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{{Short description|Space manufacturing and fluid behavior}}
{{orphan|date=August 2024}}
'''Low-gravity process engineering''' is a specialized field that focuses on the design, development, and optimization of industrial processes and manufacturing techniques in environments with reduced [[gravitational]] forces.<ref name=":2">{{Cite journal |last=Ostrach |first=S |date=January 1982 |title=Low-Gravity Fluid Flows |url=https://www.annualreviews.org/doi/10.1146/annurev.fl.14.010182.001525 |journal=Annual Review of Fluid Mechanics |language=en |volume=14 |issue=1 |pages=313–345 |doi=10.1146/annurev.fl.14.010182.001525 |bibcode=1982AnRFM..14..313O |issn=0066-4189|url-access=subscription }}</ref> This discipline encompasses a wide range of applications, from [[Weightlessness|microgravity]] conditions experienced in Earth orbit to the partial gravity environments found on celestial bodies such as the [[Moon]] and [[Mars]].<ref>{{Cite book |url=https://www.taylorfrancis.com/books/9781482265057 |title=Physics of Fluids in Microgravity |date=2002-01-10 |publisher=CRC Press |isbn=978-0-429-17706-4 |editor-last=Monti |editor-first=Rodolfo |edition=0 |language=en |doi=10.1201/9781482265057}}</ref>
As humanity extends its reach beyond Earth, the ability to efficiently produce materials, manage fluids, and conduct chemical processes in reduced gravity becomes crucial for sustained space missions and potential [[Space colonization|colonization]] efforts.<ref name=":3">{{Cite journal |
The historical context of low-gravity research dates back to the early days of [[space exploration]]. Initial experiments conducted during the Mercury and Gemini programs in the 1960s provided the first insights into fluid behavior in microgravity.<ref name=":4">{{Cite book |url=https://arc.aiaa.org/doi/book/10.2514/4.866036 |title=Low-Gravity Fluid Dynamics and Transport Phenomena |date=1990-01-01 |publisher=American Institute of Aeronautics and Astronautics |isbn=978-0-930403-74-4 |editor-last=Sani |editor-first=Robert L. |___location=Washington DC |language=en |doi=10.2514/5.9781600866036.0003.0014 |editor-last2=Koster |editor-first2=Jean N.}}</ref> Subsequent missions, including [[Skylab]] and the [[Space Shuttle program]], expanded our understanding of materials processing and [[fluid dynamics]] in space.<ref name=":5">{{Cite journal |
== Fundamentals of low-gravity environments ==
Low-gravity environments, encompassing both microgravity and reduced gravity conditions, exhibit unique characteristics that significantly alter physical phenomena compared to [[Gravity of Earth|Earth's gravitational field]]. These environments are typically characterized by [[gravitational acceleration]]s ranging from <math>10^{-6}</math><math>g</math> to <math>10^{-2}</math><math>g</math>, where <math>g</math> represents Earth's standard gravitational acceleration <math>(9.81 m/s^2)</math>.<ref>{{Cite journal |
Microgravity, often experienced in [[Spacecraft|orbiting spacecraft]], is characterized by the near absence of perceptible weight. In contrast, reduced gravity conditions, such as those on the Moon (<math>0.16g</math>) or Mars (<math>0.37g</math>), maintain a fractional gravitational pull relative to Earth.<ref>{{Cite web |title=Planetary Fact Sheet |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/ |access-date=2024-08-08 |website=nssdc.gsfc.nasa.gov}}</ref>
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# Absence of natural convection: On Earth, density differences in fluids due to temperature gradients drive [[natural convection]]. In microgravity, this effect is negligible, leading to diffusion-dominated heat and mass transfer.<ref name="auto1">{{Cite book |url=https://doi.org/10.1016/B978-0-08-044508-3.X5000-2 |title=Fluids, Materials and Microgravity |date=2004 |publisher=Elsevier |isbn=978-0-08-044508-3 |doi=10.1016/b978-0-08-044508-3.x5000-2}}</ref>
# Surface tension dominance: Without the overwhelming force of gravity, [[surface tension]] becomes a dominant force in fluid behavior, significantly affecting liquid spreading and containment.<ref>{{Cite book |last=Myshkis |first=A. D. |url=http://archive.org/details/lowgravityfluidm0000mysh |title=Low-Gravity Fluid Mechanics: Mathematical |date=1987-06-02 |publisher=Springer |others=Internet Archive |isbn=978-3-540-16189-9}}</ref>
# Particle suspension: In low-gravity environments, particles in fluids remain suspended for extended periods, as [[sedimentation]] and [[buoyancy]] effects are minimal.<ref name=":0">{{Cite journal |last=Todd |first=P. |date=1989-08-02 |title=Gravity-dependent phenomena at the scale of the single cell
=== Effects of low-gravity conditions on various physical processes ===
==== Fluid dynamics ====
