Tribology of Space Mechanisms

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (28 February 2020) | Viewed by 34102

Special Issue Editor


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Guest Editor
Institut Femto-st, CNRS UMR 6174, Department of Applied Mechanics, 24 rue de l’Epitaphe, 25030 Besançon, France
Interests: tribology; thin coatings; vacuum; tribochemistry; dry lubricants; molybdenum compounds; composite coatings; micromechanics of materials
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Special Issue Information

Dear Colleagues,

From the very beginning of space exploration, “space tribology” has been a specific field of competences in its own right. Over the last 70 years, researchers and engineers have developed a keen understanding of the fact that tribology in space is a real challenge. The constant increase of complexity of space mechanisms and a requirement for increasingly longer lifetime with no possible maintenance once in space make tribology of primary importance in the success or failure of a mission. Another important factor to take into account is ground tests. Every single mechanism, even one-shot mechanisms, has to be tested to certify that they will resist launching operations and then properly function in space. Those tests are performed in environments that are as representative of the mechanism’s final destination environment as possible, but also in standard laboratory conditions (cleanrooms) at room temperature (even some systems intended to work under cryogenic conditions!). Ground operations can amount to as high as 30% of the total mechanism’s working lifetime. Consequently, lubrication in space mechanisms must be sustained in multiple physicochemical and mechanical environments successively, making it the great challenge of space tribology.

This Special Issue aims to promote the current advances and future trends in the field of space tribology, which is not limited to vacuum tribology. Papers dealing with both fundamental and application-driven studies of lubricants to meet the challenge of lubricating space mechanisms are welcome. Lubricants that are of interest in this Special Issue include but are not limited to solid lubricants (bulk, coatings, composites), fluid lubricants, and greases. Moreover, theoretical and experimental work are also of interest. Researchers working in space tribology and related fields are gratefully invited to submit their paper. Both academic and industrial contributions are welcome.

I look forward to receiving your contributions.

Dr. Guillaume Colas
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Tribology
  • Space mechanism
  • Fluid lubricants
  • Grease
  • Dry lubricants
  • Vacuum

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Published Papers (6 papers)

