Darius Nikanpour

Optical switching of vanadium dioxide thin films deposited by reactive pulsed laser deposition

The parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films. It is observed that the O2 concentration in Ar gas and the total deposition pressure are critical in stabilizing the single VO2 phase. Thermochromic VO2 and V1−xWxO2 (x=0.014) thin films were synthesized on various substrates (silicon, quartz, and sapphire) at 5% of O2/Ar ratio gas and total pressure of 90 mTorr. The structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100 °C. The observed transition temperature was about 36 °C for W-doped VO2 compared to 68 °C for VO2 films. This transition temperature was then lowered by about 22.85 °C per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/°C for VO2 and about 1.90%/°C for W-doped VO2. Using the pump...

Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) smart coatings grown by reactive pulsed laser deposition

Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) (LSMO) smart coatings were synthesized on (100) silicon and (0001) sapphire substrates by means of reactive pulsed laser deposition process at relatively low substrate temperature (500°C) and without postannealing. X-ray diffraction patterns indicated that all deposited LSMO films have polycrystalline structures. The energy dispersive x-ray spectroscopy analysis indicated approximately the same La∕Sr ratio in the formed LSMO coatings as in their corresponding targets. While, the x-ray photoelectron spectroscopy analysis of the LSMO/sapphire revealed that the strontium segregate at the film surface. The thermochromism of LSMO coatings was investigated by measuring their infrared reflectance as a function of temperature (up to 160°C). It was observed that the reflectance decreased as the temperature increased. Reflectance switching of about 25% was achieved in La0.7Sr0.3MnO3∕Si at a wavelength of 5μm. The sheet electrical resistivity as a function of temperature (up to 130°C) of LSMO/sapphire was investigated by means of the standard four-point probe technique. The resistivity decreased with increasing the temperature and no metallic-to-insulator transition was observed. However, it is found that the resistivity is very sensitive to the concentration level of Sr dopant: the resistivity decreased as the concentration of Sr increased. In addition, at room temperature, a higher temperature coefficient of resistance of −2.30%∕°C was achieved in La0.9Sr0.1MnO3 thin films. Finally, these LSMO smart coatings are promising materials for optical switching and IR uncooled bolometer devices.Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) (LSMO) smart coatings were synthesized on (100) silicon and (0001) sapphire substrates by means of reactive pulsed laser deposition process at relatively low substrate temperature (500°C) and without postannealing. X-ray diffraction patterns indicated that all deposited LSMO films have polycrystalline structures. The energy dispersive x-ray spectroscopy analysis indicated approximately the same La∕Sr ratio in the formed LSMO coatings as in their corresponding targets. While, the x-ray photoelectron spectroscopy analysis of the LSMO/sapphire revealed that the strontium segregate at the film surface. The thermochromism of LSMO coatings was investigated by measuring their infrared reflectance as a function of temperature (up to 160°C). It was observed that the reflectance decreased as the temperature increased. Reflectance switching of about 25% was achieved in La0.7Sr0.3MnO3∕Si at a wavelength of 5μm. The sheet electrical resistivity as a function of temper...

Phoenix Mars Lander Mission: Thermal and CFD Modeling of the Meteorological Instrument based on Flight Data

