L NASA/TM-2003-211184 

Crop Production for Advanced Life Support Systems - 

Observations From the Kennedy Space Center 

Breadboard Project 

R. M. Wheeler, J.C. Sager, R.P. Prince, and W.M. Knott 

NASA Kennedy Space Center Biological Sciences Office 

C. L. Mackowiak, G. W. Stutte, N.C. Yorio, L.M. Ruffe, B. V. Peterson, 

G.D. Goins, and C.R. Hinkle 

Dynamac Corporation, Kennedy Space Center, Florida 

W.L. Berry 

University of California, Los Angeles, California 

February 2003 0 
‘ 

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1 NASNTM-2003-211184 

Crop Production for Advanced Life Support Systems - 

Observations From the Kennedy Space Center 

Breadboard Project 

R.M. Wheeler, J.C. Sager, R.P. Prince, and W.M. Knoit 

NASA Kennedy Space Center Biological Sciences Office 

C.L. Mackowiak, G. W. Stuite, N.C. Yorio, L.M. Ruffe, B. V. Peterson, 

G.D. Goins, and C.R. Hinkle 0 Dynamac Corporation, Kennedy Space Center, Florida 

W.L. Berry 

University of California, Los Angeles, California 

National Aeronautics and Space Administration 

John F. Kennedy Space Center, Kennedy Space Center, Florida 32899-0001 

February 2003 
ACKNOWLEDGEMENTS 

Numerous individuals participated in various ways to support the crop research activities 

for the Kennedy Space Center Advanced Life Support efforts. The project could not have succeeded without their help, and they have our sincere thanks. 

EngineeringKomputer 

NASA 

Coates, Dave 

Dickey, Duane 

Hilding, Susanne 

Jones, Jeff 

Mack, Tommy 

Poppert, John 

Bionetics 

Benjamin, Joe 

Fortson, Russ 

Godfrey, Steve 

Hargrove, Cliff 

Koller, Mike 

Markwell, Glenn 

Martinez, Joe 

Thurston, Scott 

Boeina CorDoration 

Drysdale, Alan 

Dvnamac 

Alazraki, Mike 

Bledsoe, Jim 

Chetirkin, Peter 

Finger, Barry 

Galloway, Matt 

Simpson, Morga 

Young, Scott 

Biology/Chemistry 

Bionetics 

Chetirkin, Katrina 

Fields, Norm 

Hall, Patrice 

Lowry, Wendy 

Sumner, Randy 

Dvnamac 

Black, Steve 

Brown, Chris 

Cranston, Nat 

Drese, John 

Dreschel, Tom 

Edney. Sharon 

Englert, Teresa 

Garland, Jay 

Levine, Lanfang 

Levy, John 

Loader, Colleen 

Strayer, Dick 

Stryjewski, Liz 

National Research Council 

Lea-Cox, John 

Subbarao, Guntur 

Universitv of Massachusetts 

Corey, Ken 

Administrative/ 

Programmatic 

NASA 

Averner, Me1 

Bredt, Jim 

Buchanan, Paul 

Guidi, Cris 

Hoff ler , W yc ke 

Koller, AI 

Bionetics 

Puleo, Rudy 

Dvnamac 

Britt, Doug 

ii 
. 

ABSTRACT 

The use of plants for bioregenerative life support for space missions was first studied by 

the US Air Force in the 1950s and 1960s. Extensive testing was also conducted from the 

1960s through the 1980s by Russian researchers located at the Institute of Biophysics in 

Krasnoyarsk, Siberia, and the Institute for Biomedical Problems in Moscow. NASA initiated 

bioregenerative research in the 1960s (e.g., Hydrogenomonas) but this research did not include 

testing with plants until about 1980, with the start of the Controlled Ecological Life Support 

System (CELSS) Program. The NASA CELSS research was carried out at universities, private 

corporations, and NASA field centers, including Kennedy Space Center (KSC). The project at 

KSC began in 1985 and was called the CELSS Breadboard Project to indicate the capability for 

“plugging in” and testing various life support technologies; this name has since been dropped 

but bioregenerative testing at KSC has continued to the present under the NASA’s Advanced 

Life Support (ALS) Program. A primary objective of the KSC testing was to conduct preintegration tests with plants (crops) in a large, atmospherically closed test chamber called the 

Biomass Production Chamber (BPC). Test protocols for the BPC were based on observations 

and growing procedures developed by university investigators, as well as procedures developed 

in plant growth chamber studies at KSC. Growth chamber studies to support BPC testing 

focused on plant responses to different carbon dioxide (Con) concentrations, different spectral 

qualities from various electric lamps, and nutrient film hydroponic culture techniques. 

This Technical Memorandum (TM) gives an overview of activities leading up to the KSC 

Breadboard Project, a description of the BPC, and summaries of crop test data, including the 

following: 

Environmental and horticultural approaches. 

Observations on growth and development. 

Crop biomass and oxygen yields. 

Proximate composition of biomass. 

Whole stand photosynthesis and respiration rates and responses. 

0 Nutrient solution measurements, including water use, nutrient uptake, and acid additions for 

pH control. 

Ethylene and other volatile organic compound production by plants. 

Because of the extent and diversity of crop testing at KSC during the 1985 to 2002 time 

frame, the results and discussion are limited primarily to BPC studies with wheat, potatoes, 

soybeans, lettuce, and tomato. An expanded bibliography of plant-related CELSS/ALS 

research is included at the end of the document. 

as well as a template for compiling a user’s guide or handbook for growing crops for Advanced 

Life Support systems in space. Because knowledge on growing plants for life support is 

continually expanding, the specific set points and outputs from ALS cropping systems will 

continue to be refined and improved. A crop handbook detailing these outputs and horticultural 

approaches may one day provide an invaluable reference for sustaining life support “farms” and 

the success of future space missions. 

The intent of this TM is to provide both a general summary of the crop studies at KSC 

iii 
TABLE OF CONTENTS 

Section 

1. 

2. 

2.1 

2.2 

2.3 

2.4 

2.4.1 

2.4.2 

2.4.3 

2.4.4 

2.4.5 

2.5.1 

2.5.2 

2.5.3 

2.5 

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

CROP TESTING AT KENNEDY SPACE CENTER ............................ 2 

Plant growth facilities at KSC ........................................................... Environmental management and horticultural approach.. ............ ..... Measurements and data .......................................... ..... .. ... ................. Results and discussion .... .... ......... ..... ...... ... .. .. .. ...... ........ ... ................. Horticultural procedures. .. . . . . . . . . . . . . . . . . .. . . . .. .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Crop yields .................................................................................. Water, nutrient, and acid use ....................................................... CO2 exchange rates ..................................................................... Ethylene and volatile organic compounds.. ...... .... . . .. .... .. ... . . ... ..... Other observations.. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . Hydroponic system operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . Materials handling .. ... . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Sanitation .................. ...................... ... .............. . ..... .. ...... ..... ........ 

4 

8 

14 

16 

16 

17 

20 

25 

26 

32 

32 

33 

33 

3. FUTURE CONSIDERATIONS ....... ..... ............ .. .......... . ....... ... ....... . ....... 34 

4. REFERENCES AND EXTENDED BIBLIOGRAPHY FOR ALS 

CROP STUDIES ..................................................................................... 36 

APPENDIX A TIMELINE OF DEVELOPMENT AND ENGINEERJNG 

MODIFICATIONS TO THE BIOMASS PRODUCTION CHAMBER 

(BPC) AT KENNEDY SPACE CENTER, FL ....................................... TIMELINE FOR CROP AND RESOURCE RECOVERY 

RESEARCH FOR ADVANCED LIFE SUPPORT (ALS) ACTIVITIES 

ACTIVITIES AT KENNEDY SPACE CENTER ..... .... . .......... ... .... . ...... 57 

APPENDIX C MEMBERS OF KENNEDY SPACE CENTER CELSS/ALS 

RESEARCH TEAM ................................................................................ 58 

56 

APPENDIX B 

PZMSWORDMASATMdNASA W-2003-21184 iv 
LIST OF FIGURES 

Fiqure - Title Pase 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

@ :: 

13 

14 

15 

16 

17 

Proposed CELSS testbed at KSC ........................................................ BPC located at Hangar L at KSC, FL (front view, 1986) ....................... BPC located at Hangar L at KSC, FL (rear view, 1986) ........................ Nutrient solution delivery tanks and plumbing system used to support 

crop growth in the BPC (1988). ............................................................ Tray covers for supporting wheat seedlings above a flowing nutrient 

solution . . . .. ... . .. . ................... . . . .. ... .. . .... .......... .... ...... ... . .... ... . .. . . ... .. .. ... . . . . Potato tubers ready for harvest from NFT culture trays at 105 days 

after planting .... . . . . . . . . .. . . . ... ... . .. . . ....... ... . . . .. .. . .. . . .. . . . ......... ... .. . . .... . ...... . . . .. . Productivity of total and edible biomass of different crops in the BPC 

(20-m area) as a function of daily PAR ............................................... Examples of water use, nutrient uptake (stock solution use), and acid 

use (for pH control) for 20-m2 crops of wheat, soybean, lettuce, and 

potato ... . . .. . .... . . ........ ......... ...... . . . . ..... ..... .. . ... .. . .. . . ...... . . .... . . ........ . ... . ... . .... Biomass production, water use, cation uptake, and acid addition as a 

function of PAR provided to crops of wheat, soybean, lettuce, and 

potato grown in the BPC ...................................................................... Repeating Con drawdown from photosynthesis (li ht period) and C02 

increase from respiration (dark period) of a 20-m soybean stand in 

the BPC. .............................................................................................. C02 drawdown by a 20-m2 stand of wheat in the BPC ......................... C02 exchange throughout growth and development of a 20-m2 stand 

of wheat ............................................................................................... C02 exchange throughout growth and development of a 20-m2 

stand of soybean .................................................................................. C02 exchange throughout growth and development of a 20-m2 stand 

of lettuce .............................................................................................. C02 exchange throughout growth and development of a 20-m2 stand 

of potato ............................................................................................... Plant stand gas exchange rates as a function of PPF .......................... Ethylene concentrations in the Biomass Production Chamber over 

time for crops of wheat, soybean, lettuce, and potato .......................... 

2 

P 

3 

5 

6 

7 

13 

13 

20 

23 

24 

27 

27 

28 

28 

29 

29 

30 

31 

V 
LIST OF TABLES 

Table 

9 

10 

. Title 

Possible crops for Advanced Life Support (ALS) systems ....................... Environmental set points used for ALS candidate crops in KSC testing .. 

Nutrient solution for ALS crops grown in NFT ......................................... Developmental characteristics of ALS candidate crops ........................... Life support outputs of crops grown in the BPC ...................................... Yields and PAR levels for ALS crops ...................................................... Proximate composition of controlled environment and field-grown 

crops ....................................................................................................... Water. nutrient (cation). and acid (for pH control) requirements for crops 

Some volatile organic compounds from humans and plants .................... 

