NASA A Researcher’s Guide to International Space Station : Fluid Physics

National Aeronautics and Space Administration
A Researcher’s Guide to:
Fluid Physics

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This International Space Station (ISS) Researcher’s Guide is published by the NASA ISS Program
Science Office.
Authors:
David F. Chao, Ph.D.*
Robert D. Green, Ph.D. **
Tyler Hatch*
John B. McQuillen*
William V. Meyer, Ph.D.***
Henry Nahra, Ph.D.*
Padetha Tin, Ph.D.***
Brian J. Motil, Ph.D.**
Executive Editor: Bryan Dansberry
Editor: Carrie Gilder
Designer: Cory Duke
Published: October 2015
Revision: January 2020
Cover and back cover:
Front:
The Zero Boil-Off Tank experiment used perfluoro-n-pentane to simulate a cryogenic
propellant to study the pressurization of a volatile fluid as the fluid absorbs heat. Mixing the
tank can be used to reduce the pressure. During this particular test, as the fluid was mixed
and the pressure dropped, residual heat in the metallic components at the tank exit nucleated
smaller bubbles that were circulated in the tank around the large vapor bubble or tank ullage.
(Image credit: NASA)
Back:
The Observation and Analysis of Smectic Islands in Space (OASIS) experiment was conducted
aboard the ISS in the Microgravity Science Glovebox. It examined the unique characteristics of
freely suspended liquid crystals in a microgravity environment to advance the understanding of
two-dimensional hydrodynamics. The image is a microscopic view of the thin film liquid that
contains multiple layers of liquid crystals that alter the localized color of the film. Two layers of
crystals are black, approximately 10 layers are white, 25 layers are yellow, 50 layers are red and
60 layers are blue. (Image credit: NASA)
*Low-gravity Exploration Technology Branch, NASA’s Glenn Research Center, Ohio 44135
**Thermal Systems and Transport Processes Branch, NASA’s Glenn Research Center, Ohio 44135
***University Space Research Association, NASA’s Glenn Research Center, Ohio 44135

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The Lab is Open
Orbiting 250 miles above the Earth, the International Space Station (ISS)
provides a platform for research to improve life on Earth, enable space
exploration, and understand the universe. The intent of this researcher’s
guide is to help potential ISS fluid physics researchers plan experiments
using the microgravity environment to understand how heat and mass
transfer affect fluid flows and behavior. It covers the nature of the
acceleration environment on ISS, available facilities for conducting fluid
physics research, examples of previous microgravity research, and current
fluid physics projects being developed for execution on the ISS.
European Space Agency astronaut Commander Alex Gerst conducts operations to reconfigure the Light Microscopy
Module (LMM) from Advanced Colloids Experiment-Temperature-7 (ACE-T-7) experiment operations to Biophysics
experiment operations. He is holding a removed ACE Module. (Image credit: NASA)
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5
Unique Features of the ISS
Research Environment
1.
Microgravity, or apparent weightlessness, alters many observable
phenomena within the physical and life sciences. Systems and processes
affected by microgravity include surface wetting and interfacial tension,
multiphase flow and heat transfer, multiphase system dynamics,
solidification, and fire phenomena and combustion. Microgravity induces
a vast array of changes in organisms ranging from bacteria to humans,
including global alterations in gene expression and three-dimensional (3D)
aggregation of cells into tissue-like architecture.
2.
Extreme external environmental conditions imposed on the ISS
include exposure to extreme heat and cold cycling, ultra-vacuum, atomic
oxygen, and high-energy radiation. Testing and qualification of materials
exposed to these extreme conditions have provided data to enable the
manufacturing of long-life, reliable components used on Earth as well as in
the world’s most sophisticated satellite and spacecraft components.
3.
Low-Earth orbit at 51 degrees orbital inclination and at a 90-minute orbit
affords ISS a unique vantage point with an altitude of approximately 250
miles (400 kilometers) and an orbital path over 90 percent of the Earth’s
population. This orbital path can provide improved spatial resolution and
variable lighting conditions compared to the sun-synchronous orbits of
typical Earth remote-sensing satellites.
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Table of Contents
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The Lab is Open 3
Unique Features of the ISS Research Environment 5
Why Use the ISS as a Laboratory for Fluid Physics? 7
Results from Past Research on Fluid Physics in Space 8
Complex Fluids 8
Colloids 8
Liquid Crystals 14
Multiphase Flow and Heat Transfer 18
Boiling eXperiment Facility 19
Zero Boil-off Tank Experiment 21
Packed Bed Reactor Experiment 22
Constrained Vapor Bubble Experiment 23
Interfacial Phenomena/Capillary Flow 25
Opportunities for Research in Fluid Physics on ISS 31
Complex Fluids 31
Colloids and Suspensions 31
Liquid Crystals 32
Foams 33
Granular Materials 33
Particulate Management 34
Magnetorheological Fluids 34
Polymer Fluids 35
Multiphase Flow 35
Zero Boil-off Tank Experiment Series 36
ElectroHydroDynamics 36
Adiabatic Gas-Liquid Flow Experiments 36
Flow Boiling and Condensation Experiment 37
Capillary, Thermocapillary and Solutocapillary Flow Phenomena 38
Lessons Learned 40
ISS Facilities for Research of Fluid Physics 41
Acceleration Measurement and Environment Characterization 41
Fluids Integrated Rack 41
Light Microscopy Module 42
Microgravity Science Glovebox 42
EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Racks 43
Developing and Flying Fluid Physics Research to ISS 44
Funding, Developing and Launching Research to ISS 45
ISS U.S. National Laboratory 46
Other Government Agencies 46
International Funding Sources 47
Citations 48
Acronyms 51

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Why Use the ISS as a
Laboratory for Fluid Physics?
A fluid is any material that flows in response to an applied force; thus, both liquids
and gases are fluids. Nearly all life support processes, environmental and biological,
take place in the fluid phase. Fluid motion accounts for most transport and mixing
in both natural and man-made processes as well as within all living organisms.
Fluid physics is the study of the motions of liquids and gases and the associated
transport of mass, momentum and energy. The need for a better understanding of
fluid behavior has created a vigorous, multidisciplinary research community whose
ongoing vitality is marked by the continuous emergence of new fields in both basic
and applied science. In particular, the low-gravity environment offers a unique
opportunity for the study of fluid physics and transport phenomena. The nearly
weightless conditions allow researchers to observe and control fluid phenomena in
ways that are not possible on Earth.
Experiments conducted in space have yielded rich results. Some outcomes were
unexpected and most cannot be observed in Earth-based labs. These results have
provided valuable insights into fundamental fluid behavior that apply to both
terrestrial and space environments. In addition, research on fluid management and
heat transfer for both propulsion and life-support systems has contributed greatly to
U.S. leadership in space exploration.
Much is still unknown or not fully understood. In order to design for the
human or robotic exploration of space and other planetary environments, it is
necessary to understand how engineering and fluid systems perform in the near-
weightless environment experienced during space travel or in the reduced-gravity
environments found on the moon or Mars.
The differences in the behavior of fluid systems in space or on other planetary
bodies can be attributed primarily to buoyancy. The near elimination of buoyancy
and sedimentation within inhomogeneous fluids in the low-gravity environment
provided by the ISS allows scientists to study the behavior of a whole range of
fluids. While these conditions can be achieved in free-fall facilities such as drop
towers and aircraft, the limited duration of these tests is insufficient for fluids
experiments that require minutes, hours or even days to be performed successfully.
The fluid physics discipline, which focuses on gravity-related research issues,
includes the study of complex fluids, multiphase flow and heat transfer, and
interfacial phenomena (including capillary flow).

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Results from Past Research
on Fluid Physics in Space
Gravity strongly affects fluid behavior by creating forces that drive motion, shape,
phase boundaries and squeeze gases. One significant gravity-driven motion is
buoyancy-induced flow in which lighter, less-dense fluids flow upward while
denser fluids flow downward. An example of this type of flow can be found in
boiling water in which steam bubbles rise as cooler, and denser water flows down.
Sedimentation is a similar gravity-driven phenomenon. In microgravity, the
effects of these gravity-driven processes are nearly eliminated. The absence of these
phenomena allows scientists to observe other phenomena that are present under the
influence of Earth’s gravity but are usually obscured.
Complex Fluids
Complex fluids include non-Newtonian fluids such as colloids, polymers, foams,
microemulsions, gels, granular materials, and a number of biological materials
such as proteins, biomembranes and cells. Complex fluids comprise a large class of
materials ranging in size from sub-nanometer to micron scales with their physical
properties determined by the interplay of entropic and structural intermolecular
forces and interfacial interactions.
Descriptions of sample research into colloids, liquid crystals, and the behavior of
smectic bubbles conducted on ISS are provided in the following sections.
Colloids
Prior to the ISS, a series of microgravity experiments were flown that yielded many
new and interesting results. Some of the early experiments included Colloidal
Disorder-Order Transition, Colloidal Gellation-2, and Physics of Hard Spheres,
all flown on the space shuttle.
They revealed the first observations of dendritic growth in hard-sphere colloidal
systems. Research results established that colloidal samples remaining in a glassy
phase on Earth (i.e., do not crystallize on Earth), become ordered (i.e., crystallize)
in microgravity.
On the ISS, the Physics of Colloids in Space (PCS) experiment studied the phase
behavior, growth dynamics, morphology and mechanical properties of different
types of colloidal suspensions, including binary colloidal alloys (Figure 1), colloidal
polymer mixtures, fractal colloidal aggregates, and the natural entropy-driven
transition from a disordered glassy state to an ordered crystalline one (Figure 2).