The Phoenix Mars Lander, launched on August 4, 2007, landed in the northern Vastitas Borealis region on May 25, 2008 and operated successfully in this harsh environment for more than five months (far beyond its planned 90-day lifespan). The Lander was equipped with instruments designed to investigate the Martian mineralogy, geochemistry and atmosphere. One of these instruments, the Canadian Meteorological Instrument (MET), has successfully measured the location and the extent of clouds, fog and dust in Mars’ lower atmosphere, as well as the gas temperature and pressure. These measurements have provided Canadian scientists a unique opportunity to study the Martian atmosphere and enhanced the understanding of Canadian expertise of the red planet. The MET instrument was composed of multiple elements in order to fulfil the science objectives. The MET Light Imaging Detection and Ranging (LIDAR) probed the atmosphere by sending out laser pulses and measuring the backscattered returns. The MET mast, instrumented with three thermocouples, measured the atmosphere temperature at three different heights; and a Telltale, installed at the tip of the mast, measured wind speed and direction. The upper Payload Electronic Box (PEB) housed the MET barometric pressure sensor and the MET main electronics. From this successful mission, substantial amounts of data were collected to satisfy the science goals, but very few data for validation and correction of the instrument measurements. In the thermal design and analysis of the MET instruments, many assumptions were made. One of the key assumptions was the determination of the proper convective heat transfer coefficients between the instrument surfaces and Martian atmosphere, applicable both inside and outside the instrument. These coefficients determined from empirical relations were then corrected using heat balance tests on Earth under simulated conditions, taking into account the difference in gravity, pressure, density and gas compositions on Mars. This paper will present the results of the thermal and Computational Fluid Dynamics (CFD) analyses of the LIDAR and the full Lander, based on environmental thermal conditions determined from meteorological measurements of the Martian atmosphere in combination with a simplified thermal atmospheric tool. Special attention will be focussed on the determination of the convective heat transfer coefficients, both through classical empirical relations and the CFD analysis.

A Laboratory Setup for Observation of Loop Heat Pipe Characteristics

Heat pipes, loop heat pipes and capillary pumped loops are heat transfer devices driven by capillary forces with high-effectiveness & performance, offering high- reliability & flexibility in varying g-environments. They are suitable for spacecraft thermal control where the mass, volume, and power budgets are very limited. The Canadian Space Agency is developing loop heat pipe hardware aimed at understanding the thermal performance of two-phase heat transfer devices and in developing numerical simulation techniques using thermo-hydraulic mathematical models, to enable development of novel thermal control technologies. This loop heat pipe consists of a cylindrical evaporator, compensation chamber, condenser along with vapor and liquid lines, which can be easily assembled/disassembled for test purposes. This laboratory setup is especially designed to enable the visualization of fluid flow and phase change phenomena. There are transparent windows in the compensation chamber that enable the monitoring of the fluid characteristic. The setup demonstrated typical loop heat pipe performance. Three working fluids (water, acetone and methanol) were used in the characterization of the loop heat pipe. Visual observations have confirmed an opinion, generally held among heat pipe specialists, that loop heat pipes are tolerant to bubble generation in the compensation chamber; this tolerance however strongly depends on the intensity of boiling.

Passive dynamically-variable thin-film smart radiator device

This paper describes a new approach to spacecraft thermal control based on a passive thin-film smart radiator device (SRD) that employs a variable heat-transfer/emitter structure. The SRD employs an integrated thin-film structure based on V 1 - x - y M x N y O n that can be applied to existing Al thermal radiators. The SRD operates passively in response to changes in the temperature of the space structure. The V 1 - x - y M x N y O n exhibits a metal/insulator transition with temperature, varying from an IR transmissive insulating state at lower temperatures, to a semiconducting state at higher temperatures. Dopants, M and N, are employed to tailor the thermo-optic characteristics and the transition temperature of the passive SRD. The transition temperature can be preset over a wide range from below -30°C to above 68°C using suitable dopants. A proprietary SRD structure has been developed that facilitates emissivities below 0.2 to dark space at lower temperatures to reduce heater requirements. As the spacecraft temperature increases above the selected transition temperature, the thermal emissivity of the SRD to dark space increases by a factor of 2.5 to 3. The thin-film SRD methodology has significant advantages over competitive technologies in terms of weight, cost, power requirements, mechanical simplicity and reliability Preliminary results on an active electrochromic SRD based on the VO 2 system are also presented.

Visual Observations of Flow and Phase Phenomena in Loop Heat Pipes

The Canadian Space Agency is developing loop heat pipe hardware aimed at understanding the thermal performance of two‐phase heat transfer devices and in developing numerical simulation techniques using thermohydraulic mathematical models, to enable development of novel thermal control technologies. This loop heat pipe consists of a cylindrical evaporator, compensation chamber, condenser along with vapor and liquid lines, which can be easily assembled/disassembled for test purposes. This laboratory setup is especially designed to enable the visualization of fluid flow and phase change phenomena. There are transparent windows in the compensation chamber and transparent lines for vapor line, liquid returning line, and sections of condenser that enable the monitoring of the fluid phase and flowing characteristics along the loop. The setup demonstrated typical loop heat pipe performance. Three working fluids (water, acetone and methanol) were used in the characterization of the loop heat pipe. Visual observati...

