A hydroponic system is presented that is designed for use in microgravity or gravity experiments. The system uses a sponge-like growing medium installed in tubular modules. The modules contain the plant roots and manage the flow of the nutrient solution. The physical design and materials considerations are discussed, as are modifications of the basic design for use in microgravity or gravity experiments. The major external environmental requirements are also presented

Fielder, Judith

Leggett, Nickolaus

English

NASA Technical Reports Server

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N91-22173
A HYDROPONIC DESIGN FOR MICROGRAVITY
AND GRAvlt Y FNSTALLATION$
Judith Fielder and Nlckolaus Leggett
Reston, Virginia
A hydroponic system is presented that is designed for use in microgravity or
gravity environments. The system utiliz_.q a sportive-like growing medium
installed in tubular modules. The modules c aln the plant root., and manage
the flow of nutrient solution. The physical design arm materials considerations
are discussed as are modifications of the basic design for use in microgravtty or
gravity environments. The major external environmental requirements are also
presented.
INTRODUCTION
This paper presents a design for a hydroponic system capable of supporting
plant growth from seed through maturity. This system can operate in either
microgravity or lunar/planetary base environments with only minor modifications
requir.._d to transition between these environments.
The hydroponic system provides a dark, moist, nutrient-rich, well-aerated
environrrent that is suited for the growth of plant roots. A supporting medi_Jm
holds the seeds and growing plants which have access to a lighted external en,_i-
ronment. In --ldttion, containment is provided to keep solution flows ur,,ier
control in a microgravity environment.
PHYSICAL DESIGN
The basic hydroponic design consists of tubular structures of suffic'ent size
to a,.commodate the types of plants being grown. Each tubular structure is a
cylindrical module with an open slit extending for the majority of th_ length of
the cylinder This open slit accommodates a sandwich of a foam-iike, spongy
substance that holds seeds or growing plants. The slit is orienteq.l towards the
lighting system.
The sandwich consists of two strips of spongy material that are inserted into
" the open slitto filltheentirelengthof theslitinthe cylind,_r.Crop seedsor
plantsare placedbetween the two layers.The portionof the stripsexposed to
thelighti._coatedwithan impermeable,opaquecoating.
The tubularstructuresare installedinarraysthatmake optimum useof the
lightingsystem and theavailablepressurizedvolume. Each tube isconnectedto
a nutrientsolutionfeed lineand a nutrientsolutionremoval line.Both thefeed
and removal lineshave valvesand bypasslines o thatindividualmodules can be
taken out of servicewithout disruptingthe operationof the entiregrowing
system.
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NUTRIENT FLO_
In the microgravity configuration, the nutrient solution feed system is a
flattened pressurized feed line inserted near the surface of each strip of sponge.
(Fig. I) A pressuriz_'_'d flow of aerated nutrient solution is intr__uc_ into thc
FigureI. Microgravitysystem configuration.
spongestrips.The flowisdirectedaway from the exteriortowardsthe '"oottom"
of the cylinder.Thisflow ismaintainedand reinforcedby a longitudinalirflow
establishedwithinthe cylinderand by the removal of excessand spent nutrient
solutionby a suctionsystem. (Fig.2) In = _icrogravityenvironmentthispres-
surizedflowof nutrientsolutionmay aid in orientingroot growth towards the
interiorof the cylinder.What rootsdo grow intothe exteriorwilllikelybe air-
prunedintodirectiollality.
¸-'-
6 6 6
Figure2. Nutrientflowinmicrogravity.
Inthegravityenvironment,the nutrientsolutionisintroducedintothe cyl-
inderin an ebb and now schedule.The cylinderisallowedto fillwith nutrient
solutionand thenthe nutrientsolutionisdrainedaway. (Fig.3). This ebb _nd
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Figure 3. Nutrient flow in gravity.
flow eyclhg ensures that the roots are well aerated in addition to being supplied
with nutrient solution• The ebb and flow cycles are more frequent during periods
when the plants are lighted and transpiration is at a peak than during the dark
periods.
NUTRIENT MANAGE_%C_.NTAND CONTROLS
The nutrient solutions used in this system must contair, aP macro nutrients
and micronutrien,s required for plant germination, growth, and maturation. The
solutions will need to be formulated for Ladividual crop types to ensure optimum
growth rates and yields.
Hydroponic systems tend to be unforg'ving of failures in nutrient flows.
This system partially mitigates this problem with the limited nutrient solution
holding capacity of the sponge. Redundant reservoirs of pre-mixed nutrient
solution will be required to replace the existing nutrient solution system reser-
voir should it become contaminated or lost.
Periodic sterilization of the circulating nutrient solution is recommended to
contrgl pathogens, ln-l_ne filters will limit the movement of plant materials and
some types of pathogens through the system. Plant toxins, pH, and soluble solids
