SAE TECHNICAL
PAPER SERIES
2002-01-2386
Flow and Distribution of Fluid Phases through
Porous Plant Growth Media in Microgravity:
Progress to Date
Susan L. Steinberg
Universities Space Research Association
Nihad E. Daidzic
National Center for Microgravity Research, NASA Glenn Research Center
Scott Jones and Dani Or
Utah State University
Gerard Kluitenberg and Lakshmi Reddi
Kansas State University
J. Iwan D. Alexander
Case Western Reserve University
Markus Tuller
University of Idaho
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2002-01-2386
Flow and Distribution of Fluid Phases through Porous Plant
Growth Media in Microgravity: Progress to Date
Susan L. Steinberg
Universities Space Research Association
Nihad E. Daidzic
National Center for Microgravity Research, NASA Glenn Research Center
Scott Jones and Dani Or
Utah State University
Gerard Kluitenberg and Lakshmi Reddi
Kansas State University
J. Iwan D. Alexander
Case Western Reserve University
Markus Tuller
University of Idaho
Copyright © 2002 Society of Automotive Engineers, Inc.
ABSTRACT
Results from plant growth experiments utilizing
particulate growth media during space flight revealed
difficulties associated with providing reliable reproducible
gaseous and water supply to plant roots.
These
limitations were attributed to insufficient understanding of
liquid configuration and growth media transport
processes in reduced gravity. The objective of this
NASA-funded research program is to develop a
framework for modeling and quantitative characterization
of physical processes associated with flow of wetting and
non-wetting phases in particulate plant growth media in
microgravity.
This paper provides an overview of
research plans and current status of research activities.
Magnetic Resonance Imaging (MRI) to detect and track
the evolution of liquid configuration and dynamics within
TM
thin slices of opaque porous media (Aquafoam with
mean pore size of 50 µm).
Both two- and three dimensional temporal MRI imaging
TM
has been performed in thin Aquafoam slices positioned
vertically and horizontally (to simulate the effect of
gravity). The wetting front exhibited percolation-type
patterns and fingering. Preliminary results show that
gravity dominates liquid flow even for low Bond numbers.
Although the capillary forces are very strong the small
hydrostatic pressure built in the initial liquid volume
determines the subsequent evolution of the wetting front.
INTRODUCTION
Characterization and modeling of substrate water
retention and transport properties in microgravity is key
to management and control of gas and liquid fluxes
within plant root zones. Modeling efforts will focus on
both 1) a pore network model for describing
discontinuous fluid phase transport (ganglia/blobs) and
2) a statistical distribution model describing water
retention and hydraulic conductivity as functions of
various pore configurations. Minimizing hydrostatic
forces within porous media by using thin samples on
earth may provide an approximation to microgravity
conditions. In our preliminary study we have used
Limited understanding of the effects of reduced gravity
on liquid and gaseous supply necessary for plant
physiological functions hinders progress in plant
research and crop production in space. Problems with
controlling the plant environment have made it
impossible to isolate microgravity as a variable of study
(16). Over the last 10 years as much as 30 million dollars
may have been spent on flight experiments with plants.
Although a number of environmental factors such as light
and air quality, and ventilation impact plant growth in
microgravity, none have had such a limiting effect as
control of water, air and nutrients in the root zone (2,16).
NASA’s Advanced Life Support program currently
believes that particulate solid substrates are best suited
to meet short and long-term plant production needs.
These needs include longevity and repeated use,
repeated crops in the same substrate, eventual use of
local Lunar or Martian materials, and recovery of roots
for research purposes. Therefore, it is crucial that water,
air and nutrient transport in small volumes of porous
media be well understood. In particular, the ability to
predict and tailor water and nutrient transport conditions
in porous growth media under a variety of gravity
conditions ranging from near weightlessness to reduced
gravity environments such as the Moon or Mars is critical
to the development of reliable, well characterized
experimental and production facilities.
To date, development of plant growth systems for
microgravity have typically been driven by mass, volume
and power constraints and the need to recycle water,
nutrients, and growth media (1,4). Due to these
constraints suggested criteria of success for plant
production in a Controlled Environment Life Support
System (CELSS) include the maximization of yield per
mole photon (power), unit area or volume. Mass and
volume constraints will minimize space allotted to root
modules which will likely result in high root densities.