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Figure 1. Ground vs. space: The two PCS photos above are of white light shown through binary alloy samples (Manley,
et al, 2004). The left sample was grown on the ground and the right sample (sample AB6) was grown on the ISS during
Increment 2. The different colors are the result of different wavelengths of light being diffracted by the crystal nuclei,
indicating the ordered placement of particles in the suspension. A sharply defined spectrum reveals a highly ordered
particle placement in the colloidal suspension
The Binary Colloidal Alloy Tests (BCAT)-3/4/5/6 experiments were a set of
notebook-sized
science investigations
that contained 10
samples each. Once
in the microgravity
environment aboard
the ISS, these samples
were individually
mixed until their
structures were
randomized and
the samples were
photographed as the
structures evolved.
Many different areas
of fluid physics were
addressed.
Figure 2. Investigations conducted by Physics of Colloids in Space principal
investigators have yielded some unexpected and pleasantly surprising results: solu-
tions that formed glasses on Earth formed crystals and dendritic growth in space;
and nucleation and growth that was anticipated by preliminary studies but never
observed during the crystal growth process (Cheng, et al., 2002).
The BCAT experiments on seeded growth showed that glassy (completely
disordered) samples crystallize differently in the absence of gravitational
sedimentation and jamming as shown in Figure 3. The use of seed particles were
predicted to cause heterogeneous nucleation (many different crystals) rather than
large homogeneous crystals.

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Figure 3. Scanning Electroid Microscope (SEM) images of a mixture of 3.8 micron diameter “seed” particles together
with the bulk colloid (0.33 micron diameter polymethyl methacrylate (PMMA) spheres). Crystal nucleation on the
spherical surfaces could produce small nuclei that grow radially outward. Because of curvature that makes it difficult to
maintain an unstrained structure, they should detach from the surface, allowing the seed to produce new crystal nuclei.
Another focus of the BCAT experiments is the study of phase separation with
model-critical fluid samples on the ISS. These model systems do not require the
micro-Kelvin temperature control of traditional critical fluids. They serve as a model
for understanding ideal systems formed from same-size (monodisperse) particles
whose attractive force can be adjusted by the addition of a polymer. Depletion
attraction is used to determine the effective attractive force between particles. From
these studies, it was found that the critical point is not where the literature predicted
(this literature was based on observing phase separation in the presence of gravity).
A true microgravity environment is needed to probe these physics.
The competition between a phase-separation process and an order-disorder transition
remains largely unstudied. BCAT measurements capturing the arrest of phase
separation by crystallization are the focus of the “Complete” Samples. Improved
understanding of these processes will lead to more refined manufacturing processes
and commercial products. Some exciting and pleasantly surprising results are shown
in Figure 4.
Magnetorheological (MR) fluids are suspensions of small (micron-sized)
superparamagnetic particles in a nonmagnetic medium. These controllable fluids
can quickly transition into a nearly solid-like state when exposed to a magnetic

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field and return to their original liquid state when the magnetic field is removed.
Their rheological properties (how they deform and flow) can be controlled by
manipulating the strength of the magnetic field. Because of the rapid response that
can be achieved between mechanical components and electronic controls, MR fluids
can be used to improve or develop new brake systems, seat suspensions, robotics,
clutches, and airplane landing gear.
Figure 4. Images of the samples in microgravity. The left five images show sample 2 evolving from time t=0 to t=53 h.
Domains in the 19 and 53 h images have exactly the same pattern. Crystal visibility was improved in the 53 h image by
an illumination change. The two images to the right show the other two samples at comparable times. Each of these
seven images shows the full width of the cuvette. The three images on the far right show a 2.5 mm wide region of each
sample with a prominent crystal: sample 1 at the top to sample 3 at the bottom. The crystal size is comparable to the
liquid domain size. Figure and caption from Sabin, et al, 2012.
The Investigating the Structures of Paramagnetic Aggregates from Colloidal
Emulsions experiment studied the fundamental behavior of MR fluids under the
application of constant and pulsed magnetic fields (Furst, et al., 2011). Observations
of the microscopic structures yielded a better understanding of the interplay of
magnetic, surface and repulsion forces between structures in these fluids. These fluids
are classified as smart materials because they transition to a solid-like state by the
formation and cross-linking of microstructures in the presence of a magnetic field.
On Earth, these materials are used for vibration dampening systems that can be
activated as needed. This technology shows promise for designing structures such as
bridges and buildings that can better tolerate earthquake damage.
The Shear History Extensional Rheology Experiment was designed to investigate
the effect of preshearing (rotation) on the stress and strain response of a polymer
fluid (a complex fluid containing long chains of polymer molecules) being stretched
in microgravity (Hall, et al., 2006). This information is particularly relevant for
understanding the deformation and evolution of non-Newtonian thin fluid columns

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(threads) in a wide variety of industrial processes such as fiber spinning, film coating,
enhanced oil recovery, injection molding, drag reduction for advanced aircraft,
boats and submarines, or food and consumer product processing. In fiber spinning,
the fluid experiences a complex transient shear deformation as it flows through the
spinneret before it is stretched axially. Additionally, a fundamental understanding
and measurement of the extensional rheology of complex fluids is important for
understanding the stability and breakup of jets and containerless processing. It is
an important operation for fabrication of parts, such as adhesives or fillers, using
elastomeric materials on future exploration missions.
In a microgravity environment, there is a large increase in the radial dimension of an
initial liquid bridge because of the absence of gravitational body forces. When the
initial radius increases, the viscous force is increased and the time evolution of the
tensile force becomes slow enough to be measurable for extended times, permitting
the long dynamics of the filament thinning to be monitored. A stable microgravity
environment enables the understanding of the effect of the initial conditions on
capillary thinning and time to breakup.
A 3D confocal capability was added to the Light Microscopy Module (LMM), a
microgravity microscope in the Fluids Integrated Rack on the ISS, with sample
temperature control. These changes moved microgravity colloids research from
the macroscopic to the microscopic, enabling discoveries important for “colloidal
engineering,” such as the self-assembly of microstructures in a controlled fashion.
One of the first Advanced Colloids Experiments with sample temperature control
(ACE-T) to use confocal microscopy studied the behavior of mixtures made from
colloids of slightly different sized particles commonly found in commercial products.
The study of these polydispersed colloids in ground-based laboratories suffers from
their tendency to sediment because of gravity.
In many commercial applications, the manufacturer strives for the formation of a
colloidal gel, a connected network of colloidal particles that can stabilize the system
against sedimentation. As a colloidal gel, the product is in an arrested state of
transition between a fluid and a solid, and the aim of the manufacturer is to keep the
product in this state for as long as possible to maximize shelf life.
Matthew Lynch of Procter Gamble is the Principal Investigator of the ACE-T6
experiment. He discovered that two sizes of stabilizer particles (2.2 micron and 1.8
micron in diameter) behave quite differently in microgravity. The larger particles
build scaffolding (product stabilizers) while the smaller particles swarm about

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the larger particles. The discovery of this behavior is a step toward understanding
polydisperse colloidal systems and how polydispersity could affect the stability of
colloidal gels.
The science team led by Weitz from Harvard has been able to observe novel behavior
with the ACE-M2R experiment, which studied a kinetically arrested gel phase which
had never been theorized before (Kodger, et.al., 2017). They were able to measure
this kinetic arrest and long-term stability of their sample for 100 million seconds,
orders of magnitude longer than similar experiments carried out on earth.
Both of the above experiments should shed insight into the long-term stability of
a variety of complex-fluid systems, such as the personal-care products, food and
medicines. This insight is being applied on Earth (Proctor and Gamble was awarded
four patents) and should improve the shelf life of products needed for long-term
human space exploration and habitation beyond low-earth orbit.
The ACE-T1 investigation, led by Chang-Soo Lee from Chungnam National
University in Daejeon, South Korea, demonstrated controlling the rotational
diffusion coefficient of colloidal particles. The results of this colloidal engineering
study of has an emphasis on self-assembly, used to form precisely organized
structures spontaneously by thermodynamic equilibrium. The complex structures
that result from self-assembly at the molecular level are regulated by highly specific
and directional interactions. The ACE-T1 experiment found that the 3D rotational
Brownian motion of anisotropic particles can be controlled by choosing the
amount of their surface that is hydrophobic. The study of the Brownian motion
of anisotropic particles provided insights important for the following topics: (1)
equilibrium and non-equilibrium statistical physics, (2) biophysics, (3) soft matter,
(4) artificial Brownian motor, (5) micro-rheology, (6) micro robotics, (8) self-
assembly of anisotropic particles, and (8) anisotropic molecules in membranes.
The ACE-T7 investigation, led by Prof. Paul Chaikin of New York University,
observed 3D formations of “super-cubes” that self-organize into crystalline
structures. This ability to design functional structures based on micron-scale building
blocks with a variety of well-controlled 3D bonding symmetries will enable the
development of new devices for chemical energy, communication, and photonics,
including photonic materials to control and manipulate light. This capability
underpins the rapidly growing fields of 3D printing and additive manufacturing that
rely on the assembly and sintering of particle aggregates as well as the preparation
of high-density slurries and pastes of different colloidal materials with different
rheological and mechanical properties.

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Liquid Crystals
Smectic liquid crystals are composed of fluid layers that can be made to form freely
suspended, single component fluid films as thin as a single molecular layer (3 nm).
They are the thinnest known stable fluid structures and have the largest surface-
to-volume ratio of any fluid concoction, making them ideal for the study of two-
dimensional phase transitions, fluid flow, and fluctuation and interface phenomena.
They offer unique opportunities to use microgravity effectively to extend the study of
basic capillary phenomena to ultrathin fluid films.
Smectic layering forces films to be an integral number of layers thick and to be
physically homogeneous with respect to the layer structure over the entire area.
This fluid-layer structure and the low vapor pressure of smectics stabilize the freely
suspended, single component fluid film for detailed study.
The Observation and Analysis of Smectic Islands in Space (OASIS) experiments, led
by Prof. Noel Clark from the University of Colorado at Boulder, focused on using a
novel collective system of interacting one-dimensional interfaces in two-dimensional
fluids (Clark et al, 2017). This system was ideal for studying fundamental fluid
physics such as collective molecular ordering, defect and fluctuation phenomena,
hydrodynamics, and nonequilibrium behavior in two dimensions (2D), including
serving as models of complex biological membranes. Smectic films were prepared
as bubbles supported on an inflation tube. The dynamics of emulsions of smectic
islands (thicker regions on thin background films) and of microdroplet inclusions in
spherical films, as well as thermocapillary effects, were studied over extended periods
within the OASIS (Stannarius, et al., 2019). The technical details of the OASIS
hardware and preliminary observations are presented below.
Plateau-Rayleigh Instability
A two-dimensional equivalent of the Plateau-Rayleigh instability was observed in
a thin bubble of smectic A (SmA) liquid crystal. In this experiment, a thin bubble
was created and the temperature was raised locally to approximately 35ºC using
a heated needle located near the north pole of the bubble. A gentle stream of air
was applied across the top of the bubble, causing flow within the bubble film that
eventually dragged residual material originally located near the inflation needle
into a continuous ribbon of thicker material in the flow direction and around
the bubble as shown in Figure 5. This steady-state motion of the ribbon could be
continued indefinitely.

