Paper No: FL01104

An ASAE Meeting Presentation

Design and Control of Interior Climate of Martian Greenhouses

By

P. A. Fowler, Dynamac Corp., Kennedy Space Center, FLV. Y. Rygalov, University of Florida, Gainesville, FLR. A. Bucklin, University of Florida, Gainesville, FLR. M. Wheeler. NASA Kennedy Space Center, FL

Written for Presentation at the 2001 ASAE Florida Section Annual Conference

Sponsored by ASAE

Cocoa Beach Oceanfront ResortCocoa Beach, Florida

May 9-12, 2001

Atmospheric Climate Design and Control for Martian GreenhousesDr. Philip A. Fowler Ph. D. Dynamac Corp.

Dr. Vadim Rygalov Ph.D. University of FloridaDr. Ray Bucklin Ph.D. University of Florida

Dr. Ray Wheeler Ph.D. NASA

Abstract

When humans travel to Mars, they will need to be provided the sustenance of life, e.g. clean water, breathable air, and food. The ability to grow food in a hostile environment such as Mars will require the use of protective enclosures or “greenhouses” to create an environment suitable for plant cultivation. The feasibility of such concepts will depend largely on their mission costs, which are affected by the mass, energy requirements, and crew-time to operate the systems. Operating plant production systems at low total pressure can reduce the overall mass and therefore mission costs. This paper develops preliminary concepts for developing and operating a low-pressure plant growth system. A description of important atmospheric constraints is given (dynamics of carbon dioxide, oxygen and water vapor), along with issues related to maintaining the “greenhouse climate” (temperature and humidity ranges). Results from studies of plant transpiration responses and water recycling needs at different pressures and carbon dioxide concentrations are also presented.

Key words

Martian Greenhouse (MG), plant transpiration, saturated water vapor, atmospheric composition, low-pressure ventilation, artificial climate design, automation, indigenous Martian resources.

Introduction: Plant requirements and Martian environment; greenhouse cost effectiveness

Table. 1 gives a comparison of the requirements of Earth plants to Martian environmental conditions.The cost of delivering a package to Mars is accounted for by the amount of mass in that package. The conditions on Mars require that some containment must be used to protect living organisms from the low-pressure and low temperature. In order to maintain an “Earth-like” atmosphere of 101 kPa in a less than1 kPa indigenous environment, a large massive structure would be required due to the high-pressure difference. To reduce high structural stresses and consequently reduce the overall mass, reducing the pressure in the structure is required. A detailed analysis can show the relationship of structure mass to differences in pressure. Hence the goal of these experiments is to find the lowest pressure in which plants will grow and be productive. An ideal structure will provide a controlled low-pressure atmosphere with minimal human-machine interaction. This is

due to the fact that the structure will not be human rated. A large degree of automation to control this semi-closed environment will be required to achieve this goal. From this we can formulate at least three requirements for the Martian Greenhouse concept:

1. The greenhouse should provide the conditions for plant growth and development in the rigorous Martian environment;

2. The construction should be as light and simple as possible;3. The greenhouse should operate completely autonomously;4. The system should operate reliably.

Outline of Martian Greenhouse concept

A cost effective MG should be based on use of indigenous resources such as the surrounding atmosphere, water and soil (Drysdale, 2000; Rygalov et al., 2001). It should operate completely autonomously and be deployed within a 100 to 120 day period before the crew arrives and then be able to function as a sub-system in conjunction with a crewed mission. The artificial greenhouse atmosphere will be primarily collected from the Martian atmosphere with the non-indigenous gases supplied from onboard resources. The total pressure of this atmosphere will be ~ 10 kPa (Table. 2). The Martian Greenhouse must operate at the lowest possible pressure in order to reduce the mass of the Martian Greenhouse. The stresses in structural elements of the greenhouse will decrease as the difference between inside and outside pressures decreases, so that at low operating pressures, structures with lower mass can be used. Atmospheric composition will be maintained by a ventilation system as plants photosynthesize and grow. The ventilation system will draw gases as needed from the Martian atmosphere which contains ~ 95 % CO2 and the O2 generated by plants will be scrubbed and stored. After the arrival of the crew the greenhouse could be used as part of a closed cycle in conjunction with the crew to recycle their waste and generate edible biomass for consumption. Water also will be collected from in situ resources (atmosphere or possibly ground water). This water will be treated and maintained in a closed water cycle during plant growth. Periodically water will be added from outside storage to compensate for the growing plant biomass and leaks. Nutrient salts might be obtained from Martian soil. This soil should also be collected and treated before crew arrival. The intensity of Photosynthetically Active Radiation (PAR) for Mars is about 180 W/m2 . This level is adequate for plant growth. PAR will be adequate except during periods of global dust storms when the illumination may decrease down to ~ 30 W/m2. During prolonged dust storms, it may be useful to utilize techniques for plant survival in long-term dark periods. Due to low outside temperatures, methods must be developed to maintain heat within the structure. Table. 2 list the minimal requirements for a Martian Greenhouse environment.

