Tech Briefs

Special Semaphore Scheme for UHF Spacecraft Communications

A semaphore scheme has been devised to satisfy a requirement to enable ultrahigh- frequency (UHF) radio communication between a spacecraft descending from orbit to a landing on Mars and a spacecraft, in orbit about Mars, that relays communications between Earth and the lander spacecraft. There are also two subsidiary requirements: (1) to use UHF transceivers, built and qualified for operation aboard the spacecraft that operate with residual-carrier binary phase-shift-keying (BPSK) modulation at a selectable data rate of 8, 32, 128, or 256 kb/s; and (2) to enable low-rate signaling even when received signals become so weak as to prevent communication at the minimum BPSK rate of 8 kHz. The scheme involves exploitation of Manchester encoding, which is used in conjunction with residual-carrier modulation to aid the carrier-tracking loop. By choosing various sequences of 1s, 0s, or 1s alternating with 0s to be fed to the residual- carrier modulator, one would cause the modulator to generate sidebands at a fundamental frequency of 4 or 8 kHz and harmonics thereof. These sidebands would constitute the desired semaphores. In reception, the semaphores would be detected by a software demodulator.

Posted in: Briefs, TSP, Information Sciences, Radio equipment, Telecommunications systems, Spacecraft
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Simulator for Testing Spacecraft Separation Devices

A report describes the main features of a system for testing pyrotechnic and mechanical devices used to separate spacecraft and modules of spacecraft during flight. The system includes a spacecraft simulator [also denoted a large mobility base (LMB)] equipped with air thrusters, sensors, and data-acquisition equipment. The spacecraft simulator floats on air bearings over an epoxy-covered concrete floor. This free-flotation arrangement enables simulation of motion in outer space in three degrees of freedom: translation along two orthogonal horizontal axes and rotation about a vertical axis. The system also includes a static stand. In one application, the system was used to test a boltretraction system (BRS) intended for separation of the lifting-body and deorbitpropulsion stages of the X-38 spacecraft. The LMB was connected via the BRS to the static stand, then pyrotechnic devices that actuate the BRS were fired. The separation distance and acceleration were measured. The report cites a document, not yet published at the time of reporting the information for this article, that is said to present additional detailed information.

Posted in: Briefs, Test & Measurement, Finite element analysis, Scale models, Test equipment and instrumentation, Spacecraft
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Apparatus for Hot Impact Testing of Material Specimens

It is not necessary to cool and reheat the furnace between tests.

An apparatus for positioning and holding material specimens is a major subsystem of a system for impact testing of the specimens at temperatures up to 1,500 °C. This apparatus and the rest of the system are designed especially for hot impact testing of advanced ceramics, composites, and coating materials.

Posted in: Briefs, TSP, Test & Measurement, Ceramics, Coatings Colorants and Finishes, Coatings, colorants, and finishes, Composite materials, Impact tests, Test equipment and instrumentation
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Instrument for Aircraft-Icing and Cloud-Physics Measurements

Data on cloud water content are deduced from hot-wire power a levels.

The figure shows a compact, rugged, simple sensor head that is part of an instrumentation system for making measurements to characterize the severity of aircraft-icing conditions and/or to perform research on cloud physics. The quantities that are calculated from measurement data acquired by this system and that are used to quantify the severity of icing conditions include sizes of cloud water drops, cloud liquid water content (LWC),cloud ice water content (IWC), and cloud total water content (TWC).

Posted in: Briefs, Test & Measurement, Measurements, Sensors and actuators, Sensors and actuators, Humidity, Icing and ice detection
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Improved Apparatus for Testing Monoball Bearings

Automated tests can be performed over wide ranges of conditions.

A desk-sized apparatus for testing monoball bearings and their lubricants offers advantages, relative to prior such apparatuses, of (1) a greater degree of automation and (2) capability of operation under wider and more realistic ranges of test conditions. The ranges of attainable test conditions include load from 100 to >50,000 lb (445 to >2.22 × 105 N), resisting torque up to 30,000 lbin. (≈3,390 N-m), oscillating rotation through an angle as large as 280°, and oscillation frequency from 0 to 6 Hz. With addition of some components and without major modification of the apparatus, it is also possible to perform tests under environmental conditions that include temperature from –320 to 1,000 °F (–196 to +538 °C), relative humidity from 0 to 100 percent, and either air at ambient pressure, high vacuum, or an atmosphere of monatomic oxygen.

