Tech Briefs

Formation-Initialization Algorithm for N Spacecraft

A paper presents an algorithm to initialize a formation of N distributed spacecraft in deep space. Such formations will enable variable-baseline interferometers in future NASA missions designed to study the structure and origin of the universe. The algorithm described in the paper reflects some basic assumptions:

Each spacecraft is capable of omnidirectional radio communication with any other spacecraft, Each spacecraft is equipped with a limited field-of-view sensor relative position sensor (RPS) to measure the relative positions and velocities of other formation members, and Spacecraft maneuvers must satisfy Sun-angle pointing constraints to shield sensitive optical equipment from direct sunlight.
Posted in: Briefs, TSP, Mechanical Components, Mechanics, Mathematical models, Test equipment and instrumentation, Spacecraft

DNSs of Multicomponent Gaseous and Drop-Laden Mixing Layers Achieving Transition to Turbulence

A paper describes direct numerical simulations (DNSs) of three-dimensional mixing-layer flows undergoing transition to turbulence; the mixing layers may or may not be laden with evaporating liquid drops. In contrast to most studies in this field, the general case is investigated here where both the gas and the liquid drops’ composition encompasses a very large number of species. The simulations were performed using a mathematical model discussed in several prior NASA Tech Briefs articles; the prior studies described a laminar mixing layer, whereas the present study describes a mixing layer that has all attributes of turbulence. The model includes governing equations in an Eulerian and a Lagrangian reference frame for the gas and drops, respectively. To mathematically describe the myriad of species, the model relies on continuous thermodynamics concepts. The paper succinctly reiterates the model and discusses results of the new numerical simulations. Comparisons are performed with previous single-species similar simulations and with the laminar simulations using the same model. The paper presents several conclusions, the main one being that differences between single- and multi-species turbulent flows having the same initial conditions are so significant that neither experiments on, nor theoretical studies of, single-species flows are adequate as surrogates for studies of multi-species flows.

Posted in: Briefs, TSP, Physical Sciences, Computer simulation, Mathematical models, Turbulence

Noise-Canceling Helmet Audio System

Voice communication is enhanced by digital processing to suppress noise.

A prototype helmet audio system has been developed to improve voice communication for the wearer in a noisy environment. The system was originally intended to be used in a space suit, wherein noise generated by airflow of the spacesuit life-support system can make it difficult for remote listeners to understand the astronaut’s speech and can interfere with the astronaut’s attempt to issue vocal commands to a voice-controlled robot. The system could be adapted to terrestrial use in helmets of protective suits that are typically worn in noisy settings: examples include biohazard, fire, rescue, and diving suits.

Posted in: Briefs, Electronics & Computers, Audio equipment, Wireless communication systems, Audio equipment, Wireless communication systems, Product development, Helmets, Protective equipment, Spacesuits

Program Analyzes Spacecraft/Ground Radio Links

A versatile computer program analyzes the link-design control table necessary for designing the telecommunication subsystem of a spacecraft in orbit around the Earth or on a deep-space mission. The program helps to calculate all the important parameter values for spacecraft-to-ground telemetry links and ground-to-spacecraft command links. The program also enables the design of turn-around ranging and one-way ranging links, which are very useful for determining the positions of spacecraft and for satisfying various other operational needs. The user can specify several aspects of spacecraft telecommunication- subsystem design, including the nature of the antenna (paraboloidal reflector, patch, dipole, etc.), the power-amplifier rating, and the link data rate.

Posted in: Briefs, TSP, Software, Computer software / hardware, Computer software and hardware, Radio equipment, Telecommunications, Computer software / hardware, Computer software and hardware, Radio equipment, Telecommunications, Spacecraft

Six-Message Electromechanical Display System

This system would overcome the three-message limit of prior such systems.