The main areas that require testing of MG technology in Earth based experiments are:1. The limits of plant physiology at low temperatures and low total pressure;2. Artificial MG climate design;3. MG – Martian environment interaction at low atmospheric pressure.4. Scenario of Martian Greenhouse deployment and operation.

The general outline of approach to MG investigation is presented at Fig. 1.

Figure 1 Overall model for Martian Greenhouse design

Martian environment & greenhouse simulation

Initial low-pressure studies were conducted in 1998 at Kennedy Space Center (KSC) in a large vacuum chamber called a Thermotron (Fig 2.). These tests first looked at the problems of simulating a low-pressure growth environment. They involved testing of instruments at low-pressure to observe their response when placed in this extreme environment.

Figure 2 NASA Thermotron vacuum chamber.

Some of the results from these tests are given in NASA Technical Memorandum 2000-208577 (Fowler et al, 2000). Initial plant tests conducted by Ken Corey showed the possibility of plant survival at low-pressures in the range of 5 to 10 kPa. These tests also showed the shortcomings of using a chamber not designed for plant growth experiments. Shortcomings included excessive heat build-up from light sources, inability to control humidity, and difficulties of interfacing instrumentation with equipment in a vacuum. Testing then progressed to using a small vacuum oven that was converted into an environmental chamber (Fig 3.). This small chamber called “Little Chamber M” was used to study the effects of low-pressure and water vapor concentration. The tests were conducted to determine:- saturated water vapor concentration;- water cycle intensity at low total pressure;- artificial climate design requirements at low pressure.

Figure 3 Little Vacuum Chamber M

The latest tests involve the use of an enclosed dome structure (Fig 4.) that will be placed inside the Thermotron. The dome creates a closed system for plant growth in a configuration similar to those being proposed for use on Mars. The need to isolate the high humidity atmosphere required to grow plants from the vacuum chamber mechanisms was another important reason for using an enclosed dome for tests. This high (70-90% RH) humidity was not tolerated by the vacuum system used in the Thermotron.

Figure 4 Martian Dome.

The dome will also be the proving ground for many recycling and automation concepts. It is currently under construction and preliminary testing.

The experiments conducted to date include:- artificial climate design in rarified atmosphere;- water cycle under low total pressure investigation;- plant low pressure transpiration tests;- artificial atmosphere composition control;- nutrient solution supply;- short-term low-pressure plant growth.

The results of these tests in relation to the entire Martian greenhouse concept are presented below.

Artificial climate design, plant response

Comparison of Martian environmental conditions with the requirements of Earth plants (Table.1) shows the need to create a greenhouse with a high technological level. This Greenhouse should be able to maintain certain climatic parameters approaching the lower physiological limits of plants (Table. 2). At low total pressure, the dominant mechanisms of mass and heat transport change. So, at certain levels of illumination the correlation of temperature and RH will differ from what is normal in Earth’s atmosphere (Henderson et al., 1997; Johnson, 1999). Maintaining environmental parameters in a low-pressure environment will require a different set of logic to control the atmosphere. The artificial climate design tests were done to determine interconnections and define the means of control (Table. 3).

