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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

PTTI applications to deep space navigation

Radio metric deep space navigation relies nearly exclusively upon coherent, two way, Doppler and ranging for all precise applications. These data types and the navigational accuracies they can produce are reviewed. The deployment of hydrogen maser frequency standards and the development of Very Long Baseline Interferometry (VLBI) systems within the Deep Space Network are used in the development of non-coherent, one way data forms that promise much greater inherent navigational accuracy. The underlying structure between each data class and clock performance is charted. VLBI observations of the natural radio sources are the planned instrument for the synchronization task. This method and a navigational scheme using differential measurements between the spacecraft and nearby quasars are described.

Curkendall, D. W.↗
NASA NTRS1979

Shuttle/TDRSS modelling and link simulation study

A Shuttle/TDRSS S-band and Ku-band link simulation package called LinCsim was developed for the evaluation of link performance for specific Shuttle signal designs. The link models were described in detail and the transmitter distortion parameters or user constraints were carefully defined. The overall link degradation (excluding hardware degradations) relative to an ideal BPSK channel were given for various sets of user constraint values. The performance sensitivity to each individual user constraint was then illustrated. The effect of excessive Spacelab clock jitter on the return link BER performance was also investigated as was the problem of subcarrier recovery for the K-band Shuttle return link signal.

Braun, W. R.↗
NASA NTRS1977

Comparison of circadian rhythms in male and female humans

Heart rate (HR) and rectal temperature (RT) data were obtained from 12 female and 27 male subjects. The subjects were housed in a facility where the environment was controlled. Human male and female RT and HR exhibit a circadian rhythm with an excursion of about 1.2 C and 30 beats/min, respectively. The acrophases, amplitudes, and level crossings are only slightly different between the sexes. The male HR and RT circadian wave forms are more stable than those of the females. However, the actual RT and HR of males were always lower than that of females at all time points around the clock. The HR during sleep in females is 15 per cent below the daily mean heart rate and in males, 22 per cent.

Winget, C. M.↗
NASA NTRS1978

An airborne meteorological data collection system using satellite relay /ASDAR/

The paper describes the aircraft to satellite data relay (ASDAR) project which processes information collected by the navigation and data systems of widebody jet aircraft which cross data-sparse areas of the tropics and southern hemisphere. The ASDAR system consists of a data acquisition and control unit to acquire, store, and format latitude, longitude, altitude, wind speed, wind direction, and outside air temperature data; a transmitter to relay the formatted data via satellite to the ground; and a clock to time the data sampling and transmission periods.

Bagwell, J. W.↗
NASA NTRS1979

Geodetic interferometry submission for the IUGG Quadrennial Report

The present paper reviews the activities of two major VLBI (Very Long Baseline Interferometry) groups, within the United States, which have been concentrating on geodetic measurements for a number of years. The activities have resulted in the development of transportable VLBI terminals for regional surveying applications; development of VLBI techniques for obtaining station positions; establishment of relative epochs and rates of the hydrogen maser clocks at the stations; the acquisition of polar motion and earth rotation data in support of deep space tracking functions; and the development of VLBI techniques necessary for tectonic measurements on trans- and intercontinental baselines and for astrometry, polar-motion and earth-rotation observations.

Clark, T. A.↗
NASA NTRS1981

Timing signal propagates without phase shift

Continous monitoring of transmission delay corrects for phase shift. Nodes in Master/Slave Returnable Timing System (MSRTS) are arranged in hierarchy, with each node serving as master to several slave nodes. As signal at each slave is synchronized with original master, it serves as master to synchronize following slave nodes. System improves performance of phased microwave antenna arrays in solar-powered satellites and clock distribution systems in avionics and computers.

Kantak, A. V.↗
NASA NTRS1979

Digital PSK to BiO-L demodulator for 2 sup nx(bit rate) carrier

A phase shift key (PSK) to BiO-L demodulator which uses standard digital integrated circuits is discussed. The demodulator produces NRZ-L, bit clock, and BiO-L outputs from digital PSK input signals for which the carrier is a 2 to the Nth multiple of the bit rate. Various bit and carrier rates which are accommodated by changing various component values within the demodulator are described. The use of the unit for sinusoidal inputs as well as digital inputs is discussed.

Shull, T. A.↗
NASA NTRS1979

Gravitational redshift space-probe experiment

A Scout D rocket was launched from Wallops Island, Virginia, carrying an atomic hydrogen maser oscillator system as the payload. The frequency of signals from the oscillator was monitored on the ground at Merritt Island, Florida, by using two hydrogen masers as comparison oscillators. The first-order Doppler shift in the signals was eliminated by a go-return transponder link to the payload, and the resulting data, representing the relativistic shifts, were recovered and recorded. The objective was to measure directly the effect of gravitational potential on the frequency of an atomic hydrogen maser assuming it to be a 'proper' clock. A gravitational effect amounting to some 4.5 parts in 10 to the 10th power was measured with an oscillator having a stability better than 1 part in 10 to the 14th power. Therefore, to make the best possible use of the oscillator, all frequency shifts at the 2 to 5 X 10 to the -15 power level in delta f/f in the system must be accounted for. This includes all the phase variations that can cause such a shift to appear. The experiment, the data available and the manner in which they were processed, and the results are described.