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Research

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15 pages, 9774 KiB  
Communication
Cold Welding in Hold Down Points of Space Mechanisms Due to Fretting When Omitting Grease
by Andreas Merstallinger, Roland Holzbauer and Nathan Bamsey
Lubricants 2021, 9(8), 72; https://doi.org/10.3390/lubricants9080072 - 21 Jul 2021
Cited by 8 | Viewed by 4321
Abstract
Cold welding refers to an effect related to space (vacuum). The heavy vibrations during a launch subject interfaces (hold down points) to oscillating motions which may lead to formation of a kind of “friction weld”. If so, these mechanisms may get stuck, and [...] Read more.
Cold welding refers to an effect related to space (vacuum). The heavy vibrations during a launch subject interfaces (hold down points) to oscillating motions which may lead to formation of a kind of “friction weld”. If so, these mechanisms may get stuck, and deployment will be hindered. This may endanger the functionality of the mission (instruments) or even the whole spacecraft (if solar panels do not open). Several studies have been done to characterize material combinations (including coatings) for their ability to cold welding in space. Meanwhile, also during launch grease free contacts are demanded. If grease hat to be omitted, the risk of cold welding under fretting was found to increase (when testing in high vacuum). To rate this risk under launch conditions, the test method was recently extended for testing under launch conditions. The new tests procedure consists of fretting applied in the sequence in air, low vacuum and high vacuum. The paper shall present first results gained with this new method of testing in launch conditions and compare them to previous studies done in vacuum. Following the need of space industry on mechanisms for launch and in-orbit life, a first set of combinations of materials and coatings were selected for this new test sequence where fretting is now applied in a sequence of air, low vacuum and high vacuum. Under this sequence, the measured levels of adhesion and it’s evolvement was found to differ strongly from tests done formerly. The paper outlines these first results and compares them to existing data. Full article
(This article belongs to the Special Issue Tribology of Space Mechanisms)
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31 pages, 44644 KiB  
Article
Experimental Analysis of Friction and Wear of Self-Lubricating Composites Used for Dry Lubrication of Ball Bearing for Space Applications
by Guillaume Colas, Aurélien Saulot, Yann Michel, Tobin Filleter and Andreas Merstallinger
Lubricants 2021, 9(4), 38; https://doi.org/10.3390/lubricants9040038 - 3 Apr 2021
Cited by 9 | Viewed by 4033
Abstract
Lubricating space mechanisms are a challenge. Lubrication must be sustained in different environments, for a very long period of time, and without any maintenance possible. This study focuses on the self-lubricating composite used in the double transfer lubrication of ball bearing. Ball/races contacts [...] Read more.
Lubricating space mechanisms are a challenge. Lubrication must be sustained in different environments, for a very long period of time, and without any maintenance possible. This study focuses on the self-lubricating composite used in the double transfer lubrication of ball bearing. Ball/races contacts are lubricated via the transfer of materials from the cage that is made of the composite. A dedicated tribometer has been designed for the study. A specificity of the tribometer is to not fully constrain the composite sample but to let it move, as the cage would do in the bearing. Four composites (PTFE, MoS2, glass or mineral fibers) where tested in ultrahigh vacuum and humid air environments. Transfer was achieved with morphologies and composition similar to what is observed on real bearings. Adhesion measurements performed on composite materials before and after friction allowed one to explain the differences in tribological behaviors observed (transfer quality and contact instabilities). Beyond strengthening the composites, fibers are shown to be critical in trapping mechanically and chemically the transferred material to lubricate and prevent instabilities. Equilibrium between internal cohesion of transferred material, and adhesion to counterparts must be satisfied. Mass spectrometry showed that water appears also critical in the establishment of stable transfer film, even in vacuum. Full article
(This article belongs to the Special Issue Tribology of Space Mechanisms)
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14 pages, 3344 KiB  
Article
CERES Gimbal Performance on Terra
by John C. Butler
Lubricants 2020, 8(8), 79; https://doi.org/10.3390/lubricants8080079 - 27 Jul 2020
Cited by 1 | Viewed by 3327
Abstract
The Terra satellite has been operating in orbit for 20 years. The Terra satellite is also called the flagship earth-observing satellite. The two Clouds and the Earth’s Radiant Energy System CERES instruments on board continue to function nominally. Their expected mission lifetime was [...] Read more.
The Terra satellite has been operating in orbit for 20 years. The Terra satellite is also called the flagship earth-observing satellite. The two Clouds and the Earth’s Radiant Energy System CERES instruments on board continue to function nominally. Their expected mission lifetime was 7 years. Critical to their performance is the longevity of the scanning gimbals. This can be traced to the performance of the fluid-lubricated bearings. Two metrics are used to estimate their lifetime and health. Both lend themselves to readily available data and ease of interpretation. One is predicting the evaporative lubricant loss. This analysis indicates that the lubricant supply is adequate for the continual life of the gimbals. The second is trending the torque with time. Torque precursors are sampled quarterly. These data are converted to torque. Two types of torque behavior were examined. Contrasting torque data have supported the conclusion that the gimbals are operating nominally. This can be partially attributed to the design choices for the bearings and lubricant. The aim of this paper is to quantitatively describe the present health and expected life of the CERES gimbals on the Terra satellite. Full article
(This article belongs to the Special Issue Tribology of Space Mechanisms)
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11 pages, 2177 KiB  
Article
High Temperature Microtribological Studies of MoS2 Lubrication for Low Earth Orbit
by Peter Serles, Khaled Gaber, Simo Pajovic, Guillaume Colas and Tobin Filleter
Lubricants 2020, 8(4), 49; https://doi.org/10.3390/lubricants8040049 - 24 Apr 2020
Cited by 26 | Viewed by 3868
Abstract
Molybdenum disulfide is one of the most common lubricant coatings for space systems but it displays enormous susceptibility to environmental conditions making it hard to predict performance throughout the entire lifetime. The majority of mechanisms for space operate in low Earth orbit where [...] Read more.
Molybdenum disulfide is one of the most common lubricant coatings for space systems but it displays enormous susceptibility to environmental conditions making it hard to predict performance throughout the entire lifetime. The majority of mechanisms for space operate in low Earth orbit where temperatures typically reach 120 °C along with exposure to highly reactive atomic oxygen which can be detrimental to lubricant performance. In the present study, a MoS2 lubricant coating is tested using friction force microscopy under different environmental conditions including air and dry nitrogen environments with temperatures ranging from 25 °C to 120 °C. The increased temperature was found to be beneficial for friction behaviour in air up to 100 °C as ambient humidity is removed from the contact, but higher temperatures become detrimental as increased reactivity leads to oxidation. These competing effects resulted in a minimum coefficient of friction at 110 °C in the air environment. The high temperature also increases the wear of the coatings as the intrinsic shear strength decreases with thermal energy which in turn disrupts tribofilm formation leading to increased friction. The run-in duration and magnitude are both found to decrease with temperature as the energy barrier to optimal reconfiguration is reduced. Finally, contextualization of the present findings for mechanisms operating in low earth orbit is discussed. Full article
(This article belongs to the Special Issue Tribology of Space Mechanisms)
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Review