The results of these tests show:- RH in closed water cycle depends mainly on the interrelation between the temperature of the environment

and the coolant system;- Theoretical analysis shows that total pressure does not influence RH directly (Rygalov et al, 2001). There is

an indirect influence when the pressure is decreased from the effect of heat transfer changes in the system. - Temperature increases because convection is reduced and direct radiation is the prime source of heating;

Short-term tests (about 24 hours) with lettuce plants placed in these conditions (total pressure ~3 to 5 kPa; illumination ~ 89.3 W/m2 PAR; temperature ~ 25 to 27 oC; RH ~ 50 to 60 %; CO2 partial pressure ~ 1 to 1.5 kPa) showed their ability to survive. From these initial results, it is believed that it should be possible to create and control the climate in a MG adequate for Earth plants to grow and develop. A basic concept required for development is a system of maintaining heat in the greenhouse during Martian nights that are extremely cold.

Water cycle in a Marian Greenhouse, and plant transpiration response

Resupplying water to the greenhouse will be a problem due to the lack of large quantities of liquid water on Mars. This problem can be reduced by controlling the water cycle in the greenhouse enclosure (Experimental…, 1975; Lysovsky, 1979). But the water cycle under low total pressure differs from the natural water cycle at Earth atmospheric pressure. Tests in the Thermotron and Little Chamber M showed (Rygalov et al., 2001) that the saturated water vapor pressure does not change with changes in total atmospheric pressure (Fig. 5):

Figure 5 Dependence of saturated vapor pressure on total atmospheric pressure

That is in agreement with earlier obtained results (Wiederhold, 1997). However, the specific rate of evaporation increases as total pressures (Fig. 6):

So, the intensity of water cycle will increase as total pressure decreases (Fig. 7):

Figure 6 Dependence of specific rate of evaporation on the total atmospheric pressure.

Figure 7 The Intensity of Water Cycle in Closed System versus Total Atmospheric Pressure.

The transpiration load for plants under these conditions will increase (Fig. 8). Physiological limits exist (varying for different plants) when long term-accelerated transpiration occurs. These limits should be investigated with complete grow-out tests.

These data are in agreement with those previously obtained (Corey et al., 2000). These experiments imply that plants could survive in a high intensity water cycle. Further investigation of plant physiological limits is needed.

Martian Greenhouse atmospheric composition, plant photosynthesis-breathing influences

Comparison of atmospheric parameters on Mars and Earth (Table. 4) and also plant requirements for carbon dioxide (Table. 1) show the possibilities of using the Martian atmosphere as a source of gaseous carbon. This supply could be provided by regular ventilation of MG volume. In this process, outside CO2 will be introduced into the greenhouse volume. O2 produced by plant will be scrubbed and stored. Experiments were done to show that it is possible effectively control atmospheric composition inside the enclosure by changing the rate of ventilation (Fig. 9).

Figure 8 Plant transpiration response at low total pressure.

Figure 9 Dependence CO2 concentration on ventilation rate (Dome set up).

Controlled ventilation could provide an appropriate MG atmospheric composition for plant growth. This will require pumps that will work at low total pressure against a small pressure gradient.

Nutrient solution supply, possible plant growth response

An outline of nutrient supply requirements for a MG is presented in Table. 5 (Rygalov et al., 2000).

Automation & Computerization

The concept of having a low-pressure greenhouse that is operated at pressures below what is considered man-rated requires that the environment be remotely or autonomously controlled. When conducting experiments in a vacuum chamber, there is also a need for this type of control. Interfacing equipment across pressure differentials increases the potential for leaks at that interface. Each penetration is another area of concern, so it is best to keep these through-holes to a minimum. A completely autonomous system will be self-sufficient and thereby reduce the need for communication to the outside world. A truly autonomous system could be developed by relaying information by radio or light transmission.

At low total pressure, the water cycle for plants is accelerated (Rygalov et al., 2001). This fact and because the system is semi-closed requires the use of an atmospheric control system. This system must recycle water by removing it from the air and returning it to the plants, regulate the gas composition, and maintain the proper humidity and temperature. A system has been designed (Fig 10) called an Atmospheric Tower Management System (ATMS). The system works by forcing air across a cold condensing coil and collecting the condensate. The cooling coil’s temperature is monitored and then regulated by bypassing the cooling fluid back to the cooling system. The air is then conditioned by use of a temperature sensing system that activates an air heater to maintain the desired air temperature. The goal of the system is to maintain a 70 ~ 85 % relative humidity. The water temperature is also regulated by internal temperature sensing that is used to activate a heater to maintain the desired water temperature. This water is then sent through a distribution manifold that precisely meters

water to each plant. Water requirements for each plant are determined by the use of scales set under each plant. The weight is monitored and when a deficit is reached, the irrigation system is activated. The collection tank for the water is also on a scale in order to determine water usage and make up requirements.