In microgravity, fluid behavior is primarily governed by [[surface tension]], viscous forces, and inertia. This leads to phenomena such as large stable liquid bridges, spherical droplet formation, and [[Capillary action|capillary flow]] dominance.<ref name=":6">{{Cite journal |
==== Heat transfer ====
The lack of natural convection in microgravity significantly impacts heat transfer processes. [[Thermal conduction|Conduction]] and [[radiation]] become the primary modes of heat transfer, while forced convection must be induced [[Artificiality|artificially]]. This alteration affects cooling systems, boiling processes, and thermal management in spacecraft and space-based manufacturing.<ref name=":7">{{Citation |last=Straub |first=Johannes |title=Boiling Heat Transfer and Bubble Dynamics in Microgravity |date=2001-01-01 |
==== Material behavior ====
Low-gravity environments offer unique conditions for materials processing. The absence of buoyancy-driven convection and sedimentation allows for more uniform crystal growth and the formation of novel alloys and composites.<ref>{{Cite book |url=https://link.springer.com/book/9781468416855 |title=Materials Processing in Space |language=en}}</ref> Additionally, the reduced [[Stress (mechanics)|mechanical stresses]] in microgravity can lead to changes in material properties and behavior, influencing fields such as [[materials science]] and [[pharmaceutical research]].<ref name="auto">{{Cite journal |last=Ronney |first=Paul D. |date=1998-01-01 |title=Understanding combustion processes through microgravity research |url=https://www.sciencedirect.com/science/article/pii/S008207849880101X |journal=Symposium (International) on Combustion |volume=27 |issue=2 |pages=2485–2506 |doi=10.1016/S0082-0784(98)80101-X |hdl=2060/20000000185 |issn=0082-0784|hdl-access=free |url-access=subscription }}</ref>
== Challenges ==
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The absence of buoyancy and the dominance of surface tension in low-gravity environments significantly alter fluid behavior, presenting several challenges:
# Liquid-gas separation: Without buoyancy, separating liquids and gases becomes difficult, affecting processes such as [[Fuel-management systems|fuel management]] and [[Life-support system|life support systems]].<ref>{{Cite journal |
# Capillary effects: Surface tension dominance leads to unexpected fluid migrations and containment issues, requiring specialized designs for fluid handling systems.<ref>{{Cite journal |last=Weislogel |first=Mark Milton |date=1996-11-01 |title=Capillary Flow in an Interior Corner |url=https://ntrs.nasa.gov/citations/19970010346 |journal=NASA Technical Memorandum 107364 |language=en}}</ref>
# Bubble formation and coalescence: In microgravity, [[Bubble (physics)|bubbles]] tend to persist and coalesce more readily, potentially disrupting fluid processes and heat transfer mechanisms.<ref name=":8">{{Cite journal |last=Zhao |first=Jian-fu |date=2010-02-01 |title=Two-phase flow and pool boiling heat transfer in microgravity |url=https://www.sciencedirect.com/science/article/pii/S0301932209001451 |journal=International Journal of Multiphase Flow |series=Special Issue: Multiphase Flow Research in China |volume=36 |issue=2 |pages=135–143 |doi=10.1016/j.ijmultiphaseflow.2009.09.001 |bibcode=2010IJMF...36..135Z |issn=0301-9322|url-access=subscription }}</ref>
=== Heat transfer limitations ===
The lack of natural convection in low-gravity environments poses significant challenges for heat transfer processes:
# Reduced convective heat transfer: Without buoyancy-driven flows, heat transfer becomes primarily dependent on conduction and [[radiation]], potentially leading to localized hot spots and thermal management issues.<ref name=":9">{{Cite journal |
# Boiling and condensation: These [[Phase transition|phase change]] processes behave differently in microgravity, affecting cooling systems and thermal management strategies.<ref name=":7"/>
# Temperature gradients: The absence of natural mixing can result in sharp [[temperature gradient]]s, impacting reaction kinetics and material processing.<ref name="auto1"/>
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Designing equipment for low-gravity operations requires addressing several unique factors
