Croponauts

https://youtu.be/i2JqZq59XIE

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Introduction: the S.P.I.G.A. project

Ensuring that spacecraft food systems provide palatable, safe and nutritious foods is obviously critical to any space mission. The longer ones have included semi-closed food systems, with periodic replenishment and transient exposure to unique and fresh products, but the longer exploration missions will have a more limited food system due to the greater distance from the Earth. To solve this problem, longer missions will feature food grown on a planetary surface or even on a spacecraft. In this context, our deployable module is particularly convenient: it turns out to be light, compact, protective and in particular modular.

Nutrition: choice of vegetables and quantity

The daily caloric intake of an astronaut should be calculated following the guidelines of the World Health Organization, as well as the studies conducted directly on astronauts, considering the sex, weight, age and physical activity performed. Of the total daily calories, 12-15% should come from protein, 30-35% from fats and 50-55% from carbohydrates.

Our objective is to partially introduce in the diet a portion of vegetables grown in situ, both for conveniency and psychological aspects. The module enables us to produce different types of crops. We chose the following three as our case study:

- Crisphead Lettuce (lettuce)

- Daucus Carota (carrot)

-Spinacia Oleracea (spinach)

We created a code (pots_calculation.m) to evaluate the necessary amount of plants to guarantee a weekly production of: 

·      Lettuce: 4 kg of ripe lettuce (500g per head, 8 heads), supposing a consumption of 200g of lettuce per person for 4 days a week. The lettuce seed is germinated for 2 weeks and then inserted into the aeroponic structure for 50 days. Each lettuce pot contains 6 sites, so the number of pots used for lettuce cultivation are 7, allowing the growth of 42 seedlings (n ° of growth sites).

·      Carrots: 1.5 kg of carrots (100g per carrot, 15 carrots), supposing a consumption of 100g of carrots per person for 3 days a week. The carrot seed is germinated for 2 weeks and then inserted into the aeroponic structure for 45 days. Each carrot pot contains 6 sites, so the necessary pots are 12, allowing the growth of 72 seedlings (n ° growth sites).

·      Spinach: 1.5 kg of spinach (50 g per spinach, 30 spinach), supposing a consumption of 100g of spinach per person for 3 days a week. The carrot seed is germinated for 1 week and then inserted into the aeroponic structure for 35 days. Each carrot pot contains 6 sites and in total the pots used for cultivation are 12, allowing the growth of 72 seedings (n ° growth sites).

TABLE OF NUTRITIONAL VALUES {1}

Being able to eat fresh food would not only help astronauts from a nutritional point of view, due to the contribution of beneficial macro and micronutrients, but also psychologically, as they will have the opportunity to feel the texture of a non-pre-packaged food. Moreover, working on simple tasks like gardening can be a stress reliever during a long interplanetary mission.

{3} Taking into consideration health issues, the oxidative stress that affects astronauts during and after space flight is a crucial matter. Evidence of this exist in multiple tissues, in urinary and blood biomarkers of damage to DNA, in lipids and proteins and in gene expression. Long-term exposure to space stressors reduces the body's protective antioxidant and intensifies lipid peroxidation. In order to minimize or mitigate the damage, the astronauts' ration should contain biologically active substances with antioxidant properties: bioflavonoids, water-soluble vitamins (vitamin C and vitamin B), fat-soluble vitamins (vitamins A and E, beta-carotene) and minerals (Zn, Se, Mn). The plants we have chosen for our project contain many of these substances.

Structural part: load-bearing structure, fabric, deployment, doors

A key aspect of our project is that the 4 m diameter by 7 m module is inflatable, in order to have a reduced stowage volume when compared with the effective useful volume {4-5}. From a literature review of the methods of folding, we chose an “origami folding” which, from our first estimates, allows us to reduce the stowage volume of 35% (considering also two cargo zones at the tips that are rigid and each one of approximately 10 m3).  The dimensions of the stowed structure were chosen taking into consideration the dimensions of currently used or in developing launch systems and can be fit in different payload fairing, such that of the SLS which will be employed in the future lunar exploration {5}.