Figure 10 Dome design for atmospheric control

The overall make-up of the gas is a 5/3/2 combination of gases that is 5 kPa O2 , 3 kPa H2O, and 2 kPa CO2. O2 is a primary gas of concern in the growing system. The root zone of plants requires O2 for respiration. Due to the low pressures it is not possible to maintain the O2 level required in a hydroponic solution that is favored by many space plant-growing systems. Plants in this system will be maintained in a soil matrix with aeration supplied from within the soil. The use of an airponic system may be possible to resolve this problem.

As the plants grow they consume CO2 and generate O2 that eventually leads to a build up of excess O2 levels in the system. To maintain the proper gas make up an O2 scrubbing system is used that consist of molecular sieves which separate the O2 from the gas and return the gas to the system. The O2 is stored as a resource for other uses such as breathing air and propellant production.

Control of a closed system requires that all aspects of the plants’ growth cycle be maintained (Wheeler et al., 2000). This includes delivering nutrients to the plants, re-supplying CO2, re-supplying water, monitoring gas levels (ethylene), and logging data. This system incorporates an internal microcontrolled monitoring and control system. The electronics package is located at the base of the tower and is interfaced as a mechatronic system. Mechatronics is concerned with the blending of mechanical, electronic, software, and control theory engineering topics into a unified framework that enhances the design process (Ashely, 1997). Implementation of computer-controlled logic to a systems level can be achieved in many different fashions but when it comes to cost effective small systems, the best choice is a microcontroller. A microcontroller is effectively a computer on

a chip with the entire infrastructure required to interface with outside components such as high-powered relays, communications, real-time inputs, and timers. This controller is connected with the rest of the system through an interface board (MIB-1, Rigel Corp.) that in turn is wired to all of the sensors and solid-state relays. Software is being developed that will use the sensor outputs to create a feedback system for control. The sensors include temperature, humidity, CO2, O2, weight, light, and pressure. Each sensor requires some sort of conditioning to read the signal. The software evaluates each sensor and combines data to make the necessary control adjustments, such as opening solenoids or turn on/off pumps. The complete system will operate independently of outside control. The system has an outside connection to external monitoring, control, and logging capabilities.

Other problems: MG mechanical stability, dust storms, Martian soil oxidizing properties, trace elements contamination, microbial evolution

A short outline of accompanying to MG implementation problems is presented at Table. 6 (Wheeler et al., 2000; Rygalov et al., 2000).

Low pressure physical side effects

Throughout the project, problems have been discovered that affect the ability to grow plants in a low pressure environment. It is important to test equipment that will be used at low-pressure. Equipment should be inspected for sealed compartments that may be stressed when pressure changes are made. A good example of this is a membrane keypad. Electrical properties of equipment should be examined to check for adequate insulation. HPS lamps would not restart after being turned off at low-pressure. Instead of restarting, a corona would develop. This is an example of Paschen’s minimum (Dakin and Works, 1966). Not all instruments will work as designed at low-pressure. A Vaisala sensor used to measure CO2 that works correctly at 1 atmosphere gives incorrect values at any other pressure and must be corrected for pressure change. A rather dramatic effect of low pressure is changing convection coefficients, which cause materials to heat up or fail to cool down in the same manner as at normal pressure. This can affect sensor readings and mass heat transfer.

Scenario for deploying the Martian Greenhouse

The scenario taking into account the cost effective method of greenhouse deployment is presented in Table 7.

Summary of current problems

Tests results revealed problems that should be summarized and require further investigation:1. Water cycle management and control;2. Artificial climate design; 3. Plant nutrient supply;5. Requirements of illumination system;6. Problems of mechanical stability;7. Automation.

Conclusions

1. It should be possible to create a cost effective automatic Martian Greenhouse.2. There is a need for more detailed investigation of plant cultivation at low atmospheric pressure.3. There is a need to develop and test technologies for MG-Martian environment interaction.

