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Throughout human history, food and nutrition have been key determinants in the success—or failure—of exploration missions. The National Aeronautics and Space Administration (NASA) is planning missions that will put the first woman and next man on the moon this decade and will send humans to Mars next decade. Greater propulsion capability is needed to supply missions as distance from Earth increases and planetary physics makes regular resupply unfeasible. Hence, providing food and nutrition becomes a significant challenge. The 20th anniversary of continuous human presence on the International Space Station (ISS) is approaching. NASA has provided a safe food system for astronauts on 4- to 11-mo missions in low-Earth orbit. However, limited water, storage, crew time, and food preparation capability (e.g., add water, heat) restrict the crew to a limited choice of shelf-stable, single-serving food products either in their natural form or preserved by dehydration, retort thermostabilization, or irradiation. Astronauts select ∼20% of their food items and beverages, whereas ∼80% of their diet comes from a shared, standard set of foods. Resupply vehicles arrive several times a year, bringing some fresh fruits and vegetables and some semi-shelf-stable specialty items. Astronauts report that these deliveries provide profound psychological benefits. The degree to which these intermittent deliveries stave off nutritional deficiencies is not easy to quantify because the variety and amount of fresh fruit and vegetables vary, and they are shelf-life limited to a few days or weeks. Although Apollo astronauts reported hot water to be “essential and non-negotiable” on ∼10-d lunar missions (1), resource constraints on upcoming lunar missions may preclude hot water or a food warmer for at least part of the mission. Food mass and volume will be highly constrained, despite frequent and intense lunar walks increasing energy expenditure and limiting available time to eat. Concerns arise as to whether a limited diet of cold foods for up to 8 d will affect intake, performance, and morale and if these may risk accomplishing mission objectives. Requests to reduce the mass of the lunar food system by ∼10% led to “meal replacement bars” intended to replace the calories and nutrients of a meal (∼750 kcal). One test of these bars in a 30-d closed-chamber study found reduced food intake and behavioral implications in high-performing individuals (2). Developing a food system for Mars missions will be tremendously more challenging than for lunar or ISS missions. A likely Mars mission has crews spending 6 mo speeding away from their home planet: a journey analogous to an ISS trip but without the occasional deliveries of fresh foods. This journey ends with the crew spending 18 mo on the surface of Mars with no possibility of resupply or emergency return, and then the crew will embark on a 6-mo return journey to Earth. The psychological impact of watching Earth get smaller and communication with Earth taking longer is daunting, as are the effects of radiation, microgravity, isolation, and confinement (3). Food is the one countermeasure to physiological and behavioral decrements that we know will be on board—the question is, can we optimize the food system to mitigate negative consequences of the space environment while minimizing resource utilization and maintaining food palatability throughout the mission? Although many food systems exist on Earth, the ability of these to meet spaceflight demands has not yet been established, and their feasibility within cost and schedule limits remains unclear. Although often considered a secondary issue to get to Mars, we highlight here the extensive challenges of developing a food system for space exploration. Even if the rocket and engineering systems work perfectly, if the food system fails to meet any of these criteria, the journey will have the same epilogue as many other expeditions that never even left the home planet but went horribly wrong solely because of food and nutrition system failures. Historic polar expeditions were devastated by insufficient (thiamine and vitamin C) or excessive amounts of vitamins or minerals (vitamin A and lead) in the diet (4, 5), some of which were directly related to advances in food preservation at the time (6). In short, and as highlighted in Figure 1, any space food system must meet basic criteria: Safety. It is paramount that we understand and minimize any food-associated risk to astronaut health and to the vehicle. The ISS food system undergoes extensive ground processing and testing to minimize the risk of food poisoning. Foods grown in the spacecraft will have microbiological testing and cleaning requirements, as well as introduce waste streams into the habitat air, water, and waste systems. Current microbiological and nutritional analyses require substantial resources and waste-processing capacity that will not transfer as is to the resource-restricted spacecraft. Stability. Current designs for Mars missions require food system stability (and/or ingredients and equipment) through at least 5 y of storage. While the use of refrigerators and freezers is possible, inclusion of this equipment will have to be considered against mission volume, mass, and power constraints. No food system to date has been devised or tested or has demonstrated it can provide adequate acceptability and nutrition for 5 y, let alone one that also meets the restricted mass, volume, and storage in the hostile spaceflight environment (e.g., radiation exposure, temperature extremes). Palatability. A food system could meet all requisite criteria, but if it is not palatable, it will not be consumed in adequate amounts to support health, performance, and morale. A common misperception is that high-performing individuals, such as astronauts, will consume whatever is required to successfully complete a mission. The astronauts must be willing and able to prepare and consume the foods available for the duration of any mission, and familiar and acceptable food becomes