Publication archive

Publication archive

The fourteenth day of January 2005 was one of mankind's major milestones, which, like most milestones probably, passed unnoticed by the vast majority. On this day, at 11:30 UTC a spacecraft from planet Earth landed on the surface of Titan, after a journey of more than 3,000,000,000 km. There, the probe remained busy for its short lifetime of a mere seventy minutes before it fell into an eternal sleep. That probe was Huygens, and this article describes the Cassini-Huygens mission and some of the results it returned about the mysterious moon, Titan.

This article is based on a talk given by Professor Nicolas Thomas of the Physikalisches Institut of the Universität Bern to the Pro ISSI.
Published: 01 November 2005

Abstract

The Solar Orbiter mission is presently in assessment phase by the Science Payload and Advanced Concepts Office of the European Space Agency. The mission is confirmed in the Cosmic Vision programme, with the objective of a launch in October 2013 and no later than May 2015. The Solar Orbiter mission incorporates both a near-Sun (~0.22 AU) and a high-latitude (~ 35 deg) phase, posing new challenges in terms of protection from the intense solar radiation and related spacecraft thermal control, to remain compatible with the programmatic constraints of a medium class mission. This paper provides an overview of the assessment study activities, with specific emphasis on the definition of the model payload and its accommodation in the spacecraft. The main results of the industrial activities conducted with Alcatel Space and EADS-Astrium are summarized.
Published: 01 August 2005
We discuss the potential benefits of using compound semiconductors for the detection of X- and gamma-ray radiation. While Si and Ge have become detection standards for energy dispersive spectroscopy in the laboratory, their use for an increasing range of applications is becoming marginalized by one or more of their physical limitations; namely the need for ancillary cooling systems or bulky cryogenics, their modest stopping powers and radiation intolerance. Compound semiconductors encompass such a wide range of physical properties that it is technically feasible to engineer a material to any application. Wide band-gap compounds offer the ability to operate in a wide range of thermal and radiation environments, whilst still maintaining sub-keV spectral resolution at hard X-ray wavelengths. Narrow band-gap materials, on the other hand, offer the potential of exceeding the spectral resolution of both Si and Ge, by as much as a factor of 3. Assuming that the total system noise can be reduced to a level commensurate with Fano noise, spectroscopic detectors could work in the XUV, effectively bridging the gap between the ultraviolet and soft X-ray wavebands. Thus, in principle, compound semiconductor detectors can provide continuous spectroscopic coverage from the far infrared through to gamma-ray wavelengths. However, while they are routinely used at infrared and optical wavelengths, in other bands, their development has been plagued by material and fabrication problems. This is particularly true at hard X- and gamma-ray wavelengths, where only a few compounds (e.g., GaAs, CdZnTe and HgI2) have evolved sufficiently to produce working detection systems. In this paper, we examine the current status of research in compound semiconductors and by a careful examination of material properties and future requirements, recommend a number of compounds for further development.
Published: 22 September 2004

Ten to twenty years from now, a succession of clever new spacecraft will need to be ready to fly in ESA's continuing Science Programme, now called Cosmic Vision. They will tackle some of the big scientific questions that are high on the agenda of research across Europe (and, indeed, worldwide) concerning the Universe and our place in it:

  • what are the conditions for planet formation and the emergence of life?
  • how does the Solar System work?
  • what are the fundamental physical laws of the Universe?
  • how did the Universe originate and what is it made of?

This brochure gives a detailed overview of the Cosmic Vision 2015-2025 plan. The opportunities under the above four main headings are presented, and specific aspects of each general theme that are judged to be especially ripe for investigation by new space tools in the period 2015-2025 are identified. A review of the technology that will have to be developed is given.

The presented planning on behalf of the scientific community and aerospace industry takes into account the Science Directorate's preliminary reckoning of the practical constraints of technology. In the section 'Proposed Strategies and Their Implementation', the outcome of these deliberations is summarised in four tables that correspond to the above four key questions.

