What food will we be eating on our journey to Mars?

Abstract The aim of this review is to show the possibilities of food production during space travel and to demonstrate the potential of technological solutions that can play a significant role in achieving the goal of colonizing other planets. The paper briefly outlines the conditions of space flight and the associated possible threats that may occur. It is assumed that the basic problem is cosmic radiation, which not only can significantly affect the health of astronauts, but also prevent potential cultivation of plants or animal breeding on board a spacecraft. The solution to this problem proposed here is a shield which provides protection against collisions with high kinetic energy particles, while reducing the speed of corpuscular radiation. Particular attention is given to various biotechnological and bioengineering methods that could be used for food production on board a spacecraft. Technological development in the field of bioprinting or genetic modification of organisms may play a key role in the success of long-distance technological missions. Moreover, organisms such as algae, fungi and insects are indicated as a potential source of energy for future colonizers. In sum, the review covers both the field of engineering and biotechnology, as well as the possibility of checking these technological methods in the test flights.


Introduction
Once the first artificial earth satellite was launched in 1957, and the first human flight into space took place in 1961, preceding the first flight to the Moon less than ten years later, a fashion for space flight planning and colonization had begun all over the world. Salut 1 was already the first space station to orbit the Earth in 1971, and since 2001, the International Space Station is being established. The next step is the colonization of celestial bodies other than the Earth. Interplanetary travel, however, is associated with much greater danger than all previous space missions. It is, therefore, necessary to analyze the risk of space flights beyond the orbit of the Moon. The experience of nearly 60 years of space flights shows that all flights so far have relied on supplies taken from Earth. However, the calculation of the necessary supplies for flights reaching further than the Moon shows that it is imperative to analyze potential new food sources for the crews. Complete nutrition is crucial to maintaining the health of the crew during and after space flight [1]. Previous space missions and research show that finding solutions to provide astronauts with wholesome meals that will allow them to maintain their physical condition should be an important point of the entire mission.
In this respect, food production methods closely related to bioengineering and biotechnology can prove extremely helpful. Alternative food sources seem to be the best solution for providing astronauts with nutrition. The methods discussed in this paper may additionally contribute to the health of astronauts. It is believed that many of the examples presented below are healthier alternatives to the products we know. For example, eating insects provides the human body with more calcium, zinc, copper, vitamin C and magnesium than when eating meat [2].
The journey to the Red Planet, which will last many months, is associated with high costs. For this reason, efforts are being made to turn it into as economical an endeavor as possible. Without a doubt, one of the biggest expenses is feeding the astronauts. Although the simplest solution seems to be to eat freeze-dried food prepared on Earth, it is not the most efficient option, because a trip, for example to Mars, will take much longer than a trip to the International Space Station or the Moon. This paper reviews various projects for food production on board of a spacecraft and ideas for reducing the risks associated with space missions. This course of action will not only enable the reduction of expenses related to a colonization mission but also gives hope for a potential terraforming of the Red Planet and enabling people to live there for longer periods.

Space flight conditions
The Sun is the largest object in our solar system. It is a spectral type G star, i.e. a star whose photosphere has a temperature in the range of 5000-6000 K. The sun radiates both electromagnetic and corpuscular radiation. This is the solar wind, or proton-electron plasma [3]. Other elements of the sun's activity are solar flares in its atmosphere [4], as well as coronal mass ejections that throw plasma clouds into the interplanetary space of our solar system at speeds of up to 2000 km/s [5]. They cause, among others, the destruction of power grids on the ground. Moreover, in outer space, there is cosmic radiation, electromagnetic radiation and high-energy elementary particles from outside our solar system [6]. These phenomena are deadly to the human body. Even a spacesuit does not offer complete protection in open space. Dangerous events have already taken place on the moon. The phenomenon of the coronal mass ejection in the sun, which occurred in 1989 (esp. on March 13-14, 1989 [7]) caused massive damage to the power network in the Canadian province of Quebec [8]. Such events are a risk to the life of an astronaut [9].
Another threat is interplanetary dust. These are elementary particles with a size of about 10 −8 m to about 10 −3 m (0.01-1000 µm) [10,11]. They cause surface corrosion. Larger objects-meteoroids, i.e. rock crumbs with a mass from 6-10 to 103 kg and a conventional diameter from 10 −4 m to 10 m [12]-cause collisions and penetrate the entire cross-section of the spacecraft, which may cause rapid de-pressurization and death of the crew. Thus, it is necessary to analyze both what we can eat and how to protect ourselves if we want to plan a human mission to Mars.

