High-altitude Satellites Research Articles

Precise orbit determination of high-earth elliptical orbiters using differenced Doppler and ranging measurements

Recent advances in NASA's Deep Space Network station calibration methods have led to renewed interest in the use of differenced radio metric data types for interplanetary navigation, particularly differenced Doppler and range. An orbit determination error analysis is described which compares the performance of these differenced data types when used in concert with conventional two-way Doppler for precise navigation for high-earth orbiters. Three highly elliptical orbits were investigated, with apogee heights on the order of 20000, 70000, and 156000 km. The analysis assumes that each orbiter's downlink antennas has no ground footprint limitation in the near apogee regime. Results indicate that the most significant navigational accuracy improvements are seen for the lowest altitude orbit by using differenced Doppler measurements in conjunction with two-way Doppler. The results for the two higher-altitude orbits, although less dramatic, suggest accuracy improvements can also be achieved when differenced range measurements are combined with two-way Doppler.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In-situ observations of magnetospheric electron scattering by a VLF transmitter

High resolution pitch angle measurements of outer zone electrons in the energy range 12 keV−1.6 MeV were obtained at high altitude in the region of the high power VLF transmitter UMS [300 kW radiated at 17.1 kHz ( Watt A. D., 1967, VLF Radio Engineering, Pergamon Press, Oxford)] while a resonant wave-particle interaction was in progress. Additional complementary electron measurements in the range of 36–316 keV were obtained in the drift loss cone by another satellite at low altitude along the drift path 75° east of the interaction region. The data from the low-altitude satellite confirm that UMS was precipitating particles in the inner zone, in the slot, and in the outer zone at the time that the high-altitude satellite was obtaining its data. The high-altitude pitch angle distributions indicate that, for this event, two types of scattering interactions were in progress. Particles with small pitch angles, up to 17.2° at the Equator, were being removed, resulting in an enhanced loss cone. Particles which were mirroring between 6500 km and the altitude of the spacecraft (7200) km were also being strongly scattered, resulting in a relative minimum in the pitch angle distribution around 90°. The data are interpreted as indicating that a cyclotron mode interaction with UMS waves was precipitating electrons with equatorial pitch angles up to 17.2° and that another process, perhaps electrostatic (ES) waves arising from the UMS radiations through a mode-conversion process, was present in the region above 6500 km and was efficiently scattering those particles which mirrored in that region

Thermal Effects on Very Large Space Structures

Radiation thermal effects are studied simultaneously on the orbital motion, attitude motion, and axial deformation of a very large, axially flexible space structure describing a planar pitch motion around the earth. The relative importance of the three known sources of radiation in space environment—direct solar, Earth's albedo, and direct Earth—are studied for low Earth orbit (LEO) and geosynchronous Earth orbit (GEO). Influences of the area‐to‐mass ratio of the structure on thermal effects have been investigated for elliptical orbit. Radiation thermal effects are found to be significant in causing structural deformation and in producing libration in the attitude angle of a large space structure. However, on the orbital parameters of the space structure, the thermal effects are negligible. In LEO, effects of the earth's albedo and its direct radiation on the structure are appreciable, whereas in higher altitude orbits such as GEO, these may be neglected. The area‐to‐mass ratio of the structure is realized to cause a drastic change in the thermal effects on a large space structure.

Thick dielectric charging on high-altitude spacecraft

Thick dielectric charging, in which energetic electrons embed within bulk dielectrics, building up to potentials in excess of the breakdown potential of the dielectric, is shown to be a causative factor in anomalous operation of high-altitude satellites. A table of maximum expected electron fluxes in various altitude orbits is presented. Consideration of these maximum fluxes and the fact that the energy associated with a bulk dielectric breakdown is small demonstrates that bulk charging can be eliminated as a spacecrafts problem through minimal shielding (400 mg/cm 2) of all cables and circuit boards otherwise exposed to the environment, and through desensitizing digital logic inputs which are serviced by cables.

