•The NASA InSight Mars mission payload includes a surface heat flow probe.•A small penetrator implements a string of temperature sensors in the soil.•The penetrator is equipped with sensors to ...measure the thermal conductivity.•Unfortunately, the penetrator did not reach the required depth.•Lessons learned for future attempts to penetrate in the Martian soil are discussed.
The NASA InSight lander mission to Mars payload includes the Heat Flow and Physical Properties Package HP3 to measure the surface heat flow. The package was designed to use a small penetrator - nicknamed the mole - to implement a vertical string of temperature sensors in the soil to a depth of 5 m. The mole itself is equipped with sensors to measure a thermal conductivity-depth profile as it proceeds to depth. The heat flow is calculated from the product of the temperature gradient and the thermal conductivity. To avoid the perturbation caused by annual surface temperature variations, the measurements need to be taken at a depth between 3 m and 5 m. The mole is designed to penetrate cohesionless soil similar in rheology to quartz sand which is expected to provide a good analogue material for Martian sand. The sand would provide friction to the buried mole hull to balance the remaining recoil of the mole hammer mechanism that drives the mole forward. Unfortunately, the mole did not penetrate more than 40 cm, roughly a mole length. The failure to penetrate deeper is largely due to a cohesive duricrust of a few tens of centimeter thickness that failed to provide the required friction. Although a suppressor mass and spring as part of the mole hammer mechanism absorb much of the recoil, the available mass did not allow designing a system that fully eliminated the recoil. The mole penetrated to 40 cm depth benefiting from friction provided by springs in the support structure from which it was deployed and from friction and direct support provided by the InSight Instrument Deployment Arm. In addition, the Martian soil provided unexpected levels of penetration resistance that would have motivated designing a more powerful mole. The low weight of the mole support structure was not sufficient to guide the mole penetrating vertically. Roughly doubling the overall mass of the instrument package would have allowed to design a more robust system with little or no recoil, more energy of the mole hammer mechanism and a more massive support structure. In addition, to cope with duricrust a mechanism to support the mole to a depth of about two mole lengths should be considered.
The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary and primordial processes. The peculiar bilobed shape of comet ...67P/Churyumov-Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes. Here we report that the comet's major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov-Gerasimenko is an accreted body of two distinct objects with 'onion-like' stratification, which formed before they merged. We conclude that gentle, low-velocity collisions occurred between two fully formed kilometre-sized cometesimals in the early stages of the Solar System. The notable structural similarities between the two lobes of comet 67P/Churyumov-Gerasimenko indicate that the early-forming cometesimals experienced similar primordial stratified accretion, even though they formed independently.
Thermal and mechanical material properties determine comet evolution and even solar system formation because comets are considered remnant volatile-rich planetesimals. Using data from the ...Multipurpose Sensors for Surface and Sub-Surface Science (MUPUS) instrument package gathered at the Philae landing site Abydos on comet 67P/Churyumov-Gerasimenko, we found the diurnal temperature to vary between 90 and 130 K. The surface emissivity was 0.97, and the local thermal inertia was 85 ± 35 J m
−2
K
−1
s
-1/2
. The MUPUS thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength. A sintered near-surface microporous dust-ice layer with a porosity of 30 to 65% is consistent with the data.
The MASCOT radiometer MARA on board the Hayabusa2 mission will measure surface brightness temperatures on the surface of asteroid (162173) Ryugu in six wavelength bands. Here we present a method to ...constrain surface thermophysical properties from MARA measurements. Moreover, uncertainties when determining surface thermal inertia as well as emissivity are estimated. Using data from all filters and assuming constant emissivity, thermal inertia of a homogeneous surface can be determined with an uncertainty range of 250 ±16 Jm−2K−1s−1/2, while the emissivity uncertainty is below 6%. Similar results are obtained if emissivity is allowed to vary as a function of wavelength and if the MARA channels with the best signal-to-noise ratio are used to constrain thermal inertia. If the observed surface is heterogeneous and two morphologically different units are present in the instrument's field of view, thermal inertia of the subunits can be retrieved independently if their contrast in terms of thermophysical properties is large enough. If, for example, the surface is covered by equal area fractions of fine-grained and coarse-grained material, then thermal inertia is found to be retrievable with uncertainties of 658 ±78 and 54 ±22 Jm−2K−1s−1/2 for the coarse-grained and fine-grained fraction, respectively.
