Miniaturized Laser-Based Measurement Capability Aids Scramjet Engine Performance Analysis Published July 16, 2008 By Thomas Brown Propulsion Directorate WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- AFRL scientists are working with industry partner Southwest Sciences, Inc., to prepare for the first flight test of a diode-laser-based measurement platform. The test is part of the Hypersonic International Flight Research and Experimentation (HIFiRE) program and is receiving support from the Air Force International Cooperation Research and Development, Air Force Small Business Innovation Research, and Department of Defense Test and Evaluation/Science and Technology (high-speed/hypersonic test focus area) programs. The team has adapted and miniaturized laser-based telecommunications technologies and custom digital signal processing electronics to develop a unique measurement platform employing tunable diode laser absorption spectroscopy (TDLAS). The TDLAS platform provides a novel approach to measuring gas species and velocity within an engine flowpath in flight. The method employs a highly sensitive measurement technique known as wavelength modulation spectroscopy, along with kilohertz frequency sampling rates, in order to gain maximum information from flight experiments. This effort marks the first time that the technology has undergone miniaturization for use at scales suitable for sounding rocket flight experiments, wherein the instrument mass and power requirements are ~2 kg and ~2 W, respectively. HIFiRE represents a 7-year bilateral agreement with Australia to conduct research in the exploration and development of fundamental hypersonic aerospace technologies. TDLAS experiments are scheduled for three of the HIFiRE sounding rocket flights. These activities will focus on developing new, flight-qualified, nonintrusive techniques capable of measuring core flow properties in real time in order to characterize critical vehicle/engine parameters, such as air mass capture, stability limits, and combustion progress. Scientists have qualified the diode-laser flight hardware to operate over unprecedented temperature and vibration conditions. The initial flight, scheduled to occur in 2008, will transition the TDLAS experiments from Technology Readiness Level (TRL) 2 (i.e., technology concept and/or application formulation) to TRL 4 (i.e., component and/or breadboard validation in laboratory environment). Two additional flights are slated for 2009 and 2010, respectively. The team expects that the TDLAS measurement platform will achieve TRL 6 status (i.e., system/subsystem model or prototype demonstration in relevant environment, ground or space) upon completion of HIFiRE's culminating exercise, a Mach 8 scramjet [supersonic combustion ramjet] propulsion flight.