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Figure 5: Plateau-Rayleigh Instability: the line tension
(the two-dimensional equivalent of surface tension) becomes
unstable to small shape perturbations and pinches off
into islands.
However, when the heater needle
temperature was increased to 45ºC,
a dramatic transition in the shape of
the liquid ribbon occurred, with the
ribbon breaking into a chain of small
disks (the two-dimensional equivalent
of droplets), which then continued to
flow around the film. It is theorized
that this increase in temperature
sufficiently lowered the line tension
(the two-dimensional equivalent of
surface tension) of the ribbon so that
it became unstable to small shape
perturbations and pinched off into
islands, similar to the behavior of a
water jet in three dimensions.
Island Emulsion Coarsening
Air jets were used to create extensional flow in an initially homogeneously thin
bubble film. The air flow broke the thicker material into small, disk-like inclusions
called islands that then formed a 2D emulsion on the bubble surface shown in
Figure 6.
Figure 6: The coarsening dynamics of island emulsions on the two-dimensional surface of bubbles of smectic liquid crystal.

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On Earth, such island emulsions would rapidly sediment to the lowest point of the
bubble and coalesce; but in microgravity, coarsening of the emulsion was observed
free of gravitational effects. Early observations of 15 mm diameter smectic A liquid
crystal bubbles confirm that an emulsion of small islands evolves to a significantly
coarser ensemble of islands within about one hour. Much of the coarsening appears
to be the result of island coalescence events.
Ostwald Ripening and Collapse of Islands in Smectic Bubble
The Ostwald ripening of essentially 2D smectic A and C islands occurs as a result of
the system’s tendency to reduce its energy through a decrease in the total length of
the boundaries of the islands. This process is generally dependent on the (thickness-
dependent) surface and line tension, the disjoining pressure of the island, and
the excess air pressure inside the bubble. Smaller islands generally have a higher
disjoining pressure than their larger neighbors, resulting in permeative flow from
the smaller to the larger islands. In smectic bubbles, pressure in the films is mainly
determined not by the meniscus, but instead by the excess pressure in the bubble,
inducing a change in the physics of collapse and ripening of islands in smectic films.
Figure 7: ISLANDS IN A SmC BUBBLE:
(a) Time dependence of area of the smallest island in upper left image (Island 1). The island collapses and disappears.
The solid curve is the fit of the experiment data by a power law dependence S=A(t0-t)β
. For the exponent β, the fit gives
a value of 0.749±0.02.
(b) Area of the two smallest islands in the images (Islands 1 and 2) as a function of time. The solid curve is the same
power dependence as in (a) plotted in a wide temporal range. The experiment data for Island 2 are shifted along the
horizontal axis to the theoretical curve. The experiment data for both islands can be described by the same dependence
(the slope of the dependence S(t) for Island 2 is close to the slope of the theoretical curve).
Figure 7 shows images of islands in a SmC bubble. The photograph (b) was taken
7.5 min after photograph (a). The behavior of islands 1-6 is different: island 1
disappears in image b while an increase of size of the remaining islands is observed.
This behavior is a manifestation of Ostwald ripening. The change of size of islands
with time is shown in detail in Figure 7a and Figure 7b. The horizontal size of the
images is 335 μm.

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Time and Space Periodic Structures of Isotropic Inclusions (Droplets) on Smectic Bubbles
Collective behavior of isotropic droplets dispersed over a spherical smectic bubble
was studied in microgravity conditions. Droplets can form two-dimensional
hexagonal structures. The one-dimensional motion of droplets with non-uniform
velocity demonstrated a peculiar periodic in time ordering of the droplets. This
behavior can be considered a classical analogue of discrete “time crystal.” The concept
of time crystals was put forward by Frank Wilczek. The essential feature of a time
crystal is that it restores the same state at specific moments of time.
Figure 8: Hexagonal ordering is formed by droplets in the smectic film at certain moments of time. The droplets denoted 1,
2 and 4, 5 move in opposite directions with respect to the row of droplets 3, 6, and 7. Hexagonal ordering (a) is destroyed
(b) and then reconstructed after some time (c). Numbers indicate droplets forming the hexagonal structure in frame (a).
White dots in frames (a, c) show the droplets with hexagonal ordering. Dots in (b) denote the droplets that formed the
hexagonal structure in frame (a). Frame (b) is taken 55 s after frame (a), frame (c) 95 s after frame (a). The horizontal size of
the images is 191 μm.
In Figure 8a, the droplets move nearly along the bigger diagonal of the hexagon
(the horizontal direction in Figure 4a with velocity gradient in the perpendicular
direction). To facilitate tracking, droplet centers that formed a hexagon in Figure 8a
were marked by white dots and numbered. The velocity of droplets in the upper and
lower sides of the hexagon with respect to its center differed in terms of magnitude
and direction, leading to the destruction of the hexagonal structure (Figure 8b)
and its reappearance later. Then the hexagonal ordering was again destroyed. The
structure formed by droplets in which the hexagonal order periodically disappears
and reappears can be considered to be an analogue of the classical “time crystal.” In
our observation, a nearly constant gradient of mean velocity was created only in the
nearest three rows of droplets.
It is worth noting that if the constant gradient of velocity were created in a larger
number of rows, one would expect a much richer behavior; e.g., appearance of a line
of hexagons perpendicular to the motion of droplets in discrete moments of time.
These outcomes are determined by the velocity of the row of hexagons with the
smallest velocity.

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Discrete time crystals were realized in several quantum systems, but this result may
be the first observation of time crystalline behavior in classical systems.
Multiphase Flow and Heat Transfer
This research area, which has applications in the fluid flow and engineering of
thermal management and purification systems, focuses on complex problems of
two-phase fluid flow (Chiaramonte and Joshi, 2004). Scientists are seeking to
understand how gravity-dependent processes such as boiling and steam condensation
occur in microgravity. Boiling is known to be an efficient way to transfer heat, and
it is often used for cooling and energy conversion systems. In space applications,
boiling is preferable to other types of energy conversion systems because it is efficient
and the apparatus needed to generate power is smaller. Diffusive transport is another
mechanism by which energy and matter (atoms, molecules, particles, etc.) move
through liquids and gases.
The way atoms and molecules diffuse through a liquid or gas is due primarily to
differences in concentration or temperature. Researchers use microgravity to study
diffusion in complex systems, a process that would normally be eclipsed by the force
of gravity. Understanding the physics of multiphase flow and heat transfer in space
will enhance the ability of engineers to solve problems on Earth as well. Potential
applications of this research include more effective air conditioning and refrigeration
systems and more efficient power-generating plants.
Figure 9: Zero Boil-Off Tank (ZBOT) hardware in the
Microgravity Science Glovebox (MSG) aboard ISS with
Astronaut Joe Acaba.
As precursor to ISS investigations,
three multiphase flow experiments were
conducted aboard the space shuttle.
The Vented Tank Resupply Experiment
(VTRE) was conducted to test improved
methods for in-space refueling (Chato
and Martin, 1997). VTRE used vane
Propellant Management Devices (PMDs)
to separate the liquid and gas phases of
Refrigerant 113 in low gravity.
Experiment objectives included testing the capability of the vane PMDs to retain
liquid during transfer between the two tanks, liquid-free venting of pressure, and
recovery of liquid into the PMDs after a thruster firing.

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The Tank Passive Control Experiment also used Refrigerant 113 to demonstrate
the effectiveness of a low-velocity axial jet to mix the fluid and thereby control its
pressure (Bentz, et al., 1997). Pressure increases of the volatile fluid were induced
with heaters, simulating the in-space storage of a cryogenic fluid. Pressure control
was found to be effective and repeatable at both high- and low-fluid fill levels over
a wide range of jet velocities with varying amounts of non-condensable gases in
the ullage for a variety of liquid/vapor orientations and heat inputs. Pressure spikes
caused by explosive boiling were sometimes observed during heating at low-heat
fluxes but were controllable with gentle mixing.
The Pool Boiling Experiments (PBE) conditioned liquid (R-113) to an initial,
precisely defined pressure and temperature and subjected the liquid to a step-
imposed heat flux from a semi-transparent, thin-film heater to initiate and maintain
boiling for a defined period of time at a constant pressure level (Merte, et al., 1998).
Transient measurements of the heater surface and fluid temperatures near the surface
were made, and two simultaneous views from beneath the heating surface and from
the side were recorded.
Several modes for propagation of boiling across the heater surface and subsequent
vapor bubble growth were observed. Of particular interest were the extremely
dynamic or “explosive” growths resulting from the large increase in the liquid-vapor
interface area associated with the appearance of a wavy interface, which itself is due
to the presence of an instability. Small vapor bubbles migrated toward and coalesced
with a larger bubble at the combination of the lower heat flux levels and highest
subcooling levels. This phenomenon enhanced the heat transfer by approximately
30 percent.
More recently aboard the ISS, several multiphase flow experiments have been
conducted and are described below.
Boiling eXperiment Facility
The Boiling eXperiment Facility used normal perfluorohexane to conduct two
experiments on the ISS: The Microheater Array Boiling Experiment (MABE) and
the Nucleate Pool Boiling eXperiment (NPBX).
MABE used an array of 96 transparent individually-controlled microheaters to
perform experiments over a wide range of heater and liquid temperatures, pressures
and heater sizes (Raj, et al. 2012). Experiments have revealed two regimes for
predicting pool-boiling behavior: Buoyancy Dominated Boiling (BDB) and Surface

