Thermospheric model calculations based on turbulence data

Thermospheric model calculations are presented which explain the seasonal compositional changes of helium and argon by the combined effect of seasonal-latitudinal variations of turbulence and global seasonal winds. The observational base of the model calculations is given by empirical data of upper thermospheric densities and by estimates of the turbopause height derived from composition measurements and incoherent scatter temperatures in the lower thermosphere. The results are compared with observations of the seasonal variability of atomic oxygen in the turbopause region.     

Tracking and data relay satellite system: NASA's new spacecraft data acquisition system

The growth in NASA's ground network complexity and cost triggered a search for an alternative. Through a lease service contract, Western Union will provide to NASA 10 years of space communications services with a Tracking and Data Relay Satellite System (TDRSS). A constellation of four operating satellites in geostationary orbit and a single ground terminal will provide complete tracking, telemetry and command service for all of NASA's Earth orbital satellites below an altitude of 12,000 km. The system is shared: two satellites will be dedicated to NASA service; a third will provide backup as a shared spare; the fourth satellite will be dedicated to Western Union's Advanced Westar commercial service. Western Union will operate the ground terminal and provide operational satellite control. NASA's Network Control Center will provide the focal point for scheduling user services and controlling the interface between TDRSS and the rest of the NASA communications network, project control centers and data processing facilities. TDRSS single access user spacecraft data systems should be designed for efficient time shared data relay support. Reimbursement policy and rate structure for non-NASA users are currently being developed.     

Equatorial cloud properties on Venus from pioneer orbiter infrared observations

Infrared observations of Venus from the Pioneer Orbiter have been used to study the limb darkening properties of the cloud tops at wavelengths and spatial resolutions not previously attained. The preliminary results show evidence for an extensive haze feature over the equatorial morning terminator and for small amounts of a far-infrared absorber concentrated near local noon, also near the equator. The evidence for these features is reviewed and their possible origins briefly discussed.     

Mechanisms for the discrete aurora — A review

The V-shock is identified as the primary mechanism for the acceleration of electrons responsible for the discrete aurora. A brief review of the evidence supporting the V-shock model is given, including the dynamics of auroral striations, anomalous motion of barium plasma at high altitudes and in-situ observations of large electric fields. The V-shock is a nonlinear, n = 0 ion cyclotron mode soliton, Doppler shifted to zero frequency. The V-shock is also shown to be a generalization of the one-dimensional double layer model, which is an ion acoustic soliton Doppler shifted to zero frequency. The essential difference between the double layer theory and the theory for the oblique, current-driven, laminar electrostatic shock is that the plasma dielectric constant in directions perpendicular to the magnetic field is c ²/V _a ^/2 , where V _a is the Alfvén velocity; but the plasma dielectric constant parallel to the magnetic field is unity. Otherwise, in the limit that the shock thickness perpendicular to the magnetic field is much larger than an ion gyroradius, the equations describing the double layer and the oblique shock are the same. The V-shock, while accounting for the acceleration of auroral electrons, requires an energy source and mechanism for generating large potential differences perpendicular to the magnetic field. An energy source is the earthward streaming protons coming from the distant magnetospheric tail. It is shown how these protons can be energized by the cross-tail electric field, which is the tailward extension of the polar cap dawn-to-dusk electric field. The local, large cross-field potential differences associated with the V-shock are seen to be the result of a non-linear, E × B drift turbulent cascade which transfers energy from small- to large-scale sizes. Energy at the smallest scale sizes comes from the kinetic energy in the ion cyclotron motion of the earthward streaming protons, which are unstable against the zero-frequency flute-mode instability. The review points out the gaps in our understanding of the mechanism of the diffuse aurora and the mechanism of the auroral substorm.     

