Publication archive

Publication archive

The studies that were carried out in 2001 around the possibility of re-using the Mars Express platform have proven the effectiveness of a fast approach between ESA and the scientific community. It was only in March 2001 that ESA issued a 'Call for Ideas' to react to the identified possibility of a low-cost mission based on the re-use of the platform developed for Mars Express, which will be launched in 2003. A strict schedule was imposed, in order to benefit from these special circumstances, aiming at a launch date for the new mission in 2005, which is the next 'window' for missions to Mars. In response to the Call for Ideas, the scientific community presented a wealth of interesting and challenging proposals.The studies that were carried out in 2001 around the possibility of re-using the Mars Express platform have proven the effectiveness of a fast approach between ESA and the scientific community. It was only in March 2001 that ESA issued a 'Call for Ideas' to react to the identified possibility of a low-cost mission based on the re-use of the platform developed for Mars Express, which will be launched in 2003. A strict schedule was imposed, in order to benefit from these special circumstances, aiming at a launch date for the new mission in 2005, which is the next 'window' for missions to Mars. In response to the Call for Ideas, the scientific community presented a wealth of interesting and challenging proposals.
Published: 01 February 2002
Few enterprises are more difficult or hazardous than space travel. Yet, even when compared with the achievements of its illustrious predecessors, ESA's Rosetta mission to orbit Comet Wirtanen and deploy a lander on its pristine surface must be regarded as one of the most challenging ventures ever undertaken in more than four decades of space exploration.
Published: 01 November 2002
The International Rosetta Mission was approved as a Cornerstone mission within ESA's Horizon 2000 Science Programme in November 1993. Even at this early stage, it was envisaged that the ambitious mission would be scheduled for launch in the 2003 timeframe and a number of comet rendezvous opportunities were identified. Although the original target, Comet Schwassman Wachmann 3, has since been superseded by another periodic intruder into the inner Solar System, Comet Wirtanen, there has been little shift in the original launch schedule.
Published: 01 November 2002
On the night of 12-13 January 2003, one of the most powerful rockets in the world will blast off from Kourou spaceport in French Guiana. On top of the giant Ariane-4, cocooned inside a protective fairing, will be the Rosetta comet chaser, the most ambitious scientific spacecraft ever built in Europe.
Published: 01 November 2002
First results are presented of an effort to model the storm-time distortion of the magnetic field in the inner magnetosphere using space magnetometer data. Strong geomagnetic storms are relatively rare events, represented by only a small fraction of the data used in the derivation of existing empirical geomagnetic field models. Hence using those models for the mapping of the storm-time magnetosphere is at most an extrapolation based on trends, obtained from quiet and moderately disturbed data. To overcome that limitation, a set of data was created, containing only clear-cut events with Dst <= -65 nT, with the goal to derive models of the inner and near geomagnetic field (R < 15 RE), representing strongly disturbed geomagnetic configurations and their evolution during the storm cycle. The final data set included about 143,000 records with 5-min average B-vectors, covering 37 major storms between 1996 and 2000. Most of the data came from GOES-8, -9, -10, Polar, and Geotail spacecraft, and two storms in February-March of 1998 were also partially covered by the data of Equator-S. In all cases, only those storms were selected for which concurrent solar wind and IMF data were available for the entire duration of the event. Interplanetary medium data were provided by Wind, ACE, and, to a lesser extent, by IMP 8 and Geotail. The inner magnetospheric field was represented using the newly developed T01 model [Tsyganenko, 2002a, 2002b], with a duskside partial ring current with variable amplitude and scale size, an essential part of the storm-time current system.
Published: 24 May 2003
Ulysses is now completing its second solar polar orbit, dropping back down in latitude as the Sun passes through its post-maximum phase of the solar cycle. A mid-sized circumpolar coronal hole that formed around solar maximum in the northern hemisphere has persisted and produced a highly inclined CIR, which was observed from ~70°N down to ~30°N. We find that the speed maxima in the high-speed streams follow the same slow drop in speed with decreasing latitude observed in the large polar coronal holes around solar minimum. These results suggest a solar wind acceleration effect that is related to heliolatitude or solar rotation. We also find that the solar wind dynamic pressure is significantly lower in the post-maximum phase of this solar cycle than during the previous one, indicating that while the heliosphere is larger than near solar minimum, it should be smaller than during or after the previous maximum.