20
Tension Dominated Boiling. Within the BDB regime, as the vapor bubble grows
larger the density difference between the vapor bubble and surrounding liquid
causes gravity to push the bubble off the heater surface and rise through the liquid.
Liquid rushes in behind the bubble, and the process of heating and boiling repeats.
This behavior has been observed for a wide range of acceleration (gravity) levels,
ranging from high gravity (1 g) to less than lunar gravity (1/6 g). At lower gravity
levels, the boiling behavior is controlled by surface tension whereby a bubble covers
a large portion of the total heater surface. Its growth is fed both by vaporization of
liquid and by merging with smaller vapor bubbles that surround the large bubble.
Its size is limited by condensation along the bubble surface that is in cooler liquid
away from the heater.
Based on high-quality microgravity data (a/g0.000001), a gravity scaling
parameter for heat flux was modified to account for these ISS results, primarily
based on parabolic aircraft flight experiments (a/g~0.01). While the aircraft flights
were instrumental in developing the model, residual fluctuations on the aircraft
significantly affected the boiling behavior, which is why the ISS environment
was critical.
The robustness of this framework in predicting low-gravity heat transfer is further
demonstrated by predicting many of the trends in the pool-boiling literature for
several different fluids over a range of heater sizes, gravity levels, and those that
previously could not be explained by any single model.
NPBX used a polished aluminum disc heated by strain gage heaters. Four
cylindrical cavities were located at the corners of a square with a fifth cavity in the
middle. The results of the experiments showed that a single bubble continues to
grow to the size of the chamber without departing from the heater surface (Dhir,
et al., 2012). During lateral merger of bubbles at high superheats (the difference
between the heater and liquid temperature), a large bubble may depart from the
surface but continue to hover near it. Neighboring bubbles are continuously pulled
into the large bubble. At smaller temperature differences, bubbles at neighboring
sites simply merge to yield a larger bubble. The larger bubble mostly positioned
itself in the middle of the heated surface and served as a vapor sink. The latter mode
persisted when boiling was occurring all over the heater surface. Heat fluxes for
steady-state nucleate boiling and critical heat fluxes were found to be much lower
than those obtained under 1 g.

21
Zero Boil-off Tank Experiment
The Zero Boil-Off Tank (ZBOT) experiment is a series of small tank pressurization
and pressure control experiments using perfluoro-n-pentane (PnP; C5F12), a
transparent volatile simulant fluid. The ultimate goal is to enable long duration
storage of cryogenic propellant and life support liquids and the associated pressure
control of the storage tanks. This pressure control is governed by interdependent
mechanisms of forced mixing of the liquid, gravity-dependent transport processes in
the liquid and vapor, and evaporation and condensation at the liquid/vapor interface.
A comprehensive two-phase Computational Fluid Dynamics model also has
been developed to predict tank pressure behavior for validation with microgravity
experiment data (Kassemi, et al., 2018 (A-C)).
The test cell, made of polished optical quality cast acrylic, consists of a cylindrical
midsection capped at each end by hemispherical domes. The device is equipped
with a temperature-controlled vacuum jacket and a surface-mounted strip heater
to heat the tank fluids, a temperature-controlled liquid jet flow to cool and mix the
fluids, and a screen-type liquid acquisition device (LAD) to ensure that only liquid
is withdrawn from the tank. The test-cell diagnostics include Resistance Temperature
Detectors (RTDs) for temperature measurement, a pressure sensor, image capture
of the ullage with white light illumination, and particle image velocimetry and flow
visualization with a laser light sheet.
Visible image CFD model simulation Particle Image Velocimetry
Figure 10: Zero Boil Off Tank (ZBOT) Experiment: Depiction of fluid flow and vapor bubble deformation by a liquid jet
in microgravity.

22
For vacuum jacket and strip heating, the microgravity results for tank pressure
rise are similar to that in normal gravity, although the rate and magnitude of the
pressurization are lower than in normal gravity (Kassemi, et al., 2018 (C)). Jet
mixing yielded a surprising and non-intuitive result wherein the ullage moved
towards the jet nozzle at low jet speeds, while at higher speeds, the ullage remained
in the upper portion of the tank but moved laterally to accommodate the passage
of the jet. Ullage penetration and puncture by jet impingement was never observed.
Pressure control by an uncooled jet was minimal and ineffective; a subcooled jet,
however, produced a rapid initial pressure drop followed by further depressurization
at a continuously decreasing rate. Flow visualization from the particle images showed
several vortices produced in the tank during jet mixing. Surprising and non-intuitive
immense phase change, suspected to originate at the screen LAD, was observed
during subcooled jet mixing where the tank was filled initially with small bubbles
that subsequently grew and coalesced. It is postulated that massive nucleate boiling
might have occurred at nucleation sites on the screen LAD when the saturation
temperature due to depressurization fell below the LAD temperature.
Packed Bed Reactor Experiment
The Packed Bed Reactor Experiment (PBRE) was developed and flown on the
ISS by NASA to conduct a series of fundamental studies of gas-liquid flows
through porous media. Flow through porous materials for space applications is
encountered in life support systems, fuel cells, chemical/materials processing and
when transporting nutrients to plants. These systems operate differently in the
microgravity environment because the density differences no longer cause the
phases to separate or “drain” under the force of gravity. In the absence of gravity, the
interfacial or capillary forces play a more significant role in determining operational
parameters such as phase distribution, liquid holdup, and pressure drop. This
difference is most apparent when the liquid inertia and viscous forces are minimal,
which is common for the space processes mentioned above; i.e., lower liquid flow
rates within air/water systems.
The objective of this experiment was to better understand and improve upon the
design and operation of space-based porous media flows where both a gas and liquid
phase are present. During the early days of the ISS assembly, NASA flew a series of
parabolic aircraft flights to develop a semi-empirical prediction for pressure drop
and flow pattern transition for two-phase flows through porous media (Motil, et
al., 2003). These studies included a range of packing sizes, column diameters, and
liquid viscosities. However, important limitations to the aircraft flights included only

23
a short time interval of low gravity (~20 sec) followed by a high gravity “pull-up” of
the aircraft, which quickly drained the vertically positioned test sections. The range
of flow rates typical in water reclamation processes take several minutes or longer to
develop steady flow conditions, requiring extrapolation of the semi-empirical models
developed under these earlier tests. These models were validated at the lower flow
rates during the ISS testing (Sagli and Balakotaiah, 2016).
Figure 11: Packed Bed Reactor Experiment (PBRE) Test Section and Diagnostics.
Constrained Vapor Bubble Experiment
The Constrained Vapor Bubble Experiments (CVB-1 and CVB-2) were based
on a transparent, wickless, heat pipe and studied the influence of interfacial and
intermolecular forces on the flow dynamics and heat transfer mechanisms that arise
using a perfectly wetting working fluid, pentane, and a perfectly wetting working
fluid mixture, pentane/isohexane (Plawsky and Nguyen, 2017). Three different
lengths of heat pipe were run, including a reference heat pipe that contained
no working fluid. Temperature profiles and internal pressures were measured as
functions of input power to the heater and temperature set point of the cooler.
Optical interferometry was employed to measure the liquid film thickness on the
walls of the device from which the shape of the vapor-liquid interface and flows of
liquids were determined.

24
The experiment revealed some surprising features of microgravity wickless heat
pipe operation that had never been observed before. Instead of drying out at high
heater temperatures, the hot end of the device flooded with liquid. The performance
degradation under those conditions was indistinguishable from classical dry-out.
Intermolecular forces were strong
enough to induce condensation at
the heater end even though the wall
temperatures in that region were over
100ºC above the boiling point of the
liquid inside the heat pipe. The length
of the heat pipe had a great effect on
the performance, and when the liquid
flow design capacity of the device
was exceeded, nature took over and
interfacial-force-driven (Marangoni)
rip currents were established that
increased the extent of the vapor-
liquid interface and enhanced the
evaporative capacity of the device.
Figure 12: Surface condensation on the walls of a heat pipe
is revealed by interference fringes (light and dark lines).
Within the heat pipe is an “interfacial flow region” that extends
from the hot evaporator at the top of the figure to the central
drop. The condenser heat pipe is not shown and is below
the central drop. The amount of surface condensation,
as indicated by the density of fringes, is greater near the
evaporator for the hotter heat pipe on the right than it is for the
relatively cool heat pipe on the left (Kundan, et al., 2017). The
background grid structure appears in the background because
these figures are actually composites of several images.
Figure 13: Composite images showing the development of
the interfacial flow region, the central drop morphology and
the origin and dissipation of the rip current as a function of
heat input. The same Marangoni Forces responsible for the
development of the interfacial region also serve to dissipate
the rip current as it approaches the heater wall of the device
(Kundan, et al., 2015; Nguyen, et al., 2018).
Figure 14: Left: 10X composite interferometry image
of the CVB heat pipe taken at 3W heat input when
the spontaneous rip current is the strongest. The rip
current serves to increase the interfacial area and
enhance evaporative heat transfer. Right: A magnified
image of the heat pipe highlights just the rip current
and the three main sub-regions of interest within the
overall interfacial flow region. (Kundan, et al., 2017;
Nguyen, et al., 2018).

