Test & Measurement

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.

Posted in: Briefs, Test & Measurement, Suspension systems, Measurements, Fibers, Tensile Strength


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.

Posted in: Briefs, Test & Measurement, Mathematical analysis, Gases, Test procedures


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.

Posted in: Briefs, Test & Measurement, Vibration, Flight tests, Performance tests


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.

Posted in: Briefs, Test & Measurement, Computer software and hardware, Data management, Test equipment and instrumentation


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.

Posted in: Briefs, Test & Measurement, Mathematical analysis, Spectroscopy, Noise pollution


Laser Architecture and Atomic Filter for Daytime Measurements Using Spaceborne Sodium Lidar

Goddard Space Flight Center, Greenbelt, Maryland A satellite-borne sodium lidar will provide key measurements that elucidate the complex relation between the chemistry and dynamics of the Earth’s mesosphere, and thus provide a thorough understanding of the composition and dynamics of this region. The inclusion of a well-characterized mesosphere in global models is essential for weather and climate prediction in the lower atmosphere. It also will help to elucidate the complex vertical coupling processes through which atmospheric weather affects space weather. Furthermore, once the technique is developed, it can be used to study the composition of other planetary atmospheres, which is identified as a key point in the recent Planetary Decadal Survey.

Posted in: Briefs, Test & Measurement, Architecture, Cartography, Lidar, Weather and climate, Sodium


Rangefinder for Measuring Volume of Cryogenic or Caustic Turbulent Fluids

A non-intrusive laser rangefinder yields extremely accurate fluid height measurements. Stennis Space Center, Mississippi Specific impulse (ISP), or simply impulse (change in momentum) per unit amount of propellant consumed, is a measure of rocket and jet engine efficiency. The amount of propellant, or in the case of engine testing at the Stennis Space Center (SSC), cryogen consumed during rocket engine testing must be measured to accurately quantify ISP. One way to determine the amount of cryogen used is to measure the change in cryogen fluid height within a storage/feed tank during testing and then relate the change in height to volume of cryogen consumed. A float system coupled with discrete vertically positioned Reed switches is currently used at the SSC to determine cryogen fluid height and then determine cryogen consumed during a rocket motor test firing. However, the cryogen fluid level within a run tank varies continuously and the switches are placed at discrete locations, limiting the accuracy of this method. If individual switch failures occur, the error increases due to the increased distance between switches/measurement locations. In addition, since pressurized gas is used to force the significantly cooler liquid cryogen out of the tank during a test, the liquid cryogen surface is turbulent and not flat or smooth, which can also affect accuracy.

Posted in: Briefs, Test & Measurement, Switches, Liquid propellant rocket engines, Test procedures


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