ESA Science & Technology - Publication Archive

Some studies over the last decade have indicated that the instability responsible for substorm expansion phase onset may require an external trigger such as a northward turning of the interplanetary magnetic field (IMF). Statistical investigations have lead to contrasting interpretations regarding the relationship between proposed solar wind triggers and substorm onsets identified from geomagnetic data. We therefore present the results of a study into the possible triggering of 260 substorms between 2001-2005, exploiting data from the Cluster and IMAGE satellite missions. We find that only a small fraction (<25%) of the substorms studied are associated with northward turnings of the IMF. However, the majority of the observed onsets are associated with a growth phase characterised using a subset of the criteria employed to define northward-turning IMF triggers. Based upon a case-by-case investigation and the results of an analysis using the statistics of point processes, we conclude that northward-turning structures in the IMF, while sometimes coinciding with the initial phase of individual substorms, are not required to trigger the magnetospheric instability associated with substorm expansion phase onset.

Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosheath region by Cluster. A mechanism for the generation of these structures in terms of electron-acoustic solitons and double layers is discussed. The model simulates the magnetosheath plasma by a four-component plasma system consisting of core electrons, two counterstreaming electron beams, and one type of ions. The analysis is based on the fluid equations and the Poisson equation, and employs the Sagdeev pseudopotential techniques to investigate the solitary waves. The electric field amplitudes, the time durations, and the propagation speeds of the solitary structures predicted by the model are in good agreement with the observed electric fields, pulse widths, and speeds of the electrostatic bipolar pulses.

Executive Summary of the mission study by OHB-System AG (Reference: MPL-OHB-TN-014).

This executive summary presents the results of the Marco Polo study performed under ESA contract by the industrial team led by OHB-System AG, for an ESA-defined scenario. Possible collaboration schemes associated with this scenario are not addressed here. The results presented address the mission and system design of the ESA space element of the Marco Polo mission including the analysis of critical technologies required for this ambitious mission.
The industrial team was led by OHB-System AG and included the following partners:

• GMV S.A. - focussing on mission analysis and GNC technologies
• Sener S.A. - focussing on landing and sample acquisition technologies
• Aero Sekur S.p.A. - focussing on high speed re-entry technologies
• QinetiQ Ltd - providing consultancy in the area of electric propulsion

Only a few decades ago, the origin of the Universe was a scientific topic lacking reliable data. However, scientists now know where to look for answers, and they are steadily gaining the means to do so. ESA' s ambitious Planck mission is the next step in solving many of cosmology's biggest questions.

Force limited vibration was used during the sine and random qualification tests of the NIRSpec instrument, to limit stresses in the brittle structure while demonstrating adequate qualification with regard to the environmental flight conditions. First, NASA provided a force limit curve based on their internal 'Semi-Empirical Method'. Then, strain gages were mounted on the legs of the kinematic mounts to recover interface forces during the vibration test. Two different methods were then used to determine the notches: one called the 'Apparent Mass' method that is based on sine sweep signatures and another one based on direct force measurement in the time domain during random test. The second method resulted in the most effective notch determination, allowing the justification of the notches in real time with high accuracy. The resulting RMS forces are well below the forces corresponding to static design loads that is a more conventional method.

For any space mission, the 'ground segment' is vital for operating a spacecraft and processing data received from its instruments. Planck is no different, with hardware software, telecommunications and other operations reaching from Spain to Australia.

Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center's Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 micron-atm), as were measurements made close in time (ranging from <1 to >8 micron-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC's Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2-4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity.

Reference: INSF.TCN.ASF.SPICA.00021

SPICA is a JAXA led astronomical mission. The ESA contribution to the SPICA mission, mainly entailing the provision of the cryogenic telescope assembly, is a M-class candidate in the Cosmic Vision 2015-2025 Plan. This document provides a summary of the work performed between August 2008 and September 2009 as part of the SPICA assessment phase study.

