Model calculations of the dayside ionosphere of Venus

Model calculations of the dayside ionosphere of Venus are presented. The coupled continuity and momentum equations were solved for O₂⁺, O⁺, CO₂⁺, C⁺, N⁺, He⁺, and H⁺ density distributions, which are compared with measurements from the Pioneer Venus ion mass spectrometer. The agreement between the model results and the measurements is good for some species, such as O⁺, and rather poor for others, such as N⁺, indicating that our understanding of the dayside ion composition of Venus is incomplete. The coupled heat conduction equations for ions and electrons were solved and the calculated temperatures compared with Pioneer Venus measurements. It is shown that fluctuations in the magnetic field have a significant effect on the energy balance of the ionosphere.     

Sunspot motions and magnetic shears as precusors of flares

Using full-disc white light photoheliograms, we have studied umbrae motion and variations in sunspot areas in a large activity complex over 4 solar rotations. On the basis of the observational data we illustrate with typical examples to what extent rapid spot motions are associated with flare occurrences.     

An instrument for DC electric field and AC electric and magnetic field measurements aboard ‘Intercosmos-Bulgaria-1300’ satellite

The instrument IESP-IPMP represents the complex unit measuring the vector of the DC electric field, the vectors of the electric and magnetic field in the frequency range of 0.2 – 6.5 Hz (wave form), autocorrelation functions of waves with frequencies of 0.1 – 5 kHz, and wave amplitudes in 8 bandpass channels. Some results are shown and compared in the various frequency ranges.     

Recent developments in space-borne zodiacal light photometry

The 1985 International Solar Polar Mission will provide the first opportunity to perform measurements from out of the ecliptic and from above the solar poles. Included in this mission is the Zodiacal Light/Background Starlight Experiment of the Ruhr-University Bochum, FRG (in collaboration with the State University of New York at Albany). The experiment is based on the use of a multicolor, sky-scanning photopolarimeter, which will be carried on the NASA S/C.The scientific objectives of the experiment are to investigate the intensity, polarization, and color of the diffuse sky brightness and determine the spatial distribution and physical properties of the interplanetary dust, including a possible interstellar component, as a function of S/C position in and out of the ecliptic.The instrument will allow simultaneous measurements in two separate wavelength bands. Measurements will be performed at 180, 220, 240, 280, 320, 350, 360, 440, 540, 640, 800 nm, including the state of polarization. Two different fields-of-view (1 sq deg and 5.6 sq deg) can be selected.The use of a microprocessor system in the instrument electronics will provide flexibility in measurement sequences and programs, on-board data processing and data quality control.     

IRAS observations of cometary dust

The large beam size of the Infrared Astronomy Satellite (IRAS) focal plane detector array is well suited to measuring the low level thermal emission from cometary dust. Eight comets discovered in 1983 and nine previously known periodic comets were observed by IRAS during its ten month active lifetime. Dust production rates are derived for a wide range of heliocentric distances. Grain properties are inferred from application of simple models to the long wavelength spectral energy distribution.     

Notes on SCPC-FM System Design and Performance

In many domestic satellite communication systems single-channel per-carrier FM (SCPC-FM) has become the accepted transmission method for thin route communication. The SCPC-FM modem operates over a wide range of carrier frequencies and is designed to use satellite power and bandwidth efficiently. It incorporates elements which make the signal transfer complex, so the system behavior is not immediately obvious. This article investigates the signal processes and analyzes the performance of a companded and preemphasized SCPC-FM system and it furnishes insight into the choice of crucial system parameters.     

A Performance Measure for Evaluating Aircraft Landing Trajectories

A general performance index is developed for evaluating aircraft landing trajectories. The primary term in the index is the effect of noise on people residing near the air terminal. Other terms included are passenger comfort, fuel consumed, and the time spent in the near-terminal area. Models are developed for aircraft engine noise, passenger comfort, the population distribution about a specific airport, and the aircraft flight behavior. While this performance index may be used in computing optimal trajectories, it is also useful for comparing nonoptimal trajectories which, for one reason or another, may be worthy of consideration. Some examples of such comparisons are included through simulations of landing. The aircraft considered is a Boeing 737.     

The Effects of Defruiting on the ATCRBS

The defruiter that is employed in the Air Traffic Control Radar Beacon System (ATCRBS) to prefilter asynchronous replies has a complex impact on the detection, estimation and validation properties of the detection subsystem. Its positive and negative effects are quantitatively enumerated via a simulation of the beacon processing subsystem of the Automated Radar Terminal System (ARTS III). It is concluded that the disadvantages of using the present-day defruiter in the ARTS III digital processing channel outweigh the advantages when fruit rates are below several thousand per scan. As an alternative to the total elimination of the defruiter a more general class of preprocessors is defined and their input-output relationships are derived using a Markov Chain formulation. These are found to represent an improvement over the current defruiter in that the positive effects of defruiting are retained while some of the negative effects are reduced.     

Planetary radio astronomy experiment for Voyager missions

The planetary radio astronomy experiment will measure radio spectra of planetary emissions in the range 1.2 kHz to 40.5 MHz. These emissions result from wave-particle-plasma interactions in the magnetospheres and ionospheres of the planets. At Jupiter, they are strongly modulated by the Galilean satellite Io.As the spacecraft leave the Earth's vicinity, we will observe terrestrial kilometric radiation, and for the first time, determine its polarization (RH and LH power separately). At the giant planets, the source of radio emission at low frequencies is not understood, but will be defined through comparison of the radio emission data with other particles and fields experiments aboard Voyager, as well as with optical data. Since, for Jupiter, as for the Earth, the radio data quite probably relate to particle precipitation, and to magnetic field strength and orientation in the polar ionosphere, we hope to be able to elucidate some characteristics of Jupiter auroras.Together with the plasma wave experiment, and possibly several optical experiments, our data can demonstrate the existence of lightning on the giant planets and on the satellite Titan, should it exist. Finally, the Voyager missions occur near maximum of the sunspot cycle. Solar outburst types can be identified through the radio measurements; when the spacecraft are on the opposite side of the Sun from the Earth we can identify solar flare-related events otherwise invisible on the Earth.