Vessot, R. F. C.↗
NASA NTRS1980

The Exxon rechargeable cells

The design and performance of ambient temperature secondary cells based on the titanium disulfide cathode are discussed. These limited performance products were developed for microelectronic applications such as solar rechargeable watches and clocks which require low drain rate and do not require many deep cycles.

Malachesky, P. A.↗
NASA NTRS1980

Critique of the Hughes Aircraft shuttle Ku band leading edge bit synchronizer

A bit synchronizer is analyzed via timing diagrams in a noise-free environment. It is believed that this new bit synchronizer will track the rising edge of the data bits with 25% asymmetry and up to a 90 deg phase shift between the received clock and data bit timing. In addition, the data bits will be demodulated correctly. It is not true that phase shifts larger than 90 deg will necessarily be corrected by this bit synchronizer. However, the specifications currently require the loop to operate over only a + or - 75 deg phase shift between the received data stream leading edges and the bit synchronizer leading edges; consequently, there should be no problem.

Holmes, J. K.↗
NASA NTRS1980

Shuttle Ku-band and S-band communications implementation study

Various aspects of the shuttle orbiter S-band network communication system, the S-band payload communication system, and the Ku-band communication system are considered. A method is proposed for obtaining more accurate S-band antenna patterns of the actual shuttle orbiter vehicle during flight because the preliminary antenna patterns using mock-ups are not realistic that they do not include the effects of additional appendages such as wings and tail structures. The Ku-band communication system is discussed especially the TDRS antenna pointing accuracy with respect to the orbiter and the modifications required and resulting performance characteristics of the convolutionally encoded high data rate return link to maintain bit synchronizer lock on the ground. The TDRS user constraints on data bit clock jitter and data asymmetry on unbalanced QPSK with noisy phase references are included. The S-band payload communication system study is outlined including the advantages and experimental results of a peak regulator design built and evaluated by Axiomatrix for the bent-pipe link versus the existing RMS-type regulator. The nominal sweep rate for the deep-space transponder of 250 Hz/s, and effects of phase noise on the performance of a communication system are analyzed.

Dodds, J. G.↗
NASA NTRS1980

Autonomous satellite orbit determination during the development phases of the global positioning system

An onboard navigation system was developed to aid the design and evaluation of algorithms used in autonomous satellite navigation with Global Positioning System (GPS) data. The performance of the algorithms designed for a GPS Receiver/Processor Assembly (R/PA) intended for LANDSAT-D was investigated during the development phases of the GPS (four to six satellites in the constellation). This evaluation emphasized the effects on the orbit determination accuracy of the expected user clock errors, GPS satellite visibility, force model approximations, and state and covariance propagation approximations. Results are presented giving the sensitivity of orbit determination accuracy to these constraints.

Dunham, J. B.↗
NASA NTRS1980

Phase and group delay calibration of a very long baseline interferometer by East Coast VLBI Group

Precisely timed pulses injected into the input of each receiver are used to calibrate the phase and group delay through each interferometer terminal. The short duration pulses are generated at a 1 MHz rate directly from the output of the frequency standard. The pulses are injected into the receiver at a level low enough to produce less than one percent increase in system temperature, yet can be extracted during processing with a high enough signal to noise ratio to determine the phase of the calibration rails within 1 degree in 1 second of integration. The calibration system also includes precise cable measurement electronics and a pulse echo for clock synchronization.

Rogers, A. E. E.↗
NASA NTRS1980

Mark 3 correlator hardware and software

The Mark 3 correlator system is described in some detail. The correlator system is based on a modular philosophy. Each correlator module independently processes the data from one track pair. Therefore, 28 modules are necessary to complete a full one baseline processor and 84 modules for a full 3 baseline processor. Each correlator module has two interfaces: (1) data and clock from each of the two tracks to be correlated and (2) Computer Automated Measurement and Control (CAMAC) dataway interface to the computer. The processor is organized around the IEEE CAMAC standard architecture, housing 15 correlator modules in each of 6 crates. This allows one pass processing of a full 3 baseline 28 track observation or a 6 baseline (4 station) 14 track observation. The correlator architecture allows easy expansion for up to 8 stations. The computer system is an HP 1000 system utilizing a 16 bit minicomputer with disc and tape peripherals. The processing software is also organized in a modular fashion with many independent but cooperative programs controlling the operation of the Mark 3 processor. Processing time through the correlator is normally real time or faster, with graphics displays providing real time monitor and control of the processing operation.

Whitney, A. R.↗
NASA NTRS1980

Phase delay astrometry and its geodetic applications

The accuracy inherent in the fringe phase in the determination of source positions was calculated. It is shown that accuracy can be utilized by applying differencing techniques in order to circumvent such systematic effects as clock drift and delay due to the propagation media.

Wittels, J. J.↗
NASA NTRS1980

The European VLBI network

The capabilities of the European very long baseline interferometry (VLBI) network are summarized. The range of baseline parameters, sensitivities, and recording and other equipment available are included. Plans for upgrading the recording facilities and the use of geostationary satellites for signal transfer and clock synchronization are discussed.

Schilizzi, R. T.↗
NASA NTRS1979

Satellite time transfer via TDRSS and applications

The satellite time transfer terminal design concept for the Tracking and Data Relay Satellite System (TDRSS) and the application of the time signal in autonomously operated spacecraft clock are presented. Some pertinent TDRSS parameters and corrections for the propagation delay measurement as well as the time code used to transfer the time signal are given.

Chi, A. R.↗