Thus, the need to control supply of water, oxygen and
nutrients to the root is crucial. However, ground and flight
research has been focused on hardware development
for plant growth in microgravity that meets mass, volume
and power constraints, while neglecting fundamental
processes occurring in the growth media.
On earth, for example, small containers such as root
modules commonly suffer from inadequate total water
and mineral supply, excess water content, and poor
aeration due to perched water table at the bottom (41).
Technologies related to irrigation management for
containerized production in the greenhouse or nursery
th
industry developed during most of the 20 century. Much
of their success can be attributed to the development
and characterization of potting media for shallow root
zones commonly found in the greenhouse and nursery
industry including soiless mixes, sponges, and foams
((5,6,7,18,19,20,41) and many others). By contrast,
irrigation management technologies for microgravity are
still young with limited collective time on orbit.
Particularly little attention has been paid to identifying
optimal substrates for microgravity, assessing what
problems might occur in small volumes of porous media
under microgravity, and (most importantly) how they can
be avoided. In microgravity, surface tension/capillary
forces, lack of buoyancy driven convection, and changes
in pore geometry due to particle separation and vehicle
vibrations will likely govern fluid behavior through porous
media.
The general lack of understanding flow and
transport through porous media in microgravity was
documented at a recent workshop on microgravity soil
physics (42) and is the focus of our recently funded
NASA NRA.
HISTORICAL BACKGROUND
Early researchers utilized porous media systems
consisting of small, pre-moistened aliquots of vermiculite
or soil, filter paper or agar to supply water, nutrients and
oxygen to plant roots for periods ranging from a few
hours to several days in microgravity (see review in
(45)). Solidified agar nutrient medium (21) and
Horticultural foam (29) have been used on shuttle flights
to support plant growth for as long as 8-12 days.
Particulate substrates have been used to support wheat
production ranging from a multi-day shuttle flight (35) to
full life cycle production (3) on MIR. Problems with water
and air control in the root zone have been inferred from
soil and plant measurements (3,35,36,37).
Despite nearly 20 years of plant research in microgravity,
only very recently has any attempt been made to
understand physical issues associated with water and air
transport in a porous medium in microgravity. Ivanova &
Dandolov (24), Shah et al. (40), Podolsky & Mashinsky
(34), Morrow et al. (31), and Yendler et al. (46) all
measured and described various aspects of water
transport through porous substrate in microgravity.
Repetitions in these experiments have yielded
inconsistent results, the cause of which could be
attributed to any number of things, such as unknown or
uncontrolled initial and boundary conditions, air
entrapment, particle separation, etc.
The work by Podolsky & Mashinsky (34) and Jones and
Or (25,26,27) also represent the first attempts to put
transport of water and air through porous media in
microgravity on a sound theoretical basis. In addition,
Jones & Or (25) used physically based models to
optimize particle size distribution for aeration and water
retention. Figure 1 illustrates this optimization concept
considering the tradeoff between maximizing the
inversely related processes of supplying water and
oxygen to plant roots. Additional factors such as porous
media depth and root/microbial respiration rates dictate
the critical water content where oxygen concentration
limits plant growth. Scovazzo et al. (39) recently modeled
and defined design criterion for two-phase flow of air and
water in a membrane/solid media system. Steinberg &
Henninger (43) evaluated the dynamics of water
transport through the entire membrane/solid media/plant
system.
n
∂S
∂t
[
=
∂θ
∂t
[
]
= −∇ ⋅ K (θ )∇ψ +
]
∇ ⋅ D (θ )∇θ +
∂K (θ )
∂z
∂K (θ )
∂z
=
(1)
.
Here θ=nS is the volumetric moisture content (with n
being the uniform porosity, S≤1 the saturation), K(θ) is
the unsaturated hydraulic conductivity (scalar for
isotropic medium), D(θ) is the moisture diffusivity, ψ is
the matric potential, and z is the vertical elevation.
Figure 1. Illustration of physical processes of liquid and gas content
and flux critical for optimal plant growth conditions (25).
Jones & Or (27) analysis of water transport through
porous media in microgravity focused on data from two
flight tests (3,31). Unfortunately, current understanding of
the nature of water and air transport under microgravity
conditions is not sufficiently well developed to allow
unambiguous interpretation of microgravity experiment
results. For example, published studies of water flow in
plant growth media in microgravity give no description of
details such as media packing procedure or post-packing
bulk density (3,24,31,34,46). The effect of g-forces and
vibration during launch on media compaction, water
holding and aeration properties have never been
documented. Water transport through porous media
seems to behave differently depending on whether
substrate is launched wet or dry (see analysis of (3) and
(31) in (27)).
