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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Quaternary pulse position modulation electronics for free-space laser communications

The development of a high data-rate communications electronic subsystem for future application in free-space, direct-detection laser communications is described. The dual channel subsystem uses quaternary pulse position modulation (GPPM) and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data multiplexing, and QPPM symbol encoding. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented.

Budinger, J. M.↗
NASA NTRS1991

High current, high bandwidth laser diode current driver

A laser diode current driver has been developed for free space laser communications. The driver provides 300 mA peak modulation current and exhibits an optical risetime of less than 400 ps. The current and optical pulses are well behaved and show minimal ringing. The driver is well suited for QPPM modulation at data rates up to 440 Mbit/s. Much previous work has championed current steering circuits; in contrast, the present driver is a single-ended on/off switch. This results in twice the power efficiency as a current steering driver. The driver electrical efficiency for QPPM data is 34 percent. The high speed switch is realized with a Ku-band GaAsFET transistor, with a suitable pre-drive circuit, on a hybrid microcircuit adjacent to the laser diode.

Copeland, David J.↗
NASA NTRS1991

Ka-band MMIC microstrip array for high rate communications

In a recent technology assessment of alternative communication systems for the space exploration initiative (SEI), Ka-band (18 to 40 GHz) communication technology was identified to meet the mission requirements of telecommunication, navigation, and information management. Compared to the lower frequency bands, Ka-band antennas offer higher gain and broader bandwidths; thus, they are more suitable for high data rate communications. Over the years, NASA has played an important role in monolithic microwave integrated circuit (MMIC) phased array technology development, and currently, has an ongoing contract with Texas Instrument (TI) to develop a modular Ka-band MMIC microstrip subarray (NAS3-25718). The TI contract emphasizes MMIC integration technology development and stipulates using existing MMIC devices to minimize the array development cost. The objective of this paper is to present array component technologies and integration techniques used to construct the subarray modules.

Lee, R. Q.↗
NASA NTRS1991

Ka-band MMIC microstrip array for high rate communications

In a recent technology assessment of alternative communication systems for the space exploration initiative (SEI), Ka-band (18 to 40 GHz) communication technology was identified to meet the mission requirements of telecommunication, navigation, and information management. Compared to the lower frequency bands, Ka-band antennas offer higher gain and broader bandwidths; thus, they are more suitable for high data rate communications. Over the years, NASA has played an important role in monolithic microwave integrated circuit (MMIC) phased array technology development, and currently, has an ongoing contract with Texas Instrument (TI) to develop a modular Ka-band MMIC microstrip subarray (NAS3-25718). The TI contract emphasizes MMIC integration technology development and stipulates using existing MMIC devices to minimize the array development cost. The objective of this paper is to present array component technologies and integration techniques used to construct the subarray modules.

Lee, R. Q.↗
NASA NTRS1977

Flight boundary layer transition measurements on a slender cone at Mach 20

Experimental flight boundary layer transition data have been obtained on a 3.962-m-long, 5 deg half-angle cone with an initial nose radius of 0.254 cm. The data were obtained during re-entry from altitudes of approximately 30.480 to 18.288 km at a free-stream Mach number of 20. The free-stream Reynolds number varied from 6.56 x 10 to the 6th/m to 52.5 x 10 to the 6th/m, and the total enthalpy from about 18.3 to 16.9 MJ/kg. The locations of the beginning and end of transition were determined by the intersection of curves faired throug the laminar, transitional, and turbulent heating-rate data. The temperature-history technique for determining transition as currently used (sharp break in curve) was shown to compare unfavorably with the heating-rate-distribution method. The heating-rate-history technique, which is proportional to the temperature derivative and consequently more sensitive to perturbations, gives better agreement with the heating-rate distribution transition results.

