The ambient natural vacuum of space is proposed as a basis for electron valves. Each valve is an electron controlling structure similiar to a vacuum tube that is operated without a vacuum sustaining envelope. The natural vacuum 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

Leggett, Nickolaus

English

NASA Technical Reports Server

N91-0o1
NATURAL VACUUM ELECTRONICS
Nickola_ E. Leggett
Reston, VA
Thr. ambient natural vacuum of space is propoLzd 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 vacuum 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 spaceconditions.
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. These
electron beams can be used in electron valve components.
PHYSICAL OPERATION
The basic natural vacuum componen_ uses a stream of electrons that is
emitted from a source. This electron stream travels through the ambient
vacuum environment towards a positively charged destination. This basic flow
corresponds to the flow of electrons within the diode vacuum tube of electronics
history. In the diode vacuum tube, electrons are e_nitted by a heated cathode
(thermionic emission). The emitted electrons are attracted across ti,e vacuum
by a positively charged metallic plate (the anode).
Natural vacuum components use this basic vacuum tube flow without the
r_eed for the vacuum sustaining enclosure. The cathode and anode ar_ directly
exposed to the ambient environment of space. The natural vacuum diode "tube"
provides the service of rectification where an alternating current input is con-
- verted to pulses of direct current output.
Additional functions are provided by installing electron flow modifying
structures in the electron beam. A metallic screen or grid placed in the electron
beam between the cathode and anode provides a valving action. Varying the
electric charge on the grid varies the electron beam current traveling between
:he cathode and the anode. Additional grids can be inserted i_to the electron
flow to provide additional control and to isolate against undesired coupling of
stray signals through the system.
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This type of valving is quite familiar to people in electronics who have
worked with multi-grid vacuum tubes. In the multigrid natural vacuum compo-
F..ent, *_'-,,,_ artificial vacuum maintained by the glass tube is replaced by the am-
bient environment of space. Figure I shows a natural vacuum component with
concentric grids.
Figure 1. Natural vacuum comFonent.
Magnetic fields can be used to control the electron beam also. Magnetic
fields can direct, deflect, reverse, or contain the electron beach. A limited
example of this control is the common televis2on picture tube. The ambient
environment of space frees the natural vacuum component from the heavy pic-
ture tube containment. A natural vacuum component can hang the electron gun
and magnetic coils in an open structure.
COMPONENT INNOVATIONS
Natural vacuum components are not limited to revivals of older vacuum
tube designs. The large volume of the ambient space environraent alIows the
component designer to produce 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 grids can
be deployed for different operating conditions.
The cathode can be 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 for 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 stracture can per-
form operations on a continuous electron bear_ that passes through the structure,,
Ccnnections 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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carry signals or power. While protons may not have clearly-visible advantages
over electrons, it is worthwhile to examine the concept of proton-based circuits.
One possible advantage of proton,based circuits is that protons are heavier
than electrons. Thus a beam of protons would be less pe,'turbed by ambient mag-
netic fieIds--a possible advantage in some spac_ environments.
Atomic nuclei can also be used in natural vacuum system_. Similarly, larger
masses of material can be pushed about by mass driver and magnetic separator
types of "circuit" components. The 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
functions of:
• switching
• rectification
• oscillation
• amplification
• detection
• mixing
These are the same functions provided by transistors or vacuum tubes. The
natural vacuum component is a very robust replacement for conventional solid-
state components. Entire electronic circuits can be built from natural vacuum
components or natural vacuum components can be used in conjunction with con-
ventional components.
ADVANTAGES
Natural vacuum components are very robust devices that can survive the
stresses of the space environment. Each natural vacuum component is a largely
open-metal structure that is directly exposed to the vacuum environment. This
structure is resistant to damage from ionizing radiaJon, system generated
electromagnetic pulse (SGEMP), and micro--particle impacts.
The natural vacuum components can be installed outside of the spacecraft
conserving interior space for other uses. (Fig. 2) These components can be
operated at very high power levels when suitable radiative cooling means are
provided.
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Figure 2. Configuration of externally mounted components.
The natural vacuum components can be made from space-derived 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 comlx>-
nents that may be larger than their solid state equivalents.
CONCLUSION
Natural vacuum components should be considered for space craft and lunar
base designs. These components change the vacuum of space from a problem
into an asset.
