Special Coverage

Technique Provides Security for Multi-Robot Systems
Bringing New Vision to Laser Material Processing Systems
NASA Tests Lasers’ Ability to Transmit Data from Space
Converting from Hydraulic Cylinders to Electric Actuators
Automating Optimization and Design Tasks Across Disciplines
Vibration Tables Shake Up Aerospace and Car Testing
Supercomputer Cooling System Uses Refrigerant to Replace Water
Computer Chips Calculate and Store in an Integrated Unit
Electron-to-Photon Communication for Quantum Computing

Ultralight Balloon Systems for Exploring Uranus and Neptune

A report proposes ultralight balloon systems to carry a 10-kg payload, including scientific instruments for exploring the atmospheres of Uranus and Neptune. The system masses to be transported to those planets would be kept low by not transporting balloon-inflating gases. Each system would include an upper balloon about 4 m in diameter (0.5 kg) connected via a small port (about 0.25 m in diameter) to a lower balloon about 15 m in diameter (6.4 kg). Through an opening in the lower balloon, the balloons would become filled with low-molecular-weight atmospheric gas (which has little methane content) during initial descent through the upper atmosphere. At some point in the descent, the opening would be closed. Thereafter, the collected gas would provide buoyancy in the higher-molecular-weight atmosphere (methane content ≈2 percent) in the exploration altitude range below the methane-cloud tops, and the lower balloon (used for collection only) would be dropped. The altitude could be held constant or could be regulated by alternately venting gas and dropping ballast, as is done on balloons in the terrestrial atmosphere.

Posted in: Briefs, TSP, Physical Sciences, Test equipment and instrumentation
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Foaming in Place for Outer-Space Applications

A report discusses the adaptation of foaming-in-place techniques and materials to outer-space applications. Foaming in place is used commercially in terrestrial sealing, insulating, bonding, and retrofitting applications. The room-temperature outer-space versions of foaming in place are expected not to differ much from the terrestrial versions, and experiments have confirmed that a commercial two-component liquid polyurethane foaming system could be used on Mars at and near room temperature. However, chemical formulations different from the commercial ones would be needed for foaming at low temperatures.

Posted in: Briefs, TSP, Materials, Foams
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Partial Subtractive Dither for Lossy Data Compression

A new technique provides a compromise between benefits and costs of standard subtractive dither.

A technique of partial subtractive dither has been developed to improve the performance of any of a variety of near-lossless data-compression algorithms. The technique may be applicable to compression of scientific and medical image data.

Posted in: Briefs, TSP, Information Sciences, Mathematical models
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Acquisition, Tracking, and Pointing in Optical Communication

A document in the form of lecture slides outlines a program of development of capabilities for acquisition of signals, tracking of signal sources, and pointing of transmitters and receivers in deep-space optical communications. Topics addressed on the first few slides include the benefits and challenges of optical communications and the historical and organizational background of continuing development efforts. Most of the remaining slides address selected technical aspects of acquisition, tracking and pointing (ATP) in various levels of detail; these aspects include basic principles of operation, beam-pointing requirements, sources of tracking and pointing errors, alternative approaches to tracking and pointing, concepts for the design and operation of ATP systems, and key technological developments that are necessary for attaining required levels of ATP performance. The last slide summarizes the major technical challenges; these include the difficulty of pointing the necessarily narrow transmitted laser beams, the need to suppress spacecraft vibrations in beam-pointing equipment, the need for bright beacons, and interference by scattered sunlight.

Posted in: Briefs, TSP, Electronics & Computers, Optics, Telecommunications, Optics, Telecommunications
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Software for Preprocessing of Raw SAR Data

The SAR Processing System Raw Data Processor (SPS RDS) computer program is used in the Alaska SAR Facility (ASF) to scan and decode raw data that have been downlinked from the European Remote Sensing Satellite (ERS), the Japanese Earth Resources Satellite (JERS), and the RADARSAT (a Canadian Earth-observation satellite) and recorded on high-density digital tape or disk. ["SAR" means "synthetic-aperture radar."] In its scanning role, the program reads a recorded downlink bit stream, performs PRN decoding as needed, extracts auxiliary information to identify data-acquisition times, correlates this information with spacecraft state vector information to determine locations, and maps the locations to predefined fixed frames along an orbit track. These frames are stored in an archive as they become available, and are subsequently interrogated when requests for generation of image products are received. In its decoding role, this program converts a downlink bit stream that pertains to a requested frame into files that contain decoded engineering and SAR signal data that are compatible with the computers and programs used in further processing of SAR data into final image and image data products.

