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At least 253 records · Page 14

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NASA NTRS1975

Early results of the ATS-6 solar cell flight experiment

This paper presents preliminary ATS-6 solar-cell flight-experiment data through the first 247 days in synchronous orbit. The experiment is transmitting data on forty 2 x 2-cm solar cells representing 16 solar-cell configurations. The experiment is designed to study the effect of this orbit on select solar cells and cover-glass parameters such as solar-cell thickness and base resistivity, cover-glass thickness variation, new cover processes, and materials such as 7940 and 7070 integral covers as well as the FEP covers, the COMSAT 'violet' cell, and backside irradiation effects. The in-space solar-cell data indicate short-circuit currents are running higher by 1% to 8% than in measurements made with solar simulations; maximum power varied between -1% and +6%. Degradation of short-circuit current due to ultraviolet effects was determined to be about 2% after 50 days in orbit. All cells performed well through 247 days in orbit except the FEP-covered cells, which appear to have increased their rate of degradation during the eclipse season.

Goldhammer, L. J.↗

NASA NTRS1975

Micropulsations in the morning sector. II - Satellite observations of 10to 45-s waves at synchronous orbit, ATS 1

A study of 13 wave events having 10- to 45-s periods and observed by ATS 1 in the morning sector reveals that these events, which have been called band-limited pulsations and are thought to be related to Pi 1, appear actually to be Pc 3. Digital power-spectral and coherency analysis was used to determine the characteristics of the wave activity. The average peak frequency of the events (about 0.04 Hz) and their generally narrow-band nature correspond closely with the characteristics of Pc 3. The local-time distribution of the events (peaking at 0900 LT) and their less than complete association with substorms also correspond more closely with Pc 3 characteristics. The orientation of the major axis of the polarization ellipse for these events was predominantly azimuthal, which agrees more closely with the east-west polarization of Pi 1 observed on the ground. However, some examples of radial orientation were observed in the satellite data.

Arthur, C. W.↗

NASA NTRS1975

ATS-6 - Description and performance

The Applications Technology Satellite-6 embodies a geosynchronous technology that is sensitive enough to receive signals from simple inexpensive earth-based terminals and is powerful enough to relay color television and other high-quality signals to these terminals. This was accomplished by deploying a 9.1-m parabolic reflector antenna in space, by performing precision attitude maneuvers on commands from the earth to point the reflector to selected spots on the earth's surface, and by providing communications links and necessary power to receive and rebroadcast signals transmitted from the ground. All major objectives of the ATS program have been satisfied, with specifications being met or exceeded.

Redisch, W. N.↗

NASA NTRS1975

ATS-6 - Experiment summary

A general overview is given of experiment planning and implementation for the ATS-6. Included in the review are discussions of project office activities, experiment selection, spacecraft implementation, ground terminal implementation, the operations control center, and the information processing division. A table is included summarizing the various experiments among which are communications, scientific and technological experiments.

Corrigan, J. P.↗

NASA NTRS1975

ATS-6 - Technical aspects of the Health/Education Telecommunications Experiment

An overview is given of the HET experiment on ATS-6. The paper is divided into nine parts, including a technical overview, a preliminary evaluation of the HET demonstration, a review of operations at the Denver uplink terminal, a discussion of remote ground terminals, a review of C-band comprehensive terminals and of S-band comprehensive terminals, and parts devoted to general network operations, technical management and effectiveness of the network, and the site equipment operator.

Boor, J. L.↗

NASA NTRS1975

ATS-6 - Satellite Instructional Television Experiment

The Satellite Instructional Television Experiment (SITE) is scheduled for the second year of satellite operation. Applications Technology Satellite (ATS-6) will receive C-band video signals from Ahmedabad and Delhi, India, and will retransmitt the video and two audio subcarriers at 860 MHz to 6 clusters of 400 direct-receive stations for a total of 2400 direct-receive stations. Morning programs of 1.5 hours per day are designed for classroom use, and evening programs of 2.5 hours duration are designed for village adult education. Indian production antennas and television sets have been tested and found to meet specifications, and a successful experiment is anticipated.

Miller, J. E.↗

NASA NTRS1975

ATS-6 - Television Relay Using Small Terminals Experiment

The Television Relay Using Small Terminals (TRUST) Experiment was designed to advance and promote the technology of broadcasting satellites. A constant envelope television FM signal was transmitted at C band to the ATS-6 earth coverage horn and retransmitted at 860 MHz through the 9-m antenna to a low-cost direct-readout ground station. The experiment demonstrated that high-quality television and audio can be received by low-cost direct-receive ground stations. Predetection bandwidths significantly less than predicted by Carson's rule can be utilized with minimal degradation of either monochrome or color pictures. Two separate techniques of dual audio channel transmission have been demonstrated to be suitable for low-cost applications.