Crop propagation/establishment considerations ...................................... 

grown in recirculating hydroponic systems .............................................. 

Paae 

2 

10 

11 

12 

15 

18 

19 

22 

24 

32 

vi 
ABBREVIATIONS AND ACRONYMS 

A 

AlBS 

ALS 

AOAC 

ARC 

BLSS 

BLT 

BPC 

BSAB 

BSB 

BTM 

BWP 

BWT 

"C 

ca 

CE 

CEA 

CEEF 

CELSS 

@ con CPEF 

CSTR 

dc 

DI 

EC 

FI D 

GC 

h 

HEPA 

HPS 

ICP 

I ES 

incan 

JSC 

KSC 

kW 

LED 

m 

MELISSA 

MH 

mol 

NFT 

ampere 

American Institute of Biological Sciences 

Advanced Life Support 

Association of Official Analytical Chemists 

Ames Research Center 

Bioregenerative Life Support Systems 

BPC Lettuce (Experiment Series) 

Biomass Production Chamber 

Breadboard Scale Aerobic Bioreactor 

BPC Soybean (Experiment Series) 

BPC Tomato (Experiment Series) 

BPC Potato (Experiment Series) 

BPC Wheat (Experiment Series) 

degree Celsius 

circa 

controlled environment 

controlled environment agriculture 

closed ecology experiment facility 

Controlled Ecological Life Support System; Closed Ecology Life 

Support System 

carbon dioxide 

closed plant experiment facility 

continuous stirred tank reactor 

direct current 

deionized water 

electrical conductivity (units typically as dS m-') 

flame-ionization detector 

gas chromatography 

hour 

high-eff iciency particulate air 

high-pressure sodium 

inductively coupled plasma 

Institute of Environmental Science 

incandescent 

Johnson Space Center 

Kennedy Space Center 

kilowatt 

light-emitting diode 

meter 

Micro-Ecological Life Support System Alternative 

metal halide 

mole 

Nutrient Film Technique (form of hydroponic culture) 

vii 
PAR 

PID 

PPb 

PPF 

PPm 

TI F 

TM 

VHO 

voc 

VPD 

PM 

ABBREVIATIONS AND ACRONYMS (cont) 

-2 -1 photosynthetically active radiation (units typically as pmol m s or W m-*) 

photo-ionization detector 

parts per billion 

photosynthetic photon flux (units as pmol m s ) 

parts per million 

tuber induction factor 

Technical Memorandum 

very high output 

volatile organic compound 

vapor pressure deficit 

micromole per liter 

-2 -1 

viii 
1. 

CROP PRODUCTION FOR ADVANCED LIFE SUPPORT SYSTEMS - 

OBSERVATIONS FROM THE KENNEDY SPACE CENTER 

BREADBOARD PROJECT 

INTRODUCTION 

The concept of using biological systems for life support in space has been studied since 

the 1950s and was considered even before this (Myers, 1954; Krall and Kok, 1960; Golueke 

and Oswald, 1964). Early studies were sponsored by the US Air Force and focused on algae 

(e.g., Chlorella) for atmospheric regeneration (Krall and Kok, 1960, Golueke and Oswald, 1964; 

Eley and Myers, 1964; Miller and Ward, 1966), while related studies sponsored by NASA included tests with chemoautotrophic organisms, such as Hydrogenomonas, in combination with 

physico-chemical methods (electrolysis) for atmospheric regeneration and biomass production 

(Bongers and Medici, 1968). Testing was expanded in the late 1960s and 1970s by Russian 

researchers to include higher plants, and studies using crops to support human crews (the 

BIOS Projects) were carried out in closed systems (Gitelson et al., 1989; Salisbury et al., 1997). 

In the late 1970s, NASA initiated the Controlled Ecological Life Support System (CELSS) program to continue research on bioregenerative life support, with much of the effort focused on 

controlled environment production of higher plants (MacElroy and Bredt, 1985; Galston, 1992). 

CELSS studies were conducted at several universities, corporations, and NASA field centers 

throughout the 1980s and early 1990s, after which the program merged with NASA’s physicochemical life support research efforts under the Advanced Life Support Program (Averner, 

1993). Studies of bioregenerative life support concepts have continued under the NASA ALS 

Program, as well as at the Japanese Institute for Environmental Sciences (Tako et al., 2001) 

and the European Space Agency’s Micro-Ecological Life Support System Alternative or 

MELISSA Project (Lasseur and Savage, 2001). 

As interest in the CELSS program expanded to include testing with higher plants 

(crops), questions arose as to which species should be considered for space life support. The 

topic was first addressed at a “Space Biologistics Symposium” held at Wright-Patterson Air 

Force Base in 1962, which produced a list of suggested leafy vegetables and root crops (Boeing, 1962). Additional crop recommendation panels were commissioned by CELSS and ALS 

programs and findings from these panels and other groups have been published in several 

documents, including Tibbitts and Alford, 1982; Hoff et al., 1982a; Salisbury 1991 ; Salisbury 

and Clark, 1996a, b; and Mitchell et al., 1996 (Table 1). Criteria considered for selecting these 

crops included crop yield, nutritional value, harvest index (edible dry masdtotal dry mass), horticultural requirements, and processing requirements (Tibbitts and Alford, 1982; Hoff et al., 

1982a). In addition, all of the crops were C3 photosynthesis types, which are slightly more efficient than C4 types at enriched C02 concentrations. Generally, the lists focused on “staple” 

crops to address bulk dietary requirements (carbohydrate, protein, and fat) but also included 

supplemental vegetables/fruits to provide some vitamins, minerals, and dietary variety. It is important to note that none of these lists provided a complete diet, and for some missions meeting 

all the nutritional demands for space crews might be achieved more efficiently through a combination of in situ grown plant foods along with some imported supplements, e.g., highly processed foods, flavorings, vitamins, minerals, etc. (Hoff et al., 1982a; Tibbitts and Alford, 1982). 

0 

1 
Table 1. Possible crops for Advanced Life Support (ALS) systems. 

Boeing Tibbitts and Hoff , et al. Salisbury and 

Company (1 962) Alford (1 982) (1 982a) Clark (1 996) 

Sweet potato Wheat Wheat Wheat 

Tampala Soybean Soybean Rice 

Lettuce Potato Potato Sweetpotato 

Chinese Cabbage Lettuce Rice Brocco I i 

Cabbage Sweetpotato Peanut Kale 

Cauliflower Peanut Dry Bean Lettuce 

Kale Rice Tomato Carrot 

Collards Sugar Beet Carrot Canola 

Turnip Taro Chard Soybean 

Swiss Chard Winged Bean Cabbage Peanut 

Endive Broccoli Chickpea 

Dandelion Onion Lentil 

Radish Strawberry Tomato 

New Zealand Onion 

Spinach Chili Pepper 

Gitelson and 

Okladnikov 

Tests 

Wheat 

Potato 

Carrot 

Radish 

Beet 

Nut Sedge 

Onion 

Cabbage 

Tomato 

Pea 

Dill 

Cucumber 

Salad Species 

(1 994) BIOS-3 

2. CROP TESTING AT KENNEDY SPACE CENTER 

Interest in bioregenerative life support at NASA's Kennedy Space Center began in the 

late 1970s when a proposal was submitted to NASA Headquarters to develop a Closed Ecology 

Life Support System (CELSS) testbed (Buchanan et al., 1978). This project proposed to retrofit 

the two large (Apollo) vacuum chambers in the Operations and Checkout Building at KSC and 

develop a plant production system in one chamber and then link this to a human habitat and 

waste processing system in the second chamber (Buchanan et al., 1978) (Figure 1). 

This proposal was not funded; subsequently, a smaller project was proposed to develop 

a testbed for crop production and biological waste processing only (Le., no attached human 

habitat) for the CELSS program (Prince and Knott, 1986, 1989; Knott, 1992). Dr. Arnauld 

Nicagossian, NASA Life Sciences Director, approved the latter project, named the CELSS 

Breadboard Project, and facilities construction activities began in 1985. These Breadboard 

Project objectives initially encompassed biological approaches for food and atmospheric 

regeneration (through crop production), biological waste treatment and recycling approaches, 

and food processing tests using controlled-environment-grown crops (Prince and Knott, 1 989). 

External advisory panels were established through the American Institute of Biological Sciences 

(AIBS) to provide oversight and annual reviews in each focus area. The food processing 

research program was abandoned due to funding and staff limitations, and the project 

continued with crop testing and waste treatmenthecycling approaches. 

2 
Figure 1. Proposed CELSS testbed at KSC. 

(Two large vacuum chambers used during the Apollo Program would have 

sewed as (a) a plant (crop) production module to supply food, oxygen, and 

clean water to the crew (Buchanan et at., 1978) and (b) human living quarters 

with control center and waste processing systems.) 

3 
The following provides a general summary of crop test results from the KSC Breadboard 

Project. Results and discussion from waste treatmenthecycling tests are reported only where 

they were part of crop studies and hence are generally not included in this document. 

2.1 Plant growth facilities at KSC 

Crop research for the KSC Breadboard Project involved both conventional growth 

chambers (Tibbitts and Kozlowski, 1979), as well as a large, atmospherically closed chamber 

that formerly served as a hypobaric test chamber for the Mercury Program (Prince and Knott, 

1986,1989). This large chamber became known as the Biomass Production Chamber or BPC 

(Figures 2 and 3). The BPC’s design and sizing were chosen to provide the food, water, and 

atmospheric regeneration needs for approximately 1 person using a bioregenerative approach 

(Prince and Knott, 1986, 1989). 

The BPC was an upright cylindrical chamber (7.5 meters (m) high, 3.7 m in diameter) 

that provided two-stories with direct access (Figures 2 and 3). The chamber enclosed four annular crop rowing shelves stacked vertical (two per story), with each shelf providing approximately 5 m of crop growing area (20 m2 total). Internal volume including air ducting was 1 13 

m3, with air circulation of about 400 m3 min-’ provided by two 30-kilowatt (kW) fans. Cooling 

and dehumidification were provided by two copper heat-exchange coils (one in the upper and 

one in the lower air handling system) using chilled water from two 15-ton (53 kW) chilling units 

(these were later replaced by a single 40-ton (1 40 kW) unit; Appendix A). Following each cold 

coil was a reheat coil supplied by hot water from resistance heating elements (up to 150-kW 

capacity). Lighting was provided by 96 400-W high-pressure sodium (HPS) lamps operated on 

dimming ballasts, thereby providing about 2 kW of input electrical power per m2 of growing 

area. Lamps were separated from the plants by clear glass or acrylic barriers. Plants were 

grown in 64 plastic (PVC or ABS) hydroponic growing trays (-0.3 m2 each). Nutrient solution 

circulated continuously through the trays and back to four tanks (one for each shelf) located 

outside the chamber (Figure 4). Tank headspaces were vented back to the chamber to maintain atmospheric closure. Although the chamber was used for hypobaric testing during the 

Mercury Program, the addition of air ducting and plumbing penetrations increased leakage and 

prevented large atmospheric pressure differentials from developing. Nonetheless, atmospheric 

leakage could be kept as low as 5 to 10% of the chamber volume per day when the chamber 

doors were closed (Wheeler et al., 1991 a). This allowed close tracking of C02 exchange rates 

(net photosynthesis and respiration), evapotranspiration, and the quantification of some volatile 

organic compounds using closed or semi-closed gas exchange calculations (Coombs et al., 

1985; Wheeler, 1992). Further engineering details and operational specifications can be found 

in Prince et al., 1987, 1992; Sager et al., 1988a; Wheeler et al., 1990, 1996; and Wheeler 1992. 

