-
Norbert I Kömle,
Erika S Hütter,
Wolfgang Macher,
Erika Kaufmann,
Günter Kargl, Jörg Knollenberg,
Matthias Grott,
Tilman Spohn,
Roman Wawrzaszek,
Marek Banaszkiewicz,
Karoly Seweryn,
Axel Hagermann
[show abstract]
[hide abstract]
ABSTRACT: The thermo-mechanical properties of planetary surface and subsurface layers control to a high extent in which way a body interacts with its environment, in particular how it responds to solar irradiation and how it interacts with a potentially existing atmosphere. Furthermore, if the natural temperature profile over a certain depth can be measured in situ, this gives important information about the heat flux from the interior and thus about the thermal evolution of the body. Therefore, in most of the recent and planned planetary lander missions experiment packages for determining thermo-mechanical properties are part of the payload. Examples are the experiment MUPUS on Rosetta's comet lander Philae, the TECP instrument aboard NASA's Mars polar lander Phoenix, and the mole-type instrument HP(3) currently developed for use on upcoming lunar and Mars missions. In this review we describe several methods applied for measuring thermal conductivity and heat flux and discuss the particular difficulties faced when these properties have to be measured in a low pressure and low temperature environment. We point out the abilities and disadvantages of the different instruments and outline the evaluation procedures necessary to extract reliable thermal conductivity and heat flux data from in situ measurements.
Planetary and Space Science 06/2011; 59(8):639-660. · 2.22 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Cometary activity arises from the sublimation of surface ices into the gas phase. Dust is entrained in the gas and is accelerated by gas drag as the gas escapes into interplanetary space. Previous observations [1, 2] of cometary nuclei have shown remarkable, diverse structures in the near‐nucleus dust distribution. The gas from the comet expands into vacuum and the flow therefore passes through a wide range of densities and pressures and hence though different flow regimes. While a direct simulation Monte Carlo (DSMC) simulation [3] should give, in all cases, accurate results if applied correctly, the calculation becomes slow in denser regions. Solving the Euler equations (EE) is in these cases faster, but they are only an approximation for dilute gas. A direct comparison between DSMC and EE was made by Lukianov et al. [4] for water vapor subliming from an ice sphere into vacuum. He found that the Euler equation with correct boundary conditions gives a good approximation to the velocity and density field in the supersonic region even at global Kn>10−3. We have performed further comparisons of the DSMC and EE methods for a case with an ‘active cap’: A region with a half opening angle of 10° has twice the production rate compared with the rest of the sphere. We found that far away from the active cap, the flow is like one from a sphere and our results are in a very good agreement with Lukianov et al.’s [4]. However the Euler equations start to fail close to and at the sides of the jet produced by the active area at lower Knudsen numbers.
AIP Conference Proceedings. 05/2011; 1333(1):1151-1156.
-
Horst Uwe Keller,
Laurent Jorda,
Michael Küppers,
Pedro J Gutierrez,
Stubbe F Hviid, Jörg Knollenberg,
Luisa-Maria Lara,
Holger Sierks,
Cesare Barbieri,
Philippe Lamy,
Hans Rickman,
Rafael Rodrigo
[show abstract]
[hide abstract]
ABSTRACT: The OSIRIS cameras (optical, spectroscopic, and infrared remote imaging system) onboard the European Space Agency's Rosetta spacecraft observed comet 9P/Tempel 1 for 17 days continuously around the time of NASA's Deep Impact mission. The cyanide-to-water production ratio was slightly enhanced in the impact cloud, compared with that of normal comet activity. Dust particles were flowing outward in the coma at >160 meters per second, accelerated by the gas. The slope of the brightness increase showed a dip about 200 seconds after the impact. Dust Afrho values before and long after the impact confirm the slight decrease of cometary activity. The dust-to-water mass ratio was much larger than 1.
Science 11/2005; 310(5746):281-3. · 31.20 Impact Factor
-
Michael Küppers,
Ivano Bertini,
Sonia Fornasier,
Pedro J Gutierrez,
Stubbe F Hviid,
Laurent Jorda,
Horst Uwe Keller, Jörg Knollenberg,
Detlef Koschny,
Rainer Kramm,
Luisa-Maria Lara,
Holger Sierks,
Nicolas Thomas,
Cesare Barbieri,
Philippe Lamy,
Hans Rickman,
Rafael Rodrigo
[show abstract]
[hide abstract]
ABSTRACT: 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 (1.5 10(32) water molecules or 4.5 10(6) kg) and the cross-section of the dust (330 km2 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 110 m s(-1) and 300 m s(-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.