Future directions

1. Artificial climate design tests with the physical Martian Greenhouse model in the chamber imitating native Martian environment.2. Cultivation of plants from seed to seed in the above mentioned conditions.3. Testing of technologies needed for interaction between Martian Greenhouse environment and surroundings.4. Automation and Control of Martian Greenhouse.5. Testing of Martian Greenhouse deployment.

Acknowledgements

The authors wish to thank to Kennedy Space Center NASA, Life Science Department, the Dynamac Corporation KSC NASA and the University of Florida for support of this project.

References. 1. Henderson M. , Perry R. L. , Young J. H. Principles of Process Engineering.ASAE. The Society for Engineering in Agricultural, Food and Biological Systems,1997, 353 p.2. Drysdale A. E. Cost Effectiveness Issues. Mars Greenhouses: Concepts and Challenges, Proceedings from a 1999 Workshop. Edit. by R. M. Wheeler and C. Martin-Brennan. NASA Technical Memorandum 2000-208577, August 2000, pp.27-38.3. Fowler P. A., Wheeler R. M., Bucklin R. A., Corey K. A. Low Pressure Greenhouse Concept for Mars. Mars Greenhouses: Concepts and Challenges, Proceedings from a 1999 Workshop, edited by R. M. Wheeler and C. Martin-Brennan. NASA Technical Memorandum 2000-208577, 2000, pp. 116-123. 4. Gribovskaya I. V., Rygalov V. Ye. Trace Element’s Exchange in Experimental Closed Life Support Systems. Proceedings of the Sixth European Symposium on Space Environmental Control Systems, Noordvijk, The Netherlands, 20-22 May 1997 (ESA SP-400, August 1997), pp. 859-862. 5. Johnson A. T. Biological Process Engineering.John Wiley & Sons, Inc. 1999, 732 p.

6. Wiederhold P. R. Water Vapor Measurement.Marcel Dekker,Inc. 1997, 357 p.7. Lysovsky, G. M., Editor. Closed System: Man-Higher Plants ( 4-th Months Experiment ). Novosibirsk: Nauka,1979, 160 p.8. Experimental Fcologycal Systems Including Men. The Problems of Space Biology, V. 28. Moskow: Nauka,1975, 312 p. 9. Levin G. V. and Levin R. L. Liquid Water and Life on Mars.http://www.biospherics.com/mars/spie2/spie98.htm, 2000, 14 p.10. Hiscox J. A. Biology and the Planetary Engineering of Mars. http://spot.colorado.edu/~marscase/cfm/articles/biorev3.htr , 2000, 22 p. 11. Wallace J. M. and Hobbs P. V. Atmospheric Science (An Introductory Survey).University of Washington. Academic press, 1977, 469 p.12. Hodgman C. D. Handbook of Chemistry and Physics, A Ready – Reference book of Chemical and Physical Data. Chemical Rubber Publishing Co., Cleveland, Ohio, 1949, 2737 p.13. Wheeler R. M. and Martin – Brennan C., Mars Greenhouses: Concepts and Challenges, Proceedings from a 1999 Workshop. NASA Technical Memorandum 2000 – 208577, NASA KSC, 2000, 141 p.14. Ksanfomality L. V. The planets rediscovered. Moscow: Nauka, 1978, 152 p.15. Odum E. Ecology. Moscow: Mir, 1986, v. 1, 328 p.; v. 2, 376 p.16. Rygalov V. Ye. Cultivation of Plants in Space: Their Contribution to Stabilizing Atmospheric Composition in Closed Ecological Systems. Adv. Space Res. Vol. 18, No. 4/5, pp.(4/5)165-(4/5)176, 1996, 1995 COSPAR.17. Rygalov V. Ye., Shylenko M. P., Lisovsky G. M. Minor Component’s Composition in Closed Ecological System Atmosphere: Mechanisms of Formation. IAF/IAA-95-G.4.03. 46th International Astronautical Congress, October 2-6, 1995 / Oslo, Norwey, 9 P. 18. Rygalov V. Ye., Bucklin R. A., Fowler P. A., and Wheeler R. M. Preliminary Estimates of Possibilities for

DevelopingDeployable Greenhouse for a Planetary Surface (Mars). Mars Greenhouses: Concepts and Challenges, Proceedings from a 1999 Workshop. Edit. by R. M. Wheeler and C. Martin-Brennan. NASA Technical Memorandum 2000-208577, August 2000, pp.105-115.