Published: 16 October 2005
Comets spend most of their life in a low-temperature environment far from the Sun. They are therefore relatively unprocessed and maintain information about the formation conditions of the planetary system, but the structure and composition of their nuclei are poorly understood. Although in situ and remote measurements have derived the global properties of some cometary nuclei, little is known about their interiors. The Deep Impact mission shot a projectile into comet 9P/Tempel 1 in order to investigate its interior. Here we report the water vapour content (1.5x1032 water molecules or 4.5x 106 kg) and the cross-section of the dust (330km² assuming an albedo of 0.1) created by the impact. The corresponding dust/ice mass ratio is probably larger than one, suggesting that comets are 'icy dirtballs' rather than 'dirty snowballs' as commonly believed. High dust velocities (between 110ms-1 and 300ms-1) imply acceleration in the comet's coma, probably by water molecules sublimated by solar radiation. We did not find evidence of enhanced activity of 9P/Tempel 1 in the days after the impact, suggesting that in general impacts of meteoroids are not the cause of cometary outbursts.
Published: 14 October 2005
Reprinted from Space Science Reviews, Volume 118, Nos. 1-4, 2005. Contents:
  • The Near-Earth Solar Wind
    M. L. Goldstein, et al.
  • The Foreshock
    J. P. Eastwood, et al.
  • The Magnetosheath
    E. A. Lucek, et al.
  • Cluster at the Bow Shock: Introduction
    A. Balogh, et al.
  • Quasi-perpendicular Shock Structure and Processes
    S. D. Bale, et al.
  • Quasi-parallel Shock Structure and Processes
    D. Burgess, et al.
  • Cluster at the Bow Shock: Status and Outlook
    M. Scholer, et al.
  • Magnetopause and Boundary Layer
    J. Keyser, et al.
  • Cluster at the Magnetospheric Cusps
    P. J. Cargill, et al.
  • Magnetopause Processes
    T. D. Phan, et al.
Published: 16 September 2005
A little more than four years after its launch, the first magnetospheric, multi-satellite mission Cluster has already tremendously contributed to our understanding about the coupled solar wind - magnetosphere - ionosphere system. This is mostly due to its ability, for the first time, to provide instantaneous spatial views of structures in the system, to separate temporal and spatial variations, and to derive velocities and directions of moving structures. Ground-based data have an important complementary impact on Cluster-related research, as they provide a larger-scale context to put the spacecraft data in, allow to virtually enlarge the spacecrafts' field of view, and make it possible to study in detail the coupling between the magnetosphere and the ionosphere in a spatially extended domain. With this paper we present an interim review of cooperative research done with Cluster and ground-based instruments, including the support of other space-based data. We first give a short overview of the instrumentation used, and present some specific data analysis and modeling techniques that have been devised for the combined analysis of Cluster and ground-based data. Then we review highlighted results of the research using Cluster and ground-based data, ordered into dayside and nightside processes. Such highlights include, for example, the identification of the spatio-temporal signatures of the different modes of reconnection on the dayside, and the detailed analysis of the electrodynamic magnetosphere-ionosphere coupling of bursty bulk flows in the tail plasma sheet on the nightside. The aim of this paper is to provide a "sourcebook" for the Cluster and ground-based community that summarises the work that has been done in this field of research, and to identify open questions and possible directions for future studies.
Published: 16 September 2005
Turbulence in fluids and plasmas is a ubiquitous phenomenon driven by a variety of sources-currents, sheared flows, gradients in density and temperature, and so on. Turbulence involves fluctuations of physical properties on many different scales, which interact nonlinearly to produce self-organized structures in the form of vortices. Vortex motion in fluids and magnetized plasmas is typically governed by nonlinear equations, examples of which include the Navier-Stokes equation, the Charney-Hasegawa-Mima equations and their numerous generalizations. These nonlinear equations admit solutions in the form of different types of vortices that are frequently observed in a variety of contexts: in atmospheres, in oceans and planetary systems, in the heliosphere, in the Earth's ionosphere and magnetosphere, and in laboratory plasma experiments. Here we report the discovery by the Cluster satellites of a distinct class of vortex motion-short-scale drift-kinetic Alfvén (DKA) vortices-in the Earth's magnetospheric cusp region. As is the case for the larger Kelvin-Helmholtz vortices observed previously, these dynamic structures should provide a channel for transporting plasma particles and energy through the magnetospheric boundary layers.
Published: 12 August 2005
The Van Allen radiation belts are two regions encircling the Earth in which energetic charged particles are trapped inside the Earth's magnetic field. Their properties vary according to solar activity and they represent a hazard to satellites and humans in space. An important challenge has been to explain how the charged particles within these belts are accelerated to very high energies of several million electron volts. Here we show, on the basis of the analysis of a rare event where the outer radiation belt was depleted and then re-formed closer to the Earth, that the long established theory of acceleration by radial diffusion is inadequate; the electrons are accelerated more effectively by electromagnetic waves at frequencies of a few kilohertz. Wave acceleration can increase the electron flux by more than three orders of magnitude over the observed timescale of one to two days, more than sufficient to explain the new radiation belt. Wave acceleration could also be important for Jupiter, Saturn and other astrophysical objects with magnetic fields.
Published: 09 September 2005
The four-satellite Cluster mission serves as both a 'Microscope' and a 'telescope' for magnetospheric scientists. Using its suite of state-of-the-art instruments, it is providing a close-up view of complex smallscale physical processes occurring around the Earth. These processes are often reflections of other, sometimes violent processes that are taking place much further away from our spacecraft, which means that Cluster also serves as a 'telescope' for observing those more distant processes.
Published: 15 February 2005
In proceedings of the 4th International Spacecraft Propulsion Conference (ESA SP-555). 2-9 June, 2004, Chia Laguna (Cagliari), Sardinia, Italy. Editor: A.Wilson. Published on CDROM., p.88.1