25
Interfacial Phenomena/Capillary Flow
Fluid dynamics, instabilities and interfacial or capillary flows constitute another
important subset of fluid physics. Capillary flows and phenomena are applicable
to a myriad of fluids management systems in low-g, including fuel and cryogen
storage systems, thermal control systems (e.g., vapor/liquid separation), life support
systems (e.g., water recycling), and materials processing. In fact, NASA’s near-term
exploration missions plan larger liquid propellant tanks than have ever flown
for interplanetary missions. Under microgravity conditions, capillary forces can
be exploited to control fluid orientation so that large mission-critical systems
perform predictably.
Interfacial phenomena are driven by surface tension and the contact angle or degree
of wetting, which depend on both the fluid and the adjoining surface. Capillary
forces are masked by the gravitational force exerted on fluids, hence the need to
study these phenomena under low-gravity conditions. Because hydrostatic pressure
is absent in microgravity, technologies for liquid management in space use capillary
forces to position and transport liquids. On Earth, the effect of capillary forces
is limited to a few millimeters. In space, these forces still affect free surfaces that
extend over meters. For the application of open channels in propellant tanks of
spacecraft, design knowledge of the limitations of open capillary channel flow is a
requirement. These limitations are based on the restriction that the liquid fuel must
be free of bubbles prior to entering the thrusters.
Early drop tower experiments established the need to understand the effects of
interfacial phenomena in a microgravity environment (Siegel, 1961). The first
spaceflight microgravity experiment was an interfacial phenomena investigation
performed by astronaut Scott Carpenter on Mercury flight MA-07 in 1962. In
particular, it tested fluid equilibrium configurations in a cylindrical-baffle-in-a-
sphere geometry (Petrash, et al, 1962; Petrash, et al, 1963).
Recent experiments flown on the ISS include the Capillary Flow Experiments
(CFE- 1, CFE-2) and the Capillary Channel Flow (CCF) experiment. CFE-1
and CFE-2 were a suite of experiments that investigated capillary flows and
flows of fluids in containers with complex geometries. CCF investigated capillary
and interfacial phenomena in inertial-dominated flows. Results from these
experiments are expected to improve current computer models that are used by
designers of low-gravity flow systems and lead to improved fluid transfer systems
on future spacecraft.

26
CFE-1 was a simple fundamental scientific study and consisted of a set of six separate
fluid physics flight vessels that investigated capillary flows in low gravity.
The CFE data are crucial to aid in design of fluid management systems, including
fuels/cryogen storage, thermal control, water recycling and materials processing.
Under low-gravity conditions, capillary forces can be exploited to control fluid
orientation so that these mission-critical systems perform predictably.
The experiments provided critical results to the capillary flow community:
• Dynamic effects associated with a moving contact boundary condition.
• Capillary-driven flow in interior corner networks (Weislogel, 2012).
• Critical wetting phenomena in complex geometries.
Figure 15. Image sequence of Interior Corner Flow2 bubble migration where each image is approximately 60 seconds
apart. The bubble location measurements, z1 and z2, are tracked and compared with analytic and numeric predictions.
CFE included the Interior Corner Flow (ICF1, ICF2), the Vane Gap (VG1, VG2),
and the Contact Line (CL1, CL2) experimental units. All units used similar fluid
injection hardware, had simple and similarly sized test chambers, and relied solely
on video for highly quantitative data. The test fluid was a silicone oil with viscosities
selected for each unit. Other differences between units were wetting conditions and
test cell cross-section. The ICF experiment investigated propellant management and
passive capillary flow in tapered geometries for which boundary conditions are not
well understood or modeled. The initial and secondary imbibition was investigated
in two different tapering interior corner geometries. This set of experiments also
tested the ability of these type of geometries to passively separate gas/liquid mixtures
under low-gravity conditions. Figure 15 contains several time-sequenced images of
the slow secondary imbibition in the ICF2 geometry.

27
Quadrant
Average (experiment)
Large gap (analysis)
Average (experiment)
Small gap (analysis)
60
50
40
30
20
10
0
0 1 2 3 4 5
Critical
vane
angle
a
(deg)
Figure 16. (a) Science image of the Capillary Flow Experiments Vane Gap-1 vessel at a 45° vane angle. A large “finger” of
fluid has filled the gap between the vane and chamber inside the surface closest to the camera view at the critical angle
of 45 degrees (within ±1.5 degrees of predicted value); (b) Test points like this one provide experimental verification of
present analytic and numerical methods to predict such nearly discontinuous static and dynamic phenomena.
The VG experiment investigated the critical wetting condition when interior corners
do not actually make contact, specifically the corner and gap formed by an interior
vane and the interior wall of a propellant tank. The critical wetting angles have been
measured to within ±0.5 degrees, nearly four times more accurate than planned
(Chen, et al., 2012). In addition, a bulk shift phenomena has been discovered that
has implications for spacecraft tank design asymmetries. Figure 16 contains an image
of a critical wetting angle along with a plot of experimental wetting angle results
versus theory predictions. Figure 17 contains a sequence of images of various angle
positions during a complete 360-degree sweep of the vane in the test chamber.
The CL experiment studied the impact of the dynamic contact line. The contact line
controls the interface shape, stability and dynamics of capillary systems in low-g. The
two CL units are identical except for their respective wetting characteristics. For the
CL experiments, data from over 350 primary and ancillary science events have been
reduced, and significant contributions were found for both experimental results and
numerical comparisons. The complete database can be found at http://cfe.pdx.edu.
To date, the damped interface oscillations (frequency and decay) as functions of
fluid properties, wetting, contact line condition, disturbance type and amplitude

28
have been pursued. Figure 18
provides example images of the
static and dynamic states for an
experimental run.
Figure 17. Equilibrium interfaces for Vane Gap-1 for several vane
dial angles: 0, 36, 43, 53, 59.5, 90, 127.5, 134.5, 150.5, 180
degrees (from top left to bottom right).
The CFE-2 is a continuation of
CFE-1 and investigates increasing
complex capillary flow geometries.
Four re-flight units and seven new
units have been operated on ISS.
The CCF experiment is a versatile
flight experiment for studying a
critical variety of inertial-capillary
dominated flows and is critical to
spacecraft systems that cannot be
studied on the ground.
Figure 18. Image of Contact Line 2 showing smooth and pinning edge boundary conditions under (a) equilibrium, and
(b) dynamic states.
The results of CCF will help innovate existing applications and inspire new ones in
the portion of the aerospace community challenged by the containment, storage and
handling of large liquid inventories (fuels, cryogens, and water) aboard spacecraft.
The results will be immediately useful for the design, testing and instrumentation
for verification and validation of liquid management systems of current orbiting,
and future spacecraft envisioned for lunar and Mars missions. Results will also be

29
used to improve
life support system
design, separate the
gas and liquid phases
and enhance current
system reliability.
Figure 19. Capillary Channel Flow image of Experimental Unit #2 using second
Microgravity Science Glovebox camera. The bubble in lower portion of image indicates
the critical flow rate has been reached for this test point.
CCF examines flows
in parallel plate
channels, grooves
and interior corner
capillary conduits.
These conduits
represent a class of
practical capillary
geometries that
are implemented in designs of spacecraft fluid processing equipment. Validation
of theoretical models developed for these geometries will increase confidence in
the theory so that it may be applied to other geometries pertinent to advanced
microgravity fluid systems development.
The test matrix for Experimental Unit #1, which included the parallel plate and
groove channel geometries, collected over 1,300 data points with 900 consisting of
high-speed, high-resolution video image (100+ GB of video data). Data analysis has
verified model predictions for a number of critical conditions where the maximum
flow rate occurs (Haake, et al., 2010). In general, the measured critical flow rates for
the parallel plate and groove channel were within 3 percent of each other. Results
also discovered several “new” unstable conditions, which do not appear to match
existing theoretical models.
Over 3,000 test points were collected for the Experimental Unit #2. Figure 19 is
from a video image of the critical velocity being reached during an experimental
run. A series of regime maps have been generated that identify the passive gas/liquid
separation regimes for the wedge-shaped geometry (Jenson, et al., 2014).
Further work is needed that emphasizes fluids challenges related to propellant tanks
and water processing for life support. In particular, capillary-flow geometries that
are tolerant to fickle wetting conditions, such as those that occur in spacecraft urine
collection and water recycling systems, need to be further investigated.

30
Although ground-based work is already being pursued in these newer areas, the
long-duration microgravity environment provided by ISS is needed for further
experimental investigations such as:
•
Experiments using capillary flow geometries that can purposely perform passive
gas/liquid phase separation.
•
Capillary flow investigations that include non-isothermal effects (evaporation/
condensation), normally encountered in cryogenic systems, but also are
encountered in proposed Environmental Control and Life Support Systems
(ECLSS) that influence wetting conditions/contact angle.
•
Fundamental areas of capillary flow, investigations that use idealized pore
geometries to gain insight into capillary wicks, water uptake in soils, etc.
•
Testing capillary geometries of interest in micro-fluidic applications such as for
micro-scale diagnostic devices (also referred to as Lab-on-a-Chip), along with
pumping and valving techniques, could be investigated before the manufacturing
methods for fabricating these micro-scale features are available.

31
Opportunities for Research
in Fluid Physics on ISS
Complex Fluids
The study of complex fluids encompasses diverse fields such as phase transitions,
nucleation and crystal growth, glass formation, chaos, field theory, and much
more. Furthermore, research in complex fluids provides the underpinnings of
applications related to NASA exploration of planetary surfaces as well as terrestrial
applications in industries such as pharmaceutical, chemical, plastics, petroleum,
electronics, liquid crystals, and the next generation of high-resolution inks for
additive manufacturing. According to the National Research Council Decadal
Survey (Space Studies Board, 2011), these industries contribute over $1 trillion
annually to U.S. manufacturing output.
The need to conduct research in a microgravity environment is clear. Because of the
relatively large size of the basic structures, gravitational forces dominate, causing
sedimentation, particle jamming, convective flows and other induced gradients,
and obscuring weaker forces such as surface tension and entropic forces. In granular
materials, stresses and yield properties are also sensitive to gravity.
Colloids and Suspensions
Future fundamental studies of order, including the role of colloidal particle shape on
structure and complex processes such as self-assembly, motility and non-biological
self-replication, are key research areas to address and will require a microscope with
the following desired capabilities:
•
Faster imaging rate for quickly constructing 3D confocal images with a higher-
resolution. Scientists are beginning to observe new and interesting behaviors
when the frame rate is increased above 100 frames-per-second.
•
Particle and cluster manipulation capabilities using dynamic laser tweezers
that allow scientists to manipulate samples and to introduce defects to see and
understand how nature heals. Dynamic laser tweezers will also enable scientists
to grow ordered structures from patterned layers that can be laid down by the
laser tweezers, patterns whose spacing can also be manipulated in this way. This
technology will enable scientists to see what nature prefers and how to best coax
her when another structure or pattern is needed to realize a needed technology.
•
Homodyne dynamic light scattering to measure particle diffusion coefficients in
regular sample cells and in temperature gradient cells (to provide phase diagram
location and translational and rotational diffusion coefficients).
•
Spectrometry capabilities for quantifying new colloidal crystals and their
growth rates. This option will be useful for investigations such as seeded growth

