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At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Satellite time and frequency transfer (STIFT)

The concept of placing a hydrogen maser high stability clock in Earth orbit to provide accurate time and frequency comparisons worldwide to major timing centers and to a large number of radio observatory antenna sites involved in VLBI measurements was studied. The proposal was chiefly directed toward studies and initial hardware designs for time comparisons between hydrogen maser frequency standards and to modifications of the hydrogen maser for long-term use in space.

Vessot, R. F. C.↗
NASA NTRS1982

Thematic mapper protoflight model preshipment review data package. Volume 4: Appendix. Part A: Multiplexer data book 2

Final performance test data for the thematic mapper flight model multiplexer are presented in tables. Aspects covered include A/D thresholds for bands 5, 6, and 7; cross talk; the thermistor; bilevel commands signal parameters; A/D threshold ambient, voltage margin low bus; serial data and bit clock parameters; and the wire check. Tests were conducted at ambient temperature.

Source record↗
NASA NTRS1983

LANDSAT-4 to ground station interface description

The LANDSAT 4 to ground station interface is described in detail. The radiometric specifications, internal calibration, sensor output format, and data processing constants for the multispectral scanner and the thematic mapper are discussed. The mission payload telemetry, onboard computer telemetry, and engineering telemetry formats are described. In addition, the telemetry time signals and the onboard clock resetting procedure are addressed.

Source record↗
NASA NTRS1983

Distributed multiport memory architecture

A multiport memory architecture is diclosed for each of a plurality of task centers connected to a command and data bus. Each task center, includes a memory and a plurality of devices which request direct memory access as needed. The memory includes an internal data bus and an internal address bus to which the devices are connected, and direct timing and control logic comprised of a 10-state ring counter for allocating memory devices by enabling AND gates connected to the request signal lines of the devices. The outputs of AND gates connected to the same device are combined by OR gates to form an acknowledgement signal that enables the devices to address the memory during the next clock period. The length of the ring counter may be effectively lengthened to any multiple of ten to allow for more direct memory access intervals in one repetitive sequence. One device is a network bus adapter which serially shifts onto the command and data bus, a data word (8 bits plus control and parity bits) during the next ten direct memory access intervals after it has been granted access. The NBA is therefore allocated only one access in every ten intervals, which is a predetermined interval for all centers. The ring counters of all centers are periodically synchronized by DMA SYNC signal to assure that all NBAs be able to function in synchronism for data transfer from one center to another.

Kohl, W. H.↗
NASA NTRS1983

Time transfer between the Goddard Optical Research Facility and the U.S. Naval Observatory using 100 picosecond laser pulses

A horizontal two-way time comparison link in air between the University of Maryland laser ranging and time transfer equipment at the Goddard Optical Research Facility (GORF) 1.2 m telescope and the Time Services Division of the U.S. Naval Observatory (USNO) was established. Flat mirrors of 25 cm and 30 cm diameter respectively were placed on top of the Washington Cathedral and on a water tower at the Beltsville Agricultural Research Center. Two optical corner reflectors at the USNO reflect the laser pulses back to the GORF. Light pulses of 100 ps duration and an energy of several hundred microjoules are sent at the rate of 10 pulses per second. The detection at the USNO is by means of an RCA C30902E avalanche photodiode and the timing is accomplished by an HP 5370A computing counter and an HP 1000 computer with respect to a 10 pps pulse train from the Master Clock.

Alley, C. O.↗
NASA NTRS1983

Narrow 87Rb and 133Cs hyperfine transitions in evacuated wall-coated cells

An extension of work on wall-coated cells was made to include observation by a triple resonance technique of the 0-0 hyperfine transitions in 87Rb and 133Cs. Conventional RF excited lamps were used. Interest in such cells is for possible application in atomic clocks. The Rb cell would appear to remain especially promising in this respect.

Robinson, H. G.↗
NASA NTRS1983

Timing subsystem development: Network synchronization experiments

This paper describes a program in which several experimental timing subsystem prototypes were designed, fabricated, and field tested using a small network of troposcatter and microwave digital communication links. This equipment was responsible for modem/radio interfacing, time interval measurement, clock adjustment and distribution, synchronization technique, and node to node information exchange. Presented are discussions of the design approach, measurement plan, and performance assessment methods. Recommendations are made based on the findings of the test program and an evaluation of the design of both the hardware and software elements of the timing subsystem prototypes.

Backe, K. R.↗
NASA NTRS1983

Test results of the STI GPS time transfer receiver

Global time transfer, or synchronization, between a user clock and USNO UTC time can be performed using the Global Positioning System (GPS), and commercially available time transfer receivers. This paper presents the test results of time transfer using the GPS system and a Stanford Telecommunications, Inc. (STI) Time Transfer System (TTS) Model 502. Tests at the GPS Master Control Site (MCS) in Vandenburg, California and at the United States Naval Observatory (USNO) in Washington, D.C. are described. An overview of GPS, and the STI TTS 502 is presented. A discussion of the time transfer process and test concepts is included.

Hall, D. L.↗
NASA NTRS1983

One nanosecond time synchronization using series and GPS

Subnanosecond time sychronization between two remote rubidium frequency standards is verified by a traveling clock comparison. Using a novel, code ignorant Global Positioning System (GPS) receiver developed at JPL, the SERIES geodetic baseline measurement system is applied to establish the offset between the 1 Hz. outputs of the remote standards. Results of the two intercomparison experiments to date are presented as well as experimental details.