Wright, R. L.↗
NASA NTRS1993

SLR data screening; location of peak of data distribution

At the 5th Laser Ranging Instrumentation Workshop held at Herstmonceux in 1984, consideration was given to the formation of on-site normal points by laser stations, and an algorithm was formulated. The algorithm included a recommendation that an iterated 3.0 x rms rejection criterion should be used to screen the data, and that arithmetic means should be formed within the normal point bins of the retained data. From Sept. 1990 onwards, this algorithm and screening criterion have been brought into effect by various laser stations for forming on-site normal points, and small variants of the algorithm are used by most analysis centers for forming normal points from full-rate data, although the data screening criterion they use ranges from about 2.5 to 3.0 x rms. At the CSTG Satellite Laser Ranging (SLR) Subcommission, a working group was set up in Mar. 1991 to review the recommended screening procedure. This paper has been influenced by the discussions of this working group, although the views expressed are primarily those of this author. The main thrust of this paper is that, particularly for single photon systems, a more important issue than data screening is the determination of the peak of a data distribution and hence, the determination of the bias of the peak from the mean. Several methods of determining the peak are discussed.

Sinclair, Andrew T.↗
NASA NTRS2013

GRAIL Science Data System Orbit Determination : Approach, Strategy, and Performance

This paper details orbit determination techniques and strategies employed within each stage of the larger iterative process of preprocessing raw GRAIL data into the gravity science measurements used within gravity field solutions. Each orbit determination pass used different data, corrections to them, and/or estimation parameters. We compare performance metrics among these passes. For example, for the primary mission, the magnitude of residuals using our orbits progressed from approximately or equal to19.4 to 0.077 approximately or equal to m/s for inter-satellite range rate data and from approximately or equal to 0.4 to approximately or equal to 0.1 mm/s for Doppler data.

Gravity Recovery and Interior Laboratory (GRAIL)↗
NASA NTRS1982

LANDSAT-D data format control book. Volume 2: Telemetry

The formats used for the transmission of LANDSAT-D and LANDSAT-D Prime spacecraft telemetry data through either the TDRS/GSTDN via the NASCOM Network to the CSF are described as well as the telemetry flow from the command and data handling subsystem, a telemetry list and telemetry matrix assignment for the mission and engineering formats. The on-board computer (OBC) controlled format and the dwell format are also discussed. The OBCs contribution to telemetry, and the format of the reports, are covered. The high rate data channel includes the payload correction data format, the narrowband tape recorder and the OBC dump formats.

Talipsky, R.↗
NASA NTRS1986

Adaptive Quantizer for Burst Synthetic-Aperture Radar

Adaptive quantizer for burst-mode synthetic-aperture radar reduces data rate of return signal. Device, called block floating-point quantizer (BFPQ) basically analog-to-digital converter that covers wide dynamic range and discards appropriate lower order bits. BFPQ is, in effect, digital approximator with automatic gain control. Moves floatingpoint marker binary representation of signal data in accordance with perceived dynamic range. Available step sizes thus limited to multiples of underlying smallest quantization step (represented by lowest order bit). Retains only first K most significant bits of signal; (L,K) BFPQ is one that does K-bit quantization of signal originally quantized to L bits. Quantization error simply difference between actual signal level and its binary approximation. Other potential applications for BFPQ include speech compression and picture data compression.

Joo, T. H.↗
NASA NTRS2006

The Mars Express - NASA Project at JPL

This viewgraph presentation gives a general overview of the Mars Express NASA Project at JPL. The contents include: 1) Mars Express/NASA Project Overview; 2) Experiment-Investigator Matrix; 3) Mars Express Support of NASA's Mars Exploration Objectives; 4) U.S./NASA Support of Mars Express; 5) Mars Express Schedule (2003-2007); 6) Mars Express Data Rates; 7) MARSIS Overview Results; 8) MARSIS with Antennas Deployed; 9) MARSIS Science Objectives; 10) Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) Experiment Overview; 11) Mars Express Orbit Evolution; 12) MARSIS Science - Subsurface Sounding; 13) MARSIS-North Polar Ice Cap; 14) MARSIS Data-Buried Basin; 15) MARSIS over a Crater Basin; 16) MARSIS-Buried Basin; 17) Ionogram - Orbit 2032 (example from Science paper); 18) Ionogram-Orbit 2018 (example from Science paper); and 19) Recent MARSIS Results ESA Press Releases.