19. Rygalov V. Ye. et al. Water vapor under the low total pressure. University of Florida, 2001, 7 p., in press.20. Rygalov V. Ye. et al. Closed Water Cycle Under Low Total Pressure. Life Support & Biosphere Sciences, 2001, 17 p., in press.21. Rygalov V. Ye., Bucklin R. A., Drysdale A. E., Fowler P. A., Wheeler R. M. The Potential for Reducing the Weight of a Martian Greenhouse. ICES Meeting, 2001, 14 p.22. Wheeler R. M., Peterson B. V., Sager J. C., Knott W. M. Ethylene Production by Plants in a Closed Environment. Adv. Space Res., Vol. 18, No. 4/5, pp. (4/5)193-(4/5)196, 1996, 1995 COSPAR.23. Ashely, Steven. http://www.memagazine.org/backissues/may97/features/mechtron/mechtron.html24. Rigel Corporation, POB 90040, Gainesville, FL 3260725. Dakin, T.W. and C.N. Works, Measurement of Corona Discharge Behavior at Low Pressure and Vacuum, Scientific Paper 66-1B5-CORNA-P3, Westinghouse Research Laboratories, May 19, 1966.26. Corey K. A., Fowler P. A., and Wheeler R. M. Plant Responses to Rarified Atmospheres. Mars Greenhouses: Concepts and

Challenges, Proceedings from a 1999 Workshop. Edit. by R. M. Wheeler and C. Martin-Brennan. NASA Technical Memorandum 2000-208577, August 2000, pp. 48-57.

Bucklin R. A., Fowler P. A., and Leary J. D. Design Needs for Mars Deployable Greenhouse. Mars Greenhouses: Concepts and Challenges, Proceedings from a 1999 Workshop. Edit. by R. M. Wheeler and C. Martin-Brennan. NASA Technical Memorandum 2000-208577, August 2000, pp. 98-104.

Table. 1. Comparison of plants requirements and environmental conditions on Mars.

## Parameter, unit Low value High value Optimal value

Expected native Martian range

Comments(source of data for Mars and Earth)

1 Temperature, C ~ +5.0 ~ +35.0 ~ +20 to +27

~ -125 to +23 Data for Mars from (Ksanfomality, 1978; Wheeler et al., 2000)

2 Atmospheric pressure, kPa

~ 7 to 10 (?)

>100 ~ 100 ~ 0.5 to 10 Data for Mars from (Ksanfomality, 1978; Wheeler et al., 2000)

3 Photosynthetically active light (400 to 700 nm), W/m2

~ 50 > 500 ~ 150 to 200

~ 0 to 277 (Martian surface) or ~ 0 to 117 (inside DG)

Data for Mars from (Ksanfomality, 1978)Data for DG based on truthful supposition and calculation from (Rygalov et al., 2000)

4 Mean distance from Sun (million km)

149.6 227.94 (Hodgman et al.,1949)

5 Solar Constant (W/m2)

1380 ~ 589 +/- 142 (Kuhn and Atreya, 1979) for Mars.

6 Photosynthetically active radiation(W/m2)(micromol/m2sec)

4182000

181860

Assumes similarity to visible portion of Solar spectrum of Earth.

7 Photosynthetically active radiation during global dust storm(W/m2)(micromol/m2sec)

------

27128

Estimate assumes 6.5 % of Earth incident radiation of 1380 W/m2 (Drake, 1998); ~ 30 % of that value was assumed to be in the visible part (400 – 700 nm).

8 Ultraviolet radiation (W/m2)UV – C (200 – 280 nm)UV – B (280 – 315 nm)UV – A (315 – 400nm)

02.056.8

3.47.931.1

(Cockell and Andrady, 1999)

9 Day length, relative unites

1.0 - - 1.027 (Ksanfomality, 1978)

10 Year length, relative units

1.0 - - 1.88 (Ksanfomality, 1978; Wheeler et al., 2000)

9 Partial pressure CO2, kPa

~ 0.03 ~ 3.0 to 5.0 ~ 0.1 to 0.2 ~ 0.5; ~ 95% of volume of Martian atmosphere

Data for Mars from (Ksanfomality, 1978; Wheeler et al., 2000)

