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

The Health/Education Telecommunications (HET) Experiment involved six different experiments conducted under the auspices of the Department of Health, Education, and Welfare (HEW) with technical assistance from NASA. The HET Experiment on ATS-6 was operated and controlled from a network coordination center in Denver, Colo., which included a 4-and 6-GHz Earth station. The HET Experiment used remote Earth terminals with 3-m-diameter dishes having a 35 dB gain at 2.5 GHz. In addition, comprehensive terminals operating at both C-band and S-band were used for communications with Alaska. The total network involved a complex of satellite and land links at C-band, S-band, and very high frequency (VHF), using the ATS-1, ATS-3, and ATS-6 satellites. The network performance exceeded expectations with remote terminal operations exhibiting a peak-to-peak signal to weighted rms noise ratio of 49 dB at least 99 percent of the time. The remote site operators performed well and were well motivated although they had little previous technical experience.     

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.     

ETS-II Experiments Part IV: Characteristics of Millimeter and Centimeter Wavelength Propagation

Preliminary results of the ETS-II millimeter and centimeter wavelength propagation experiments are presented based on data collected over one year. Rain attenuation is discussed primarily from the statistical point of view. At 34.5 GHz attenuation in excess of 5, 10, and 19.5 dB were observed 1, 0.3, and 0.1 percent of the test time (5500 hr), respectively. At 11.5 GHz attenuation in excess of 2.5, 4.3, 6.3, 10, and 15.5 dB were observed 0.1, 0.03, 0.01, 0.003, and 0.001 percent of the test time, respectively. Duration time of attenuation is also examined for the benefit of a link design. The longest duration of attenuation of the 34.5-GHz wave exceeding 5 dB was about 150 min. At 11.5 GHz, the longest duration of attenuation in excess of 3 dB, was 60 min and that in excess of 6 dB was 10 min. Rain attenuation is discussed also with relation to the radar and the rain gauge data. Depolarization data of 34.5-GHz and 11.5-GHz waves are orocessed statistically, and it is shown that cross-polarization discriminations in excess of 21.5 dB and 29 dB are observed 0.1 percent of the test time at 34.5 GHz and 11.5 GHz, respectively.     

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.     

Ka频段卫星通信雨衰分析及解决对策

Ka频段卫星通信中,降雨引起的信号衰减对通信链路的通断起着非常重要的作用.本文在阐述雨衰原理的基础上,分析了Ka频段雨衰对信道特性的影响,提出了Ka频段抗雨衰的各种对策,并通过实例说明了对策的有效性.     

Recent progress in satellite radio beacon studies with particular emphasis on the ATS-6 radio beacon experiment

In May 1974 a new era in satellite radio beacon studies of the ionosphere opened with the ATS-6 Radio Beacon Experiment. The history of radio beacon studies up to that time is reviewed briefly and the particular features of the ATS-6 beacon are discussed together with the basic theory required to interpret the measurements. The main emphasis is on the ATS-6 beacon experiment but other beacon data are discussed which provide the necessary background. The diurnal and seasonal variations of the total electron content and the plasmaspheric content are presented for the U.S.A. and Europe. In winter the plasmaspheric content over the Western Hemisphere maximizes at night while in Europe and the Pacific it appears to peak near noon. This is thought to be caused by flow of plasma from the local and conjugate ionospheres. Night maxima of total electron content are found showing that they do not arise from depletions of the plasmaspheric content. The plasmaspheric content is highly sensitive to solarterrestrial disturbance, it reaches a minimum on the third day of a storm and may take between 10 and 20 days of partial filling and emptying to recover. Traveling disturbances in U.S.A., Europe, and India show similarities of speeds but not of direction. Beacon observations of micropulsations in total content, tropospheric fluctuations and Fresnel diffraction by intense ionospheric irregularities are discussed together with radio wave scintillations and some applications of beacon radio data to communications and navigation.     

ATS-6 Spacecraft Attitude Precision Pointing & 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 h of on-line control with no serious anomalies. Attitude stabilization relative to a prescribed target has been achieved to better than 0.007° in pitch and roll and 0.020° in yaw for a period of 43 min. Ground tracks were generated which had maximum latitude/longitude deviations less than 0.150 from reference.     