32
studies where growth rates and other properties of homogeneous and controlled
heterogeneous crystals can be compared.
•
Variable crossed-polarizers for quantifying the polarization rotation predicted for
liquid crystals and new types of materials.
•
Vibration cancelling three axes Piezo-platform for holding samples that will
significantly improve submicron imaging and 3D confocal image sectioning and
image reconstruction.
In addition, the Physics of Colloids in Space (PCS) experiment studied the phase
behavior, growth dynamics, morphology and mechanical properties of different
types of colloidal suspensions, including binary colloidal alloys, colloidal polymer
mixtures, fractal colloidal aggregates, and the natural entropy-driven transition from
a disordered glassy state to an ordered crystalline one. This EXpedite the PRocessing
of Experiments to Space Station (EXPRESS) Rack hardware, with its dynamic light
scattering, Bragg scattering, and low-angle scattering measurement capabilities, was
put into bonded-storage for possible future use on ISS.
Liquid Crystals
An important area of soft condensed matter physics and chemistry that has
seen major discoveries and rapid advancement with immediate application for
consumer electronics is the study of liquid crystals. Increased understanding of the
dynamics, morphology and structures of liquid crystals significantly enhances the
ability to control the properties of this type of complex fluid. Liquid crystals are
incredibly important as a fundamental material for modern display and information
storage and processing technologies as well as possible high-efficiency energy
conversion devices.
The study examines the two-dimensional fluid physics of freely suspended liquid
crystalline (FSLC) films, including overall fluid motion, diffusion and merging
of extra film layers called islands. In the microgravity environment, recent
experiments tested theories of 2D hydrodynamic flow, of relaxation of hydrodynamic
perturbations, and 2D hydrodynamic interactions. Since there is no natural
convection in microgravity, freely suspended bubbles present an ideal fluid system
for the study of 2D hydrodynamics.
While much work has been done in understanding the growth kinetics process in
other systems such as crystallization and the phase separation of binary alloys, only
recently has the phase ordering process been studied in systems that form liquid

33
crystals. Systems that form liquid crystal are good candidates for studying
phase ordering kinetics since they can be observed directly using Depolarized
Reflective Light Microscopy, which will be available in the near future aboard
station fluid facilities.
Foams
Foams are dispersions of gas into liquid or solid matrices. Typically, they are made
in conditions where the matrix is liquid. The behavior of foams in microgravity is
different from on Earth because the process of drainage is absent in microgravity
conditions. Drainage is the irreversible flow of liquid through the foam leading to
the accumulation of liquid at the foam bottom and to a decrease of global liquid
content within the foam; in this case, the gas bubbles conform to the polyhedra in
the upper portion of the foam, creating a so-called “dry foam.” When the liquid
films between the bubbles become very thin, they break, collapsing the foam. This
happens in the absence of suitable stabilizing agents (well-chosen surfactants or solid
particles for aqueous foams).
Microgravity offers the opportunity to investigate the so-called “wet” foams, which
cannot be stabilized on Earth because of the drainage problem. New behaviors or
regimes are expected to appear for wet foams, masked by convective instabilities
on Earth. In addition, elastic and viscous properties of wet foams are expected to
be strongly modified by the presence of solid particles. The physics of wet foams is,
therefore, poorly understood.
Granular Materials
Granular matter is the most common and pervasive medium after air and water,
yet the understanding of its statics and dynamics lags significantly behind that
of conventional solids and fluids. Specifically, the rationally derived constitutive
relationships between strain, or strain rates, and the stresses in granular media are
not understood. Without this understanding, the ability to predict the dynamics of
granular materials and to design the associated equipment is severely limited.
ISS flight experiments could develop and test models for both static (jammed)
and dynamic (flowing) states. In parallel, an experiment could be developed to
conduct simulated technology applications for this research area to include
studying “icy regolith” flows where the effects of ice and water on material handling
are investigated.

34
Particulate Management
Particulate management is similar to the behavior of granular materials; however,
the concentration of the solid particles is extremely low in the bulk fluid but can
accumulate in localized volumes to have detrimental effects. “Dust” can have varying
effects on system components. It can degrade the movement of mechanical parts,
penetrate seals, obscure optical surfaces (e.g., windows) and sensors, and short out
electronic components. Airborne or suspended micron- and sub-micron-size particles
are particularly problematic since their persistence in large concentrations can pose
acute health problems.
The fundamentals of aerosol transport are well known for terrestrial applications.
However, given the indefinite residence times in transit and orbiting vehicles, the
dust capturing that takes place in the ventilation and filtration systems leads to
extended particle-to-particle interactions. Areas of poor ventilation or flow stagnation
regions are more susceptible to dust buildup. A detailed look at these mechanisms
under the microgravity environment and large aggregate loading conditions provides
valuable engineering information on the best approaches for dust capturing controls.
These approaches can include investigations on fibrous capturing mechanisms,
impaction, interception and diffusion, and alternate approaches such as inertial,
electrostatics and surface/fiber coatings. The added effects of reduced-pressure
environments are also factors.
Magnetorheological Fluids
Magnetorheological fluid suspensions are normally stable fluid suspensions that
undergo a dynamic mechanical transition to a solid within milliseconds after the
application of an external magnetic field. This rapid and reversible transition in the
material’s mechanical behavior is due to the distinct microstructural transition in the
fluid driven by the polarization of particles. The mechanical energy required to strain
and disrupt such networks leads to elasticity and yielding, but the suspension reverts
to liquid-like behavior almost immediately after removing the field.
Magnetorheological fluid provides the basis for technologies ranging from actively
controlled dampers and actuators to magnetically sealed bearings and sensitive
stress transducers.
Applications in space exploration include potential use in robots, rovers and crew
suits (mobility augmentation), especially for endurance and fatigue countermeasure
designs that aid in lifting, moving and supporting loads during extra-vehicular
activities (i.e., spacewalks). In addition to their immediate applications in mechanical
systems, Magnetorheological fluid suspensions have become important components

35
in microfluidic devices that could lead to compact medical instrumentation and
diagnostics for Earth-based and long-duration spaceflight applications.
Polymer Fluids
The combination of both shearing and extensional flows is common in many
polymer processing operations such as extrusion, blow molding and fiber spinning.
Therefore, knowledge of the complete rheological properties of the polymeric
fluid being processed is required in order to accurately predict and account for its
flow behavior. In addition, if numerical simulations are to serve as a priori design
tools for optimizing polymer processing operations, then it is critical to have an
accurate knowledge of the extensional viscosity and its variation with temperature,
concentration, molecular weight and strain rate.
Multiphase Flow
The gas-liquid interface is the focus of multiple phenomena involving interactions
among bubbles, drops and solid objects. It is also the boundary across which
momentum, mass and heat transfer occur. Although studies have been conducted on
the interactions of the interface in reduced gravity, most careful measurements have
been made with limited systems consisting of only a handful of bubbles and drops
and have not been complicated by bulk fluid motion and phase change. The results
of these studies are not sufficient to develop predictive models to describe multiphase
flow behavior in microgravity.
Phase density and interfacial tension dominate the behavior of multiphase systems in
reduced gravity unlike that in normal gravity. While phase density in normal gravity
results in a buoyancy-driven segregation of the phases and distortion of the shape of
the interface, the impact of the phase-density difference is primarily evident in the
flow momentum, which is demonstrated by the flow distribution in splitting tees
and cyclonic separators. Interfacial tension in reduced gravity causes the gas-liquid
interface to become more spherical at larger length scales. It is necessary to develop
a fundamental understanding of multiphase flow behavior and of the momentum,
heat and mass transfer processes in microgravity. Discrete critical parameters should
be measured experimentally to develop and validate predictive models (Lahey, et
al., 2004). These models are essential tools needed by designers of life support,
propulsion, power and other systems for use in space and on the moon and Mars.
It is necessary to examine Two Phase Flow Instability Mechanisms. These
mechanisms are heavily influenced by the gas/vapor phase density and its compliance

36
(Ledinegg Instability) with system controls such as pressure control systems or pump
characteristics. Phase distribution in manifolds for parallel channel evaporators and
condensers is governed by both phase momentum and interfacial phenomena.
Zero Boil-off Tank Experiment Series
The storage, conditioning and transfer of volatile fluids is the focus of the series
of experiments planning to use the Zero Boil-Off Tank experiment hardware.
The ZBOT hardware is a highly instrumented tank and flow loop and includes
visualization and other diagnostics to capture the simulant fluid behavior within a
transparent tank in an effort to understand the governing parameters required for
cryogenic fluid and thermal management. Planned uses include examining the effect
of non-condensable gases on the thermal conditioning and pressurization of volatile
fluid, active cooling through use of spray bars and/or cold fingers, and transfer line
and receiving tank chill down.
ElectroHydroDynamics
Application of an electric field on the order of 1 kV/cm (or higher) to a dielectric
fluid (semi-insulating fluid) results in electrohydrodynamic (EHD) pumping of
the dielectric fluid. The EHD conduction pumping is based on the interaction of
fluid flow field and external electric field via the Coulomb force, which involves
the dissociation and recombination of neutral species where the rate of dissociation
exceeds that of recombination.
In addition to EHD conduction pumping, a second EHD mechanism is based on
the dielectrophoretic (DEP) force. Unlike the Coulomb force, the DEP force acts
on polarized charges and can be used to significantly influence vapor bubble motion
(e.g., effectively extracting the vapor bubbles away from the heated surface) during
nucleate boiling.
The EHD experiment seeks to develop fundamental understanding on the
interaction of electric and flow fields in the presence of phase change (liquid/
vapor). The EHD experiment is a parametric investigation of thin film liquid
boiling phenomenon employing a dielectric fluid as the liquid. The schematic of
the experiment and a photo of the test cell showing the EHD disc and the DEP
electrodes in Figure 20.
Adiabatic Gas-Liquid Flow Experiments
The Packed Bed Reactor Experiment (PBRE) provides a nitrogen gas and water