A development time-line for systems additions/improvements to the Biomass Production 

Chamber is show in Appendix A. 

9 

4 
Figure 2. BPC located at Hangar L at KSC, FL (front view, 1986). (The chamber provided a 

closed atmospheric volume of about 113 cubic meters (including air ducting) with 

20 square meters of crop growing area. External nutrient solution tanks were not in place 

at the time of this photo.) 

5 
6 
Figure 4. Nutrient solution delivery tanks and plumbing system used to support crop growth in 

the BPC (1 988). (Tanks typically ran with a volume of 225 liters of half strength, modified 

Hoagland/Arnon (1 950) solution that circulated continuously to trays inside the chamber 

(Wheeler et al., 1998). Trays were inclined slightly to maintain a thin film of nutrient solution.) 

7 
Smaller plant growth chambers for KSC studies included both reach-in and walk-in commercial 

chambers that controlled lighting, temperature, humidity, and C02 concentrations (Sager et al., 

1988a). Lighting was provided by fluorescent (48 or 96 inch, VHO-1.5 A), high-pressure sodium (400-w), or metal halide (400-w) lamps. For most studies in the BPC and growth chambers, temperature, humidity, and C02 were monitored continuously using a computer with custom-developed monitoring and control software (Sager et al., 1988a; Bledsoe et al., 1993). The 

sequences of smaller growth chamber and lab-scale tests with waste processinghesource recovery and how they both supported the larger, Breadboard Scale tests are shown in Appendix 

B. 

2.2 Environmental management and horticultural approach 

Most crops differ in their environmental requirements for producing acceptable 

morphological traits and high yields (Langhans and Tibbitts, 1997). For example, rice, 

sweetpotato, and peanut prefer warm temperatures (Bonsi et al., 1994; Mackowiak et al., 1998; 

Frantz and Bugbee, 2002), whereas potato and wheat prefer cool temperatures (Wheeler et al., 

1986c; Bugbee, 1995a); soybean, potato, rice, and strawberry are short-day crops, whereas 

wheat grows well under long days (Salisbury, 1981). The entire issue is complicated by the fact 

that environmental factors can interact with regard to their effects on crop growth (Thomas and 

Raper, 1983a, b; Wheeler et al, 1986c, 1991 b). Due to time and staffing constraints, 

exhaustive testing of environmental responses for each crop was not conducted; consequently, 

environmental settings for KSC crop tests were based largely on findings by university 

researchers (e.g., Bugbee, 1995a; Bugbee and Salisbury, 1988; Knight and Mitchell, 1983a, 

1988a; Thomas and Raper, 1983a, Wheeler et all 1986c, 1991 b). Environmental tests 

conducted in growth chambers focused mainly on features that were either unique to the BPC 

or conditions that were not commonly addressed in university studies. These included studies 

on the effects of HPS lighting (Wheeler et al., 19991 b, Yorio et all 1995), the effects different 

COS concentrations (Wheeler et al., 1993b, 1999b; Mackowiak and Wheeler, 1996), and crop 

growth and development using nutrient film technique (Mackowiak et al., 1989, 1998; Wheeler 

et al., 1990, 1999). For most crop tests, maximum growth chamber lighting was used, with 

HPS lighting studies ranging from -500 to 800 pmol m s and fluorescent lighting studies from 

-250 to 350 pmol m-2 s-’ (Table 2). For some studies, HPS lighting was deliberately dimmed to 

produce desired growth traits, e.g., to reduce tipburn injury in lettuce (Collier and Tibbitts, 

1982). Dimming was also used in several growth chamber studies with HPS lamps. A 

summary of environmental set points, modes of propagation, planting densities, and 

developmental characteristics for a range of crops tested in the KSC Breadboard Project are 

presented in Tables 2, 3, and 5. 

For each crop species, several cultivars were usually compared in early testing, which 

provided an initial selection of genotypes for controlled environment performance (Table 3). But 

as with environmental response testing, cultivar testing at KSC was limited and selections relied 

heavily on recommendations by university researchers. The best performing cultivars from 

KSC tests are shown in Table 3, but these results are somewhat dated by continuing tests of 

new cultivars by other ALS researchers. For example, recent studies with rice by Utah State 

University investigators (Frantz and Bugbee, 2002) indicate the ‘Super Dwarf’ rice is more 

appropriate for ALS applications than ‘Ai-Nan Tsao,’ and continued improvements in genotype 

(cultivar) selections for other species are inevitable. 

-2 -1 

8 
After considering a range of horticultural approaches, a recirculating nutrient film 

technique (Graves, 1983) was selected as the method for water and nutrient delivery (Prince 

and Knott, 1989). Nutrient film technique was amenable to a range of species, including root 

zone crops, reduced the need for large volumes of standing water, eliminated the need for solid 

media, and permitted close tracking of water and nutrient uptake. On the other hand, because 

of the limited water volume and buffering capacity, NFT systems are susceptible to crop stress 

or possible loss if system malfunctions are not dealt with promptly (e.g., loss of circulating 

pumps). A typical NFT system at KSC continuously pumped nutrient solution from a reservoir 

to a slightly elevated end of a tray, after which the solution flowed through the tray and back to 

the reservoir (Graves, 1983; Mackowiak et al., 1989). Clearly, such hydroponic approaches are 

gravity-dependent and would not function in the microgravity of spaceflight, yet the findings 

should still be pertinent for planetary settings (e.g., Moon or Mars) where gravity can be used 

for return flow. Although not reviewed in this document, testing has been and continues to be 

carried out at KSC to develop watering techniques for microgravity (e.g., low-Earth orbit andor 

planetary transit), and these are reported in Wright et al., 1988; Dreschel and Sager, 1989; 

Koontz et al., 1990; Brown et al., 1992; Goins et al., 1997b; Levine, 1999; and Levine et al., 

2002. 

Use of recirculating hydroponics requires monitoring and control of solution pH, 

electrical conductivity (EC), and water volume (Graves, 1983; Bugbee, 1989). For KSC studies, 

water levels and nutrient concentrations of hydroponic solutions were maintained by first adding 

either deionized water or condensate passed through ion-exchange columns (BPC studies) to 

the reservoirs to maintain a constant volume. Following this, a concentrated nutrient stock 

solution was added to maintain an EC set point of 0.12 S m-' (Table 4) (Mackowiak et al., 1989; 

Wheeler et al., 1999a). The starting solutions and make-up stock solutions provided all the 

essential elements for plant growth and were based on formulations developed by Hoagland 

and Arnon, 1950. For most studies, NOa salts provided the sole source of nitrogen; 

consequently solution pH levels would usually rise over time as a result of nutrient uptake 

(Marschner, 1995). To offset this, dilute nitric acid (0.2 or 0.4 mol L-') was added to maintain a 

pH set point of 5.8 k 0.2. For most KSC studies, including early BPC tests, nutrient solution 

temperatures were not controlled. For BPC studies after 1992 and certain growth chamber 

studies, water temperatures were controlled using stainless-steel coils submerged in the 

nutrient solution reservoirs. Cooling was then provided by chilled water circulated through the 

coils. 

placed against nylon (Nitex) wicks supported between tensioned strips of white-on-black 

polyethylene film (Prince and Knott, 1989; Mackowiak et al., 1989; 1996a) (Table 3; Figure 5). 

The ends of nylon wicks were kept in contact with the flowing nutrient solution in the trays. 

Potatoes, sweetpotatoes, and strawberry were propagated vegetatively using in vitro grown 

plantlets (potato), stem cuttings (sweetpotato), or runner plantlets (strawberry). Plantlets or 

cuttings were wrapped with pliable foam (sponge) collars and placed in white-on-black 

polyethylene tray covers with the roots kept in contact with the flowing nutrient solution 

(Wheeler et al., 1985, 1990). Following planting, trays were typically covered for 2 to 4 days 

with white translucent covers to maintain high humidity to promote germination and 

establishment. Seeds, seedlings, and plantlets under these covers were sprayed manually 

each day with deionized water to reduce water stress. Planting densities were highest for the 

grass species wheat and rice. A summary of planting densities, mode of propagation, seedling 

establishment periods, and times of plant thinning (to final spacing) for a range of crops 

Most of the species were seed-propagated, where either dry or imbibed seeds were 

9 
Table 2. Environmental set points used for ALS candidate crops in KSC testing. 

Crop (Genus species) Nutrient Air Tempera- Photosynthetic Photoperiod 

Solution ture Photon Flux (LighVDark) 

Temperature (LighVDark) (PPF) 

Staple Crops ("C) 

Wheat (Triticum aestivum) ' -1 8 

Soybean (Glycine max) -24 

Potato (Solanum tuberosum) -1 8 

Sweetpotato (Ipomoea batatas) -24 

Peanut (Arachis hypogaea) -24 

Rice (Oryza sativa) -24 

Bean ( Pbaseolus vulgaris) -26 

Supplemental Crops 

Lettuce (Lactuca sativa) - 23 

Spinach (Spinacia oleracea) - 23 

Tomato (Lycopersicon - 24 

Chard (Beta vulgaris) - 23 

Radish (Rapbanus sativus) - 23 

Red Beet (Beta vulgaris) - 23 

esculentum) * 

Strawberry (Fragaria x ananassa) - 18 

2011 6 

26122 

2011 6 

26122 

26122 

28124 

28124 

23 

23 

24 

23 

23 

23 

2011 6 

750 - 800 

500 - 800 

500 - 800 

500 - 800 

500 - 750 

750 - 800 

350 - 400 

300 

300 

500 - 750 

300 

300 

300 

400 - 600 

2014 or 2410 

12/12 

12/12 

12/12 

12/12 

12/12 

1816 

1 618 

1 618 

12/12 

1 618 

1 618 

1 618 

12/12 

' Higher PPFs and long photoperiods (up to 24 h) can be used for wheat, with yields being a strong function of total light provided (mol m-2 d-'). 

Soybean leaves can become chlorotic under high PPF from HPS lamps, but photosynthetic rates and 

productivity seem to remain high. 

Warm temperatures (e.g., >24"C) should be avoided for potato roots and shoots as these tend to suppress tuber initiation. 

High PPF (-800 pmol m-2 s-') from HPS lamps can cause chlorosis and bleaching of young sweetpotato 

leaves, but effects are usually transient. 

