Ionospheric electron content and irregularities deduced from BE-C satellite transmissions.
Ionospheric electron content variation across sunrise and sunset lines deduced from radio-beacon satellite transmissions
IONOSPHERIC IRREGULARITY↗
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Tidal parameters derived from the perturbations in the orbital inclinations of the BE-C, GEOS-1 and GEOS-2 satellites
Effective tidal Love numbers and phase angles for the O sub one, K sub one, M sub two, K sub two, P sub one, and S sub two, tides are recovered. The effective tidal phase angles tend to be on the order of a few degrees. The effective tidal Love numbers are generally less than the solid earth Love number K sub two, of about 0.30. This supports the contention that the ocean tides give an apparent depression of the solid earth Love number. Ocean tide amplitudes and phases are calculated for the above tides assuming K sub two = 0.30 and the solid earth lag angle O sub two = 0. The results show good agreement on GEOS-1 but not on GEOS-II.
Rubincam, D. P.↗
Satellite tracking and earth dynamics research programs
The SAO laser site in Arequipa continued routine operations throughout the reporting period except for the months of March and April when upgrading was underway. The laser in Orroral Valley was operational through March. Together with the cooperating stations in Wettzell, Grasse, Kootwikj, San Fernando, Helwan, and Metsahove the laser stations obtained a total of 37,099 quick-look observations on 978 passes of BE-C, Starlette, and LAGEOS. The Network continued to track LAGEOS at highest priority for polar motion and Earth rotation studies, and for other geophysical investigations, including crustal dynamics, Earth and ocean tides, and the general development of precision orbit determination. The Network performed regular tracking of BE-C and Starlette for refined determinations of station coordinate and the Earth's gravity field and for studies of solid earth dynamics. Monthly statistics of the passes and points are given by station and by satellite.
Source record↗
Measurements of satellite range with a ruby laser
Range measurements of GEOS-I and BE-C satellites with ruby laser
SATELLITE TRACKING↗
An analysis of the GSFC laser ranging data
Laser tracking data from BE-C and Geos-A satellites, and analytical and statistical techniques employed
Moss, S. J.↗
GSFC orbit computations for ISAGEX operations
The objective of the program is to collect a set of homogeneous and well distributed precise laser and camera satellite observations for the purpose of dynamic and geometric geodesy. The data gathering portion of the experiment extended from December 15, 1970 to August 31, 1971 and consisted of seven three-week saturation tracking periods. The seven geodetic satellites tracked were BE-B, BE-C, GEOS-1, GEOS-2, DI-C, DI-D, and PEOLE. The techniques employed to generate acquisition data for the two lasers are described. Analyses of the quick-look Astrosoviet NAFA-25 camera data indicated that the accuracy of these data was on the order of a few minutes of arc. These data were useful in definitive orbit determination.
Agreen, R. W.↗
On the tidal effects in the motion of artificial satellites.
The general perturbations in the elliptic and vectorial elements of a satellite as caused by the tidal deformations of the non-spherical Earth are developed into trigonometric series in the standard ecliptical arguments of Hill-Brown lunar theory and in the equatorial elements of the satellite. The integration of the differential equations for variation of elements of the satellite in this theory is easy because all arguments are linear or nearly linear in time. The trigonometrical expansion permits a judgment about the relative significance of the amplitudes and periods of different tidal 'waves' over a long period of time. Graphs are presented of the tidal perturbations in the elliptic elements of the BE-C satellite which illustrate long term periodic behavior. The tidal effects are clearly noticeable in the observations and their comparison with the theory permits improvement of the 'global' Love numbers for the Earth.
Musen, P.↗
Calculation of retroreflector array transfer functions
Computer programs have been developed for calculating the transfer function of a retroreflector array. The transfer functions provide range corrections and effective reflecting areas for the retroreflector arrays carried by satellites now in orbit. This information can be used to estimate laser echo signal strengths and to correct laser range measurements in order to obtain the range to the center of mass of the satellite. The values are tabulated for various angles of incidence of the laser beam with respect to the symmetry axis of the satellite. Transfer functions have been computed for the following satellites: BE-B, BE-C, Geos 1, D1C, D1D, Geos 2, Peole, and Geos C.
Arnold, D. A.↗
Computations of M sub 2 and K sub 1 ocean tidal perturbations in satellite elements
Semi-analytic perturbation equations for the influence of M2 and K1 ocean tidal constituents on satellite motion are expanded into multi-dimensional Fourier series and calculations made for the BE-C satellite. Perturbation in the orbital elements are compared to those of the long period solid earth tides.
