When one considers travel to other planets, resupply costs will force even more recycling and even-
tually some in situ food production on these missions. At this point, plants and bioregenerative systems
may be an option. Mars would likely be the first planet visited by humans, and early Mars missions would
rely heavily on stowage and resupply [13]. But as mission durations increase, so will the need for greater
autonomy and closure, not only to reduce costs but also to provide contingencies for mission delays or
failures [9]. Even prior to the establishment of surface colonies, plants could play an important role for
Earth-orbiting space stations or planetary transit vehicles by providing fresh food for the diet. This con-
cept has often been referred to as a “salad machine,” where a small amount of vegetables and fruits could
be provided to the crew [15]. Although this would not have a large impact on total dietary needs, the fresh
food supplements could have a positive psychological effect on the humans living in confined space habi-
tats; moreover, the presence of plants, their lighting systems, and the humidities and aromas associated
with the plants could have positive effects on the crew [16].
C. Crop Selection
Criteria for choosing life support crops include obvious attributes, such as crop yield, nutritional value,
horticulture, and processing requirements [17–20]. For space applications, it will be important to optimize
yield as well as minimize the area requirements and associated infrastructure costs for growing plants
(e.g., lighting and watering system components). Thus high yield per unit area per unit time (i.e., g m^2
day^1 ) is especially important [9,17,21]. In addition, characteristics such as high harvest index (ratio of
edible to total biomass) and short stature are important to minimize inedible wastes and allow the crops
to fit in volume-limited systems [9,17,22]. Processing requirements for converting the harvested biomass
into useful foods must also be considered, and crops that require extensive processing may be too costly
to include, especially for early missions where processing equipment may not be available [13,17,18].
Table 1 lists some crop species that have been suggested for bioregenerative life support. These lists
were based largely on human nutritional requirements, but meeting all these nutritional requirements will
be difficult with such short lists. It is more economical to provide minor nutrients (e.g., vitamin B 12 ) with
supplements from Earth rather than producing them on site [13,17–19].
II. GROWING PLANTS FOR LIFE SUPPORT
A. Environmental Management
Because of the harsh environment of space, growing crops for life support will require protected envi-
ronments. Light, CO 2 , temperature, humidity, and mineral nutrition will all need to be managed carefully
PLANT GROWTH AND LIFE SUPPORT IN SPACE 927
TABLE 1 Possible Crops for Life Support Systems in Space
Tibbitts and Alford Hoff, Howe, and Mitchell Salisbury and Clark BIOS-3 tests
Wheat Wheat Wheat Wheat
Soybean Potato Rice Potato
Potato Soybean Sweetpotato Carrot
Lettuce Rice Broccoli Radish
Sweetpotato Peanut Kale Beet
Peanut Dry bean Lettuce Nut sedge (chuffa)
Rice Tomato Carrot Onion
Sugar beet Carrot Rape seed (canola) Cabbage
Pea Chard Soybean Tomato
Taro Cabbage Peanut Pea
Winged bean Chickpea Dill
Broccoli Lentil Cucumber
Onion Tomato Salad spp.
Strawberry Onion
Chili pepperSources:Tibbitts and Alford [17]; Hoff, Howe, and Mitchell [18]; Salisbury and Clark [19]; Gitelson and Okladnikov [4]—
diet also included supplemental animal protein and sugar.