Recent evidence from Frantz and Bugbee, 2002 suggests rice does well at warmer temperatures (e.g., 

Lettuce is susceptible to leaf tipburn when plants are grown rapidly to a heading stage. Mild tipburn was 

observed in BPC studies with 'Waldmann's Green' lettuce grown 1000 ppm COP and 300 pmol m-2 5.' 

PPF with a 16-h photoperiod (-1 7 mol m-2 d-'). 

Spinach is a long-day plant for flowering but can be grown successfully under long days if harvested prior 

to bolting. 

Long photoperiods (> 18 h) can be injurious for tomatoes and some potato cultivars. 

Many strawberry cvs. require short photoperiods and cool temperatures for flowering and fruit set 

(Durner and Poling, 1988). Manual pollination of enhances both fruit quality and total yield. Different environmental set points (e.g., longer photoperiods) may be needed to force "runner" for vegetatively 

propagating strawberry. 

2 

4 

-3OOC). 

7 

9 

10 
Table 3. Crop propagation/establishment considerations. 

Crop (Genus species) Best Performing Propagation Plant Density Seedling Thinning 

Cultivar and Germi- (initiallfinal) Establish- Time 

(from KSC tests) nation ment 

Wheat ( Triticum aestivum) Apogee Seed ’ -1200 4 NA 

Soybean (Glycine max) Hoyt Seed 32/12-16 5 10 

Potato (Solanum tuberosum) Norland Plantlets 12l6-8 NA 10 

Sweetpotato (Ipomoea batatas) TU - 155 Cuttings 12/6-8 NA 7 

Bean (fhaseolus vulgaris) Etna Seed 32/12-16 4 10 

Peanut (Arachis hypogaea) Pronto Seed 12l6-8 4 14 

Rice (Oryza sativa) Ai-Nan Tsao Seed ’ - 800 4 NA 

Supplemental Crops 

Lettuce (Lactuca sativa) Waldmann’s Seed 40120-24 4 10 

Tomato (Lycopersicon Reimann Philipp Seed 2011 0 6 10 

Radish (Raphanus sativus) Giant White Globe Seed 50140 4 7 

Green 

Spinach (Spinacia oleracea) Nordic IV Seed 40120-24 10 14 

esculentum) 

Chard (Beta vulgaris) Ruby Red Seed5 40120 4 10 

Red Beet (Beta vulgaris) Ruby Queen Seed 40120 7 14 

Strawberry (Fragaria x Os0 Grande Runners 12-1 6 NA 14 

ananassa) 

’ Dry seed was initially aerated in deionized (DI) water for 30 minutes. Following this, wet seed was wrapped in 

moist toweling and kept at room temperature for 1 day (rice) or refrigerated (-4°C) over night (wheat). Following 

sowing, seeds were sprayed daily with DI water and a translucent plastic cover was placed over the trays to maintain high humidity during germination and establishment. Recent work by Klassen and Bugbee, 2002 suggests ‘Super Dwarf‘ as the preferred rice cultivar. 

Dry seed was aerated for 1 day and seed skin was removed (peanut only) prior to planting onto tray insert. Seeds 

were sprayed daily with DI water and a translucent plastic cover was used to maintain high humidity during the 

germination. 

Nodal explants were cultured on Murashigee and Skoog (agar solidified) medium without growth regulators. Plantlets were grown in vitro for 28-42 days under 25”C, a 12/12 photoperiod, with -150 pmol m-‘ s-’ CWF light. Plantlets were removed from culture vessels, agar was gently rinsed from the roots, and plantlets were transplanted to 

tray covers (white or black plastic film) and a translucent plastic cover was used to maintain high humidity during 

the 4-day acclimation process. Plantlets were supported in tray covers with pliable polyurethane (sponge) plugs by 

placing -113 of the shoot above the plug and -2/3 of shoot below to allow roots to contact the water. 

Stem cuttings were rooted in aerated DI water for 7-1 0 days. Cuttings were wrapped with a sponge (foam) plug 

and then positioned in hydroponic trays. No further acclimation was required. 

Dry seed was planted directly in contact with wicking material on tray insert. Seeds were sprayed daily with DI water and a translucent plastic cover used to maintain high humidity during the germination process. 

Dry seed was aerated for 6 days in DI water to initiate germination. Seedlings were then transferred to tray inserts 

and a translucent plastic cover was used to maintain high humidity during the 4-day acclimation process. For spinach, germination was carried out in a refrigerator at 4 to 5°C. 

hydroponic trays. 

0 

4 

6 

’ Plantlets produced from mother plants (runners) were wrapped with sponge (foam) plugs and then positioned in 

11 
Table 4. Nutrient solution for ALS crops grown in NFT. * 

Macronutrients 

Salt 

Startup Concentration 7.5 0.5 3.0 2.5 1 .o 1 .o 

Refill Concentration 70 10 56 12 10 10 

Micronutrients 

Fe Mn Zn cu B Mo 

mmol I--' 

Startup Concentration 50 7.4 0.96 0.52 9.5 0.01 

Refill Concentration 134.0 96.0 12.5 6.8 123.5 0.13 

Micronutrients were mixed in a combined stock solution using the following salts: H3B03; MnC12'4H20; 

ZnSO4'7H20 ; CuS04'5H20; (NH4)6M024'4H20. 

Fe-HEDTA mixed by adding FeCl3.6H20 and HEDTA. 

For sweetpotato, periods of nutrient (particularly N) depletion may be helpful for initiating storage root and limiting shoot growth. This can be achieved by only replenishing nutrients (EC set points) 1 or 2 times per week. 

Recent studies with potatoes in NFT suggest that lower EC set points with daily replenishment result in earlier 

tuber initiation and reduced shoot growth. 

For determinate crops such as wheat and some soybean varieties, reducing nutrients (e.g., lower EC set points) 

during seed filling might be considered. 

With nitrate being the sole source of N for this nutrient formulation, solution pH values tend to rise (go basic) 

during periods of high-nitrate uptake. This typically requires the addition of acid to control pH to a favorable 

range. A 0.4 M "03 and 0.4 M KOH were typically used for pH control in KSC testing. 

12 
Figure 5. Tray covers for supporting whea seedlings above a flowing nutrient solution. 

Figure 6. Potato tubers ready for harvest from NFT culture trays at 105 days after planting. 

12 
studied at KSC are shown in Table 3. Production cycles ranged from 18 days (radish) to 120 

days (sweetpotato and peanut), while canopy heights ranged from -20 cm (radish) to -80 cm 

or more sweetpotato, potato, peanut and rice (Table 5). Because canopy heights varied among 

cultivars and were influenced by environmental conditions (e.g., Wheeler et al., 1991 c), the 

values in Table 5 should only be used as a rough guide. 

2.3 Measurements and data 

Temperature, humidity, photoperiod, and C02 were monitored continuously using a 

computer and different versions of custom-developed software (Sager et al., 1988a; Bledsoe et 

al., 1993). Canopy level photosynthetic photon flux (PPF) was monitored manually above each 

tray weekly using a Li-Cor quantum sensor. Nutrient solution pH, EC, and volume were 

measured continuously for BPC studies or manually each day for most growth chamber studies 

(some growth chamber studies included continuous monitoring). This permitted a nearcontinuous tracking of plant water use, nutrient uptake, and acid requirements throughout each 

experiment. Nutrient solution samples were typically analyzed weekly or bi-weekly for 

elemental composition using Inductively Coupled Plasma (ICP) spectrometry. This provided 

guidance for making any adjustments to the replenishment stock solutions as well as helping 

assess potential plant deficiencies or toxicities. For BPC studies, evapotranspiration was 

monitored from water uptake from the nutrient delivery systems and from condensate recovery 

from the air handling system. Crop photosynthesis rates in the BPC were monitored using both 

closed and semi-closed approaches (Coombs et al., 1985), where chamber C02 drawdown 

rates were calculated immediately following dark cycles each day, or C02 mass flow additions 

were monitored during the light cycle (Wheeler and Sager, 1990; Wheeler, 1992). Crop 

respiration rates were monitored by calculating C02 increases during dark cycles (Wheeler and 

Sager, 1990). The accumulation of volatile organic compounds (VOCs), especially ethylene 

was also tracked for most BPC studies using gas chromatography/photo-ionization detector 

(GC/PID) or flame-ionization detector (FID) or mass spectrometry (GC/MS) (Wheeler, 1992; 

Batten et al., 1996; Wheeler et al., 1996b; Stutte and Wheeler, 1997). 

Plant measurements for BPC and growth chamber studies typically included general 

observations on growth and development, fresh biomass (for certain species, e.g. tomato fruit, 

potato tubers), oven-dry biomass of different plant parts, and canopy height. Oven drying 

involved placing plant materials in paper bags and then drying in a forced-air oven at 60 to 70°C 

for 48 to 96 h. When possible, data were expressed as rates per unit area; for example g m-2 

d-’, rather than g m-2 or g plant-’. This required dividing the yields by the available growing area 

and the time of growth. Growing area estimates were kept conservative to avoid over 

estimating productivities, and in some growth chamber studies, screening was used to reduce 

“side lighting” that would cause overestimation of productivities (Went, 1957; Bugbee, 1995a). 

For BPC plantings, an area of 20 m2 was assigned based on estimates of area enclosed 

between two arcs defining the front and back boundaries of each growing shelf (Wheeler, 

1992). Because “fixed spacing was used from planting to harvest in most studies, area 

utilization was relatively inefficient for widely spaced crops (Le., most of the light was not 

intercepted by crop foliage during early growth). Nonetheless, the entire space for the 

complete growth cycle was used to calculate final productivities. This kept productivity 

estimates conservative compared to what might be achievable in systems that incorporate 

14 
Table 5. Developmental characteristics of ALS candidate crops. 

Crop (Genus species) Anthesis/, Duration of 

Flowering Grow-Out 

Canopy Height Harvest 

at Maturity Index 

Staple Crops 

Wheat (Triticum aestivum) 

Soybean (Glycine maw) 

Potato (Solanum tuberosum) 5, 

Sweetpotato (Ipomoea batatas) 

Peanut (Arachis hypogaea) 

Rice (Oryza sativa) 

Bean (Phaseolus vulgaris) 

Supplemental Crops 

Lettuce (Lactuca sativa) 

Spinach (Spinach oleracea) 

Tomato (Lycopersicon esculentum) 

Chard (Beta vulgaris) 

Radish (Raphanus sativus) 

Red Beet (Beta vulgaris) 

Strawberry (Fragaria x ananassa) 

-35 

-28 

NA 

NA 

-35 

-45 

-28 

NA 

NA 

-35 

NA 

NA 

NA 

-60 

85 

90 - 97 

84- 105 

120 

120 

105 

70 

28 

28 

84 

40 + 

21 -25 

35 - 42 

140 

- 50 -30-45 

- 45 - 70' - 40 

-50-80 - 60 - 80 

-50-80' -20-60 

-60-80' -20-30 

- 35 - 45 

- 80 - 30 

- 50 

-20-30 - 90 

-20-30 - 90 

-35-45 -40-50 

-40-50 - 60 + 

- 20 - 50 

-40-50 - 60 + 

-20-30 -30-40 

Times to flowering and final harvest are dependent on environmental conditions. Values stated in this table are 

approximate for set points given in Table 2. * Shoot growth in peanut, sweetpotato, and potato can be excessive in hydroponic culture with continuous EC and 

pH control. Control of nutrient levels may be important to control shoot growth and harvest index. 