A proposed electromechanical display system would be capable of presenting as many as six distinct messages. This system would be a more capable and more complex successor to the proposed system reported in “Four-Message Electromechanical Display System” (MFS-31368), NASA Tech Briefs, Vol. 24, No. 4 (April 2000), page 32. In contrast to the now-proposed six-message system and the previously proposed four-message system, a typical conventional electromechanical display system is limited to three messages.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Displays, Displays

Two-Way Communication Using RFID Equipment and Techniques

Dynamic data could be exchanged, in addition to conventional static RFID data.

Equipment and techniques used in radio-frequency identification (RFID) would be extended, according to a proposal, to enable short-range, two-way communication between electronic products and host computers. In one example of a typical contemplated application, the purpose of the short-range radio communication would be to transfer image data from a user’s digital still or video camera to the user’s computer for recording and/or processing. The concept is also applicable to consumer electronic products other than digital cameras (for example, cellular telephones, portable computers, or motion sensors in alarm systems), and to a variety of industrial and scientific sensors and other devices that generate data.

Posted in: Briefs, TSP, Electronics & Computers, Architecture, Data exchange, Imaging, Imaging and visualization, Radio equipment, Wireless communication systems, Architecture, Data exchange, Imaging, Imaging and visualization, Radio equipment, Wireless communication systems

Compact Packaging of Photonic Millimeter-Wave Receiver

Bulky positioning mechanisms are not needed

A carrier structure made from a single silicon substrate is the basis of a compact, lightweight, relatively inexpensive package that holds the main optical/electronic coupling components of a photonic millimeter- wave receiver based on a lithium niobate resonator disk. The design of the package is simple and provides for precise relative placement of optical components, eliminating the need for complex, bulky positioning mechanisms like those commonly used to align optical components to optimize focus and coupling. Although a prototype of the package was fabricated as a discrete unit, the design is amenable to integration of the package into a larger photonic and/or electronic receiver system.

Posted in: Briefs, TSP, Physical Sciences, Optics, Optics, Packaging

Fabrication of Submillimeter Axisymmetric Optical Components

Surfaces of components can be arbitrarily shaped to optimize spectral responses.

It is now possible to fashion transparent crystalline materials into axisymmetric optical components having diameters ranging from hundreds down to tens of micrometers, whereas previously, the smallest attainable diameter was 500 m. A major step in the fabrication process that makes this possible can be characterized as diamond turning or computer numerically controlled machining on an ultrahigh-precision lathe. This process affords the flexibility to make arbitrary axisymmetric shapes that have various degrees of complexity: examples include a flat disk or a torus supported by a cylinder (see figure), or multiple closely axially spaced disks or tori supported by a cylinder. Such optical components are intended mainly for use as whispering-gallery- mode optical resonators in diverse actual and potential applications, including wavelength filtering, modulation, photonic generation and detection of microwaves, and research in quantum electrodynamics and quantum optics.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Optics, Optics, Fabrication

Mapping Nearby Terrain in 3D by Use of a Grid of Laser Spots

A relatively simple system would utilize triangulation.

A proposed optoelectronic system, to be mounted aboard an exploratory robotic vehicle, would be used to generate a three-dimensional (3D) map of nearby terrain and obstacles for purposes of navigating the vehicle across the terrain and avoiding the obstacles. Like some other systems that have been, variously, developed and proposed to perform similar functions, this system would include (1) a light source that would project a known pattern of bright spots onto the terrain, (2) an electronic camera that would be laterally offset from the light source by a known baseline distance, (3) circuitry to digitize the output of the camera during imaging of the light spots, and (4) a computer that would calculate the 3D coordinates of the illuminated spots from their positions in the images by triangulation.

Posted in: Briefs, TSP, Electronics & Computers, Imaging, Imaging and visualization, Imaging, Imaging and visualization, Terrain, Robotics

Wide-Band, High-Quantum-Efficiency Photodetector

This device could detect single photons.

A design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 μm. This and similar photodetectors would afford a capability for detecting single photons — a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys.

Posted in: Briefs, TSP, Physical Sciences, Optics, Optics, Research and development

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