Another area of concern is possible constraint of the air
phase, which can cause fingering of the liquid flows (17).
In order to contain particulate media in microgravity root
modules are covered with plastic lids. The small
openings in the lids for plants contain foam or wick
material. Air exchange between the root module and
cabin air has not been adequately addressed. These
information gaps make it impossible to conclusively
determine whether the culturing technique or
microgravity significantly affects water and air transport
in microgravity.
LIMITATIONS IN CURRENT UNDERSTANDING
OF WATER FLOW THROUGH POROUS MEDIA
The simplest and most widely applied mechanistic
approach is Richards equation (22) which is based on a
diffusive-like motion of the liquid phase into a porous
medium.
There are several reasons why this model may be
inadequate for describing water transport through small
volumes of media in microgravity. Jones & Or (27)
eliminated the gravity term (∂K(θ)/∂z) from Equation (1),
to simulate microgravity, and obtained accentuated
hysteresis, reduced hydraulic conductivity and an altered
soil-water characteristic curve. They hypothesize that
differences between terrestrial and microgravity behavior
may be attributed to mechanisms such as enhanced
interfacial flow, particle rearrangement (24,28,30), and
air entrapment (28). While weightless conditions can
apparently be simulated simply by neglecting the gravity
term in Equation (1), it is not clear whether experimental
quasi-steady state measurements of the hydraulic
conductivity under 1g conditions implicitly reflect the
influence of gravity on transport and, thus, are unsuitable
for simulating zero-g behavior.
Secondly, the lack of consideration of adsorptive forces
and liquid films have been identified as a major
deficiency in current theories of transport and flow in
porous media (12,32). Given the absence of a
hydrostatic pressure gradient under weightless
conditions, it is important that the role of liquid films and
absorption are properly accounted for.
Recent
developments (33,44), involve using an Augmented
Young-Laplace (AYL) equation to calculate equilibrium
liquid configurations in partially saturated porous media
and provide a basis for the incorporation of adsorptive
and capillary contributions to the matric potential and
hydraulic conductivity.
Lastly, an implicit assumption in Equation (1) is that both
water and air exist as interconnected phases throughout
the porous medium. While this assumption is valid for
field scale terrestrial applications, it may not be valid for
the small root zone volumes used in space flight. An
important aspect of flow in porous media is the possibility
that the liquid, as well as the gas phase, becomes
discontinuous and forms ganglia (isolated blobs). The
motion of ganglia under microgravity conditions may,
along with the previously mentioned pore-scale
processes, strongly affect the nature of the transport
conditions.
In porous media containing water and air, the moisture
content distribution is often controlled by the nature of air
entrapment, which itself depends on the pore structure of
the media and the water infiltration mode. These
processes are poorly understood even under 1g
conditions. In the absence of gravity, the capillary forces
can dominate the discontinuous phase entrapment and
the absence of natural convection will prevent or inhibit
the "upward" migration of air pockets. Particle separation
and the associated pore architecture will generally result
in different local liquid configurations under microgravity
conditions compared to 1g conditions (27).
RESEARCH OBJECTIVES
Our primary objective is to acquire a fundamental
understanding of fluid flow and distribution through
porous media under 1g and simulated microgravity
conditions. This will be accomplished by the following
synergistic combination of ground-based experiments
and theoretical modeling aimed at examining water
retention, matric potential and unsaturated hydraulic
conductivity:
(1). Characterization of dry and wet media pore space
including the effects of packing and launch vibrations.
Subjecting the porous media to shaking table vibrations
will simulate launch and on-orbit vehicle vibrations. The
fluid phase distributions will be observed under a range
of test conditions using a macro-lens equipped video
camera or a CCD camera connected to a digital image
analysis system.
(2). Characterization of fluid flow and distribution during
infiltration (wet up) and steady flow at the micro (one or
several pores) and sample (many pores) scale, using
microgravity simulators such as manipulation of media
depth and pore size, or neutral buoyancy fluid pairs.
