Special Coverage

How Model Rockets Launch Tomorrow's Engineers
Lost in Space: Smart Spacesuits Feature 'Home' Button
With a Commercial Printer, Researchers Manufacture Motion Sensors in Bulk
NASA Supercomputer Simulations Reveal 'Noisy' Aerodynamics
Is It Hot in Here? New Double-Sided Fabric Will Find Your 'Comfortable' Temperature
Sound-Off: Thermoset Composites vs. Traditional Metals
Electric ‘Smart’ Paper Picks Up on Pipe Leaks
Using Microwaves to Produce High-Quality Graphene
Transducer-Actuator Systems for On-Machine Measurements and Automatic Part Alignment
Wide-Area Surveillance Using HD LWIR Uncooled Sensors
Heavy Lift Wing in Ground (WIG) Cargo Flying Boat

Seven-Element Circularly Polarized Patch Antenna

A seven-element microstrip patch antenna is designed to operate with circular polarization and high gain at a frequency of 2.2875 GHz. The antenna was developed in the early 1990s as a potential replacement for a helical antenna aboard the Advanced Tracking and Data Relay Satellite. Recently, the Federal Communications Commission allocated frequencies around 2.4 GHz for commercial communication systems. The present antenna is well suited for these systems, not only because it provides high gain in the desired frequency range, but also because like other patch antennas, it is lightweight, can be fabricated easily, can be mounted with a low profile, and is inexpensive. In addition, its circular polarization is especially advantageous in cellular-telephone and mobile communications, in that circular polarization can mitigate multipath fading, which is severe in urban environments.

Posted in: Briefs, TSP, Electronics & Computers, Antennas, Wireless communication systems, Antennas, Wireless communication systems, Satellites

Camera Images Hydrogen Fires in Three Wavelength Bands

A special-purpose multispectral video camera has been designed to provide an enhanced capability for viewing hydrogen fires. Hydrogen fires do not emit sufficient visible light to be seen by the unaided human eye, but they do emit strongly at other wavelengths — especially in the infrared and near-infrared portions of the spectrum. Therefore, like some other video cameras developed previously for the same purpose, this camera is designed to respond to infrared light emitted by hot water molecules in hydrogen flames. Going beyond previous designs, this camera provides a combination of imaging in three wavelength bands and processing of the three images, all for the purposes of (1) reducing spurious responses to background light and solar radiation, and (2) synthesizing an image of a hydrogen flame overlaid on an ordinary visible-light image of the scene that contains the flame.

Posted in: ptb catchall, Tech Briefs, Briefs, Photonics, Optics, Optics, Hydrogen fuel, Fire

Improved Inlets for T-38 Airplane

A change in the design of the engine inlets of the T-38 airplane significantly reduces takeoff distances while increasing safety margins. Although the newer inlet design (see Figure 1) is based on well-known engineering principles, it is unique and will prove invaluable to the NASA fleet and to other T-38 fleets; e.g., the fleets flown by the United States Air Force (USAF) and by foreign governments. The change in design was needed because in an inlet of the older design, separation of flow in the lower third of the inlet degraded efficiency, even under normal takeoff conditions. Johnson Space Center (JSC) engineers compensated for this deficiency in formulating the newer design by adopting an inlet shaped according to aerodynamical considerations; the shape was chosen to minimize separation of flow to produce greater engine thrust as the T-38 accelerates to takeoff speed.

Posted in: Briefs, Mechanical Components, Mechanics, Design processes, Engines, Aerodynamics

Biotelemetry Using Implanted Unit To Monitor Preterm Labor

A biotelemetric system for monitoring key physiological parameters of a fetus and its uterine environment is undergoing development. The main purpose of the monitoring is to detect preterm labor in order to enable timely treatment. At the present stage of development, the system monitors pressure changes and temperature. The pressure changes serve as direct indications of intrauterine contractions that could be associated with the onset of preterm labor. Future versions of the system are expected to monitor additional parameters, including pH and the heart rate of the fetus.

