Low-gravity process engineering: Difference between revisions

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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 |url=https://pubmed.ncbi.nlm.nih.gov/11540086/ |journal=ASGSB Bulletin: Publication of the American Society for Gravitational and Space Biology |volume=2 |pages=95–113 |issn=0898-4697 |pmid=11540086}}</ref>

=== Effects of low-gravity conditions on various physical processes ===

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==== 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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# Mass and volume constraints: Space missions have strict limitations on [[payload]] mass and volume, necessitating compact and lightweight designs.<ref>{{Cite journal |last1=Werkheiser |first1=Mary J. |last2=Fiske |first2=Michael |last3=Edmunson |first3=Jennifer |last4=Khoshnevis |first4=Behrokh |date=2015-08-31 |title=On The Development of Additive Construction Technologies for Application to Development of Lunar/Martian Surface Structures Using In-Situ Materials |url=https://arc.aiaa.org/doi/10.2514/6.2015-4451 |journal=AIAA 2015-4451 Session: Space Habitat Construction Methods |language=en |publisher=American Institute of Aeronautics and Astronautics |doi=10.2514/6.2015-4451 |hdl=2060/20150021416 |isbn=978-1-62410-334-6|hdl-access=free }}</ref>

# 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 |url=https://ieeexplore.ieee.org/document/258052 |journal=IEEE Transactions on Robotics and Automation |volume=9 |issue=5 |pages=592–606 |doi=10.1109/70.258052|url-access=subscription }}</ref>

# 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 |url=https://pubmed.ncbi.nlm.nih.gov/11537405/ |journal=BioScience |volume=42 |issue=7 |pages=526–535 |doi=10.2307/1311883 |jstor=1311883 |issn=0006-3568 |pmid=11537405}}</ref>

# Multi-functionality: Due to resource constraints, equipment is often designed to serve multiple purposes, increasing complexity but reducing overall payload requirements.<ref>{{Cite journal |last1=Menezes |first1=Amor A. |last2=Cumbers |first2=John |last3=Hogan |first3=John A. |last4=Arkin |first4=Adam P. |date=2015-01-06 |title=Towards synthetic biological approaches to resource utilization on space missions |journal=Journal of the Royal Society Interface |language=en |volume=12 |issue=102 |pages=20140715 |doi=10.1098/rsif.2014.0715 |issn=1742-5689 |pmc=4277073 |pmid=25376875}}</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 |doi-broken-date=1 November 2024 |issn=1355-8382|url-access=subscription }}</ref> Space-grown crystals have applications in electronics, [[optics]], and pharmaceutical research.<ref>{{Cite journal |last1=Littke |first1=Walter |last2=John |first2=Christina |date=1986-08-02 |title=Protein single crystal growth under microgravity |url=https://dx.doi.org/10.1016/0022-0248%2886%2990183-1 |journal=Journal of Crystal Growth |volume=76 |issue=3 |pages=663–672 |doi=10.1016/0022-0248(86)90183-1 |bibcode=1986JCrGr..76..663L |issn=0022-0248|url-access=subscription }}</ref>

[[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" />

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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 |last1=DeLucas |first1=L. J. |last2=Smith |first2=C. D. |last3=Smith |first3=H. W. |last4=Vijay-Kumar |first4=S. |last5=Senadhi |first5=S. E. |last6=Ealick |first6=S. E. |last7=Carter |first7=D. C. |last8=Snyder |first8=R. S. |last9=Weber |first9=P. C. |last10=Salemme |first10=F. R. |date=1989-11-03 |title=Protein crystal growth in microgravity |url=https://pubmed.ncbi.nlm.nih.gov/2510297/ |journal=Science |volume=246 |issue=4930 |pages=651–654 |doi=10.1126/science.2510297 |issn=0036-8075 |pmid=2510297|bibcode=1989Sci...246..651D }}</ref> The microgravity environment reduces sedimentation and convection, allowing for more uniform crystal growth.<ref>{{Cite journal |last1=McPherson |first1=Alexander |last2=DeLucas |first2=Lawrence James |date=2015-09-03 |title=Microgravity protein crystallization |journal=npj Microgravity |language=en |volume=1 |issue=1 |page=15010 |doi=10.1038/npjmgrav.2015.10 |pmid=28725714 |pmc=5515504 |issn=2373-8065}}</ref>

[[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 |last1=Grimm |first1=Daniela |last2=Wehland |first2=Markus |last3=Pietsch |first3=Jessica |last4=Aleshcheva |first4=Ganna |last5=Wise |first5=Petra |last6=van Loon |first6=Jack |last7=Ulbrich |first7=Claudia |last8=Magnusson |first8=Nils E. |last9=Infanger |first9=Manfred |last10=Bauer |first10=Johann |date=2014-04-04 |title=Growing tissues in real and simulated microgravity: new methods for tissue engineering |journal=Tissue Engineering. Part B, Reviews |volume=20 |issue=6 |pages=555–566 |doi=10.1089/ten.TEB.2013.0704 |issn=1937-3376 |pmc=4241976 |pmid=24597549}}</ref> Such studies contribute to our understanding of [[Cell biology|cellular biology]] and may lead to advancements in [[regenerative medicine]].<ref>{{Cite journal |last1=Becker |first1=Jeanne L. |last2=Souza |first2=Glauco R. |date=2013-04-12 |title=Using space-based investigations to inform cancer research on Earth |url=https://www.nature.com/articles/nrc3507 |journal=Nature Reviews Cancer |language=en |volume=13 |issue=5 |pages=315–327 |doi=10.1038/nrc3507 |pmid=23584334 |issn=1474-1768|url-access=subscription }}</ref>

