49th International Conference on Environmental Systems ICES-2019-203 7-11 July 2019, Boston, Massachusetts

Passive no moving parts capillary solutions for spacecraft life support systems

Mark M. Weislogel1 and Ryan M. Jenson2 IRPI LLC, Portland, Oregon, 97223

Life support systems for plant, animal, and crew habitats are replete with the challenges of managing poorly wetting aqueous solutions in a low-g environment. A brief review of noteworthy on-orbit system failures provides ample renewed motivation to understand microgravity capillary phenomena to the point such failures may be avoided in the future. Historic and recent NASA-funded low-g experiments are highlighted that greatly expand our experience base and comfort level to prepare for and preferably exploit capillary forces. Our specific aim is to replace the passive role of gravity on earth with the combined passive roles of surface tension, wetting, and container geometry in space. We demonstrate a general approach highlighting high-TRL examples pertinent to urine collection and processing. From this specific example we demonstrate more specific applications to passive in-line separator devices, beverage cups, and bio-sample de-bubblers. Broader applications can be made to other challenging processes such as brine drying, condensing heat exchangers, liquid sorbent CO2 scrubbers, wet lab unit operations, and habitats for plants and animals.

I. Introduction n earth, we take it for granted how gravity passively separates gases from liquids. In space, however, without O buoyancy, nearly all fluids to various degrees become mixtures of gases and liquids that can be difficult to re- separate. In other words, most fluid systems aboard spacecraft are or become multiphase fluid systems. Unfortunately, not knowing the location of liquids and gases in such systems can lead to trouble. As examples, a single bubble lodges in a circular tube preventing the flow of water in the primary hydrolysis oxygen generator.1 A capillary flow is halted by a ‘manifold’ deactivating a large thermal control system.2 Contamination of rotating machinery leads to fouling and failure of the primary waste water control system.3-5 Routine operation of a condensing heat exchanger6 in a water recovery loop leads to dry out, coating failure, and ejection of liquid droplets into the cabin air stream. Condensate 7,8 droplets in astronaut backpacks corrupt the output of a CO2 sensor leading to the premature termination of EVAs. A fluid physics flight experiment is irretrievably ruined at initiation when a fluid interface is destabilized following an initial retraction of a sliding lid.9 Plant habitats are persistently foiled by lethal root-water management issues.10 The list goes on, demonstrating a strong need to address our ‘fluidic shortcomings’ in low-gravity environments— especially those that enable space exploration. Poor fluid system design can lead to disastrous consequences,11 but for the most part, and for life support systems in general, crew time12-14 is consumed by repair and maintenance of mundane life support equipment to keep operations at acceptable, if not tolerable levels. A perfect example is the approximately 5 hours per month of crew time spent simply bleeding bubbles from Teflon CWC-I and PWR water supply bags on ISS.15 Such conditions may not be satisfactory for NASA’s longer duration Moon and Mars exploration missions. What leads to such troublesome equipment is a general lack of familiarity with large length scale capillary fluidic phenomena that precludes inspired robust routine design. If future long-term missions are to be successful and efficient, something as mundane as low-g plumbing must be well understood and practically deployed. We seek next- generation capillary fluidics solutions for passive and semi-passive phase separations that are critical to the reliable operation of current and future spacecraft life support systems, plant and animal habitat systems, propellant and coolant management systems, bio-fluidics sequencers and processors, and passive fluids delivery and control systems for life and physical sciences experiments. We seek solutions that are low-cost, fast-to-flight, and COTS wherever permissible. We believe we are in an historically unique era to support a rapid advance of practical capillary fluidics solutions for advanced fluids management aboard ISS and future exploration spacecraft. The increasing amount of

1Principle Engineer, 11535 SW 67th Ave. 2President, Lead Engineer, 11535 SW 67th Ave.

Copyright © 2019 IRPI LLC NASA-enabled fundamental and applied research using ground-based facilities (i.e., drop towers) and the ISS is establishing a pathway for accelerating the deployment of new solutions with expectations of greater simplicity and reliability. Proven methods for passive phase separation and containment16-18 have leveraged further engineering solutions concerning microgravity well-plate design for microbial monitoring, ISS hydrosol concentration for drinking water diagnosis, super-hydrophilic coatings development for contaminated aqueous streams, condensate water capture devices, urine collection devices, brine distribution and drying, low-g CO2 scrubbing, Lab-On-Chip and Organ-On- Chip in space, and others. We are finding that the more we become aware of the shortcomings of current spacecraft fluid systems designs, the more challenges with ready capillary solutions or improvements we identify. In this paper we first briefly review a small selection of experiments performed aboard spacecraft, the results of which should be common knowledge to the designers of capillary fluidics systems. Such a review could be greatly expanded. We then highlight a single example of an early capillary solution for a urine collection system. The accumulating successes from one low-g demonstration to another provide a general approach to such passive phase separation challenges. We then provide subsequent examples of the design process for TRL6 to TRL9 development and demonstration for passive in-line separators, drinking cups, and bio-sample de-bubblers. For brevity, we confine our purview largely to the efforts of the authors and co-workers.

