48
Plant Growth and Human Life Support for Space
Travel
Raymond M. Wheeler
National Aeronautics and Space Administration, Kennedy Space Center, Florida
Gary W. Stutte, G. V. Subbarao*, and Neil C. Yorio
Dynamac Corporation, Kennedy Space Center, Florida
925I. BIOREGENERATIVE SYSTEMS
A. Background
The balance of the carbon dioxide (CO 2 ), oxygen (O 2 ), and water in Earth’s biosphere is largely depen-
dent on photosynthetic and transpiration processes of green plants. Indeed, it is photosynthesis that
ultimately provides the food and energy that humans and other animals depend on. As technology levels
advance, humans will eventually be able to travel away from Earth’s sustaining biosphere on long-term
space travel. One approach to providing consumables for space travel would be to grow plants (crops) as
part of a bioregenerative life support system.
The concept of using bioregenerative life support for space has been studied since the 1950s and
1960s, with most of these early studies centered on the use of algae (e.g., Chlorella) for O 2 production
and CO 2 removal [1–3]. Testing was expanded in the late 1960s and 1970s by Russian researchers to in-
clude higher plants [4,5] and in the late 1970s by the U.S. National Aeronautics and Space Administra-
tion (NASA) under the Controlled Ecological Life Support System, or CELSS program [6]. The CELSS
plant research consisted primarily of laboratory-scale studies carried out at U.S. universities and by sev-
eral European and Japanese investigators [6–8]. These studies were coupled with large-scale, closed-sys-
tem tests conducted at NASA’s Kennedy Space Center and Johnson Space Center to assess the perfor-
mance of plants in prototype life support systems [9–11] (Figure 1). The CELSS or bioregenerative life
support research is currently consolidated under NASA’s Advanced Life Support (ALS) program.
B. Mission Constraints: When Would Plants Have a Role?
To date, human space travel has been short in duration and close to the Earth; for example, NASA space
shuttle missions are typically 7 to 14 days. Even when missions have been longer, such as with the orbit-
ing Mir Space Station, the distance from Earth is still relatively short. This has allowed most of the life sup-
port consumables to be stowed or replenished from Earth on a continuing basis. But supply-line economics
dictate that as mission distances increase, so will the costs of stowage and resupply [12,13]. This has forced
spaceflight engineers to explore regenerative approaches for providing human life support [14]. Physico-
chemical regenerative technologies have already been used for water recycling on Mir and are planned for
use along with CO 2 reduction and O 2 production systems on the International Space Station [14].
*Current affiliation:Japan International Research Center for Agricultural Sciences, Ibaraki, Japan