ATS-6 Interferometer

The Applications Technology Satellite-6 (ATS-6) RF interferometer is utilized primarily as a precision 3-axis attitude sensor having an unambiguous field of view of 350°. This function requires two separated ground transmitters, each using one of the two available frequency channels or sharing a single channel by time multiplexing. For 3-axis control, one uplink transmitter can provide 2-axis attitude (pitch and roll) with other sensors (e.g., a Polaris tracker) providing yaw attitude. By utilizing two uplink transmitters and the Earth sensor or three time multiplexed uplink transmitters, the interferometer can also provide measurements of ATS-6 spacecraft orbit position. Uplink frequencies are 6.150 and 6.155 GHz. The receiving antennas are spaced at 19.95 wavelengths (?) for the vernier baseline and 1.66 ? for the coarse baseline. Spacecraft system weight is 8.39 kg (18.5 lb) and power requirement is 15.5 W. Flight evaluation results are given for the interferometer including R F link budgets, modulation of uplink carrier, signal-to-noise ratio, and dropout behavior. A hardware calibration model is described, containing major biases in the phase measurements. Techniques for flight calibration as both an attitude and spacecraft position sensor are outlined . Flight testing has shown that on-line calibration of receiver/converter biases must be performed on a short term routine basis. Interferometer resolution was found to be 0.00140 space angle with negligible noise (jitter) at transmitted power levels above 72 dBW. As an attitude sensor, the interferometer has demonstrated the ability to provide stabilization to better than 0.     

ATS-6 Radio Beacon Experiment: The First Year

The Radio Beacon Experiment is designed to measure the total electron content and ionospheric content between the satellite and any observer within its field of view. Since Applications Technology Satellite-6 (ATS-6) is visible from about 43 percent of the Earth's surface, an international community of observers have made measurements using it. The radio parameters have to be measured to an accuracy of a few percent, which requires good system calibration and stability. The spaceborne beacon transmits signals on frequencies of 40, 140, and 360 MHz with amplitude modulations of 1 MHz and/or 0.1 MHz for the measurement of modulation phase, Faraday rotation, and amplitude. The overall system objectives and requirements are discussed along with the design of the ATS-6 transmitter and the receiver in Boulder, Colo. The role of the principal investigator in the context of the international program is considered with particular reference to the joint National Oceanic and Atmospheric Administration (NOAA)/Max Planck Institute (MPI) observation program. Monthly median hourly values of total content, plasmaspheric content, and shape factor show distinct diurnal and seasonal variations. A specific event is described to illustrate the use of a spaced receiver network.     

MMW system trade-offs

A brief review is given of the current state of knowledge of millimeter-wave atmospheric propagation and clutter characteristics and the detection performance of two air-to-ground fire-control systems evaluated in terms of their ability to detect a 40-m² target in the presence of atmospheric attenuation and three types of clutter. Generally, the 35-GHz system considered performed better in terms of signal-to-noise ratio performance and in signal-to-clutter ratio performance for light clutter. In heavy clutter, the 95-GHz system performed significantly better than the 35-GHz system. For 300-m altitude with refrozen snow clutter background, neither system developed a large enough signal-to-clutter radio to detect the target reliably     

Substorm-associated injections of energetic ions observed by GEOS-1 and ATS-6 in and near synchronous altitude

Energetic ion measurements of GEOS-1 and ATS-6 are analysed for the period of geomagnetic activity following the arrival of a solar wind shock at 0027 UT on July 29, 1977. GEOS crossed the magnetopause at 6.9 R _E and 0027 UT (1312 LT). Although the difference in local time to ATS at 6.6 R _E is only 2 h ATS seems to remain well inside the magnetopause. During the second orbital pass on this day GEOS crossed the geostationary orbit at the onset time of a major substorm developing at 1120 UT. At this time the local time difference of GEOS and ATS was 12 h. The considerably different energy dispersions are discussed. An azimuthal anisotropy of approximately 20% observed in the GEOS data is interpreted to be the result of a particle density gradient.NOAA-SEL, Boulder, Colo., U.S.A.     

Orbit Determination Accuracies Using Satellite-to-Satellite Tracking

The results are reported of the ATS-6/GEOS-3 and the ATS-6 NIMBUS-6 satellite-to-satellite orbit determination experiments. NASA intends to use the tracking data relay satellite system for operational orbit determination of NASA satellites. Hence, in the near future, satellite-to-satellite tracking data will be routinely processed to obtain orbits. The satellite-to-satellite tracking system used in the ATS-6/NIMBUS-6 and ATS-6/GEOS-3 experiments performed with a resolution of 1 to 2 m in range and less than 1 mm/s in range rate for a 10-s averaging. A Bayesian least squares estimation technique utilizing independent ranging to the synchronous relay satellite was determined to be the most effective procedure for estimating orbits from satellite-to-satellite tracking data. The use of this technique yields estimates of user satellite orbits which are comparable in accuracy to what is usually obtained from ground based systems.     

