BNSC/RAS Town Meeting

In London on 20 September, the British National Space Centre and the Royal Astronomical Society convened a ‘Town Meeting’, a usage picked up from NASA. Basically it was a debate without the competetive element, whose topic was the next two of the European Space Agency's four ‘Cornestone’ projects for the ‘Horizon 2000’ programme, total budget 584 million ECU (about £467 million). The question in September was which would be no. 3 and which no. 4. Duncan Lunan reports on the discussion and the choices made.     

Meteoroid orbits

Numerically-speaking, the orbits of meteoroids dominate our knowledge of the orbital parameters of Earth-crossing small bodies: the meteoroid orbit database outstrips the numbers of observed Earth-crossing asteroids and comets by over two orders of magnitude. Whilst it is often imagined that small meteoroids are predominantly derived from comets through stream formation, and thus must have comet-like orbits, in fact the majority of observed meteoroid orbits are more similar to those of Apollo and Aten asteroids, with small, low-inclination orbits. In all about 69 000 meteoroid orbits are available from the IAU Meteor Data Center in Lund, Sweden, having been measured in various optical and radar observation programs based in the U.S.A., Canada, the former Soviet Union, Somalia, the Czech Republic, Japan, and Australia. Depending upon the detection method used, the original meteoroids producing the observed meteoric phenomena range in size from 100 m to 10 cm. Here the raw orbital, radiant and speed distributions are presented for the major surveys, a common format being used so that they may be intercompared such that general conclusions may be drawn, and the differences between the survey results identified. These data, collected over the past several decades, provide an important source of information on the origin and evolution of the small bodies in the solar system.     

A system for obstacle detection during rotorcraft low altitudeflight

An airborne vehicle such as a rotorcraft must avoid obstacles like antennas, towers, poles, fences, tree branches, and wires strung across the flight path. Automatic detection of the obstacles and generation of appropriate guidance and control actions for the vehicle to avoid these obstacles would facilitate autonomous navigation. The requirements of an obstacle detection system for rotorcraft in low-altitude Nap-of-the-Earth (NOE) flight based on various rotorcraft motion constraints is analyzed here in detail. It is argued that an automated obstacle detection system for the rotorcraft scenario should include both passive and active sensors to be effective. Consequently, it introduces a maximally passive system which involves the use of passive sensors (TV, FLIR) as well as the selective use of an active (laser) sensor. The passive component is concerned with estimating range using optical flow-based motion analysis and binocular stereo. The optical flow-based motion analysis that is combined with on-board inertial navigation system (INS) to compute ranges to visible scene points is described. Experimental results obtained using land vehicle data illustrate the particular approach to motion analysis     

Overlapping search with scanned beam applications

Acquisition and false acquisition probabilities are derived for search including overlap between observation regions. (Gap-free search, important in many applications, frequently involves overlap.) Search patterns are included, together with system parameters and observation sequences minimizing search time. Design curves applicable to laser, radar, sonar, and other methods are used in practical examples. These examples, accounting for beam shape and receiver characteristics, show that the small overlap in these patterns compensates for beam edge effects     

The Effect of Ground Reflections and Scattering on an Interferometer Direction Finder

The azimuth and elevation angles of an airborne beacon transmitter can be determined using a direction finder comprised of two orthogonal interferometers located near the earth's surface. In this paper we consider the reflection of the incident electromagnetic field by the earth's surface and the resultant effect on the direction-finding system. The analysis yields an upper bound or limit to the interferometer phase error and the corresponding error in bearing angle that can result because of specular reflection and diffuse scattering.     

鲁南机床:在国产高端装备发展之路上越走越好

经过后金融危机环境下市场经济的考验,山东鲁南机床有限公司在发展中调整,在调整中谋发展.该公司董事长徐龙泉说,结构决定机体的科学合理性和适应性,即生命力,结构决定成败,结构优则事半功倍.延续十一五发展思路,十二五期间,鲁南机床将努力实现由生产制造型企业向服务制造型企业转型.通过优化产品结构,进一步提高产品结构质量,提升产品档次,推进高档产品的产业化发展,为精准制造和企业整体素质的全面提升夯实基础.     

Promoting UK involvement in the ISS: a space station lifeboat?

The Space Development Council, an organisation of UK space interest groups, is calling for Britain to become re-involved in manned spaceflight. NASA previously offered UK astronaut training in return for participation in the X-38 Crew Return Vehicle, now postponed. A one-person return vehicle might provide an effective and useful alternative. Two designs have been put forward based on Waverider, at one time proposed to be the man-carrying payload for Blue Streak. The more sophisticated of the two is a flex-wing Waverider carrying a one-person escape capsule, designed for long-term on-orbit storage.     

Face-dependent impact probabilities, velocities and angles upon LDEF by space debris and natural meteoroids

For specified geocentric orbits the impact probabilities, velocities and angles upon the different faces of the Long Duration Exposure Facility (LDEF) are calculated, and it is found that quite different distributions of micro-cratering are to be expected. In particular the flux to the East (leading) face should exceed that to the West (trailing) face by a very large ratio. The North and South faces receive exposures slightly in excess of the East face for lower-velocity impacts from low-inclination orbits, but much lower exposures than the East face for high-velocity impacts from high-inclination orbits. The Space face (pointing directly away from the Earth) and the Earth face (pointing directly towards the Earth) will have been subject to very few impacts from geocentric orbits. Therefore, whilst three sides (the East, North and South) will have been hit many times by artificial space debris, the other three (the West, Space and Earth) will have been impacted almost solely by natural meteoroids from heliocentric orbits, and may be used to determine the flux of such particles in the vicinity of the Earth. The ratios of impacts upon the East, West and Space faces will be useful indicators of the velocity/orbit distribution of meteoroids.