Reverse-Bias Second Breakdown of High-Power Darlington Transistors

The reverse-bias second breakdown (RBSB) characteristics of high power Darlington transistors are discussed. The Darlingtons investigated are rated at 400 V maximum voltage and 100 A maximum current. Devices with and without speed-up diodes (connected between the bases of the input and output transistors) were studied. A nondestructive system for characterizing the RBSB behavior of these devices is described. The RBSB behavior was found to vary unpredictably with varying reverse base current magnitude. It was also found that the RBSB behavior of the Darlingtons was a function of the forward base current magnitude. This is in marked contrast to what has been found for discrete devices. The presence of a speed-up diode also influenced the RBSB behavior of these devices.     

Changes in the micro-structure of the vestibular apparatus of tadpoles (Rana temporaria) developed in simulated weightlessness

The vestibular apparatus of tadpoles (Rana temporaria) exposed to simulated weightlessness was examined by electron microscopy. Extended exposure to simulated weightlessness is followed by significant alterations in the sensory epithelia and also in the otolith membrane. Large vacuoles, filled with necrobiotic mitochondria and fragments of endoplasmic reticulum, were concentrated in the region where an otolith membrane covers the hair cells but were mostly absent in zones of the epithelia with undifferentiated cells. The number of otoconia in the otolith membrane was diminished. The results were compared with data from space flight experiments and some concordance was noted. The possible connection between some unusual behavior of the tadpoles after weightlessness simulation and the structural alterations in the gravitational sensors was discussed.     

Absorbers seen near the Venus cloud tops from pioneer Venus

Spin-scan images from the Pioneer Venus Orbiter UV Spectrometer and the Cloud Photopolarimeter provide a set of planetary contrast measurements in the wavelength range 1990A to 3650A and phase angles from 33°–130°. The planet is darkest at the point where the UVS line of sight penetrates perpendicular to the cloud tops: thus the absorbing material responsible must be deep in the atmosphere. Sulfur dioxide absorption can explain the amount of contrast seen between 2000A and 3200A. At the longer wavelengths, the persistence of contrast requires another absorber which is deeper in the atmosphere and strongly associated with the location of the SO₂. Part of the observed contrast is due to the high-lying haze discovered from Pioneer Venus polarimetry. The correlation between planetary contrast and polarization does not support large scale clearing or major vertical motions of the cloud tops as the sole cause of the observed contrast. However, a scheme in which absorbers subject to photochemical destruction are mixed upward into the cloud top region provides a consistent explanation for the origin of these markings.     

Aerospace Capability and Systems Analysis Applied to Urban Problems?Some Views from a Social Scientist

Much has been written about the development of a general systems theory for application to civil problems, but very little documentation exists in the sense of case studies of large-scale programs implemented using the systems approach. The Model Urban Neighborhood Demonstration Program, operating in an inner-city poverty neighborhood in Baltimore, offers some lessons in this regard. With the present state of the art, the techniques of systems analysis are most effective at the subsystem level, and the necessary funding and development time should be afforded to extend their usefulness in the civil order. Existing aerospace companies provide an operating institutional base, with extenasive resources, that can be beneficially translated to solving problems in the public order.     

Connections between short-period (Pc 1) pulsations and ionospheric parameters

Short-period pulsations recorded at five stations in Finland during the IMS have been compared. The morning occurrences accepted as Pc 1's showed certain peculiarities in their dependence on latitude. A connection was found between the averaged daily duration of Pc 1's and the foF2 parameter. This hints at the influence of propagation conditions. It was found that, after certain geomagnetic storms, the mid-latitude ionospheric absorption of LF radio waves can significantly increase when the Pc 1 activity is also enhanced at each high-latitude station.     

The Berkeley parasitic SETI program

Parasitic programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. We describe a microprocessor-based automated SETI acquisition system which searches for and records spectra of narrowband signals in the IF band of an observatory receiver. Data taken with this system over 35 days at the Hat Creek Radio Observatory at 1612 MHz are discussed. Out of approximately 10⁵ spectra processed during this period, 4000 were identified by the system as containing narrowband signals and were recorded. Subsequent analysis indicates that over 3900 of these are due to local RF contamination. The remainder are undergoing further investigation.