37
flow to a replaceable test section and diagnostics and can provide opportunities to
conduct a number of different types of future experiments. A wide range of precisely
controlled gas and liquid flows can be provided that envelop the flow ranges typically
encountered in most adiabatic two-phase devices used for water processing or
thermal control. Diagnostics including high speed video, pressure drop, and flow
rates are available. Testing can include new reactor beds as well as fluid components
and systems.
DEP electrode increases
local liquid circulation and
vapor bubble extraction
Vapor moves to
periphery of disc
where it condenses
Thin liquid ﬁlm pumped
radially inward by EHD
conduction
Condenser surface –
heat is dissipated to
bottom chamber Heater surface where
boiling occurs
Figure 20: Left: This experiment concept for the test chamber: a dielectrophoretic (DEP) electrode removes vapor
bubbles from the heater. The surrounding circular electrode strips centered on the heater pump cool the single-phase
liquid back toward the heater. Right: Image of prototype test chamber.
Flow Boiling and Condensation Experiment
The Flow Boiling and Condensation Experiment (FBCE) is a two-phase flow
boiling/condensation facility aboard the ISS that serves as the primary platform for
obtaining two-phase flow and heat transfer data in microgravity. The key objectives
of the experiment are:
•
Develop an experimentally validated mechanistic model for microgravity flow
boiling Critical Heat Flux (CHF) and dimensionless criteria to predict minimum
flow velocity required to ensure gravity-independent CHF.
•
Develop experimentally validated mechanistic model for microgravity annular
condensation and dimensionless criteria to predict minimum flow velocity
required to ensure gravity-independent annular condensation. In addition,
develop correlations for other condensation regimes in microgravity.
•
Obtain flow boiling data (heat flux, the wall temperature difference) in long
duration microgravity environments for a well characterized heating surface as
functions of liquid inlet mass velocity and sub-cooling.
•
Obtain flow condensation data (heat flux, the wall temperature difference) in
long duration microgravity environments for a well-characterized condensing
surface as functions of inlet quality and flow rate of condensing vapor.

38
The FBCE hardware conditions the test fluid (normal-perfluorohexane or nPFH-
C6F14) to the proper thermodynamic state before entering the Flow Boiling or the
Condensation test modules and reconditioning of the test fluid to enter the pump as
a subcooled liquid.
Figure 21: Flow Boiling and Condensation Experiment (FBCE) Test
Sections: Top: Condensation Module-Heat Transfer (CM-HT), Middle:
Condensation Module-Flow Visualization (CM-FV) Bottom: Flow Boiling
Module (FBM).
The FBCE will be conducted
in the Fluids Integrated Rack
(FIR) on board the station.
Three different test modules are
planned (Figure 21):
1)
The Flow Boiling Module
(FBM) includes a boiling
section with a rectangular
cross-section and individually
powered wall heaters on the
top and and bottom of the
test section. This module is
highly instrumented with
therma couples and can be
visualized with a high-speed
imager along its length.
2)
The condensation module-heat transfer (CM-HT) is configured with the test
fluid flowing inside a cylindrical tube while water flowing outside the tube
removes the heat released from condensation. The test section is highly
instrumented with thermocouples.
3)
The condensation module-flow visualization (CM-FV) is designed so that the
cooling water flows inside a tube while the vapor condenses on the tube exterior.
CM-FV also measures temperatures but not as comprehensively as CM-HT.
Capillary, Thermocapillary and Solutocapillary Flow Phenomena
Capillary flows and phenomena are applicable to a myriad of fluids management
systems in low-g, including fuel and cryogen storage systems, thermal control
systems (e.g., vapor/liquid separation), life support systems (e.g., water recycling),
and materials processing in the liquid state. In fact, NASA’s near-term exploration
missions plan larger masses of liquid propellant than have ever flown on
interplanetary missions. Under microgravity conditions, capillary forces can be

39
exploited to control fluid orientation so that such large, mission-critical systems
perform predictably.
Many multiphase flow phenomena in reduced gravity are driven by variations
in surface tension caused intentionally or inadvertently because of gradients
in temperature, concentration or wetting conditions. Such flows, also called
thermocapillary/solutocapillary flows or Marangoni convection, find application in
most fluid systems in space such as propellant management systems, thermal control
systems, cryogenic fluid systems, life support systems, etc. Fluid systems in which
bubbles, drops and nucleation phenomena occur are particularly susceptible to flows
driven by surface tension gradients.
For example, a capillary-based
approach is needed to provide
sufficient hydration and aeration to
the root zone for growing plants.
Plants require water for nutrient
transport, biochemical processes, and
thermal management. Aeration is
required for the root zone to exhale
carbon dioxide and inhale oxygen at
a minimal but necessary level. The
Plant Water Management experiment
is a technical demonstration of
new techniques in capillary flow
phenomena. This experiment intends
to demonstrate methods that exploit
passive and semi-passive control of
poorly wetting capillary liquids that mimic the role of gravity on earth. Specifically,
we intend to demonstrate the extent to which capillary forces may be exploited to
control numerous effects on low-g plant watering for both soil-based growth media
and hydroponics channels while considering critical challenges of saturation, de-
gassing, aeration, stability, and more.
Figure 22: Simulated plants constructed of felt foliage and
string roots mimic plant water uptake. Plant Water Management
involves addressing challenges in both hydroponics channels
(left) and soil-based media (right) using capillary fluidics.

40
Lessons Learned
The NASA Colloids Program has prompted several paradigm shifts in soft condensed
matter physics. New areas of inquiry stem from the following recent findings:
•
observations of the disorder-to-order transition (glasses on Earth crystallizing in
microgravity),
•
crystallization arresting phase separation,
•
fluids with critical points far from where theory predicted them to be; e.g.,
bi-disperse systems showing unexpected behaviors, such as particle stabilizer
particles that are 20 percent smaller do not form clusters in the presence of
dilatant attractants in the same way as larger particles,
•
seed particles affecting the type of nucleation being observed.
Analysis of experiment data revealed interesting elastic instabilities on the free
surface of a fluid sample. The data showed the formation of beads-on-a-string
structures in the absence of gravitational sagging. The development and evolution
of such phenomena upon cessation of elongation have not yet been described.
The design of a heat transfer experiment should account for extreme heating
that could cause thermal decomposition of the test fluid. Consequently, heater
temperatures should be measured directly and incorporated into control/protection
circuit, and these heaters and other convective heat devices should be derated from
normal to microgravity operation. The electrical system of any experiment should
be designed so failed components can be isolated in order to maintain maximum
capabilities in the event of a failure by individually fusing heaters and using
independent controls to activate/deactivate them.
Complexity of the experiment should be minimized if at all possible. Science
requirements that add complexity not only add additional cost to the development,
but often lengthen the development time, making turnover an issue for both the
project team and, in particular, for the principal investigator and his/her science
team when the experiment timeline extends beyond the typical tenure of a Ph.D.
student. It is important to design the experiment to be both flexible and repairable.
Unlike the space shuttle experiment days, the ISS operates more like a laboratory
on Earth where crew members often gain rather good experimental skills while
operating a particular experiment over months rather than a week or so. As a result,
they can become quite adept at experiment repair if this capability is designed into
the experiment and clear, straightforward procedures are provided.

41
ISS Facilities for Research of
Fluid Physics
Acceleration Measurement and Environment Characterization
The Space Acceleration Measurement System (SAMS) and the Microgravity
Acceleration Measurement System (MAMS) provide continuous measurement of
the ISS vibratory and quasi-steady acceleration environment, respectively. SAMS
measurement capability extends to all three laboratories, while MAMS data can be
mathematically mapped to any arbitrary location using rigid-body assumptions.
SAMS and MAMS support NASA’s Physical Sciences Research Program. Along
with Principal Investigator Microgravity Services analyses, these systems serve a
critical, ongoing role in support of vehicle/loads monitoring. SAMS and MAMS
monitor vehicle dynamic loads and assist technology developers and principal
investigators in various disciplines. The goal is to characterize and understand the
acceleration environment as related to a wide array of disturbances and events that
routinely or uniquely take place on the ISS.
Fluids Integrated Rack
The Fluids Integrated Rack (FIR) was designed to test and understand critical
technologies needed for advanced life support and future spacecraft thermal control,
research in complex fluids (colloids), and life science experiments. The hardware
was delivered on STS-128 (August 2009) to the ISS and installed in the Fluids
and Combustion Facility of the U.S. Lab. The FIR contains the hardware and
software necessary for conducting fluid physics science experiments. It is designed
to accommodate a range of fluids experiments while meeting ISS requirements and
limitations such as safety, power and energy, cooling, mass, crew time, stowage,
resupply flights, and data downlink.
The FIR uses six major subsystems to accommodate the broad scope of fluids
physics experiments. The major FIR subsystems are structural, environmental,
electrical, gaseous, command and data management, and diagnostics. These
subsystems combined with payload- unique hardware allow the FIR to conduct
world-class science. It also provides the largest contiguous volume for experimental
hardware of any ISS facility, easily reconfigurable diagnostics, customizable
software, active rack-level vibration isolation and other subsystems required
to support a wide range of gravity-dependent fluid physics and life science
investigations. The LMM, or microgravity microscope, is an integral part of
this facility.

