Promoting research and education in basic space science: the approach of the UN/ESA workshops

UN-affiliated regional centres for space science and technology education are being established or are in operation in Africa (Morocco, Nigeria), Asia and the Pacific (India), Latin America and the Caribbean (Brazil, Mexico), and Western Asia (Jordan). Education curricula at the university level, embracing remote sensing, satellite communications, satellite meteorology, and space science have been developed for these centres. This article briefly reports on the structure of the most recent updated education curricula in the four disciplines that have been made available for implementation in 2002 and 2003, in the six official languages of the United Nations. This is also an effort to bridge the gap between such education curricula as they vary significantly between nations and among educational institutions in nations.     

Investigation of dynamics of discrete framed structures by a numerical wave-based method and an analytical homogenization approach

In this article, the analytical homogenization method of periodic discrete media (HPDM) and the numerical condensed wave finite element method (CWFEM) are employed to study the lon-gitudinal and transverse vibrations of framed structures. The valid frequency range of the HPDM is re-evaluated using the wave propagation feature identified by the CWFEM. The relative error of the wavenumber by the HPDM compared to that by the CWFEM is illustrated in functions of fre-quency and scale ratio. A parametric study on the thickness of the structure is carried out where the dispersion relation and the relative error are given for three different thicknesses. The dynamics of a finite structure such as natural frequency and forced response are also investigated using the HPDM and the CWFEM.     

The soft X-ray superoutburst of VW hydri: 14 second periodicity

EXOSAT observations of the dwarf nova VW Hydri reveal a strong soft X-ray flux during optical superoutburst. The onset of the X-ray outburst was delayed by 2.5 days compared to the optical outburst. A modulation of the extreme soft X-ray flux was detected, consistent with a coherent (0 >x 10⁷) pulsation with a period of 14.07 seconds, probably reflecting the rotation period of the white dwarf.IIf this is indeed the case, VW Hydri is the fastest rotating white dwarf detected so far.     

Progress in basic space science education and research: The UNBSSI

This report describes recent progress in the UN Basic Space Science Initiative (UNBSSI), which aims to facilitate space science education and research, and attendant resources in developing countries. In addition to holding workshops across the developing world, the UN Committee on the Peaceful Uses of Outer Space (COPUOS) successfully implemented the International Heliophysical Year (IHY) as a catalyst for improving understanding of the Sun and of solar-terrestrial physics. Building on this it is now preparing for the International Space Weather Initiative (ISWI). Achievements of the former are discussed, as are the goals and anticipated activities of the latter.     

Plasma and electromagnetic wave simulations of meteors

Every day billions of meteoroids impact and disintegrate in the Earth’s atmosphere. Current estimates for this global meteor flux vary from 2000 to 200,000 tons per year, and estimates for the average velocity range between 10 km/s and 70 km/s. The basic properties of this global meteor flux, such as the average mass, velocity, and chemical composition remain poorly constrained. We believe much of the mystery surrounding the basic parameters of the interplanetary meteor flux exists for the following reason, the unknown sampling characteristics of different radar meteor observation techniques, which are used to derive or constrain most models. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. We present our results on meteor plasmas simulations of head echoes using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross section of the simulated meteor plasmas. These simulations have shown that the radar cross section depends in a complex manner on a number of parameters. These include the angle between radar and meteor entry, a large dependence on radar frequency, which shows that for a given meteor plasma size and density, the reflectivity as a function of probing radar frequency varies, but typically peaks below 100 MHz.     

Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites

Of the terrestrial planets, Earth and Mercury have self-sustained fields while Mars and Venus do not. Magnetic field data recorded at Ganymede have been interpreted as evidence of a self-generated magnetic field. The other icy Galilean satellites have magnetic fields induced in their subsurface oceans while Io and the Saturnian satellite Titan apparently are lacking magnetic fields of internal origin altogether. Parts of the lunar crust are remanently magnetized as are parts of the crust of Mars. While it is widely accepted that the magnetization of the Martian crust has been caused by an early magnetic field, for the Moon alternative explanations link the magnetization to plasma generated by large impacts. The necessary conditions for a dynamo in the terrestrial planets and satellites are the existence of an iron-rich core that is undergoing intense fluid motion. It is widely accepted that the fluid motion is caused by convection driven either by thermal buoyancy or by chemical buoyancy or by both. The chemical buoyancy is released upon the growth of an inner core. The latter requires a light alloying element in the core that is enriched in the outer core as the solid inner core grows. In most models, the light alloying element is assumed to be sulfur, but other elements such as, e.g., oxygen, silicon, and hydrogen are possible. The existence of cores in the terrestrial planets is either proven beyond reasonable doubt (Earth, Mars, and Mercury) or the case for a core is compelling as for Venus and the Moon. The Galilean satellites Io and Ganymede are likely to have cores judging from Galileo radio tracking data of the gravity fields of these satellites. The case is less clear cut for Europa. Callisto is widely taken as undifferentiated or only partially differentiated, thereby lacking an iron-rich core. Whether or not Titan has a core is not known at the present time. The terrestrial planets that do have magnetic fields either have a well-established inner core with known radius and density such as Earth or are widely agreed to have an inner core such as Mercury. The absence of an inner core in Venus, Mars, and the Moon (terrestrial bodies that lack fields) is not as well established although considered likely. The composition of the Martian core may be close to the Fe–FeS eutectic which would prevent an inner core to grow as long as the core has not cooled to temperatures around 1500 Kelvin. Venus may be on the verge of growing an inner core in which case a chemical dynamo may begin to operate in the geologically near future. The remanent magnetization of the Martian and the lunar crust is evidence for a dynamo in Mars’ and possibly the Moon’s early evolution and suggests that powerful thermally driven dynamos are possible. Both the thermally and the chemically driven dynamo require that the core is cooled at a sufficient rate by the mantle. For the thermally driven dynamo, the heat flow from the core into the mantle must by larger than the heat conducted along the core adiabat to allow a convecting core. This threshold is a few mW?m^?2 for small planets such as Mercury, Ganymede, and the Moon but can be as large as a few tens mW?m^?2 for Earth and Venus. The buoyancy for both dynamos must be sufficiently strong to overcome Ohmic dissipation. On Earth, plate tectonics and mantle convection cool the core efficiently. Stagnant lid convection on Mars and Venus are less efficient to cool the core but it is possible and has been suggested that Mars had plate tectonics in its early evolution and that Venus has experienced episodic resurfacing and mantle turnover. Both may have had profound implications for the evolution of the cores of these planets. It is even possible that inner cores started to grow in Mars and Venus but that the growth was frustrated as the mantles heated following the cessation of plate tectonics and resurfacing. The generation of Ganymede’s magnetic field is widely debated. Models range from magneto-hydrodynamic convection in which case the field will not be self-sustained to chemical and thermally-driven dynamos. The wide range of possible compositions for Ganymede’s core allows models with a completely liquid near eutectic Fe–FeS composition as well as models with Fe inner cores or cores in with iron snowfall.     

Modelling and simulation of the space mission MICROSCOPE

MICROSCOPE is a French space mission for testing the weak equivalence principle (WEP). The mission goal is the determination of the Eötvös parameter $\eta$ with an accuracy of 10^?15. The French space agency CNES is responsible for the satellite which is developed and produced within the Myriade series. The satellite's payload T-SAGE (Twin Space Accelerometer for Gravitation Experimentation) is developed and built by the French institute ONERA. It consists of two high-precision capacitive differential accelerometers. One accelerometer is used as reference sensor with two test masses of platinum, the science sensor contains a platinum and a titanium proof mass. The detection of the test mass movement and their control is done via a complex electrode system. As a member of the MICROSCOPE performance team, the German department ZARM will be involved in the data analysis of the MICROSCOPE mission. For this purpose, mission simulations and the preparation of the mission data evaluation in close cooperation with the French partners CNES, ONERA and OCA are realised. The development status of the simulation tool which will represent the complex spacecraft dynamics and all error sources in order to design and test data reduction procedures is presented and some features are discussed in detail.     

Experimental investigation of hot and cold side jet interaction with a supersonic cross-flow

This paper reports on experimental aerodynamic investigations on a high-speed missile with side jet control especially with regard to the interaction of cold and hot side jets with supersonic cross-flow. The hot jets were generated with solid propellants. To analyze the effect of the hot jet in relation to side jet control, wall pressure distributions were measured in the area of jet interaction. As a test parameter, the jet pressure ratio was varied and schlieren images were taken to visualize the shocks. In addition, the development of large-scale vortex structures on hot gas jets was detected with high-speed videos. The frame sequences show periodical turbulent jet structures and permit the manual evaluation of their spatial distribution. Analyzing the images, the convection velocities of the large-scale structures and their convection angles were determined. The convection velocities reach the magnitude of cross-flow velocity shortly behind the hot jet exit.