Nature 11/2005; 437(7061):987-90. · 36.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper investigates the physical limits of a solar collector for orbit deflection of near-Earth asteroids (NEAs) on a collision course with Earth. For decades of warning time a small change of NEA orbital velocity Δv by a few mm/s might suffice to alter the collision path into an Earth fly-by and consequently avert a local or even global catastrophe. In principle this can be achieved by a spacecraft that carries a large solar collector. The latter focuses sunlight onto the NEA surface in order to vaporize surface material, hence transferring a continuous momentum to the NEA. We model evaporation process and vapour expansion to show that the functionality exists. From the analysis of focussing misalignments and collector degradation we find that a considerable operational effort is required to maintain operating conditions. The most important result is that the collector lifetime is limited to only a few minutes. Therefore a solar collector might only be applicable to NEAs with size < 250 m if Δv<0.1 mm/s is required. We also discuss capabilities for the prolongation of collector lifetime and hence an increase of NEA application size range.ZusammenfassungDiese Arbeit untersucht die physikalischen Grenzen eines Sonnenspiegels bei der Bahnablenkung erdnaher Asteroiden (NEAs), die sich auf Kollisionskurs mit der Erde befinden. Für eine Vorwarnzeit von Jahrzehnten genügt eine geringe Änderung der NEA-Bahngeschwindigkeit Δv um wenige mm/s, um die Kollisionsbahn in einen Erdvorbeiflug zu ändern, und somit eine lokale oder sogar globale Katastrophe abzuwenden. Prinzipiell kann dies durch ein Raumfahrzeug erreicht werden, dass einen großen Sonnenspiegel trägt. Mit diesem wird Sonnenlicht auf die NEA-Oberfläche fokussiert, um Oberflächenmaterial zu verdampfen und dadurch einen kontinuierlichen Impuls auf den NEA zu übertragen. Wir modellieren den Verdampfungsprozess und die Gasausbreitung, um zu zeigen, dass die Funktionalität gegeben ist. Die Analyse von Fokusausrichtungsfehlern und Spiegeldegradation zeigt, dass ein erheblicher Betriebsaufwand erforderlich ist, um die Betriebsbedingungen zu gewährleisten. Das wichtigste Ergebnis ist die geringe Spiegellebensdauer von nur wenigen Minuten. Deshalb kann ein Sonnenspiegel nur auf NEAs mit einer Größe < 250 m angewandt werden falls Δv<0.1 mm/s beträgt. Wir diskutieren außerdem Möglichkeiten der Lebensdauerverlängerung des Spiegels, um das Einsatzgebiet auf einen größeren Bereich von NEAs zu erweitern.
Aerospace Science and Technology.
-
Michael Küppers,
Ivano Bertini,
Sonia Fornasier,
Pedro J. Gutierrez,
Stubbe F. Hviid,
Laurent Jorda,
Horst Uwe Keller, Jörg Knollenberg,
Detlef Koschny,
Rainer Kramm, [......],
E. Kührt,
A. Llebaria,
J. J. Lopez Moreno,
F. Marzari,
G. Naletto,
L. Sabau,
A. Sanz Andrés,
J. P. Sivan,
G. Tondello,
K.-P. Wenzel
Nature. 437(2005-10-13):987-990.
-
Ground-based Geophysics on the Moon;
-
1. IPEWG;
-
Ref. No: 102009048739.5
-
Michael Küppers,
Ivano Bertini,
Sonia Fornasier,
Pedro J Gutierrez,
Stubbe F. Hviid,
Laurent Jorda,
Horst Uwe Keller, Jörg Knollenberg,
Detlef Koschny,
Rainer Kramm,
Luisa-Maria Lara,
Holger Sierks,
Nicolas Thomas,
Cesare Barbieri,
Philippe Lamy,
Hans Rickman,
Rafael Rodrigo,
The OSIRIS team
-
Horst Uwe Keller,
Michael Küppers,
Sonia Fornasier,
Pedro J. Gutiérrez,
Stubbe F. Hviid,
Laurent Jorda, Jörg Knollenberg,
Stephen C. Lowry,
Miriam Rengel,
Ivano Bertini, [......],
Stefano Debei,
Marco Fulle,
Fritz Gliem,
Olivier Groussin,
José J. Lopez Moreno,
Francesco Marzari,
Giampiero Naletto,
Lola Sabau,
Angel Sanz Andrés,
Klaus-Peter Wenzel
[show abstract]
[hide abstract]
ABSTRACT: The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain.
Icarus.
-
[show abstract]
[hide abstract]
ABSTRACT: This paper investigates the physical limits of a solar collector for orbit deflection of near-Earth asteroids (NEAs) on a collision course with Earth. For decades of warning time a small change of NEA orbital velocity Δv by a few mm/s might suffice to alter the collision path into an Earth fly-by and consequently avert a local or even global catastrophe. In principle this can be achieved by a spacecraft that carries a large solar collector. The latter focuses sunlight onto the NEA surface in order to vaporize surface material, hence transferring a continuous momentum to the NEA. We model evaporation process and vapour expansion to show that the functionality exists. From the analysis of focussing misalignments and collector degradation we find that a considerable operational effort is required to maintain operating conditions. The most important result is that the collector lifetime is limited to only a few minutes. Therefore a solar collector might only be applicable to NEAs with size ‹ 250 m if Δv ‹ 0.1 mm/s is required. We also discuss capabilities for the prolongation of collector lifetime and hence an increase of NEA application size range.
Aerospace Science and Technology. 10(3):256-263.
