Tech Briefs

Fiber-Optic Gratings for Lidar Measurements of Water Vapor

These are highly selective, lightweight, tunable optical filters. Narrow-band filters in the form of phase-shifted Fabry-Perot Bragg gratings incorporated into optical fibers are being developed for differential-absorption lidar (DIAL) instruments used to measure concentrations of atmospheric water vapor. The basic idea is to measure the relative amounts of pulsed laser light scattered from the atmosphere at two nearly equal wavelengths, one of which coincides with an absorption spectral peak of water molecules and the other corresponding to no water vapor absorption. As part of the DIAL measurement process, the scattered light is made to pass through a filter on the way to a photodetector. Omitting other details of DIAL for the sake of brevity, what is required of the filter is to provide a stop band that

Posted in: Briefs, TSP, Physical Sciences, Fiber optics, Lidar, Humidity, Product development


Magnetic Field Solvers

The Magnetic Field Solver computer program calculates the magnetic field generated by a group of collinear, cylindrical axisymmetric electromagnet coils. Given the current flowing in, and the number of turns, axial position, and axial and radial dimensions of each coil, the program calculates matrix coefficients for a finite-difference system of equations that approximates a two-dimensional partial differential equation for the magnetic potential contributed by the coil. The program iteratively solves these finite-difference equations by use of the modified incomplete Cholesky preconditioned-conjugate-gradient method. The total magnetic potential as a function of axial (z) and radial (r) position is then calculated as a sum of the magnetic potentials of the individual coils, using a high-accuracy interpolation scheme. Then the r and z components of the magnetic field as functions of r and z are calculated from the total magnetic potential by use of a high-accuracy finite-difference scheme. Notably, for the finite-difference calculations, the program generates nonuniform two-dimensional computational meshes from nonuniform one-dimensional meshes. Each mesh is generated in such a way as to minimize the numerical error for a benchmark one-dimensional magnetostatic problem.

Posted in: Briefs, Physical Sciences, Mathematical models, Computer software and hardware, Electromagnetic compatibility


Silicon-Based Optical Modulator With Ferroelectric Layer

This device would remain switched even with power turned off. According to a proposal, a silicon dioxide layer in a high speed, low power, silicon-based electro-optical modulator would be replaced by a layer of lead zirconate titanate or other ferroelectric oxide material. The purpose of this modification is to enhance the power performance and functionality of the modulator.

Posted in: Briefs, TSP, Semiconductors & ICs, Capacitors, Switches, Performance upgrades, Ferrous metals and alloys, Semiconductors, Silicon alloys


Multiplexing Transducers Based on Tunnel-Diode Oscillators

Compact, low-power transducers could operate over wide temperature ranges. Multiplexing and differential transducers based on tunnel-diode oscillators (TDOs) would be developed, according to a proposal, for operation at very low and/or widely varying temperatures in applications that involve requirements to minimize the power and mass of transducer electronic circuitry. It has been known since 1975 that TDOs are useful for making high-resolution (of the order of 10–9) measurements at low temperatures. Since that time, TDO transducers have been found to offer the following additional advantages, which the present proposal is intended to exploit:

Posted in: Briefs, TSP, Semiconductors & ICs, Downsizing, Capacitors, Product development, Semiconductors


Scheduling With Automatic Resolution of Conflicts

DSN Requirement Scheduler is a computer program that automatically schedules, reschedules, and resolves conflicts for allocations of resources of NASA’s Deep Space Network (DSN) on the basis of ever changing project requirements for DSN services. As used here, “resources” signifies, primarily, DSN antennas, ancillary equipment, and times during which they are available. Examples of project-required DSN services include arraying, segmentation, very-long-baseline interferometry, and multiple spacecraft per aperture. Requirements can include periodic reservations of specific or optional resources during specific time intervals or within ranges specified in terms of starting times and durations. This program is built on the Automated Scheduling and Planning Environment (ASPEN) software system (aspects of which have been described in previous NASA Tech Briefs articles), with customization to reflect requirements and constraints involved in allocation of DSN resources. Unlike prior DSN-resource scheduling programs that make single passes through the requirements and require human intervention to resolve conflicts, this program makes repeated passes in a continuing search for all possible allocations, provides a best-effort solution at any time, and presents alternative solutions among which users can choose.

Posted in: Briefs, TSP, Software, Artificial intelligence, Computer software and hardware, Wireless communication systems, Logistics, Systems management


Computing for Aiming a Spaceborne Bistatic-Radar Transmitter

BISTAT is a computer program for use in aiming a spaceborne bistatic-radar transmitting antenna at a remote planet that has an atmosphere, such that after refraction by the atmosphere and reflection from the surface of the planet, the radar signal travels toward a receiver on Earth.  BISTAT includes an algorithm that neglects atmospheric refraction and calculates a specular reflection point for a spacecraft at a given location. The specular-reflection point is then used as an initial guess for a modified limb-track algorithm that takes atmospheric refraction into account. The output of BISTAT for all spacecraft positions of interest constitutes a pointing profile; the output data are in the form of an inertial-vector file and a Doppler-residual file. The inertial-vector file is used to command the attitude of the spacecraft; the Doppler residual file is used to determine a downlink frequency file for the receiver.

Posted in: Briefs, TSP, Software, Antennas, Attitude control, Communication protocols, Computer software and hardware, Radar, Spacecraft


Symbolic Constraint Maintenance Grid

Version 3.1 of Symbolic Constraint Maintenance Grid (SCMG) is a software system that provides a general conceptual framework for utilizing pre-existing programming techniques to perform symbolic transformations of data.  SCMG also provides a language (and an associated communication method and protocol) for representing constraints on the original nonsymbolic data. SCMG provides a facility for exchanging information between numeric and symbolic components without knowing the details of the components themselves. In essence, it integrates symbolic software tools (for diagnosis, prognosis, and planning) with non-artificial-intelligence software. SCMG executes a process of symbolic summarization and monitoring of continuous time series data that are being abstractly represented as symbolic templates of information exchange. This summarization process enables such symbolic-reasoning computing systems as artificial-intelligence planning systems to evaluate the significance and effects of channels of data more efficiently than would otherwise be possible. As a result of the increased efficiency in representation, reasoning software can monitor more channels and is thus able to perform monitoring and control functions more effectively.

Posted in: Briefs, TSP, Software, Computer software and hardware, Cryptography, Terminology


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