II. Low-g Capillary Fluidics Foundations A line of spaceflight fluid physics experiments supported in large part by NASA over the past 30 years serves today as a foundation from which to design practical spaceflight engineering systems. Samples of such fundamental results may be cited.19 For example here, we cite the Space Shuttle Interface Configuration Experiments which demonstrated how multiple asymmetric interface configurations can arise in a single simple axisymmetric container,20 and that mathematical equilibrium can eventually be achieved for partially wetting systems despite significant contact angle hysteresis.21 Such results can be employed to re-interpret the results of earlier spaceflight experiments.22 The ISS Capillary Flow Vane Gap Experiments23 demonstrated critical geometric wetting conditions leading to large shifts in liquid position following miniscule changes to container geometry. The ISS Capillary Flow Interior Corner Flow Experiments24 demonstrated a variety of passive capillary-driven flows in containers with interior corners, flows that serve as building blocks for passive fluid migrations, positioning, containment, and bubble separations. The ISS Capillary Channel Flow Experiments25 demonstrated the open-channel ingestion limits of forced inertial-capillary flows as well as the limits of passive bubble phase separations in open wedge conduits.26 Though other such threads of research could be identified, this short list provides warnings, bounds, and potential for advanced capillary fluidics systems design: warnings—when certain desirable surface configurations may be unstable or even unphysical, bounds—what the limits of desired operation are for a given process or device, and potential—that increasingly effective tools and experience are in hand to exploit the ever-present passive capillary force through the judicious control of wetting conditions and system geometry.

III. Example of Low-g Capillary Fluidics Solution: Urine Collection System Urine collection and processing in space presents challenges that are difficult to overcome in a highly reliable manner. Though potentially problematic mechanically-driven rotary separators may be required to process such wastes, geometric considerations that enable concurrent capillary fluidic function can boost reliability without introducing weight, mass, or power penalties. In some situations, mechanical solutions can be entirely avoided. One such capillary fluidics solution for the urine collection and separation process was proposed with scale models built and successfully tested aboard low-g aircraft.27 A schematic of the system is re-presented in Figure 1 for the purpose of recounting the capillary fluidics functions of device geometry. The device of Figure 1 succeeds in large part due the knowledge that low-liquid content gas-driven two-phase flows of a poorly wetting liquid will produce wall-bound rivulet flows.28 Introducing an interior corner along such a conduit provides a low energy state for the rivulet which serves as a guide creating an initial passive phase separation (Ref. Figure 1a, sections A-A and B-B). The expansion region maintains the interior corner geometry promoting continuous capillary connection while significantly diffusing the motive gas stream, which is driven by a downstream fan (sections B-B and C-C). The liquid accumulates in the vane structure of the reservoir (section C-C) where it may be drained as desired, the motive air passing above through the gas outlet port. Low-g tests conducted with both highly and poorly wetting liquids established conditions where 100% liquid and 100% gas separations occur, Ref. Figure 1b. Except for the downstream fan and liquid draining pump, this urine collection example provides a completely passive phase separation function. The solutions arise primarily as a result of careful geometry selection.

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Diffuse backlight Video camera A A-A Test Air A article

B-B 2-phase B B C

Air pump Air C-C C

Liquid Liquid pump a) Liquid b)

Figure 1. Passive phase separation concept for urine collection system: a) Schematic with singly separated and guided rivulet flow established by section A-A, maintained through diffuser section B-B, and collected or otherwise wicked into containment section C-C. b) Image of low-g aircraft experiment hardware.