10 Partial pressure O2, kPa

~ 3 to 5 ~ 27 to 30 ~ 7 to 22 Trace levels Data for Mars from (Ksanfomality, 1978; Wheeler et al., 2000)

11 Relative Humidity (RH), %

55 100 70 to 90 ~ 0.044; ~ 0.1 to 0.3% of volume of Martian atmosphere

Data for Mars calculated from (Ksanfomality, 1978; Wheeler et al., 2000)

12 Stock of liquid water

_ _ Earth’s ocean area ~ 361 million km2 with average depth ~ (3.5 to 4.5) *1000 m

Uncertain;estimates gives equivalent to a layer of water over the planet 13 m to 100 m

Data for Earth from (Hodgman et al., 1949)Data for Mars from (Levin et al., 2000; Hiscox, 2000)

13 Nutrient elements composition

Table. 5

14 Acceleration due to gravity at surface, cm/sec2

~ 0 > 980 ~ 980 ~ 392 Data for Earth and Mars from (Hodgman et al., 1949)

15 Wind conditions, m/sec

~ 0 Determined by mechanical resistance

~ 3 to 5 Dust and send storm when wind speed ~ 100;Duration of storm ~ 50 to100 days;Height of storm ~ up to 7 to 15 km

Data for Mars from (Ksanfomality, 1978)

Table. 2. Possible low level requirements for artificial environment for plantcultivation on Mars.

## Environmental parameter, units Value Comments1 Illumination, W/m2 Above 50 Expected value ~ 47 to 194

(Rygalov et al., 2000)2 Temperature, C Above +5.03 Relative Humidity, % Above 554 Total pressure, kPa ~ 10.8 (100 %) O2 enriched atmosphere what

is dangerous in relation to fire5 CO2 pressure, kPa ~ 0.031 (0.3 %) Probably could be higher for

fire safety6 O2 pressure, kPa ~ 7.6 (70.5 %) Requirements for root

respiration (Fowler et al., 2000)

7 H2O vapor pressure, kPa ~ 3.2 (29.2 %) Probably could be lower in closed water cycle

Table. 3. Artificial Climate Design Test* (Experimental reproduction of artificial climatic conditions, Little Chamber M).

* Light intensity:- outside 1138.3 micromol/s*m2 (Solar Constant analog);- inside 212.6 micromol/s*m2.(dimming by the window).-

Table. 4. Atmospheric composition on Mars and Earth in comparison.(Abundance by volume (Partial pressure or Comments)).

Species Mars (from Hiscox, 2000) Earth (from Hodgman, 1949)CO2 0.9532 (7 mbar) 0.000325 (~ 0.305 mbar)N2 0.027 (0.2 mbar) 0.7803 (~ 791.7 mbar)Ar 0.016 (minor) 0.0094 (~ 9.5 mbar)O2 0.0013 (minor) 0.2099 (~ 213.2 mbar)CO 0.0007 (minor) ~ 12 ppm (very minor) [Nitta et al. , 1996]H2O 0.0003 (minor) 0.01 to 0.04 (~ 30 mbar, saturated vapor)Ne 2.5 ppm (very minor) 12.0 to 18.0 ppm (very minor)Kr 0.3 ppm (very minor) 1.0 ppm [Wallace et al. , 1977] Xe 0.8 ppm (very minor) -O3 0.04 to 0.2 ppm (extremely

minor) 0 to 12 ppm (ozone’s layer protecting the Biosphere of the planet) [Wallace et al. , 1977]

H2 - 0.00005 to 0.0001(minor)He - 4.0 to 5.0 ppm (very minor)Total pressure

~ 7 mbar ~ 1015 mbar

Relative humidity, %

Temperature of environment, oC

Vacuum, in Hg Total pressure, kPa

Temperature ofcoolant, oC

83.581.279.071.4

26.727.227.827.9

0.09.7719.8128.74

101.568.5534.74.6

22.022.022.022.0

53.353.452.247.0

25.525.525.726.4

0.010.320.3529.15

101.566.832.93.2

11.811.811.811.8

42.142.240.932.8

22.322.623.724.5

0.010.3519.9329.47

101.566.634.32.1

3.03.03.03.0

Table. 5. Problems for plants nutrient supply on Mars (from Rygalov et al., 2000).

