Electrical behavior of a Shuttle Electrodynamic Tether System (SETS)

Many novel electrodynamic and space plasma physics experiments can be done from the space shuttle using a gravity gradient stabilized sub-satellite tethered 10–30 km above the Orbiter via a long, conducting wire which is insulated from the ionospheric plasma. This system, called the Shuttle Electrodynamic Tether System (SETS), is described in the present paper with emphasis upon the various electrical processes which determine its coupling to the ambient plasma. The three most important physical effects include sheath formation and electron collection by the sub-satellite, the generation of a large emf through the orbital motion of the tether across geomagnetic field lines, and the active ejection of electrons from the Orbiter into the surrounding ionosphere. An electrical circuit analogy is presented for SETS together with a brief outline of possible areas related to the artificial generation of magnetohydrodynamic waves.     

Measurements of the thermal plasma environment of the space shuttle

The paper presents some initial results on measurements of the thermal plasma environment obtained by a spherical retarding potential analyzer and a Langmuir probe flown on the third space shuttle flight (STS-3) as part of the NASA Office of Space Science-1 (OSS-1) payload in March 1982. One of the major effects observed is a higher degree of turbulence in the ambient plasma compared to what is observed from similar instruments flown on unmanned satellites. In addition we see the temperature of the thermal electrons elevated to values of 4000–5000 K. Associated with elevated electron temperatures are regions of enhanced plasma density resulting from the appearance of high densities of molecular ions. The thermal plasma data also show clear effects of an induced V × B · L potential at the location of the probes which matches that produced by an L vector linking the probes to the engine nozzles; thereby establishing the prime return current location on the Orbiter. The final observations discussed are the pronounced and complex wake effects resulting both from the main structure of the Orbiter and from the complex shapes of appendages attached to the Orbiter.     

The diversity of diversity: a critique of geodemographic classification

We report on an examination of two geodemographic classification systems based on an analysis of 1991 census variables, for districts, wards and census enumeration districts in England and Wales. We also review the associations among the variables examined, the extent to which certain underlying components might account for the overall variation and the types of areas that are least typical. The results show that small areas are different in many different ways; a few dimensions cannot provide enough information to describe an area fully. Diversity on most scales remains even after geodemographicclassification, emphasizing the advantages of task-specific classification.     

Backus averaging,scattering and drift1

Differences between traveltimes from sonic to seismic frequencies, commonly known as drift, can be attributed to a combination of multiple scattering and absorption. The portion due to scattering can be estimated directly by calculating synthetic seismograms from sonic logs. A simple alternative approach is suggested by the long-wave equivalent averaging formulae for the effective elastic properties of a stack of thin layers, which gives the same traveltime delays as the low-frequency limit of the scattering dispersion. We consider the application of these averaging formulae over a frequency-dependent window with the hope of extending their use to frequencies higher than those allowed by the original validity conditions. However, comparison of the time delay due to window-averaging with the scattering dispersion predicted by the O'Doherty-Anstey formula reveals that it is not possible to specify a form of window that will fit the dispersion across the spectrum for arbitrary log statistics. A window with a width proportional to the wavelength squared matches the behaviour at the low-frequency end of the dispersive range for most logs, and allows an almost exact match of the drift across the entire spectrum for exponential correlation functions. We examine a real log, taken from a hole in nearly plane-layered geology, which displays strong quasi-cyclical variations on one scale as well as more random, smaller-scale fluctuations. The details of its drift behaviour are studied using simple models of the gross features. The form of window which gave a good theoretical fit to the dispersion for an exponential log correlation function can only fit the computed drift at high or low frequencies, confirming that there are at least two significant scale-lengths of fluctuation. A better overall fit is obtained for a window whose width is proportional to the wavelength. The calculated scattering drift is significantly less than that observed from a vertical seismic profile, but the difference cannot be wholly ascribed to absorption. This is because the source frequency of the sonic tool is not appropriate for its resolution (receiver spacing) so that the scattering drift from sonic to seismic frequencies cannot be fully estimated from the layer model derived from the log.     