Wheat stands in controlled environments are susceptible to lodging, and canopy supports should be considered. 

For BPC studies, wire grids were positioned about 30 cm above and parallel to the tray surface to support the 

stand. However, use of any canopy support systems will affect harvesting and materials handling. Harvesting and 

threshing are labor-intensive and produce dust and debris (also true for rice and soybean). 

No canopy support system required with Soybean cv. Hoyt, whereas support is required with indeterminate cultivars such as McCall. Lower canopy leaves tend to abscise during maturation and periodic removal of leaf litter 

provides good air circulation and tray surface reflection. 

Tuberization in potato in NFT can be suppressed when stolons are submerged in solution. NFT simplifies harvesting in comparison to solid media. Alternative methods for propagating potatoes (e.g., use of mini tubers) should be 

explored to eliminate the need for in vitro plants. Recent studies at KSC have shown that using the same recirculated nutrient solution for successive plantings caused a premature tuber initiation and stunted shoot growth, which 

resulted in lower yields due to incomplete canopy cover. The effect can be removed by passing the water through 

a charcoal filter (Wheeler et al., 1995). Management of recirculating systems with potatoes will require further testing to develop strategies for consistent yields. 

Oedema (intumescence or callus-like lesions) can occur on leaves of potato, tomato, and sweetpotato, and on 

stems bean under HPS lighting or low UV light environments. 

BPC tests with the tomato cv. Reimann Philipp have produced good fruit set and high yields without assisted pollination. 

1 

4 

7 

15 
transplanting or automated spacing schemes to improve space utilization and light interception 

(Prince and Bartok, 1978; Knox, 1986). Portions of biomass from final harvests were analyzed 

for elemental composition using inductively coupled plasma (ICP) or direct current (dc) arc 

spectrometry (Alexander and McAnulty, 1981 ), and samples for several studies were sent to a 

commercial laboratory for proximate composition analysis using standard Association of Official 

Analytical Chemists (AOAC) procedures, including ash by muffle furnace, protein by Kjeldahl N 

(6.25 conversion factor), fat by ether extraction of acid hydrolysis, and carbohydrate by 

difference (Wheeler et al., 1993~). Some samples were also analyzed for total dietary fiber and 

nitrate composition (Wheeler et al., 1996c, 1997a). 

2.4 Results and discussion 

2.4.1 Horticultural procedures. As with any effort in controlled environment agriculture, 

techniques and approaches for growing plants improved with experience. Some more 

significant horticultural observations from the large-scale testing include: 

Germination and establishment of seedling (e.g., wheat, lettuce) were most successful if 

high humidities and good wick contact with the solution were maintained for the first few 

days until roots had reached the flowing solution. Daily manual misting of seeds and 

seedlings under the tray covers was especially important to promote good seedling 

establishment. 

In early studies with lettuce, seeds were germinated using a single nylon wick, but seedling survival was sometimes poor. This was improved by using two adjacent wicks, 

which allowed seedling roots to grow between the wicks prior to reaching the flowing 

water below. 

0 Initial BPC tests with potato (BWP911 and 91 2) resulted in mediocre tuber yields (Tables 6 and 7). Nutrient solution temperatures during these tests were often 3 to 4 "C 

warmer than air temperatures (e.g., up to 24°C) due to inefficient cooling capabilities in 

the solution reservoirs. For subsequent potato studies (BWP921 , 931, 941), auxiliary 

cooling was added using stainless-steel coils submerged in the reservoirs. This allowed 

solution temperatures to be held near 18 "C, which increased tuber yields (Burton, 

1 972). 

Providing adequate shoot support to prevent lodging (stand collapse) was important for 

some crops; an example of how lodging reduced stand photosynthetic rates in soybean 

study BSB891 is shown in Figure 13. For subsequent soybean studies, plant shoots 

were supported by wire mesh grids (fencing) positioned horizontally -25-30 cm above 

the tray covers. Similar support techniques were used for wheat, potatoes, and some 

tomato studies. Smaller crops (e.g., lettuce and radish) and dwarf cultivars (e.g., Hoyt 

soybean) did not require additional supports. 

Planting of densely spaced crops (e.g., wheat) and harvesting of seed crops (e.g., 

wheat, soybean, rice) was labor-intensive. In addition, harvesting and threshing seed 

crops were dusty and required adequate ventilation or breathing masks for protection. 

16 
This suggests that both planting and harvesting operations of seed crops are important 

targets for mechanized or even automated procedures. 

With the exception of potato study BWP941 and several growth chamber studies (Mackowiak et al., 1989), KSC crop studies typically ran for one production cycle. Study 

BW P941 showed that four successive generations of potato could be sustained without 

exchanging the nutrient solutions, and that staggered plantings (e.g., two-tray blocks) 

provided a more continuous yield and photosynthetic gas exchange (Wheeler, 1996; 

Stutte et al., 1999). Creating gaps in the canopy by staggered harvests may have had a 

positive effect by adding some “side lighting” to adjacent trays (Stutte et al., 1999). 

Successive plantings of potatoes in the same nutrient solution during several growth 

chamber studies in 1993 and then in BPC study BWP941 showed that a growth regulating compound accumulated in the nutrient solution over time (Wheeler et al., 1995; 

Stutte and Yorio, 1998). This compound or factor resulted in reduced shoot growth and 

early tuber initiation, and methods for managing this factor in continuous production 

tests with potato are still under study (Stutte, Yorio, and Edney, unpublished). 

On several occasions, water pumps were inoperable due to losses of electrical power 

(e.g., thunderstorms, hurricanes). To prevent water stress, NFT trays were elevated at 

the drain end to “pond” nutrient solution in the tray and provide a water reserve (2 to 3 

cm) for the plants. 

2.4.2 Crop vields. Harvest results (dry mass) from BPC 20 m2 stands of wheat, soybean, 

lettuce, potato, and tomato are shown in Table 6. Equivalent levels of C02 fixed and O2 

produced (based on biomass carbon content; Wheeler et al., 1996a), along with the total mass 

of water collected as condensate from each crop are also presented (Table 6). The highest 

biomass yields from BPC tests were obtained from wheat plantings, which received the most 

PAR (Table 6). The highest edible biomass yields were obtained from potato plantings, due in 

large part to the high harvest index of potato crops (Tables 6 and 7). In some studies, tubers 

accounted for > 80% of a mature potato plant’s biomass (Le., harvest indices >8O%). Biomass 

productivities (g m2 d-’) along with daily photosynthetically active radiation, (mol m-2 d-’) for each 

BPC study are shown in Table 7. By dividing productivities by daily PAR, radiation conversion 

efficiencies (g biomass per mol PAR) can be calculated for each experiment (Table 7). These 

radiation conversion efficiencies for the C3crops in the BPC ranged from -0.4 to 0.9 g mol“’ for 

total biomass and -0.2 to 0.6 g mol-‘ for edible biomass (Table 7). These results compare 

favorably with the 0.7 g mol-’ conversion value listed for corn (C,) canopies under optimal field 

conditions (Norman and Arkebauer, 1991). If transplanting schemes had been implemented for 

widely spaced crops (e.g., potato, lettuce, soybean, and tomato), productivities and radiation 

conversion efficiencies could have been improved. For example, lettuce productivities based 

on the full use of 20 m2 for 28 days were -7 g m-* d-’. But by growing seedlings in smaller 

areas (e.g., nursery) for 10 to 12 days before transplantin to the final spacing, productivity and 

radiation use efficiency would have increased to -1 0 g m- d-’ and -0.6 g mol-’ , respectively. 

An overall comparison of the influence of light (photosynthetically active radiation) and 

productivity are shown in Figure 7. The data show a near-linear response in productivity to 

PAR across the range of -15 to 60 mol m-2 d-’ (Figure 7) and emphasize the importance of light 

in driving crop yields for life support systems (Sinclair, 1991). 

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19 
50 I 

40 

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20 

10 

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I3 Wheat 

A Potato 

0 Soybean 

0 Lettuce 

V Tomato A 

Total 

Biomass 9 

d Edible 

Biomass t 0 

A 

01 I I 1 I I I 

10 20 30 40 50 60 70 

Daily PAR (mol m-* day’) 

Figure 7. Productivity of total and edible biomass of different crops in the BPC (20 m2 area) 

as a function of daily PAR. (Open symbols represent total biomass and closed 

symbols represent edible biomass.) 

Comparisons of proximate composition of plant tissues grown in controlled environment 

tests (from ALS studies at KSC and Purdue University) with values reported for field grown 

plants (Duke and Atchley, 1986) are shown in Table 8. Because the analyses did not always 

include the same cultivars (genotypes), the comparisons should be taken cautiously. But in 

general, controlled environment grown crops tended to have higher ash content and protein 

(estimated from total nitrogen content). This suggests that the horticultural approaches and 

conditions used in the controlled environment testing (e.g., the hydroponic culture) promoted 

greater nutrient uptake (Wheeler et al., 1993c; 1997a). 

2.4.3 Water, nutrient and acid use. Examples of water, nutrient (stock solution), and acid 

(pH control) additions to the NFT hydroponic system throughout the growth and development of 

wheat, soybean, lettuce, and potato crops are shown in Figure 8. Water use increased during 

early growth as the canopies “closed” and the total evaporating surface of foliage increased. 

Following this, water uptake rates remained relatively constant through stand maturation for 

wheat or declined slowly with age for soybean and potato stands (Figure 8). The particular 

example for soybean water use shows a large increase ca. 30 days, which coincided with a 

reduction in the humidity resulting from control system adjustments (study BSB902-upper 

chamber). Over the course of development, water use rates averaged 2 - 5 L m-* d” (Table 9), 

while maximum rates ranged form 5 - 9 L m d depending on the species and the water vapor 

pressure deficit (Figure 8). Since most of the tests at KSC were conducted with “enriched Con 

20 

-2 -1 
concentrations (e.g., 1000 or 1200 pmol mol-’), water use rates would likely be higher at lower 

Con (e.g., 400 pmol mol-’) or at super elevated levels (e.g., >5000 pmol mol-’) (Wheeler et al., 

1993b, 1999; Mackowiak and Wheeler, 1996). 

early in growth, whereas soybean, lettuce, and potato stands showed slow initial uptake rates 

followed by a rapid increase (Figure 8). In each case, the periods of rapid increase correlated 

closely with periods of rapid vegetative growth. With the exception of lettuce, nutrient 

replenishment declined as stands matured and shifted into reproductive growth (Figure 8). 

Because lettuce was harvested during rapid vegetative growth, there was no apparent drop in 

nutrient uptake at the time of harvest. The particular example of nutrient uptake data for 

soybean in Figure 8 showed a large overshoot in nutrient addition ca. 45 days, which 

corresponded to calibration adjustments in the EC monitoring and control system for that study. 