We investigated whether the MASCOT/MARA thermal radiometer can be used to determine regolith particle size and porosity on the asteroid Ryugu in the Hayabusa2 mission. We used a one-dimensional heat ...flow model and our own thermal conductivity model for regolith to compare MARA's performance and the expected Ryugu surface temperatures of various particle sizes and porosities. The results showed that MARA is capable of constraining particle size with ±30% uncertainty if particle size is near 4.25 mm and near-surface porosity is near 60% (a fraction of void spaces between regolith particles in a unit volume), assuming certain physical properties of regolith particles. The porosity cannot be constrained meaningfully through MARA observations alone; however, it is constrained with uncertainty of ±10% around 50% and ±5% around 70% with 2σ probability if other supportive observations (by the MASCOT camera) provide the particle size. The results also show that nighttime temperature is more sensitive to the particle size and porosity variations and its observation is essential to achieve the small error ranges, while MARA is the only instrument to observe the nighttime temperature on Ryugu. In this study, the surface roughness effect in insolation and thermal radiations was neglected. The roughness effect is presumed to be less influential in nighttime, however, this effect must be carefully considered in actual data analysis of MARA.
•Regolith particle size and porosity influenced surface temperature on virtual Ryugu.•MARA on Hayabusa2/MASCOT has a capability to constrain regolith particle size.•Cooperative observation of MARA and MasCam can constrain porosity.
The Japanese MMX sample return mission to Phobos by JAXA will carry a rover developed by CNES and DLR that will be deployed on Phobos to perform in situ analysis of the Martian moon’s surface ...properties. Past images of the surface of Phobos show that it is covered by a layer of regolith. However, the mechanical and compositional properties of this regolith are poorly constrained. In particular, from current remote images, very little is known regarding the particle sizes, their chemical composition, the packing density of the regolith as well as other parameters such as friction and cohesion that influence surface dynamics. Understanding the properties and dynamics of the regolith in the low-gravity environment of Phobos is important to trace back its history and surface evolution. Moreover, this information is also important to support the interpretation of data obtained by instruments onboard the main MMX spacecraft, and to minimize the risks involved in the spacecraft sampling operations. The instruments onboard the Rover are a Raman spectrometer (RAX), an infrared radiometer (miniRad), two forward-looking cameras for navigation and science purposes (NavCams), and two cameras observing the interactions of regolith and the rover wheels (WheelCams). The Rover will be deployed before the MMX spacecraft samples Phobos’ surface and will be the first rover to drive on the surface of a Martian moon and in a very low gravity environment.
Graphic Abstract
Mechanical properties, in particular, strength (tensile, shear, compressive) and porosity, are important parameters for understanding the evolution and activity of comets. However, they are ...notoriously difficult to measure. Unfortunately, neither Deep Impact nor other comet observations prior to Rosetta provided firm data on the strength of cometary material. This changed with the Rosetta mission and its detailed close observation data and with the landing(s) of Philae in 2014. There are already many articles and reviews in the literature that derive or compile many different strength values from various Rosetta and Philae data. In this paper, we attempt to provide an overview of the available direct and indirect data; we focus on comet Churyumov–Gerasimenko/67P but include a discussion on the Deep Impact strength results. As a prerequisite, we start by giving precise definitions of ‘strength’, discuss soil mechanics based on the Mohr–Coulomb ‘law’ of micro-gravity, and discuss bulk density and porosity, sintering, and the physics of the strength of a cohesive granular medium. We proceed by discussing the scaling of strength with the size and strain rate, which is needed to understand the observational data. We show how measured elastic properties and thermal (conductivity) data can be correlated with strength. Finally, a singular very high strength value is reviewed as well as some particularly small-strength values inferred from the bouncing motion of Philae, data from its collisions with the surface of the comet, and scratch marks it left, allegedly, on the surface close to its final resting site. The synthesis is presented as an overview figure of the tensile and compressive strength of cometary matter as a function of the size scale; conclusions about the size dependence and apparent natural variability of strength are drawn.