Analysis of Thermal Design and On-Orbit Performance of the Horizon Scanners of RADARSAT-1

Spacecraft attitude control provides the basic stability so that sensors, solar panels, antennas and other hardware are properly oriented to perform their functions. A Horizon scanner can automatically seek the earth horizon by detecting the sharp discontinuity in InfraRed intensity at the outer edge of the Earths mesopause for purposes of a spacecrafts orientation and control. As a satellite in a Low Earth Orbit (LEO) and three-axis stabilized, the Canadian satellite RADARSAT-1 is equipped with two horizon scanners (HS) in order to scan dynamically across the Earths disc and to establish the attitude relative to the Earth. This paper discusses the thermal design and analyzes the on-orbit thermal oerformance of the HS.

Design and fabrication of a lightweight laser scanning mirror from metal-matrix composites

This paper discusses the design and fabrication of ultra lightweight laser scanning mirrors from two types of metal-matrix composites for the next generation Space Vision System (SVS). The materials selected for this study were SiC particulate reinforced aluminum composite and beryllium-aluminum (AlBeMet) composite. Three mirror designs were made and compared in terms of mass, rotating inertia and first mode natural frequency. Mirror surface layer selection and processing were discussed. Problems encountered during the mirror fabrication and the ways to solve it were presented.

MULTIFUNCTION SMART COATINGS FOR SPACE APPLICATIONS

This paper describes a new multifunction smart coating that can provide atomic oxygen (AO) and electrostatic discharge (ESD) protection, while also improving the thermal control of space structures. The methodology is based on a passive thin-film structure employing VOn transition metal oxides that exhibit a metal to insulator transition. The coating, depending on its formulation, can provide a variable heat-transfer/emitter structure that operates passively in response to changes in the temperature of the space structure, by dynamically varying the ratio of solar absorptance (α) to thermal emittance (ε). This enhances self-heating of the structure at lower temperatures and cooling through thermal radiation at elevated temperatures. Work is currently underway to apply this coating to various polymers and membranes to improve their performance in space. In the space environment, such as low Earth orbit (LEO), the coating will be subject to various stresses including VUV radiation and AO. Atomic oxygen testing in a simulated environment at CSA indicated no resolvable change in the morphology or thickness of the coatings. The thermo-optic characteristics after AO exposure were similar to the “as deposited” films. Additional long-term radiation exposure at the Centre National d’Etudes Spatiales—France (CNES), equivalent to three years in a geostationary orbit (GEO) environment, resulted in a change in the coating ε and α of less than 0.002.

THE STUDY OF THE EFFECTS OF ATOMIC OXYGEN EROSION ON THE MICROSTRUCTURE AND PROPERTY OF VO2 THERMOCHROMIC COATING USING CSA'S SPACE SIMULATION APPARATUS

In this study, a thermochromic VO2 coating, which has been studied for spacecraft smart thermal radiator application, was exposed to a ground-based atomic oxygen flux to determine the potential effects of space environment on its performance. The coating sample was prepared using laser ablation deposition technique. Atomic oxygen exposure experiment was conducted on the samples for equivalent 6 months and 3 years in typical LEO environment. Mass loss of the coating samples due to atomic oxygen exposure was measured. Characterization of total hemispherical emittance of the coating before and after atomic oxygen exposure indicates that the atomic oxygen erosion affects the thermal-optical performance of the coating to an extent. X-ray photoelectron spectroscope (XPS) analysis of the coating samples was performed and an increase in the oxygen concentration in outermost layer of the coating due to the atomic oxygen exposure was identified. Possible mechanism for the change in thermo-optical property of the coating was discussed.