A satellite interference location system using differential timeand phase measurement techniques

The design and development of a system for inferring the position of terrestrial satellite uplink stations using existing domestic satellites with minimal disruption to normal satellite operation are described. Two methods are presented by which a quantity measured at a terrestrial receiving site is mapped into a curve of possible uplink locations on the Earth's surface. One method involves measuring differential time delays of a single uplink signal observed through two adjacent spacecraft. The other uses a short baseline interferometer composed of the two cross-polarized and spatially separated antenna feeds aboard an affected satellite. A unique location is obtained by using an appropriate combination of the two methods. A system for measurement of the required differential delays and phases and experimental work performed to demonstrate the feasibility of the location methods are described     

Correlation of macro and micro cardiovascular function during weightlessness and simulated weightlessness

The investigation of cardiovascular function necessarily involves a consideration of the exchange of substances at the capillary. If cardiovascular function is compromised or in any way altered during exposure to zero gravity in space, then it stands to reason that microvascular function is also modified. We have shown that an increase in cardiac output similar to that reported during simulated weightlessness is associated with a doubling of the number of post-capillary venules and a reduction in the number of arterioles by 35%. If the weightlessness of space travel produces similar changes in cardiopulmonary volume and cardiac output, a reasonable expectation is that astronauts will undergo venous neovascularization. We have developed an animal model in which to correlate microvascular and systemic cardiovascular function. The microcirculatory preparation consists of a lightweight, thermo-neutral chamber implanted around intact skeletal muscle on the back of a rat. Using this technique, the performed microvasculature of the cutaneous maximus muscle may be observed in the conscious, unanesthetized animal. Microcirculatory variables which may be obtained include venular and arteriolar numbers, lengths and diameters, single vessel flow velocities, vasomotion, capillary hematocrit anastomoses and orders of branching. Systemic hemodynamic monitoring of cardiac output by electromagnetic flowmetry, and arterial and venous pressures allows correlation of macro- and microcirculatory changes at the same time, in the same animal. Observed and calculated hemodynamic variables also include pulse pressure, heart rate, stroke volume, total peripheral resistance, aortic compliance, minute work, peak aortic flow velocity and systolic time interval. In this manner, an integrated assessment of total cardiovascular function may be obtained in the same animal without the complicating influence of anesthetics.     

The Scientific Measurement System of the Gravity Recovery and Interior Laboratory (GRAIL) Mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon utilized an integrated scientific measurement system comprised of flight, ground, mission, and data system elements in order to meet the end-to-end performance required to achieve its scientific objectives. Modeling and simulation efforts were carried out early in the mission that influenced and optimized the design, implementation, and testing of these elements. Because the two prime scientific observables, range between the two spacecraft and range rates between each spacecraft and ground stations, can be affected by the performance of any element of the mission, we treated every element as part of an extended science instrument, a science system. All simulations and modeling took into account the design and configuration of each element to compute the expected performance and error budgets. In the process, scientific requirements were converted to engineering specifications that became the primary drivers for development and testing. Extensive simulations demonstrated that the scientific objectives could in most cases be met with significant margin. Errors are grouped into dynamic or kinematic sources and the largest source of non-gravitational error comes from spacecraft thermal radiation. With all error models included, the baseline solution shows that estimation of the lunar gravity field is robust against both dynamic and kinematic errors and a nominal field of degree 300 or better could be achieved according to the scaled Kaula rule for the Moon. The core signature is more sensitive to modeling errors and can be recovered with a small margin.     

A multiple type-II burst associated with a coronal transient and its MHD simulation

A large coronal transient took place on 8 May 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type II bursts. The velocities of the type II bursts were in the range 1100–1800 kms^?1, in excess of the transient velocity of 500–1000 kms^?1. Two dimensional positions of the type II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. We carry out two dimensional MHD simulations of the event, taking into account the observed velocity, position, and size of the type II bursts. We simulate the multiple shocks observed during the event and their interaction, and discuss some results of the simulation.     

