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


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