Combining the Effects of Rain-Induced Attenuation and Depolarization in Digital Satellite Systems

Rain depolarization causes crosstalk on a dual polarization communications link. The effects of depolarization can be expressed as a degradation of the carrier-to-noise ratio (CNR) which can then be combined with the rain-induced attenuation to yield an effective attenuation. The effective attenuation is computed for a hypothetical satellite link at 11, 14, 20, and 30 GHz. It is shown that at 20/ 30 GHz the increase in system margin required by dual polarized use is small.     

ATS-6 Solar Cell Flight Experiment After 325 Days in Synchronous Orbit

Preliminary Applications Technology Satellite-6 (ATS-6) solar cell flight experiment data through the first 325 days in synchronous orbit is present. The experiment is transmitting data on 16 different solar cell/cover glass 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 and adhesive processes and materials such as 7940 and 7070 integral covers and the fluorinated ethylene propylene (FEP) covers, the COMSAT "violet" cell, and backside irradiation effects. The in-spece solar cell data indicate short circuit currents are higher by 1 to 8 percent than measurements made with solar simulations; maximum power varied between -1 to +6 percent . Degradation of /sc due to ultraviolet effects was determined to be about 2 percent after 50 days in orbit. All cells performed well through 325 days in orbit, except the FEP-covered cells, which appear to have increased their rate of degradation during the first eclipse season.     

Japan's CS (Sakura) Communications Satellite Experiments

The Japanese Communications Satellite (CS), called Sakura, is a "Medium Capacity Communications Satellite for Experimental Purposes" and is the first experimental communications satellite in which 30/20 GHz bands were adopted and were developed for practical domestic use. Large scale field trials have been carried out for more than three years in order to evaluate 30/20 GHz (Ka-band) and 6/4 GHz (C-band) domestic satellite communications system technologies under actual operational conditions by using the CS Sakura launched in December 1977. Through the various experiments on Kand C-band large fixed and small transportable Earth station systems, satellite control experiments, and Ka-band propagation measurements, it has been verified that the medium capacity satellite communications system meets the design objectives.     

ATS-6 Significance

The Applications Technology Satellite (ATS-6), the most powerful, most sophisticated, most versatile communications satellite flown to date, is the last of NASA's experimental satellites intended to demonstrate major advances in communications and spacecraft technology. It is a multipurpose, multidisciplinary spacecraft whose principal objectives were to demonstrate a large, unfurlable antenna structure and precise pointing and attitude control in the synchronous orbit The spacecraft carries 27 different experiments, 3 of which demonstrate users' applications of satellite communications. Significant advances in antenna technology, precise attitude control, materials technology, spacecraft structures, and thermal control have been successfully demonstrated. The most significant accomplishments of the ATS-6 mission are the demonstration of the practicality of satellite broadcasting to small, simple, inexpensive ground stations and the uses of this potential service in the solution of social problems involving education and health care. The success of these initial demonstrations has led ATS-6 experimenters and potential users to incorporate a Public Service Satellite Consortium dedicated to the provision of satellite broadcasting services for educational and health-care applications.     

ATS-6 Synchronousi Orbit Trapped Radiation Studies with an Electron-Proton Spectrometer

The University of Minnesota Electron-Proton Spectrometer Experiment consists of two nearly identical detector assemblies. One of these assemblies was mounted in a position fixed on the satellite in the Environmental Measurements Experiments (EME) east direction and the other was rotated so that the spectrometer scanned a range of spatial directions covering 1800 from EME north to EME south through west. Each of the detector assemblies is a magnetic spectrometer containing four gold-silicon surface barrier detectors. This instrument provides a very clean separation between protons and electrons by the combination of pulse height analysis and magnetic deflection. Each detector assembly measures protons in three nominal energy ranges (30-50 keV), (50-160 keV), and (120-514 keV). Electrons also are measured in three energy intervals (30-50 keV), (150-214 keV), and (more than 500 keV). Data are transmitted from the experiment at rates as high as 8 measurements/s. Decreases in the flux of the energetic electrons and protons followed by very rapid increases are frequently observed on the nightside during periods of geomagnetic activity. Separation of temporal and spatial effects is possible using proton gradient information obtained when the detector systems are oppositely directed. Using this technique, the decreases have been interpreted as motion of the trapping region equatorward and Earthward of the satellite. The boundary motion associated with the particle recovery shows a marked local time dependence. Particle increases observed in the evening sector have been interpreted as motion from Earthward and equatorward of Applications Technology Satellite-6 (ATS-6).     

Additional Measurements on Pit Shielding for Communications Satellite Earth Stations

This correspondence reports measurements taken in both the 4- and 6-GHz frequency bands of the protection afforded a pit-shielded Earth-station antenna. The measurement program described is an expansion of a previous one and was designed to determine the effects of artificial site shielding for a range of satellite locations rather than a single position.     

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.