The structure is composed by a rigid skeleton with six transversal frames and five longitudinal ribs, in addition to the two rigid cargo zones. The flexible cover is made by different layers (ordered from inner to outer layer): 

o   Inner layer made of Nomex: protection from fire, abrasion, scratches, chemical agents and noise insulation.

o   Bladder made with a combination of Polyurethane and Saran laminate: maintain air inside the module.

o   Restraint layer made of Kevlar and in a configuration like the Bigelow Expandable Activity Module one or the TransHab one: structural layer, it supports the bladder.

o   Flexible Multi-Shock Shield made of a Nextel layer, an Open Cell Foam layer and a Kevlar layer: for protection from micro meteoroids. 

o   Thermal insulation layer made by an MLI blanket

o   Radiation protection thanks to the Kevlar present both in the restraint layer and in the multi-shock shield

It can be noted that some of these layers may be substituted by a regolith shield that can protect from meteoroids impacts and radiation giving also a thermal insulation, in the case in which the module is used on the body surface.

Each module has a double hatch door for each end, enabling both the docking and access in orbit/deep space scenarios with a standard IDSS door {7} and the usability during surface operation with a larger embedded hatch door. The doors are interlockable with other modules, allowing to have a larger space farm with multiple modules, for example in a Moon colony scenario or during an interplanetary mission to Mars.

Systems

The internal configuration of the pots was chosen to take maximum advantage of the available space, having in mind the fundamental possibility for astronauts to comfortably spend time inside the greenhouse. In fact, each pot can be easily assembled and rotated to be oriented according to the different mission necessities, to fulfil both the necessity of a microgravity environment or of a planet surface. Not all the components are represented in the CAD model: for example an UV sterilizer can be used to avoid contamination; under the floor all the components of the systems will be included.

An example of internal arrangement:

Standard 40 pots configuration:

Additional pots can be added with the double arm supports:

The internal modular design is composed of pots with internal piping for irrigation, the pots are supported by arms on both ends with adjustable orientation. The arms are bolted to the main shelf. The arms can slide to adjust length and the shelf supports are locked with the main structural frame.

Shelf support:

Supporting arm:

Pot locking:

Additional double supporting arms are considered to increase the farm productivity, as we can see in the following images.

Here we can appreciate the internal piping of the pots with feeders and spry nozzels. On the bottom of the pots we considered a drainage hole for condensation.

All the pots are connected with a main feeder and waste piping system with non rigid tubes, not designed in the CAD.

Each internal component is standardized and can be detached, sanitized and substituted easily. This also guarantees a high reliability of the global system. The components can also easily be printed via a 3D printed, enhancing the advantages furthermore.

Regarding the electrical system, it was assumed to use solar panels as the power source. In particular, solar panels with a Gallium arsenide cell were chosen and an efficiency coefficient of 30% used. It was necessary to estimate the amount of light necessary for plants to live. This was done by considering the light spectrum of Photosynthetically Active Radiation which is roughly equal to 41% of the total solar irradiance, mostly in the red and blue wavelength. Thus the plants need a power of 560 W/m2. Considering an efficiency of the LEDS used for the illumination equal to 120 lumen/W corresponding to an efficiency of 0.18, the total power needed inside the greenhouse is (assuming a surface area of 10 m2) 5600 W and thus an illumination power of roughly 31 kW. Some technical papers highlighted the fact that in such an environment the 80 % of the power is due to the illumination, so the total surface of solar panels needed is of 95 m2. This analysis, even with the limitations of not considering the radiation damage during solar panels life or the angle forming between the panels and the sun (but it is acceptable to imply the presence of an adjusting system) and without considering the necessity to recharge batteries for shadow periods (that are strongly dependant on the chosen site or application) highlighted the necessity of a solar panels surface of roughly ten times the cultivated surface.

