Is there a need for an African space agency?

Over the past few years, the view has been expressed in some quarters that Africa should establish a continental space agency. Various arguments are advanced for this, but they are generally not compelling and rely mostly on pointing to the existence of other regional space cooperation organisations, or to benefits that are debatable. The article considers these arguments and concludes that there is an insufficient case for the establishment of an African space agency at this point in the development of the space arena in Africa. Instead, greater emphasis should be placed on strengthening nascent national space programmes, fostering intra-regional cooperation and raising the profile of space activities in Africa's national and regional political structures.     

Criteria for developing and testing Transparency and Confidence-Building Measures (TCBMs) for outer space activities

Space systems play an important role in sustaining the development, prosperity and security of many nations. As more nations become critically reliant on space systems, questions of maintaining safety and strategic stability in outer space have come to the fore. Transparency and Confidence-Building Measures (TCBMs) for outer space activities have an important role to play in providing clarity about the intentions of States and in articulating norms of behaviour in outer space. TCBMs take several forms. They may be the elaboration of basic principles related to the exploration and use of outer space, political measures related to establishing norms of conduct, information-sharing activities to improve the transparency of outer space activities, operational practices which demonstrate a commitment to mutual cooperation in outer space, or consultative mechanisms. We present an analytical framework for evaluating potential TCBMs and illustrate the application of this framework to examples of potential operational, regulatory, treaty-based and declaratory TCBMs.     

Spacecraft detumbling using movable telescoping appendages

The dynamics of detumbling a randomly spinning spacecraft using externally mounted, movable telescoping appendages are studied both analytically and numerically. Two types of telescoping appendages are considered: (a) where an end mass is mounted at the end of an (assumed) massless boom; and (b) where the appendage is assumed to consist of a uniformly distributed homogeneous mass throughout its length. From an application of Lyapunov's second method, boom extension maneuvers can be determined to approach either of two desired final states: close to a zero inertial angular velocity state and a final spin rate about only one of the principal axes. Recovery dynamics are evaluated analytically for the case of symmetrical deployment. Numerical examination of other asymmetrical cases verifies the practicality of using movable appendages to recover a randomly tumbling spacecraft.     

Chemical and biological evolution in space

Astronomical infrared spectra are used to confirm the existence of complex organic molecules produced by ultraviolet photoprocessing of interstellar grain mantles. This material is shown to be the major component of the interstellar grains between the sun and the galactic center and, by inference, constitutes more than 10 million solar masses — or close to one part in a thousand of the entire mass of the milky way galaxy. It may be demonstrated that the primitive chemistry of the earth's surface was dominated by these extraterrestrial molecules after aggregated into comets if the rate of comet impacts with the earth was comparable with that required to account for the extinction of species over the past 300 million years.

Ultraviolet irradiation of bacterial spores has been studied for the first time under simulated interstellar conditions. The inactivation time predicted for the less dense regions of space is at most several hundred years. Within molecukar clouds it is shown on theoretical and experimental grounds that this t the estimated cloud. However survival of spores during their initial exposure to the solar ultraviolet presents a problem for panspermia because it requires that in the process of ejection from the earth's surface they must be enclosed within a cocoon (or mantle) of ultraviolet absorbing material of 0.6 μm thickness. Thus, although panspermia can not be rejected on the basis of lack of interstellar survival there may remain insurmountable obstacles to its occuring because of the very special protective shield requirements during ejection from its planetary source.     

Evolution of the Moon: The 1974 model

The geology of the decade of Apollo and Luna probably will become one of the fundamental turning points in the history of all science. For the first time, the scientists of the Earth have been presented with the opportunity to interpret their home planet through the direct investigations of another. Mankind can be proud and take heart in this fact. The interpretive evolution of the Moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows:

1. The Beginning — 4.6 billion years ago.
2. The Melted Shell — 4.6–4.4 billion years ago.
3. The Cratered Highlands — 4.4–4.1 billion years ago.
4. The Large Basins — 4.1–3.9 billion years ago.
5. The Light-colored Plains — 3.9–3.8 billion years ago.
6. The Basaltic Maria — 3.8–3.0 (?) billion years ago.
7. The Quiet Crust — 3.0 (?) billion years ago to the present.

The Apollo and Luna explorations that permit us to study these stages of evolution each have contributed in progressive and significant ways. Through them we now can look with new insight into the early differentiation of the Earth, the nature of the Earth's protocrust, the influence of the formation of large impact basins in that crust, the effects of early partial melting of the protomantle and possibly the earliest stages of the breakup of the protocrust into continents and ocean basins.     

Calibration of the VIS-channel of meteosat-2

The “VIS-channel” (the channel is sensitive between about .4 and 1.1 μm wavelength) of the European geostationary satellite Meteosat-2 is calibrated by the method of “vicarious calibration by means of calculated radiances”. The calibration constant, which connects the 6-bit-counts of the VIS-channel of the Meteosat-2 with the corresponding “effective radiances” is determined to be c_SAT = 2.3 W·m^?2·sr^?1/count with an accuracy of ± 10% (preliminary values). The calibration constant is valid for “gain 0” and the period until October 1981. The result means, that the VIS-channel of Meteosat-2 at the beginning of its lifetime is about 15% more sensitive than that of Meteosat-1 was at its end.     

Dark quark `stars': do they matter for Ωmatter?

The structure of a spherically symmetric stable dark `star' is discussed, at zero temperature, containing 1) a core of quarks in the deconfined phase and antileptons 2) a shell of hadrons in particular n, p, and <sup>–</sup> and leptons or antileptons and 3) a shell of hydrogen in the superfluid phase. If the superfluid hydrogen phase goes over into the electromagnetic plasma phase at densities well below one atom (10 fm)<sup>3</sup>, as is usually assumed, the hydrogen shell is insignificant for the mass and the radius of the `star'. These quantities are then determined approximatively: mass = 1.8 solar masses, radius = 9.2 km.     

The Sixth Catalogue of galactic Wolf-Rayet stars,their past and present

This paper presents the Sixth Catalogue of galactic Wolf-Rayet stars (Pop. I), a short history on the five earlier WR catalogues, improved spectral classification, finding charts, a discussion on related objects, and a review of the current status of Wolf-Rayet star research.The appendix presents a bibliography on most of the Wolf-Rayet literature published since 1867.Visiting astronomer, Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory.Visiting astronomer, European Southern Observatory.     

The core helium flash

The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required.Our core helium flash is violent, producing a deflagration wave. This differs from the detonation wave (and subsequent disruption of the entire star) produced in previous spherically symmetric violent core helium flashes as the second dimension provides a degree of relief which allows the expansion wave to decouple itself from the burning front. Our results predict that a considerable amount of helium in the core will be burned before the horizontal branch is reached and that some envelope mass loss is likely.     

Global space exploration 2025: Europe's perspectives for partnerships

Space exploration is an emblematic domain of space activities where traditionally only established space powers have been active. However, new actors are demonstrating great interest in it, principally for international prestige reasons, with an increasing number making ambitious plans. Complementing national endeavours, international cooperation has become a central element of most countries' exploration strategy, since the costs of doing it alone are so great. Europe's development into a fully fledged actor in space exploration requires a shared assessment of the future challenges, threats and opportunities with which it will be confronted in order to derive the best options for cooperation to lead and anticipate rather than follow and endure change.