Average nutrient (total cation) addition rates ranged from 16 mmol m-2 d-’ (lettuce) to 58 mmol 

mm2 d” (wheat) (Table 9). 

Nitric acid additions for pH control showed trends similar to nutrient replenishment with 

additions increasing during periods of rapid vegetative growth and rapid nutrient uptake (Figure 

8). Comparisons of the acid and nutrient addition curves reveal some temporal differences, 

suggesting the balance of anion and cation uptake may shift throughout the growth and 

development of some crops (Marshner, 1995). The interesting bimodal peak of acid additions 

during early growth of wheat was observed in several studies and may indicate changes in the 

proportion of cation to anion uptake durin this phase of development (Figure 8). Acid 

additions reached nearly 100 mmol m-* d- for wheat studies when daily PAR and crop growth 

rates were high (Table 9). Average acid addition rates through growth and development ranged 

from approximately 5 to 40 mol m-2 d-’ depending on the crop and total lighting provided (Table 

9). For wheat studies, nitric acid additions continued at a moderate level throughout mature 

growth, even though nutrient uptake had dropped (Figure 8). The reason for this is unclear but 

may be related to microbial denitrification in the rhizosphere under these conditions. 

Plant tissues from all the BPC studies and many growth chamber studies were analyzed 

for elemental composition. Results from some of these analyses can be found in Wheeler et 

al., 1993c (wheat), Wheeler et al., 1994a (lettuce), and Wheeler et al., 1998 (soybean). ‘The 

high ash levels from proximate analyses showed that some elements were high in leaves and 

stems. This luxuriant or excessive uptake of elements such as K and N may have been a 

consequence of maintaining a constant EC set-point throughout growth, and the use of nitric 

acid for pH control. Analysis of lettuce leaves and potato stems often showed K levels ranged 

of 10 to 15% of the tissue dry weight. The high K and NOs levels in the tissue appeared to 

have no adverse effects on crop growth, but there was a concern in early testing that this was 

wasteful nutrient management for potential space applications. But concurrent resource 

recovery studies showed that many of these elements could be leached from the tissue by 

processing the inedible biomass in bioreactors (Garland and Mackowiak, 1990; Finger and 

Strayer, 1994; Mackowiak et at., 1997a). These retrieved nutrients could be then used to 

reconstitute more nutrient solution for growing subsequent generations of crops (Mackowiak et 

al., 1996, 1997a; Strayer et al., 1997). 

Nutrient replenishment (stock solution addition) for wheat stands showed a rapid rise 

9 

@ 

21 
Table 8. Proximate composition of controlled environment (CE) and field-grown crops.’ e 

Crop Growth Protein Fat Ash Carbo- No. of 

(plant part) Setting hydrate Studies 

Wheat 

(seeds) 

Soybean 

(seeds) 

Lettuce 

(leaves) 

(tubers) 

Sweetpotato 

(roots) 

Peanut 

(seeds) 

Tomato 

(fruit) 

Radish 

(roots) 

Spinach 

(leaves) 

(seeds) 

Strawberry 

(fruit) 

Potato 

Rice 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

CE 

Field 

(“w 

19.1 

14.3 

37.1 

38.2 

27.4 

22.8 

15.2 

10.4 

9.6 

5.4 

30.3 

26.7 

18.9 

16.6 

25.9 

14.9 

33.4 

29.1 

15.3 

7.6 

11.9 

7.7 

(“w 

3.1 

2.3 

20.0 

18.2 

4.6 

4.6 

0.7 

0.6 

0.5 

0.9 

43.3 

42.0 

3.6 

3.8 

3.1 

1.5 

2.3 

5.3 

3.8 

2.2 

1 .o 

4.0 

(W 

2.0 

2.2 

7.4 

5.4 

21.8 

10.4 

7.6 

5.0 

9.6 

2.6 

3.3 

2.6 

10.2 

8.1 

16.2 

11.3 

23.5 

20.9 

3.6 

3.4 

7.0 

5.8 

(“10) 

75.9 

81.1 

35.3 

38.2 

46.1 

60.0 

76.5 

84.0 

80.2 

90.9 

23.1 

28.7 

67.2 

72.3 

54.7 

72.2 

40.8 

44.7 

77.2 

86.9 

80.1 

82.5 

Data expressed on a dry weight basis; carbohydrate determined by difference. Additional comparisons 

of field and CE-grown crops of the same genotype can be found in Grant et ai., 1993; McKeehen et ai., 

1996; Nielsen et ai., 1996; Jurgonski et al., 1997; see also, Wheeler, 2000a. 

Data from NASA’s Biomass Production Chamber (Wheeler et ai., 1996a). 

Field data taken from Duke and Atchely, 1986. 

Data from growth chamber studies at Kennedy Space Center. 

Data from Wheeler et ai., 1997a. 

Data from McKeehen et ai., 1996a, b. 

1 

22 
N 

E. 
Table 9. Water, nutrient (cation), and acid (for pH control) requirements for crops 

grown in recirculating hydroponic systems. 

Soybean Wheat Potato Lettuce 

Water Use' (L m-2 d-') 4.7 4.7 4.0 2.1 

Nutr. Use2 (mmol mT2 d-') 29.2 58.3 44.7 16.3 

Acid Use3 (mmol m-2 d-') 12.5 41.6 18.0 6.1 

g DM / L Water 3.1 7.7 6.7 2.9 

g DM / mmol K, Ca, Mg 0.49 0.60 0.59 0.38 

._--_______-------______________________------------------------------- 

g DM / mmol Acid 1.14 0.85 1.47 1.02 

50 

. Biomass . Water Use Y "EJ 40- 

E 

n 30 

E 

n 

20 

10 

W 

P 

ss W W 

P 

S 

L 

L 

2 

y = -2.71 + 0.60~ (R 0.90) .' 

- Acid Use 

;/I 

20- :/-/w: L y = 0.42 + 0.84~ (R 2 = 0.91) .. y = -6.46 + 0.69~ (R 2 = 0.95) - 

c? 

v 

P) 

S 

0. : P 

'-a . Nutrient Use " n 80- 

CI) 

60 

40 

crr" 

0 

v - 

S 

0 20 40 60 0 20 40 60 . 0 

E 

' Water use includes volumes from stock solution and acid ("03). 

Nutrient use expressed as mmol of K, Ca, and Mg. 

Acid use expressed as mmol H'. 

2 

10 

-8 

-6v 

-4 J 

-2 

0 

'c 

E 

- 

-40 im 

E 

-30 +- 

v 

I 

20 5 

E 

E 

' 10 

80' 

I 

I Figure 9. Biomass production (g), water use (L), cation uptake (mmol), and acid addition (mmol) 

as a function of PAR provided to different crops of wheat (W), soybean (S), lettuce (L), and 

potato (P) grown in the BPC. (Potato study BWP911 resulted in low tuber yields and excessive 

vegetative growth; consequently, nutrient uptake was high and was not included in the nutrient 

use regression equation. No mathematical relationship is shown for water use due to differing 

vapor pressure deficits among studies.) 

24 
1 

Water use efficiencies for the different crops ranged from -3 to 8 g DM L-’ water used 

(Table 9). Nutrient (cation) use efficiencies averaged from 0.4 to 0.6 g DM mmol-’ cations (K’, 

Ca”, and Mg”) (Table 9). Average acid use efficiencies ranged from 0.85 g DM mol-’ acid 

(wheat) to -1.5 g mol-’ for potato (Table 9). Comparisons of PAR provided to the crops and the 

various nutrient solution management parameters indicate that radiation use efficiency for 

nutrient uptake was 0.84 mmol cations mol” PAR (excluding one outlier study with potato), 

while radiation use efficiencies for acid averaged 0.69 mmol acid mol-’ PAR (Figure 9). Water 

uptake rates are also plotted as a function of daily PAR in Figure 9, but no clear correlations 

existed; this was likely due to the more influential effects of different water vapor pressure 

deficits (VPDs) among the different studies. 

2.4.4 

calculated by tracking the rates of change during nocturnal increases in C02 concentration 

(dark period respiration) or by the “morning” drawdown rates (net photosynthesis) after the 

lamps came on each day (Figure 10) (Wheeler, 1992). These measurements could only be 

done while the chamber was closed without humans inside, using what is traditionally called a 

closed-system approach (Coombs et al., 1985). Measurements of C02 addition rates to 

maintain set points throughout the light period gave similar photosynthetic rates, in this case 

using a null-balance or semi-closed approach. For some experiments, changes in oxygen 

concentration were tracked simultaneously using a closed approach (Figure 10) (Wheeler, 

1992, 1996). The closed atmosphere of the chamber allowed direct manipulations of the 

environment, including deliberately shutting off the C02 supply and allowing the concentration 

to “drawdown” to a compensation point where net photosynthesis was zero (Figure 11). By 

plotting the photosynthetic rate as a function of C02 concentration, a complete Pn vs. [Con] 

response could be determined for the plant stand at that stage of development (Wheeler, 

1992). Because only C3 type photosynthesis species were tested, net photosynthesis rates 

typically saturated between -1 000 - 1500 parts per million (ppm) C02 (Coombs et al., 1985; 

Wheeler et al., 1996a), while compensation (i.e., zero net uptake) typically occurred between 50 

to 100 ppm Con. By tracking the diurnal changes in C02 each day, the stand C02 exchange 

rates could be monitored through growth and development, as shown in Figure 12 (wheat), 

Figure 13 (soybean), Figure 14 (lettuce), and Figure 15 (potato). In each case, net 

photosynthesis rates were low early in growth, prior to full canopy cover and maximum light 

interception. Rates typically peaked soon after canopy closure as the height of the stand 

increased and the incident PPF increased (Figures 12, 13, and 15), Le., as the stand grew 

closer to the lamp bank. After this, stand net photosynthesis and respiration rates gradually 

decreased with time as the stand matured and upper leaves began to senesce. Because lettuce 

stands were harvested soon after canopy closure during vegetative growth, they do not show 

the gradual decrease in photosynthesis and respiration with age (Figure 14). 

a near linear response in photosynthetic rate to incident PPF (Figure 16) (Wheeler and Sager, 

1990). The light compensation points for the stands at that stage of development (in this case, 

just following canopy closure) could then be determined from the x-intercept, where net 

photosynthesis was zero, while the stand respiration rates could be determined from the yintercept where there is no photosynthetic activity. Interestingly, light compensation points for 

crop stands in BPC studies were near 200 pmol m-2 s-’ during mid-term growth; in other words, 

these crop stands required at least 200 pmol mQ s-’ of PAR to offset their background 

respiration. This may seem high but it is important to note that the stands were grown at -700 

to 800 pmol m-2 s-’ PPF and thus their standing biomass and canopy architecture adapted to 

- exchange rates. Carbon dioxide exchange rates by plant stands in the BPC were 

@ 

As with C02 concentration, short-term manipulations with PPF were studied and showed 

25 
e that environment (Figure 16). For stands grown at higher PPF levels, the light compensation 

points tend to be even higher because of the greater standing biomass and increased 

background respiration rates (Bugbee, 1995a). On the other hand, photosynthetic rates of 

single leaves typically show much lower light compensation points but then tend to saturate at 

lower PPFs in comparison to whole stands (Figure 16). 

response to short-term changes in temperature set points (Wheeler et al., 1993b). For wheat 

stands grown at 20°C/1 6°C (lighvdark), increasing the temperature to 24°C increased 

respiration and reduced net photosynthesis, while decreasing the temperature to 16°C 

decreased respiration but had little effect on net photosynthesis (Wheeler et al., 1993b). 

