Orbit adjustment of sun-synchronous satellites with electric propulsion.
Satellite orbit adjustment, stationkeeping and attitude control of typical earth- and sun- synchronous satellites by electric propulsion systems
Barrett, C. C.↗
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Effect of environmental torques on short-term attitude prediction for a rolling-wheel spacecraft in a sun-synchronous orbit
A numerical evaluation and an analysis of the effects of environmental disturbance torques on the attitude of a hexagonal cylinder rolling wheel spacecraft were performed. The resulting perturbations caused by five such torques were found to be very small and exhibited linearity such that linearized equations of motion yielded accurate results over short periods and the separate perturbations contributed by each torque were additive in the sense of superposition. Linearity of the torque perturbations was not affected by moderate system design changes and persisted for torque-to-angular momentum ratios up to 100 times the nominal expected value. As these conditions include many possible applications, similar linear behavior might be anticipated for other rolling-wheel spacecraft.
Hodge, W. F.↗
Study of spacecraft direct readout meteorological systems
Characteristics are defined of the next generation direct readout meteorological satellite system with particular application to Tiros N. Both space and ground systems are included. The recommended space system is composed of four geosynchronous satellites and two low altitude satellites in sun-synchronous orbit. The goesynchronous satellites transmit to direct readout ground stations via a shared S-band link, relayed FOFAX satellite cloud cover pictures (visible and infrared) and weather charts (WEFAX). Basic sensor data is transmitted to regional Data Utilization Stations via the same S-band link. Basic sensor data consists of 0.5 n.m. sub-point resolution data in the 0.55 - 0.7 micron spectral region, and 4.0 n.m. resolution data in the 10.5 - 12.6 micron spectral region. The two low altitude satellites in sun-synchronous orbit provide data to direct readout ground stations via a 137 MHz link, a 400 Mhz link, and an S-band link.
Bartlett, R.↗
TIROS X Meteorological Satellite System, volume I Final engineering report
Camera, attitude control system, and component design modifications of TIROS X for near-polar sun-synchronous orbit
CAMERA↗
A stellar tracking reference system
A stellar attitude reference system concept for satellites was studied which promises to permit continuous precision pointing of payloads with accuracies of 0.001 degree without the use of gyroscopes. It is accomplished with the use of a single, clustered star tracker assembly mounted on a non-orthogonal, two gimbal mechanism, driven so as to unwind satellite orbital and orbit precession rates. A set of eight stars was found which assures the presence of an adequate inertial reference on a continuous basis in an arbitrary orbit. Acquisition and operational considerations were investigated and inherent reference redundancy/reliability was established. Preliminary designs for the gimbal mechanism, its servo drive, and the star tracker cluster with its associated signal processing were developed for a baseline sun-synchronous, noon-midnight orbit. The functions required of the onboard computer were determined and the equations to be solved were found. In addition detailed error analyses were carried out, based on structural, thermal and other operational considerations.
Klestadt, B.↗
Orbit selection considerations for earth observatory satellites
All the possible circular sun-synchronous orbits for earth observatory satellites are displayed, which have orbital altitudes between 740 and 1,115 kilometers (approximately 400 to 600 nautical miles) and have either a 16, 17, or 18 day repeat cycle for the ground trace. It was found that there are 9 orbits with a 16 day repeat cycle, 17 orbits with a 17 day repeat cycle, and 7 orbits with an 18 day repeat cycle meeting the requirements. For each of these, various characteristics such as ideal ground trace patterns, swathing patterns, and daily drift are displayed. The solar elevation angle along the orbit and the change in the solar elevation angle with season are given. This presentation of general orbital characteristics has application to finding approximate orbital elements and selecting orbits for many types of earth sensing satellite missions.
Cooley, J. L.↗
Some higher order analyses of earth and lunar orbiters
The accurate modelling of the translational behavior of a drag-free satellite in an almost circular near-earth orbit is investigated. All short and long period position fluctuations in the satellite's coordinates down to 1 m are determined. The general zonal and tesseral harmonic effects are considered as well as lunar and solar effects. A noncanonical approach is followed. A mean orbital plane is chosen so that no short period out-of-plane fluctuations greater than second order occur. Short period radial and cross-track fluctuations and in-track fluctuations are computed. Long period and secular rates of the mean elements which define the slowly varying plane of reference are determined to third order in the small quantities. The equations of motion are integrated analytically away from critical inclination and tesseral resonance. The resonant situation of a sun-synchronous orbit is discussed as a special case. The long-period behavior of a lunar orbiter is also considered, including the effects due to the inclination of the earth's apparent orbit about the moon and those described by Cassini laws on the equations of motion. Both resonant and nonresonant low orbits, and high orbits are discussed.
