The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSORING/MONITORING AGENCY REPORT NUMBER(S) AFRL-ML-WP-TP-2006-456 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. SUPPLEMENTARY NOTESThis is a Small Business Innovation Research (SBIR) Phase II report. This paper contains color. PAO Case Number: AFRL/WS 06-1287, 15 May 2006. This work, resulting in whole or in part from Department of the Air Force contract FA8650-05-C-5045, has been submitted to the AIAA for publication in the AIAA Journal of Thermophysics and Heat Transfer Guidelines. If published, AIAA may assert copyright. The United States has for itself and others acting on its behalf an unlimited, paid-up, nonexclusive, irrevocable worldwide license to use, modify, reproduce, release, perform, display, or disclose the work by or on behalf of the Government. All other rights are reserved by the copyright owner. ABSTRACTThis report was developed under a SBIR contract. This paper describes a heat flux-based method for measuring emissivity of a surface. In this method the emissivity of a surface is calculated using direct measurement of the heat flux passing through the surface. Unlike storage-based calorimetric methods, this method does not require application of known amounts of heat to the surface or the temperature history of a known amount of thermal mass to calculate the surface emissivity. Application and operation of this method is much simpler than calorimetric methods as it does not require careful thermal insulation of the heat radiating body from the surroundings. This technique allows emissivity measurements of the newly developed variable emissivity surfaces with significantly lighter and energy efficient measurement equipment that can operate for long term space missions. In this study, a commercially available thermopile heat flux sensor was used to measure the emissivity of a black paint and a variable emissivity surface, Electrostatic Switched Radiator (ESR). This paper details the concept, experimental setup, and the experiment results. Maryland, College Park, MD, 20742 Abstract. This paper describes a heat flux-based method for measuring emissivity of a surface. In this method the emissivity of a surface is calculated using direct measurement of the heat flux passing through the surface. Unlike storage-based calorimetric methods, this method does not require application of known amounts of heat to the surface or the temperature history of a known amount of thermal mass to calculate the surf...

The steady-state and transient behaviors of packaged IR LED arrays have been studied via numerical simulations. The waste heat generated by LEDs must be removed through a cold plate or a cryogenic cold finger attached to the backside of the driver array. Therefore, this heat must travel across the LED array-driver interface and through the driver array. The modeling results demonstrate that the thermal resistance of these components can be significant. The steady-state temperature profiles across several configurations are used to identify the thermal bottlenecks. Transient simulations are used to quantify the rise and fall times of the IR LEDs, and the fall times can be significantly reduced by changes in the LED layout. These proposed guidelines to minimize thermal issues in LED arrays should result in better performing and more reliable IR LED arrays.

The heat-flux-based emissivity measurement technique developed in our earlier work has been used to study the performance of an electrostatic switched radiator. The capability of fast and accurate measurement of the real-time changes in emissivity enabled by this technique allowed understanding of the transient behavior during activation, as well as identification of a major failure mode of the second-generation electrostatic radiator. A solution for resolution of this failure mode was then proposed and successfully tested, producing accurate and repeatable results over many cycles. A change in emissivity of 0.52 was achieved with 280 V applied, among the best consistent results achieved through electrostatic technology. The current work offers further understanding of electrostatic radiator performance and its application to space vehicles.