Precision orbit computations for Starlette

The Starlette satellite, launched in February 1975 by the French Centre National d'Etudes Spatiales, was designed to minimize the effects of non-gravitational forces and to obtain the highest possible accuracy for laser range measurements. Analyses of the first four months of laser tracking data from nine stations. have confirmed the stability of the orbit and the precision to which the satellite's position can be established. Initial orbit computations using the GSFC GEM-7 gravity model produced rms fits of about 8 to 10 meters for arc lengths of 5 days. After tailoring a gravity model specifically to Starlette, the rms fits for the 5 day arcs were reduced significantly to the 1 to 2 meter level. An rms fit of 4.3 meters was obtained for a 90 day arc. Five day arcs overlapped by 2.5 days showed rms satellite position differences generally less than 2 meters. Prediction errors at the end of two months were less than 30 milliseconds.     

Implications from inclusions in topaz for greisenisation and mineralisation in the Hensbarrow topaz granite, Cornwall, England

Textural and geochemical studies of inclusions in topaz from greisens in the Hensbarrow topaz granite stock (St. Austell, Cornwall) are used to constrain the composition of fluids responsible for late stage greisening and mineralisation. The topaz contains an abundant and varied suite of inclusions including aqueous liquid + vapour (L + V), quartz, zinnwaldite, albite, K-feldspar, muscovite, ilmenorutile, apatite, columbite, zircon, varlamoffite [(Sn, Fe)(O, OH)₂] and qitianlingite [(Fe⁺²,Mn⁺²)₂(Nb,Ta)₂W⁺⁶O₁₀]. Primary L + V inclusions in topaz show relatively high T _h (mainly 300 to >500 °C) and a narrow range of salinities (23–30 wt % NaCl equivalent) compared with those in greisen quartz (150–450 °C, 0–50 wt % NaCl equivalent). Textures indicate that topaz formed earlier than quartz and the fluid inclusion data are interpreted as indicating a cooling of the hydrothermal fluids during greisenisation, mixing with meteoric waters and a decrease in pressure causing intermittent boiling. The presence of early-formed albite and K-feldspar as inclusions in the topaz is likely to indicate that the greisen-forming fluid became progressively more acid during greisenisation. The most distinctive inclusions in the topaz are wisp- and bleb-shaped quartz, < 50 μm in size, which show textural characteristics indicating former high degrees of plasticity. They often have multiple shrinkage bubbles at their margins rich in Sn, Fe, Mn, S and Cl and, more rarely, contain euhedral albite, K-feldspar, stannite or pyrrhotite crystals up to 40 μm in size. The quartz inclusions show similar morphologies to inclusions in topaz from quartz-topaz rocks elsewhere which have been interpreted as trapped “silicate melt”. Their compositions are, however, very different to those expected for late stage topaz-normative granitic melts. From their textural and chemical characteristics they are interpreted as representing crystallised silica colloid, probably trapped as a hydro gel during greisenisation. There is also evidence for the colloidal origin of inclusions of varlamoffite in the topaz. These occurrences offer the first reported evidence in natural systems for the formation of colloids in high temperature hydrothermal fluids. Their high ore carrying potential is suggested by the presence of varlamoffite and the occurrence of stannite, pyrrhotite and SnCl within the quartz inclusions. Received: 9 April 1996 / Accepted: 12 November 1996     

Marine administration and spatial data infrastructure

This paper reviews the emergence of the spatial dimension of marine and coastal zone administration, and examines several initiatives around the world that contribute to this idea. Spatial data have been recognised as an important resource to improve decision-making and resource management in both the land and marine environments in terms of sustainable development. Many countries are developing Spatial Data Infrastructures (SDIs) to improve access and sharing of spatial data, however, most of these initiatives stop at the coastline. Recently, global and regional activities such as the 3rd United Nations Convention on the Law of the Sea (UNCLOS) and the Sustainable Development Strategy for the Seas of East Asia (SDS-SEA) have brought to international attention the importance of effective administration of the marine and coastal environments.