# Mass and volume constraints: Space missions have strict limitations on [[payload]] mass and volume, necessitating compact and lightweight designs.<ref>{{Cite journal |
# Automation and remote operation: Many processes must be designed for [[Autonomous robot|autonomous]] or remote operation due to limited human presence in space environments.<ref>{{Cite journal |last=Sheridan |first=T.B. |date=October 1993 |title=Space teleoperation through time delay: review and prognosis
# Reliability and redundancy: The inaccessibility of space environments demands highly reliable systems with built-in [[Redundancy (engineering)|redundancies]] to mitigate potential failures.<ref>{{Cite book |url=https://isulibrary.isunet.edu/index.php?lvl=notice_display&id=10279 |title=Space Safety and Human Performance |date=2017-11-10 |publisher=Butterworth-Heinemann |isbn=978-0-08-101869-9 |language=en-US}}</ref>
# Microgravity-specific mechanisms: Equipment must often incorporate novel mechanisms to replace gravity-dependent functions, such as pumps for fluid transport or [[centrifuge]]s for separation processes.<ref>{{Cite journal |last=Schwartzkopf |first=S. H. |date=1992 |title=Design of a controlled ecological life support system: regenerative technologies are necessary for implementation in a lunar base CELSS
# Multi-functionality: Due to resource constraints, equipment is often designed to serve multiple purposes, increasing complexity but reducing overall payload requirements.<ref>{{Cite journal |
Addressing these challenges requires [[Interdisciplinarity|interdisciplinary]] approaches, combining insights from fluid dynamics, heat transfer, materials science, and [[aerospace engineering]]. As research in low-gravity process engineering progresses, new solutions and technologies continue to emerge, expanding the possibilities for space-based manufacturing and resource utilization.<ref>{{Cite web |date=2024-03-06 |title=ISS National Lab Releases In-Space Production Applications Funding Opportunity |url=https://www.issnationallab.org/release-nlra-2024-6/ |access-date=2024-08-08 |language=en-US}}</ref>
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Materials processing in space offers unique opportunities for producing novel materials and improving existing manufacturing techniques.
[[Crystal growth]] in space benefits from the absence of gravity-induced convection and sedimentation. This environment allows for the growth of larger, more perfect crystals with fewer defects.<ref>{{Cite journal |last=Ferré-D'Amaré |first=Adrian R. |date=1999-07-01 |title=Crystallization of Biological Macromolecules, by Alexander McPherson. 1999. Cold Spring Harbor, New York: Cold Spring Harbor Laboratory Press. Hardcover, 586 pp. $97 |url=https://www.cambridge.org/core/journals/rna/article/abs/crystallization-of-biological-macromolecules-by-alexander-mcpherson-1999-cold-spring-harbor-new-york-cold-spring-harbor-laboratory-press-hardcover-586-pp-97/2AAB312C66E0152B71B44C9F5B5C5B1E |journal=RNA |language=en |volume=5 |issue=7 |pages=847–848 |article-number=S1355838299000862 |doi=10.1017/S1355838299000862 |issn=1355-8382|url-access=subscription }}</ref> Space-grown crystals have applications in electronics, [[optics]], and pharmaceutical research.<ref>{{Cite journal |
[[Metallurgy]] and [[alloy]] formation in microgravity can result in materials with unique properties. The absence of buoyancy-driven convection allows for more uniform mixing of [[Melting|molten]] metals and the creation of novel alloys and composites that are difficult or impossible to produce on Earth.<ref name=":5" />
[[Additive Manufacturing by Material Extrusion of metals and ceramics|Additive manufacturing]] in low-gravity environments presents both challenges and opportunities. While the absence of gravity can affect material deposition and layer adhesion, it also allows for the creation of complex structures without the need for support materials.<ref name=":3" /> This technology has potential applications in on-demand manufacturing of spare parts and tools for long-duration space missions.<ref>{{Cite web |
=== Biotechnology applications ===
Microgravity conditions offer unique advantages for various [[biotechnology]] applications.
[[Protein crystallization]] in space often results in larger, more well-ordered crystals compared to those grown on Earth. These high-quality crystals are valuable for [[structural biology]] studies and drug design.<ref>{{Cite journal |
[[Cell culturing in open microfluidics|Cell culturing]] and tissue engineering benefit from the reduced mechanical stresses in microgravity. This environment allows for [[Three-dimensional space|three-dimensional]] cell growth and the formation of tissue-like structures that more closely resemble [[in vivo]] conditions.<ref>{{Cite journal |
Pharmaceutical production in space has the potential to yield purer drugs with improved [[efficacy]]. The absence of convection and sedimentation can lead to more uniform crystallization and particle formation, potentially enhancing drug properties.<ref>{{Cite journal |
=== Chemical engineering processes ===
[[Chemical engineering]] processes in microgravity often exhibit different behaviors compared to their terrestrial counterparts.
