The Venus ionosphere

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000 km for solar zenith angles from 0° to 180°. In addition, information on ion transport velocities, ionopause altitudes, and magnetic field characteristics of the Venus ionosphere, are presented in tabular or graphical form. Also discussed is the solar control of the physical properties of the Venus ionosphere.     

Millimeter wave radiation sources visible in solar corona

Coronal millimeter wave sources (CMMS) have been observed at radio frequencies 22–90 GHz (at wavelengths 3–13 mm). The observed CMMS have been classified into three different categories according to their time scale and relation to other wave-length events. The CMMS indicate enhancement of electron density in the corona, as well as magnetic loop structures. The CMMS are evidence of dynamical processes taking place at the lower levels of the corona, propagating into the higher levels.     

Stability Analysis of a Buck Regulator Employing Input Filter Compensation

The interaction between the input filter and the regulator often causes serious degradation of performance. The reduction in loop gain due to input filter interaction can result in system instability. An exact stability analysis of the buck regulator system is presented. The input filter parameter values are varied and system instability is predicted for the case without feedforward. The eigenvalues of the system can be brought back into the unit circle and the system thus stabilized with the addition of the feedforward loop. Measurements made for the cases with and without feedforward confirm the analytical prediction.     

Effect of KOH concentration on LEO cycle life of IPVnickel-hydrogen flight cell-update II

For update I see Energy and Environment: A Continuing Partnership, vol.3, American Nuclear Society (1991). An update of validation test results confirming the breakthrough in the low-Earth-orbit (LEO) cycle life of nickel-hydrogen cells containing 26% KOH electrolyte is presented. The results are part of an investigation of the effect of KOH concentration on life cycle. The cycle life of boiler plate cells was about 40000 LEO cycles compared to 3500 cycles for cells containing 31% KOH. The cycle regime was a stressful accelerated LEO, which consisted of a 27.5 min charge followed by a 17.5 min discharge (2×normal rate). The depth-of-discharge (DOD) was 80%. The cell temperature was maintained at 23°C. Results for six 48-Ah recirculation design IPV nickel-hydrogen flight battery cells currently being evaluated to validate the above findings are reported. Three of the cells contain 26% KOH (test cells), and three contain 31% KOH (control cells). They are undergoing real-time LEO cycle life testing. The 31% KOH cells failed at cycles 3729, 4165, and 11355. One of the 26% KOH cells failed at cycle 15314. The other two 26% KOH cells have been cycled for over 16600 cycles without failure     

Overwintering in the Antarctica as an analog for long term manned spaceflight.

As a part of Polar Psychological Project planned by SCAR group on Antarctic-Space-Related-Human-Factors-Research, a series of psychological tests were conducted on the Japanese wintering-over personnel. The main purpose of the research was to study the behavioral characteristics, such as depression, insomnia, anxiety, and hostility, which might develop during the course of wintering-over period, and it involves a detailed study of the individuals and interpersonal relationship.     

Radiation chemistry of the hippocampal brain slice.

The in vitro hippocampal brain slice is a 0.4 mm thick neural network that can be used to study brain responses to radiation and related injuries. This preparation is unique in that it responds to ionizing radiation within minutes after exposure without complications from changes in vascularity, blood flow, blood pressure, etc. Electrophysiological studies have shown that x- and gamma-rays alter synaptic transmission and spike generation, elements of normal brain activity. To evaluate the role of hydroxyl free radicals (OH) in these changes, slices were exposed to dilute H2O2 solutions. EPR spin trapping experiments verified that OH is produced. Neural responses, while similar, were not identical to those due to radiation, possibly because of a different distribution of OH. Although H2O2 is freely diffusible, it produces OH at specific sites where, e.g. iron reduces it. In contrast, x- and gamma-rays produce OH more uniformly throughout the tissue. H2O2 may provide a better model for high-LET radiation where yields of radical products of water radiolysis are decreased and peroxide reactions predominate.     

Solar total irradiance and sunspot area in 1981

Precise observations of the total solar irradiance in 1980 from the Solar Maximum Mission showed a strong correlation with the projected total sunspot area. This correlation “explained” about half of the variance (r ～ 0.75) in the total-irradiance data, leaving the other half for other solar phenomena and errors in the data. We have now begun the analysis of the intervening three years of “spin-mode” data, which have reduced coverage. We find that the correlation persists at about the same qualitative level, but with increased scatter that can be attributed to the smaller amount of data. The flatness of the distribution of areas of sunspot groups makes it possible to estimate PSI approximately from only the large groups.     

Enhancing filter robustness in cascaded GPS-INS integrations

Filter robustness is defined herein as the ability of the Global Positioning System/Inertial Navigation System (GPS-INS) Kalman filter to cope with adverse environments and input conditions, to successfully identify such conditions and to take evasive action. The formulation of two such techniques for a cascaded GPS-INS Kalman filter integration is discussed This is an integration in which the navigation solution from a GPS receiver is used as a measurement in the filter to estimate inertial errors and instrument biases. The first technique presented discusses the handling of GPS position biases. These are due to errors in the GPS satellite segment, and are known to be unobservable. They change levels when a satellite constellation change occurs, at which point they introduce undesirable filter response transients. A method of suppressing these transients is presented. The second technique presented deals with the proper identification of the filter measurement noise. Successful formulation of the noise statistics is a factor vital to the healthy estimation of the filter gains and operation. Furthermore, confidence in the formulation of these statistics can lead to the proper screening and rejection of bad data in the filter. A method of formulating the filter noise statistics dynamically based on inputs from the GPS and the INS is discussed     

Communicating across the solar system

The technological advances of the Space Age have enabled us to project our senses through complex instruments to the edge of the Solar System and beyond. The link back to Earth by the communication channel has provided us with a wealth of information. The vast improvement in communication capability, by a factor of 10¹⁸, from the launching of the first earth satellites to the capacity of the Voyager telecommunications link across the Solar System, is symbolic of both our technical prowess and our cultural development. The combination of data rate and extreme distance at the Voyager 2 encounters with Uranus and Neptune in 1986 and 1989 will require the ground network to perform an engineering feat of unequalled magnitude. This paper describes the engineering challenge of communicating with spacecraft at the limits of the Solar System and the engineering responses to that challenge.     

The message and the experience of the site project

The Satellite Instructional Television Experiment (SITE) was a unique effort aimed at studying the possibilities of satellite broadcasting for education and national development. This one-year joint India-USA project was carried out in 1975–1976 using the ATS-6 spacecraft. This paper briefly describes the experiment and its major findings. It goes on to distill the learning experiences derived from SITE and analyses the extent to which these have influenced the design and configuration of India's domestic satellite system, INSAT. INSAT-1B, which will serve as a replacement for the short-lived INSAT-1A, will be launched shortly and will be operational by the end of 1983. Its payload includes two S-band TV transponders capable of broadcasting directly to augmented TV sets. The paper examines which lessons of SITE are being applied in the planning and operationalisation of the TV system and discusses why others are not being taken account of. Major issues confronting TV system planners in developing countries like India are highlighted and the possible role of satellite broadcasting discussed in this context. The paper concludes by outlining an “ideal scenario” for a large, multilingual country like India, towards which TV planners could attempt to strive.