The determination and comparison of the GRARR MADGAR site location
Improved coordinates for MADGAR range and range rate tracking site, Madagascar, estimated from Explorer 29 /GEOS 1/ satellite data
Doll, C. E.↗
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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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Evaluation of the Goddard range and range rate at Rosman by intercomparison with GEOS-1 long arc orbital solutions
Goddard range and range rate tracking system at Rosman, N.C., evaluated using Explorer 29 /GEOS 1/ long arc orbital solutions
Lerch, F. J.↗
NASA laser systems accuracy in satellite tracking.
NASA laser systems for satellite tracking, determining ranging accuracy by comparing laser and computed reference orbital data
Moss, S. J.↗
Data analysis in connection with the national geodetic satellite program /2/ Semiannual status report, Feb. - Jul. 1970
SECOR observations, satellite tracking, and range difference study
Source record↗
A guide to onboard checkout. Volume 7: RF communications
The radio frequency communications subsystem for a space station is considered, with respect to onboard checkout requirements. The subsystem comprises all equipment necessary for transmitting and receiving, tracking and ranging, command, multiple voice and television information, and broadband experiment data. The communications subsystem provides a radio frequency interface between the space station and ground stations, either directly or indirectly, through a data relay satellite system, independent free-flying experiment modules, and logistics vehicles. Reliability, maintenance, and failure analyses are discussed, and computer programming techniques are presented.
Source record↗
ATS simultaneous and turnaround ranging experiments
This report explains the data reduction and spacecraft position determination used in conjunction with two ATS experiments - Trilateration and Turnaround Ranging - and describes in detail a multilateration program that is used for part of the data reduction process. The process described is for the determination of the inertial position of the satellite, and for formating input for related programs. In the trilateration procedure, a geometric determination of satellite position is made from near simultaneous range measurements made by three different tracking stations. Turnaround ranging involves two stations; one, the master station, transmits the signal to the satellite and the satellite retransmits the signal to the slave station which turns the signal around to the satellite which in turn retransmits the signal to the master station. The results of the satellite position computations using the multilateration program are compared to results of other position determination programs used at Goddard. All programs give nearly the same results which indicates that because of its simplicity and computational speed the trilateration technique is useful in obtaining spacecraft positions for near synchronous satellites.
Watson, J. S.↗
Earth and ocean dynamics satellites and systems
An overview is presented of the present state of satellite and ground systems making observations of the dynamics of the solid earth and the oceans. Emphasis is placed on applications of space technology for practical use. Topics discussed include: satellite missions and results over the last two decades in the areas of earth gravity field, polar motions, earth tides, magnetic anomalies, and satellite-to-satellite tracking; laser ranging systems; development of the Very Long Baseline Interferometer; and Skylab radar altimeter data applications.
Vonbun, F. O.↗
Trajectory optimization for the Atlas/Centaur launch vehicle
A method for finding solutions to complex trajectory optimization problems with detailed hardware and launch vehicle constraints is presented. The trajectory optimization problem is formulated as a constrained function minimization problem by modeling the control by a function of a finite number of parameters. Although any parametric control model may be selected, the natural choice of parameters is the actual parameters of the parametric guidance equations flown on the flight digital computer. A variation of the method of multipliers is presented for performing the constrained function minimization. A functional is proposed that allows incorporation of state variable inequality constraints. Finally, optimization of the HEAO-A direct-ascent trajectory is discussed. The HEAO-A mission demonstrates profile optimization to meet range safety, tracking, heating, structural integrity, and attitude rate constraints.
