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The effect of variations in sun angle and haze level on the accuracy of automatic classification of Earth Resources Technology Satellite-1 (ERTS-1) data was studied by classifying ERTS imagery in which such variations were computer-simulated. It was found that relatively small changes in sun angle and haze level can substantially reduce classification accuracy.
Turbulence in the solar wind near the sun is investigated using records of changes in the integrated electron columnar content along the line of sight to Mariners 6, 7, and 9. The comoving turbulence spectrum is found to be well represented by a power law with an index of about 3.9. The turbulence is shown to decline with heliocentric distance, and the data suggest a region of enhanced turbulence near the sun. The Mariner-9 spectral amplitudes are found to correspond with Zurich sunspot numbers. Implications of the present observations are discussed for contemporary theories on solar-wind heating.
Sun calibration data from Landsat-2 are presented and compared with those from Landsat-1 (ERTS-1). The data support the hypothesis that organic contamination caused the poor performance of the Landsat-1 sun calibration mirror, since extra cleanliness precautions were taken with the Landsat-2 mirror. These precautions are described; of particular importance was the aluminum foil covering kept close to the reflective surfaces of the second mirror during the prelaunch period.
An approximative model is formulated for assessing these perturbations that significantly affect long term modal motion of sun synchronous orbits. Computer simulations with several independent computer programs consider zonal and tesseral gravitational harmonics, third body gravitational disturbances induced by the sun and the moon, and atmospheric drag. A pendulum model consisting of evenzonal harmonics through order 4 and solar gravity dominated nodal motion approximation. This pendulum motion results from solar gravity inducing an inclination oscillation which couples into the nodal precession induced by the earth's oblateness. The pendulum model correlated well with simulations observed flight data.
A sun detector developed for the Mariner Jupiter/Saturn mission is described. Redundant photopotentiometers for both pitch and yaw axes, positioned below slit apertures, provide spacecraft stabilization and biased operation over plus or minus 20-deg fields of view. The biased (off-sun) operation is required for pointing the 366-cm-diameter (spacecraft-fixed) radio antenna toward earth. Configuration and fabrication processes are presented, along with a summary of development history. Particular attention is given to the properties of cadmium sulfide as these affect adaptation to this application.
When spacecraft are tracked near the line-of-sight of the sun, the ground antenna sidelobes see the solar noise. The solar noise increases the ground system operating noise temperature and degrades the downlink RF reception performance. At specific antenna azimuthal angles relative to the sun, noise peaks and nulls occur periodically throughout a day's tracking pass due to the quadripod support leg-generated sidelobes. This article documents this effect while tracking Helios 1, illustrates the time of the peaks, and compares the predicted time of the noise temperature peaks with the measured data.
A computer program (CTS 41B) used to determine the trajectory of a spacecraft signal raypath was updated to increase its usefulness during solar conjunctions (CTS 41C). The closest point of approach of the raypath to the sun is projected onto the surface and the solar latitude and longitude calculated. A sample computation and plots are given for the 1976 Viking solar conjunction. Eventually it may be possible to predict the communication link performance degradation in the near sun region due to solar activity.
The possible processes in the lower atmosphere of the earth initiated or controlled by changes in the output of the sun are investigated. These changes can include solar variation in radiation (as in the constant, or in specific wavelength regions), in particles (as in physical properties of the solar wind, or in solar cosmic rays, or solar-modulated galactic cosmic rays), and in the extended magnetic field of the sun (as in circumstances of the passage of interplanetary sector boundaries). Changes of short term (in the weather) as well as long term (in regional or global climate) are considered.
The influence of the sector structure on the fundamental quantities (densities, temperatures, pressure, composition, electric and magnetic fields, etc.) in the magnetosphere, ionosphere and atmosphere is discussed, and daily synoptic observations of these quantities are recommended for future sun-weather investigations. Extended Shuttle missions are proposed to carry out these observations. Continuous observations of the interplanetary quantities such as the solar wind velocity, density, temperature and composition, the vector interplanetary magnetic field, and energetic particle fluxes through a wide range of energies are also recommended for understanding the extraterrestrial causes of terrestrial effects. The Heliocentric Spacecraft of the International Sun-Earth Explorer Project which remains 0.01 astronomical units from the earth is found to be the best means of carrying out these interplanetary observations.
The structure of the sun and its surface temperature and brightness are discussed as background for explaining the ASTP joint experiment to photograph the solar corona from Soyuz while the Apollo spacecraft created an artificial eclipse by blocking out the sun. Stellar spectra, stellar evolution, and the Milky Way galaxy are explored in relation to the MA-083 experiment to survey the sky for extreme ultraviolet sources and background radiation. Interstellar gas and the spectrum of helium are discussed in relation to the MA-088 experiment designed to detect interstellar helium entering the solar system and to measure its density and motion.
