This benefit results from reducing the launch mass cost of complete nitrous oxide –hydrocarbon propellant delivery.However, as described in §S3, the overall mass and time costs render nitrous oxide –hydrocarbon bio-manufacture impractical for now.It is expected that near-future space synthetic biology efforts on methanogenic bacteria will concentrate on minimizing nutrient use and improving bioreactor nutrient recycling percentages, rather than increasing productivity.This is due to the already high methane purity and production rates that have been previously reported in the literature.Because the analysis in §3.2.1 indicates that significant reductions of production-plant mass are possible and that a bio-manufacture time that is less than half of Mars residence time can be realized, it is feasible to trade-off a portion of these mass and time savings for greater nutrient efficiency.This may require directed evolution experiments, where selection for high methane production is conducted, whereas the bacteria grow in reduced or minimal media and in conditions that emulate anticipated nutrient recycling processes.Future solutions to the biological space production of nitrous oxide–hydrocarbon could include the following approaches.The first involves synthetic biology improvements to methanogenic bacteria and cyanobacteria to enhance ethane production and bypass the acetate intermediate.The cited references describe bacteria that are capable of producing small quantities of ethane under various conditions: in the case of methanogenic bacteria, when incubated under hydrogen,hydroponic dutch buckets exposed to halogenated hydrocarbons or stimulated by reduced, ethylated sulfur compounds, and in the case of cyanobacteria, when vanadium and iron nitrogenases reduce acetylene.

As indicated by Lee et al., the vanadium nitrogenase can yield ethane and propane by reducing carbon monoxide, and it has also been shown that remodelled nitrogenase can reduce carbon dioxide to methane and be coupled to the reduction of other substrates.Thus, two possible synthetic biology investigations are the following: the reduction of carbon dioxide to ethane in cyanobacteria with the vanadium nitrogenase , or the reduction of carbon dioxide to ethane in cyanobacteria with the remodelled nitrogenase.A second similar potential synthetic biology development involves increasing the cyanobacterial production of ethylene with a carbon dioxide substrate from the current experimental maximum rate of 171 mg per litre per day in SynechocysThis sp.PCC 6803by a few orders of magnitude, because ethylene is an alternative hydrocarbon that can be blended with nitrous oxide.Lastly, synthetic biology refinements of glycogen-accumulating organisms to accomplish both nitrification when in oxygen as well as anaerobic denitrification to nitrous oxide are desirable.References and specify a rate of 1.83 kg of required food mass per crew member per day based on current ISS food container provisions, resulting in a total of 10 058 kg of similarly prepared food that needs to be shipped for the entire long-stay Mars mission.More accurate complete-meal ‘wet-food’ numbers can be obtained by scaling up the recent detailed mission results in from 600 to 916 days.This process suggests that 10 403 kg of vegetarian food without packaging is necessary for the complete Mars voyage, with 5861 kg of this amount coming from local crops at a food cost of 4542 kg in shipped mass.An alternative varied or ‘mixed’ menu results in a total of 9537 kg of required food without packaging, of which 4542 kg is grown locally and the remaining 4995 kg of bulk commodities, minors and prepared foods constitute the shipped food cost.Thus, the expected wet-food cost of a Mars mission is between 4.5 and 5.0 T.A proportional estimate for a Moon mission puts the cost at between 0.62 and 0.68 T of shipped, unpackaged wet-food.Over the course of 706 days of Mars stay and return travel to Earth for six crew members, the approximate mass cost can be calculated to be 3501 kg of vegetarian unpackaged wet-food, or 3850 kg of mixed unpackaged wet-food.

If the switch is made during these 706 days to dry-food biomass, all of which would be produced on Mars during the 496 day residence on the planet, only 0.617 kg of completely dehydrated biomass is required to be consumed by a crew member per day.This implies that 2614 kg of nutritious biomass has to be generated on Mars and analysed for shipped mass cost.A similar switch during a four-person lunar mission upon Moon arrival necessitates the generation of 453 kg of nutritious biomass, the cost of which must be compared with costs of either 607 kg of vegetarian unpackaged wet-food, or 667 kg of mixed unpackaged wet-food.The chief food- and glucose-producing biological options are autotrophs like photosynthetic bacteria and plants.Fortunately, these organisms primarily require only those elemental and compound resources that are readily available on lunar and Martian missions.The case for using photosynthetic bacteria as an extraterrestrial food production option is effectively made in the comprehensive papers, where the nutritionally rich Arthrospira platensis and Arthrospira maxima are identified as a competitive option to plant-based space farming.Here, we compute the potential savings espoused by these works.Spirulina is currently experimentally produced at about 1gl21 d21 of dry weight biomass in a closed bioreactor.With three 2000 l bioreactors each having a working volume of 1757 l, it is possible to produce 5.271 kg of Spirulina per day.Over 496 days of Mars residence, this rate resultsin the production of the entire 2614 kg amount of nutritious Spirulina biomass that must be generated for use by six crew members during their stay on that planet and on the return journey to the Earth.Assuming nutrient extraction from the Martian environs as well as complete nutrient recycling , the mass cost of the food-producing bioreactors is 2382 kg.This computes to a saving of 32% over the mass cost of vegetarian unpackaged wet-food, and 38% over the mass cost of mixed-menu unpackaged wet-food.The bioreactors will draw 12.687 W of power and require a volume of 14.844 m3.A single 2000 l bioreactor producing 2 kg of Spirulina per day generates 360 kg of nutritious biomass over 180 days, which is 79% of the amount that is required for a four-person lunar stay and return voyage.However, the mass cost of this bioreactor, at 794 kg, exceeds the mass costs of wet-food provisions.