Mars Express Mission↗
NASA NTRS2012

Scalable SCPPM Decoder

A decoder was developed that decodes a serial concatenated pulse position modulation (SCPPM) encoded information sequence. The decoder takes as input a sequence of four bit log-likelihood ratios (LLR) for each PPM slot in a codeword via a XAUI 10-Gb/s quad optical fiber interface. If the decoder is unavailable, it passes the LLRs on to the next decoder via a XAUI 10-Gb/s quad optical fiber interface. Otherwise, it decodes the sequence and outputs information bits through a 1-GB/s Ethernet UDP/IP (User Datagram Protocol/Internet Protocol) interface. The throughput for a single decoder unit is 150-Mb/s at an average of four decoding iterations; by connecting a number of decoder units in series, a decoding rate equal to that of the aggregate rate is achieved. The unit is controlled through a 1-GB/s Ethernet UDP/IP interface. This ground station decoder was developed to demonstrate a deep space optical communication link capability, and is unique in the scalable design to achieve real-time SCPP decoding at the aggregate data rate.

Quir, Kevin J.↗
NASA NTRSDate not supplied

Continuous Spacecraft Communications via Make-Before-Break Antenna Array Beam Steering

Active phased array (APA) antennas can electronically form multiple beams to track several targets simultaneously. Spacecraft equipped with these antennas can achieve continuous communications through a constellation of relay satellites by forming a second beam to an upcoming relay satellite before the spacecraft moves beyond the current relay’s line of sight. These make-before-break operations have utility for streaming critical data without gaps. Using characterization data from a commercially-available APA-based satellite communications terminal, we simulate performance from low-Earth orbit to a representative geosynchronous relay satellite system at Ka-band. Average data rates of 3 Mbps are achievable with a minimum rate of 0.8 Mbps during worst-case handovers. We prototype the beam-splitting algorithm in the terminal hardware and evaluate its performance in an antenna range. In an over-the-air test emulating a handover between two relays we observe error-free data in the combined telemetry stream.

active phased array antennas↗
NASA NTRS2011

A Pragmatic Path to Investigating Europa's Habitability

Assessment of Europa's habitability, as an overarching science goal, will progress via a comprehensive investigation of Europa's subsurface ocean, chemical composition, and internal dynamical processes, The National Research Council's Planetary Decadal Survey placed an extremely high priority on Europa science but noted that the budget profile for the Jupiter Europa Orbiter (1EO) mission concept is incompatible with NASA's projected planetary science budget Thus, NASA enlisted a small Europa Science Definition Team (ESDT) to consider more pragmatic Europa mission options, In its preliminary findings (May, 2011), the ESDT embraces a science scope and instrument complement comparable to the science "floor" for JEO, but with a radically different mission implementation. The ESDT is studying a two-element mission architecture, in which two relatively low-cost spacecraft would fulfill the Europa science objectives, An envisioned Europa orbital element would carry only a very small geophysics payload, addressing those investigations that are best carried out from Europa orbit An envisioned separate multiple Europa flyby element (in orbit about Jupiter) would emphasize remote sensing, This mission architecture would provide for a subset of radiation-shielded instruments (all relatively low mass, power, and data rate) to be delivered into Europa orbit by a modest spacecraft, saving on propellant and other spacecraft resources, More resource-intensive remote sensing instruments would achieve their science objectives through a conservative multiple-flyby approach, that is better situated to handle larger masses and higher data volumes, and which aims to limit radiation exposure, Separation of the payload into two spacecraft elements, phased in time, would permit costs to be spread more uniformly over mUltiple years, avoiding an excessively high peak in the funding profile, Implementation of each spacecraft would be greatly simplified compared to previous Europa mission concepts, minimizing new development while achieving the key Europa science objectives. We will report on the status of this evolving concept, and will solicit community feedback, as we pursue an innovative and low-cost ways to explore Europa and investigate its habitability.