IV. Example of Two Capillary Fluidic Devices

A. In-Line Phase Separator (TRL6) As demonstrated above as on numerous occasions on ISS29-32 the interior corner geometry is readily exploited as a passive bubble separating construction for applications where the effects of buoyancy or other body forces are small. For example, the passive bubble-exuding characteristic26 of the wedge is further exploited by bisecting it into narrower wedges via the similarly tapering vane sketched in Figure 2. A range of bubble, slug, and annular flows are introduced into the conduit where bubbles are resisted from entering the wedge by the wedge geometry, while bubbles residing in the wedge passively migrate to the free surface where they coalesce with other bubbles and leave the liquid stream in an identical manner as the Capillary Channel Flow investigation.26 In so doing, the device provides a significant passive phase separation operation (100% in certain regimes). Drop tower test results prove this point as shown in Fig. 3. For fixed liquid Ql and gas Qg flow rates, the results are identical at steady state regardless of initial orientation with respect to gravity.

Plugged pilot hole C D A B

2-f flow Gas out

2f in A-A B-B Vane Plugged C-C a) D-D b) Liquid out pilot holes

Figure 2. a) Low-g schematic of inline passive phase separation device. b) Transparent 3-D SLA printed version of device: Inlet and return lines identified and positioned for diagnostic camera FOV.

For this application, to design such a device to respond within the brief low-g time afforded by the drop tower, the design guides and observations of previous work are combined to compute the unique geometry with appropriate dimensions and materials to assure performance following a single and highly compressed design cycle. The test cells of Figs. 2 and 3 are 3-D printed using transparent polymer Accura-60 and the stereo lithographic approach. The equilibrium interface configurations and stability of all critical surfaces are analyzed using the IRPI personnel- developed SE-FIT® software33,34 as well as full CFD as warranted.

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Qg 100% gas return 1-go Qg Qg

a) Q a. l Gas out Q 1 cm l

Ql 100% liquid return

Qg 100% gas return 0-go Liquid out

Qg 2-f in

Q b)b. l c.c)

Ql 100% liquid return blind access ports

Figure 3. a) Terrestrial and b) low-g steady flow two-phase distributions during a 2.1s drop tower test of a wedge geometry-based bubble phase separator (ref. Fig. 2a). The test fluid is HFE-7500 at gas-liquid volumetric flow ratio of 1:1 (Qg = 0.6 ml/s). In a) gravity separates the fluid phases. In b) the 1-g stratified flow gives way to a bubble-slug flow in low- g which is readily and completely separated by the device. The steady behavior of the device is identical when inverted. c) Transparent version of low-g certified transparent 3-D printed passive phase separator for in-line installation aboard spacecraft.

B. Omni-g Beverage Cup (TRL9) A different style of phase separating device is the Space Cup demonstrated aboard the ISS as part of the Capillary Beverage Experiment.35,36 Representative images from tests performed aboard the ISS are provided in Fig. 4. This effort was pursued in part with the purpose of demonstrating that the role of gravity in the drinking process can be replace by the combined roles of surface tension and container geometry in space. It was also conducted for purposes of capillary fluidic design verification and validation. With the general knowledge of large length scale capillarity highlighted above, engineering models of such a cup were designed and printed, scale models drop tower tested to assure low-g performance, flight models fabricated and certified, with flight demonstrations occurring within months.

a) b) c) d)

Figure 4. a) Transparent 3D-printed Space Cup. b) Astronaut Kjell Lindgren conducts Capillary Beverage experiment during Expedition 44/45. c) Particle image velocimetry during steady drain tests performed by astronaut Scott Kelly with d) full CFD numerical comparison.36

The design succeeds by providing a continuous capillary gradient along its tapering interior corner which terminates at the lip of the cup. Any physical contact with the lip of the cup makes capillary contact with the liquid within it allowing the contents to be drained through an earth-like drinking experience. In effect, in low-g, the ‘lip’ of the cup is, energetically speaking, the ‘bottom’ of the cup. The interior corner provides the passive roles of liquid collection, bubble separation, and stable containment against mechanical perturbations during handling. The cup function does not require highly controlled wetting conditions, or even favorable geometric wetting conditions, and excellent performance could be demonstrated for poorly wetting ‘contaminated’ liquids such as clean water, tea, coffee, cocoa, lemonade, lime drink, fruit punch, and peach mango smoothie. In fact, the highest drain rates were achieved for the least wetting liquids with 100% drainage (0% hold-up). The Capillary Beverage experiment provides a light-hearted example of a serious demonstration of the 4 International Conference on Environmental Systems

state of the art capillary fluidics design process for device development on spacecraft. The general method is repeatedly applied for more pressing engineering systems.

