摘要:

The Geoscience Laser Altimetry System (GLAS) instrument which is the sole instrument on ICESat was launched on January 12, 2003. GLAS utilizes the very first actively controlled propylene Loop Heat Pipes (LHPs) as the core of its thermal system that are tightly controlled (to +/− 0.1°C.) The LHPs started quickly when the Dale Ohm starter heaters were powered and have started, as designed, several additional times in the mission. The low control heater power and on‐orbit tight temperature control appear independent of gravity effects when comparing ground testing to flight data. The use of coupling blocks was also unique to these LHPs. Their application reduced control heater power by reducing the subcooling from the radiator. The effectiveness in reducing subcooling of the coupler blocks decreased during flight from ground testing, but internal thermal isolation in the compensation chamber between the subcooled returning liquid increased in flight resulting in no net increase in control heater power versus ground measurements. Overall the application of LHPs in the thermal system for GLAS met instrument requirements and provided flexibility for the overall system as last minute requirements became known. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649561

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper describes development of and test results for an electrostatically switched radiator (ESR). This is a device that can control the radiation emitted from a surface by controlling the position of a thin membrane. The present structure has been fabricated for flight testing on NASA’s ST5 New Millennium program. It consists of 4 separately controlled radiator sections with a total active area of 57.6 cm2. As opposed to the original approach, this structure has the outer membrane at ground potential and is constructed onto a printed circuit board. In this paper we discuss the current state of development of the ESR, including device fabrication and test results. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649562

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Altitude control and three axis stabilization of the solar sail is critically important and may be accomplished either through a mechanical arrangement or through the use of variable solar reflectance/transmittance coatings (VSRCs/VSTCs). Electrochromic coatings that change reflectance or transmittance in response to the application of an electric potential may be used for this purpose. The primary objective of this work is to evaluate the effect of changes in the emittance of the front and rear surfaces of a solar sail on the thrust modulation efficiency. The results presented in this article demonstrate that the most efficient change in thrust for a solar sail panel with a VSRC is reached when the side shaded from the sun has the higher emittance than the side facing the sun. For a solar sail panel with a VSTC, the condition for the most efficient change in thrust occurs when the side facing the sun has the higher emittance than the side shaded from the sun. Also, it was highlighted that an opaque VSRC is more compatible with an opaque reflective solar sail thruster than a transparent VSTC. This design of a solar sail altitude control system with VSRC panels is recommended for further development. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649563

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Small light‐weight satellites and space vehicles under development for future NASA missions have reduced thermal mass and are strongly affected by changes in orbital conditions, resulting in large temperature variations. Restrictions on payload weight and volume limit the usefulness of many thermal control technologies. One thermal control approach, being considered by NASA in both nano‐ and micro‐ spacecraft applications, involves the use of electrochromic (EC) variable emittance devices (VEDs). VEDs operating in the harsh space environment (UV radiation, atomic oxygen) must be properly protected if they are to reach their design operational life. In this paper, we discuss the design of an all‐solid‐state EC VED built on a silicon wafer. The silicon wafer serves as a window for IR radiation and protects EC layers from the space environment. This paper also discusses the expected limits of emittance modulation of the EC VED on the silicon substrate as well as possible impact of an antireflective coating on IR emittance modulation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649564

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The trend to smaller satellites with limited resources in weight and power requires a new approach to thermal control to replace heaters with emittance‐controlled radiators. There are a number of approaches to variable emittance radiators such as variable emittance coatings or louvers. This paper describes an actively controlled radiator based on a micro electromechanical (MEMS) thermal switch. The switch operates by electrostatically switching a high emittance membrane in and out of contact with the substrate. The radiator is covered with an array of large numbers of these switches, which allows an almost digital control of the apparent emittance of the radiator. The thermal and electromechanical design of the MEMS device is discussed. A proof‐of‐concept design has been fabricated and tested that uses a gold membrane suspended on polymer posts. In the open position, actuation voltages range from 8 to 25 volts; this was consistent with our electromechanical model for the devices. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649565

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Heat exchanges during boiling are of high interest for cooling systems. The objective of this work is to investigate heat transfer around a single vapor bubble, the influence of the liquid subcooling and of the heat flux applied on the nucleation surface. Experiments on subcooled pool boiling at atmospheric pressure for a single vapor bubble were conducted and the obtained results are presented. The bubble was created on a downward facing heating element. Generation of the single bubble was achieved on an artificial cavity; the indentation was made on a fluxmeter (Captec Entreprise®). FC‐72 was used as the test liquid, and its subcooling was maintained to 8 and 14K. Two heating powers were applied on the nucleation surface, and maintained constant during each experiment. Evolutions of bubble size and shape, as a function of wall superheat and liquid subcooling, were followed and studied using a 25 fps video camera. The effect of heating power and subcooling on growth periods were found to be significant. Total heat fluxes during bubble growth were measured using the fluxmeter, for different levels of subcooling and heating powers. Image and data processing has enabled us to show up influence of bubble growth on heat transfer and to determine nucleation periodicity. These preliminary results are discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649566