Automatic charge control system for geosynchronous satellites

An autonomous system to detect both absolute and differential spacecraft charging aboard high-altitude satellites, and to reduce those potentials before hazardous arcing levels are reached, is now being developed under the Air Force program on Space Systems Environmental Interaction Technology. Operation of the system is based on the empirical results of the Space Test Program SCATHA (P78-2) and NASA ATS-6 satellites, both of which successfully demonstrated the principle of safely reducing spacecraft charging levels by the emission of a low-energy neutral plasma —effectively shorting the spacecraft and charge dielectric surfaces to the ambient space plasma. The Charge Control System now being built at Hughes Research Laboratories in Malibu, CA, will utilize a xenon-based plasma source that can be ignited without any warm-up, and that will produce a plasma capable of furnishing a neutralizing ion current greater than 1 mA. The spacecraft charging level will be detected by sensors similar to those that operated aboard SCATHA. Satellite frame potential (relative to the ambient space plasma) will be determined by an elestrostatic analyzer capable of detecting both ions and electrons in the energy range 50 eV - 20 keV. Differential charging (relative spacecraft frame ground) will be determined by a surface-potential monitor utilizing two different dielectric surfaces, and covering a range of ±20kV with a response time of one second. A transient pulse monitor will detect the presence of exterior spacecraft arcing by measuring its electrostatic field pulse. Automatic operation of the system will be accomplished by a microprocessor controller which interpret the sensor data and activate the plasma source when predetermined threshold levels are exceeded. The gas supply will provide for more than 2000 hours of plasma source operation in space, which under nominal conditions, would be sufficient for up to 10 years of on-orbit spacecraft protection. The breadboard model has already operated successfully under simulated spacecraft charging conditions — with sensors and plasma source in a vacuum chamber at 5×10 −6 Torr, all irradiated by energetic electrons (up to 10 keV). Each sensor individually, as well as with all the sensors operating collectively, responded to the threshold charging level and activated the plasma source automatically, reducing the charging level to zero. The flight system will be completed by mid-1988, and could be flight-tested at geosynchronous orbit in the 1989–1992 time period.

A model for the electron temperature variation along geomagnetic field lines and its effect on electron density profiles and VLF paths

A realistic model for the temperature variation along geomagnetic field lines is described. For high altitudes (>1500 km) the temperature is taken to increase as the nth power of radial distance ( n−2), giving temperatures consistent with those measured in situ by high altitude satellites. For realistic temperatures at low altitude an extra term is included. The temperature gradient along the field line is then 0.9–1.6° km −1 during the day and 0.5–0.7° km −1 during the night at 1000 km, reducing to about half these values at 2000 km, for the latitude range 35–50°. This is consistent with calculations made from nearly simultaneous satellite measurements at 1000 and 2500 km. It is shown that assuming diffusive equilibrium, including the new temperature model, more realistic equatorial electron density profiles result than for isothermal field lines. The temperature gradient model is also purposely formulated to be of a form that enables the temperature modified geopotential height to be obtained without numerical integration. This renders the model particularly suitable for ray-tracing calculations. A ray-tracing model is developed and it is shown that unducted ray paths are significantly altered from the corresponding paths in an equivalent isothermal model; there is greater refraction and magnetospheric reflection takes place at lower altitudes. For summer day conditions, an inter-hemispheric unducted ray path becomes possible from 26° latitude that can reach the ground at the conjugate.

Safeguarding Our Military Space Systems

The vulnerability military space systems depends on their orbits, functions, and other characteristics. The high-altitude satellites needed for warning and communications in particular could be vulnerable to prompt destruction by certain space-based systems and, in the future, possibly by ground-based high power lasers. A combination of passive countermeasures and arms control agreements could give these satellites some protection against such attack. Deployment of strategic defensive systems with the capability to reach far into space would invalidate this approach.

