| 1. |
|
|
| 2. |
- Martin-Torres, Javier, et al.
(författare)
-
Brine-Induced Tribocorrosion Accelerates Wear on Stainless Steel: Implications for Mars Exploration
- 2021
-
Ingår i: Advances in Astronomy. - : Hindawi Publishing Corporation. - 1687-7969 .- 1687-7977. ; 2021
-
Tidskriftsartikel (refereegranskat)abstract
- Tribocorrosion is a degradation phenomenon of material surfaces subjected to the combined action of mechanical loading and corrosion attack caused by the environment. Although corrosive chemical species such as materials like chloride atoms, chlorides, and perchlorates have been detected on the Martian surface, there is a lack of studies of its impact on materials for landed spacecraft and structures that will support surface operations on Mars. Here, we present a series of experiments on the stainless-steel material of the ExoMars 2020 Rosalind Franklin rover wheels. We show how tribocorrosion induced by brines accelerates wear on the materials of the wheels. Our results do not compromise the nominal ExoMars mission but have implications for future long-term surface operations in support of future human exploration or extended robotic missions on Mars.
|
|
| 3. |
- Nyberg, Erik, 1986-
(författare)
-
Ionic Liquid Lubricants for Space Applications
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lubrication is critical to the efficient and reliable operation of machine elements such as gears, bearings, or any other moving mechanical assembly (MMA). On Earth, machine designers are accustomed to the access of a wide range of liquid lubricants that enable predictable and reliable long-term operations of high performance MMA. In space applications on the other hand, engineers are constrained to a comparatively limited choice of lubricant candidates that can meet the stringent demands of tribosystems operating in a space environment. At the same time, repair or maintenance are seldom options that are possible in space, and consequently lubricant failures are potentially critical. As international space agencies are converging on the goal of establishing a permanently crewed lunar Gateway for human presence on the Moon and eventually onwards to Mars, there is a need for radical improvements in many aspects of space exploration technology, including space tribology and space grade lubricants. Liquid lubricants are enablers of high performance. A thin fluid film – even in the submicron scale – is often sufficient to separate opposing surface boundaries from direct contact, and thereby prevent excessive friction and wear. Liquid lubricants are therefore attractive for use in space mechanisms. Unfortunately, liquid lubricants must overcome several issues in order to be effective in the space environment. Vacuum, microgravity, and low temperatures are all factors that oppose the effective supply of liquid lubricants into the tribological contact of MMA. If the tribological contact becomes starved of oil, the surfaces enter the boundary lubrication regime where seizure is an ever-present threat. There are very few types of fluids available that meet the stringent space grade lubricant requirements. Perfluoropolyalkylethers (PFPE), or multiply alkylated cyclopentanes (MAC) are two fluids with significant heritage in space applications. These fluids are currently employed as lubricants in a wide range of space applications, as they are rare examples of fluids that meet the high demands on resistance to vacuum outgassing. Unfortunately, these compounds are susceptible to degradation under boundary lubrication conditions, and unlike conventional lubricants employed on Earth, these fluids have poor compatibility with the boundary lubrication additives that are commonly employed in conventional oils. Ionic liquids (ILs) have emerged as potential liquid lubricant candidates in space. These synthetic fluids are composed of anions and cations. The resulting ionic interaction enables the substance to have low vapor pressure with relatively low molecular weight. For this reason, ILs have been advocated as one of the candidate lubricants for space applications. When employing ILs as lubricants, the ionic charge provides Coulombic interaction with surfaces to enable the formation of a boundary lubricating film. This is an important part of the IL lubricating mechanism, but successful lubricant performance requires integrating the lubricant candidate into the tribosystem, taking into account operating conditions and environment. Therefore, the boundary film formation should be tunable to the application at hand. Ionic liquids are designable fluids, with properties dependent on the combination of anion and cation as well as incorporated functional groups. Based on this background, this work focused on evaluating the feasibility of employing ionic liquid lubricants for space applications. In this thesis, the molecular design of an IL lubricant was described Paper [1], and the resulting hydrocarbon-mimicking ionic liquid (P-SiSO) was evaluated in tribological experiments in boundary lubricated conditions. Boundary film formation by neat P-SiSO was studied in Paper [2], and in Paper [3] we describe the use of P-SiSO as a multipurpose performance ingredient in MAC. A test methodology was devised in Paper [4] in order to evaluate the lubrication performance under component scale experiments in space relevant conditions. The designed ionic liquid lubricant was evaluated in Paper [5] by the specific methodology. Advanced surface analysis was employed to understand the tribo-mechanism of P-SiSO in both the model scale experiments as well as the component scale. The lubricated surfaces were analyzed in terms of surface topography- and chemistry, and mechanisms of lubrication are discussed. A highly effective boundary film based on ionic adsorption and formation of silicate was observed by these ionic liquids. This thesis demonstrates the feasibility of employing ionic liquids for lubrication of moving mechanical assemblies in space applications.
|
|
| 4. |
- Arridge, Christopher S., et al.
(författare)
-
Uranus Pathfinder : exploring the origins and evolution of Ice Giant planets
- 2012
-
Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 753-791
-
Tidskriftsartikel (refereegranskat)abstract
- The "Ice Giants" Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA's Cosmic Vision 2015-2025. UP was proposed to the European Space Agency's M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines the need to develop power sources suitable for the outer Solar System. The UP science case is based around exploring the origins, evolution, and processes at work in Ice Giant planetary systems. Three broad themes were identified: (1) Uranus as an Ice Giant, (2) An Ice Giant planetary system, and (3) An asymmetric magnetosphere. Due to the long interplanetary transfer from Earth to Uranus a significant cruise-phase science theme was also developed. The UP mission concept calls for the use of a Mars Express/Rosetta-type platform to launch on a Soyuz-Fregat in 2021 and entering into an eccentric polar orbit around Uranus in the 2036-2037 timeframe. The science payload has a strong heritage in Europe and beyond and requires no significant technology developments.
|
|
| 5. |
|
|
| 6. |
- Azua-Bustos, Armando, et al.