Dasenbrock, R. R.↗
Sensor lighting considerations for earth observatory satellite missions
Facets of sensor lighting conditions for Earth observatory satellite missions are considered. Assuming onboard sensors of a given width viewing perpendicular to the subsatellite ground track along sun-synchronous orbits with various nodes, the ground trace of the ends of the sensor coverage were found, as well as the variation in solar illumination on the ground across the line covered by the sensor during the day for any point along the orbit. The changes with season and variation during the year were also found.
Cooley, J. L.↗
Wide area coverage radar imaging satellite for earth applications
A preliminary study was made of a radar imaging satellite for earth applications. A side-looking synthetic-aperture radar was considered and the feasibility of obtaining a wide area coverage to reduce the time required to image a given area was investigated. Two basic approaches were examined; low altitude sun-synchronous orbits using a multibeam/multifrequency radar system and equatorial orbits up to near-synchronous altitude using a single beam system. Surveillance and mapping of ice on the Great Lakes was used as a typical application to focus the study effort.
Stevens, G. H.↗
Earth Observatory Satellite (EOS) Definition Phase Report, Volume 1
System definition studies were conducted of the Earth Observatory Satellite (EOS). The studies show that the concept of an Earth Observatory Satellite in a near-earth, sun-synchronous orbit would make a unique contribution to the goals of a coordinated program for acquisition of data for environmental research with applications to earth resource inventory and management. The technical details for the proposed development of sensors, spacecraft, and a ground data processing system are presented.
Source record↗
New sensor on NOAA-2 satellite monitors the 1972-73 Great Lakes ice season
The NOAA-2 satellite was launched Oct. 15, 1972 in a 790 nautical mile-high near-polar sun-synchronous orbit. The Very High Resolution Radiometer (VHRR) views earth in both the visible and thermal-IR regions of the electromagnetic spectrum at 1-kilometer resolution. Its orbit permits the satellite to acquire imagery on a daily basis over any given location at approximately 0900 and 2100 local time. Visible data at 1-kilometer resolution represents a 16-fold increase in data density over previous NOAA satellite capabilities. Thermal data are now available over an area at 100 times the previous NOAA-1 thermal data density. Following the onset of ice formation in Lake Erie early in January, ice buildup and thaw were observed as cloud cover permitted throughout the short winter season.
Strong, A. E.↗
Mission analysis for satellite measurements of stratospheric constituents by solar occultation
Orbital characteristics and launch vehicle requirements for a solar occultation experiment measuring atmospheric constituents, such as aerosols or ozone, during the Nimbus-G and Applications Explorer Missions are analyzed. The experiment to be flown is basically a sun photometer which measures the spectral attenuation of solar radiation by the earth's atmosphere during spacecraft sunrise and sunset, yielding two aerosol and/or ozone stratospheric profiles per orbit. The tangent latitudes and longitudes as well as frequency of these measurements are analyzed for various spacecraft orbits to define maximum geographical coverage capability. Results indicate that a 50 deg inclined orbit for Applications Explorer provides latitude coverage from approximately 70 deg north to 70 deg south every 2-1/2 weeks. A high-moon, sun-synchronous orbit with an inclination of 99 deg for Nimbus-G will provide for coverage of occultation measurements at high latitudes near the polar regions (i.e., 64 to 80 deg north and south). The solar pointing requirements of the experiment in terms of yaw and pitch angles are also defined.