Published: 23 May 2003
The launch of the X-ray Multi-Mirror (XMM) telescope on flight V119, the first commercial launch of Ariane-5, will mark another important milestone for European Space and the Agency's Scientific Programme. The mission, conceived in the late 1970s, entered the assessment-study phase in 1982 and was adopted as a 'Cornerstone Mission' in the then new Horizon 2000 Programme approved by the Science Programme Committee in 1984. The industrial studies were completed in 1988 and the scientific payload selected in 1989.
Published: 01 December 1999
"As the first spacecraft to use primary electric propulsion in conjunction with gravity manoeuvres, and as Europe's first mission to the Moon, SMART-1 opens up new horizons in space engineering and scientific discovery. Moreover,we promise frequent news and pictures, so that everyone can share in our lunar adventure."
Published: 01 February 2003
The spectroscopic study of atomic and molecular lines in the infrared, optical and ultraviolet regions of the electromagnetic spectrum has provided us with knowledge and understanding of the physics of normal stars. Spectrallines in the gamma-ray region are produced by new and different processes. These include radioactivity, nuclear excitation, electron- positron annihilation and radiation in the vicinity of magnetic fields. Gamma-ray lines are indicators of all these processes and have now been observed at astrophysical sites.They provide powerful diagnostics for the high-energy processes occurring in some of the most violent and exotic objects in the Universe. The key features of the Integral satellite will allow us to study in great detail these, and other sites of key interest in today's astrophysical research, with high sensitivity combined with very good energy resolution and very good imaging capabilities (in order to avoid source confusion) using two main instruments, an 'Imager' and a 'Spectrometer'.
Published: 02 July 1994
On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, betai ~ 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded Vx ~ 700 km/s and a diameter of ~1 Re. The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were ~15-19 nA m-2. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA m-2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.
Published: 03 April 2003
The SOHO mission is a major element of the joint ESA/NASA International Solar Terrestrial Programme (ISTP). ESA was responsible for the spacecraft's procurement, integration and testing. NASA provided the launcher, launch services and ground-segment system and is responsible for in-flight operations following the launch on 2 December 1995. The SOHO mission operations are therefore conducted under a NASA/Goddard Space Flight Center (GSFC) contract with Allied-Signal Technology Corporation (ATSC). Following the spacecraft's in-orbit checkout and the transit from low Earth orbit to its operational halo orbit around the Lagrangian point (L1) between the Earth and the Sun, the SOHO mission was declared fully operational in April 1996. SOHO then completed its two-year primary mission and entered an extended-mission phase in May 1998. On 25 June 1998, all contact with SOHO was lost.
Published: 01 March 1999
Experimental evidence is provided for the existence of slow-mode magnetosonic solitons in the collisionless plasma at the magnetopause boundary layer. The solitons were detected by the fleet of Cluster spacecraft at the dusk flank of the magnetosphere as magnetic field depressions (up to 85%) accompanied with enhancement of the plasma density and temperature by a factor of 2. The solitons propagate 250 km/s with respect to the satellites and have perpendicular size of 1000-2000 km, which is a few ion inertial scale lengths. The comparison with numerical solutions of a theoretical model shows quantitative agreement between the model and observations.
Published: 27 February 2003
The Faint Sky Variability Survey is aimed at finding photometric and/or astrometric variable objects in the brightness range between ~16th and ~24th magnitude on timescales between tens of minutes and years with photometric precisions ranging from 3 millimagnitudes for the brightest to 0.2 magnitudes for the faintest objects. An area of ~23 square degrees, located at mid and high Galactic latitudes, has been covered using the Wide Field Camera on the 2.5m Isaac Newton Telescope on La Palma. Here we describe the main goals of the Faint Sky Variability Survey and the data reduction process.
Published: 15 February 2003
Cataclysmic Variables' (CVs) are a distinct class of interacting binaries, transferring mass from a donor star to a degenerate accretor, a white dwarf (WD). In all observational determinations, and as is required by theory for stable mass transfer, the donor star is of lower mass than the accretor.
Published: 01 February 2003
The current sheet structure and motion at XGSM = -19.5 RE, observed by Cluster/FGM during 1055-1107 UT on 29 August 2001, is examined. It is found that during the interval 1055-1102 UT the current sheet moves vertically up and down with a velocity of about 60 km s-1. During this interval the current sheet has a bifurcated structure: electric current is concentrated in two sheets with an extended layer of weak nearly uniform magnetic field in between. In the interval 1103-1107 UT the current sheet moves slowly upward and the current sheet has a Harris-type structure. By using four-spacecraft timing analysis, it is shown that the fast motion and bifurcation of the current sheet are associated with a wave-like transient propagating in the dawn-to-dusk direction.