Miller, J. E.↗

NASA NTRS1975

ATS-6 - Radio Frequency Interference Measurement Experiment

The frequency band from 5.925 to 6.425 GHz is served by fixed satellites and by terrestrial microwave links. There is a possibility of microwave links pointed at the horizon causing interference to the uplinks of domestic and international communications satellites sharing the same frequency band. A mathematical model has been derived for predicting the fields at geostationary orbit based on the known characteristics and known distribution of the terrestrial microwave relay system. The Applications Technology Satellite-6 (ATS-6) is sensitive to signals in the range of 10 dBW radiated in the direction of the satellite. Signals in the range of 10-30 dBW have been recorded over various parts of the United States.

Henry, V. F.↗

NASA NTRS1975

ATS-6 - Preliminary results from the 13/18-GHz COMSAT Propagation Experiment

The 13/18-GHz COMSAT Propagation Experiment (CPE) is reviewed, the data acquisition and processing are discussed, and samples of preliminary results are presented. The need for measurements of both hydrometeor-induced attenuation statistics and diversity effectiveness is brought out. The facilitation of the experiment - CPE dual frequency and diversity site location, the CPE ground transmit terminals, the CPE transponder on Applications Technology Satellite-6 (ATS-6), and the CPE receive and data acquisition system - is briefly examined. The on-line preprocessing of the received signal is reviewed, followed by a discussion of the off-line processing of this database to remove signal fluctuations not due to hydrometeors. Finally, samples of the results of first-level analysis of the resultant data for the 18-GHz diversity site near Boston, Mass., and for the dual frequency 13/18-GHz site near Detroit, Mich., are presented and discussed.

Hyde, G.↗

NASA NTRS1975

ATS-6 - The Geosynchronous Very High Resolution Radiometer

The Geosynchronous Very High Resolution Radiometer (GVHRR), flown on the three-axis stabilized geosynchronous satellite, Applications Technology Satellite-6 (ATS-6), collected meteorological data for two months during the summer of 1974. Several hundred images were successfully taken. Data collection terminated when the instrument chopper motor failed. The instrument, its supporting ground equipment, and the data collected in orbit are described.

Shenk, W. E.↗

NASA NTRS1975

ATS-6 - UCLA fluxgate magnetometer

A summary of the design of the University of California at Los Angeles' fluxgate magnetometer is presented. Instrument noise in the bandwidth 0.001 to 1.0 Hz is of order 85 m gamma. The DC field of the spacecraft transverse to the earth-pointing axis is 1.0 + or - 21 gamma in the X direction and -2.4 + or - 1.3 gamma in the Y direction. The spacecraft field parallel to this axis is less than 5 gamma. The small spacecraft field has made possible studies of the macroscopic field not previously possible at synchronous orbit. At the 96 W longitude of Applications Technology Satellite-6 (ATS-6), the earth's field is typically inclined 30 deg to the dipole axis at local noon. Most perturbations of the field are due to substorms. These consist of a rotation in the meridian to a more radial field followed by a subsequent rotation back. The rotation back is normally accompanied by transient variations in the azimuthal field. The exact timing of these perturbations is a function of satellite location and the details of substorm development.

Mcpherron, R. L.↗

NASA NTRS1975

ATS-6 - UCSD auroral particles experiment

The University of California at San Diego Auroral Particles Experiment aboard Applications Technology Satellite-6 (ATS-6) is discussed. The experiment is designed to investigate the time development of geomagnetic substorm particles, the confinement and loss of such particles, and the roles of plasma wave instabilities and characteristic system periodicities in substorm and general magnetospheric processes. The instrumentation includes a complement of five electrostatic charged particle detectors. Two detector assemblies are capable of rotation through 220 deg. The electrostatic curved plate energy/unit charge analyzers are ovoid, requiring particles to be bent only 55 deg to obtain azimuthal focusing. The inside of the plates is serrated to eliminate particles striking the sides. A post-analysis electrostatic lens consisting of two wire grids, one at the potential of the inner plate and one at the potential of ground, focuses particles strongly upon the center of the sensor. A spiraltron particle sensor detects the charged particles. The system has an energy range of five orders of magnitude with a lower extreme of less than 1 eV. Preliminary data are presented to illustrate phenomena which are observed as a result of the novel features described.

