Avoiding collisions: the Spaceguard Foundation

The Earth has a long and violent history of collisions with extraterrestrial bodies such as asteroids and comet nuclei. Several of these impacts have been large enough to produce major environmental changes, causing mass extinctions and severe alterations to weather patterns and geography. There is no reason to suppose that the likelihood of such collisions will be any less in the future and the spread of human settlement, civilisation, and particularly urbanisation, makes it much more likely that a future impact, even relatively small, could result in the massive loss of human life and property. Despite the fact that the technology exists to predict and to some extent prevent such events, there is currently no co-ordinated international response to this threat. This article presents a realistic assessment of the threat to Earth from NEOs, describes the (underfunded) efforts so far made to counter it and makes a plea for further action to produce a fully functioning Spaceguard Foundation.     

Double Langmuir Probes for Hypervelocity Wakes

Double Langmuir probes have been used to measure the ionization intensity in the wake of a hypervelocity projectile; subsidiary experiments to check the validity of the results are described. The spectral characteristic of the fluctuating part of the probe signal has been examined. Because of theoretical and experimental difficulties the results can at most be regarded as giving a qualitative picture of the turbulent structure of the wake. They do show, however, the predominant part played by eddies of roughly the wake diameter, agreeing on the average with the results of Clay et al. [1].     

The Student Dust Counter on the New Horizons Mission

The Student Dust Counter (SDC) experiment of the New Horizons Mission is an impact dust detector to map the spatial and size distribution of dust along the trajectory of the spacecraft across the solar system. The sensors are thin, permanently polarized polyvinylidene fluoride (PVDF) plastic films that generate an electrical signal when dust particles penetrate their surface. SDC is capable of detecting particles with masses m>10^?12 g, and it has a total sensitive surface area of about 0.1 m², pointing most of the time close to the ram direction of the spacecraft. SDC is part of the Education and Public Outreach (EPO) effort of this mission. The instrument was designed, built, tested, integrated, and now is operated by students.