Nutrition projects in space
Currently, NASA classifies food consumed by astronauts into the following categories: A/S Artificial Sweetener, (B) Beverage, (FF) Fresh Food, (IM) Intermediate Moisture, (I) Irradiated, (NF) Natural Form, (R) Rehydratable, (T) Thermostabilized. Although the astronauts' menu includes products such as Carrot Sticks (FF), Celery Sticks (FF) or Shortbread (NF), Crackers and Butter (NF) [13], the astronaut menu is currently based mainly on dehydrated products.
The main requirements when designing packaging for space food are minimizing the weight, volume and potential amount of 'waste' . For this reason, water-free products seem to be a very economical solution.
To diversify the diet of astronauts on a spacecraft, there are also intermediate moisture foods, in which water is only 15-20 percent [82]. Although these two categories are the main types of food eaten outside the Earth, sometimes astronauts also consume frozen, fresh, thermostabilized and irradiated foods. By using alternative techniques, however, it is possible to increase the variety of product types. In addition, the ability to manufacture products on board the ship would eliminate the need to transport large amounts of food from Earth.
The modern developments in botany and agriculture, as well as fields such as biotechnology, bioengineering and genetics, offer opportunities to achieve these goals. Modern technologies rely on the hope that living on a foreign planet and traveling there for many hours will be possible. Below, a variety of ideas that, over the years, have been proposed as potential options for feeding astronauts will be presented.

Fungi and mycoproteins
Although advanced technology such as bioprinting or in vitro methods is necessary to produce food on a spacecraft, it is worth analyzing and describing in detail the organisms that could play a key role in the nutrition of astronauts. It is believed that fungi should be introduced into the diet. In addition to containing important nutrients, they play an important role in the production of compounds such as antibiotics [14], vitamins [15] and enzymes [16]. Additionally, the mycelium can be used for water filtration and biomining systems [17]. Cloning techniques that emerged in the second half of the twentieth century also made it possible to produce products from fungi such as bioethanol and biofuel [18], which could play an important role in the production of rocket fuel for future colonies on Mars. Moreover, microorganisms such as bacteria, fungi and actinomycetes [19] can recycle organic matter. This ability can be used to transform organic waste into feedstock [20]. That method could solve the problem of storing waste on board a spacecraft. For example, Aspergillus awamori and other Aspergillus sp. can be used for the utilization of bread and bakery waste [21]. Therefore, fungi can play an important role in the degradation of pollutants during space travel. So far, the best candidate for long space travel seems to be the species Aspergillus niger [73]. It is used both in the food and pharmaceutical industries, as well as to produce textiles, plastics and flavor enhancers [22]. Moreover, during the digestion process, this microorganism produces biopolymer (e.g. cellulose, pectin) hydrolyzing enzymes. These, in turn, can be used to produce other enzymes. However, A. niger has gained popularity in the space industry not only due to its wide range of applications but also due to its high resistance to climatic conditions. It can grow at temperatures ranging from 10 °C to as much as 50 °C, with a pH ranging from 2 to 11, and in nutrient-poor soil. The research carried out so far on the International Space Station also shows that this fungus can withstand the conditions of low gravity and cosmic radiation. Despite the many advantages of A. niger, the production of food from these organisms on board a spacecraft also carries a potential risk. These micro-organisms can spread very quickly, and human inhalation of their spores can trigger various undesirable reactions, including respiratory infections [74], sleep disorders or damage of the immune system [23]. This, in turn, suggests that the process of biosynthesis and isolation on board a spacecraft must take place in properly adjusted conditions that will prevent the spread of dangerous spores. It is believed that the use of standard operating procedures (SOPs) should protect astronauts from this particular danger [73,74].
In the context of fungi, it is also worth paying attention to Quorn, i.e. a meat substitute made from mycoproteins [24,25] obtained from Fusarium venenatum mold. Growing this species in culture would save money by eliminating the need for the hypothetical transport of farm animals. Interestingly, consuming mycoproteins instead of meat reduces the risk of heart attack and diabetes (Denny A. et al. 2008). unfortunately, the production of food from this species is quite difficult. First, the fungus has to be grown in water-based medium, which means one will need to use hydroponic methods. The more troublesome step in the production of Quorn, however, is that the fungal biomass has to be heated, as this is the only way to remove excess RNA. Attempts have been made to use fermentation techniques, but all attempts so far have failed [26]. It is possible, however, that if the methods related to the 3D printer were used [27,28], a separate heating step would not be required. Therefore, mycoproteins are considered a potential product that may be included in astronauts' menu in the future [29].