Titan aerosol analogues: analysis of the nonvolatile tholins

Laboratory experiments that produced tholins in a simulated Titan atmosphere were conducted. We report the first systematic analyses of these compounds using Fourier-transform ion cyclotron resonance mass spectrometry. The findings suggest surprising simplicity and nonrandomness in the mass distribution and regularity in species clusters. The degree of unsaturation generally increased with increasing molecular weight in a predictable fashion, and nitrogen is proposed as the dominant carrier of unsaturation. In detected compounds with a general formula of C(x)H(y)N(z), the carbon to nitrogen ratio (x/z) varied only slightly within a narrow limit, and decreased with increasing molecular weights. These compounds are of potential prebiotic interest since they sediment to the surface of Titan, and would dissolve readily in transient aqueous pools that might be generated from time to time by impacts and volcanic     

Type-III radio bursts and their interpretation

The observations of type-III solar radio bursts are briefly reviewed to set requirements on a model for their interpretation. The most important of these requirements is that the source must be an electron stream which is in a state of continuous quasilinear relaxation and which initially must have a nearly monotonically decreasing velocity distribution. The problem of constructing a model is broken into three parts: (1) The plasma wave source which depends on the interaction of the electron stream with electron plasma waves. (2) The radiation source which depends on the interaction of plasma waves and transverse electromagnetic waves or in a magnetized plasma the ordinary and extraordinary modes of magnetoionic theory. (3) The propagation of radiation between the source and the observer which depends on the transmission of radiation through a scattering refracting absorbing magnetized plasma.Progress on a model for the plasma wave source is reviewed and it is concluded that no existing models are adequate. The equations which would lead to an adequate model are written down, but not solved. These include, in addition to collisional damping, Landau damping both by the exciting stream and the background plasma, and spontaneous and induced processes for a three-dimensional distribution of plasma waves. Possible limitations to a quasilinear approach such as pile-up of plasma waves and nonlinear effects are considered. Processes which affect the gross structure of the source such as electron trajectories in coronal streamers and electron scattering by inhomogeneities are reviewed.Progress on the radiation source is considered both in the absence and presence of a magnetic field. At high frequencies (e.g., 80 MHz) observations of radiation near the fundamental and second harmonic of the plasma frequency allow a unique determination of source size and the energy density in plasma waves within the uncertainties of geometry by source ray tracing. This determination is extremely critical because the fundamental must be amplified and thus production of the fundamental is effectively a much more highly nonlinear process than production of the second harmonic. At low frequencies (e.g., 500 kHz) the second harmonic is shown to be dominant because amplification of the fundamental becomes an inefficient process.Calculations of scattering of radiation in a random medium are reviewed. It is concluded that these are adequate at high and low frequencies, but have not been carried out properly at intermediate frequencies where amplification of the fundamental may still be present. It is shown in particular that when scattering is taken into account at high frequencies all observations can be explained by isotropic emission near the second harmonic. At low frequencies the nature of the scatterers is determined by source occultations unlike the case at high frequencies where these are free parameters. This fact allows the possibility of determining true source sizes at low frequencies by subtracting out the contribution due to scattering. A mechanism for producing the possibly observed linear or highly elliptical polarization of type-III bursts, which must be imposed far from the source due to Faraday rotation, is reviewed.Finally, the questions of what remains to be done and what we can hope to obtain upon completion of this work are briefly considered.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Run Diameter Statistics as a Measure of Image Texture

The new concept of "run circles" and their "run diameters," which can be used as a statistical measure of the spacing between points in a two-dimensional image, are presented. For synthetic aperture radar (SAR) images the spacing between bright spots in the image is a useful measure of image texture. The histogram of the run diameters for a set of points has been found to be useful in characterizing the spacings of the points. These histograms can be classified either using features of the histogram such as mode or median, or using classical linear classifiers. As an example, the histogram of run diameters is used to detect a set of points with approximately equal spacing interspersed with a background set of randomly located points.     

Time delay techniques for satellite interference location system

Describes the development of a system for inferring the position of uplink ground stations, using existing domestic satellites, with minimal disruption of normal operation. The system uses the differential time delay of a single uplink signal passing through two adjacent spacecraft to infer the relative position of the uplink transmitter. A system for the measurement of such differential time delays is described. Since this technique alone does not provide an unambiguous determination of uplink transmitter location, the use of an interferometer to resolve such ambiguities is discussed     

Generation Schemes for Wind Power Plants

This paper reviews various electric generation schemes for wind energy conversion suitable for interconnection with a power grid. The schemes can be generally classified as constant speed constant frequency (CSCF) and variable speed constant frequency (VSCF) systems. Historically, only CSCF systems have been used for large power generation in wind power plants. However, with the advent of power electronics and the availability of solid state devices capable of handling large amounts of power, VSCF systems are becoming competitive. Various schemes under each classification are discussed and compared. It is stressed, however, that the optimum choice of the generating scheme is not decided by considering the generator alone. The optimum choice is one which minimizes the cost of energy generated by the wind power plant.