Statistical method for ground and sky coverage calculation

A novel statistical method has been devised for evaluating the ground and the sky coverage of an observation experiment on board a satellite. Owing to its unrivalled rapidity compared with other conventional calculation techniques, the method can be applied to evaluate the coverage percentages for the whole globe or any area on it, to calculate the visibility percentages for one or more ground stations and to determine the percentages of observation time of any given celestial direction including Sun, Moon, Earth and Ground Stations constraints. The orbits considered can be elliptical and account is taken of the drift due to the Earth's oblateness.     

On the breakdown of wave fronts of characteristics in an ideal dissociating gas

Using the method of characteristics, the problem of breaking or non-breaking of waves is studied in a plane cylindrically or spherically symmetric flow of an ideal dissociating gas. It is investigated as to how the effects of dissociation and that of the wave front curvature influence the breaking or non-breaking of waves. In a symmetrical converging gas motion a remarkable difference between the behaviours of cylindrical and spherical waves is discovered.     

The evolution of a serviceable EURECA

Within the European space platform program the EURECA is being established as a ground-based platform for short microgravity missions. The development towards a serviceable platform for longer, scientific missions is described. The plan of an advanced space-based platform for increasing payload demands is outlined. The platform design and the adaptation to scientific missions and servicing operations are investigated. The cost-effective utilization of the different platform types using new operational concepts is analyzed in parametric life cycle cost calculations for different payloads and mission scenarios.     

Reconstituting the US space programme

This response to Alex Roland's article, ‘Priorities in space for the USA’, argues that his analysis and conclusions are based on shaky historical evidence. Professor Roland's interpretation of NASA's priorities since 1959 is challenged, and it is pointed out that the manned spaceflight programme has widespread support in the USA. The most important issue, raised by the article but not treated extensively enough, is whether the pursuit of the widely accepted emphasis on manned spaceflight is a large-scale societal mistake.     

Main medical results of extended flights on space station Mir in 1986-1990

During 1986-1990 seven prime spacecrews (16 cosmonauts) have flown on-board the Mir orbital complex. The longest space mission duration was 366 days The principal objectives of the medical tasks were the maintenance of good health and performance of the spacecrews and conducting medical research programs which included study of the cardiovascular, motor, endocrine, blood, immune, and metabolic systems. Results obtained point to the ability of humans to readily adapt to a year-long stay in space and maintain good health and performance. Readaptation had a similar course as after other previous long-term space flights of up to 8 months in duration. Primary body system changes were not qualitatively different from findings after flights aboard the Salyut 6 and 7 space stations. In this case, during and after an 11-12 month flight, body system alterations were even less severe which was a result of adequate countermeasure use, their systematic and creative employment and maintenance of required environments to support life and work in space.     

Ensuring equal access to the benefits of space technologies for all countries

There is a concern in the developing world that industrialized countries have not done all they might under Article 1 of the Outer Space Treaty to make the benefits of space technology available to all countries; some are now seeking codification of rights and responsibilities in this sphere. This article discusses recent debate on the issues by COPUOS and its Legal Subcommittee on whether an additional legal framework is necessary to ensure a fairer distribution of benefits. G77 countries were strongly in favour of some form of technology and information transfer, while industrialized countries favoured the existing practice of developing international cooperative space projects. The author believes that a new set of principles will be formulated in the next few years and that organizations like Intelsat and Inmarsat can provide valuable models for ensuring access through cooperative programmes.     

Risk-taking during wayfinding is modulated by external stressors and personality traits

ABSTRACT

Two experiments examined cue reliance and risk-taking during desktop virtual wayfinding, and how they might be modulated by personality traits and external stressors. Participants navigated a series of virtual buildings and we manipulated the strength of probabilistic cues available to guide turn decisions. Navigators frequently discounted probabilistic cues and instead took risks, particularly when costs were low and potential benefits were high. Risk-taking was predicted by higher sense of direction and lower need for structure. Introducing a time stressor lowered risk-taking, with a higher relative reliance on probability-based information. This was most pronounced in females and those with a high need for structure. Results provide novel evidence that spatial cue reliance is modulated by individual differences and contextual constraints.     

French research program on the physiological problems caused by weightlessness. Use of the primate model

The need to acquire a better knowledge of the main biological problems induced by microgravity implies--in addition to human experimentation--the use of animal models, and primates seem to be particularly well adapted to this type of research. The major areas of investigation to be considered are the phospho-calcium metabolism and the metabolism of supporting tissues, the hydroelectrolytic metabolism, the cardiovascular function, awakeness, sleep-awakeness cycles, the physiology of equilibrium and the pathophysiology of space sickness. Considering this program, the Centre d'Etudes et de Recherches de Medecine Aerospatiale, under the sponsorship of the Centre National d'Etudes Spatiales, developed both a program of research on restrained primates for the French-U.S. space cooperation (Spacelab program) and for the French-Soviet space cooperation (Bio-cosmos program), and simulation of the effects of microgravity by head-down bedrest. Its major characteristics are discussed in the study.     

Analyse du fonctionnement d'un propulseur a éjection modulée

ONERA developed, for studying the response of a propellant to a pressure or velocity fluctuation, an experimental rocket engine whose nozzle throat area can be modulated by a toothed disk.The paper presents a linearized theory of the functioning of this engine in the low frequency domain, i.e. when there is no wave propagation within the combuster.To describe the functioning of this motor, the Ryazantsev-Novozhilov method, which assumes that the gas response is instantaneous, is used. This analysis takes into account the erosion and radiation effects, the combustion efficiency and the thermal losses through the walls.Two particular cases are described, for two values of the Damköhler parameter $\text{D}{}_1\text{=}\text{t}{}_{\mathrm{c}}\text{t}{}_{\mathrm{th}}$, where t_c is the residence time in the combuster and t_th the characteristic thermal time of the heat penetration into the solid propellant. These two cases correspond, one to a classical propellant D₁ > 1, the other to a particular propellant of low burning rate ($\text{J}{}_{\mathrm{b}}\text{? 0.2}\text{to}\text{0.4}\text{mm s}{}^{\mathrm{?1}}$) D₁ < 1. The stability conditions are analysed as well as the pressure amplitute and phase as a function of the nozzle throat modulation frequency.Still in linearized theory, the complete solutions of the problem are presented, using a method of numerical resolution.     

The Soviet manned lunar programme and its legacy

In the last two years the USSR has not only acknowledged publicly for the first time that it was trying to ‘race’ the USA to put the first man on the Moon, but they have finally given some details of the programme, the equipment and the political in-fighting which ensured that the programme was a failure. This article traces the history of the Soviet manned lunar programme and also discusses the implications for the future development of the Soviet manned programme of the giant N-1 booster's cancellation in 1974.