Buennagel, A. A.↗
NASA NTRS1982

Fission track studies of xenolithic chondrites - Implications regarding brecciation and metamorphism

Fission tracks in phosphates from one gas-poor chondrite and three gas-rich ones are studied to determine their thermal history and brecciation time scales. Model fission track ages are calculated for given track densities due to Pu-244 and U-238; track densities and uranium measurements for whitlockite are shown, and possible sources of the tracks are mentioned. Details of track density and uranium measurements are discussed for each meteorite separately. Whitlockites from all the meteorites give model fission track ages of 4.4 Gyr assuming a Pu/U ratio at 4.55 Gyr of 0.045. The final brecciation event definitely did not reset the track clock in phosphates of one meteor and probably not in another two. It is concluded that the observed fission track ages date the end of metamorphic cooling in the meteorite parent bodies and support the planetesimal model for the formation of xenolithic chondrites.

Kothari, B. K.↗
NASA NTRS1983

The rotational spectrum of g-modes in the sun

Observations and calculations are presented which strongly suggest that the unique sequence of rotation rates due to g-modes is active in the sun. It is found that all angular harmonics from 1 = 2-11 appear to be resolved, while higher harmonics up to at least 1 = 20 also seem to be active. The extreme narrowness of many of the spectral lines indicates that the g-modes are locked in sets of constant 1 by a local mechanism which excites the modes and possibly regulates the long-term precision of their rotation. These sets act as a system of resonant, or nearly resonant, clocks which impose a degree of periodicity upon solar activity and measure the mean solar interior rotation

Wolff, C. L.↗
NASA NTRS1982

The software-implemented fault tolerance /SIFT/ approach to fault tolerant computing

SIFT is an experimental computer designed for highly reliable flight-control service in advanced air transports. Its development was intended to integrate and demonstrate the latest techniques in fault-tolerant computing. During its development, several new problems of some generality were uncovered and solved. The technology developed for the validation of its design is seen as being perhaps as important as the design itself. The SIFT design is described, as is the way in which the design and its validation were shaped by the requirements of its intended application. Attention is also given to reliability and fault tolerance. The most significant feature of the hardware design is the absence of elements that can generate multiple faults, such as shared clocks or data buses. It is noted that the software is realized in only 800 lines of code, of which 80% are in a high-level language.

Goldberg, J.↗
NASA NTRS1983

Questions on universal constants and four-dimensional symmetry from a broad viewpoint. I

It is demonstrated that there is a flexibility in clock synchronizations and that four-dimensional symmetry framework can be viewed broadly. The true universality of basic constants is discussed, considering a class of measurement processes based on the velocity = distance/time interval, which always yields some number when used by an observer. The four-dimensional symmetry framework based on common time for all observers is formulated, and related processes of measuring light speed are discussed. Invariant 'action functions' for physical laws in the new four-dimensional symmetry framework with the common time are established to discuss universal constants. Truly universal constants are demonstrated, and it is shown that physics in this new framework and in special relativity are equivalent as far as one-particle systems and the S-matrix in field theories are concerned.

Hsu, J. P.↗
NASA NTRS1982

VOR area navigation - Techniques and results

Several methods for deriving position from VOR (without DME) have been developed and evaluated in this study. These methods permit navigation to arbitrary waypoints using either two VOR's or one VOR and a clock. These algorithms have been tested in computer simulations and in flight tests. The single VOR method appears to be the most practical and is a candidate for an automated light plane area navigation system, called VORNAV.

Ragsdale, W. A.↗
NASA NTRS1983

Factors controlling the location of the Venus bow shock

The location of the Venus bow shock determined from magnetic field measurements during the first and third years of Pioneer Venus orbiter operation is examined and compared with nearly simultaneously obtained interplanetary solar wind data to determine those factors that control the size of the Venus bow shock. The location of the intersection of the bow shock with the terminator that is best determined by the data does not vary significantly between years 1979 and 1981 and is only 16 percent more distant than the Venera 9 and 10 shock when account is taken of solar wind aberration. Alfvenic Mach number and magnetosonic Mach number affect the size of the bow shock significantly. Solar wind dynamic pressure has a lesser effect. No significant asymmetries in the shock shape were found either as a result of the orientation of the clock angle of the IMF in the terminator plane or the angle of the IMF relative to the shock normal.

Tatrallyay, M.↗
NASA NTRS1985

Temperature-Stabilized Phase Detector

Precise temperature stabilized phase detector for clock signal distribution maintains 100-MHz signal with stability of 5 parts in 10 to the 16th power even for step changes of 20 degrees C in ambient temperature. Stabilization achieved by heating unit to 45 degrees C and maintaining temperature through bridge circuit.

Yeeman, L.↗
NASA NTRS1985

Solar-Powered Water Distillation

Solar-powered still produces pure water at rate of 6,000 gallons per year. Still fully automatic and gravity-fed. Only outside electric power is timer clock and solenoid-operated valve. Still saves $5,000 yearly in energy costs and pays for itself in 3 1/2 years.

Menninger, F. J.↗
NASA NTRS1983

Studies of highly variable galactic X-ray sources with HEAO-1

Analysis HEAO-Al data on MXB1659-29 revealed a 7.1 hour period from this X-ray burst source. The erratic dips seen in both SAS-3 and HEAO-Al data were concentrated within 1.5 hours (about 25%) of the orbital cycle. There appeared to be a stable dip at the end of the 1.5 h of erratic varibility. It was established that the stable dip was a true eclipse of the central X-ray emitting object. MXB1659-29 is the first X-ray burster to show eclipses and a precise orbital clock.

Cominsky, L.↗