(författare)
-
Aeolian transport of viable microbial life across the Atacama Desert, Chile : Implications for Mars
- 2019
-
Ingår i: Scientific Reports. - : Springer. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Here we inspect whether microbial life may disperse using dust transported by wind in the Atacama Desert in northern Chile, a well-known Mars analog model. By setting a simple experiment across the hyperarid core of the Atacama we found that a number of viable bacteria and fungi are in fact able to traverse the driest and most UV irradiated desert on Earth unscathed using wind-transported dust, particularly in the later afternoon hours. This finding suggests that microbial life on Mars, extant or past, may have similarly benefited from aeolian transport to move across the planet and find suitable habitats to thrive and evolve.
|
|
| 7. |
- Bhardwaj, Anshuman, et al.
(författare)
-
A review on remotely sensed land surface temperature anomaly as an earthquake precursor
- 2017
-
Ingår i: International Journal of Applied Earth Observation and Geoinformation. - : Elsevier. - 1569-8432 .- 1872-826X. ; 63, s. 158-166
-
Tidskriftsartikel (refereegranskat)abstract
- The low predictability of earthquakes and the high uncertainty associated with their forecasts make earthquakes one of the worst natural calamities, capable of causing instant loss of life and property. Here, we discuss the studies reporting the observed anomalies in the satellite-derived Land Surface Temperature (LST) before an earthquake. We compile the conclusions of these studies and evaluate the use of remotely sensed LST anomalies as precursors of earthquakes. The arrival times and the amplitudes of the anomalies vary widely, thus making it difficult to consider them as universal markers to issue earthquake warnings. Based on the randomness in the observations of these precursors, we support employing a global-scale monitoring system to detect statistically robust anomalous geophysical signals prior to earthquakes before considering them as definite precursors.
|
|
| 8. |
- Bhardwaj, Anshuman, et al.
(författare)
-
Are Slope Streaks Indicative of Global‐Scale Aqueous Processes on Contemporary Mars?
- 2019
-
Ingår i: Reviews of geophysics. - : American Geophysical Union (AGU). - 8755-1209 .- 1944-9208. ; 57:1, s. 48-77
-
Tidskriftsartikel (refereegranskat)abstract
- Slope streaks are prevalent and intriguing dark albedo surface features on contemporary Mars. Slope streaks are readily observed in the equatorial and subequatorial dusty regolith regions with low thermal inertia. They gradually fade over decadal timescales. The proposed mechanisms for their formation vary widely based on several physicochemical and geomorphological explanations. The scientific community is divided in proposing both dry and wet mechanisms for the formation of slope streaks. Here we perform a systematic evaluation of the literature for these wet and dry mechanisms. We discuss the probable constraints on the various proposed mechanisms and provide perspectives on the plausible process driving global‐scale slope streak formation on contemporary Mars. Although per our understanding, a thorough consideration of the global distribution of slope streaks, their morphology and topography, flow characteristics, physicochemical and atmospheric coincidences, and terrestrial analogies weighs more in favor of several wet mechanisms, we acknowledge that such wet mechanisms cannot explain all the reported morphological and terrain variations of slope streaks. Thus, we suggest that explanations considering both dry and wet processes can more holistically describe all the observed morphological variations among slope streaks. We further acknowledge the constraints on the resolutions of remote sensing data and on our understanding of the Martian mineralogy, climate, and atmosphere and recommend continuous investigations in this direction using future remote sensing acquisitions and simulations. In this regard, finding more wet and dry terrestrial analogs for Martian slope streaks and studying them at high spatiotemporal resolutions can greatly improve our understanding.
|
|
| 9. |
- Bhardwaj, Anshuman, et al.
(författare)
-
Discovery of recurring slope lineae candidates in Mawrth Vallis, Mars
- 2019
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Several interpretations of recurring slope lineae (RSL) have related RSL to the potential presence of transient liquid water on Mars. Such probable signs of liquid water have implications for Mars exploration in terms of rover safety, planetary protection during rover operations, and the current habitability of the planet. Mawrth Vallis has always been a prime target to be considered for Mars rover missions due to its rich mineralogy. Most recently, Mawrth Vallis was one of the two final candidates selected by the European Space Agency as a landing site for the ExoMars 2020 mission. Therefore, all surface features and landforms in Mawrth Vallis that may be of special interest in terms of scientific goals, rover safety, and operations must be scrutinised to better assess it for future Mars missions. Here, we report on the initial detection of RSL candidates in two craters of Mawrth Vallis. The new sightings were made outside of established RSL regions and further prompt the inclusion of a new geographical region within the RSL candidate group. Our inferences on the RSL candidates are based on several morphological and geophysical evidences and analogies: (i) the dimensions of the RSL candidates are consistent with confirmed mid-latitude RSL; (ii) albedo and thermal inertia values are comparable to those of other mid-latitude RSL sites; and (iii) features are found in a summer season image and on the steep and warmest slopes. These results denote the plausible presence of transient liquid brines close to the previously proposed landing ellipse of the ExoMars rover, rendering this site particularly relevant to the search of life. Further investigations of Mawrth Vallis carried out at higher spatial and temporal resolutions are needed to identify more of such features at local scales to maximize the scientific return from the future Mars rovers, to prevent probable biological contamination during rover operations, to evade damage to rover components as brines can be highly corrosive, and to quantify the ability of the regolith at mid-latitudes to capture atmospheric water which is relevant for in-situ-resource utilization.
|
|
| 10. |
|
|