Estes, R. H.↗
Determination of the geocentric gravitational constant from laser ranging on near-earth satellites
Laser range observations taken on the near-earth satellites of Lageos (a = 1.92 e.r.), Starlette (a = 1.15 e.r.), BE-C (a = 1.18 e.r.), and Geos-3 (a = 1.13 e.r.) have been combined to determine an improved value of the geocentric gravitational constant (GM). The value of GM is 398600.61 cu km/sec per sec, based upon a speed of light, c, of 299792.5 km/sec. Using the IAG-adopted value of c equalling 299792.458 km/sec scales GM to 398600.44 cu km/sec per sec. The uncertainty in this value is assessed to be plus or minus 0.02 cu km/sec per sec. Determinations of GM from the data taken on these four satellites individually show variations of only .04 cu km/sec per sec from the combined result. The Lageos information dominated the combined solution, and gave the most consistent results in its data subset solutions. The value obtained for GM from near-earth laser ranging compares quite favorably with the most recent results of the lunar laser and interplanetary experiments.
Lerch, F. J.↗
Gravity model improvement using GEOS 3 /GEM 9 and 10/
Although errors in previous gravity models have produced large uncertainties in the orbital position of GEOS 3, significant improvement has been obtained with new geopotential solutions, Goddard Earth Model (GEM) 9 and 10. The GEM 9 and 10 solutions for the potential coefficients and station coordinates are presented along with a discussion of the new techniques employed. Also presented and discussed are solutions for three fundamental geodetic reference parameters, viz. the mean radius of the earth, the gravitational constant, and mean equatorial gravity. Evaluation of the gravity field is examined together with evaluation of GEM 9 and 10 for orbit determination accuracy. The major objectives of GEM 9 and 10 are achieved. GEOS 3 orbital accuracies from these models are about 1 m in their radial components for 5-day arc lengths. Both models yield significantly improved results over GEM solutions when compared to surface gravimetry, Skylab and GEOS 3 altimetry, and highly accurate BE-C (Beacon Explorer-C) laser ranges. The new values of the parameters discussed are given.
Lerch, F. J.↗
Satellite-tracking and Earth dynamics research programs
The major focus for operations during this period was the preliminary MERIT Campaign and its intensive tracking of LAGEOS for polar motion and Earth rotation studies. The data acquired from LAGEOS were used for other geophysical investigations, including studies of crustal dynamics, and Earth and ocean tides, and for the general development of precision orbit determination. The network performed regular tracking of several other retroreflector satellites including GEOS-1, GEOS-3, BE-C, and Starlette for refined determinations of station coordinates and Earth's gravity field and for studies of solid Earth dynamics.
Source record↗
Satellite-tracking and Earth dynamics research programs
The activities carried out by the Smithsonian Astrophysical Observatory (SAO) are described. The SAO network continued to track LAGEOS at highest priority for polar motion and Earth rotation studies, and for other geophysical investigations, including crustal dynamics, Earth and ocean tides, and the general development of precision orbit determination. The network performed regular tracking of several other retroreflector satellites including GEOS-1, GEOS-3, BE-C, and Starlette for refined determinations of station coordinates and the Earth's gravity field and for studies of solid Earth dynamics. A major program in laser upgrading continued to improve ranging accuracy and data yield. This program includes an increase in pulse repetition rate from 8 ppm to 30 ppm, a reduction in laser pulse width from 6 nsec to 2 to 3 nsec, improvements in the photoreceiver and the electronics to improve daylight ranging, and an analog pulse detection system to improve range noise and accuracy. Data processing hardware and software are discussed.
Source record↗
Satellite-tracking and Earth dynamics research programs
Tracking of LAGEOS for polar motion and Earth rotation studies and for other geophysical investigations, including crustal dynamics, Earth and ocean tides, and the general development of precision orbit determination continues. The BE-C and Starlette satellites were tracked for refined determinations of station coordinates and the Earth's gravity field and for studies of solid Earth dynamics.
Source record↗
Satellite tracking and Earth dynamics research programs
Following an upgrading program, ranging performance capabilities of a satellite-tracking pulsed laser system were assessed in terms of range accuracy, range noise, data yield, and reliability. With a shorter laser pulse duration (2.5 to 3.0 NSEC) and a new analog pulse processing system, the systematic range errors were reduced to 3 to 5 cm and range noise was reduced to 5 to 16 cm and range noise was reduced to 5 to 15 cm on Starlette and BE-C, and 10 to 18 cm on LAGEOS. Maximum pulse repetition rate was increased to 30 pulses per minute and significant improvement was made in signal to noise ratio by installing a 3 A interference filter and by reducing the range gate window to 200 to 400 nsec. The solution to a problem involving leakage of a fraction of the laser oscillator pulse through the pulse chopper was outlined.
Pearlman, M. R.↗