Physical Sciences

JWST Integrated Science Instrument Module Alignment Optimization Tool

During cryogenic vacuum testing of the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM), the global alignment of the ISIM with respect to the designed interface of the JWST optical telescope element (OTE) will be measured through a series of optical characterization tests. These tests will determine the locations and orientations of the JWST science instrument projected focal surfaces and entrance pupils with respect to their corresponding OTE optical interfaces. If any optical performance non-compliances are identified, the ISIM will be adjusted to improve its performance. In order to understand how to manipulate the ISIM’s degrees of freedom properly and to prepare for the ISIM flight model testing, a series of opticalmechanical analyses have been completed to develop and identify the best approaches for bringing a non-compliant ISIM element into compliance.

Posted in: Briefs, TSP, Physical Sciences, Optics, Performance tests, Test procedures

Radar Range Sidelobe Reduction Using Adaptive Pulse Compression Technique

There is significant improvement on sidelobe performance.

Pulse compression has been widely used in radars so that low-power, long RF pulses can be transmitted, rather than a high-power short pulse. Pulse compression radars offer a number of advantages over high-power short pulsed radars, such as no need of highpower RF circuitry, no need of high-voltage electronics, compact size and light weight, better range resolution, and better reliability. However, range sidelobe associated with pulse compression has prevented the use of this technique on spaceborne radars since surface returns detected by range sidelobes may mask the returns from a nearby weak cloud or precipitation particles. Research on adaptive pulse compression was carried out utilizing a field-programmable gate array (FPGA) waveform generation board and a radar transceiver simulator. The results have shown significant improvements in pulse compression sidelobe performance.

Posted in: Briefs, TSP, Physical Sciences, Radar, Research and development, Spacecraft

Digitally Calibrated TR Modules Enabling Real-Time Beamforming SweepSAR Architectures

Civilian and military remote sensing instruments could benefit from this work, as well as military intelligence applications.

SweepSAR, a novel radar architecture that depends on a DBF (digital beamforming) array, requires calibration accuracies that are order(s) of magnitude greater than is possible with traditional techniques, such as a priori characterization of TR (transmit/receive) modules in thermal vacuum chambers, or simple loop-back of the calibration signal. The advantages of a SweepSAR architecture are so great that it is worth applying significant resources to calibration efforts.

Posted in: Briefs, TSP, Physical Sciences, Calibration, Architecture, Radar

Electro-Optic Time-to-Space Converter for Optical Detector Jitter Mitigation

The ability to more precisely measure the arrival time of an optical pulse is valuable in free space optical communications, lidar, and quantum key distribution.

A common problem in optical detection is determining the arrival time of a weak optical pulse that may comprise only one to a few photons. Currently, this problem is solved by using a photodetector to convert the optical signal to an electronic signal. The timing of the electrical signal is used to infer the timing of the optical pulse, but error is introduced by random delay between the absorption of the optical pulse and the creation of the electrical one. To eliminate this error, a time-to-space converter separates a sequence of optical pulses and sends them to different photodetectors, depending on their arrival time.

Posted in: Briefs, TSP, Physical Sciences, Failure analysis, Optics, Sensors and actuators

Partially Transparent Petaled Mask/Occulter for Visible-Range Spectrum

The intensity along the optical axis can be suppressed up to ten orders of magnitude.

The presence of the Poisson Spot, also known as the spot of Arago, has been known since the 18th century. This spot is the consequence of constructive interference of light diffracted by the edge of the obstacle where the central position can be determined by symmetry of the object. More recently, many NASA missions require the suppression of this spot in the visible range. For instance, the exoplanetary missions involving space telescopes require telescopes to image the planetary bodies orbiting central stars. For this purpose, the starlight needs to be suppressed by several orders of magnitude in order to image the reflected light from the orbiting planet. For the Earth-like planets, this suppression needs to be at least ten orders of magnitude. One of the common methods of suppression involves sharp binary petaled occulters envisioned to be placed many thousands of miles away from the telescope blocking the starlight.

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

Fast, High-Precision Readout Circuit for Detector Arrays

The GEO-CAPE mission described in NASA’s Earth Science and Applications Decadal Survey requires high spatial, temporal, and spectral resolution measurements to monitor and characterize the rapidly changing chemistry of the troposphere over North and South Americas. High-frame-rate focal plane arrays (FPAs) with many pixels are needed to enable such measurements.

Posted in: Briefs, TSP, Physical Sciences, Test & Measurement, Measurements, Antennas, Integrated circuits, Weather and climate

A System for Measuring the Sway of the Vehicle Assembly Building

Tests have shown that the existing facility is safe.

A system was developed to measure the sway of the Vehicle Assembly Building (VAB) at Kennedy Space Center. This system was installed in the VAB and gathered more than one total year of data. The building movement was correlated with measurements provided by three wind towers in order to determine the maximum deflection of the building during high-wind events.

Posted in: Briefs, TSP, Physical Sciences, Test & Measurement, Measurements, Air transportation facilities, Test equipment and instrumentation, Aerodynamics

ISS Ammonia Leak Detection Through X-Ray Fluorescence

An astrophysics instrument can be used to detect and localize ISS ammonia leaks.

Ammonia leaks are a significant concern for the International Space Station (ISS). The ISS has external transport lines that direct liquid ammonia to radiator panels where the ammonia is cooled and then brought back to thermal control units. These transport lines and radiator panels are subject to stress from micrometeorites and temperature variations, and have developed small leaks. The ISS can accommodate these leaks at their present rate, but if the rate increased by a factor of ten, it could potentially deplete the ammonia supply and impact the proper functioning of the ISS thermal control system, causing a serious safety risk.

Posted in: Briefs, TSP, Physical Sciences, Test & Measurement, Hoses, Radiators, Hazardous materials, Risk assessments, Spacecraft

Hydrometeor Size Distribution Measurements by Imaging the Attenuation of a Laser Spot

Measurement of the DSD’s second moment is made by way of the Beer-Lambert law.

The optical extinction of a laser due to scattering of particles is a well-known phenomenon. In a laboratory environment, this physical principle is known as the Beer-Lambert law, and is often used to measure the concentration of scattering particles in a fluid or gas. This method has been experimentally shown to be a usable means to measure the dust density from a rocket plume interaction with the lunar surface. Using the same principles and experimental arrangement, this technique can be applied to hydrometeor size distributions, and for launch-pad operations, specifically as a passive hail detection and measurement system.

Posted in: Briefs, TSP, Physical Sciences, Test & Measurement, Measurements, Lasers, Particulate matter (PM), Refractory materials, Test equipment and instrumentation

Victim Simulator for Victim Detection Radar

This simulator can be placed for long periods of time in environments that would be unsafe for a human subject.

Testing of victim detection radars has traditionally used human subjects who volunteer to be buried in, or climb into a space within, a rubble pile. This is not only uncomfortable, but can be hazardous or impractical when typical disaster scenarios are considered, including fire, mud, or liquid waste. Human subjects are also inconsistent from day to day (i.e., they do not have the same radar properties), so quantitative performance testing is difficult. Finally, testing a multiple-victim scenario is difficult and expensive because of the need for multiple human subjects who must all be coordinated.

Posted in: Briefs, TSP, Physical Sciences, Test & Measurement, Computer simulation, Radar, Disaster and emergency management, Emergency management, Anthropometric test devices, Test equipment and instrumentation

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