Engineering topics
Lebreton, J.-P.
Publications and source records attributed to Lebreton, J.-P..
Interplanetary Coronal Mass Ejection Observed at STEREO-A, Mars, Comet 67P/Churyumov-Gerasimenko, Saturn,and New Horizons En Route to Pluto: Comparison of Its Forbush Decreases at 1.4, 3.1, and 9.9 AU
We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116deg, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
Science Goals and Mission Concept for the Future Exploration of Titan and Enceladus
Saturn׳s moons, Titan and Enceladus, are two of the Solar System׳s most enigmatic bodies and are prime targets for future space exploration. Titan provides an analogue for many processes relevant to the Earth, more generally to outer Solar System bodies, and a growing host of newly discovered icy exoplanets. Processes represented include atmospheric dynamics, complex organic chemistry, meteorological cycles (with methane as a working fluid), astrobiology, surface liquids and lakes, geology, fluvial and aeolian erosion, and interactions with an external plasma environment. In addition, exploring Enceladus over multiple targeted flybys will give us a unique opportunity to further study the most active icy moon in our Solar System as revealed by Cassini and to analyse in situ its active plume with highly capable instrumentation addressing its complex chemistry and dynamics. Enceladus׳ plume likely represents the most accessible samples from an extra-terrestrial liquid water environment in the Solar system, which has far reaching implications for many areas of planetary and biological science. Titan with its massive atmosphere and Enceladus with its active plume are prime planetary objects in the Outer Solar System to perform in situ investigations. In the present paper, we describe the science goals and key measurements to be performed by a future exploration mission involving a Saturn-Titan orbiter and a Titan balloon, which was proposed to ESA in response to the call for definition of the science themes of the next Large-class mission in 2013. The mission scenario is built around three complementary science goals: (A) Titan as an Earth-like system; (B) Enceladus as an active cryovolcanic moon; and (C) Chemistry of Titan and Enceladus - clues for the origin of life. The proposed measurements would provide a step change in our understanding of planetary processes and evolution, with many orders of magnitude improvement in temporal, spatial, and chemical resolution over that which is possible with Cassini-Huygens. This mission concept builds upon the successes of Cassini-Huygens and takes advantage of previous mission heritage in both remote sensing and in situ measurement technologies.
Scientific Rationale for Saturn's in Situ Exploration
Remote sensing observations meet some limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. A remarkable example of the superiority of in situ probe measurements is illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases׳ abundances and the precise measurement of the helium mixing ratio have only been made available through in situ measurements by the Galileo probe. This paper describes the main scientific goals to be addressed by the future in situ exploration of Saturn placing the Galileo probe exploration of Jupiter in a broader context and before the future probe exploration of the more remote ice giants. In situ exploration of Saturn's atmosphere addresses two broad themes that are discussed throughout this paper: first, the formation history of our solar system and second, the processes at play in planetary atmospheres. In this context, we detail the reasons why measurements of Saturn's bulk elemental and isotopic composition would place important constraints on the volatile reservoirs in the protosolar nebula. We also show that the in situ measurement of CO (or any other disequilibrium species that is depleted by reaction with water) in Saturn's upper troposphere may help constraining its bulk O/H ratio. We compare predictions of Jupiter and Saturn's bulk compositions from different formation scenarios, and highlight the key measurements required to distinguish competing theories to shed light on giant planet formation as a common process in planetary systems with potential applications to most extrasolar systems. In situ measurements of Saturn's stratospheric and tropospheric dynamics, chemistry and cloud-forming processes will provide access to phenomena unreachable to remote sensing studies. Different mission architectures are envisaged, which would benefit from strong international collaborations, all based on an entry probe that would descend through Saturn's stratosphere and troposphere under parachute down to a minimum of 10 bar of atmospheric pressure. We finally discuss the science payload required on a Saturn probe to match the measurement requirements.