[[Chemical kinetics|Reaction kinetics]] in microgravity can be altered due to the absence of buoyancy-driven [[convection]]. This can lead to more uniform reaction conditions and potentially different reaction rates or product distributions.<ref name="auto"/><ref>{{Cite journal |
Separation processes, such as distillation and extraction, face unique challenges in low-gravity environments. The lack of buoyancy affects phase separation and mass transfer, requiring novel approaches to achieve efficient separations.<ref>{{Cite journal |
Catalysis in space presents opportunities for studying fundamental catalytic processes without the interfering effects of gravity. The absence of natural convection and sedimentation can lead to more uniform catalyst distributions and potentially different reaction pathways.<ref name=":2" /> This research may contribute to the development of more efficient catalysts for both space and terrestrial applications.<ref>{{Cite journal |
== Experimental platforms and simulation techniques ==
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=== Drop towers and parabolic flights ===
[https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Research/Drop_towers Drop towers] provide short-duration microgravity environments by allowing experiments to free-fall in evacuated shafts. These facilities typically offer
[[Reduced-gravity aircraft|Parabolic flights]], often referred to as "vomit comets," create repeated periods of microgravity lasting
=== Sounding rockets and suborbital flights ===
[[Sounding rocket]]s offer extended microgravity durations ranging from 3 to 14 minutes, depending on the rocket's apogee.<ref>{{Cite report |url=https://ui.adsabs.harvard.edu/abs/2006hsrc.rept.....S |title=The History of Sounding Rockets and Their Contribution to European Space Research |last=Seibert |first=Günther |journal=The History of Sounding Rockets and Their Contribution to European Space Research / Günther Seibert |date=2006-11-01 |volume=38 |issue=
[[Sub-orbital spaceflight|Suborbital flights]], such as those planned by commercial spaceflight companies, present new opportunities for microgravity research. These flights can offer several minutes of microgravity time and the potential for frequent, cost-effective access to space-like conditions.<ref>{{Cite journal |
=== International space station facilities ===
The International Space Station serves as a permanent microgravity laboratory, offering long-duration experiments in various scientific disciplines.<ref>{{Cite journal |
# [[Fluid Science Laboratory|Fluid Science Laboratory (FSL)]]: Designed for studying fluid physics in microgravity.<ref>{{Cite web |title=Fluid Science Laboratory |url=https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Columbus/Fluid_Science_Laboratory |access-date=2024-08-08 |website=www.esa.int |language=en}}</ref>
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# [[Microgravity Science Glovebox|Microgravity Science Glovebox (MSG)]]: A multipurpose facility for conducting a wide range of microgravity experiments.<ref>{{Cite web |title=Microgravity Science Glovebox |url=https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Columbus/Microgravity_Science_Glovebox |access-date=2024-08-08 |website=www.esa.int |language=en}}</ref>
These facilities enable researchers to conduct complex, long-term studies in a true microgravity environment, advancing our understanding of fundamental physical processes and developing new technologies for space exploration.<ref>{{Cite journal |
=== Computational fluid dynamics for low-gravity simulations ===
[[Computational fluid dynamics|Computational Fluid Dynamics (CFD)]] plays a crucial role in predicting and analyzing fluid behavior in low-gravity environments. CFD simulations complement experimental research by:
# Providing insights into phenomena difficult to observe experimentally.<ref>{{Citation |last=Lappa |first=Marcello |title=CHAPTER 1 - Space research |date=2004-01-01 |work=Fluids, Materials and Microgravity |pages=1–37 |editor-last=Lappa |editor-first=Marcello |url=https://www.sciencedirect.com/science/article/pii/B9780080445083500025 |access-date=2024-08-08 |place=Oxford |publisher=Elsevier |doi=10.1016/b978-008044508-3/50002-5 |isbn=978-0-08-044508-3|url-access=subscription }}</ref>
# Allowing parametric studies across a wide range of conditions.<ref>{{Cite journal |
# Aiding in the design and optimization of space-based systems.<ref>{{Cite journal |
CFD models for low-gravity applications often require modifications to account for the dominance of surface tension forces and the absence of buoyancy-driven flows.<ref>{{Cite journal |
As [[Moore's law|computational power]] increases, CFD simulations are becoming increasingly sophisticated, enabling more accurate predictions of complex multiphase flows and heat transfer processes in microgravity.<ref name=":8" />
== References ==
{{reflist}}
[[Category:Material handling]]
[[Category:Crystallography]]
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