Harrison, E. F.↗
Annual review of earth observations from space
An overview is given of the present state of satellites making observations of the earth. Satellite systems discussed include the NOAA series of Synchronous Meteorological Satellites (SMS) and sun-synchronous satellites, the two LANDSATS (formerly called ERTS), and the NIMBUS series. Examples are presented of the types of observations being made as well as their purposes. These include observations of synoptic and mesoscale atmospheric processes for daily weather forecasting, global atmospheric processes for long-range weather forecasting, planetary radiation budget and ocean circulation for monitoring climatic trends, earth dynamics and tectonic structure for mineral exploration and assessing earthquake hazards, atmospheric composition and water quality for environment monitoring, and thematic mapping for monitoring land use, managing crops and water resources, and assessing environmental impacts.
Nordberg, W.↗
User data dissemination concepts for earth resources: Executive summary
The impact of the future capabilities of earth-resources data sensors (both satellite and airborne) and their requirements on the data dissemination network were investigated and optimum ways of configuring this network were determined. The scope of this study was limited to the continental U.S.A. (including Alaska) and to the 1985-1995 time period. Some of the conclusions and recommendations reached were: (1) Data from satellites in sun-synchronous polar orbits (700-920 km) will generate most of the earth-resources data in the specified time period. (2) Data from aircraft and shuttle sorties cannot be readily integrated in a data-dissemination network unless already preprocessed in a digitized form to a standard geometric coordinate system. (3) Data transmission between readout stations and central preprocessing facilities, and between processing facilities and user facilities are most economically performed by domestic communication satellites. (4) The effect of the following factors should be studied: cloud cover, expanded coverage, pricing strategies, multidiscipline missions.
Davies, R.↗
Status of SERT 2 thrusters and spacecraft 1976
The historical record of the SERT II ion thrusters and spacecraft performance for 6 1/2 years since the February 1970 launch is reviewed. The most recent ion thruster operation test shows no changes since 1974. Thruster 2 is fully operational with no performance degradation. Thruster 1 has a high voltage grid short, but continues to demonstrate cathode and discharge relight capability. Spacecraft orbit and dynamic analysis indicates a stable, sun-synchronous spacecraft orientation by 1979. An attitude adjustment maneuver was performed in August 1976 to achieve this orientation and provide sufficient continuous solar power for thruster operation in 1979.
Kerslake, W. R.↗
Status of SERT II thrusters and spacecraft - 1976
The historical record of the SERT II ion thrustors and spacecraft performance for 6-1/2 years since the February 1970 launch is reviewed. The most recent ion thrustor operation test shows no changes since 1974. Thrustor 2 is fully operational with no performance degradation. Thrustor 1 has a high voltage grid short, but continues to demonstrate cathode and discharge relight capability. Spacecraft orbit and dynamic analysis indicates a stable, sun-synchronous spacecraft orientation by 1979. An attitude adjustment maneuver was performed in August 1976 to achieve this orientation and provide sufficient continuous solar power for thrustor operation in 1979.
Kerslake, W. R.↗
Satellite cloud climatology of summertime cumulus research areas
Defense Meteorological Satellite Program data available for the summer of 1974 was used to construct a cloud climatology of areas where weather modification experiments are currently being conducted or planned; the three High Plains Experiment sites at Colby, Kansas, Big Springs, Texas, and Miles City, Montana; South Park, Colorado, where the South Park Area Cumulus Experiment is being conducted; and the National Hail Research Experiment area in northeastern Colorado. Digital data tapes were produced from the transparencies, obtained from the sun-synchronous polar-orbiting satellite passing over the study areas at about 1200 local time, and a computer analysis was carried out, producing areas and numbers of clouds for each area and day as well as providing data for cumulative averages over selected time periods for each study area.
Stodt, R. W.↗
Sampling analysis for the Earth Radiation Budget Satellite System mission based on orbital coverage and cloud variability
The reported study represents an extension of an investigation by Harrison et al. (1976). Based on the results of sampling studies, two 98 deg inclined orbits coupled with a 56 deg inclination orbit appear to satisfy the science requirements on both regional and zonal scales. The NOAA sun-synchronous satellites in the TIROS-N series could adequately cover the high latitudes and a satellite having an inclination of 56 deg could provide sampling in the mid and low latitude areas where variations in radiation energetics are most dynamic. Attention is given to studies of time and space coverage, zonal evaluations, a regional analysis, and statistics describing the regional variations of cloud cover. A table is presented with data concerning the uncertainty of monthly mean reflected irradiance due to cloud variability for selected northern hemisphere regions.
Harrison, E. F.↗