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Knowledge of aerothermally induced convective heat transfer and plume induced radiative heat transfer loads is essential to the design of thermal protection systems (TPS) for launch vehicles. Aerothermal and radiative models are typically calibrated via the data from cylindrical, in‐flight, flush‐mounted surface heat flux gauges that are exposed to the external thermal and velocity boundary layers as well as thermal radiation. Typically, Schmidt‐Boelter gauges, taking advantage of the 1‐Dimensional Fourier’s law, measure the incident heat flux. This instrumentation, when surrounded by low‐conductivity insulation, has an exposed surface temperature significantly lower than the insulation. As a result of this substantial disturbance to the thermal boundary layer, the heat flux incident on the gauge tends to be considerably higher (potentially by factors of 2 or more) than it would have been on the insulation had the calorimeter not been there. In addition, the gauge can receive energy radially from the hotter insulation, contributing to the increase of the indicated heat flux. This paper will present an overview of an effort to model the heat flux gauge under typical flight conditions that includes an installation surrounded by high temperature insulation. The goal is to correct the measurements to reflect the local heat flux on the insulation had the instrument not been present. The three major components of this effort include: 1) a three‐dimensional computational thermal math model including the internal conduction heat transfer details of a Schmidt‐Boelter gauge, 2) a two‐dimensional Navier‐Stokes computational fluid dynamics (CFD) analysis to determine the effects on measurement of the rapidly changing thermal boundary layer over the near step changes in wall temperature, and 3) testing performed on flat plates exposed to an aerothermal environment in the Marshall Space Flight Center (MSFC) Improved Hot Gas Facility (IHGF). A brief summary of calibration issues will be presented, followed by the analytical efforts, as well as an update on testing results and preliminary model calibration results. Finally, recommendations will be made for installation and flight data corrections. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649567

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

High temperature heat pipes are being evaluated for use in energy conversion applications such as fuel cells, gas turbine re‐combustors, and Stirling cycle heat sources; with the resurgence of space nuclear power, additional applications include reactor heat removal elements and radiator elements. Long operating life and reliable performance are critical requirements for these applications. Accordingly long‐term materials compatibility is being evaluated through the use of high temperature life test heat pipes. Thermacore, Inc. has carried out several sodium heat pipe life tests to establish long term operating reliability. Four sodium heat pipes have recently demonstrated favorable materials compatibility and heat transport characteristics at high operating temperatures in air over long time periods. A 316L stainless steel heat pipe with a sintered porous nickel wick structure and an integral brazed cartridge heater has successfully operated at 650C to 700C for over 115,000 hours without signs of failure. A second 316L stainless steel heat pipe with a specially‐designed Inconel 601 rupture disk and a sintered nickel powder wick has demonstrated over 83,000 hours at 600C to 650C with similar success. A representative one‐tenth segment Stirling Space Power Converter heat pipe with an Inconel 718 envelope and a stainless steel screen wick has operated for over 41,000 hours at nearly 700C. A hybrid (i.e. gas‐fired and solar) heat pipe with a Haynes 230 envelope and a sintered porous nickel wick structure was operated for about 20,000 hours at nearly 700C without signs of degradation. These life test results collectively have demonstrated the potential for high temperature heat pipes to serve as reliable energy conversion system components for power applications that require long operating lifetime with high reliability. Detailed design specifications, operating history, and test results are described for each of these sodium heat pipes. Lessons learned and future life test plans are also discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649568

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

To support development and hardware‐based testing of various space reactor concepts, the Early Flight Fission‐Test Facility (EFF‐TF) team established a specialized glove box unit with ancillary systems to handle/process alkali metals. Recently, these systems have been commissioned with sodium supporting the fill of stainless steel heat pipe modules for use with a 100 kW thermal heat pipe reactor design. As part of this effort, procedures were developed and refined to govern each segment of the process covering: fill, leak check, vacuum processing, weld closeout, and final “wet in”. A series of 316 stainless steel modules, used as precursors to the actual 321 stainless steel modules, were filled with 35 +/−1 grams of sodium using a known volume canister to control the dispensed mass. Each module was leak checked to <10−10std cc/sec helium and vacuum conditioned at 250 °C to assist in the removal of trapped gases. A welding procedure was developed to close out the fill stem preventing external gases from entering the evacuated module. Finally the completed modules were vacuum fired at 750 °C allowing the sodium to fully wet the internal surface and wick structure of the heat pipe module. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649569

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this paper a database of sessile drop evaporation on a heated surface under gravity conditions is presented. For this an experimental setup is presented. It includes the part which allows evaporating the drop under controlled conditions and the data acquisition system. The drop is deposited on a heated surface maintained at constant temperature. Two systems were studied: water PTFE (non wetting couple) in which the wetting angle is higher than &pgr;/2 and water‐aluminum (wetting couple) in which the wetting angle is less than &pgr;/2. Two types of measurements are implemented: the first one is an optical method which enables measurements of drop geometrical parameters and consequently the drop evaporation rate. The second one corresponds to a thermal fluxmeter. This later allows the determination of the heat flux and drop temperature. The evaporation rate as well as the geometrical parameters (contact angle, wetting diameter) are determined for several operating conditions: wall temperature and drop size for the two systems considered. For the evaporation rate two different behaviors are found according to drop wetting. The experimental results are discussed and analyzed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649570

出版商:AIP    

年代:1904

数据来源: AIP