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Christensen, C. S.

Publications and source records attributed to Christensen, C. S..

17 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

High-precision radiometric tracking for planetary approach and encounter in the inner solar system

The benefits of improved radiometric tracking data have been studied for planetary approach within the inner Solar System using the Mars Rover Sample Return trajectory as a model. It was found that the benefit of improved data to approach and encounter navigation was highly dependent on the a priori uncertainties assumed for several non-estimated parameters, including those for frame-tie, Earth orientation, troposphere delay, and station locations. With these errors at their current levels, navigational performance was found to be insensitive to enhancements in data accuracy. However, when expected improvements in these errors are modeled, performance with current-accuracy data significantly improves, with substantial further improvements possible with enhancements in data accuracy.

Christensen, C. S.↗
NASA NTRS1989

VLBI using a telescope in Earth orbit. I - The observations

A VLBI experiment has been conducted at a frequency of 2.3 GHz, using an antenna in Earth orbit. The observational procedure for the orbiting antenna, part of the Tracking and Data Relay Satellite System, is described. Nonstandard VLBI procedures were necessary to obtain adequate phase stability and to correlate the data. Several technical concepts necessary for a dedicated space VLBI mission were successfully tested.

Levy, G. S.↗
NASA NTRS1988

Very long baseline interferometry observations using the tracking and data relay satellite as an orbiting radio telescope

An antenna in geostationary orbit was used for VLBI observations at 2.3 GHz, in combination with ground antennas in Australia and Japan. 23 of the 25 observed sources were detected on orbiter-ground baselines, with baseline lengths as large as 2.15 earth diameters. Brightness temperatures between 10 to the 12th K and 4 x 10 to the 12th K were measured for 10 sources.

Linfield, R. P.↗
NASA NTRS1986

Very long baseline interferometric observations made with an orbiting radio telescope

An orbiting spacecraft and ground observatories have been used to obtain interferometric observations of cosmic radio sources. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting observatory in conjunction with two 64-meter radio telescopes at ground observatories, one in Australia and one in Japan. The quasars 1730-130 (NRAO 530), 1510-089, and 1741-038 were observed at a frequency of 2.3 gigahertz, and a maximum projected baseline of 1.4 earth diameters was achieved. All quasar observations for which valid data were acquired resulted in detected fringes. Many of the techniques proposed for a dedicated very long baseline interferometry observatory in space were used successfully in this experiment.

Levy, G. S.↗
NASA NTRS1986

Communications considerations of the very long baseline interferometry demonstration using the tracking and data relay satellite system

A desire for increased angular resolution at microwave frequencies has led to the development of radio telescopes with very lage effective apertures. Very long baseline interferometry (VLBI) has made it possible to synthesize telescopes with effective dimensions of a large fraction of an earth diameter. By using a satellite-borne radio telescope as part of a VLBI array, the dimensions of the earth cease to be a limitation. A demonstration was performed to show that the orbiting VLBI (OVLBI) concept is feasible. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting element of the VLBI demonstration. Stability tests were made before the observations to determine the suitability of the TDRSS for OVLBI use. The first successful OVLBI observations were performed using the 64-m antenna observatories of NASA's Deep Space Network in Tidbinbilla, Australia, and of the Institute for Space and Astronautical Science in Usuda, Japan in conjunction with the TDRSS.

Levy, G. S.↗
NASA NTRS1986

Status of the very long baseline interferometry demonstration using the tracking and data relay satellite system

Very long baseline interferometry (VLBI) has been developed to the point where angular resolution at any given wavelength is limited by the dimensions of the earth. This limitation can be removed by placing a VLBI radio telescope in orbit. A demonstration of the feasibility of this approach was arranged. The Tracking and Data Relay Satellite System was used as an orbiting observatory in conjunction with the NASA Deep Space Network 64-m telescope in Tidbinbilla, Australia, and the Institute for Space and Astronautical Science 64-m antenna in Usuda, Japan. Interferometric fringes were successfully obtained from three quasars. The longest projected baseline was 1.4 earth diameters.

Levy, G. S.↗
NASA NTRS1985

Study of navigation accuracy for the proposed QUASAT mission

A covariance analysis has been performed for the proposed QUASAT, an earth orbiting radio telescope. Conventional (Doppler and range) and advanced (diifferenced and doubly differenced one-way range) radio metric data types are used to evaluate the navigation accuracy that can be achieved. It is found that the mission requirements are met by conventional data types, while advanced data types can provide an order of magnitude improvement with less measurements, provided the three NASA DSN stations are augmented by more closely spaced stations.