Insects
Invertebrates, particularly insects, are not only an excellent source of protein but can potentially be used to produce bioenergy. The topic of insects in the diet of astronauts was raised by the authors of the Eatlikeamartian website [30].
In the article 'Feeding One Million People on Mars' [31], insects are described as a potential type of food that provides high calories with low water and feed requirements. This means they can be a great alternative to meat. Insects are much more cost-effective, easier to transport and provide a more digestible type of protein than plants.
It is also believed that insects farmed on good quality forage have a much higher food conversion factor than other animals. Currently, research on making cricket flour that could be used in a variety of dishes is being conducted. This product is already available in France. The owners of Kinjao [32] offer a series of nutrients and flour made from insects. Although according to their ideas, the target group is athletes who need products with high energy content every day, the product could also be used by astronauts, and in particular future Mars colonizers.
Another company that offers insect flour is the Norwegian Acheta [33]. Its owners say that the flour they produce has 15% more iron than spinach, two times more protein and five times more magnesium than pork, the same amount of vitamin B12 as salmon, and the optimal omega ratio of 3/6. Astronauts and future colonizers of Mars would benefit from the idea of Spiselige Insekter [34]. The company produces various types of insect sweets. These include, among others, insects in chocolate and protein bars made of worms. The originators of unconventional snacks believe that the main advantage of their products is the ecological aspect of the project. Insect breeding requires about fifteen times less surface area, more than two times less water, and at the same time produces 12 times less carbon dioxide. The latter aspect may be especially important when establishing a colony on Mars [35] because the atmosphere there is so rich in CO 2 that its overproduction could make the mission even more difficult.
Naturally, in order to use insects as food for astronauts, there needs to be appropriate infrastructure. Without space-adapted terrariums, there is a risk that these small organisms will spread through the spacecraft, posing a risk to the crew. Before any insects are sent into space, it should be investigated whether they are being properly protected. Otherwise, another incident like the one that took place on the International Space Station in 2008 may occur. At that time, the larvae of fruit flies, which were in a special box, escaped, multiplying on a huge scale [84].
The production of insect flour consists of five main stages, which are described in detail in a recently published article on the use of edible insect proteins in food [36]: pre-treatment, defatting, solubilization and recovery, purification and drying. Many of these processes take place at very high temperatures. This means that the costs associated with the equipment that astronauts will need to turn insects into food can turn out to be a significant burden. Currently, attempts are underway to create a 3D printer that could do the work from turning oats into maca to making edible products out of it. Such a solution could also eliminate the potential factor that deters people from eating insects, related to the aesthetics of the dishes [37].

Algae
Algae are another excellent source of protein. They contain vitamins A, B, C, D, E, K, magnesium and beta-carotene. Their advantage is also the fact that they can produce oxygen as part of the photosynthesis process. This fact was mentioned before the flight of Yuri Gagarin in 1961, as early as 1952 by Wernher von Braun. He indicated Chlorella algae as an oxygen producer at the space station [38]. A notable project associated with this type of living organism is the so-called photobioreactor, a bioreactor powered by algae. From May 6, 2019, it is on the International Space Station, where it is currently being tested. The originators of the project are the German Aerospace Center (DLR) cooperating with NASA. The target machine is to work with the Advanced Closed Loop System (ACLS) [39]. ACLS was delivered to the International Space Station a year earlier and is used to extract methane, water, and CO 2 onboard a spacecraft. The bioreactor is to use the extracted carbon dioxide to produce oxygen and edible biomass. It is believed that the biomass produced could make up 30% of the astronauts' total food. This, in turn, would significantly reduce the cost of space missions, as it would eliminate the need of carrying large amounts of food from Earth.

