Special Coverage

Home

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: Physical Sciences, Briefs, TSP

Read More >>

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: Physical Sciences, Briefs, TSP

Read More >>

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: Physical Sciences, Briefs, TSP

Read More >>

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: Physical Sciences, Briefs, TSP

Read More >>

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: Physical Sciences, Test & Measurement, Briefs, TSP

Read More >>

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: Physical Sciences, Test & Measurement, Briefs, TSP

Read More >>

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: Physical Sciences, Test & Measurement, Briefs, TSP

Read More >>