Mauk, B. H.↗

NASA NTRS1975

ATS-6 - Synchronous orbit trapped radiation studies with an electron-proton spectrometer

The paper discusses the University of Minnesota experiment on ATS-6 designed to study the origin and dynamics of high-energy electrons and protons in the outer radiation belt and in the near-earth plasma sheet. The experiment consists of two nearly identical detector assemblies, each of which is a magnetic spectrometer containing four gold-silicon surface barrier detectors. The instrument provides a clean separation between protons and electrons by the combination of pulse height analysis and magnetic deflection.

Walker, R. J.↗

NASA NTRS1975

ATS-6 - Energetic particle radiation measurement at synchronous altitude

The energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 3.9 MeV, and measures energetic protons in five energy channels between 2.3 and 80 MeV and energetic alpha particles in three channels between 9.4 and 94 Mev. After more than a year of operation in orbit, the experiment continues to return excellent data on the behavior of energetic magnetospheric electrons as well as information regarding the fluxes of solar protons and alpha particles.

Paulikas, G. A.↗

NASA NTRS1975

ATS-6 - Spacecraft Attitude Precision Pointing and Slewing Adaptive Control Experiment

The primary objective of the Spacecraft Attitude Precision Pointing and Slewing Adaptive Control (SAPPSAC) experiment is to establish feasibility and evaluate capabilities of a ground-based spacecraft attitude control system, wherein RF command and telemetry links, together with a ground station on-line minicomputer, perform closed loop attitude control of the Applications Technology Satellite-6 (ATS-6). The ground processor is described, including operational characteristics and the controller software. Attitude maneuvers include precision pointing to fixed targets, slewing between targets, and generation of prescribed ground tracks. Test results show high performance and reliability for over 30 hours of on-line control with no serious anomalies. Attitude stabilization relative to a prescribed target has been achieved to better than 0.007 deg in pitch and roll and 0.02 deg in yaw for a period of 43 min. Ground tracks were generated which had maximum latitude/longitude deviations less than 0.15 deg from reference.

Isley, W. C.↗

NASA NTRS1975

ATS-6 - Interferometer

The ATS-6 interferometer provides precision, 3-axis attitude sensing capability. It incorporates a C-band receiver which measures the phase difference of continuous ground station signals received at paired antenna elements and converts this phase difference into digital data that is transmitted to the ground, and is also used as direct input to the onboard digital operations controller for conversion to attitude information. It uses 6 onboard horn antennas, placed in the earth viewing module, with three antennas arranged along each of two orthogonal baselines parallel to the satellite pitch and roll axes, one antenna used as a measurement reference on each baseline, and the remaining two horns, placed to provide phase measurements relative to the respective reference antenna.

Isley, W. C.↗

NASA NTRS1975

ATS-6 - Solar cell flight experiment after 325 days in synchronous orbit

Preliminary results of the Applications Technology Satellite-6 (ATS-6) solar cell flight experiment to isolate and identify solar cell degradation mechanisms resulting from particulate radiation and to obtain specific design data applicable to extended synchronous spacecraft missions are presented. The experiment includes 80 individual cells representing 16 different solar cell/cover glass configurations. Most of the cells are 0.030 cm thick boron doped n/p cells with 10 ohm cm resistivity and solder-coated AgTi contacts. The voltage-current characteristics were measured regularly. The data for the first 325 days of flight show short circuit currents 1-8% higher than measurements made with solar simulations. Maximum power varied between -1 and +6%. After 50 days in orbit the degradation of short circuit current due to ultraviolet effects was determined to be about 2%. All cells except those with fluorinated ethylene propylene covers performed well after 325 days.

Goldhammer, L. J.↗

NASA NTRS1975

ATS-6 - Cesium bombardment engine north-south stationkeeping experiment

Two 0.004 N thrust cesium bombardment ion thrustors have been developed and used for north-south stationkeeping in the geostationary Applications Technology Satellite-6 (ATS-6). The thrustor subsystems are mounted on the north and south faces of the earth viewing module such that 0.0026 N of thrust is applied normal to the orbit plane and 0.0036 N is applied radially upward. The change in the orbit inclination of the satellite is maintained at zero by operating the two thrustors alternately so that their thrust components, normal to the orbital plane, are symmetrically applied about the nodal crossings. Initial operation of the thrustors was successful. There was no interference with the satellite communications systems and the predicted spacecraft operating potential was verified. Subsequent trials failed due to a defect in the operation of the propellant reservoirs in zero g. A feed line valve is under development to correct this difficulty.

Worlock, R. M.↗