In Situ Probe Science at Saturn
A fundamental goal of solar system exploration is to understand the origin of the solar sys-tem, the initial stages, conditions, and processes by which the solar system formed, how the formation pro-cess was initiated, and the nature of the interstellar seed material from which the solar system was born. Key to understanding solar system formation and subsequent dynamical and chemical evolution is the origin and evolution of the giant planets and their atmospheres. Several theories have been put forward to explain the process of solar system formation, and the origin and evolution of the giant planets and their atmospheres. Each theory offers quantifiable predictions of the abundances of noble gases He, Ne, Ar, Kr, and Xe, and abundances of key isotopic ratios 4He3He, DH, 15N14N, 18O16O, and 13C12C. Detection of certain dis-equilibrium species, diagnostic of deeper internal pro-cesses and dynamics of the atmosphere, would also help discriminate between competing theories. Measurements of the critical abundance profiles of these key constituents into the deeper well-mixed at-mosphere must be complemented by measurements of the profiles of atmospheric structure and dynamics at high vertical resolution and also require in situ explora-tion. The atmospheres of the giant planets can also serve as laboratories to better understand the atmospheric chem-istries, dynamics, processes, and climates on all planets including Earth, and offer a context and provide a ground truth for exoplanets and exoplanetary systems. Additionally, Giant planets have long been thought to play a critical role in the development of potentially habitable planetary systems. In the context of giant planet science provided by the Galileo, Juno, and Cassini missions to Jupiter and Sat-urn, a small, relatively shallow Saturn probe capable of measuring abundances and isotopic ratios of key at-mospheric constituents, and atmospheric structure in-cluding pressures, temperatures, dynamics, and cloud locations and properties not accessible by remote sens-ing can serve to test competing theories of solar system and giant planet origin, chemical, and dynamical evolution.
In situ Probe Science at Saturn
A fundamental goal of solar system exploration is to understand the origin of the solar system, the initial stages, conditions, and processes by which the solar system formed, how the formation process was initiated, and the nature of the interstellar seed material from which the solar system was born. Key to understanding solar system formation and subsequent dynamical and chemical evolution is the origin and evolution of the giant planets and their atmospheres.
DEMETER Observations of Highly Structured Plasma Density and Associated ELF Electric Field and Magnetic Field Irregularities at Middle and Low Latitudes
The DEMETER spacecraft frequently encounters structured plasma and electric field irregularities associated with equatorial spread-F. However, during severe geo~nagnetic storms, the spacecraft detects broader regions of density structures that extend to higher latitudes, in some instances to the sub-auroral regions. In addition to the electric field irregularities, ELF magnetic field irregularities are sometimes observed. for example, on the walls of the density structures, and appear related to finely-structured spatial currents and/or Alfven waves. The mid-latitude irregularities are compared with those of equatorial spread-F as well as wit11 intense irregularities associated with the trough region observed at sub-auroral latitudes.
Irregularities at Sub-Auroral, Middle, and Low Latitudes in the Topside Ionosphere Observed During Geomagnetic Storms with the DEMETER and DMSP Satellites
Detailed observations of the plasma structure and irregularities that characterize the topside ionosphere at sub-auroral, middle, and low-latitudes are presented that were gathered with probes on the DEMETER and DMSP satellites during geomagnetic storms. Data from successive orbits reveal how the density structure and irregularities evolve with changes in the Dst. The observations reveal that precisely during the main phase of severe geomagnetic storms, increased ambient plasma densities and broad regions of irregularities are observed at 700 km, initially at storm commencement near the magnetic equator and then extending to mid- and sub-auroral latitudes within the approximately 8 hour period corresponding to the negative Dst excursions. Furthermore, intense, broadband electric and magnetic field irregularities are often observed at sub-auroral latitudes and are typically associated with the trough region and its poleward plasma density gradient. The observations provide a general framework showing how low, mid, and sub-auroral latitude plasma density structuring and associated irregularities respond to geomagnetic storms.
