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At least 289 records · Page 16
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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

Tectonic motion site survey of the National Radio Astronomy Observatory, Green Bank, West Virginia

A geological and geophysical site survey was made of the area around the National Radio Astronomy Observatory (NRAO) to determine whether there are at present local tectonic movements that could introduce significant errors to Very Long Baseline Interferometry (VLBI) geodetic measurements. The site survey consisted of a literature search, photogeologic mapping with Landsat and Skylab photographs, a field reconnaissance, and installation of a seismometer at the NRAO. It is concluded that local tectonic movement will not contribute significantly to VLBI errors. It is recommended that similar site surveys be made of all locations used for VLBI or laser ranging.

Webster, W. J., Jr.↗
NASA NTRS1978

Estimability and simple dynamical analyses of range (range-rate range-difference) observations to artificial satellites

Non-Bayesian statistics were used in simulation studies centered around laser range observations to LAGEOS. The capabilities of satellite laser ranging especially in connection with relative station positioning are evaluated. The satellite measurement system under investigation may fall short in precise determinations of the earth's orientation (precession and nutation) and earth's rotation as opposed to systems as very long baseline interferometry (VLBI) and lunar laser ranging (LLR). Relative station positioning, determination of (differential) polar motion, positioning of stations with respect to the earth's center of mass and determination of the earth's gravity field should be easily realized by satellite laser ranging (SLR). The last two features should be considered as best (or solely) determinable by SLR in contrast to VLBI and LLR.

Vangelder, B. H. W.↗
NASA NTRS1979

Connection and validation of narrow-band delta VLBI phase observations

Narrow-band differential very long baseline interferometry required phase connections between consecutive scans. An efficient computer aided scheme for this purpose is presented. This scheme is an iteration process alternating between a grand fit on many scans and integer quantization of the phase shift cycles to be assigned to the scans. Only linear simultaneous equations of a few unknowns need to be solved. A simulation analysis indicates that faultless phase connection can be expected when there is no localized systematic noise. When systematic noise of moderate level exists, the possible incorrect phase connection can be detected and connected for by comparing the connected phases from the two alternating observations, after removing the residual diurnal effects.

Wu, S. C.↗
NASA NTRS1979

Multi-Mission Receiver (MMR)

An introduction to the Multi-Mission Receiver (MMR) is presented. The MMR contains occultation receiver channels (OCC) and very long baseline interferometry channels. The design considerations, performance and implementation of the OCC channels are discussed.

Donnelly, H.↗
NASA NTRS1979

Satellite emission radio interferometric earth surveying series - GPS geodetic system

A concept called SERIES (satellite emissions radio interferometric earth surveying) which makes use of GPS (global positioning system) radio transmissions without any satellite modifications, is described. Through the use of very long baseline interferometry (VLBI) and its calibration methods, 0.5 to 3 cm three dimensional baseline accuracy can be achieved over distances of 2 to 200 km respectively, with only 2 hours of on-site data acquisition. Attention is given to such areas as: the radio flux equivalent of GPS transmissions, synthesized delay precision, transmission and frequency subsystem requirements, tropospheric and ionospheric errors. Applications covered include geodesy and seismic tectonics.

Macdoran, P. F.↗
NASA NTRS1980

Long baseline vector determinations and intercomparisons

The East Coast very long baseline interferometry (VLBI) group has performed about 60 experiments over the last 10 years in the process of developing and exploiting advanced VLBI techniques. Of those, the most recent 14 experiments are briefly described.

Knight, C. A.↗
NASA NTRS1980

Polar motion and UT1: Comparison of VLBI, lunar laser, satellite laser, satellite Doppler, and conventional astrometric determinations

Very long baseline interferometry observations made with a 3900 km baseline interferometer (Haystack Observatory in Massachusetts to Owens Valley Observation in California) were used to estimate changes in the X-component of the position of the Earth's pole and in UT1. These estimates are compared with corresponding ones from lunar laser ranging, satellite laser ranging, satellite Doppler, and stellar observations.

Robertson, D. S.↗
NASA NTRS1980

Scandinavia studies of recent crustal movements and the space geodetic baseline network

A brief review of crustal movements within the Fenno-Scandia shield is given. Results from postglacial studies, projects for measuring active fault regions, and dynamic ocean loading experiments are presented. The 1979 Scandinavian Doppler Campaign Network is discussed. This network includes Doppler translocation baseline determination of future very long baseline interferometry baselines to be measured in Scandinavia. Intercomparison of earlier Doppler translocation measurements with a high precision terrestrial geodetic baseline in Scandinavia has yielded internal agreement of 6 cm over 887 km. This is a precision of better than 1 part in to the 7th power.