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A HYDROPONIC DESIGN FOR MICROGRAVITY
AND GRAVITY INSTALLATIONS
Judith Fielder and Nickolaus Leggett
Reston, Virginia
A hydroponic system is presented that is designed for use in microgravity or
gravity environments. The system utilizes a sponge-like growing medium
installed in tubular modules. The modules contain the plant roots and manage
the flow of nutrient solution. The physical design and materials considerations
are discussed as are modifications of the basic design for use in microgravity 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
required to transition between these environments.
The hydroponic system provides a dark, moist, nutrient-rich, well-aerated
environment that is suited for the growth of plant roots. A supporting medium
holds the seeds and growing plants which have access to a lighted external envi-
ronment. In addition, containment is provided to keep solution flows under
control in a microgravity environment.
PHYSICAL DESIGN
The basic hydroponic design consists of tubular structures of sufficient size
to accommodate the types of plants being grown. Each tubular structure is a
cylindrical module with an open slit extending for the majority of the length of
the cylinder. This open slit accommodates a sandwich of a foam-like, spongy
substance that holds seeds or growing plants. The slit is oriented towards the
lighting system.
The sandwich consists of two strips of spongy material that are inserted into
the open slit to fill the entire length of the slit in the cylinder. Crop seeds or
plants are placed between the two layers. The portion of the strips exposed to
the light is coated with an impermeable, opaque coating.
The tubular structures are installed in arrays that make optimum use of the
lighting system and the available pressurized volume. Each tube is connected to
a nutrient solution feed line and a nutrient solution removal line. Both the feed
and removal lines have valves and bypass line,_ so that individual modules can be
taken out of service without disrupting the operation of the entire growing
system.
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NUTRIENT FLOWS
" ity --- "...... :-- "" ....... '-- _ "a,, the rr,icrograv _v.tl_ula_lu,, _,= r,utrient nu_u.u. eeu system is d
flattened pressurized feed line inserted near the surface of each strip of sponge.
(Fig. 1) A pressurized flow of aerated nutrient solution is introduced into the
_..."
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Figure 1. Microgravity system configuration.
sponge strips. The flow is directed away from the exterior towards the "bottom"
of the cylinder. This flow is maintained and reinforced by a longitudinal air flow
established within the cylinder and by the removal of excess and spent nutrient
solution by a suction system. (Fig. 2) In a microgravity environment this pres-
surized flow of nutrient solution may aid in orienting root growth towards the
interior of the cylinder. What roots do grow into the exterior will likely be air-
pruned into directionality.
6 6 _ 6 6
Figure 2. Nutrient flow in microgravity.
In the gravity environment, the nutrient solution is introduced into the cyl-
inder in an ebb and flow schedule. The cylinder is allowed to fill with nutrient
solution and then the nutrient solution is drained away. (Fig. 3). This ebb and
4,q2
Figure 3. Nutrient flow in gravity.
flow cycling 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 MANAGEMENT AND CONTROLS
The nutrient solutions used in this system must contain all macro nutrients
and micronutrients required for plant germination, growth, and maturation. The
solutiens will need to be formulated for individual crop types to ensure optimum
growth rates and yields.
Hydroponic systems tend to be unforgiving 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
control pathogens. In-line 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 replaced
in entirety. Provision should be made for the reconstituting of the spent nutrient
solution and for the recy,-ling of organic wastes. These major requirements are
not easily achieved in a hydroponic system.
EXTERNAL ENVIRONMENT
The environment outside of the cylinder should replicate many of the
features of the earth's environment. The plants should be fully and evenly lit
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with light provided in a regulated day/night cycle. Broad spectrum lighting in
the 400 to g00 nanometer range is required with infrared emissions kept _.o a
minimum. The light intensity should be 200 to 400 watts per square meter for
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 32°C. A standard nitrogen, oxygen, and carbon dioxide atmosphere is
required. A pressure of 800 mb or above is stror_gly recommended. 'this atmo-
sphere is intermittently moved by the plants at a speed of 1-6 kin/hour to circu-
late fresh air, prevent CO 2 depletion, facilitate temperature control, and
provide some thigmonastical stimulation.
The plants may need other environmental features such as the presence of a
steady state magnetic field. The exploration of these features should 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 appropriate due to the possi-
bility of coating failure either by accidental impact or 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 witE the plants and nutrient solutions must
be highly resistant to corrosion. Ther_ should be little or no interaction between
the materials, nutrient solutions, plant-released organic acids, and other com-
pounds. Aluminum components in particular should be avoided because of their
corrosion susceptibility and toxicity to plants.
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