Abstract

Deep space manned missions is a goal that has regain thrust in recent years from governments and private industries. New orbital space stations for Earth and Mars, as also manned surface exploration of the Moon and asteroids, and even permanent settlements in Mars, are under the plans of public space agencies and private sector companies [1]. To accomplish these endeavors, sustainability in the broad sense of the concept must be addressed as a key issue for these missions to be successful. Until now, except for the relatively brief Apollo Moon missions during the ‘60s and early ’70s, all manned missions have been performed in Low Earth Orbit (LEO), where food, spare parts and other necessities, can be satisfy with short resupply missions from Earth. This will be no longer feasible in practical terms for deep space missions, where the time-frame between each launch window, costs and even political factors, can put in jeopardy the whole mission, including the crew and the expensive infrastructure invested. In fact, these costs and risks are among the most critical aspects that currently halt the exploration of deep space [2]. To achieve sustainability in long-term manned deep space missions, the In-Situ Resources Utilization or ISRU must be considered along the goals of each system, including: life-support, food production, spare parts, building blocks and many others. It must also be considered that full sustainability, understood as complete independence from Earth resupplies, will be achievable progressively, partial sustainability is preferred over complete dependence from Earth, since it will simplify the amount and type of supply essentials required to be send, overestimates can be apply to foresee possible future supply cuts, reducing overall risks for the mission. Therefor is clear that a critical factor to achieve sustainability lays into develop manufacturing capabilities “on-site” or even “on-flight” as a way to use this local, as also initially imported resources, to produce what the mission requires. Along the manufacturing technologies that have proved efficiency in terms of the use of materials are many of the additive technologies in use today, like fuse deposition modeling or FDM which was already tested under micro-gravity conditions on board of the ISS [3], this presents a great opportunity to research and development solutions in these regards [4]. The last can be that case of future orbital space station or surface settlement on Mars, where many, but perhaps not all the elements necessary to sustain life in long terms can be obtained in an efficient or practical way from the atmosphere or soil resources. The use of FDM machinery, among other technologies, could manufacture from In-Situ resources, plus materials from resupply missions from Earth, most, if not all, the necessary components to sustain and even extend life beyond our planet. Earth resupply missions could have less schedule restrictions, providing higher amounts of fewer types of raw materials instead of small amounts of many specific spare parts or components. To address the issue of sustainability of food production for deep-space stations and surface settlements, as in Mars future missions, the whole process must be designed to be optimized for those exigencies, considering the optimal way to use the available and imported resources. Hydroponics growth systems, have been proved to work in micro-gravity environment, as also experimental growths have been produced using Moon and Mars soil simulants with good results [5], although additional analysis are required to discard potential secondary effects on the human body of the food produced [3]. During the research, FDM technologies would be implemented to develop a hydroponic system able to produce growth of certain target eatable plants (three types), in conditions similar to a space station environment (atmosphere gases composition, temperatures, among others.), as also using as much Mars resources as possible (soil simulant, habitat gas composition), and finally also with a control group growth under normal conditions (organics will be added). The solution would incorporate all the necessary components to assembly the system itself as also to expand it (plant pods, tubes and connectors, supports, etc.), where the pods will be develop to optimize the growing of specific plants using special patterns that could improve the root density as also help with the plant health conditions in general. In terms of materials, just in recent years engineering thermoplastics has become available to FDM machines due the high temperatures involved to make them manageable, previously this plastic was only available for traditional injection molding process and high end 3D printers that use it in form of pellets. The advantage of this is that with engineering thermoplastics is possible to not only produce prototype part, but also parts ready to use, that not only are strong, flame retardant, chemical resistant and approved for human use, but also many of them have space flight inheritance [6]. This will allow to produce strong and resistant parts that could be reused a number of times in manned space mission, as also among other things, fulfill specific requirements of a hydroponic growing system, like sterilization of the pods, implementation of protection mechanisms for the plant (pressure lost, dropping temperature). A hydroponic growth system for deep space mission should also consider the use of sensors to detect the state of many parameters of the environment (soil pH, humidity, arsenics, heavy metals, temperature, gas mix), as also the process to install and use in an efficient and safety way this components by the crew. The crew should be able to communicate with the system as also set parameters and receive alerts; schedule requirements for system maintenance must be reduced as much as possible to optimize crew time into other activities. Electronics components will be more likely a supply to receive from Earth for a long time, although at least theoretically they could be produced from Mars surface and atmosphere resources on the long run [2], but for now the technology to manufacture high density electronic is too delicate to be consider possible to implement outside Earth. Nevertheless, the system must target been able to be used even without any electronic component in a complete manual way. Along the potential available materials, many new magnetic and conductive filaments are becoming available also for FDM machines; these materials will be incorporated under the research to target the implementation of 3D printed embedded electric paths that could facilitate the installation of sensors, lights, heater, screens and control boards into the system. Understanding that the crew safety will be always one of the most critical aspect to consider in any space mission, we must consider that many traditional manufacturing technologies like soldering in electronics will be prohibits or widely restricted due to the risk of the task that usually involve high heat to melt the solder. Potentially with this magnetic and conductive filaments, heaters and conductive path could be printed embedded with the hydroponic system parts, in that way the crew after print for instance the pod for a plant, can easily just snap-into place sensors, screens or many other electronics, reducing installation risks and time as also improving reusability of those components. The production of polymers for many thermoplastics is technically feasible using Mars resources [2], nevertheless at least in initial stages, it seems more optimal to send raw polymer materials in the form of filaments that can be later also be recycled and used again on site. New models, adaptations or improvements on the system can be made on Earth and send it, or be made by the crew itself to be later printed. The research will incorporate current and new hydroponics methods that could be implemented using FDM additive technologies and engineering thermoplastics as PEEK, PEI, PES and PPS, studying their performance and then comparing the results of the control group with the growths of 3 specific eatable plants under specific space station environmental conditions as also with simulated Mars resources. The research will also incorporate a time study for the system schedule requirements as also a safety study for the manufacturing, installation and operation of the hydroponic system as a whole. The research will closely follow the efforts from NASA to develop standards for certification of additively manufactured parts [7].