Regarding the thermal control system, it was considered that in the worst case the power received by the Sun is equal to the solar constant at Earth distance, equal to 1367 W/m2, times the projection of the lateral surface of the cylinder which is equal to 24.5 m2. Thus the power to be dissipated is 33.5 kW plus the power dissipated by the internal components which can be estimated using the efficiency of the LED lights which, as seen, constitute almost all of the power requirement. This leads to a total of 66 kW. Disregarding the differences in temperatures created by the illumination, which can be reduced with the thermal insulation system and also the fact that a part of the incoming light power can be reflected using a specific coating, the thermal control system can be imagined as a series of heat exchangers that uses a fluid, such as ammonia, to refrigerate the air inside of the greenhouse. Imagining to need a temperature of 25°C, equal to 298.15K,  and that the refrigerating fluid is in equilibrium with air when it exits the heat exchanger, the surface of thermal radiators facing space should be equal to almost 150 m2.

Regarding the aeroponics system, this configuration was chosen because it showed many advantages with respect to traditional cultivation system and also hydroponics system. In fact it doesn’t need much water and there’s no need of soil. It is also established that with such a system there are the lest flow losses possible, conducting to the minimal amount of water required. It consists in a closed loop cycle in which a solution of water and nutrients is circulated and vaporized through nozzles in a chamber in which the roots of the single plant reside. The choice of such a system is also good because it can permits the functioning also in a microgravity environment.  Moreover a system consisting of a secondary pipeline can be introduced to collect the water that condenses on the walls of the roots chambers and resend it in the principal loop. This can be also integrated in a broader water recycling system of astronauts' waste. Regarding the atmosphere inside of the module it was supposed to be at ambient pressure but it was noted that a richer CO2 composition permits a faster growth of the vegetables. Thus the CO2 concentration is set to 1000ppm which leads to a global volume of CO2 of 0.09 m3 or 0.18 kg. It must be noted that this is not a danger for people entering the greenhouse since the maximum amount is set to 1500 ppm and sometimes more. In any case the atmosphere composition can be modified before the entrance of astronauts. It was also calculated that the CO2 consumed by the plants is equal to 5.6e-7 kg/(m2 s) leading to a total consumption of 5.6 e-6 kg/s. The CO2 produced by the astronauts is roughly equal to 5e-2 kg/s thus the atmosphere composition in the greenhouse can be maintained constant, still having a great amount of CO2 to be regenerated. It is also possible to have a complete automation of this system with automatic control and disregarding human participation a part from the harvesting.

Conclusions

In conclusion, our project allows to have freshly in situ grown crops during different kinds of space missions: it was in fact designed with having in mind the applicability of the same module with slight variations during both surface exploration of Moon and Mars and in orbit missions. Other benefits include high reliability and maintainability since many of the components are standardized and interchangeable. The usage of an aeroponic system permits to lower to almost zero the water losses, creating a close cycle that is integrated with the rest of the base or spaceship, allowing to use human waste like CO2. There is also the possibility, in case of  a lunar south pole mission, to use water that can be extracted in situ, while also exploiting the lunar soil to build a shield from radiation. 

It Is also necessary to note that a simpler and economically viable iteration of the project (for example eliminating the protection layers of the structure and eliminating the need for solar panels) can constitute a kit to be mass produced and deployed in harsh zones of Earth and for example at the Earth poles to produce food for scientific researchers and expedition.

In future iterations of the project some elements can be modified or added and also an analysis of debris impact risk can be done with tools such as ESABASE2 and NASA MEM 3. Also the 3D adaptability must be addressed in oder to make possible to build replacement components in situ.  The cultivation surface can be enhanced to improve production and satisfy almost totally the caloric necessities of astronauts. This can be done by including different types of species like potatoes, crops, beans and soy. However more scientific experiments are necessary to explore the possibility for this species to grow in low and microgravity environment. Other food sources can be added, such as insects to be raised in a separate and optimized environment. For example it was demonstrated that tenebrio molitor can grow in such an environment and can be used to produce high protein flour without much psychological inconvenient. It is also believed that the exposition of this species to UV wavelength can increase the content of D vitamin of the produced flour, which is an important and currently missing micronutrient in astronauts’ diet. It is also possible to deepen the concept of a photobioreactor to grow some specific species of microalgae that can be used both as a nutrition element and as a CO2 – O2 conversion system. Other aspects that still has to be developed are the detailed design of the structures which also depends on the deployment environment of the greenhouse and the detailed design of the systems, specifically the aeroponic system, together with more detailed analysis of the vegetables growth in the described conditions.