White dwarfs typically have masses in a narrow range centered at about 0.6 solar mass (M). Only a few ultramassive white dwarfs (mass > 1.2 M) are known. Those in binary systems are of particular interest, because a small amount of accreted mass could drive them above the Chandrasekhar limit, beyond which they become gravitationally unstable. Using data from the X-ray multimirror mission (XMM)-Newton satellite, we show that the x-ray pulsator RX J0648.0-4418 is a white dwarf with mass > 1.2 M, based on dynamical measurements only. This ultramassive white dwarf in a post-common envelope binary with a hot subdwarf can reach the Chandrasekhar limit, and possibly explode as a type Ia supernova, when its helium-rich companion will transfer mass at an increased rate through Roche lobe overflow.

In "Optical System Alignment, Tolerancing, and Verification III", edited by José Sasian, Richard N. Youngworth, Proc. of SPIE Vol. 7433, 74330P, (2009), doi: 10.1117/12.826286

The Mid Infrared Instrument (MIRI), one of the four instruments on the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST), supports all of the science objectives of the observatory. MIRI optical alignment is an important step in the verification process, directly affecting mission success. The MIRI optical alignment is verified on the ground at the integrated ISIM level using an element in the MIRI Filter Wheel, the pupil alignment reference (PAR), developed by NASA GSFC and provided to MIRI. It is a ~2.3g aluminum piece that has a flat, specularly reflective, 3mm diameter surface in its center, with laser-etched fiducials within its aperture. The PAR is illuminated via an optical stimulus (ground support equipment) and imaged using a pupil imaging camera, during the ISIM test program in order to determine absolute and relative changes in the alignment that impact pupil shear and roll. Here we describe the MIRI PAR; its physical properties and challenges during its design, manufacturing, and testing.

Infrared Systems and Photoelectronic Technology IV. Edited by Dereniak, Eustace L.; Hartke, John P.; Levan, Paul D.; Longshore, Randolph E.; Sood, Ashok K. Proceedings of the SPIE, Volume 7419, pp. 741907-741907-10 (2009)

The James Webb Space Telescope, an infrared-optimized space telescope being developed by NASA for launch in 2014, will utilize cutting-edge detector technology in its investigation of fundamental questions in astrophysics. JWST's near infrared spectrograph, NIRSpec utilizes two 2048 × 2048 HdCdTe arrays with Sidecar ASIC readout electronics developed by Teledyne to provide spectral coverage from 0.6 microns to 5 microns. We present recent test and calibration results for the "pathfinder NIRSpec detector subsystem" as well as data processing routines for noise reduction and cosmic ray rejection.

Darrouzet, F., De Keyser, J., Pierrard, V. (Eds.) 2009, IV, 296 pages, 100 illus., 60 in colour, Hardcover. ISBN: 978-1-4419-1322-7 (Print), 978-1-4419-1323-4 (Online) Reprinted from Space Science Reviews journal, Vol. 145/1-2, 2009. This book reviews the state of the art in plasmaspheric science based on the modern observations provided by ESA's Cluster and NASA's IMAGE spacecraft. The plasmasphere, discovered at the beginning of the space age, has remained largely unexplored territory. Now, with innovative observational techniques, new light is being shed on this key region of the magnetosphere. This book sketches the emerging overall picture of a highly structured plasma, sculpted by the ever-changing electromagnetic fields that result from the interaction of the solar wind with the magnetosphere. The Earth's Plasmasphere, written by an international group of scientists representative of the world-wide community, is aimed at researchers and graduate students with an interest in magnetospheric physics, space plasma physics and geophysics. Table of Contents Preface (J. L. Burch & C. P. Escoubet) Foreword (F. Darrouzet, J. De Keyser, & V. Pierrard) CLUSTER and IMAGE: New Ways to Study the Earth's Plasmasphere (J. De Keyser, et al.) Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions (F. Darrouzet, et al.) Electric Fields and Magnetic Fields in the Plasmasphere: A Perspective from CLUSTER and IMAGE (H. Matsui, et al.) Advances in Plasmaspheric Wave Research with CLUSTER and IMAGE Observations (A. Masson, et al.) Recent Progress in Physics-Based Models of the Plasmasphere (V. Pierrard, et al.) Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data (B. W. Reinisch, et al.)

