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.     

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 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-5 Millimeter Wave Propagation Experiment

This paper describes the design of the millimeter wave experiment aboard the ATS-5 satellite. This equipment is the first millimeter wave communications equipment in space. The function of the equipment is to provide earthspace propagation data at Ku- and Ka- band frequencies. The designs of the phase locked Ka- band receiver, the Ku-band transmitter, the antennas, and the telemetry and processing equipment are described. Mechanical and environmental problems are also discussed.     

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.     

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 my. The DC field of the spacecraft transverse to the Earth-pointing axis is Sx = 1.0 ±2.1?, SY = -2.4 ± 1.3?. The spacecraft field parallel to this axis is less than 5?. The small spacecraft field has made possible studies of the macroscopic field not previously possible at synchronous orbit. At the 96° west longitude of Applications Technology Satellite-6 (ATS-6), the Earth's field is typically inclined 300 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.     

ATS-6 UCSD Auroral Particles Experiment

The University of California at San Diego (UCSD) Auroral Particles Experiment on the Applications Technology Satellite-6 (ATS-6) consists of five electrostatic charged particle detectors. The features which contribute to the uniqueness of the UCSD data include a rotation capability which often allows sampling very near the direction of the magnetic field, an energy range of five orders of magnitude with a lower extreme of less than 1 eV, and a very large geometric factor which results both from a postenergy analysis electrostatic lens and from the unique ovoidal shape of the analyzing plates. A preliminary look at a subset of UCSD magnetospheric data emphasizes those phenomena which are observed as a result of the new features described. These phenomena include intense magnetic field aligned auroral particles, a persistent and very low energy dusk region enhancement, and low energy 1-10-s fluctuations tentatively identified as Alfven waves.     

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 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.     

ATS-6 Millimeter Wave Propagation and Communications Experiments at 20 and 30 GHz

The Applications Technology Satellite (ATS-6) Millimeter Wave Experiment, developed and implemented by the NASA Goddard Space Flight Center, has provided the first direct measurements of 20-and 30-GHz Earth-space links from an orbiting satellite. Studies at eleven locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques In addition to direct measurements on the 20-and 30-GHz links, methods of attenuation prediction with radars, rain gauges, and radiometers were developed and compared with the directly measured attenuation. This paper presents a review of the major results of the first year of measurements with ATS-6, with emphasis on the impact of the measurements on millimeter wave space systems design.     

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.     

ATS-6 Energetic Particle Radiation Measurement at Synchronous Altitude

The Aerospace Corporation energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 32 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.     

ATS-6 Parabolic Antenna for Mounting Solar Cells

Calculations are made to obtain the raw electrical power that can be generated by using an ATS-6 type deployable parabolic dish as a surface for mounting solar cells without seriously interfering with its normal function as an antenna. A minimum of a few hundred watts to a maximum of a few kilowatts are generated during the apparent course of the Sun around the spacecraft. Academically, it seems that deployable solar cell panels along with their booms can be avoided.     

ATS-6 Experiment Summary

The ATS-6 is the most advanced experimental satellite that has evolved from the Application Technology Satellite Program conducted and implemented by NASA Goddard Space Flight Center (NASA/GSFC). This project utilizes a state-of-the-art spacecraft and ground terminal network to perform advance studies and to conduct technological demonstrations in a large number of scientific areas. The design and implementation of this unique spacecraft permitted multiple experimentation simultaneously. The control of the spacecraft is performed at ATS Operational Control Center (ATSOCC) located at NASA/GSFC. Experimentation which was performed covered a wide spectrum of communications, technological, meterorological, and scientific subjects. Three principal ground terminals are utilized to assist the experimenters to acquire data. Data reduction and analysis are performed by the many facilities at NASA/GSFC in support of the experimenters.     

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.     

高负荷跨音压气机叶尖间隙流动的数值分析与比较

利用自行开发的叶轮机三维数值模拟软件对高负荷跨音压气机ATS-2转子进行了带叶尖间隙的三维流动数值模拟,并与实验的结果进行了比较。结果表明,数值模拟得到的流场结构与实验结果一致。对粘性与无粘结果的比较显示,由泄漏流所产生的激波后阻塞区是由激波-漏流干扰所致,粘性的作用将削弱其面积和强度。随叶尖间隙增大,激波后阻塞区的径向和轴向尺度增大,压比、效率和流量下降。      

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 Television Relay Using Small Terminals Experiment

The Television Relay Using Small Terminals (TRUST) Experiment was designed to advance and prornote the technology of broadcasting satellites. A constant envelope television FM signal was transmitted at C band to the ATS-6 Earth coverage hom 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 lowcost 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.