Studies on the scale of several pores (microscale) will
focus on the formation and evolution of liquid films, and
the effect of changes in pore throat sizes on mobilization,
break-up and coalescence process of individual
ganglion. Sample scale measurements will include
characterization of liquid retention and diffusivity,
evaluating the effect of gravity on liquid configuration in
different pore sized media during KC135 flight, and
examination of unsteady phenomena such as fingering.
Figure 2 shows a wetting front and air entrapment in an
experimental Hele-Shaw cell filled with Barium Titanate
beads (9,15). The repacking and renormalization of the
beads is also clearly visible. The wetting front does not
always move smoothly or continuously and can proceed
in a series of discontinuous jumps. The effect of capillary
fingering could be the enclosure and entrapment of air
“pockets” or ganglia by the wetting phase (water), or the
formation of locally immobile pockets of liquid.
Figure 2. Particle redistribution, wetting front and air entrapment in
loosely packed 50-micrometer glass beads in a Hele-Shaw (2D) cell.
The front moves from right to left. A packing discontinuity is visible at
the front and entrapped air can be seen behind the front.
Concurrent to the investigations outlined above, an
additional experimental program is in progress to
determine the pore-scale distribution of water and air
phases in discontinuous ganglia form.
Surrogate
immiscible fluids such as water and Hexadecane will be
used to simulate the behavior of water and air phases
under microgravity conditions (Figure 3). The fluid phase
distributions on the sample scale will be used to validate
a mathematical model and in an upscaling approach to
determine moisture-retention characteristics.
Figure 3. Representative picture of ganglia (purple) obtained by the
solidification of Hexadecane, a non-aqueous phase liquid surrogate for
air medium.
(3). Development of both a) a pore network model for
describing discontinuous fluid phase (ganglia/blobs)
transport and b) a model of pore scale hydraulic
functions for saturated and unsaturated hydraulic
conductivity based on equilibrium liquid configurations.
Reddi et al. (38) documented a number of analytical
solutions possible for predicting the spatial distribution of
discontinuous ganglia. Such solutions can be used to
obtain the ganglia distribution in the root module.
A
recently developed AYL-based framework for calculating
equilibrium liquid configurations in partially saturated
porous media (33,44) will be modified and adjusted to
provide pore-scale expressions for liquid retention under
microgravity conditions for various idealized pore
geometries.
(4). Upscaling techniques to integrate microscale flow
and transport properties with macroscopic behavior to
provide a quantitative link between these two processes
on scales relevant to the plant root and bulk media. This
will expand upon an existing statistical distribution model
describing water retention and hydraulic conductivity as
functions of various pore configurations (33), as well as
the incorporation of ganglia distributions. The fluid phase
distributions observed in the experimental program will
be used to validate the mathematical model(s) and in an
upscaling approach to determine moisture-retention
characteristics.
(5). Identification, development and implementation of
measurements and methods necessary to validate
model(s) in ground based tests. We will focus on
measurements made at the root module scale using
methods compatible with space flight. Thermal methods
have been used on previous space flights to monitor the
water content of plant growth media (3). We anticipate
concentrating on thermal measurement methods, while
considering any new developments in sensor
technology. The strengths and weaknesses of various
thermal sensors will be evaluated by measuring the
thermal properties of substrates as a function of water
content, as well as by the theoretical examination of the
effect of microgravity on thermal methods of water
content measurement.
PRELIMINARY RESULTS
An important component of our research plan is the use
of Nuclear Magnetic Resonance Imaging (MRI)
(11,13,14,15,23) for spatial and temporal imaging of 2-D
and 3-D fingering, ganglia development, wetting front
dynamics, saturation and velocity fields. MRI will also
allow us to evaluate air containment, effective
measurement scales of sensors and identify appropriate
scales for upscaling. The advantages of MRI) include (a)
non-invasiveness, (b) lack of directional preference, (c)
ability to simultaneously measure many parameters, and
(d) not being adversely affected by optical opaqueness.
MRI is especially well suited for transport phenomena
studies because it measures statistical averages of
various parameters over a range of spatial and temporal
scales that can readily be compared to averaged
transport theories.