Posted in: Briefs, TSP, Electronics & Computers, Sensors and actuators, Telemetry, Sensors and actuators, Telemetry, Medical equipment and supplies, Product development

Foam Heat Exchangers

Experiments have demonstrated the feasibility of heat exchangers with flow channels containing open-cell metallic foams. Nonmetallic foams could also be used. One proposed design calls for an open-cell foam in the annular region between an inner and an outer tube, with a heat-transfer fluid flowing along the annular region while either the outer or the inner tube is heated by flowing hot gas. Heat would be transferred from the heated tube wall to the fluid with an efficiency greater than that of a simple tube heat exchanger. The increase in heat-transfer efficiency would result from the large surface area of the foam in contact with the cooling fluid and from turbulence induced by the ligaments of the foam in the flow path. Thermal conduction between the wall and the foam would also make a small contribution. Greater heat-transfer efficiency should make it possible to design smaller, lighter heat exchangers for some applications. Another advantage of foam heat exchangers is that all flow paths through foam are interconnected, so that if a flow becomes obstructed by debris lodged in foam at one place in a channel, the flow can continue elsewhere in the channel; in other words, complete blockage of a channel is unlikely. This is in contrast to the situation in a heat exchanger containing narrow brazed tubes and/or narrow, precisely machined channels, which can become blocked more readily. Moreover, in comparison with machined-channel and brazed-tube heat exchangers, foam heat exchangers can be fabricated more easily and at lower cost. Remarkably, a properly designed foam heat exchanger exhibits less back pressure than does a machined-channel or brazed-tube heat exchanger of equal heat-transfer capacity. Thus, a smaller pump can be used to circulate the heat-transfer fluid.

Posted in: Briefs, TSP, Physical Sciences, Heat exchangers, Heat transfer, Heat exchangers, Heat transfer, Product development, Foams

High-Altitude Flight Test of the Perseus B Airplane

The Perseus B remotely piloted vehicle (RPV) has achieved a record altitude for a single-engine, propeller-driven airplane of 60,260 ft (18,367 m) on June 27, 1998. The Perseus B is one of the test-bed aircraft developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program for use in conducting high-altitude, long-duration missions carrying atmospheric sampling and sensing payloads for the scientific community within NASA and other agencies.

Posted in: Briefs, Mechanical Components, Mechanics, Rotary engines, Flight tests, Fixed-wing aircraft, Unmanned aerial vehicles

Stable, Soft-Opening/Soft-Closing Pressure-Relief Valves

Improved pressure-relief valves have been developed for systems that contain gases and liquids in a variety of pneumatic, hydraulic, and cryogenic applications. These valves could prove especially beneficial in both cryogenic and noncryogenic systems that contain oxygen. The improved valves are designed to suppress instabilities that shorten operational lifetimes and create hazards in the operation of older pressure-relief valves.

Posted in: Briefs, Mechanical Components, Mechanics, Oxygen, Valves

Inflatable Fresnel Lenses as Concentrators for Solar Power

Inflatable Fresnel lenses are being developed for use as optical concentrators in solar power systems. These lenses are of two types: dome (point-focus) lenses and cylindrical (line-focus) lenses (see Figure 1). Originally intended for supplying power to spacecraft, these lenses might also be adaptable to some terrestrial solar-power systems in cases in which optical aberrations caused by gravitational and wind-loading distortions of lens shapes could be tolerated.

Posted in: Briefs, Physical Sciences, Optics, Optics, Solar energy, Elastomers, Spacecraft

Hybrid Acoustic/Electrostatic Levitation Apparatus

The figure schematically illustrates a developmental automated hybrid acoustic/electrostatic apparatus for levitating both electrically charged and electrically neutral liquid drops with sizes up to about 1 mm. The apparatus is particularly suitable for experiments on the growth of protein crystals from solution and on the growth of cells and tissues, all under controlled conditions. In addition to the obvious advantage of levitation for preventing the chemical and thermal contamination that accompanies contact between drops and external objects, this apparatus provides controllable rotation about a horizontal axis (for example, to reduce sedimentation). Moreover, the direction of rotation can be varied to randomize the effective direction of gravitation. Thus, on Earth, the apparatus is expected to provide some of the advantages of low gravitation for suppressing the buoyancy-induced flows that interfere with the growth of high-quality protein crystals and for reducing the adverse effects that gravitation exerts on some cell and tissue cultures.

Posted in: Briefs, TSP, Physical Sciences, Product development, Automation, Acoustics, Acoustics, Test equipment and instrumentation

Low-Distortion Imaging Spectrometers

"Pushbroom" imaging spectrometers of a proposed type would exhibit little or no distortion in either the spectral or spatial direction. These spectrometers would feature modified Offner optics, which afford a desirable combination of compactness and a high degree of optical correction. Although Offner optics have been used in some spectrometer designs, their potential for eliminating distortion does not appear to have been exploited.

Posted in: Briefs, TSP, Physical Sciences, Measurements, Imaging, Imaging and visualization, Optics, Spectroscopy, Imaging, Imaging and visualization, Optics, Spectroscopy

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