A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas.

Simultaneous observations of Venus by Visible and Infrared Thermal Imaging Spectrometer and Venus Monitoring Camera onboard the Venus Express spacecraft are used to map the cloud top altitude and to relate it to the ultraviolet (UV) markings. The cloud top altitude is retrieved from the depth of CO₂ absorption band at 1.6 microns. In low and middle latitudes the cloud top is located at 74 ± 1 km. It decreases poleward of ±50° and reaches 63-69 km in the polar regions. This depression coincides with the eye of the planetary vortex. At the same latitude and hour angle, cloud top can experience fast variations of about 1 km in tens of hours, while larger long-term variations of several kilometers have been observed only at high latitudes. UV markings correlate with the cloud altimetry, however, the difference between adjacent UV dark and bright regions does not exceed several hundred meters. Surprisingly, CO₂ absorption bands are often weaker in the dark UV features, indicating that these clouds may be a few hundred meters higher or have a larger scale height than neighboring clouds. Ultraviolet dark spiral arms, which are often seen at about ~70°, correspond to higher altitudes or to the regions with strong latitudinal gradient of the cloud top altitude. Cloud altimetry in the polar region reveals the structure that correlates with the thermal emission maps but is invisible in UV images. This implies that the UV optically thick polar hood is transparent in the near IR.

Methane clouds, lakes and most fluvial features on Saturn's moon Titan have been observed in the moist high latitudes, while the tropics have been nearly devoid of convective clouds and have shown an abundance of wind-carved surface features like dunes. The presence of small-scale channels and dry riverbeds near the equator observed by the Huygens probe at latitudes thought incapable of supporting convection (and thus strong rain) has been suggested to be due to geological seepage or other mechanisms not related to precipitation. Here we report the presence of bright, transient, tropospheric clouds in tropical latitudes. We find that the initial pulse of cloud activity generated planetary waves that instigated cloud activity at other latitudes across Titan that had been cloud-free for at least several years. These observations show that convective pulses at one latitude can trigger short-term convection at other latitudes, even those not generally considered capable of supporting convection, and may also explain the presence of methane-carved rivers and channels near the Huygens landing site.

In the present paper, we first examine some interplanetary directional discontinuities with very small B_n /B (<0.1) using intraspacecraft timing method. It is found that the velocity and magnetic field fluctuations of these directional discontinuities satisfy the Walén relation. We suggest that these directional discontinuities are rotational discontinuities. In addition, we investigate the stability of interplanetary rotational discontinuities using one-dimensional hybrid simulations and found that rotational discontinuities with all values of B_n /B can stably exist in the solar wind. In one simulation run, we find that the rotational discontinuity (RD) is still stable when the ratio, B_n /B, equals 0.0001. Finally, from one-dimensional hybrid simulation, we further find that the ratio is significantly reduced after interaction with interplanetary fast shocks. There are a few mechanisms for generation of RDs. Among them, two mechanisms are well accepted. One is nonlinear evolution of Alfvén waves in the solar wind, and another is magnetic reconnection near the solar surface. For magnetic reconnection, the reconnection rate, V_1n /V_A1(= B_n /B), in the magnetosphere and solar wind, is usually <0.2. Therefore the generated RDs also have B_n /B < 0.2. On the other hand, the nonlinear evolution of Alfvén waves in the solar wind can generate RDs at all values of B_n /B, which contradicts to the Cluster results. We suggest that interplanetary RDs with small B_n /B are likely been generated through magnetic reconnection.