Posted in: Briefs, TSP, Information Sciences, Computer software / hardware, Computer software and hardware, Data acquisition and handling, Remote sensing, Computer software / hardware, Computer software and hardware, Data acquisition and handling, Remote sensing
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Variable Telemetry Playback Rate for Increased Data Return

The rate is adjusted nearly continuously according to a predicted signal-to-noise ratio.

In a scheme to increase the overall data return from a phase-modulation, suppressed-carrier telemetry transmitter, the telemetry playback symbol rate is adjusted essentially continuously. More precisely, the playback symbol rate is adjusted frequently (as often as once per symbol period) in small increments. The adjustment of the rate is made in accordance with the principle that the supportable data rate at any given instant is a function of the instantaneous total signal-power-to-noise spectral-density ratio (PT/N0) at the receiver. The scheme was devised for transmission of telemetric data from deep-space missions, but could also be applied to satellites in orbit around the Earth.

Posted in: Briefs, TSP, Electronics & Computers, Telemetry, Telemetry, Spacecraft
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Software for Locating Heterogeneous Data in Different Places

The Object Oriented Data Technology group at NASA's Jet Propulsion Laboratory is developing software for locating data — especially scientific data — stored in various formats on heterogeneous computer systems at different locations. The software is intended to exploit and extend advances in Internet software and in distributed object-oriented software to overcome the technological obstacles to integration of heterogeneous computing environments. The approach taken in this development involves refocusing effort on the development of metadata, which would be used to describe the available data resources and to support interoperability of computing systems. The software would manage a hierarchical conglomerate of data-set-resource definitions that would make it possible for application programs to locate the data that they require, without advance knowledge of which computer data systems and catalogs to search. This software would utilize the Extensible Markup Language (XML) and the Common Object Request Broker Architecture (CORBA) to support for interchange of data among heterogeneous sources. CORBA would enable over-the-wire exchange of XML-based profiles that would contain descriptions of data stored in remote computer systems.

Posted in: Briefs, TSP, Information Sciences, Computer software / hardware, Computer software and hardware, Data acquisition and handling, Computer software / hardware, Computer software and hardware, Data acquisition and handling
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Measuring Contact Angles of a Sessile Drop and Imaging Convection Within It

Ordinary and laser-shadowgraph images yield valuable information.

Figure 1 depicts an apparatus that simultaneously and synchronously records magnified ordinary top-view video images and laser-shadowgraph video images of a sessile drop. The real-time values of contact angle and rate of evaporation of the drop as functions of time can be calculated from the apparent diameters of the drop in the sequences of the images. In addition, the shadowgraphs contain flow patterns indicative of thermocapillary convection (if any) within the drop. These time-dependent parameters and flow patterns are important for understanding the physical processes involved in the spreading of evaporating liquids in such diverse technological applications as coating (including painting), film cooling, processing of materials, lubrication, and boiling. Study of the spreading of drops can also contribute to understanding of the spreading of biological cells.

Posted in: Briefs, TSP, Test & Measurement, Imaging, Imaging and visualization, Imaging, Imaging and visualization
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Improved Encryption-Mode GPS Receiver

An auxiliary antenna is used to improve the estimate of the GPS A-code.

An improved Global Positioning System (GPS) receiver, which processes an encrypted P-code signal without knowledge of the encryption code (denoted here as A-codeless mode), includes an auxiliary antenna and associated additional signal-processing circuitry. The improved design of this receiver makes it possible to achieve signal-to-noise ratios (SNRs) greater than that of prior A-codeless-mode GPS receivers, especially when GPS satellites appear at low elevation angles.

Posted in: Briefs, TSP, Electronics & Computers, Antennas, Global positioning systems, Global positioning systems (GPS), Antennas, Global positioning systems, Global positioning systems (GPS)
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Low-Power, Sparse-Sampling GPS Receiver

Performance can approach that of a heavier, higher-power, full-fledged GPS receiver.

The term "microGPS" denotes a Global Positioning System (GPS) receiver design concept that combines relatively simple, lightweight, low-power-consumption hardware with portable, efficient software. The power demand of a microGPS receiver can be made low because it is designed to sample sparsely; that is, to "awaken" from a "sleep" mode only occasionally to sample GPS signals during short intervals. MicroGPS was conceived for navigational use aboard some small Earth-orbiting satellites for which full-fledged GPS receivers would be too complex, massive, and power hungry, and for which positioning errors as large as a few hundred meters would be acceptable as part of the price of low mass and low power consumption. The microGPS concept may also prove attractive for terrestrial applications that involve similar design tradeoffs.

Posted in: Briefs, TSP, Electronics & Computers, Architecture, Global positioning systems, Global positioning systems (GPS), Architecture, Global positioning systems, Global positioning systems (GPS), Satellites
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