MRI ANALYSIS
Magnetic Resonance imaging experiments were
performed in the New Mexico Resonance facility on
TM
Aquafoam-Oasis (mean pore size of 50 µm) using a 30
cm, 1.9T Oxford super-conducting magnet with a
TECMAG Libra spectrometer (Tecmag, Inc., Houston,
TX). Two different imaging strategies were employed
depending on whether the water in the foam sample was
static or moving. Wet foam samples with stationary water
distributions were imaged with the standard Fourier
imaging method (8). Two and three-dimensional images
were obtained with a resolution of 0.5 mm in each
direction. This method acquires data from all parts of
region of interest in the time domain. The data is then
Fourier transformed, where each frequency corresponds
to a different location in space.
Because the Fourier imaging method collects data from
the full region of interest at each scan, artifacts can arise
in the image if the water distribution in the sample
changes during a scan. Therefore, time-resolved imaging
to study water uptake in the foam was done by line-scan
imaging technique (10). Unlike Fourier imaging, line scan
techniques spatially scan the sample space, more in
analogy with most other imaging techniques. The line
scan technique takes a line (1D) image of a thin slice,
then shifts to a new position and takes another 1D
image. Thus, a 2D image can be generated by
sequentially sweeping the line over the object. The line
was swept over 32 positions to make a 256x32 image
every 1.8 s. The image was interpolated to give equal
resolution in each direction. The third dimension can be
resolved, but was not obtained in this study.
In Figure 4, we show a two dimensional MRI image of a
TM
horizontal Aquafoam-Oasis section. The wetting front
spreads radially from the center suggesting that the
sample is isotropic (9,15). Note that the wetting front is
locally irregular. Figure 5 shows the spreading of a liquid
front in a horizontal thin section. The front shows local
irregularities and larger scale fingers (9).
TM
A 2D MRI image of a horizontal Aquafoam-Oasis is
presented in Figure 6. Here the contours depict the
temporal evolution of the wetting front in the horizontal
test section. The front propagation velocity and the
saturation levels can be calculated from these images.
To illustrate the effect of gravity Figure 7 shows an MRI
TM
image of a vertical Aquafoam-Oasis
section. The
contours depict the evolution of the wetting front. The
liquid spreads as if it is filling an empty container. Liquid
introduced at a single point at the top of the sample
streams downward in a relatively thin column and
spreads outward and upward from the base. This shows
that, although capillary forces are strong, gravity
dominates the evolution of the wetting front (9,15).
Figure 6. Evolution of a wetting front in a horizontal test section.
Contours show successive positions of the front. Note the local
irregularities in the front as it percolates through the sample (9,15).
Figure 4. Radial spreading of a wetting front from the center of a
horizontal thin sample (9). These results showed that the medium is
isotropic.
Figure 7. Vertical infiltration of a foam sample. Contours represent
successive positions of the wetting front (isochrones). The liquid
spreads as if it is filling an empty container (9,15). The needle location
is only significant during the initial stages.
Figure 5. Spreading of a liquid front in a horizontal section. The
irregularity (fingering) of the wetting front is real and not an aperture
error (9).
CONCLUSION
Developers of plant growth systems for space flight have
faced serious challenges that include mass, volume, and
power constraints; water containment; and water/air
phase separation. Because of the small size of root
modules the ability to manage the root zone environment
will be critical for the success of plant growth systems. It
is unlikely that further significant progress can be made
in design of root modules or control of water delivery
without
increased
knowledge
of
fundamental
mechanisms and processes related to water and air
movement through plant growth media in microgravity.
Improvements in understanding the motion and
disposition of liquids in unsaturated porous media under
microgravity conditions are essential for the successful
control of water and air delivery to plant roots in
microgravity plant production systems.
REFERENCES
1. Averner, M. M. 1989. Controlled Ecological Life
Support System. p.145-153. In D. W. Ming and D. L.
Henninger (ed.) Lunar Base Agriculture. American
Society of Agronomy, Madison, WI.
2. Bingham, G. E., M. A. Levinskikh, V. N. Sytchev, and
I. G. Podolsky. 2000. Effects of gravity on plant
growth. J. Gravitat. Phys. 7:5-8.
3. Bingham, G., S. B. Jones, I. Podolsky, and B. S.
Yendler. 1996. Porous substrate water relations
observed during the greenhouse-2 flight experiment.
Soc. Automot. Eng. Techn. Paper 961547. SAE,
Warrendale, PA.
4. Bugbee, B. G. and F. B. Salisbury. 1989. Controlled
environment crop production: Hydroponic vs. lunar
regolith. p.107-130. In D. W. Ming and D. L.
