Planetary science: Tunguska at 100
The most dramatic cosmic impact in recent history has gathered up almost as many weird explanations as it knocked down trees, writes Duncan Steel.
Synergistic approach of asteroid exploitation and planetary protection
The asteroid and cometary impact hazard has long been recognised as an important issue requiring risk assessment and contingency planning. At the same time asteroids have also been acknowledged as possible sources of raw materials for future large-scale space engineering ventures. This paper explores possible synergies between these two apparently opposed views; planetary protection and space resource exploitation. In particular, the paper assumes a 5 tonne low-thrust spacecraft as a baseline for asteroid deflection and capture (or resource transport) missions. The system is assumed to land on the asteroid and provide a continuous thrust able to modify the orbit of the asteroid according to the mission objective. The paper analyses the capability of such a near-term system to provide both planetary protection and asteroid resources to Earth. Results show that a 5 tonne spacecraft could provide a high level of protection for modest impact hazards: airburst and local damage events (caused by 15–170 m diameter objects). At the same time, the same spacecraft could also be used to transport to bound Earth orbits significant quantities of material through judicious use of orbital dynamics and passively safe aero-capture manoeuvres or low energy ballistic capture. As will be shown, a 5 tonne low-thrust spacecraft could potentially transport between 12 and 350 times its own mass of asteroid resources by means of ballistic capture or aero-capture trajectories that pose very low dynamical pressures on the object.
XV. Notes on the Geological Survey Memoir—“The Geology of the Glasgow District.”
Introductory. During the late summer the Geological Survey issued a map of the Glasgow district which will prove a boon not only to the members of this Society, but also to the increasing number of those who, although not members, still take an interest in geology as a branch of liberal education. The present map differs from its predecessors in that it is colour-printed, and the printing and general details are brought out more clearly than was possible in the hand-coloured maps. This fact has been taken advantage of to add an enormous amount of detail, which is often of such a minute character that after study one feels inclined to wish that he were gifted with microscopic eyes or that the map had been drawn to a larger scale. Not the least of its benefits is the low price at which it is sold (2s. on paper, and 3s. on cloth), the price of the previous maps having lately become prohibitive (19s. 3d. on paper). It will be observed that the long way of the map is from north to south. This has doubtless been adopted for good and sufficient reasons, if we only knew them; but I, at least, would have preferred that the long way should have been east and west, with Glasgow in the centre. The map is accompanied by an extensive memoir of the geology of the district, and the more one reads of it the more one is impressed with the This 250-word extract was created in the absence of an abstract