Science objectives of the MMX rover Ulamec, Stephan; Michel, Patrick; Grott, Matthias ...
Acta astronautica,
September 2023, 2023-09-00, 2023-09, Letnik:
210
Journal Article
Recenzirano
Odprti dostop
The Martian Moons eXploration (MMX) mission by the Japan Aerospace Exploration Agency, JAXA, will explore the Martian moons Phobos and Deimos. In addition to investigating the moons remotely and ...returning samples from Phobos, MMX will also deliver a small (about 25 kg) Rover to the surface of Phobos. The payload of the Rover consists of four scientific instruments: RAX, a Raman spectrometer to measure signatures of the mineralogical composition of the surface material, NavCam, a stereo pair of cameras to investigate the terrain and allow for navigation, miniRAD a radiometer to measure the surface brightness temperature of both, regolith and rocks, and two WheelCams which will observe the wheel-surface interface, and thus investigate the properties and dynamics of the regolith. The cameras, will serve both, technological and scientific needs.
The rover will be deployed during the rehearsal phase of the landing operations for the main spacecraft and will thus land in proximity to the first sampling area. During its operational lifetime on Phobos (about 100 days), the in-situ measurements performed with the rover payload will provide scientific context for the returned samples, provide ground truth, study the surface heterogeneity and obtain information on the physical properties of undisturbed surface material. The MMX launch is planned for September 2024 and the Rover delivery is scheduled for 2027.
The Rover is a contribution by the Centre National d’Etudes Spatiales (CNES) and the German erospace Center (DLR) with additional contributions from INTA (Spain) and JAXA.
•In this paper we give an overview of the rover, which will be part of the MMX mission to Phobos.•The MMX rover will explore the surface of Phobos with cameras, a Raman spectrometer and a radiometer.•Scientific objectives and the mission outline are discussed.
The HP³ Mole system is part of the HP³ payload on the InSight discovery class mission, which will place a geophysical lander onto the surface of Mars in 2018. DLR's HP³ - instrument (Heat Flow and ...Physical Properties Package) will measure Mars' interior heat flux and thermal gradient down to a depth of 5 m and thus penetrates deeper below the Martian surface than any other instrument before. Being the locomotion system of the instrument, the HP³ Mole acts as a self-impelling nail in order to accomplish this goal. The inner hammering mechanism is spring driven and periodically loaded by a cylindrical cam mechanism. The innovative impact driven locomotion principle enables a minimum in required energy and mass, but leads to complex system behaviour and dependence of the inner mechanism dynamics on the outer force conditions exerted by the soil.
The scope of this paper is to provide an overview of the Mole, its role in the mission and payload, as well as to give a brief overview about its subsystems, its interfaces and working principle.
•Detailed presentation of a flight design subsurface access device (“mole”).•This mole is a contribution to the recently landed InSight mission on Mars.•Presentation of the design process, i.e. testing alongside with simulation.
Abstract
On 2014 November 12 Rosetta’s comet lander Philae arrived on the surface of Comet 67P/Churyumov-Gerasimenko. Among the data collected by the instruments on board are images from the panorama ...camera CIVA and the down looking camera ROLIS, as well as temperature measurements recorded by the sensors of the MUPUS experiment and by various housekeeping sensors. In combination with remote observations by the cameras OSIRIS and NAVCAM and other instruments on the Rosetta Orbiter, it was possible to construct a reasonable model of the terrain in the close vicinity of the landing site Abydos. We have collected all available information on the position and orientation of Philae, as well as on Abydos, where the terrain can be partially reconstructed with a resolution in the decimetre range. On this basis, a 3D model for the determination of solar irradiation and thermal evolution of the region was developed. Our calculations comprise the heating and cooling process of the local surface features around Philae. Two different scenarios are studied: non-volatile material (dust mantle) covering the whole surface, and a non-volatile surface containing spots of volatile water ice where free sublimation is possible. The presented 3D model also has the potential to be applied to thermal evolution studies of other regions on the comet, for which high-resolution digital terrain models are available.
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