V. Example of COTS-Like Design Method A more specific and practical example is the passive bubble separation device designed, developed, demonstrated, flight certified, and flight verified for improved detection of microbes in ISS potable water.18 Images of the effort are provided in Fig. 5 that depict InnovaPrep LLC’s concentration and extraction system with integral ‘de-bubbler’ device identified. In such situations the fluid sample volume is small enough and time responses short enough that drop tower tests are adequate to demonstrate equilibrium behavior. Thus, the full-scale transparent 3D-printed passive separation device could be developed as a high-TRL product using our accelerated design approach.

g g sample

- 1

b)

g g sample

- 0 d)

sample e) a) c) collection

Figure 1: a) Image of InnovaPrep LLC’s microbe concentrator for remote sampling for biome monitoring on ISS with IPRI-designed integral passive bubble separating device (‘de-bubbler’) identified. b) Advanced debubbler demonstration on ISS by astronaut Ricky Arnold. c) Close-up image of device in flight configuration. d) Sequence of images during worst- case passive reorientation of single phase liquid during 2.1 s drop tower test (time increasing left to right, top to bottom). Identical tests with bubbly liquid samples demonstrate passive separation and coalescence events during the 1-g to low-g transition. e) Magnified image of final low-g equilibrium configuration with liquid collected over sample drain port. Nearly all of the liquid can be drained from this single port.

The design exploits knowledge gained from example experiments and demonstrations cited herein. Following customer specification, the device was quickly designed and 3D-printed, with high fidelity qualification tests performed with flight liquids using a high rate drop tower.38 Approximately 50 drop tower tests were performed on short order certifying TRL6 for the device preflight. The (debubbler) unit was then flown to the ISS for advanced demonstrations as part of the WetLab-2 Experiment.37 Astronaut Ricky Arnold performed the successful demonstrations aboard the ISS establishing TRL9 for the device (October 2018). Additional devices are anticipated to be delivered to ISS for routine biome-level inspections. The ‘debubbler-family’ of passive phase separating device geometries is now an effectively COTS solution for such low hold-up batch mode liquid/bubble phase separations in space. Following specification of the device requirements, the design, fabrication, and delivery of TRL6 solutions can occur within weeks. Dozens of similar capillary device development examples could be cited.

VI. Conclusion The difficulties of passive fluid control aboard spacecraft stems from a general lack of exposure to such phenomena within the spacecraft fluid system design community. We are at a unique juncture where the successes of recent microgravity fluid physics research aboard ISS can be applied to improve advanced engineering equipment for future exploration missions (i.e., fuels, coolants, and life support hardware). Illustrative examples are provided herein where project specifications are rapidly met with devices developed on short order with unusually high expectations of success. In certain cases, drop tower testing can produce TRL6 devices within weeks to several months in what is an essentially COTS design delivery process. The continuing ISS era is ideal for such passive device development and demonstration with expectations of TRL9. In an historic return to the positive perspective of engineers at the dawn of the space age, passive fluidic elements continue to offer increasingly favorable options for systems of increased reliability for two main reasons: The high quantitative awareness of capillarity (1) prevents deleterious unexpected

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consequences and allows (2) no moving parts designs that provide primary or secondary motive mechanisms for fluid control without significant mass, volume, and power penalties.

Acknowledgments We acknowledge central role of NASA and our commercial partners in the expansion and maturation of capillary fluidics design capabilities for applications aboard spacecraft.