Henninger (ed.) Lunar base agriculture: soils for
plant growth. American Society of Agronomy,
Madison, WI.
5. Bunt, A. C. 1961. Some physical properties of pot
plant composts and their effect on plant growth. III.
Compaction. Plant Soil 15:228-242.
6. Bunt, A. C. 1974. Some physical and chemical
characteristics of loamless pot-plant substrates and
their relation to plant growth. Acta Hort. 37:19541965.
7. Bunt, A. C. 1988. Media and mixes for containergrown plants.Unwin Hyman, London .
8. Callaghan, P. T. 1991. Principles of Magnetic
Resonance Microscopy.Clarendon, Oxford.
9. Caprihan, A., N. E. Daidzic, E. Fukushima, and J. I.
D. Alexander. 2001. MR imaging of wetting front
dynamics: The effect of gravity. Proc: 6th
International Conference on Magnetic Resonance
Microscopy. Jubilee Campus, University of
Nottingham.
10. Caprihan, A., Fukushima E., Rosato A.D., and Kos
M. 1997. Magnetic resonance imaging of vibrating
granular beds by spatial imaging. Rev. Sci. Instrum.
68:4217.
11. Caprihan A., E. F. 1990. Flow Measurements by
NMR. Physics Reports. Physics Letters 198:195235.
12. Celia, M. A., P. C. Reeves, and L. A. Ferrand. 1995.
Pore scale models for multi-phase flow in porous
media, U.S. Natl. Rep. Int. Union Geod. Geophys.
1991-1994. Rev. Geophys. 33:1049-1057.
13. Chang C.T.P. and A. T. Watson. 1999. NMR Imaging
of Flow Velocity in Porous Media. AIChE Journal 45.
14. Daidzic, N. E., J. I. D. Alexander, and C. A.
Camardo. 2001. Some aspects of the fluid flow in a
porous media in the microgravity conditions for the
space
plant production systems. Magnetic
Resonance Imaging, Special Issue 19:593.
15. Daidzic, N. E., E. Fukushima, A. Caprihan, S. Codd,
and S. Altobelli. 2002. MR Imaging of the wetting
front dynamics in porous media: The effect of gravity.
Transp. Porous Media In Preparation.
16. Dutcher, F. D., E. L. Hess, and T. W. Halstead.
1994. Progress in plant research in space. Adv.
Space Res. 14:159-171.
17. Flühler, H., A. J. Peck, and L. H. Stolzy. 1986. Air
pressure measurement. p.1161-1171. In A. Klute
(ed.) Methods of soil analysis. Part I Physical and
Mineralogical Methods. ASA, SSSA, Madison, WI.
18. Hanan, J., C. Olympios, and C. Pittas. 1981. Bulk
density, porosity, percolation and salinity control in
shallow, freely draining, potting soils. Journal of the
American Society of Horticultural Science 106:742746.
19. Hanan, J. J. 1998. Greenhouses.CRC Press, Boca
Raton, FL.
20. Handreck, K. A. 1983. Particle size and the physical
properties of growing media for containers. Comm. in
Soil Sci. Plant Anal. 14:209-222.
21. Heyenga, A. G. 1994. Application of a water
replenished solidified nutrient media support system
in long term cultivation of wheat. American
Association of Gravitational and Space Biology 8:40.
22. Hillel, D. 1982. Introduction to soil physics.Academic,
New York .
23. Irwin N.C., S. A. Altobelli, and R. A. Greenkorn.
1999.
Concentration
and
Velocity
Field
Measurements by Magnetic Resonance Imaging in
Aperiodic Heterogeneous Porous Media. Magn.
Reson. Imaging 17: 909-917.
24. Ivanova, T. and I. Dandolov. 1992. Moistening of the
substrate in microgravity. Microgravity sci. techn.
3:151-155.
25. Jones, S. B. and D. Or. 1998. Design of porous
media for optimal gas and liquid fluxes to plant roots.
Soil Sci. Soc. Am. J. 62:563-573.
26. Jones, S. B. and D. Or. 1998. Particulated growth
media for optimal liquid and gaseous fluxes to plant
roots in microgravity. Adv. Space Res. 22:14131418.
27. Jones, S. B. and D. Or. 1999. Microgravity effects on
water flow and distribution in unsaturated porous
media: Analysis of flight experiments. Water Resour.
Res. 35:929-942.