For most BPC studies, photosynthesis and respiration rates were also measured in 

2.4.5 Ethylene and volatile orqanic compounds. The closed atmosphere of the BPC also 

permitted tracking of volatile organic compounds through growth and development (Batten et 

al., 1996; Wheeler et al., 1996b; Stutte and Wheeler, 1997). Examples of ethylene gas 

concentrations in the BPC throughout growth and development of wheat, soybean, lettuce, and 

potato are shown in Figure 17. Ethylene accumulation in the BPC varied depending on the 

species, the amount of standing biomass, and the stage of development for the crop (Figure 

17). By dividing the ethylene cotbentrations in the chamber by the standing biomass, a relative 

rate of ethylene production over time can be plotted, which showed that ethylene production 

rates by the wheat, soybean, lettuce, and potato stands were generally highest during early, 

vegetative growth (Figure 17). Based on observations from wheat tests on the Russian Mir 

space station (Salisbury, 1997; Bingham et al., 1999), the relatively low harvest indices of wheat 

(-30% study BWT881, 882) in the BPC may have been due in part to deleterious effects of 

ethylene on pollination and seed set (Figure 17). 

Ethylene measurements were also taken throughout growth and development of two 

tomato crops (BTM951, BTM961) and in each case showed relatively low concentrations during 

vegetative growth, followed by sharp increases during fruit ripening, reaching levels of 400 to 

500 parts per billion (ppb) prior to the periodic fruit harvests (data not shown). Tomato fruits go 

through a so-called climacteric ripening sequence, which is typically accompanied by increased 

respiration and elevated ethylene production (Abeles et al., 1992). Tomato study BTM961 

included a comparison of ethylene filtered (using potassium permanganate coated pellets) and 

unfiltered air in the upper and lower halves of the chamber. Although the ethylene scrubbing 

efficacy was intermittent, the results showed that reducing the amount of ethylene in the 

atmosphere slowed tomato fruit ripening. These results emphasize the potentially critical role of 

managing ethylene in ALS crop production systems. The influence of chronic ethylene 

exposure to ALS crops is currently being studied at Utah State University (e.g., Klassen and 

Bugbee, 2002). 

In addition to ethylene, many other volatile organics can accumulate in the atmosphere 

above plant growing systems (Table 10). Some of these compounds emanate from the 

materials in the chamber (e.g., plastics, glues, paints, etc.), while others appear to be biogenic, 

(Le., from the plants) (Batten et al., 1996; Stutte and Wheeler, 1997). In addition, the rates of 

production and types of compounds can vary depending on environmental conditions and the 

stage of development (Charron et al., 1996; Batten et al., 1996). 

26 
22.5 

n 

8 

'= 22.0 E! 

W 

C 

0 

.c.r 

S 

a, 

0 

S 

0 

0 

c 21.5 

Q> 

m 

> 

6 

21 .o 

0 10 20 30 40 50 

Time (hours) 

I 2500 

2000 

Q 

Q 

C 

W 

1500 o 

E! 

.- 

-I-- 

-I-- 

S 

S 

0 

0 

0 

1000 

500 0" 

0 

Figure 10. Repeating C02 drawdown from photosynthesis (light period) and C02 increase from 

respiration (dark period) of a 20-m2 soybean stand in the BPC. (Simultaneous measurements 

show an increase in oxygen during the light period and decrease during the dark.) e 

3000 , 

2500 

2000 

1500 

1000 

500 

0 

0 2 4 6 8 10 

Time (hours) 

Figure 11. C02 drawdown by a 20-m2 stand of wheat in the BPC. (Data were recorded by 

raising the C02 and then deactivating any further C02 addition. By taking the first 

derivative of the drawdown rate and plotting as a function of Con, stand net 

photosynthesis vs. C02 is obtained [inset]). 

27 
40 I I I I I I I I I I 1 

6 c Chamber 

- Dark Period Respiration Overheated 

---- Second Study 

1 Net Photosynthesis -----e---- 

30 

I Dqrk Period R,espirqtion I -20 I I 

I I I 

0 20 40 60 80 100 

Days After Planting 

Figure 12. Con exchange throughout growth and development of a 20-m2 stand of wheat 

(cv. Yecora Rojo). (Stands were grown at - 700 pmol m” s-’ for the first study but 

reduced to -400 pmol m-2 s-’ at 28 days in second study.) 

Soybean cv. McCall 

1 I 1 I 

a, 

ccf 

c 

-=. 

Days After Planting 

Figure 13. C02 exchange throughout growth and development of a 20-m2 stand of soybean 

(cv. McCall). (Stands were grown at high light [-800 pmol m-2 s-l] 

or low light [-400 pmol mT2 s-’I.) 

28 
Lettuce cv. Waldmann’s Green 

l5 . 

10 - 

5. 

Net Photosynthesis rn 

1 BLT911 Pn 

0 BLT911 Rs 

A BLT902Pn 

A BLT902Rs A 

A 

A 

rn 

MH Lamps 

rn\ 

\A 

HPS Lamps 

A 

Arnrn A 

I Dark Period Respiration I 

-10 ’ I 

10 12 14 16 18 20 22 24 26 28 30 

Days After Planting 

Figure 14. C02 exchange throughout growth and development of a 20-m2 stand of lettuce 

(cv. Waldmann’s Green). (Stands were grown at -300 pmol m-2 s-’ under HPS (BLT911) 

or MH light (BLT902). HPS grown plants tended to stretch more during early growth 

resulting in more rapid canopy cover.) 

60 

n 0 BWP911 Pnet 

& 50t 

B 0 

E e 

0 

E 

3 - 401 30 

R-o, 0 x, 

D% n 

t 

-20 ’ I I I I I I I I I I 

0 20 40 60 80 100 

Days After Planting 

Figure 15. CO, exchange throughout growth and development of a 20-m2 stand of potato. 

(Study BWP911 used cvs. Denali and Norland grown under HPS (upper chamber) or 2/3 HPS 

and 1/3 MH (lower chamber), and study BWP912 used cv. Norland grown under HPS.) 

29 
50 

40 

30 

20 

10 

0 

-1 0 

Canopy vs. Single Leaf Photosynthesis 

- Potato 

/ + Wheat Light 

I - Soybean Point 

Saturation 

I I I I I I I 1 I 

0 200 400 600 800 1000 1200 

PPF(pmol m s ) -2 -1 

Figure 16. Plant stand gas exchange rates as a function of PPF. (Measurements were taken 

soon after full canopy cover for each species. PPF compensation point for stands was -200 pmol 

m-* s” for all three species, which were grown at maximum lighting in the BPC. Note that a single 

leaf (e.g., soybean) saturated at a lower PPF than the whole stands [data measured with ADC 

portable photosynthetic system].) 

I 

30 
m 

Q 

0000000000000 g $ 00000~0 wln*mNr mPmNr momcu 

(By) sseLuo!a 

31 
Table 10. Some volatile organic compounds from humans and plants. 

____~ ~ 

1 Humans 

acetaldehyde 

acetone 

ammonia 

n-butyl alcohol 

carbon monoxide 

caprylic acid 

ethanol 

ethyl mercaptan 

hydrogen 

hydrogen sulfide 

indole 

methanol 

methane 

methyl mercaptan 

propyl mercaptan 

pyruvic acid 

skatole 

valeraldeh yde 

valeric acid 

Plants * 

benzaldehyde 

2-butanone 

carbon disulfide 

ethylene 

2-ethyl-1 -hexanol 

heptanal 

hexanal 

2-hexen-1 -01 acetate 

isoprene 

limonene 

2-methylfuran 

nonanal 

ocimene 

a-pinene 

p-pinene 

a-terpinene 

tetrahydrofuran 

tet ramet hyl u rea 

thiobismethane 

' Reed and Coulter (1999). 

Stutte and Wheeler (1997); Stutte (7999). 

2.5 Other observations 

2.5.1 Hvdroponic svstem operations. For many of the smaller growth chamber studies, 

water, nutrient, and acid (for pH control) replenishments of the hydroponic solutions were 

carried out manually each day. For BPC studies these activities were automated, but the larger 

reservoirs of stock solution and acid still required periodic manual preparation and filling (also, 

before 1990, condensate and hydroponic tanks were manually emptied and filled, respectively). 

Further automation may help reduce labor requirements somewhat but fundamentally different 

approaches for hydroponic system management may be required. Similarly, engineering 

upkeep and maintenance of pumps, sensors, and filters of the hydroponic systems, as well as 

other aspects of the plant chambers (lamps, fans, electrical components, etc.) will require 

32 
. 

t 

various levels of crew time, which must be considered in overall mission costs and demands. 

(Note that many engineering aspects of crop production for life support have not been included 

in this document and it is our hope that a similar document on engineering issues for 

bioregenerative life support will follow at a future date.) 

2.5.2 Materials handling. Most of the planting and harvesting activities for crop studies in the 

BPC and smaller growth chambers were carried out manually and were labor intensive. For 

example, wheat seed sowing took several “person-hours” for the 20-m2 BPG. Likewise, 

harvesting required manually removing the tray covers and crop materials from the chamber 

and then clipping or picking seed heads (wheat), pods (soybeans), or tubers (potatoes) by 

hand. To save time, threshing of wheat heads was done mechanically. Clearly further 

mechanization or even some automation should be considered for more sophisticated life 

support systems, thereby reducing crew time requirements. Regardless of whether threshing 

was manual or mechanical, cleaning wheat and soybeans seeds was a dusty process. These 

operations were carried out in open, ventilated settings (e.g., outside behind Hangar L), but 

such options will not exist in closed life support systems and dust control will be a serious 

challenge. Following harvest, inedible biomass (leaves, stems, fibrous roots) was typically 

oven-dried to obtain dry mass data. This was required for research purposes but would not be 

needed for a functional bioregenerative system. Likewise, post-harvest processing of inedible 

materials typically used the oven-dried biomass (Finger and Strayer, 1994). Direct processing 

of fresh biomass would be more energy efficient but will require additional studies, e.g., wet 

grindingkhopping methods, use of alternative dehydratiodwater retrieval methods, etc. 

