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Walkinshaw, C.H. and S.G. Galliano. 1990. New crops for space bases. p. 532-535. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.

New Crops for Space Bases

C.H. Walkinshaw and S.G. Galliano


  1. INTRODUCTION
  2. BIOLOGICAL STUDIES
  3. PROBLEMS IN SPACE HORTICULTURE
    1. Choice of Crop
    2. Soil Packing
    3. Pressure
    4. Reduced Geomagnetic Field
    5. Space Greenhouses
  4. THE FUTURE
  5. REFERENCES
  6. Table 1
  7. Fig. 1

INTRODUCTION

Since the Apollo flights of the early seventies, interest in growing plants in space has increased because of the emphasis on long missions. During the past 18 years, the results of Apollo investigations and of horticultural research, have strengthened the possibility of eventually growing crops inside space bases. This presents two overall challenges: growing plants for food in an international space base and adapting terrestrial plants to unique conditions in space bases for the development of an independent food supply

This paper examines previous research in space-plant studies, particularly the Apollo botanical studies and other selected experiments in simulated space environments. Variables that might regulate plant growth in lunar and Mars bases are outlined. We conclude that establishing crops in space bases is feasible as an international effort.

BIOLOGICAL STUDIES

Biological studies from Apollo 11 and 12 indicated that lunar material could provide mineral nutrients for germinating seeds, liverworts, and plant tissue cultures (Walkinshaw et al. 1970). The variation in composition of Apollo 11 through 15 lunar materials used in botanical studies was described by Johnson et al. (1972). Seeds germinated in Apollo 14 lunar material accumulated large quantities of iron, titanium, and other minerals (Walkinshaw and Johnson 1971). Gamma spectrometry and autoradiography revealed that lettuce seedlings exposed to neutron-activated Apollo 11 and 14 lunar fines absorbed scandium, cobalt, manganese, and a variety of elements that included rare earth elements (Baur et al. 1974).

Apollo 16 investigations showed that cabbage seedlings grown in contact with lunar material accumulated high concentrations of aluminum. To prevent this, excess aluminum could be removed by leaching lunar soil with slightly acidic hygienic waste water from lunar base activities as simulated by others (Johnson et al. 1972, Stumm and Furrer 1987).

Apollo lunar samples successfully stimulated growth of small, germ-free plants such as Bryophyllum, Lycopodium, and liverworts. Lunar samples similarly stimulated germination and growth of the sensitive fern Onoclea sensibilis L. All stages of the fern, the germinating spore, gametophyte, and the sporophyte exhibited increased greening and growth in response to Apollo 11, 12, and 14 lunar materials.

Light microscope examinations of callus cultures sprinkled with lunar fines demonstrated normal cell morphology for carrot, Haplopappus, longleaf pine, maize, soybean, spurge, and sugar pine. Lunar particles were observed adjacent to densely staining and actively dividing tissue culture cells. Biochemical analyses verified the accelerated development of chloroplasts in tobacco tissue cultures treated with Apollo 11, 12, 14 and 15 lunar samples. When compared with untreated issues, treated cultures contained 21 to 35% more total pigment of chlorophyll. A variety of other plants and tissue cultures as described by Walkinshaw et al. (1970) underwent increased greening in response to lunar material. An increase in chlorophyll was demonstrated for tobacco (Weete and Walkinshaw 1972).

The main component of the Apollo 11, 12, and 14 samples, lunar mare basalt stimulated growth according to the ability of plants to absorb elements from the basalt and incorporate them. Because of the reduced state of lunar basalt, it appears to be a good source of certain essential elements for crop plants.

PROBLEMS IN SPACE HORTICULTURE

Choice of Crop

Growing plants in space bases presents unique problems. Because of the absence of wind and insects, crops whose flowers require assistance for pollination will have development problems. Therefore, short-season, bisexual self-pollinated plants such as broccoli and garden peas which have a low rate of outcrossing, would be ideal candidates for a totally automatic space greenhouse. Plants such as cucumber and squash, which require special pollination, would need mechanical assistance or a modified sonic or vibration system. Tomatoes also may need pollinating assistance.

Refinement of cultivation of Brassicas in small areas by P.H. Williams at the University of Wisconsin makes it an ideal plant system to be considered in an initial space base (Williams and Hill 1986). These species could produce useful building materials and edible plant parts. Because seeds mature rapidly and do not exhibit dormancy, seed sowing to flower production would require only 14 days. Many of the plants in this genus are small, are a component of our terrestrial diet and complete many cycles per year. Female fertility is high, and nuclei are receptive to introduced genes that may be useful in space horticulture.

Soil Packing

Some studies of terrestrial and lunar basalts suggest that the fine lunar particles are so small they would compact into a clay-like mass when watered, and minimize root aeration. To reduce packing, the fine particles could be mixed with particles the size of sand grains. Composting lunar fines with waste products from the base also could reduce packing.