must be monitored on a continuous basis.
The circulating nutrient solution must be refreshed and periodically repla,','d
in entirety. Provision shot_:d be made for the reconstitating of the spent nutrient
solution and for the recycling of organic wastes. These major requirements are
not easil; achieved in a hydroponic system.
EXTERNAL ENVIRONMENT
The environment outside of the cylinder should replicate many of the
features of the earth.; environment. The plants should be fully and evenly lit
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] 991012826-438
with light provided in a regulated day/night cycle. Broad spectrum lighting in
the 400 to 800 naaometer range is required with infrared emissions kept to a :;,
minimum. The light intensity should be 200 to 4r_0 watts per square meter _or
optimum plant response. This lighting system will generate waste heat that must
be removed from the agricultural area.
Temperature in the agricultural areas should be maintained in the range of
15°C to 320C. A standard nitrogen, oxygen, and carbon dioxide atmosphere is
required. A pressure of 800 mb or above is strongly recommended. This atmo-
sphere is intermittently moved by the plants at a speed of 1-6 km/hour to circu-
late fresh air, prevent CO2 depletion, facilitate temperature control, and
provide some thigmonastical stimulation.
The pla;:ts may need other environmental features such as the presence of a
steady state magnetic field. The exploration of these features shculd be an
important mission for space station and lunar base plant growth experiments.
MATERIALS ENGINEERING CONSIDERATIONS
All materials used in this system must be non-toxic to both plants and crew
members. This includes the cylinders, sponge strips, feed lines, valves, circulat-
ing pumps, and other components that come in contact with the plants or the
nutrient solution. Coated toxic materials are not appropri,_.te due to the possi-
bility of coatir'g failure either by accidental impact _r abrasion.
The foam-like sponge strips must be engineered for appropriate water reten-
tion and aeration properties required by their gravity environment It would be
advantageous to create the sponge out of a recyclable material that does not
have to be imported from the earth.
All of the materials in contact with the plants and nutrient solutions must
be highly resistant to corrosion. There should be little or no interaction between
the lnaterials, nutrient sok, tions, plant-released organic acids, and other com-
pounds. Aluminum components in particular should be avoided b_cause of their
corrosion susceptibility and toxicity to plants.
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i 99i Oi2826-439
NATURAL VACUUM ELECTRONICS
Nickolaus E. Leggett
Reston, VA
The ambient natural vacuum of space is proposed as a basis for electron valves.
Each valve is an electron-controlling structure similar to a vacuum tube that is
operated without a vacuum sustaining envelope.
The natural _,acuur.. electron valves discussed offer a viable substitute for
solid state devices. The natural vacuum valve is highly resistant to ionizing
radiation, system generated electromagnetic pulse, current transients, and direct
exposure to space conditions.
INTRODUCTION
This paper proposes the use of the natural vacuum of space as a basis for
electronic components. The space environment offers a natural vacuum that is
suitable for the passage of electron beams over rather long distances. T_ese
• electron beams can be used in electron valve components.
PHYSICAL OPERATION
The basic natural vacuum component uses a stream of electrons that is
emitted from a source. This electron stream travels through the ambient
vacuum environment towards a positively cho,rged destination. This basic flow
corresponds to the flow of electr_:ns within the diode vacuum tube of electronics
history. In the diode vacuum tube, electrom, are emitted by a heated cathode
(thermionic emission). The emitted electrons are attracted across the vacuum
by a positively charged metallic plate (the anode).
Na :ural vacuum components use this b_sic vacuum tube flow without the
need for the vacuum sustaining enclosure. T,_e cathode and anode are di-ectly
exposed to the ambient environment of space. The natural vacuum diode "tube"
provides the service of rectification where an alternating current input !s con-
verted to pulses of direct current output.
Additional functions are provided by installing electron flow modifying
structures in the electron beam. A metailic screen or grid placed in the electron
beam between the cathode and anode provides a valving action. Varying the
electric charge on the grid vaTies the electron beam current traveling betweel_
the cathode and the anode. Additiona! grids can be inserted into the electron
flow to provide additional contrcl and to isolate against undesired coupling of
stray signals through the system.
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This type of valving is quite famiiiar to people in electronics who have
worked with w ulti-grid vacuum tubes. In the multigrid natural vacuum compo-
nent, the artificial vacuurr, rn_int_in,_ _,y *_'e ,,1,,r_................. b,, _o tube is replaced by the am-