Posted in: Briefs, TSP, Test & Measurement, Automation, Bearings, Test equipment and instrumentation
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Advances in Measurement of Skin Friction in Airflow

This system implements a combination of established experimental techniques and advanced image processing.

The surface interferometric skin-friction (SISF) measurement system is an instrument for determining the distribution of surface shear stress (skin friction) on a wind-tunnel model. The SISF system utilizes the established oil-film interference method, along with advanced image-data-processing techniques and mathematical models that express the relationship between interferograms and skin friction, to determine the distribution of skin friction over an observed region of the surface of a model during a single wind-tunnel test.

Posted in: Briefs, TSP, Test & Measurement, Mathematical models, Measurements, Wind tunnel tests, Aerodynamics
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Infrared Instrument for Detecting Hydrogen Fires

Spatial information is utilized to discriminate against reflected light from other sources.

The figure shows an instrument incorporating an infrared camera for detecting small hydrogen fires. The instrument has been developed as an improved replacement for prior infrared and ultraviolet instruments used to detect hydrogen fires. The need for this or any such instrument arises because hydrogen fires (e.g., those associated with leaks from tanks, valves, and ducts) pose a great danger, yet they emit so little visible light that they are mostly undetectable by the unaided human eye. The main performance advantage offered by the present instrument over prior hydrogen-fire-detecting instruments lies in its greater ability to avoid false alarms by discriminating against reflected infrared light, including that originating in (1) the Sun, (2) welding torches, and (3) deliberately ignited hydrogen flames (e.g., ullage-burn-off flames) that are nearby but outside the field of view intended to be monitored by the instrument.

Posted in: Briefs, Electronics & Computers, Imaging and visualization, Optics, Chemicals, Fire detection
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Modified Coaxial Probe Feeds for Layered Antennas

Coaxial shields are connected to radiator and ground planes at standing-wave nodes.

In a modified configuration of a coaxial probe feed for a layered printed-circuit antenna (e.g., a microstrip antenna), the outer conductor of the coaxial cable extends through the thickness of at least one dielectric layer and is connected to both the ground-plane conductor and a radiator-plane conductor. This modified configuration simplifies the incorporation of such radio-frequency integrated circuits as power dividers, filters, and low-noise amplifiers. It also simplifies the design and fabrication of stacked antennas with aperture feeds.

Posted in: Briefs, Electronics & Computers, Antennas
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Detecting Negative Obstacles by Use of Radar

Changes in diffraction and reflection would be used to detect abrupt downslopes.

Because such wavelengths are comparable to the characteristic dimensions of terrain features associated with negative hazards, a significant amount of diffraction would occur at such features. In effect, the diffraction would afford a limited ability to see corners and to see around corners. Hence, the system might utilize diffraction to detect corners associated with negative obstacles. At the time of reporting the information for this article, preliminary analyses of diffraction at simple negative obstacles had been performed, but an explicit description of how the system would utilize diffraction was not available.

Posted in: Briefs, TSP, Electronics & Computers, Radar, Terrain
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Simulator for Testing Spacecraft Separation Devices

A report describes the main features of a system for testing pyrotechnic and mechanical devices used to separate spacecraft and modules of spacecraft during flight. The system includes a spacecraft simulator [also denoted a large mobility base (LMB)] equipped with air thrusters, sensors, and data-acquisition equipment. The spacecraft simulator floats on air bearings over an epoxy-covered concrete floor. This free-flotation arrangement enables simulation of motion in outer space in three degrees of freedom: translation along two orthogonal horizontal axes and rotation about a vertical axis. The system also includes a static stand. In one application, the system was used to test a boltretraction system (BRS) intended for separation of the lifting-body and deorbitpropulsion stages of the X-38 spacecraft. The LMB was connected via the BRS to the static stand, then pyrotechnic devices that actuate the BRS were fired. The separation distance and acceleration were measured. The report cites a document, not yet published at the time of reporting the information for this article, that is said to present additional detailed information.

Posted in: Briefs, Test & Measurement, Test equipment and instrumentation, Spacecraft
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