Pressure

We have subjected plants at 34 kPa (256 mm Hg) pressure to a sudden change to 101 kPa (760 mm Hg). Pressure changes neither hindered seed production nor caused the plants to wilt (Walkinshaw 1986). Throughout the experiment reduced pressure and the gaseous environment had little effect on seed germination, growth, or plant morphology.

In chambers at the National Aeronautics Space Administration facilities in Houston, we tested crop plants for their ability to germinate and grow in low atmospheric pressure and altered gas composition. These tests revealed that edible plants tolerate low levels of oxygen and carbon dioxide, and deletion of nitrogen during germination and growth (Table 1). Substituting helium for nitrogen did not affect seed germination or growth and at low pressures (11 to 13 kPa, 80 to 100 mm Hg), oxygen and water vapor were sufficient for germination of certain crop plants.

The protein content of soybeans grown under 33, 67, and 101 kPa pressures did not differ in the total micrograms of protein (221, 198, and 224, respectively) per culture.

Reduced Geomagnetic Field

Another environmental extreme tolerated by edible plants was reduced geomagnetic field. Tests in a Mu-metal room with geomagnetic forces reduced from the terrestrial value of 55,000 to 75-140 gammas showed germination, seedling growth, and tissue cultures to be unaffected. Chlorophyll a, b, and carotenoids of 2-, 3-, and 4-week-old lettuce seedlings were not different in the low and normal terrestrial magnetic field. Held for 20 or 30 days in the reduced magnetic field, lettuce tissue cultures exhibited a 40% decrease in overall respiration. The low geomagnetic field did not affect root and stem lengths of germinating Brussels sprouts, cabbage, lettuce, and radish; nor did the altered environment affect soybean respiration or their fresh and dry weights.

Space Greenhouses

If plants are unable to withstand aspects of a space environment that cannot be readily changed, we must house them economically to keep them from extremes of temperature and to provide moisture. Usually, artists depict a lunar or Mars greenhouse as a rigid dome of metal and plastic. This design does not recognize the serious problems associated with proton and high-Z-particles (energetic particles with atomic numbers from 8 to 26) that penetrate several meters of soil. Neither does the design compensate for the safety problem of lunar or Mars extremes in surface temperatures.

Locating greenhouses in caverns created and fined with bags of lunar fines could perhaps minimize environmental effects (Fig. 1). These plastic bags that contain surface materials would screen high-Z-particles and protons. Thickness of this shield should be several meters to absorb these damaging high energy particles. Storing fresh or waste water on top and at the entry of the greenhouse should help absorb particles and shield plants from any micrometeorites.

On the moon and Mars, direct lighting would necessitate major cooling which translates into a need for energy. Direct lighting would also subject plants to high-Z-particles and protons that can kill both dividing and resting cells.

For a Mars or lunar base, we suggest using mirrors to reflect sunlight into the greenhouse. The reflected sunlight could be supplemented with strobe lighting (Cathey and Campbell 1977). Strobe lighting would reduce energy required for cooling and may result in increased crop yields. Nuclear, chemical or thermal generators could provide energy for the strobes. In a lunar base, a geostationary solar reflector would reduce the problem of the 14-day/night cycle.

THE FUTURE

It is not feasible for the United States alone to build extraterrestrial greenhouses. Since 1975, the USSR has included on-board plants in its space missions. Their ground chamber simulations of 1-year duration have paralleled the flight experiments. In their spaceships, the Soviets have grown cabbage, lettuce, oats, peas, radish, wheat, and onions (Milov and Rusakova 1980). An oazis (growing bed) has been flown on every flight since 1975. Soviet literature on space research is rich in details of aerospace horticulture (Gazenko 1983, Mashinskiy and Nechitaylo 1983).

Because of the Soviet Union's extensive experience as principal investigators in space plant research, the Soviets qualify as leaders of any cooperative venture to colonize the Moon or Mars. A cooperative effort between the USSR and the United States seems to be the logical and most beneficial way to face the advantages and challenges offered by growing plants for food on the moon or Mars.

The likely progression of space bases will be lunar, Mars, and then to other moons in the solar system. These developments should be initiated before 2030. The driving force for the establishment of a lunar base should be the testing of components for a Mars space base. Plant systems would be on the list of the vital space base components to be tested.

REFERENCES


Table 1. Effect of pressure on germination and growth of crop plants after seven days in air or air containing 10% carbon dioxide (+) with 12-hour photoperiod.

Crop Pressurez (kPa) Germination (%) Stem length (cm)
Bean 14 75 8
14+ 71 19
101 83 10
Cotton 14 90 7
14+ 100 8
101 100 9
Lettuce 14 100 2
14+ 100 4
101 100 3
Maize 14 100 15
14+ 100 31
101 100 30
Sorghum 14 71 10
14+ 80 16
101 69 13
Wheat 14 90 13
14+ 100 23
101 100 18
z105, 105+, and 760 mm Hg, respectively.


Fig. 1. Lunar greenhouse recessed in a cavern and lined with surface materials to reduce temperature fluctuations and lethal radiation.


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