Tech Briefs

Room-Temperature Infrared Instrument Detects Trace Gases

Times for measuring concentrations of gases can be as short as a few seconds.A compact, portable, mid-infrared, laser-based instrument that operates at room temperature has been developed for use in detecting trace concentrations of CO or any of several other gases in air. The instrument utilizes infrared absorption spectroscopy in a sample cell which either holds an air sample or is exposed to an airflow. The laser beam that interrogates the cell is formed by difference-frequency generation (DFG) in a bulk nonlinear optical medium excited by two laser beams.

Posted in: Briefs, TSP, Test & Measurement, Lasers, Carbon monoxide, Gases, Test equipment and instrumentation


Personal Cabin Pressure Alarm

Aircraft crewmembers would be alerted to prevent hypoxia.Compact instruments, similar in appearance to common personal pagers, have been proposed for warning aircraft crewmembers that cabin air pressure has decreased to a potentially dangerous level. An instrument of this type, called a "personal cabin pressure monitor and warning system" (PCPMWS), implements a warning protocol consistent with Federal Aviation Administration (FAA) requirements for commercial flight crews to (1) use supplemental oxygen after a 30-minute exposure to a cabin pressure altitude between 10,000 and 12,000 ft (about 3,050 and 3,660 m), or (2) immediately when the cabin pressure altitude exceeds 12,000 ft. The PCPMWS would provide both 10,000- and 12,000-ft warnings. The elapsed time between these two warning altitudes could also serve as an indication of the rate of decompression, and thus of the urgency of the situation.

Posted in: Briefs, TSP, Test & Measurement, Cabin pressurization


Software Predicts Noise From Rotor-Wake/Stator Interactions

V072 is a computer program that predicts the noise generated by the interaction between the rotor-blade wake (fan wake) and the stator vanes of a turbofan engine. The program is a combination of subroutines from prior NASA programs, with many added features.

Posted in: Briefs, Mechanical Components, Mechanics, Computer software and hardware, Noise, Turbojet engines


Software for Obtaining Ideal SAR Chirps

A computer program introduces a predistortion into the chirp signal used to frequency-modulate a synthetic-aperture-radar (SAR) signal at the transmitter. The predistortion is intended to compensate for distortions introduced by nonideal performance of the various pieces of SAR equipment — especially the transmitter. More specifically, the predistortion is intended to make the signal in the receiver an ideal SAR signal in that it exhibits optimum correlation performance. The program is run as a calibration routine. It is used in conjunction with a closed calibration loop that includes the SAR transmitter and receiver, plus an arbitrary-waveform generator (AWG), which generates the predistorted chirp under computer control. The program causes the AWG to adjust the predistorted chirp iteratively until the chirp in the receiver differs from an optimum or reference chirp by less than a prescribed small measure of error. In a test in which a bad elliptical filter was used to simulate (with respect to distortion) the transmitting and receiving equipment of an SAR system, the program succeeded in generating a simulated receiver chirp within less than 1 dB of optimum.

Posted in: Briefs, TSP, Software, Computer software and hardware, Radar


Interlocking Wing-Leading-Edge Thermal-Protection Tiles

These tiles are shaped to prevent damage at inter-tile gaps.Insulating tiles with interlocking shaped gaps have been developed for use in protecting the leading edges of the wings of aerospacecraft against excessive heating during hypersonic flight (including re-entry into the atmosphere). Other thermal-protection systems have been studied for this application, including those based on active transpiration cooling and heat-sink concepts. These systems have been described extensively in literature during the past thirty years and recently have been proposed for use on two hypersonic vehicles: the National Aerospace Plane (NASP) and the Slender Hypervelocity Aerothermodynamic Research Probe (SHARP). However, because these systems are very heavy and are expensive (millions of dollars) to fabricate and to install, the probability of using these systems in the near term on the surfaces of commercially operated reusable launch vehicles is low.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Wings, Thermal management, Insulation, Entry, descent, and landing, Reusable launch vehicles and shuttles


Glass Cure Plates for Fabricating Flat Composite Panels

Costs are lower than those of aluminum cure plates.Glass plates are used as cure plates in a modified process for the fabrication of flat composite-material (matrix/fiber) panels. In the unmodified previous version of the process the cure plates were made of aluminum.

Posted in: Briefs, Manufacturing & Prototyping, Body panels, Fabrication, Composite materials, Glass


Modifications of a Hydrazine Fueling Procedure and Equipment

Workers could safely wear less-restrictive protective garments.A combination of procedure and equipment for loading liquid hydrazine into a spacecraft fuel tank that contains a diaphragm or bladder would be modified, according to a proposal. The purpose of the modifications is to enable fueling technicians to work safely, during all but a small part of the loading process, in less-restrictive protective attire.

Posted in: Briefs, TSP, Physical Sciences, Hydrazines, Fueling safety, Spacecraft


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