ESA's ambition of inter-planetary exploration using a fast-track low cost industrial programme was well achieved with Mars Express. Reusing the platform architecture for the service module and specifically the Propulsion system enabled Venus Express to benefit from several lessons learnt from the Mars Express experience. Using all existing components qualified for previous programmes, many of them commercial telecommunication spacecraft programmes with components available from stock, an industrial organisation familiar from Mars Express was able to compress the schedule to make the November 2005 launch window a realistic target. While initial inspection of the CPS schematic indicates a modified Eurostar type architecture, - a similar system using some Eurostar components - would be a fairer description. The use of many parts of the system on arrival at the destination (Mars or Venus in this case) is a departure from the usual mode of operation, where many components are used during the initial few weeks of GTO or GEO. The system modifications over the basic Eurostar system have catered for this in terms of reliability contingencies by replacing components, or providing different levels of test capability or isolation in flight. This paper aims to provide an introduction to the system, address the evolution from Eurostar, and provide an initial assessment of the success of these modifications using the Mars Express experience, and how measures have been adopted specifically for Venus Express.

Published: 16 October 2004
In proceedings of the 4th International Spacecraft Propulsion Conference (ESA SP-555), 2-9 June, 2004, Chia Laguna (Cagliari), Sardinia, Italy. Editor: A.Wilson. Published on CDROM., p.115.1

An insufficient amount of pressurant gas in the propulsion system or a working temperature in the pressurant tank outside the qualification limits can cause a decrease in the performance of the thrusters or even the loss of the mission. This paper presents an engineering tool used able to compute the Pressurant budget of a mission and the effects of influencing parameters. The updated tool allows to also compute the temperature, pressure and mass evolution inside the pressurant tank during the various mission phases. The tool has been used to verify the calculations done by Astrium Stevenage for Mars Express and Venus Express. The pressurant gas used for both cases was helium. The tool permits to use other combinations of pressurant gases and propellants for different propellant systems (monopropellant and bipropellant systems).

Published: 16 October 2004
In proceeding of "Workshop Astronomy with Radioactivities V", Clemson SC, USA, Sep 5-9 2005, Editors R. Diehl, D. Hartmann, E. Zinner, in New Reviews in Astronomy, Elsevier

The gamma-ray observatory INTEGRAL was launched in October 2002 and produces since then a wealth of discoveries and important new results. I will present a selection of scientific highlights obtained during the first 2.5 years of the mission.

Published: 06 September 2005
In: Proceedings of the 5th International Conference on Space Optics (ICSO 2004), Toulouse, France. Ed.: B. Warmbein. ESA SP-554, Noordwijk, Netherlands: ESA Publications Division, ISBN 92-9092-865-4

A new concept of a high-resolution near-IR spectrometer consisting of an echelle grating combined with an acousto-optic tunable filter (AOTF) for separation of diffraction orders, is developed for space-borne studies of planetary atmospheres. A compact design with no moving parts within the mass budget of 3-5 kg allows to reach the resolving power 20 000-30 000. Only a small piece of spectrum in high diffraction orders can be measured at a time, but thanks to flexibility of the AOTF electrical tuning, such pieces of spectrum can be measured randomly and rapidly within the spectral range. This development can be used for accurate measurements of important atmospheric gases, such as CO2 in terrestrial atmosphere, isotopic ratios and minor gases. A spectrometer, based on this principle, SOIR (Solar Occultation InfraRed) is being built for Venus Express (2005) ESA mission. Instruments based on this principle have high potential for the studies of the Earth, in particular for measurements of isotopes of water in the lower atmosphere, either in solar occultation profiling (tangent altitude <10 km), or observing solar glint for integral quantities of the components. Small size of hardware makes them ideal for micro-satellites, which are now agile enough to provide necessary pointing for solar occultation or glint observations. Also, the atmosphere of Mars has never been observed at local scales with such a high spectral resolution. A laboratory prototype consisting of 275-mm echelle spectrometer with Hamamatsu InGaAs 512-pixel linear array and the AOTF has demonstrated a resolving power of 30 000 in the spectral range of 1-1.7 µm. The next set up, covering the spectral ranges of 1-1.7 µm and 2.3-4.3 µm, and the Venus Express SOIR are briefly discussed.