Most of the BPC studies used batch plantings where the entire chamber was either 

planted or harvested in a single day. This was done to accommodate the research mission but 

resulted in episodic, labor-intensive events. In addition, this approach required dedicated 

storage capabilities for keeping the biomass. A more manageable approach would be to 

stagger the plantings and harvests over more frequent intervals, which would reduce the singleday labor requirements and allow a reduction in the processing and storage system 

components (Drysdale et al., 1994b). Moreover, by staggering the crop harvests, a portion of 

the system would always be photosynthetically active, thereby providing continuous O2 

production, C02 scrubbing, and water recycling (Drysdale et al., 1994; Wheeler, 1996; Stutte et 

al., 1999). 

2.5.3 Sanitation. Plant pathogens are a constant concern in terrestrial controlled environment 

agriculture (CEA), but most of these systems are relatively open to the surrounding 

environment, e.g., ventilated greenhouses. Because the BPC’s atmospheric system was 

relatively closed, many of the risks were reduced. Despite this, early plans for operation of the 

BPC considered sterilization protocols for much of the materials handling. The impracticality of 

this approach was quickly realized and sterile procedures were abandoned in favor of sanitation 

and avoiding overt risks. For example, seeds and plant materials were obtained from certified 

or reputable sources, seeds were surface sterilized for many studies, transplants (potato 

plantlets) were taken from sterile in vitro cultures, “tacky” mats were positioned at each 

entrance of the chamber to remove shoe dirt, and plant growing trays, tray covers, germination 

wicks, and plumbing systems were cleaned between crops. In addition, extraneous plant 

materials (including lunch vegetables and cigarettes) and soil were not permitted in or near the 

chamber. Initial studies included disinfecting the hydroponic systems with either a hypochlorite 

(bleach) solution or nitric acid between plantings, but this was later abandoned in favor of 

physically cleaning and flushing the system. High-eff iciency particulate air (HEPA) filters were 

used in the air ducts for early studies to remove airborne microbes and spores, but these were 

33 
removed with little consequence on atmospheric and surface microbial counts (N. Fields, 

personal communication). 

studies over the -1 2 years of operation. There were isolated examples of decay spots on some 

potato tubers or fungal growth on the crowns of isolated wheat plants, but none of these 

appeared to spread to other plants. The exception to this was a root zone pathogen on cv. 

Apogee wheat plants grown in a study in 1997. The infection appeared as "water-soaked" 

areas in the roots and continued to spread slowly among trays, resulting in decreased plant 

vigor and poor yields. The symptoms were typical of a Pyfhium organism, which was supported 

by evidence from some water-agar assays (M. Stanghellini, Univ. of Arizona, personal 

communication). The origin of the infestation was never determined and resolution to the 

problem involved terminating the study and sanitizing the trays and hydroponic systems. 

Potatoes were growing in the chamber during the same study but in separate hydroponic 

systems and showed no adverse symptoms. In another wheat study (BWT941), extensive 

fungal growth occurred on the dead leaves and stem sheaths following a high temperature 

event (air temperature briefly reached -50°C). Plants were harvested about 10 days after this 

event and the saprophytic fungus probably had little effect on the crop, but numerous spores 

were released to the air as the plant trays were removed from the chamber, which may present 

a health concern for humans if they were forced to work in a closed environment with these 

materials. 

The relative infrequency of obvious pathogens in the BPC studies was encouraging and 

suggests that using clean procedures and maintaining a diverse and stable microflora in the 

root zones (Strayer, 1994) may avoid many pathogen problems. Yet the serious consequences 

of an aggressive pathogen, as noted in the one wheat study indicate the pathology must be 

taken seriously and counter measures or contingencies should be part of the mission planning 

(Nelson, 1987; Schuerger, 1998). This might include the use of interplantings with multiple 

species and/or isolating different growing environments to reduce overall system risks, or 

implementing disinfection procedures if recirculating nutrient solutions are used (e.g., filtering 

nutrient solutions or treating solutions with hydrogen peroxide or ozone). Another possibility 

would be the use of fungicides, but few fungicides are cleared for use on hydroponic crops, 

particularly those that have edible structures that directly contact the nutrient solution. 

may act as havens for human pathogens. This becomes even more important when waste 

recycling systems are used to supply nutrients and water to the crops. Studies in which humanassociated organisms were deliberately added to crop hydroponic systems (small growth 

chamber studies) showed that counts of the human-associated bacteria dropped off quickly in 

the nutrient solutions and rootzones, suggesting that these organisms were generally not 

competitive in root environments (Morales et ai., 1996). Nonetheless, further testing with other 

organisms, different loading rates, and different crop management practices is needed. For 

example, if plants are co-utilized in a wastewater processing scheme, it may be prudent to only 

use seed-producing crops for this function, where there is little risk of direct water contact with 

the edible portions of the crops. 

With one exception, no widespread pathogen outbreaks were detected in the BPC crop 

Related to the topic of plant pathogens are concerns that the crop production systems 

3. FUTURE CONSIDERATIONS 

With the exception of a 41 6-day continuous production study with potatoes (four 104-d 

generations), all of the BPC studies were single generation plantings (Table 6). Tests during 

the Russian BIOS projects were also limited to 4 to 6 months maximum (Gitelson et al., 1989; 

Salisbury et al., 1997). In contrast, use of bioregenerative life support for long-duration 

34 
missions will require continuous operation of crop production systems and hence a thorough 

understanding of system performance over long durations is required. The potential risk of 

pathogen incursion, nutrient imbalances, and mechanical failures will likely increase over time, 

resulting in lower productivity. Additionally, bioregenerative systems will likely have multiple 

species cultured simultaneously, which may require combining different crops in a common 

environment. If all of the crops are grown in a common environment, allelopathic interactions 

may occur, particularly if crops share a common root-zone and/or a common nutrient solution. 

This might even include interactions between different aged plants of the same species, where 

for example older plants might outcompete younger plants for certain nutrients, e.g., potassium 

and phosphorus (Barta and Henderson, 1998). In addition, if the crops are grown in a common 

environment, it is unlikely that the temperature, Con, PPF, and photoperiod can be optimized 

simultaneously for all the species, and the consequences of such environmental compromises 

should be studied. This should include developing more complete environmental response 

surface data for modeling crop growth and yield across a range of possible conditions. As 

resources become available, it would also be prudent to expand the number of species tested 

for bioregenerative systems to increase the range of foods for internationally and culturally 

diverse crews. 

A number of significant horticultural and operational questions also remain unanswered 

and should be studied over long-duration tests. For example, can seed viability and vigor be 

maintained over time, and can vegetative propagation be used repeatedly for some crops (e.g., 

sweetpotato, potato, strawberry)? How long can growth media (solid or solution systems) be 

used for successive crop production? What are the operational life spans and spare parts 

issues for mechanical support systems, e.g., pumps, electric lamps, power supplies, and 

sensors (Fortson et al., 1994b)? What are the crew time requirements for operating crop 

production systems? (Gathering accurate data on this will be especially important for assessing 

overall system costs). What types of mechanization and automation are needed to reduce crew 

time requirements? Can the mass, volume, and power requirements of the mechanical support 

equipment be reduced? What types of failures (biological and physical) can occur and what is 

their frequency? What contingencies and safeguards are needed for minimizing these failures? 

Eventually various life support subsystems will need to be integrated and assessed from a 

larger system perspective. Projects such as the Russian BIOS tests, the Japanese Institute of 

Environmental Science's (IES) Closed Ecology Experiment Facility (CEEF), the European 

Space Agency's Micro-Ecological Life Support System Alternative (MELISSA) Project, and the 

proposed BIO-Plex facility by NASA will be needed to assess these integration issues (Gitelson 

et al., 1989; Tako, 1997; Barta et al., 1999; Lasseur and Savage, 2001). These integration 

studies should continue testing of solid and liquid waste processing that is linked with crop 

production (e.g., Finger and Strayer, 1994; Mackowiak et al., 1996a,b; Subbarao et al., 2000b) 

to assess the consequences on crop yield, mass savings through nutrient recycling, and 

potential food safety issues. 

There are many more questions that could be added to this list, including what are the 

human psychological implications of having plants present in a confined living space, and what, 

if any, are the benefits of working with the plants and consuming fresh foods (as opposed to 

stowed foods) on long-duration missions (Flagler and Poincelot, 1994; Waters et al., 2002). 

Answers to these and other questions will require long-term commitments by NASA and other 

space agencies around the world. Facilities such as the Biomass Production Chamber at 

Kennedy Space Center have been valuable tools for addressing some of these questions, and 

it is our hope that research on bioregenerative life support concepts will continue so that plants 

will one day be used as sources of food, oxygen, and C02 removal for humans as they explore 

e 

the solar system and beyond. e 35 
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55 
* 

1985 - 1987 

BPC constructed 

1989 - 1992 

Baseline crop studies with wheat 

potato, soybean, and lettuce 

May 1992 - June 1992 

Appendix A Timeline of developments and engineering modifications to the Biomass 

Production Chamber (BPC) at Kennedy Space Center, FL. 

I 

I 

Wheat growth on effluent 

degraded aerobically from inedible 

plant material 

June 1995 

BPC atmosphere connected 

with BSAB atmosphere 

Feb 1996 - April 1996 

Atmospheric study with tomato 

June 1997 

Addition of Robotic Manipulator 

to Upper Chamber 

OCt 1999 - Aug 2000 

Potato Tuber Induction 

Factor (TIF) Studies Phase I 

Lettuce production on recycled 

condensate 

Nov 1993 - Dec 1993 

I 

I 

I 

I 

Lettuce production on recycled I 

minerals 

Feb 1994 - May 1994 

- 1987 - 1988 

Early wheat grow-outs as 

chamber engineering improves: 

sealed atmosphere, computer 

control, etc. 

- April 1992 

Separation of upper and lower chambers 

Added condensate recycling 

- June 1992 - Sept 1993 

Testing of biogenic compounds with 

potato and wheat 

- January 1994 

Breadboard-Scale Aerobic 

Bioreactor (BSAB) installed 

- June 1994 - August 1995 

Continuous vs. batch production 

study of potato on aerobic effluent 

- Oct 1995 - Jan 1996 

Baseline crop study with tomato and 

soybeans 

- June 1996 - Dec 1997 

Mixed Wheat and Potato Crops 

in Same Environment 

- Mar 1998 - Oct 2001 

Development of Monitoring 

and Control Software 

- Jan 2001 - Oct 2001 

TIF Studies Phase I1 

IYVV. LUU i 

BPC Decommissioned 

56 
I 0 Appendix B: Historical timeline for crop and resource recovery research for Advanced Life 

Support (ALS) activities at Kennedy Space Center. (Lab-scale testing typically preceded 

“breadboard” scale, integration tests using the Biomass Production Chamber.) 

57 
Appendix C. Members of the Kennedy Space Center CELSS/ALS Research Team. 

58 
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unclassified unclassified unclassified 

6. AUTHOR(S) 

R.M. Wheeler, C.L. Mackowiak, G.W. Stutte, N.C. Yori0,L.M. Ruffe, 

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CELSS, ALS, crops, plants, life support, bioregenerative I 58