For our study some tools were used such as Matlab environment and Solidworks for the CAD models.

We took some data from NASA and ESA materials. The book “Human Adaptation to Spaceflight: The Role of Food and Nutrition (Second edition)” helped us to understand the problems related to the space nutrition and the oxidative damage. The dimensions of the module were established based on the data reported for the Artemis missions and NASA SLS data sheet. The general design was also inspired by the MELiSSA module of ESA described by C. Zeidler et al. Some data on the lunar south pole illumination environment were taken by the article of J. Fincannon who studied the data of Clementine mission. We took inspiration from the TransHab mission to obtain a general idea about the composition of the shield and its numerous layers.

This experience allowed us to engage in a beautiful project, very stimulating even if hectic. The challenge was chosen for passion by the whole team, being a challenge of the present that we hope we can win soon. We think that our strength was collaboration and the desire to get involved, which was fundamental in the moments we stopped. However, the challenges do not scare us and thanks to teamwork we were able to move forward. We learned that we should have read a botany book and that we should eat more vegetables. The whole team thanks Space apps Challenge for the great opportunity, especially Raffaella because she spent two days talking about Space.

o   {1} A. Bychkov et al., “The current state and future trends of space nutrition from a perspective of astronauts' physiology”, International Journal of Gastronomy and Food Science

o   {2} “Diet, nutrition and the prevention of chronic diseases”. Report of a Joint WHO/FAO Expert Consultation. WHO Technical Report Series, No. 916. Geneva: World Health Organization; 2003.

o   {3} M. Smitt et al., “Human Adaptation to Spaceflight: The Role of Food and Nutrition (Second edition)”, NASA

o   {4} https://www.jpl.nasa.gov/news/what-looks-good-on-paper-may-look-good-in-space

o   {5} M. Di Capua et al., “Design, Development, and Testing of an Inflatable Habitat Element for NASA Lunar Analogue Studies”

o   {6} SLS June 2018 Fact Sheet

o   {7} https://www.internationaldockingstandard.com/

o  TransHab Nasa.pdf

o   E.L. Christiansen, “Meteoroid/Debris Shielding”, NASA Johnson, Space Center Houston, Texas

o   E. L. Christiansenet al., “Flexible and Deployable Meteoroid/Debris Shielding for Spacecraft”, 1999, International Journal of Impact Engineering, Vol. 23.

o   L. Narici et al. “Performances of Kevlar and Polyethylene as radiation shielding on-board the International Space Station in high latitude radiation environment”

o   Food Data Central, U.S. DEPARTMENT OF AGRICULTURE

o   https://farmtek.wordpress.com/2016/05/25/sizing-a-hydroponic-system/

o   D.B.J. Bussey, “Illumination conditions at the lunar south pole”

o   J. Fincannon, “Lunar South Pole Illumination: Review, Reassessment, and Power System Implications”

o   C. Zeidler et al, “Greenhouse Module for Space System: A Lunar Greenhouse Design”, Open Agriculture

o   L. Urbinati, “Inflatable Structures for space applications”

o   “NASA Technology Roadmaps”, NASA, 2015

o   “NASA Systems Engineering Handbook”, NASA, 2007

o   “Cislunar Habitation & Environmental Control & Life Support Systems”, NASA Advisory Council Human Exploration & Operations Committee, 2017

o https://ntrs.nasa.gov/api/citations/20050182969/downloads/20050182969.pdf

#polymodular #storage #inflatable #vegetables #greenhouse #aeroponics #lunar #space #mars

This project has been submitted for consideration during the Judging process.