article deals with heat removal from computer processors in order to provide the necessary thermal conditions and temperature control of heat-generating components on integrated circuits.Methods. Methods for modeling heat exchange processes during heat transfer from a heated integral crystal to the environment are applied.Results. The power efficiency of heat rejection processors increases when using radiating thermoelectric semiconductor devices since heat is absorbed in some junctions, and instead of generating heat photons of the ultraviolet range are emitted to obtain better energy characteristics to ensure the necessary power removal from the heatgenerating components of radio-electronic circuits. This approach has a significant advantage as radiation has the maximum speed when transferring energy compared to convection and conduction, which allows for non-inertial heat removal from heat-generating components to the environment. This approach also allows increasing the efficiency of the cooling system and accelerating the transfer of heat from the heated areas to prevent heat breakdown.Conclusion. The conducted research allows concluding that light-emitting thermoelectric semiconductor devices can be used for cooling with high power efficiency, which can transfer large amounts of power to the environment with low inertia. An innovative cooling system for computer processors allows increasing the degree of integration by several orders of magnitude, which will increase the performance of computers and their speed.

<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>

Doubly-fed induction generator (DFIG) has been widely used in variable-speed constant-frequency (VSCF) wind energy generation system. Vector control is already applied to the DFIG control, which makes the DFIG gain good performance in the wind energy capturing operation. But in the two traditional vector control schemes, the stator magnetizing current is considered invariant in order to simplify the rotor current inner-loop controller. The two schemes are capable of performing very well when the grid is in normal condition. However, when the grid disturbance, such as grid voltage dip or swell fault, occurs, the control performance will be getting worse, the rotor over current will occur, which seriously reduce the ride-through ability of the DFIG wind energy generation system. Based on the accurate model of the DFIG, the deficiency of the traditional vector control is deeply investigated. The improved control schemes of the two typical traditional vector control schemes used in DFIG is proposed, and the simulation study of the proposed and traditional control schemes is carried out. The validity of the proposed modified schemes to control the rotor current and to improve the ride-through ability of the DFIG wind energy generation system is proved by the comparison study

<div class="htmlview paragraph">An investigation was performed to determine the effects of applying on-highway heavy-duty diesel engine emissions reduction technology to an off-highway version of the engine. Special attention was paid to the typical constraints of fuel consumption, heat rejection, packaging and cost-effectiveness.</div> <div class="htmlview paragraph">The primary focus of the effort was NO<sub>x</sub>, reduction while hopefully not worsening other gaseous and particulate emissions. Hardware changes were limited to “bolt-on” items, thus excluding piston and combustion chamber modifications.</div> <div class="htmlview paragraph">In the final configuration, NO<sub>x</sub> was improved by 28 percent, particulates by 58 percent, CO and HC were also better and the fuel economy penalty was limited to under 4 percent.</div> <div class="htmlview paragraph">Observations are made about the effectiveness of various individual and combined strategies, and potential problems are identified.</div>

<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">On July 2nd, 1985 the Giotto spacecraft was launched from Kourou (French Guyana) towards its encounter with Halley’s comet on 13-14 March 1986.</div> <div class="htmlview paragraph">This first European Space Agency interplanetary spacecraft was spin stabilized and weighed 960 kg at launch. Giotto was injected into a heliocentric orbit involving variations of the solar intensity by a factor of two. This fact together with the communications requirements and comet encounter geometry restricted the spacecraft attitude such that during the 9 month mission all external surfaces were illuminated by the sun, imposing severe limitations on the use of any surface for efficient heat rejection.</div> <div class="htmlview paragraph">The spacecraft thermal control subsystem included several heater circuits and three “thermal shutters” operated by ground command. The daily configuration of these items was balanced between thermal and power requirements.</div> <div class="htmlview paragraph">This paper presents an outline of the design characteristics of the spacecraft, its thermal control capabilities and a detailed summary of the flight performance.</div>

<div class="section abstract"><div class="htmlview paragraph">The aim of this work is to investigate the possibility of heat insulation by “Temperature Swing”, that is temperature fluctuation, on combustion chamber walls coated with low-heat-conductivity and low-heat-capacity materials.</div><div class="htmlview paragraph">Adiabatic engines studied in the 1980s, such as ceramic coated engines, caused constantly high temperature on combustion wall surface during the whole cycle including the intake stroke, even if it employed ceramic thermal barrier coating methods. This resulted in increase in NOx and Soot, decrease in volumetric efficiency and combustion efficiency, and facilitated the occurrence of engine knock.</div><div class="htmlview paragraph">On the other hand, “Temperature Swing” coat on the combustion chamber walls leads to a large change in surface temperature. In this case, the surface temperature with this insulation coat follows the transient gas temperature, which decreases heat loss with the prevention of intake air heating, and also which is expected to prevent NOx and Soot from increasing. In our calculations, the increase of the surface temperature fluctuation, “Temperature Swing” results from the coat of lower heat conductivity and lower heat capacity. Particularly in Gasoline engines, the coat with the appropriate thickness can reduce the heat flux from the wall to the working gas during intake stroke and can avoid engine knock.</div><div class="htmlview paragraph">Based on our calculations, it is clarified that both the prevention of intake air heating and the low heat rejection were successfully possible with the material of appropriate thermo-physical properties.</div><div class="htmlview paragraph">In addition to the calculations, a preliminary test-piece experiment was executed. It was demonstrated that the surface temperature of a porous coat, that is a candidate of “Temperature Swing” coat, immediately follows the transient gas temperature, and also the proposed insulation coat can exactly reduce the heat flux in the single-cylinder engine.</div></div>