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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 2–10 seconds of high-quality microgravity.<ref>{{Cite journal |last=Steinberg |first=Ted |date=2008 |title=Reduced Gravity Testing and Research Capabilities at Queensland University of Technology's New 2.0 Second Drop Tower |url=https://www.scientific.net/AMR.32.21 |journal=Advanced Materials Research |language=en |volume=32 |pages=21–24 |doi=10.4028/www.scientific.net/AMR.32.21 |issn=1662-8985|url-access=subscription |doi-access=free }}</ref> Notable examples include [[Glenn Research Center|NASA's Glenn Research Center]] [https://www1.grc.nasa.gov/facilities/drop/ 2.2-Second Drop Tower] and the 146-meter [[ZARM]] Drop Tower in Bremen, Germany.<ref>{{Cite journal |last1=von Kampen |first1=Peter |last2=Kaczmarczik |first2=Ulrich |last3=Rath |first3=Hans J. |date=July 2006 |title=The new Drop Tower catapult system |url=https://linkinghub.elsevier.com/retrieve/pii/S0094576506000762 |journal=Acta Astronautica |language=en |volume=59 |issue=1–5 |pages=278–283 |doi=10.1016/j.actaastro.2006.02.041|bibcode=2006AcAau..59..278V |url-access=subscription }}</ref>

[[Reduced-gravity aircraft|Parabolic flights]], often referred to as "vomit comets," create repeated periods of microgravity lasting 20–25 seconds by flying aircraft in [[Parabolic arch|parabolic arcs]].<ref>{{Cite journal |last1=Karmali |first1=Faisal |last2=Shelhamer |first2=Mark |date=September 2008 |title=The dynamics of parabolic flight: flight characteristics and passenger percepts |journal=Acta Astronautica |volume=63 |issue=5–6 |pages=594–602 |doi=10.1016/j.actaastro.2008.04.009 |issn=0094-5765 |pmc=2598414 |pmid=19727328|bibcode=2008AcAau..63..594K }}</ref> These flights allow researchers to conduct hands-on experiments and test equipment destined for space missions.<ref>{{Cite journal |last1=Pletser |first1=Vladimir |last2=Rouquette |first2=Sebastien |last3=Friedrich |first3=Ulrike |last4=Clervoy |first4=Jean-Francois |last5=Gharib |first5=Thierry |last6=Gai |first6=Frederic |last7=Mora |first7=Christophe |date=2015-09-01 |title=European parabolic flight campaigns with Airbus ZERO-G: Looking back at the A300 and looking forward to the A310 |url=https://www.sciencedirect.com/science/article/pii/S0273117715003622 |journal=Advances in Space Research |volume=56 |issue=5 |pages=1003–1013 |doi=10.1016/j.asr.2015.05.022 |bibcode=2015AdSpR..56.1003P |issn=0273-1177|url-access=subscription }}</ref>

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# 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 |last1=Balasubramaniam |first1=R. |last2=Rame |first2=E. |last3=Kizito |first3=J. |last4=Kassemi |first4=M. |date=2006-01-01 |title=Two Phase Flow Modeling: Summary of Flow Regimes and Pressure Drop Correlations in Reduced and Partial Gravity |url=https://ntrs.nasa.gov/citations/20060008906 |journal=NASA NTRS |language=en}}</ref>

# Aiding in the design and optimization of space-based systems.<ref>{{Cite journal |last1=Brendel |first1=Leon PM |last2=Weibel |first2=Justin A |last3=Braun |first3=James E |last4=Groll |first4=Eckhard A |date=2023-03-01 |title=Microgravity two-phase flow research in the context of vapor compression cycle experiments on parabolic flights |url=https://www.sciencedirect.com/science/article/pii/S0301932222003172 |journal=International Journal of Multiphase Flow |volume=160 |pagesarticle-number=104358 |doi=10.1016/j.ijmultiphaseflow.2022.104358 |bibcode=2023IJMF..16004358B |issn=0301-9322|doi-access=free }}</ref>

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 |last1=Muradoglu |first1=Metin |last2=Tryggvason |first2=Gretar |date=2008-02-01 |title=A front-tracking method for computation of interfacial flows with soluble surfactants |url=https://www.sciencedirect.com/science/article/pii/S002199910700438X |journal=Journal of Computational Physics |volume=227 |issue=4 |pages=2238–2262 |doi=10.1016/j.jcp.2007.10.003 |bibcode=2008JCoPh.227.2238M |issn=0021-9991|url-access=subscription }}</ref> Validation of these models typically involves comparison with experimental data from microgravity platforms.<ref>{{Cite journal |last1=Dhir |first1=Vijay Kumar |last2=Warrier |first2=Gopinath R. |last3=Aktinol |first3=Eduardo |last4=Chao |first4=David |last5=Eggers |first5=Jeffery |last6=Sheredy |first6=William |last7=Booth |first7=Wendell |date=2012-11-01 |title=Nucleate Pool Boiling Experiments (NPBX) on the International Space Station |url=https://doi.org/10.1007/s12217-012-9315-8 |journal=Microgravity Science and Technology |language=en |volume=24 |issue=5 |pages=307–325 |doi=10.1007/s12217-012-9315-8 |bibcode=2012MicST..24..307D |issn=1875-0494|url-access=subscription }}</ref>