Low altitude, one centimeter, space debris search at Lincoln Laboratory's (M.I.T.) experimental test system

The Experimental Test System of Lincoln Laboratory, the prototype observatory of the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) network, has been used to search for, detect, and discriminate debris as small as ⋍ 1 cm in near-Earth orbit. Although constructed to observe and search for high altitude satellites, the observatory (two 80 cm, equatorially mounted, Cassegrain instruments) has been successfully modified to perform similar tasks on asteroids, daytime observations of near-Earth satellites, and the present endeavor. In particular, the separation of the instruments and their resolution element size allows the discrimination of artificial satellites from meteors. The parallax at ⋍ 80 km elevation is ⋍ 150″ and the video line spacing is ⋍ 4″. We have successfully combined the video signals from the two electron beam, bombarded silicon target cameras for this purpose. Furthermore, by observing at the optimum times, we have increased our sensitivity. Herein we present statistical summaries of tens of hours of observing and we calculate the elevation distribution of the debris population (to B ⋍ 16 ▪5). A summary of the data collected on meteors is also included. Debris is eight times as populous as tracked satellites.

Variability of Cloudiness at Airline Cruise Altitudes from GASP Measurements

Additional statistics relating to the climatology of cloud cover at airline cruise altitudes are presented. The data were obtained between 1975 and 1979 from commercial airliners participating in the Global Atmospheric Sampling Program (GASP). The statistics describe the seasonal, latitudinal and altitudinal variation in cloudiness parameters as well as differences in the high-altitude cloud structure attributed to cyclone and convective-cloud generation processes. The latitudinal distribution of cloud cover derived form the GASP data was found to agree with high-altitude satellite observations. The relationships between three different measures of cloudiness and the relative vorticity at high altitudes is also discussed.

Autonomous navigation for high altitude satellites

The determination of the orbit of high altitude satellites with an accurate horizontal charge coupled device (CCD) sensor is considered using the extended Kalman filter. The measurement nonlinearity is removed by using a coordinate transform, and the corresponding steady state error is less than the steady state error in the Cartesian coordinate system. The performance of both of the navigational filters is evaluated for a reference geosynchronous orbit as a function of measurement error. The reduction of measurement uncertainty decreased steady state errors in position and velocity.

Multipurpose Sun Sensor using CCD Detector

In the Frame of French Earth Observation Satellite Program (SPOT) MATRA has been selected by CNES to develop the Digital Sun Sensor (SSD).The different concepts considered and the major problems encountered during the definition study are explained. Sensor performances and especially accuracy are related and a review of the means of dynamic and functional tests which allow to check them is made. The calibration principle is given, which provides optimal accuracy in flight when the sensor is associated to a SEMAT (a MATRA concept of optico-inertial attitude estimator based on decentralized intelligence) or to an on-board computer.The modular conception of this sensor will provide numerous alternative design possibilities which make it compliant with new missions of various kind in either low or high altitude orbits. A wide range of single or double axis sensors can be developped on the same baseline, with different field of view, different accuracy, or different data output rates.In a further step, upgraded verses of this sensor may also be able to aim at other targets than the sun. The multipurpose character of this sensor is underlined in the conclusion chapter.

Light Ion Mass Spectrometer for space-plasma investigations

Recent studies of the low-energy plasma population in the Earth’s space environment have revealed that this plasma population is much more complex than previously supposed and that a simple model of ionospheric evaporation cannot explain the distributions. There was a need to develop an advanced instrument to study this plasma in detail, and this paper describes the scientific background, design, development, and in-flight characteristics of such an instrument, the Light Ion Mass Spectrometer (LIMS). This instrument combines a magnetic mass spectrometer, a planar-grid retarding potential analyzer, and multidirectional sensor heads to measure the mass composition, density, temperature, and flow velocity of low-energy (E〈100 eV) plasma. The studies which were conducted leading to the final design will be discussed in detail and will illustrate certain effects which arose in the combining of energy and mass analysis into a single sensor. The instrument was flown on a high-altitude satellite in February 1979, and selected flight data will be presented to demonstrate the instrument performance.

Effect of CMOS Miniaturization on Cosmic-Ray-Induced Error Rate

As device feature size is scaled down for Very Large Scale Integration (VLSI) and Very High Speed Integrated Circuit (VHSIC) applications, consideration must be given to potential increased vulnerabiliity to single particle induced upset (memory soft error or processor logic error) from the natural radiation environment. This paper describes a detailed computer aided modeling study to predict the effect of scaling on the single event upset rate in CMOS memory cells in the galactic cosmic ray environment typical of high altitude satellite orbits.