Published: 16 June 2004
We explore the possibilities of TIMMI2 N-band observations of improving our knowledge on the physics of the short transition phase which precedes the formation of a planetary nebula. Both imaging and spectroscopic capabilities of TIMMI2 are shown to be extremely powerful and suitable to study the hidden evolution of AGB stars in their way to become planetary nebulae. These data are complementary to previously obtained ISO SWS spectra corresponding to sources at different evolutionary stages covering the whole path from the start of the AGB to the formation of a new planetary nebula. Both TIMMI2 and ISO SWS spectra are used to classify the sources as carbon-rich or oxygen-rich and to propose a tentative evolutionary sequence of spectral characteristics based on the detailed analysis of the gas phase and solid state features detected in the mid-infrared range.
Published: 02 September 2005
We use the space weather validated 3-D HAFv2 model to help us study the interplanetary propagation of the October/November 2003 solar eruptions from the Sun to >90 AU and over a wide range of heliolongitudes and heliolatitudes. The HAFv2 model predictions at ACE (1 AU), Ulysses (5.23 AU), Cassini (8.67 AU), Voyager 2 (73 AU), and Voyager 1 (93 AU) are compared with available data. These comparisons indicate the importance of asymmetric interplanetary propagation both in heliolongitude and heliolatitude. We recommend that these effects explicitly be taken into account. The HAFv2 results appear to be useful for interpreting the Voyager 2 and Voyager 1 energetic particle data in the outer heliosphere. They are consistent with the effects of the Halloween solar events observed in the energetic particle data at both spacecraft. The HAFv2 results also may be helpful for predicting the plasma wave 2-3 kHz radio emission previously associated with large shocks and their interaction with the heliopause. Our study indicates that the Halloween events may give rise to 2-3 kHz radio emission in early 2005, assuming that the shocks which propagated beyond Voyager 1 will be strong enough.
Published: 01 October 2005
Published: 28 September 2005
Soft gamma-ray repeaters (SGRs) are neutron stars that emit short (<~1 s) and energetic (<~1042 erg s-1) bursts of soft gamma-rays. Only four of them are currently known. Occasionally, SGRs have been observed to emit much more energetic "giant flares'' (~1044-1045 erg s-1). These are exceptional and rare events. We report here on serendipitous observations of the intense gamma-ray flare from SGR 1806-20 that occurred on 2004 December 27. Unique data from the Cluster and Double Star TC-2 satellites, designed to study the Earth's magnetosphere, provide the first observational evidence of three separate timescales within the early (first 100 ms) phases of this class of events. These observations reveal that in addition to the initial very steep (<0.25 ms) X-ray onset, there is first a 4.9 ms exponential rise timescale followed by a continued exponential rise in intensity on a timescale of 70 ms. These three timescales are a prominent feature of current theoretical models, including the timescale (several milliseconds) for fracture propagation in the crust of the neutron star.
Published: 16 July 2005
We have discovered rapid quasi-periodic oscillations (QPOs) in RXTE/PCA measurements of the pulsating tail of the 2004 December 27 giant flare of SGR 1806-20. QPOs at ~92.5 Hz are detected in a 50 s interval starting 170 s after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ~18 and ~30 Hz are also detected ~200-300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected in the flux of a soft gamma-ray repeater or any other magnetar candidate. We interpret the highest QPOs in terms of the coupling of toroidal seismic modes with Alfvén waves propagating along magnetospheric field lines. The lowest frequency QPO might instead provide indirect evidence on the strength of the internal magnetic field of the magnetar.
Published: 16 July 2005
With the rapid development of space science and technology, the possibility for multi-segment missions has lately received substantial focus. This is especially true for smaller spacecrafts, where they together form a formation, in order to collectively perform measurements that often surpass what a single big satellite can achieve. Satellite's formation flying is consequently a very popular but also difficult discipline of the world's space centers. Many new and exciting ideas are emerging in this area every year. This paper provides a survey of operational, as well as planned, space missions involving formation flying aspects, which have been developed by different countries and space agencies. From an analysis of these missions, by making appropriate comparisons between the satellite's constellation and formation flights, a synthesis aimed at reach appropriate definitions of formation flights are performed. Using these analysis the paper then addresses the several guidance, navigation and control problems that are native to formation flying missions. Finally, an example of system configuration (including space and ground segment), mainly emphasis on the satellite's attitude and orbit control subsystem, is given to illustrate one of the formation flying missions presently being under phase B development.
Published: 06 April 2005
23-Sep-2020 07:35 UT

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