The Electron Beam Instrument (F6) on Freja

The Electron Beam Instrument (F6) onFreja is the first attempt to apply the electron drift technique in a region of large ambient magnetic fields. The paper describes the operational principles, the technical realization, and the difficulties encountered in the derivation of the electric fields.     

Eruptive prominences as sources of magnetic clouds in the solar wind

Large amounts of coronal material are propelled outward into interplanetary space by Coronal Mass Ejections (CMEs). Thus one might expect to find evidence for expanding flux ropes in the solar wind as well. To prove this assumption magnetic clouds were analyzed and correlated with H-observations of disappearing filaments. When clouds were found to be directly associated with a disappearing filament, the magnetic structure of the cloud was compared with that of the associated filament. Additionally the expansion of magnetic clouds was examined over a wide range of the heliosphere and compared with the expansion observed for erupting prominences.     

The Freja ultraviolet imager

Auroral images acquired by satellite instrumentation have proven to be a crucial component of the scientific equiry into the physical processes of the Earth's magnetosphere. TheFreja mission provided an opportunity to extend these measurements into the temporal and spatial regime commonly associated with ground-based optical imagers. Employing the basic procedure used successfully in theViking program allowed image repetition rates of 6 s to be achieved with simultaneous exposure of all pixels within the field-of-view. Typical exposure times of 0.3 s required development of an improved image intensifier system and operational requirements resulted in image formats covering approximately one-third of a spin. Simultaneously exposing two broad-band UV cameras, the instrument generates in its normal operational mode 264.6 kbytes per image pair. Results from initial operations confirm the design approach and suggest such imagers can be routinely included on challenging low cost missions such asFreja.     

Data fusion of decentralized local tracker outputs

An approach for fusing offboard track-level data at a central fusion node is presented. The case where the offboard tracker continues to update its local track estimate with measurement and system dynamics models that are not necessarily linear is considered. An algorithm is developed to perform this fusion at a central node without having access to the offboard measurements, their noise statistics, or the location of the local estimator. The algorithm is based on an extension of results that were originally established for linear offboard trackers. A second goal of this work is to develop an inequality constraint for selecting the proper sampling interval for the incoming state estimates to the fusion node. This interval is selected to allow use of conventional Kalman filter algorithms at the fusion node without suffering error performance degradation due to processing a correlated sequence of track state estimates     

GTD Terrain Reflection Model Applied to ILS Glide Scope

The capability of calculating the reflection of electromagnetic signals from uneven terrain has many applications. One of these is the determination of instrument landing system (ILS) glide slope performance. For this application the wavelength is approximately 1 m, incidence angles are usually near grazing, and the fields are horizontally polarized, so that gross irregularities such as dropoffs and hills are more important than surface roughness. Past approaches used to calculate the ground reflections for this application have been three-dimensional physical optics models which were very cumbersome and time consuming and which neglected important diffraction and shadowing phenomenon; a two-dimensional physical optics model which was faster than the three-dimensional models but ignored many shadowing and transverse terrain variation effects; and a half-plane diffraction model which is applicable only to a specified type of terrain geometry. In this paper a terrain reflection model based on the geometrical theory of diffraction (GTD) is described which can accommodate any piecewise linear terrain profile, requires less computer time than the physical optics models, is capable of including transverse terrain effects, and determines the reflected fields with all important diffraction and blockage effects included.     

Asymptotically Stable Motions of a Gyro in a Spinning Vehicle

An analysis of the motion of a single-axis rate gyroscope mounted in a space vehicle which is spinning with uncertain constant angular velocity xz about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using the Lyapunov approach, regions are obtained in the k-xz plane where k is the torsional spring constant, for asymptotic stability and for global asymptotic stability, and an estimate of the region of stability in state space is presented. Analytical relations for the selection of the gyro parameters are derived.     

Dynamic considerations for control of closed life support systems

Reliability of closed life support systems will depend on their ability to continue supplying the crew's needs in the face of perturbations and equipment failures. These dynamic considerations interact with the basic static (equilibrium) design through the sizing of storages, the specification of excess capacities in processors, and the choice of system initial state (total mass in the system). This paper uses a very simple system flow model to examine the possibilities for system failures even when there is sufficient storage to buffer the immediate effects of the perturbation. Two control schemes are shown which have different dynamic consequences in response to component failures.     

Space telescope and cosmology

The status of institutional arrangements and of the hardware development for Space Telescope are highlighted. After a brief summary of instrument characteristics, some examples are given on the possible use of the ST to study objects of interest to cosmology.     

Cosmology and GUTs: The matter of the universe

To illustrate the interaction of Grand Unified Theories (GUTs), supersymmetry (SUSY), and cosmology, a worked example is carried out. This example is the dark matter problem, or “What is the dominant matter of the Universe?” It is shown that if GUTs are assumed then the primordial perturbations are probably adiabatic, if inflation is assumed then Ω = 1 and GUTs first name is probably SUSY. If Ω = 1, big bang nucleosynthesis tells us that the bulk of the matter is non-baryonic. SUSY-GUTs gives us some possible candidate inos to which massive neutrinos, axion or planetary mass black holes can be added. These candidates can be classified hot (or warm) or cold types of dark matter. It is shown that hot gives Ω = 1 and naturally gives large scale structure but does not give small scale structure or galaxy formation times, whereas cold gives small scale structure and formation times but cannot easily yield Ω = 1. It is concluded that either a hybrid of both hot and cold or non-random phases for the perturbations may be needed.     

New multifrequency measurements of the spectrum of the cosmic background radiation

New measurements of the Cosmic Background Radiation temperature at 12 cm, 6.3 cm, 3 cm, 0.9 cm and 0.3 cm have made in July 1982 from the White Mountain High Altitude Research Station. The results are presented and the existence of spectral distortions discussed.