The Huygens Mission at Titan: Results Highlights
After a 7-year interplanetary journey onboard the Cassini Orbiter, the Huygens Probe was released on 25 December at 02:00 UTC. It entered in the atmosphere of Titan on 14 January at about 09:06 UTC. Following the 4-min entry, 3 parachutes were deployed in sequence. The descent under parachute lasted slightly less than 2 1/2 hours. After a soft landing at about 5 m/s, the probe continued to function for several hours on the surface. During the descent under parachute and on the surface, Huygens transmitted its data at 8 kbps on two redundant channels to the over-flying Orbiter which approached Titan at a closest distance of 60000 km about 1/2 hour before landing. Data were successfully received only on one channel due to a configuration error of the receiver of the channel which was driven by the ultra-stable oscillators (USO) of the Doppler Wind Experiment (DWE). The Orbiter received data during the descent under parachute and for 72 minutes on the surface until its path moved it outside the beam of the transmitting antennas of the probe resting on the surface and at the same time as the Orbiter went below the Horizon. Additional information is included in the original extended abstract.
The Cassini/Huygens Mission to the Saturnian System
Cassini/Huygens will carry out an in-depth exploration of the Saturnian system. On October 15, 1996 the spacecraft was launched on its interplanetary journey. On the way to Saturn, Cassini/Huygens, will flyby Venus, twice (April 26, 1998; June 24, 1999), the Earth once (August 18, 1999), and Jupiter (December 30, 2000). On approach to Saturn, the small satellite Phoebe will be encountered on June 11, 2004. Upon arrival at Saturn on July 1, 2004, Cassini/Huygens will fire its main engine and go into orbit about the planet. Huygens will be delivered to Titan on November 27, 2004. After deceleration in the upper atmosphere, Huygens will deploy a parachute system and its six instruments will make scientific measurements and observations as it descends to the surface. These data then will be transmitted to the Orbiter which, in turn, will relay them to the Earth. The Orbiter will then commence a four year long tour of the Saturnian system. With its complement of 12 instruments, Cassini is capable of making a wide range of in situ and remote sensing observations. There will be repeated close flybys of Titan both to make measurements and for gravity-assisted orbit changes that will enable Cassini to visit other satellites, various parts of the magnetosphere, and obtain occultations of the rings and atmospheres of Saturn and Titan. During the span of the mission, Cassini will also record temporal changes in many of the properties that it can observe. The presentation will emphasize current status and plans for the mission. (The Cassini mission is a joint undertaking by NASA and ESA. This work was carried out at Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA.)
An overview of the Cassini mission
Cassini is a planetary mission designed to carry out a detailed exploration of the Saturnian system. The Cassini spacecraft is composed of a NASA-provided Saturn Orbiter and an ESA-supplied Titan atmospheric probe. Scheduled for launch in October 1997, Cassini will take about 7 years to reach Saturn after a journey which includes gravity assists from Venus, Earth and Jupiter. In late 2004, a few weeks after the insertion of the Cassini spacecraft in orbit around Saturn, the Huygens probe will be dropped into the atmosphere of Titan. Following the probe mission, the Saturn Orbiter will carry out a 4 year tour within the Saturn system for detailed observations of the Planet Saturn, Titan, many of the icy satellites, the rings and the magnetosphere.
Cassini/Huygens: A mission to Saturn and Titan
The Cassini/Huygens mission is designed to explore the Saturnian system. The Cassini spacecraft comprises a NASA provided Saturn orbiter and an ESA supplied Titan atmospheric probe named Huygens. The scientific objectives of the mission are described and the main characteristics of the payload are provided. Since emphasis is on ESA's contribution to the mission, a detailed description of the Huygens probe mission phase is given and the major features of the probe design are discussed. An overview of the probe operations center is provided.
Stimulation of plasma waves by electron guns on the ISEE-1 satellite
The results of the ISEE-1 satellite experiment relating to observations of the waves stimulated during electron injections, when the spacecraft is passing through the magnetosphere, the magnetosheath, and the solar wind, are discussed. It is shown that the injection of an electron beam current of the order of 10 to 60 microamperes with energies ranging from 0 to 40 eV produces enhancements in the electric wave spectrum. An attempt has been made to identify the low-frequency electrostatic wave observed below the ion plasma frequency as an ion acoustic mode, although the excitation mechanism is not clear. A coupling mechanism between the electron plasma mode and streaming electrons with energies higher than the thermal speed of the cold electron population has been proposed to explain the observations above the electron plasma frequency.