Predictive Geological Mapping of Mining Conditions in Appalachian Coal Fields: ABSTRACT

Recent case histories in the Appalachian region incorporating active mining operations with detailed geological hazards mapping prior to mining have confirmed the importance of certain geological techniques and applications. Applying these techniques to active operations in Pennsylvania, Maryland, West Virginia, southwest Virginia, and eastern Kentucky demonstrates that certain of these geological factors can be related to mining on a regional basis. Some of the applications involve the identification of weak, fractured rock zones underground through use of high-altitude satellite imagery. The simple procedure of intensity or the magnitude rating of the linear features appears to be the real key in identifying hazardous roof areas prior to mining. Composite and overlay ma ping of significant, anticipated geological factors is the most important application to identifying safe, high-production mining areas as opposed to hazardous, low production mining. Again, it is necessary to apply rating factors to each potential problem and to design a presentation technique that can achieve simplicity and workability from a multitude of complex geological factors. Although local or on-site physical and geological conditions largely dictate mining conditions, understanding and identification of regional geology and paleodepositional environments greatly enhance the more important ability to predict hazards prior to mining. Additional benefits derived from applying geologic hazards mapping are (1) identification of significant hydrologic factors which must be considered in meeting state and federal requirements for ground-water monitoring, and (2) establishment of confidence levels for coal reserve classifications. End_of_Article - Last_Page 1172------------

Thermal variations in the gregory rift of southern Kenya (?)

A compilation of thermal and seismic data collected over the last sixty years allows one to infer that tectonic phenomena and heat emanation could be linked in an oscillatory mode up and down the Kenyan part of the East African Rift. The seismic period is approximately 20–30 years during which time the loci of maximum intensity earthquakes move in a rhythmic pattern from south to north and back to south. Temperatures measured from hot springs also fluctuate over this time span increasing or decreasing in different sections of the rift.Spatial variations were measured by infrared radiometers from low altitude aircraft or high-altitude satellites. These reveal that individual thermal springs ranging from 35°C to 80°C, warm up greater than 5 km2 of the lake bottom of Magadi (only a slightly active thermal region which, however, yields greater then 300 MW). The heated area is large enough to detect by satellite imagery, making it possible to monitor the heat budget and flux over time and relate it to tectonic activity in the rift.

Aeromaneuvering orbit transfer vehicles for the space transport system

Alternatives to all-propulsive manned Orbit Transfer Vehicles (OTV) are presented that utilize aeromaneuvering in combination with propulsive maneuvering. Aeromaneuvering OTV concepts use atmospheric lift and drag forces for maneuvering (orbit plane and ΔV change) to substantially increase payload carrying capability over all-propulsive OTV capabilities. This paper includes a summary of the results of feasibility and concept definition studies and discusses the advantages and disadvantages of aeromaneuvering as compared with all-propulsive vehicles. Manned aeromaneuvering OTV concepts will be presented such as the Aeromaneurvering Orbit-to-Orbit. Shuttle (AMOOS) that can provide future orbital transportation and the Aeromaneuvering Recovery System (AMRS) that will permit emergency recovery of crewmen from high altitude orbits. The AMRS mission requires that an AMRS vehicle be placed in the mission orbit where it remains on-station attached to a manned space facility until required for emergency crew return. The main contributions of this paper are: (1) to establish the concept of the aeromaneuvering OTV for the purpose of performing manned and unmanned orbit transfer; (2) to present data regarding aeromaneuvering OTV configurations, performance, system tradeoffs and mission applications; and (3) to present data concerning major design parameters such as dynamic pressure, heating rates and guidance.