The use of radio tracking of a solar probe to estimate accurately the coefficient of the second zonal harmonic of the sun's gravitational field was examined. Preliminary results indicate that the coefficient can be estimated with a standard error of 10 to the minus 8th power or less, provided that the probe is equipped with a suitable drag-free system to compensate for the effects of non-gravitational accelerations. For signal paths that pass near the sun, dual-band ranging to the probe can provide the tracking accuracy needed to insure that the standard of error is equal to or less than 10 to minus 8th power. The possibility of achieving such accuracy with a single-band radio uplink and a dual-band downlink is discussed.
The metric tensor is given for describing the dynamical effects of the sun on a solar probe and the gravitational redshift of a probe-based clock in a covariance analysis for the detectability of the solar quadrupole moment and the solar angular momentum. Unknown parameters were determined by least squares fit to the probe tracking data. A polar orbit was assumed with perihelion at 5 solar radii and with an earth-sun-probe angle of 135 deg at perihelion. Tracking was assumed to be Doppler only, with a basic uncertainity of .1 mm/sec in the radial velocity. A drag-free system which could reduce nongravitational forces below the level of 2 times 10 to the minus 12th power was found necessary to preserve this same level of accuracy. Both one way and two way Doppler were supposed in order to determine the gravitational redshift as well as the pure spacecraft dynamics.
Photographic flights were made over an ocean acid waste dump site while dumping was in progress. The flights resulted in wide angle, broadband, spectral radiance film exposure data between the wavelengths of 500 to 900 nanometers for sun elevation angles ranging from 26 to 42 degrees. It is shown from densitometer data that the spectral signature of acid waste discharged into ocean water can be observed photographically, the influence of sun elevation upon remotely sensed apparent color can be normalized by using a single spectral band ratioing technique, and photographic quantification and mapping of acid waste through its suspended iron precipitate appears possible.
The third satellite of the international Sun-Earth Explorer program was inserted into a periodic halo orbit about L sub 1, the collinear libration point between the Sun and the Earth-Moon barycenter. A plan is presented that was developed to enable insertion into the halo orbit in case there was a large underperformance of the Delta second or third stage during the maneuver to insert the spacecraft into the transfer trajectory. After one orbit of the Earth, a maneuver would be performed near perigee to increase the energy of the orbit. A relatively small second maneuver would put the spacecraft in a transfer trajectory to the halo orbit, into which it could be inserted for a total cost within the fuel budget. Overburns (hot transfer trajectory insertions) were also studied.
Two parallel investigations into the degree, if any, to which orthogonally polarized rays are deflected differently on passing through the gravitational field of the sun were previously conducted. The first involved very long and intermediate length baseline radio interferometry. The second was initially based on observations of radiation transmitted by the Pioneer 6 spacecraft, on passing behind the sun in 1968. This work was extended by using Helios-A and Helios-B spacecraft. It was calculated that the differential deflection between orthogonally polarized components is less than one part in 10 to the 7th power of the total gravitational deflection, or less than about 10 to the -7th power arc sec, in total.
Results are reported for observations of a quiet region at the center of the sun with an interferometer operating at a wavelength of 8.33 mm and with an east-west baseline giving a maximum angular resolution of 28 arcsec. It is found that strong fluctuations occur over time scales of approximately 10 to 30 min and dominate the data at large hour angles, that smaller and more rapid fluctuations in both amplitude and phase are detected at all hour angles, and that the strong fluctuations are consistent with those that may be produced by the natural time variation of the fringe pattern during observation of a fixed source distribution. The weaker and more rapid fluctuations are tentatively attributed to antenna-tracking variations and the observation of features in a greatly extended source. The results are compared directly with those of two other interferometric studies of the quiet sun at millimeter wavelengths.
The simulation of radiation interference effects and the results of a radiation interference test on two Voyager Sun Sensor prototype detector assemblies are reported. The derivation of test levels and requirements are discussed and show that cobalt 60 gamma radiation is an effective and practical simulator of the ionization dose rate effects induced by high-energy electron flux incident on the spacecraft at a rate of 3.7 x 10 to the 8th e/sq cm-sec (10 rad(Si)/s) during closest approach to Jupiter. The test results provide information that is used to confirm an analytic correlation, and to predict satisfactory performance of a spacecraft sun sensing device having stringent angular resolution requirements. The measured detector response shows that at dose rates incident on the detector elements of 2 rad(Si)/sec, which is four times that expected during Jupiter encounter, the radiation-induced angle error is almost an order of magnitude less than that allowed by the acceptance criteria.
Application of the modern control theory to derive an optimal sun tracking control for a point focusing solar concentrator is presented. A standard tracking problem converted to regulator problem using a sun rate input achieves an almost zero steady state tracking error with the optimal control formulation. However, these control techniques are costly because optimal type algorithms require large computing systems, thus they will be used mainly as comparison standards for other types of control algorithms and help in their development.