##

Problem Possible solution Existing experience

Comments

1 Nutrient solution supply

1A. Stock of nutrient salts for supply developing plant conveyor.1B. Using the native Martian soil.

BIOS-3BIOSPHERE-2KARUSELKULONVITACYCLE

Stock of salts makes the system more heavy

1B. Native Martian soil using requires development technologies of soil collection & treatment

1 Correction of nutrient solutions

2A. Use of synthetic soil substrate for plant growth, enriched by nutrients.2B. Continual monitoring and correction of pH and nutrient levels insolutions, to optimize plant growth rates

Greenhouse SVET (IBMP- Moscow) BIOS-3, BIOSPHERE-II, CELSS,KARUSEL (at IBP - Krasnoyarsk),Others

The weight of the MG is practically the same in both variants.

2 Management of the chemistry of transpired water

Develop on Earth the requirements for the stock of correcting salts and reagents.

BIOS-3 long-term experiments, and others

This problem will appear when people arrive on Mars and MG starts to operate in more closed cycle.

3 Level of oxygen in the root zone under low total atmospheric pressure

Should be ~ 60 % of O2 in artificial Greenhouse at 10 kPa of total pressure

- Could create fire safety problems

Table. 6. Accompanying problems for Martian Greenhouse.

## Problem Possible solution Existing experience

Comments

1 Mechanical stability

Usual engineering solution for Earth

- (Bucklin et al., 2000)

2 Dust removal from MG, and additional illumination

2A. Removal of dust by automatic mechanical equipment.2B. Installation of lighting system.

Experience from BIOSPHERE-II, BIOS-3, and others.Additional experiments in rarefied atmospheres are needed.

Installation of any conventional mechanical system of dust removal increases the weight of IG.It is possible that natural processes (e.g. wind) will limit or control dust accumulation.

3 Spectral composition of light.

Combination of natural light, transmitted through transparent material, and artificial light of special spectral composition.

Greenhouse SVET, BIOS-3. Systematic transmittance experiments with the transparent materials for IG are needed.

Additional lighting...

4 Contamination by microbial & organic materials & elements of system’s shalls (may develop during long-term operations)

Catalytic thermal oxidation of microbial & organic contaminants in air.

BIOS-3 long-term experiments & the BIOSPHERE-II 2-year experiment. Additional long-term experiments are needed.

Oxidizing microbial & organic contaminants may produce oxides that are toxic for plants.Thermal oxidizing equipment will increase weight of IG(Rygalov et al., 1995; Rygalov, 1996;Gribovskaya et al., 1997).

Table. 7. Scenario of Martian Environmental Greenhouse Implementation (MEGI).

Number of stage

Stage description Combining technologies Approximate time of development, days

1 Arrival to the planet, installation and inflation of physical shall, mounting and start of engineering equipment, etc.

Engineering technologies developed for Earth, inflation of elastic shall in rarified atmosphere, etc.

Up to ~ 7, depends on DG sizes and level of technical & technological development

2 Collection of resources, creation and start of artificial climate and environment functioning including water cycle, etc.

Collection biologically active gases and water from outside atmosphere, collection and correction & enrichment of native soil, etc.

~ n*30(Earth’s), could take a months

3 Initiation of plant growth: planting and cultivation of different crops, accumulation and extraction of oxygen, etc.

Technologies developed for Earth’s greenhouses, technologies of concentration of atmospheres enriched by oxygen, etc.

~ 90 to 100, depends on the time of development of the slowest crop and artificial environment & regime cultivation

4 Arrival of personnel, extension of area of DG, improvement of technologies requiring human control, etc.

Technologies of isolation of native areas of soil and its treatment, etc.

Up to ~ n*30(Earth’s),depends on technical & technological development

5 Initiation of closed cycle of air exchange, nutrient supply and water recycling; and of harvesting, processing and transportation of solid plant matter, etc.

Technologies developed for Closed Ecological Life Support Systems( ), etc.

Up to ~180 and longer ( )

6 Initiation of interaction with native Martian environment

Technologies for semi – closed greenhouses functioning (not developed for Mars and other planet of Solar System)

Succession could take a years: ~ N*365(Earth’s)

7 Possible decreasing of functioning and conservation

Conservation technologies ~ 30, depends on degree of DG development