References 1Halvorson, T., ISS Oxygen Generator Fails for Good, Station Managers Say, May 14, 2005. (sample article): http://www.space.com/1079-iss-oxygen-generator-fails-good-station-managers.html 2Kossom, R., Brown, R., Ungar, E., Space Station Heat Pipe Advanced Radiator Element (SHARE) Flight Test Results and Analysis, 28th Aerospace Sciences Meeting, AIAA-90-0059, Reno, NV, Jan. 1990. (Author’s comment: The SHARE heat pipe worked flawlessly on the ground, but not well at all during the flight due most likely to an unanticipated and undesirable but stable capillary surface. Several modifications to the design resulted in a successful follow-on demonstration flight. This is not an uncommon story for low-g fluid systems.) 3Johnson, J. (2002). Shuttle OPS V08-Waste Collection System. Houston, NASA-JSC. 4Puttkamer, J., ISS On-Orbit Status 05/21/08, ISS Daily Report: http://www.hq.nasa.gov/osf/iss_reports/reports2008/05-21- 2008.htm 5 Oberg, J., Space station struggles with balky toilet, NBC News space analyst, May 27, 2008. (Also mentions O2 generators and CO2 scrubbers that have limped along.) http://www.msnbc.msn.com/id/24841375/ns/technology_and_science-space/: 6Clark, W.D., Zero Gravity Phase Separator Technologies—Past Present and Future, ICES, 921160, Seattle, 4/1992. 7Dietrich, D.L., Paul, H.L., Conger, B.C., Evaluation of Carbon Dioxide Sensors for the Constellation Space Suit Life Support System for Surface Exploration, 2009-01-2372, 2009. 8Lewis, J.F., Cole, H., Cronin, G., Gazda, D.B., Steele, J., EMU/ISS Coolant Loop Failure and Recovery, ICES, 2006-01-2240, July, 2006, Norfolk, VA. 9The research team is aware of over 10 experiments investigating interfacial phenomena, phase change heat transfer, crystal growth, bio-reactors, thermocapillary flow, drop deployment, interface oscillations, and capillary thermal devices that have encountered significant fluids difficulties that during the design phases of these experiments appeared for all practical purposes as mundane operations. The troubling fluid phenomena are predominantly uncontrolled bubble/void formation, irregular capillary flows and wetting issues, and interfacial instabilities. The misleading results of ground or low-g aircraft tests have also contributed to poor performing low-g fluid systems designs. 10Oscar Monje, Active Watering Systems for Food Production, ASGSR, Oct. 25-29, Cleveland, 2016. 11Weislogel, M.M., Survey of Present and Future Challenges in Low-g Fluids Transport Processes, NASA Contract Report C- 74461-N, TDA Research, Wheat Ridge, CO, 2001. 12Robinson, J, (astronaut) Witson, P. Human in the Loop: The Importance of Humans Conducting Experiments in Space, NASA Lab Aloft (ISS Research), 12/03, 2010. “There are lots of different payloads that do not work as expected once on orbit, requiring crew interactions.” http://blogs.nasa.gov/cm/blog/ISS%20Science%20Blog/posts/post_1291390819440.html 13Nimon, J., (Astronaut) Williams, S., ISS Research in the Decade Ahead, NASA Lab Aloft, April, 4 2011: http://blogs.nasa.gov/cm/newui/blog/viewpostlist.jsp?blogname=ISS%20Science%20Blog “Compared to other laboratories, being in such a harsh environment adds some unique challenges. It also requires a lot to take care of it. When a toilet brakes, when the oxygen generation system does not work, when a solar array does not supply power, the crew are the only six people who can and have to go out and fix things. Control systems have to be maintained and this reduces the amount of science we can get done, compared to 6 people in friendly environment on Earth.” 14NASA JSC STTR 2016 Topic T6.02, Liquid Quantity Sensing Capability, TA6 Human Health, Life Support and Habitation Systems; Flexible space suit Feedwater Supply Assembly (FSA). 15On ISS, Teflon-covered water storage bags are either of 22 L CWC-I or 12 L PWR types. The bags are de-gassed 15 to 20 at a time about once every three months and then put back into storage. They are then degassed again just before put into service (about once a week). It requires ~ 3 min/bag at best and 20 min/bag at worst. If the bags are not de-gassed properly and air bubbles get into the water processor, it can shut the respective systems down and require many hours of ground commanding to get the system working again. During such times the crew may not have access to US water assets. A work-around employs an air trap between bag and water processor. This solution works for a time before becoming blocked, requiring further crew interaction to remove a filter, ground calls to the crew, bleeding air from the filter, and slowing annoying everyone involved. 16Weislogel, M., Thomas, E., Graf, J. (2011) Systems and Method for Separating Multi-Phase Fluids, US Patent No. 7,905,946 B1, March 15, 2011. 17Weislogel, M.M., A.P. Wollman, R.M. Jenson, D.R. Pettit, Capillary Beverage Cup, U.S. Pat. No. 9,962,024, May 8, 2018. 18Jenson, R. (2015) Rapid Concentration and Detection of E. coli in Liquid Samples, Sub-Contract to InnovaPrep LLC. 19National Academies, Congress Appointed NRC Decadal Review of NASA, 8/2009 to 5/2012 (Physical Sciences); National Research Council, Recapturing a Future for Space Exploration, Nat. Academic Press, WA DC. (Chpt 9, Applied Physical Sciences)