Brusch, R. G.↗
Investigations of Mars dynamics and geodesy via the Viking spacecraft
Results are reported for analyses of Doppler, ranging, and tracking data from the Viking landers and orbiters of relevance to the dynamics and geodesy of Mars. Highly improved numerical results are given for the orientation of the spin axis of Mars, the planet's sidereal rotation rate, and the earth-Mars ephemeris. A refined definition of the global gravitational field of Mars is discussed, a local gravitational survey based on Viking Orbiter 2 tracking data is described, and a mass anomaly near Olympus Mons is noted. Radius data are examined which suggest an asymmetry in the figure of Mars characterized by generally higher topography in the southern than in the northern hemisphere. The mass of Phobos is determined on the basis of Orbiter 1 orbital perturbations, and the mean density of this Martian satellite is found to be approximately 2.0 g/cu cm, which is suggestive of primitive carbonaceous chondrites and, if true, implies that Phobos was formed in the asteroid belt.
Michael, W. H., Jr.↗
A method of defining topographic datums of planetary bodies
Since no known planetary bodies in the solar system other than the earth have large bodies of water, a topographical datum other than a sea-level reference must be used as a zero-elevation reference surface. The present paper discusses the definition of the topographic datums of Mars and the moon in terms of a gravity-level surface. Planetary gravitational field potentials were represented by a spherical harmonic expansion in terms of gravity coefficients measured by planetary orbiters, and the topographical datum was taken as the sum of an arbitrarily selected radius of the mean sphere and the radial deviation from the mean sphere. The datum defined for Mars on the basis of Mariner 9 data can be approximated as a triaxial ellipsoid with semimajor axes of 3394.6 and 3393.3 km and semiminor axis of 3376.3 km, based on a mean radius of 3382.9 km. For the moon, Lunar Orbiter IV tracking and ranging data give a datum approximated by a triaxial figure with semimajor axes 1738.30 and 1738.18 km and semiminor axis 1737.65 km, based on a mean radius of 1738 km. A topographic datum of Venus is also planned based on Pioneer-Venus gravity data.
Wu, S. S. C.↗
A supersensitive accelerometer for spacecraft gradiometry
An exact knowledge of the earth's gravity field is needed for advanced studies related to solid earth and ocean physics. A study (GRAVSAT-A) is currently considered by NASA to determine the gravity field with an accuracy of 2-3 mgal change and a resolution of 100 km using satellite to satellite range rate tracking techniques. The present investigation has the objective to prepare the foundation of an advanced GRAVSAT-B mission in the 1990s with an accuracy of about 1 mgal and a resolution of about 50 km. It is possible that satellite to satellite tracking will not be able to satisfy these requirements. However, it appears that a new technology, called "high sensitivity gradient gradiometry", could be employed to achieve the aims of the GRAVSAT-B mission. Attention is given to a new type of gravity gradiometer using superconducting microwave cavity oscillator accelerometers.
Reinhardt, V. S.↗
Electromagnetically-tracked free-mass gravitational wave antennas
The response to a gravitational wave of two free masses whose relative motion is monitored with an electromagnetic tracking signal is derived. The results indicate a two-feature signature in one-way data and a three-feature signature in two-way data. The effect is applied to gravitational wave experiments using laser interferometers, spacecraft Doppler tracking, planetary ranging, and pulsar timing analysis. Actual results are presented from spacecraft Doppler experiments and from pulsar timing data analysis, with new upper limits being set on a possible cosmic gravitational wave background via the pulsar data.
Hellings, R. W.↗
Review of laser and RF systems for space proximity operations
The development of ranging and tracking systems for NASA space missions is discussed. Among the systems described are: rendezvous and docking (RAD) radar systems for the Gemini and Apollo programs; the Shuttle Rendezvous Ku-band radar system; and laser and TV docking systems RAD sensors systems for the Space Station. A multi-target microwave tracking system for Shuttle applications in the future is also described.
Krishen, K.↗
Alignment System For Docking Control
Concept for alignment of vehicle approaching station based on generation of coherent, polarized light or microwave beam by station and measurement of beam propagation and polarization axes by vehicle. Intended for use in docking of spacecraft in flight and in robotics. Conical and corner-cube reflectors on vehicle disperse portions of incident light beam to sensors on vehicle and station, respectively. Station uses return signal for ranging and tracking. Known mathematical relationship among direction of beam and positions of reflected light on photodetector arrays used to calculate orientation of vehicle.
