Test & Measurement

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.

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

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.

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

Micro-Force Sensing Nanoprobe

The NGXO (Next Generation X-Ray Optics) project has several problems relating to how to bond a very thin glass mirror to a metallic structure without distortion. One problem is that all epoxies shrink (at the micron level) when they cure. This shrinkage distorts the optical quality of the mirror unacceptably. Another problem is how to correlate finite element models of thin glass mirrors to verify that they are accurately predicting the distortions that a real glass will see due to enforced displacements, such as those applied by epoxy shrinkage. The forces required to simulate epoxy shrinkage and to balance a mirror on a bed of actuators are in the 100-1000 micro-newton range. The displacements are on the order of a few microns. These tiny forces and displacements cannot be easily measured or actuated with typical lab equipment.

Posted in: Briefs, Test & Measurement, Mirrors, Sensors and actuators, Nanotechnology, Resins, Test equipment and instrumentation

High-Channel-Count, High-Scan-Rate Data Acquisition System for the NASA Langley Transonic Dynamics Tunnel

The NASA Langley Research Center (LaRC) Transonic Dynamics Tunnel (TDT) has been operational since 1960, investigating a wide range of aeroelastic and non-aeroelastic phenomena. A dedicated aeroelastic test facility, the TDT is a large, variable-pressure, transonic wind tunnel. To support unique types of aeroelastic and dynamic tests, the TDT possesses a dynamic data acquisition system (DAS) with synchronous scanning of all analog channels. Steady (static) values are simply computed as the mean of any signal. The existing TDT DAS is referred to as the Open Architecture Data Acquisition System (OA-DAS). An effort was initiated to replace OA-DAS in order to increase the scan rate, increase the channel count, increase the reliability, increase user friendliness, and improve upon some features while maintaining synchronous scanning and other unique abilities. This effort has been spearheaded by researchers within the Aeroelasticity Branch (AB) co-located with the TDT; hence, the new data system has been named AB-DAS. The new data system will serve as the primary data system and will substantially increase the scan rate capabilities and analog channel count. This synchronous and dynamic system enables high-channel-count buffet and aeroacoustic tests in addition to the range of other testing done at TDT.

Posted in: Briefs, Test & Measurement, Architecture, Data acquisition and handling, Test facilities, Wind tunnel tests

Fusible Alloy Thermometer

This work was based on the need for a relatively small passive detector of maximum temperature reached by an object that can be visually inspected. The device requirements are to be hermetically sealed for contamination control, give a clear indication of maximum temperature achieved (non-reversible) with a ~10 °C resolution, have an essentially unlimited shelf-life and insensitivity to radiation, be passive without any electronics or mechanisms, provide good thermal conductivity, and be low-cost. Prior detectors have an unclear lifetime, contamination outgassing properties, and radiation tolerance. These could be used at much higher temperatures than plastic methods (>>100 °C), though out of scope for the tests performed to date.

Posted in: Briefs, Test & Measurement, Measurements, Thermodynamics, Alloys

Small-Volume Pressurized Sample Handling System

A method was developed for effective, efficient, non-destructive, in-situ sample processing. Pressure vessels are used for sample delivery and collection, a shaker is used to keep the particles suspended, a back pressure of argon gas is used to keep the system under pressure to regulate the flow, and flow restrictors and frits are used that never come into contact with the sample slurry to avoid clogs.

Posted in: Briefs, Test & Measurement, Soils, Containers, Non-destructive tests

Live-Cell Microscopy and Traction Force Measurements with Simulated Microgravity “Clinochip”

The deleterious effects of microgravity are undeniable: reduced bone mineral density, muscle atrophy, vascular remodeling, etc. These health issues may derive from both systemic factors, and from direct alterations to intracellular components and in the local microenvironment around cells. To understand the biological mechanisms at play, detailed studies have been performed in spaceflight. However, because experiments on the International Space Station (ISS) can be prohibitively expensive, clinostats are an alternative ground-based analogue for cellular studies. Clinostats “randomize” the orientation of gravity with respect to the cell fixed-frame, thereby simulating microgravity by eliminating a preferential gravity direction.

Posted in: Briefs, TSP, Test & Measurement, Medical, health, and wellness, Biomechanics

Comparison of Three Methods for Measuring Distortion in Optical Windows

A new method for quantifying distortion based on phase-shifting interferometry has been developed.

The primary function of a window is to allow observation of, and protection from, a potentially hazardous environment. Yet, from the window designer’s point of view, ensuring protection from weather conditions in home windows; from wind, temperature, and airborne debris in automotive windows; and from extreme pressures and temperatures in aircraft and spacecraft windows has almost always taken precedence over image quality. It is more important to protect an astronaut from the vacuum of space than to provide clear imagery, yet these are not exclusive requirements. Advances in materials and material processing allow the designer to attain better optical performance while not sacrificing important material specifications such as strength. In addition, increased performance demands on spacecraft windows — which are now used for photography, telescope observation, and laser communications — require greater consideration of optical clarity.

Posted in: Briefs, TSP, Test & Measurement, Windows and windshields, Finite element analysis, Visibility, Spacecraft

Measurement of O-phthalaldehyde (OPA)

This analytical process uses high-pressure liquid chromatography (HPLC) with post-column derivatization.

O-phthalaldehyde (OPA) is a high-level disinfectant commonly used, for example, for sterilization of heat-sensitive medical instruments; it demonstrates effective microbicidal activity against a wide range of microorganisms (including mycobacteria, gramnegative bacteria, and spores). On the International Space Station (ISS), to achieve thermal control and maintain components at acceptable temperatures, systems that produce waste heat need to have that heat transferred from the ISS to space. To accomplish this, the ISS has an Internal Active Thermal Control System (IATCS) — a water-based system that works in conjunction with the EATCS (External ATCS), an ammoniabased system — to facilitate this heat transfer process.

Posted in: Briefs, Test & Measurement, Thermal management, Chemicals, Waste materials, Coolants, Spacecraft

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