bient environment of space. Figure _ shows a natural vacuum component wi_h
concentric gr_ds.
_, :_,i:_____.._- -'_----',,
Figure 1. Natural vacuum component.
Magnetic fields can be used to control the electron be__m also. Magnetic
i fields can direct, deflect, reverse, or contak', the electron beam. .'_ limited
example of this control is the common television picture tube. The ambient
! enviro.nmcn_, of space frees the natural vacuum component from the heavy pic-
ture tube containment. A natural vacuum component can hang "",,_ electron gun
and magnetic coils in an open structurp
i
COMPONENT INNOVATIONS
Natural vacuum components are not limited to revivals of older vacuum
tube designs. The large volume of the ambient space environment allows the
component designer to pr_._uce components that are not practical in small
artificial vacuum tube environments. For example, the grids within a natural
vacuum component can be mechanically deployable. Different sets of _r.!d5 can
be deployed for different operating conditions.
The cathode can toe heated by directly focused solar energy. This configu-
ration avoids the problem of filament failure that was a common problem with
terrestrial vacuum tubes.
The most profitable approach to natural vacuum electronics is to think of
the ambient environment of space as a gymnasium fur electrons. You can place
electron sources, destinations (anodes), and beam modifying devices where you
need them within the ambient environment. Your design does not have to be
limited to connected electron-valving modules. A continuous structure can per-
form operat_ ms on a continuous electron beam that passes through the structure.
Co:inections between the stages of processing are provided by the electron beam
itself (although a "ground" return conductor is required as well).
NON-ELECTRON CARRIERS
The natural vacuum approach can use carriers other than electrons. For
example, accelerator technology can be used to generate streams of protons to
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1I carry signs_s or power. While protons may not have clearly-vlsible advantages
ov_.r_,__=,;trons.it is worthwhile to examine the concept of _oton-b_sed circuits.
14
One oossible advantage of proton-based circuits is that protons are heavier •
than electrons. Thus a beam of protons would be less perturbed by ambient mag-
netic fiel_--a _ssible advantage in some space environments.
Atomic nuclei can also be used in natural vacuum systems. Similarly, larger
masses of material can be pushed about by mass driver and magnetic separator
types of "circuit" components. TL_.scope of electronics is expanded to a contin-
uum of natural vacuum functions that includes large scale energy beam manipu-
lation and materials separation and processing.
USES
The basic natural vacuum components provide the familiar active electronics
• switching
functions of:
• rectification
• oscillation
• amplification
• detectior,.
• mixing
These are the santo functions provided by transistors or vacuum tubes. The
natural vacuum component is a very robust replacement for conventional solid-
state components. Entire electronic circaits can be built from natural vacuum
components or natural vacuum components can be used in conjunction with con-
ventional components,
ADVANTAGES
Natur_l vacuum components are very robust devices that can survive the
stresses of the space environment. Each natural vacuum component is a largely
open-meta! structure that is directly exposed to the vacuum environment. This
structure ts resistant to damage from ionizing radiation, system generated
electromagnetic pulse (SGEMP), and micro-particle impacts.
The natural vacuum components can be installed outside of the spacecraft
conse_h_g Interior space for other t_ses. (Fig. 2) These components can be
operated at very high power levels when suitable radiative cooling means are
provided.
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1991012826-442
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Figure 2. Configuration oi"externally mounted components.
The natural vacuum components can be made from sp_,ce--derlved metals
and insulating materials, when these materials become available. This increases
the appeal of the natural vacuum approach for worlds such as the moon that have
excellent ambient vacuum environments and locally available materials.
DISADVANTAGES
The operation of natural vacuum components could be negatively impacted
by the poor quality of "vacuum" present in low earth orbit or near other bodies
with atmospheres. One such impact is the blockage of the free flow of electrons.
Erosion of the components due to the action of ambient molecules could occur as
well.
Another potential problem is the size and weight of natural vacuum compo-
nents that may be larger than their solid state equivalents.
CONCLUSION
Natural vacuum componen_;sshoul£ be considered for space craft and lunar
base designs. These componer,ts change the vacuum of space from a problem
into an asset.
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A hydroponic design for microgravity and gravity installations

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