Iwasaki, Richard S.↗
Atmospheric gravitational influence on geodetic satellite orbits - Starlette analysis
The atmosphere is constantly in motion. The changing gravitational force due to the air mass movement will slightly perturb the orbit of a satellite. As the instrument accuracy for geodetic satellites improves, failure to model this perturbation can result in significant systematic errors in the orbit determination. The latter, in turn, will degrade the Earth's gravity solutions. A direct modeling technique to analyze the atmospheric gravitational influence on geodetic satellite is developed. We use the global surface pressure data from the ECMWF Initial Analysis Database to compute the gravitational force due to atmospheric perturbation exerted on given satellite as a function of time during selected orbital arcs. Satellite Laser Ranging (SLR) tracking data for selected Starlette (altitude 900 km) orbital arcs are used to test the computed force model. Although only a slight reduction in the rms residuals is observed when the atmospheric gravitational perturbation is included in the force model for data reduction of the SLR data, significant improvement is obtained in the predictability of the satellite orbit. Comprehensive studies involving more definitive test criteria and more refined models are still needed.
Chao, B. F.↗
Effects of window size and shape on accuracy of subpixel centroid estimation of target images
A new algorithm is presented for increasing the accuracy of subpixel centroid estimation of (nearly) point target images in cases where the signal-to-noise ratio is low and the signal amplitude and shape vary from frame to frame. In the algorithm, the centroid is calculated over a data window that is matched in width to the image distribution. Fourier analysis is used to explain the dependency of the centroid estimate on the size of the data window, and simulation and experimental results are presented which demonstrate the effects of window size for two different noise models. The effects of window shape were also investigated for uniform and Gaussian-shaped windows. The new algorithm was developed to improve the dynamic range of a close-range photogrammetric tracking system that provides feedback for control of a large gap magnetic suspension system (LGMSS).
Welch, Sharon S.↗
Methods to Improve the Maintenance of the Earth Catalog of Satellites During Severe Solar Storms
The objective of this thesis is to investigate methods to improve the ability to maintain the inventory of orbital elements of Earth satellites during periods of atmospheric disturbance brought on by severe solar activity. Existing techniques do not account for such atmospheric dynamics, resulting in tracking errors of several seconds in predicted crossing time. Two techniques are examined to reduce of these tracking errors. First, density predicted from various atmospheric models is fit to the orbital decay rate for a number of satellites. An orbital decay model is then developed that could be used to reduce tracking errors by accounting for atmospheric changes. The second approach utilizes a Kalman filter to estimate the orbital decay rate of a satellite after every observation. The new information is used to predict the next observation. Results from the first approach demonstrated the feasibility of building an orbital decay model based on predicted atmospheric density. Correlation of atmospheric density to orbital decay was as high as 0.88. However, it is clear that contemporary: atmospheric models need further improvement in modeling density perturbations polar region brought on by solar activity. The second approach resulted in a dramatic reduction in tracking errors for certain satellites during severe solar Storms. For example, in the limited cases studied, the reduction in tracking errors ranged from 79 to 25 percent.
Wilkin, Paul G.↗
Implications of MOLA Global Roughness, Statistics, and Topography
New insights are emerging as the ongoing high-quality measurements of the Martian surface topography by Mars Orbiter Laser Altimeter (MOLA) on board the Mars Global Surveyor (MGS) spacecraft increase in coverage, resolution, and diversity. For the first time, a global characterization of the statistical properties of topography is possible. The data were collected during the aerobreaking hiatus, science phasing, and mapping orbits of MGS, and have a resolution of 300-400 m along track, a range resolution of 37.5 cm, a range precision of 1-10 m for surface slopes up to 30 deg., and an absolute accuracy of topography of 13 m. The spacecraft's orbit inclination dictates that nadir observations have latitude coverage of about 87.1S to 87.1N; the addition of observations obtained during a period of off-nadir pointing over the north pole extended coverage to 90N. Additional information is contained in the original extended abstract.
Aharonson, O.↗