Pappalardo↗
NASA NTRS1975

Tape tracking and handling for magnetic tape recorders

One of the critical performance and life limiting elements of a spacecraft tape recorder instrumentation system which has received little attention in technical literature is magnetic tape tracking and handling technology. This technology is required to understand how to gently transfer tape from one reel to another with proper alignment and a desirable uniform velocity at the read and write transducer heads. The increased demand for high data rate (i.e., multi-track spacecraft recording instrumentation systems), coupled with performance under extreme environmental conditions, requires a thorough knowledge of the various parameters which establish an optimum designed tape tracking and handling system. Stress analysis techniques are required to evaluate these parameters substantiated with test tape tracking data, to show the effect of each parameter on a tape recorder instrumentation tracking system. The technology is applicable to ground type tape recorders where the detrimental effects of edge guidance can be eliminated.

Paroby, W.↗
NASA NTRS1978

A single user efficiency measure for evaluation of parallel or pipeline computer architectures

A precise statement of the relationship between sequential computation at one rate, parallel or pipeline computation at a much higher rate, the data movement rate between levels of memory, the fraction of inherently sequential operations or data that must be processed sequentially, the fraction of data to be moved that cannot be overlapped with computation, and the relative computational complexity of the algorithms for the two processes, scalar and vector, was developed. The relationship should be applied to the multirate processes that obtain in the employment of various new or proposed computer architectures for computational aerodynamics. The relationship, an efficiency measure that the single user of the computer system perceives, argues strongly in favor of separating scalar and vector processes, sometimes referred to as loosely coupled processes, to achieve optimum use of hardware.

Jones, W. P.↗
NASA NTRS1978

Gravitational spectra from direct measurements

A simple rapid method is described for determining the spectrum of a surface field from harmonic analysis of direct measurements along great circle arcs. The method is shown to give excellent overall trends to very high degree from even a few short arcs of satellite data. Three examples are taken with perfect measurements of satellite tracking over a planet made up of hundreds of point-masses using (1) altimetric heights from a low orbiting spacecraft, (2) velocity residuals between a low and a high satellite in circular orbits, and (3) range-rate data between a station at infinity and a satellite in highly eccentric orbit. In particular, the smoothed spectrum of the Earth's gravitational field is determined to about degree 400(50 km half wavelength) from 1 D x 1 D gravimetry and the equivalent of 11 revolutions of Geos 3 and Skylab altimetry. This measurement shows there is about 46 cm of geoid height remaining in the field beyond degree 180.

Wagner, C. A.↗
NASA NTRS1990

High performance VLSI telemetry data systems

NASA's deployment of major space complexes such as Space Station Freedom (SSF) and the Earth Observing System (EOS) will demand increased functionality and performance from ground based telemetry acquisition systems well above current system capabilities. Adaptation of space telemetry data transport and processing standards such as those specified by the Consultative Committee for Space Data Systems (CCSDS) standards and those required for commercial ground distribution of telemetry data, will drive these functional and performance requirements. In addition, budget limitations will force the requirement for higher modularity, flexibility, and interchangeability at lower cost in new ground telemetry data system elements. At NASA's Goddard Space Flight Center (GSFC), the design and development of generic ground telemetry data system elements, over the last five years, has resulted in significant solutions to these problems. This solution, referred to as the functional components approach includes both hardware and software components ready for end user application. The hardware functional components consist of modern data flow architectures utilizing Application Specific Integrated Circuits (ASIC's) developed specifically to support NASA's telemetry data systems needs and designed to meet a range of data rate requirements up to 300 Mbps. Real-time operating system software components support both embedded local software intelligence, and overall system control, status, processing, and interface requirements. These components, hardware and software, form the superstructure upon which project specific elements are added to complete a telemetry ground data system installation. This paper describes the functional components approach, some specific component examples, and a project example of the evolution from VLSI component, to basic board level functional component, to integrated telemetry data system.

Chesney, J.↗