Assuming local nutrient extraction and nutrient recycling , the current break-even bioreactor mass cost of 611 kg for a 1000 l bioreactor and a 50 l bioreactor results in the production of 189 kg of biomass over 180 days, or about 42% of the requisite amount.If a lunar habitat becomes continuously manned similar to the ISS, then it should be possible to realize the savings of scale as on a Martian mission, and astronauts will be able to subsist primarily on Spirulina.The preceding lunar analysis indicates that space synthetic biology efforts in food production should target increases in the Spirulina biomass productivity rate, without which only a proof-of-concept demonstration of nutritious biomass generation for astronaut consumption on the Moon is advised.A productivity rate increase from 1 g l21 d21 is possible because of reports of 50 –100% higher Spirulina volumetric yields when employing tailored conditions and reactors: 2.1 g l21 d21 on elevated plates and 1.5 g l21 d21 in tubular photobioreactors.Of course,bato bucket eating solely dehydrated biomass for 706 days during a Mars mission would be extremely trying for astronauts, given their evolving palatability preferences and their need for sufficient menu variety.Hence, the motivation for synthetic biology techniques to not only improve the nutraceutical rate of cyanobacterial fixation of carbon dioxide, but also to enhance and diversify the flavours and textures of generated biomass, along the lines of.These techniques are better than simpler food processing approaches because they also offer the opportunity to incorporate healthful bio-active peptides that can prevent cardiovascular disease, inflammation, cancer, etc..The goal of flavour and texture enhancement is reminiscent of efforts to produce ‘yeast meat’ in the 1960s with myco protein from Fusarium venenatum A3/5 that were so successful that current yield rates of 300–350 kg of biomass h21 of Quorn are possible.However, Quorn production is significantly less energy efficient than that of Spirulina.Likewise, in vitro meat production has recently recaptured the public’s imagination with the announcement of a synthetic burger made of cultured beef.But, there is still a lot to be desired ‘with respect to taste, look, mouthfeel and nutritional value’, and also ‘fat content, protein composition and…larger fibres or full-thickness cuts of meat’.Case studies for additive manufacturing in space include that of habitat construction.A crude indication of the cost of three-dimensional printing a habitat is available via, which estimates that 3.8 T of dry salts must be shipped to the Moon to be mixed with regolith containing 9.6% MgO and locally excavated water to make ‘ink’ to construct 6 m3 of habitat encompassing 40 m3 of volume.Once associated printer and construction support material is included, the total launch mass for printing a habitat increases to about 8 T.Because the suggested minimum habitat volume is 20 m3 per crew member for missions lasting longer than four months, with a recommended habitat volume of 120 m3 per crew member for long-duration missions, the cost of three-dimensional printing a four-person habitat for a Moon mission computes to between 16 and 96 T of shipped mass, of which between 7.6 and 45.6 T is dry salts, i.e.printer feed stock.The respective habitat structure volume is between 12 and 72 m3.An approximately equal concentration of MgO in the Martian soil as the lunar regolith puts the shipped mass cost for a six-person Mars mission at between 24 and 144 T, of which between 11.4 and 68.4 T is dry salts.The respective habitat structure volume is between 18 and 108 m3.The results of the stereolithographic habitat construction process of Cesaretti et al.can also be accomplished with a three-dimensional printer that extrudes plastic media using fused deposition modelling.A comparison of the different additive manufacturing methods and possible feed stocks is included in, which explains why FDM is preferred over stereolithography for space applications.

To determine the existence of launch mass savings for three dimensional printed habitats from biological processes, this section examines the extraterrestrial manufacture of feasible three-dimensional printer raw materials like polyhydroxyal kanoate biopolymers, of which polyhydroxybutyrates are an example.A contrast of habitat structural properties when using either salt-MgO or biopolymers as printer media is beyond the scope of this paper.The bio-manufacture of PHAs is reviewed in, and Lu et al.include a list of organisms known to synthesize PHAs.It has been reported that PHA levels in bacteria can be accumulated as high as 90% of the cell dry mass, with such accumulation typically acting as a carbon and energy storage mechanism in times of nutrient stress.Thus, it is feasible to alter the biological space production of a commodity during times of minimal need of that commodity by stressing the organisms involved in the process so that they synthesize biopolymers instead.This twin-manufacture intent serves to reduce the bioreactor and feed stock mass costs that would otherwise be incurred with producing PHA separately.An example of an organism that is a candidate for the production of two commodities is the food-producing cyanobacterium of §4.2, A.platensis, which can currently accumulate PHB at up to 10% of the cell dry mass when starved of nitrogen.In some cases, PHA synthesis occurs as an interim stage of the bio-manufacture of another commodity, as for instance with the nitrous oxide-producing GAOs of electronic supplementary material, §S3: GAOs use acetate and consume their glycogen to synthesize PHA, which is then harnessed to replenish glycogen and produce nitrous oxide.Interruption of nitrous-oxide production yields PHA, and this dual manufacture possibility enhances the promise of GAOs.There exist organisms other than GAOs that take up acetate to produce PHA, accumulating as much as 89% of the cell dry mass within 7.6 h.Because acetate bio-production in space is time-consuming , we are interested in organisms that can directly convert carbon dioxide into PHAs, such as those described in.One such organism is the autotroph C.necator, also known as Ralstonia eutropha, which is well studied and can accumulate the largest percentage of cell dry mass as PHB from a C1-type substrate [131].A PHB production of rate of 1.55 g l21 h21 , i.e.37.2 g l21 d21 , has been reported for the organism while it was supplied with hydrogen and tested in the presence of a low volume of oxygen.