42
Light Microscopy Module
The Light Microscopy Module is a remotely controllable in-orbit microscope
subrack facility, allowing flexible scheduling and control of physical science and
biological science experiments within the FIR on the ISS. The LMM concept is
a modified commercial research imaging light microscope with powerful laser-
diagnostic hardware and interfaces, creating a one-of-a-kind, state-of-the- art
microscopic research facility. The microscope will house several different objectives,
corresponding to magnifications of 10x, 40x, 50x, 63x and 100x. Features of the
LMM include high-resolution, color video microscopy, bright field, dark field,
phase contrast, differential interface contrast, spectrophotometry, and confocal
microscopy combined in a single configuration. The LMM provides an enclosed
work area called the auxiliary fluids container with glove ports and an equipment
transfer module for transporting experiment samples from stowage to the LMM.
Microgravity Science Glovebox
The Microgravity Science Glovebox (MSG) is a research facility installed on the ISS
in which fundamental and applied scientific research is conducted in support of
the NASA Headquarters’ Vision for Space Exploration. This facility was designed
to accommodate small science and technology experiments in a “workbench”
type environment. Because the facility’s working volume is enclosed and held at
a negative pressure with respect to the crew living area, the requirements on the
experiments for containment of small parts, particulates, fluids and gases in the
low-gravity space station environment are substantially reduced. The concept allows
scientific flight hardware to be constructed in close parallel with bench experiments
developed in ground-based laboratories. The facility is ideally suited to provide
quick accommodations for exploration investigations that are necessary to gain
an initial understanding on the role of gravity in the physics associated with new
research areas.
Research investigations operating inside the MSG are provided a large, 255-liter
enclosed work space, 1,000 watts of dc power via a versatile supply interface
(120, 28, +12, and 5 Vdc), 1,000 watts of cooling capability, video and data
recording and real-time downlink, ground commanding capabilities, access to ISS
Vacuum Exhaust and Vacuum Resource Systems, and gaseous nitrogen supply.
These capabilities make the MSG one of the most utilized science facilities on the
ISS. In fact, the MSG has been used for over 10,000 hours of scientific payload
operations. MSG investigations involve research in cryogenic fluid management,

43
fluid physics, spacecraft fire safety, materials science, combustion, plant growth,
human health, and life support technologies. The MSG facility is ideal for
advancing our understanding of the role of gravity upon science investigations and
research, and to utilize the ISS as a technology platform for space exploration.
EXpedite the PRocessing of Experiments to Space Station
(EXPRESS) Racks
The eight EXPRESS racks are multi-use facilities, which provide standard interfaces
and resources for Middeck Locker and International Subrack Interface Standard
drawer payloads. Payloads using single-, double- or quad-locker and/or drawer
configurations can be accommodated by these racks. The racks provide a number of
services for payloads including Nitrogen, Vacuum, RS422, Ethernet, video, air, and
water-cooling.

44
Developing and Flying Fluid
Physics Research to ISS
The research community is provided specific research topics through NASA
Research Announcements. In response, the research community generates ideas
regarding the topics and submits them to NASA, which evaluates the responses and
makes selections through a peer review process. Awards are granted for ground-
based research at NASA and/or principal investigator institutions. Principal
investigators are required to pass the Science Concept Review and Requirements
Design Review. Flight research experiment concepts and designs undergo the
Preliminary Design, Critical Design, and System Acceptance Review processes
before fluids physics research is launched and conducted on the ISS.
PIs need to consider potential hazards (e.g., flammability, explosion, corrosion,
toxicity) and their impact on both crew and spacecraft when selecting test fluids.
Furthermore, additional hazards can result from the inadvertent release of the test
fluid into ISS environment and potential reaction with ISS systems such as the
catalytic converter in the Trace Contaminant Control Subassembly (TCCS). While
additional levels of containment may mitigate hazards during the storage and
operation of the experiment, other controls are needed to address the handling of
fluids during filling and sampling procedures.
Additional Guides that may be of interest to fluid physics researchers include A
Researcher's Guide to the Acceleration Environment and A Researcher's Guide to
Physical Sciences Informatics System. See https://www.nasa.gov/mission_pages/
station/research/researcher_guide.

45
Funding, Developing and
Launching Research to ISS
Supporting research in science and technology is an important part of NASA’s
overall mission. NASA solicits research through the release of NASA Research
Announcements (NRAs), which cover a wide range of scientific disciplines. All NRA
solicitations are facilitated through the web-based NASA Solicitation and Proposal
Integrated Review and Evaluation System (NSPIRES) http://nspires.nasaprs.com/
external/. Registering with NSPIRES allows investigators to stay informed of newly
released NRAs and enables them to submit proposals. NSPIRES supports the entire
lifecycle of NASA research solicitations and awards, from the release of new research
calls through the peer review and selection process.
In planning the scope of the proposal, an investigator should be aware of available
resources and the general direction guiding NASA research selection. NASA places
high priority on recommendations from the 2011 National Research Council’s
Decadal Survey (Space Council Board, 2011) and subsequent reports, which
placed emphasis on hypothesis-driven spaceflight research. In addition, principal
investigators (PIs) should be aware that spaceflight experiments may be limited by a
combination of constraints on power, crew time, or volume. Launch and/or landing
scrubs are not uncommon, and alternative implementation scenarios should be
considered in order to reduce the risk from these scrubs. Preliminary investigations
using ground-based simulators may be necessary to optimize procedures before
spaceflight. Also, many experiments require unique hardware to meet the needs of
the spaceflight experiment.
To understand previous spaceflight studies, prospective PIs should familiarize
themselves with the Physical Science Informatics Database (http://psi.nasa.gov/),
which describes research previously conducted on the ISS, including that of the
International Partners. A detailed catalog of previous, current, and proposed
experiments, facilities and results, including investigator information, research
summaries, operations, hardware information, and related publications is available
at www.nasa.gov/iss-science through the NASA ISS Program Office. Additionally,
details pertaining to research previously supported by the Space Life and Physical
Sciences Research and Applications Division of NASA’s Human Exploration
and Operations Mission Directorate can be located in the Space Life Physical
Sciences Research and Applications Division Task Book in a searchable online
database format at: https://taskbook.nasaprs.com/Publication/welcome.cfm.
Please note that NRAs are in place for research to analyze previously-acquired data
available in the PSI.

46
ISS U.S. National Laboratory
In 2011, NASA finalized a cooperative agreement with the Center for the
Advancement of Science in Space to manage the International Space Station U.S.
National Laboratory (ISS National Lab). The independent, nonprofit research
management organization ensures the station’s unique capabilities are available to
the broadest possible cross section of U.S. scientific, technological and industrial
communities.
The ISS National Lab develops and manages a varied research and development
portfolio based on U.S. national needs for basic and applied research. It establishes
a marketplace to facilitate matching research pathways with qualified funding
sources and stimulates interest in using the national lab for research and
technology demonstrations and as a platform for science, technology, engineering
and mathematics education. The goal is to support, promote and accelerate
innovations and new discoveries in science, engineering and technology that will
improve life on Earth.
More information on ISS National Lab, including proposal announcements, is
available at www.issnationallab.org.
Other Government Agencies
Potential funding for research on the ISS is also available via governmental
partnerships with ISS U.S. National Laboratory and includes (but is not limited to)
such government agencies as:
• Defense Agency Research Projects Agency (DARPA)
• Department of Energy (DOE)
• Department of Defense (DOD)
• National Science Foundation (NSF)
• National Institutes of Health (NIH)
• U.S. Department of Agriculture (USDA)

47
International Funding Sources
Unique and integral to the ISS are the partnerships established between the United
States, Russia, Japan, Canada and Europe. All partners share in the greatest
international project of all time, providing various research and experiment
opportunities for all. These organizations – Japan Aerospace Exploration Agency
(JAXA), Canadian Space Agency (CSA), ESA (European Space Agency), Russian
space agency Roscosmos, Centre National d'Etudes Spatiales (CNES), and the
German Aerospace Center (DLR) – provide potential funding opportunities for
international scientists from many diverse disciplines.

48
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51
Acronyms
2D/3D Two Dimensions, Two Dimensional/Three Dimensional
ACE-M Advanced Colloids Experiment (Microscopy)
ACE-T Advanced Colloids Experiment with sample Temperature control
BCAT Binary Colloidal Alloy Tests
BDB Buoyancy Dominated Boiling
CCF Capillary Channel Flow
CFE Capillary Flow Experiment
CHF Critical Heat Flux
CL Contact Line
CM-FV Condensation Module-Flow Visualization
CM-HT Condensation Module-Heat Transfer
CVB Constrained Vapor Bubble
DEP Dielectrophoretic
ECLSS Environmental Control and Life Support Systems
EHD Electrohydrodynamic
EXPRESS EXpedite the PRocessing of Experiments to Space Station
FBCE Flow Boiling and Condensation Experiment
FBM Flow Boiling Module
FIR Fluids Integrated Rack
FSLC Freely Suspended Liquid Crystalline
GB gigabyte(s)
ICF Interior Corner Flow
ISS International Space Station
LAD Liquid Acquisition Device
LMM Light Microscopy Module
MABE Microheater Array Boiling Experiment
MAMS Microgravity Acceleration Measurement System
MR Magnetorheological
MSG Microgravity Science Glovebox
NPBX Nucleate Pool Boiling eXperiment
NSPIRES NASA Solicitation and Proposal Integrated Review and Evaluation System
OASIS Observation and Analysis of Smectic Islands in Space
PBE Pool Boiling Experiments
PBRE Packed Bed Reactor Experiment
PCS Physics of Colloids in Space
PMD Propellant Management Device
PI Principal Investigator
RTD Resistance Temperature Detector
SAMS Space Acceleration Measurement System
SmA, SmC Smectic A, Smectic C
TCCS Trace Contaminant Control Subassembly
VG Vane Gap
VTRE Vented Tank Resupply Experiment
ZBOT Zero Boil-Off Tank experiment

52
52
The Complete ISS Researcher’s
Guide Series
1. Acceleration Environment
2. Cellular Biology and Regenerative Medicine
3. Combustion Science
4. Earth Observations
5. Fluid Physics
6. Fruit Fly Research
7. Fundamental Physics
8. GeneLab
9. Human Research
10. Macromolecular Crystal Growth
11. Microbial Research
12. Microgravity Materials Research
13. Physical Sciences Informatics Systems
14. Plant Science
15. Rodent Research
16. Space Environmental Effects
17. Technology Demonstration

53
53
For more information...
Space Station Science
https://www.nasa.gov/iss-science
Station Research Facilities/Capabilities
https://www.nasa.gov/stationfacilities
Station Research Opportunities
https://www.nasa.gov/stationopportunities
Station Research Experiments/Results
https://go.nasa.gov/researchexplorer
Station Research Benefits for Humanity
https://www.nasa.gov/stationbenefits

National Aeronautics and Space Administration
Johnson Space Center
http://www.nasa.gov/centers/johnson
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NP-2019-11-009-JSC

NASA A Researcher’s Guide to International Space Station : Fluid Physics

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