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20Concus, P. Finn, R., Weislogel, M., Capillary Surfaces in an Exotic Container: Results from Space Experiments, J. Fluid Mech. 394:119-135, October 1999. 21Concus, P. Finn, R., Weislogel, M., Measurement of Critical Contact Angle in a Microgravity Experiment, Experiments in Fluids, 28 (2000) 3, 197-205. 22Weislogel, M.M., Chen, Y., Masica, W.J., Kohl, F.J., Green, R.D., Fifty-Plus-Year Postflight Analysis of First Fluid Experiment Aboard a Spacecraft, AIAA J., 11 pages, July, 7 2016. 23Y. Chen, R. Jenson, M. Weislogel, S. Collicott, Capillary Wetting Analysis of the CFE-Vane Gap Geometry, AIAA-2008- 0817, 46th AIAA Aerospace Sci. Meeting and Exhibit, Reno, Nevada, Jan. 7-10, 2008. 24Weislogel, M.M., Baker, J.A., Jenson, R.M., Quasi-steady capillarity-driven flows in slender containers with interior edges, J. Fluid Mech., Vol. 685, 271-305 (2011). 25Conrath, M., P.J. Canfield, P.M. Bronowicki, M.E. Dreyer, M.M. Weislogel, A. Grah, Capillary channel flow experiments aboard the International Space Station, PHYSICAL REVIEW E 88, 063009 (2013), (8 pages) Rapid Communication. 26R.M. Jenson, A.P. Wollman, M.M. Weislogel, L. Sharp, R. Green, P.J. Canfield, J. Klatte, M.E. Dreyer (2014) Passive Phase Separation of Microgravity Bubbly Flows using Conduit Geometry, Int. J. Multiphase Flow, pp. 68-81, June. 27M.M. Weislogel, E.A. Thomas, J.C. Graf, A Novel Device Addressing Design Challenges for Passive Fluid Phase Separations Aboard Spacecraft, J. Microgravity Sci. Technol., Vol. 21, No. 3, pp. 257-268, July, 2009. 28Barajas, A.M., Panton, R.L., The Effects of Contact Angle on Two-Phase Flow in Capillary Tubes, Int. J. of Multiphase Flow, Vol. 19, No. 2, pp. 337-346, 1993. 29Weislogel, M.M., Jenson, R.M., Chen, Y., Collicott, S.H., Williams, S., Geometry Pumping on Spacecraft: The CFE-Vane Gap Experiments on ISS, 3rd International Symposium on Physical Sciences in Space (ISPS) 2007, Abstracts A11-2:443-444, Nara Japan, Oct. 22-26. (J. Jpn. Soc. of Microgravity Appl., Vol. 25, No. 3, 2008) 30M.M. Weislogel, R.M. Jenson, Y. Chen, S. Collicott, C.T. Bunnell, J. Klatte, M.E. Dreyer, Postflight summary of the Capillary Flow Experiments aboard the International Space Station, No. IAC-08-A2.6.A8, 59th International Astronautical Congress-2008, Glasgow, Scotland, Sept. 29-Oct. 3, 2008. 31Weislogel, M.M., Baker, J.A., Jenson, R.M. (2011) Quasi-steady capillary-driven flows in slender containers with interior edges, J. Fluid Mechanics, Vol. 685, 271-305. 32Weislogel, M.M. Compound Capillary Rise, J. Fluid Mech., Vol. 709, pp. 622-647, (2012). 33Chen, Y., B. Scheaffer, M.M. Weislogel, G. Zimmerli, (2010) Copyright SE-FIT Surface Evolver Fluid Interface Tools, open source software for fluid system design and analysis, Dec.: http://se-fit.com/ 34Chen, Y., Schaeffer, B., Weislogel, M., Zimmerli, G.(2011) Introducing SE-FIT: A Surface Evolver Based Tool for Studying Capillary Surfaces, AIAA-2011-1319, 49th AIAA Aerospace Sci. Mtg, Jan. 35The IRPI Capillary Beverage Experiment on ISS is highlighted in over 300 web articles: Search ‘Astronaut Coffee Cup’ and ‘Drinking in Space’. Both fun and scientific ISS video highlights have recently been posted: https://www.youtube.com/channel/UCkyrZKh_-vBMvlafKOkuQ8w 36Wollman, A., Large Length Scale Capillary Fluidics: From Jumping Bubbles to Drinking in Space, Ph.D. Thesis, June, 2016. 37WetLab-2 Parra: https://www.nasa.gov/ames/research/space-biosciences/wet-lab-2-parra; see also https://www.nasa.gov/mission_pages/station/research/experiments/2734.html 38DDT (2015): the Dryden Drop Tower at Portland State University: https://www.pdx.edu/dryden-drop-tower/

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