Published: 17 January 2003
We report measurement of whistler-mode chorus by the four Cluster spacecraft at close separations. We focus our analysis on the generation region close to the magnetic equatorial plane at a radial distance of 4.4 Earth's radii. We use both linear and rank correlation analysis to define perpendicular dimensions of the sources of chorus elements below one half of the electron cyclotron frequency. Correlation is significant throughout the range of separation distances of 60-260 km parallel to the field line and 7-100 km in the perpendicular plane. At these scales, the correlation coefficient is independent for parallel separations, and decreases with perpendicular separation. The observations are consistent with a statistical model of the source region assuming individual sources as gaussian peaks of radiated power with a common half-width of 35 km perpendicular to the magnetic field. This characteristic scale is comparable to the wavelength of observed waves.
Published: 16 January 2003
We have carried out a multiwavelength study of the plane of our Galaxy in order to establish a star-forming-complex catalogue which is as complete as possible. Features observed include H alpha, H109 alpha, CO, the radio continuum and absorption lines. For each complex we have determined the position, the systemic velocity, the kinematic distance and, when possible, the stellar distance and the corresponding uncertainties. All of these parameters were determined as homogeneously as possible, in particular all the stellar distances have been (re)calculated with the same calibration and the kinematic distances with the same mean Galactic rotation curve. Through the complexes with stellar distance determination, a rotation curve has been fitted. It is in good agreement with the one of Brand & Blitz (1993). We also investigated the residual velocities relative to the circular rotation model. We find that departures exist over large areas of the arms, with different values from one arm to another. From our data and in good agreement with previous studies, the Galactic warp is observed. It does not seem correlated with the departures from circular rotation. Finally, as segment-like features are noted from the complexes' distribution, we tried to find if they are indicative of a larger underlying structure. Then, we attempted to interpret the complexes' distribution in terms of spiral structure by fitting models with two, three and four logarithmic spiral arms. The four-arm model seems more appropriate to represent the grand design of our Galaxy. In this model the Norma arm and the external arm appear as being the two extremities of a single arm called the Norma-Cygnus arm. The new data and fitted model confirm the four-segment model of Georgelin & Georgelin (1976), clarifying the arms' design and extension and doubling their known length.
Published: 01 January 2003
Using the technique of point-spread function-matched image subtraction, we have analyzed archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 data to reveal details of at least two light echo structures, including some unknown before now, around SN 1993J in the galaxy M81. In particular, we see one partial sheet of material 81 pc in front of the supernova (SN) and tilted ~60° relative to the disk plane of M81 and another 220 pc in front of the SN, roughly parallel to the disk. The inferred echoing material is consistent with the H I surface density detected in this region of M81's disk; however, these data imply a fragmented covering factor for the echoing structures. We discuss prospects for future (roughly annual) visits by HST to image these and yet undiscovered echoes in the interstellar and circumstellar environment of SN 1993J.
Published: 15 December 2002
For the first time, the Cluster spacecraft have collected 3-D information on magnetic field structures at small to medium scales in the Earth's dayside magnetosphere. We focus here on the first application of the Curlometer (direct estimation of the electric current density from curl(B), using measured spatial gradients of the magnetic field) analysis technique. The applicability of this multipoint technique is tested, for selected events within the data set, in the context of various mission constraints (such as position, timing, and experimental accuracy). For the Curlometer, nonconstant spatial gradients over the spacecraft volume, time dependence, and measurement errors can degrade the quality of the estimate. The estimated divergence of the magnetic field can be used to monitor (indirectly) the effect of nonconstant gradients in the case of many magnetic field structures. For others, and at highly distorted spacecraft configurations, this test may not reflect the quality of the Curlometer well. The relative scales and relative geometry between the spacecraft array and the structures present, as well as measurement errors, all are critical to the quality of the calculation. We demonstrate that even when instrumental and other errors are known to contribute to the uncertainty in the estimate of the current, a number of current signatures within the magnetosphere can be plausibly determined in direction, if not absolute size. A number of examples show consistent currents at the magnetopause, both separate from, and nearby or in the cusp region. Field-aligned currents near the polar cap boundary are also estimated reliably. We also demonstrate one example of an anomalous current arising from the effect of a highly distorted spacecraft configuration.
Published: 20 November 2002
Plasma, electric, and magnetic field data on the Polar spacecraft have been analyzed for the 29 May 1996 magnetopause traversal searching for evidence of in situ reconnection and traversal of the separator. In this paper we confine our analysis to model-free observations and intrasensor coherence of detection of the environs of the separator.
Published: 16 October 2002
31-Oct-2020 08:36 UT

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