Anderson, A. J.↗
NASA NTRS1980

The measurement of Earth rotation on a deformable Earth

Until recently, the methods of geodetic positioning on the Earth were limited to a precision of roughly one part in 10 to the 6th power. At this level of precision, the Earth can be regarded as a rigid body since the largest departure of the Earth from rigidity is manifested in the strains of the Earth tides which are of the order of one part in 10 to the 7th power. Long baseline interferometry is expected to routinely provide global positioning to a precision of one part in 10 to the 8th power or better. At this level of precision, all parts of the Earth's surface must be regarded as being, at least potentially, in continual motion relative to the geocenter as a result of a variety of geophysical effects. The general implications of this phenomenon for the theory of the Earth's rotation is discussed. Particular attention is given to the question of the measurement of the 'Earth's rotation vector' on a deformable Earth.

Cannon, W. H.↗
NASA NTRS1980

Considerations in the placement of phase calibration tones

In the use of tones to calibrate unwanted instrumental phases for very long baseline interferometry experiments, certain problems exist which are related to the placement of these phase calibrator tones. (1) A bias exists in an analytically generated stopping function used during correlation if its frequency satisfies the following condition; f = (f sub s)x(m)/n, where f sub s = sampling frequency, m = any integer, and n = any odd integer. (2) Due to the quantized representation of sine waves in the stopping function, odd harmonics of the fundamental frequencies are generated. Several mechanisms are available through which these harmonics can cause errors in the residual phase extracted from the recorded tones. (3) When multiple tones are injected into a pass band, intermodulation products can occur. The magnitude of these effects is discussed along with strategies designed to avoid them.

Young, L. E.↗
NASA NTRS1980

Microwaves to megabits

Receiver and terminal characteristics of the Mark 3 very long baseline interferometry system are described in some detail. The Mark 3 system has 14 IF to video converters, each with built in synthesized local oscillators which have a range of 100 to 500 MHz covered in 10 kHz steps. In the normal wideband continuum mode, all 14 upper and all 14 lower sideband video outputs (each with 2 MHz bandwidth) are recorded with a total data rate of 112 Mbits/sec. In geodetic observations, two IF bands are simultaneously recorded from a dual band (5/X) receiver.

Rogers, A. E. E.↗
NASA NTRS1980

Mark 3 wideband digital recorder in perspective

The tape recorder used for the Mark 3 data acquisition and processing system is compared with earlier very long baseline interferometry recorders. Wideband 33-1/3 kbpi digital channel characteristics of instrumentation recorders and of a modern video cassette recorder are illustrated. Factors which influenced selection of the three major commercial components (transport, heads, and tape) are discussed. A brief functional description and the reasons for development of efficient signal electronics and necessary auxiliary control electronics are given. The design and operation of a digital bit synchronizer is illustrated as an example of the high degree of simplicity achieved.

Hinteregger, H. F.↗
NASA NTRS1980

Mark 3 interactive data analysis system

The interactive data analysis system, a major subset of the total Mark 3 very long baseline interferometry (VLBI) software system is described. The system consists of two major and a number of small programs. These programs provide for the scientific analysis of the observed values of delay and delay rate generated by the VLBI data reduction programs and product the geophysical and astrometric parameters which are among the ultimate products of VLBI. The two major programs are CALC and SOLVE. CALC generates the theoretical values of VLBI delay rate as well as partial derivatives based on apriori values of the geophysical and astronometric parameters. SOLVE is a least squares parameters estimation program which yields the geophysical and astrometric parameters using the observed values by the data processing system and theoretical values and partial derivatives provided by CALC. SOLVE is a highly interactive program in which the user selects the exact form of the recovered parameters and the data to be accepted into the solution.

Ryan, J. W.↗
NASA NTRS1980

Phase versus delay in geodetic VLBI

The conditions for the applicability of the phase observable in very long baseline interferometry are discussed and examples of adequate observation programs are given. These considerations apply in particular to the Mark 2 system, which is already in operation at many observatories.

Campbell, 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

Demonstration of remote clock monitoring by VLBI with three baseline closures

The capability of very long baseline interferometry (VLBI) to monitor the stability of remotely located hydrogen maser frequency standards has been demonstrated by a series of experiments conducted between Deep Space Stations in Australia, Spain, and California. The measured stabilities of the clock systems, over approximately 10 day intervals, were 1 to 3 parts in 10 to the 13th power, with the instabilities due to the oscillators, the clock distribution systems, the receiving system delays, and the VLBI measurement error. Experiments were conducted independently using two different systems (BLOCK 0 and WBDAS). Later comparison shows agreement on the order of 1 part in 10 to the 13th power. Closure was demonstrated on three separate occasions to 33, 10, and 13 ns with an error uncertainty of + or - 42 ns. The results represent an important consistency check on VLBI measurements.

Cheetham, C. M.↗