even more important as duration, distance, and isolation increase. Like Earth-bound humans, astronauts require enjoyable foods that the average person would want to consume day after day and that are easy and quick to prepare after spending long hours at work. The military understands the importance of food. Where a mission to Mars will last about 1000 d, the military limits the use of meals ready to eat to 21 consecutive days (7). Multiple factors influence loss of body mass in extreme environments, including food acceptability and menu fatigue. During spaceflight, loss of body mass is associated with musculoskeletal losses, cardiovascular deconditioning, and increased oxidative stress (8). Nutrition. The greatest number of fatalities and mission failures in the history of human exploration on Earth were due to food system inadequacies, such as deficiency of one or more nutrients, insufficient caloric supply and underconsumption, inadequate preservation, or even nutrient toxicities (9, 10). Modern nutrition and food science has prevented these issues on space missions to date, but exploration beyond low-Earth orbit will bring new unknowns. In addition, meeting minimal nutritional requirements may only prevent deficiency, whereas an optimized system (such as one including a variety of fruit and vegetables and associated bioactive compounds) has the potential to promote health and performance (11, 12). Resource minimization. All resources used (e.g., mass, volume, crew time, water, power, equipment) and all waste products created (e.g., waste water, packaging, volatiles, biological waste) by a food system are weighed against the amount and variety of acceptable, nutritious food available for astronauts. Mission planners, with input from health and medical specialists, will determine the health and performance support systems (e.g., food, exercise, medical) within the larger mission and vehicle resource constraints. Variety. Type, texture, and flavor of food all add variety. A combination of systems (e.g., prepackaged, grown) may be needed to avoid menu fatigue. Even a “perfect” food item, ingredient, or nutrient source cannot provide an entire food system (i.e., it cannot be consumed for every meal). Reliability. As is the case for loss of other systems of a space vehicle, if part or all of a food system is lost, the result could be catastrophic. This could happen if in situ foods do not grow adequately or if equipment malfunctions. All systems must also be validated in real or simulated extremes of the spaceflight environment (e.g., pressure, gravity, temperature, radiation). Usability. The food system must be easy and fast for the astronauts to prepare or produce food. Exploration missions will have very different goals from colonization missions. Crews of the initial missions will focus on exploration and science, and on these missions, astronauts will prepare food as the average person would in their kitchen after a long day of work. Ideally, astronauts would cook using bulk ingredients, but spacecraft technical considerations can make this difficult, including touch temperature limits (to eliminate the risk of burns), safety concerns, and technical challenges with containing and processing ingredients. In addition, food preparation could require resources and processes for cooking and cleanup different from those used in Earth's gravity. Development and testing of such systems must account for the realities and constraints of spaceflight while minimizing resource use. Labor- and resource-intensive food systems may be more feasible during colonization missions than during exploration missions. Space-ready appliances. To date, space food systems have only allowed astronauts to add water and/or warm food (i.e., not cooking). Food preparation equipment had to be specially developed to meet safety (e.g., touch temperature limits) and spaceflight requirements (e.g., microgravity, cabin pressure changes, radiation), often adding mass. New equipment will need to be developed for Mars class missions. Requirements of space food systems. A depiction of the many facets of and requirements for space food systems. As described in the text, each element is critical for the ultimate success of a space mission, and failure of any aspect could imperil the mission and the crew. The moon and Mars are also depicted here, reflecting two likely destinations for future human space exploration. Requirements of space food systems. A depiction of the many facets of and requirements for space food systems. As described in the text, each element is critical for the ultimate success of a space mission, and failure of any aspect could imperil the mission and the crew. The moon and Mars are also depicted here, reflecting two likely destinations for future human space exploration. In the history of humankind, explorers set off to see what was over the horizon, and literally millions did not return because of food and nutrition failures (6). The harsh reality remains: if we are going to send humans to the moon and Mars in the coming decade(s), work needs to be accomplished now to ensure the food system fits within the constraints of space vehicles and sustains and protects astronauts. We are among those working to understand and mitigate these risks, and we offer this information to others who are hoping to solve food and nutrition challenges for spaceflight. We must ensure that the next giant leaps in space exploration are well nourished. All authors (GLD, SRZ, and SMS) contributed equally to the design and writing of this manuscript. All authors have read and approved the draft and final versions of the manuscript. We thank NASA for support of our work. We thank Cindy Bush for the graphic. Author disclosures: The authors report no conflicts of interest. This work was funded by NASA, in the form of employment of the authors either directly (GLD, SMS) or through the Human Health and Performance Contract (SRZ). Abbreviations: ISS, International Space Station; NASA, National Aeronautics and Space Administration.
Douglas et al. (Mon,) studied this question.