Jacobi, N.↗
NASA NTRS1980

Differential Very Long Baseline Interferometry (delta VLBI) spacecraft tracking system demonstration. Part 2: Data acquisition and processing

A set of experiments in the use of Differential Very Long Baseline Interferometry (delta VLBI) for spacecraft navigation were completed. Data using both Voyager spacecraft and a single quasar were acquired during the Jupiter encounter time period. The data were processed and analyzed to assess the navigation accuracy of delta VLBI. The data reduction and techniques for assessing data quality and consistency are discussed.

Christensen, C. S.↗
NASA NTRS1980

Results of a demonstration of the use of Differential Very Long Baseline Interferometry data for precise navigation of interplanetary spacecraft

A set of experiments in the use of Differential Very Long Baseline Interferometry for spacecraft navigation have been completed. Data using both Voyager spacecraft and a single quasar were acquired during the Jupiter encounter time period. The data were processed and analyzed in order to assess the navigation accuracy of Differential Very Long Baseline Interferometry. The paper focuses on the data reduction and techniques for assessing data quality and consistency.

Christensen, C. S.↗
NASA NTRS1979

Interplanetary orbit determination

A general description of the Viking interplanetary orbit determination activity extending from launch to Mars encounter is given. The emphasis is on the technical fundamentals of the problem, basic strategies and data types used, quantitative results, and specific conclusions derived from the inflight experience. Special attention is given to the use of the spacecraft-based optical measurements and their first application as a principal navigational data type for an interplanetary mission. The optical-based orbit determination, in fact, was the primary contributor to the exceptional interplanetary navigation accuracy experienced by both Viking missions. The Viking application of optical orbit determination relied in large part on the technology developed and demonstrated by the Mariner 9 Optical Navigation Demonstration.

Rourke, K. H.↗
NASA NTRS1978

Delta VLBI spacecraft tracking system demonstration. Part 1: Design and planning

The current status of planned delta very long base interferometry (VLBI) navigation during Voyager Jupiter encounters is discussed. It is indicated that angular accuracies of 0.05 microrads are possible and that near real time data transmission can be achieved with minimal station hardware and software modifications. A software correlator and phase tracking program, operating on the SFOF IBM 360, used for data processing is described.

Brunn, D. L.↗
NASA NTRS1977

On achieving sufficient dual station range accuracy for deep space navigation at zero declination

Since the Voyager Mission will encounter Saturn at a time when the planet will be nearly in the earth's equatorial plane, earth-based orbit determination will be more difficult than usual because of the so-called zero-declination singularity associated with conventional radiometric observations. Simulation studies show that in order to meet the required delivery accuracy at Saturn, a relative range measurement between the Goldstone and Canberra Deep Space Stations must be accurate to 4.5 times the square root of two meters. Topics discussed include the nature of error sources, the methodology and technology required for calibration, the verification process concerning the nearly simultaneous range capability, a description of the ranging system, and tracking strategy.

Siegel, H. L.↗
NASA NTRS1977

The determination of the interplanetary orbits of Vikings 1 and 2

A description is presented of the navigation-related events of the Viking Mars mission. Orbit determination system fundamentals are discussed, taking into account the trajectory models, observation models, radio data models, range considerations, optical data models, filter models, the orbit determination process, critical orbit determination inputs, and orbit determination errors. Attention is also given to questions of orbit determination strategy, orbit determination results, optical measurements processing, aspects of approach orbit determination evaluation, and the orbit determination software system.

Rourke, K. H.↗
NASA NTRS1976

Performance of the square root information filter for navigation of the Mariner 10 spacecraft

The use is described of a sequential least squares filter in the orbit determination for the Mariner Venus-Mercury (Mariner 10) spacecraft. The orbit determination strategy outlining the use of both the sequential filter and a conventional batch filter is given. Highlighted are the mission events from launch to the first Mercury encounter with emphasis on the sequential filter performance. Advantages to the mission derived from the sequential filter are pointed out.

Christensen, C. S.↗
NASA NTRS1974

Navigation of the Mariner 10 spacecraft to Venus and Mercury

Orbit determination techniques used during the highly successful flight of Mariner 10 to Venus and Mercury are presented. Comparisons are made between different data sets, different sets of parameters, and between a conventional least squares batch filter and a sequential batch filter and smoother that was designed for this mission. The sequential filter was able to account for small spacecraft forces that the batch filter was unable to handle effectively, and hence, contributed greatly to the mission success. The sequential filter and smoother design is given as well as results for each phase of the mission.-

Christensen, C. S.↗