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56 pages, 6101 KiB  
Review
Effective Application of Solid Lubricants in Spacecraft Mechanisms
by Jeffrey R. Lince
Lubricants 2020, 8(7), 74; https://doi.org/10.3390/lubricants8070074 - 10 Jul 2020
Cited by 46 | Viewed by 13727
Abstract
Solid lubricants, antiwear coatings, and self-lubricating composites are used in applications on spacecraft where oils and greases cannot be used because of the need to avoid lubricant volatility/migration, and where the application requires significant temperature variation, accelerated testing, higher electrical conductivity, or operation [...] Read more.
Solid lubricants, antiwear coatings, and self-lubricating composites are used in applications on spacecraft where oils and greases cannot be used because of the need to avoid lubricant volatility/migration, and where the application requires significant temperature variation, accelerated testing, higher electrical conductivity, or operation in boundary conditions. The purpose of this review is to provide spacecraft designers with tools that can aid in the effective use of solid-based tribological materials, both to increase their usage, and to reduce anomalies. The various tribological material formulations are described, including how their materials, physical, and chemical properties affect their performance. Included are typical solid lubricants like PTFE and bonded or sputter-deposited MoS2, as well as low shear metal coatings, hard coatings, and composite materials (including bulk composites and nanocomposite coatings). Guidance is given on how to develop mechanisms that meet performance requirements, but also how to optimize robustness, so that success is achieved even under unforeseen circumstances. Examples of successful applications are given, as well as how to avoid potential pitfalls, and what the future of solid tribological materials may hold. Full article
(This article belongs to the Special Issue Tribology of Space Mechanisms)
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15 pages, 2521 KiB  
Review
Long-Term Storage Considerations for Spacecraft Lubricants
by Michael Buttery, Simon Lewis, Anthony Kent, Rachel Bingley and Matthew Cropper
Lubricants 2020, 8(3), 32; https://doi.org/10.3390/lubricants8030032 - 13 Mar 2020
Cited by 15 | Viewed by 3369
Abstract
Spacecraft mechanisms commonly undergo extended periods of storage, either on-ground, or in-flight and there are an increasing number of missions for which some element of long-term storage may be required. Despite the obvious potential for degradation of lubricants during storage which might impact [...] Read more.
Spacecraft mechanisms commonly undergo extended periods of storage, either on-ground, or in-flight and there are an increasing number of missions for which some element of long-term storage may be required. Despite the obvious potential for degradation of lubricants during storage which might impact mechanism functionality or life and so even become mission-threatening, today’s understanding of storage phenomena is rather incomplete. This paper provides consolidation and review of recent experimental studies in this area and considers the range of storage conditions and associated degradation phenomena which could impact different lubricants. Whilst some storage best practice guidelines exist, experimental verification of the impact of storage phenomena has rarely been carried out and test data is rather scarce and incomplete. Given the absence of comprehensive data to support design, lubricant selection or the development of storage protocols, it is shown that for all lubricant types careful control of storage and test environments combined with monitoring of the evolving tribological performance during periodic mechanism exercising are presently the most effective storage risk mitigations. Full article
(This article belongs to the Special Issue Tribology of Space Mechanisms)
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