Tech Briefs

Low-Temperature Radiometer

This technology can look for heat leaks and reflected flux in low-temperature thermal vacuum systems. Goddard Space Flight Center, Greenbelt, Maryland Many present and future NASA missions require high-performance, large-scale cryogenic systems, such as the sunshields and cold instruments for the James Webb Space Telescope (JWST). Testing these systems is problematic because of both the size and the low heat loads allowed. The heat loads can be greatly influenced by non-ideal blackbody characteristics of the test chamber, and by stray heat from warmer parts of the system and ground support equipment. Previously, stray thermal energy was not directly measured, but inferred from deviations in the expected results, which leads to errors in thermal modeling and in lack of knowledge of the thermal performance of the item under test. Technologists at NASA Goddard Space Flight Center have developed a radiometer to help identify the sources of stray heat and to make non-contact thermal emission measurements of such materials as vapor-deposited aluminum on Kapton and multilayer insulation blankets, as well as background measurements of non-ideal chamber effects such as light leaks and radiation bounces.

Posted in: Briefs, Test & Measurement

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Lightweight Internal Device to Measure Tension in Hollow-Braided Cordage

This device has applications in industries commonly using cordage, such as shipping, sailing, and lifting. NASA’s Jet Propulsion Laboratory, Pasadena, California The suspension system of parachutes is typically made from ropes (referred to as cordage). Measuring loads in the suspension system cordage has thus far proven very challenging because of the dynamic nature of the parachute. The suspension lines must be deployed along with the parachute, and experience rapid acceleration and dynamic motion as the parachute inflates. The addition of bulky load cells to the suspension lines would change the dynamics of the system and corrupt the data.

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Improved Method to Quantify Leak Rates

This method improves the quality and reliability of leak rate test results. John H. Glenn Research Center, Cleveland, Ohio One existing method to quantify the gas loss from a closed system is the mass point leak rate method. This traditional empirical method is capable of quantifying the loss of a known type of gas from a volume of known size. Using this method, measurement devices quantify the gas pressure and temperature within a closed system throughout the duration of the test. At the onset of the test, the operator establishes boundary conditions to create a pressure differential across the test article that is higher than the pressure differential of interest. During the test, the pressure differential decreases due to leakage. When the operator subjectively determines that the desired pressure differential has been achieved and sufficient data has been collected, the test is stopped. Subsequently, the data analyst identifies a subset of the collected data to be used for mass loss computations. A typical computation utilizes a linear fit of the mass-time data set, wherein the slope of the line is the mass loss rate. It is common to use the largest data subset to minimize the measurement uncertainty; however, the data set must not be so large that the curve fit is nonlinear.

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Flight Test System for Accurately Predicting Flutter

Armstrong Flight Research Center, Edwards, California Traditional methods of flight flutter testing analyze system parameters such as damping levels that vary with flight conditions to monitor aircraft stability. In the past, the actual flight envelope developed for aircraft operation was essentially determined only by flight testing. The edges of the envelope are points where either the aircraft cannot fly any faster because of engine limitations, or, with a 15% margin for error, where the damping trends indicate a flutter instability may be near. After flight testing, the envelope empirically determined is used for regular operations.

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TestEVAL Software to Assist in Mechanical Testing

Goddard Space Flight Center, Greenbelt, Maryland Typically, mechanical test data has been reviewed and processed using a combination of Excel, PDF Viewer, MATLAB, and other tools. TestEVAL provides a central tool for all these tools, and enhances their capability. Having been developed in Python, it is expendable and portable. It uses no proprietary software and an all open-source code base.

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Technique to Measure Degradation of Submillimeter-Wave Spectrometer Response to Local Oscillator Phase Noise

This technique uses one LO source with known high purity that can be fixed in frequency and the LO source under test. NASA’s Jet Propulsion Laboratory, Pasadena, California High-resolution submillimeter-wave spectroscopy is based on the heterodyne principle, where the incident signal is down-converted to a low intermediate frequency (IF) by nonlinear mixing with a local oscillator (LO) signal. The IF difference frequency output is discrete Fourier transformed into ≈1,000 frequency channels to measure the spectral power dependence of the signal. Unfortunately, the LO system cannot generate pure tones: the signal has a “skirt” of additional power in the vicinity that generally decreases in spectral power density as the frequency difference from the center increases. This extra signal is known as phase noise.

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Polymer Nanofiber-Based Reversible Nano-Switch/Sensor Schottky Diode (nanoSSSD) Device

This microsensor has applications in biomedical devices, combustion engines, and detection/switching devices used in mass transit systems. John H. Glenn Research Center, Cleveland, Ohio NASA’s Glenn Research Center has developed a groundbreaking new microsensor that detects toxic gases and explosives in a variety of environments. Most devices can perform only a unidirectional sensing task, lacking a switching feature that would allow the device to return to baseline operation after the volatile species is removed or has dissipated. Glenn’s nano-Switch Sensor Schottky Diode (nanoSSSD) device consists of a thin film of graphene deposited on a specially prepared silicon wafer. Graphene’s two-dimensional properties make this technology both extremely sensitive to different gases and highly reliable in harsh, enclosed, or embedded conditions. The nanoSSSD can be connected to a visual and/or sound alarm that is autonomously triggered as the sensor detects a selected gas, and then is returned to its passive mode when the gas is no longer present. The innovation has applications in biomedical devices, combustion engines, and detection/switching devices used in mass transit systems.

Posted in: Briefs, Electronics & Computers

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