28. Langbein, D., R. Grofbach, and W. Heide. 1990.
Parabolic flight experiments on fluid surfaces and
wetting. Appl. Microgravity Tech. 2:198-211.
29. Levine, H. G. and A. D. Krikorian. 1996. Enhanced
root production in Haplopappus gracilis grown under
spaceflight conditions. J. Gravitat. Phys. 3:17-28.
30. Levine, S., P. Reed, G. Shutts, and G. Neale. 1977.
Some Aspects of wetting/dewetting of a porous
medium. Powder Technol. 17:163-181.
31. Morrow, R. C., R. J. Bula, T. W. Tibbitts, and W. R.
Dinauer. 1994. The Astroculture flight experiment
series, validating technologies for growing plants in
space. Adv. Space Res. 14:29-37.
32. Nitao, J. J. and J. Bear. 1966. Potentials and their
role in transport in porous media. Water Resour.
Res. 32:225-250.
33. Or, D. and M. Tuller. 1999. Liquid retention and
interfacial area in variably saturated porous media:
Upscaling from single pore to sample scale model.
Water Resour. Res. 35:3591-3606.
34. Podolsky, I. and A. Mashinsky. 1994. Peculiarities of
moisture transfer in capillary-porous soil substitutes
during space flight. Adv. Space Res. 14:39-46.
35. Porterfield, D. M., D. J. Barta, D. W. Ming, R. C.
Morrow, and M. E. Musgrave. 2000. Astroculture root
metabolism and cytochemical analysis. Adv. Space
Res. 26:315-318.
36. Porterfield, D. M., T. W. Dreschel, and M. E.
Musgrave. 2000. A ground-based comparison of
nutrient delivery technologies originally developed for
growing plants in the spaceflight environment.
HortTechnology 10:179-185.
37. Porterfield, D. M., S. W. Mathews, C. J. Daugherty,
and M. E. Musgrave. 1997. Spaceflight exposure
effects on transcription, activity, and localization of
alcohol dehydrogenase in the roots of Arabidopsis
thaliana. Plant Physiol. 113:685-693.
38. Reddi, L. N., S. Menon, and A. Pant. 1998. Porescale investigations on vibratory mobilization of
LNAPL ganglia. Journal of Hazardous Materials
62:211-230.
39. Scovazzo, P., T. H. Illangasekare, A. Hoehn, and P.
Todd. 2001. Modeling of two-phase flow in
membranes and porous media in microgravity as
applied to plant irrigation in space. Water Resour.
Res. 37:1231-1243.
40. Shah, S., W. E. Faller, A. Hoehn, M. Birdsong, and
M. W. Luttges. 1993. Characterization of fluid
distribution through a porous substrate under
dynamic g conditions. Biomed. Sci. Instrum. 29:401408.
41. Spomer, L. A. 1974. Optimizing container soil
amendment: The "threshold proportion" and
prediction of porosity. HortScience 9:532-533.
42. Steinberg, S. L., D. W. Ming, and D. Henninger.
2002. Plant production systems for microgravity:
43.
44.
45.
46.
critical issues in water, air and solute transport
through unsaturated porous media. NASA/TM-2002210774. NASA/JSC.
Steinberg, S. L. and D. L. Henninger. 1997.
Response of the water status of soybean to changes
in soil water potentials controlled by the water
pressure in microporous tubes. Plant Cell Environ.
20:1506-1516.
Tuller, M., D. Or, and L. M. Dudley. 1999. Adsorption
and capillary condensation in porous media: Liquid
retention and interfacial configurations in angular
pores. Water Resour. Res. 35:1949-1964.
Wright, B. D., W. C. Bausch, and W. M. Knott. 1988.
A hydroponic system for microgravity plant
experiments. Trans. ASAE 31:440-446.
Yendler, B., B. Webbon, and I. B. R. Podolsky. 1996.
Capillary movement of liquid in granular beds in
microgravity. Adv. Space Res. 18:233-237.
CONTACT
Dr Susan L. Steinberg is a staff scientist with Universities
Space Research Association working as a principal
investigator in the Advanced Life Support Program at
Johnson Space Center/NASA in Houston, TX. She can
be reached at:
USRA,Mail Code EC3,2101 NASA Road 1,JSC/NASA,
Houston, TX 77546. Tel: 281-483-8161. Fax: 281-4832508. Email:ssteinbe@ems.jsc.nasa.gov