<div class="htmlview paragraph">Crew Health Care Systems (CHeCS) aboard Space Station Freedom will provide unprecedented on orbit capabilities targeting a wide range of nominal and contingency health concerns, from regularly scheduled exercise countermeasures and environmental monitoring, to advanced medical life support and medical transport.</div> <div class="htmlview paragraph">CHeCS design addresses unique requirements in functional performance and equipment/user interaction within the framework of physical and operational constraints imposed by the Space Station and related space vehicles.</div> <div class="htmlview paragraph">This paper presents an overview of the design and development of CHeCS for Space Station Freedom (SSF) with an emphasis on physical installation and flight crew suitability. Particular emphasis is directed at unique aspects of the system which are driven by environmental peculiarities such as limited volume and resources (electrical power, heat rejection, crew time, launch constraints), location remoteness, isolation and microgravity, while minimizing detriment to other non-related Space Station operations. Design implications resulting from phased Space Station build-up are also described. General and specific topics involve selected component and installations designs, development testing and simulation activities, and system design integration into Space Station elements. Implications introduced by CHeCS relationships to the Space Transportation System are also presented.</div>

<div class="section abstract"><div class="htmlview paragraph">An engine cooling system is required to maintain stable operating temperature for the engine and prevent it from overheating. Thermal distortion of engine parts can take place if proper cooling is not maintained and engine may loss efficiency. One of the major problem in this domain is to incorporate separate cooling systems for the different variants of engines (different power rating). A single optimized cooling unit is desired to manage the entire range of engine rated power. The factors that affect the cooling system are front end grill opening area, air recirculation, location of snorkel inlet, radiator core size, which need to be tuned to get appropriate results. The above parameters are tuned to obtain appropriate results using the Computational Fluid Dynamics (CFD) simulations. In the next stage, on road cooling trials are performed and real time data is collected. A correlation is established between physical trials and CFD results which may be helpful in future projects as well.</div><div class="htmlview paragraph">From experimental results we observed a sufficient temperature drop in both heat exchangers (radiator and intercooler) and efficient heat rejection is made possible through the heat exchanger to maintain proper functioning temperature of engine. All trials are performed at extreme conditions i.e. full throttle, 100% load and high gradient conditions, to obtain maximum possible heat rejection to coolant fluid.</div></div>

<div class="htmlview paragraph">Sciamachy is a Dutch/German Earth Observation Instrument on the European Envisat satellite, which was successfully launched on March 1<sup>st</sup>, 2002. The goal of the instrument is to observe concentrations of trace gases in the atmosphere.</div> <div class="htmlview paragraph">Due to the required optical accuracy of the instrument special thermal control methods have been incorporated in the instrument design. Amongst these are the active thermal control loops for the optical bench module.</div> <div class="htmlview paragraph">The optical bench module is therefore provided with three feedback-controlled heater loops.</div> <div class="htmlview paragraph">During the commissioning phase, the active thermal control systems in the instrument have been characterised in order to optimise their use during the operational phase of the instrument.</div> <div class="htmlview paragraph">The paper will focus on the thermal design of the optical bench, the control algorithm of the active control system, in-orbit thermal observations of the last 2 years in space, the correlation with the thermal predictions, the fine-tuning of the (temperature) setpoints of the Active Thermal Control system and the lessons learned in this process.</div> <div class="htmlview paragraph">The results show that all OBM control loops show a stability in line with predictions and well within requirements. Also the seasonal variation is in line with predictions. Only the average total power level demanded by the OBM controllers is slightly lower than predicted. However after 2 years in orbit the degradation found is significantly lower that predicted. Therefore, nominal and stable operation of the OBM will be possible for its entire lifetime.</div>

<div class="htmlview paragraph">A rotating spacecraft which encloses an atmospheric pressure vessel poses unique challenges for thermal control. In any given location, the artificial gravity vector is directed from the center to the periphery of the vehicle. Its local magnitude is determined by the mathematics of centripetal acceleration and is directly proportional to the radius at which the measurement is taken. Accordingly, we have a system with cylindrical symmetry, featuring microgravity at its core and increasingly strong gravity toward the periphery. The tendency for heat to move by convection toward the center of the craft is one consequence which must be addressed. In addition, fluid flow and thermal transfer is markedly different in this unique environment. Our strategy for thermal control represents a novel approach to address these constraints.</div> <div class="htmlview paragraph">We present data to theoretically and experimentally justify design decisions behind the Mars Gravity Biosatellite's proposed payload thermal control subassembly. The baseline system incorporates fans, thermoelectric coolers, heat fins and conducting plates to continuously and reliably remove thermal energy from the spacecraft's atmospheric pressure vessel. We present an assessment of a condensing heat exchanger with novel design enhancements to promote efficient operation in a partial gravity environment. Our approaches are validated by experimental data from a prototype of the thermal control subassembly within a new engineering mockup of the spacecraft's payload module.</div> <div class="htmlview paragraph">This work provides novel insights into issues of thermal control in artificial gravity environments. This research can inform ECLSS designs for future human-rated vehicles which may incorporate centrifugation as a countermeasure for musculoskeletal deconditioning.</div>