Explorer 45 and Imp 6 observations in the magnetosphere of injected waves from the Siple Station VLF transmitter

This paper reports the first results of a Stanford University-University of Iowa joint experiment in which VLF waves from the Siple Station transmitter in Antarctica are injected into the magnetosphere along the earth's magnetic field lines and are detected near the magnetic equatorial plane by the Explorer 45 and Imp 6 spacecraft. The purpose of this experiment is to conduct a controlled in situ study of VLF wave-particle interactions, in particular, to determine the propagation characteristics of the injected waves in the magnetosphere, to determine the regions where VLF emissions are produced, and to determine the effective volume of the magnetosphere illuminated by the Siple transmitter. During the first 3 months of the joint experiment, transmissions to the two spacecraft were attempted on 25 separate occasions when the satellites were within ±30° longitude of the magnetic field line linking Siple Station and its conjugate point at Roberval, Canada. Measurable signals were produced during 10 of these 25 passes, and these signals were observed as much as 20°E and 15°W of the Siple longitude and on various L shells between 2.9 and 5. On one pass a strong, well-defined signal was present over a 6000-km-long orbital section between L ∼ 4 and L ∼ 5, indicating that the transmitter can illuminate a large volume of the magnetosphere. Emissions stimulated by the transmitter pulses were observed on three passes, and there was evidence on one of these passes that emission stimulation and/or wave entrainment effects were taking place far from the magnetic equator. Signal amplitude measurements were available on only one pass, but these were obtained over a wide region. Amplitudes varied from 10−5 γ outside the plasmapause at L = 5 to 10−4 γ just inside the plasmapause at L ∼ 4. On the basis of these first results of the Stanford University-University of Iowa joint experiment we conclude that important possibilities exist for meaningful in situ high-altitude satellite wave measurements during VLF wave injection experiments.

Cold plasma diagnostics using satellite measurements of VLF signals from ground transmitters

A diagnostic technique to obtain the cold-plasma density profile in the magnetosphere is introduced. This method uses satellite measurements of group delay and pulse duration of VLF signals from ground transmitters in conjunction with a detailed ray-tracing analysis. An iterative method is involved which starts with an approximate density profile, computes the ray paths for that profile, and then compares the properties of the rays that reach the satellite location with the actual satellite measurements. The density profile is then modified to account for any discrepancies between the two results. The same process is repeated with the new profile until one has reasonable agreement between the data and ray-tracing results. This method is applied to the case of an Imp 6 pass, where strong signals from the Siple VLF transmitter were observed for over 25 min. Good agreement is found between the results of the proposed technique and the well-known ground whistler techniques of cold-plasma diagnostics. The results also serve to illustrate the wide diversity of propagation paths from ground transmitters to high-altitude satellites during VLF wave-injection experiments.

Doubly averaged effect of the Moon and Sun on a high altitude Earth satellite orbit

Infinite series expansions are obtained for the doubly averaged effects of the Moon and Sun on a high altitude Earth satellite, and the results used to interpret numerically integrated examples. New in this paper are: (1) both sublunar and translunar satellites are considered; (2) analytic expansions include all powers in the satellite and perturbing body semi-major axes; (3) the fact that retrograde orbits have more benign eccentricity behavior than direct orbits should be exploited for high altitude satellite systems; and (4) near circular orbits can be maintained with small expenditures of fuel in the face of an exponential driving force one forI a<I<Ib, whereI b=180°−I a andI a is somewhat less than 39.2° for sublunar orbits and somewhat greater than 39.2° for translunar orbits.

Numerical Analysis of a Transmission Line EMP Simulator

A theoretical model is defined for an electromagnetic pulse (EMP) simulator for testing EMP effects on high altitude satellites. The simulator is composed of three flat-plate transmission line sections. The first and third sections are tapered to accommodate, respectively, a generator and a terminating resistor. This problem is analyzed in the frequency domain over those frequency components which are known to contribute most significantly to a typical EMP waveform. The analysis uses a numerical technique to solve the basic problem of an unknown current distribution on a curved, tapered strip, excited by a known electric field. The unknown current is solved by the method of moments, using triangular basis functions. As a check, input impedances are computed for the triangular dipole, showing good agreement with experimental results. For the transmission line simulator, computed input impedance, VSWR, power dissipated in the terminating resistor, and the power lost to radiation are presented as a function of frequency. The computed current distributions are used to calculate the electric fields between and immediately beyond the parallel plates. Although a considerable portion of power is converted to radiation at the higher frequencies, it is shown that at least within the working volume the electric field maintains a reasonably constant level.