The detection of methane on Mars has revived the possibility of past or extant life on this planet, despite the fact that an abiogenic origin is thought to be equally plausible. An intriguing aspect of the recent observations of methane on Mars is that methane concentrations appear to be locally enhanced and change with the seasons. However, methane has a photochemical lifetime of several centuries, and is therefore expected to have a spatially uniform distribution on the planet. Here we use a global climate model of Mars with coupled chemistry to examine the implications of the recently observed variations of Martian methane for our understanding of the chemistry of methane. We find that photochemistry as currently understood does not produce measurable variations in methane concentrations, even in the case of a current, local and episodic methane release. In contrast, we find that the condensation-sublimation cycle of Mars' carbon dioxide atmosphere can generate large-scale methane variations differing from those observed. In order to reproduce local methane enhancements similar to those recently reported, we show that an atmospheric lifetime of less than 200 days is necessary, even if a local source of methane is only active around the time of the observation itself. This implies an unidentified methane loss process that is 600 times faster than predicted by standard photochemistry. The existence of such a fast loss in the Martian atmosphere is difficult to reconcile with the observed distribution of other trace gas species. In the case of a destruction mechanism only active at the surface of Mars, destruction of methane must occur with an even shorter timescale of the order of ~1 hour to explain the observations. If recent observations of spatial and temporal variations of methane are confirmed, this would suggest an extraordinarily harsh environment for the survival of organics on the planet.

Presented at the "International Conference On Environmental Systems", July 2009, Savannah, GA, USA, Session: Thermal Testing (Part 1 of 2), ID: 2009-01-2410

The Mid-Infrared Instrument (MIRI) is one of four scientific instruments on the James Webb Space Telescope (JWST) observatory, scheduled for launch in 2014. It will provide unique capabilities to probe the deeply dust-enshrouded regions of the Universe, investigating the history of star formation both near and far. The MIRI is the coldest instrument on the observatory. Its thermal design is driven by requirements to cool an Optics Module (OM) to below 15.5 K and detectors within this to below 6.7 K with a stability of \ml10 mK over 1000 seconds. The OM is accommodated within the JWST Integrated Science Instrument Module (ISIM) which is cooled passively to between 32 and 40 K. The instrument temperatures are achieved by a combination of thermal isolation of the OM and the ISIM supplemented with active cooling of the OM by a dedicated cryo-cooler. A flight representative "verification model" underwent two cryogenic thermal test campaigns at the UK's STFC Rutherford Appleton Laboratory between December 2007 and September 2008. This paper begins by summarizing the thermal design of the MIRI OM and describing the design of the cryogenic test facility. It goes on to describe the two test campaigns and the correlation of the MIRI OM thermal model to the thermal balance test measurements, concluding with the predicted in-flight thermal performance of the instrument based on this testing.

Reference: SPI-TAS-RP-100358212M

In the frame of ESA Cosmic Vision assessment study, Thales propose a 3.5m diameter Ritchey-Chretien telescope in HB-Cesic ceramics. The evaluation of its performances demonstrate that the proposed design perfectly fulfils the mission requirements. The objective of this paper is to provide to the reader an overview of the telescope design and performances of the HB-Cesic SPICA Telescope. The development plan is also addressed. It has been established to minimize risks and schedule. The last point is a sensitivity analysis to pupil diameter reduction: an interesting way to further reduce development schedule.

The rotation period of a gas giant's magnetic field (called the System III reference frame) is commonly used to infer its bulk rotation. Saturn's dipole magnetic field is not tilted relative to its rotation axis (unlike Jupiter, Uranus and Neptune), so the surrogate measure of its long-wavelength (kilometric) radiation is currently used to fix the System III rotation period. The period as measured now by the Cassini spacecraft is up to ~7 min longer than the value of 10 h 39 min 24 s measured 28 years ago by Voyager. Here we report a determination of Saturn's rotation period based on an analysis of potential vorticity. The resulting reference frame (which we call System IIIw) rotates with a period of 10 h 34 min 13 +/- 20 s. This shifted reference frame is consistent with a pattern of alternating jets on Saturn that is more symmetrical between eastward and westward flow. This suggests that Saturn's winds are much more like those of Jupiter than hitherto believed.