GMOs
Biotechnological methods, which, although already developed in the second half of the twentieth century, still seem to be up-to-date and may prove necessary during space travel. One such approach is the genetic modification of organisms [81]. Most of the research related to GMOs (Genetically Modified Organisms) is related to the CRISPR-Cas9 technique. It allows the implantation of a specially selected gene in plant cells. Scientists from the university of North Carolina [40] are researching the possibility of implanting genes from Extremophiles into plants. These organisms show high resistance to extreme conditions. Due to their ability to survive, we distinguish several groups of these microorganisms. For the colonization of Mars, the most important will be Psychrophiles, which can live at very low temperatures, and Radiophiles, which are resistant to high levels of radiation. The characteristics of these microorganisms make scientists suspect that they would be able to survive on the Red Planet, where temperature can reach even −126 °C in winter. Moreover, since the atmosphere there is only 0.7% of Earth's and thus does not provide sufficient protection against dangerous cosmic rays, the fact that extremophiles are good at dealing with radiation increases the chances of a successful colonization mission. Special attention goes to a species called Deinococcus radiodurans [41]. Research conducted on the International Space Station proved [42] that this species has great potential for survival on Mars. Of course, the use of extremophiles will become necessary only after landing and settling on Mars. Researchers assume that on the board of a ship, the plants will not have to deal with difficult conditions. For this reason, it is important to consider the possibilities of food production during a several-month flight. The idea of solving this problem was carefully researched by students from Navarra [43]. Their goal was to allow plants to grow on a spacecraft. At the same time, they wanted to prove that drugs could be produced from the seedlings they created. Thus, the project, which was dubbed 'Biogalaxy' , became doubly important for colonization missions, as it not only provided food but also produced the necessary medicines. The project was divided into several stages. To begin with, the Aequorea victoria jellyfish were isolated. In the process, a plasmid containing information on a model protein resulting from attachment of Green Fluorescent Protein to Granule-Bound Starch Synthase was used. The gene in this plasmid was responsible for the production of recombinant fluorescent proteins. These structures created as a result of recombination of genes have many advantages [44,45,76], and they are used, among others, to detect damage of nerve cells, identify neoplastic cells, mark cell structures, organelles and proteins, as well as monitor its development. The next step was to use the Agrobacterium tumefaciens bacteria, which acted as vectors to implant the above-mentioned gene in the previously modified plant. Students believe that the process is so simple that it can be carried out even on a spaceship.
Another idea, based on a similar method, is to create genetically modified lettuce. Scientists from the university of California [46] have investigated this process. Also, in this case, the plant was not intended only to serve consumption purposes, but also to enable the production of drugs-this time parathyroid hormone (PTH). It is extremely important for astronauts, as it is responsible for bone regeneration, or more precisely, for the regulation of calcium and phosphate metabolism. Reduced gravity or lack thereof during flight is associated with a high risk of bone diseases such as osteopenia. For this reason, the project of California researchers seems to perfectly match the needs of astronauts. It is widely believed that the idea is far more efficient than getting drugs from Earth. A great advantage of lettuce producing PTH is the fact that its seeds are light and small, which is important for the success of the flight. Of course, for lettuce to be more than just food for astronauts, it must be infected with the bacterium Agrobacterium tumefaciens.
This species harbors a sequence that codes for the hormone. One of the difficulties is the need to have a centrifuge that is capable of capturing PTH. However, Karen McDonald [46], who was directly involved in the research, claims that they were able to create devices that were small enough to be aboard a spacecraft without major obstacles.
Summing up, the idea of transporting genetically modified plants on a spaceship seems to be a topic worthy of attention, due to the large potential for their use. As the examples above show, plants created using biotechnological methods are not only able to survive harsh conditions (owing to extremophile transgenes) and provide food for astronauts, but can also be useful for producing medicinal compounds. It is worth combining all methods and trying to create seedlings that will have all three advantages: high resistance, the ability to produce drugs, and the possibility of using them as a wholesome meal.

Life support system
The cultivation of plants on a spaceship has been considered for many years as an element of the life support system, mainly as a source of oxygen, foodfresh vegetables), and as a way to process biological waste (urine and feces) from astronauts. However, it is much hampered due to less access to nutrients, reduced gravity, or the limit of kilos that can be taken on board (every extra kilo is associated with a significant increase in costs). Nevertheless, creating and modifying plants are not a problem that we need to face for this reason alone. After all, an important stage is also their maturation process, and for it to be effective, these organisms need appropriate conditions. NASA scientists from the Kennedy Space Center in Florida (NASA 2019) have developed the modules that make up the life support system. The aim was to create greenhouse units that would allow the cultivation of plants in limited conditions during space travel. Thus, they designed a set of cylindrical prototypes, which consist of pipes built around an aluminum frame. In addition, the system includes a small irradiation kit-based on LED technology-which accelerates the photosynthesis process in plants. Scientists say that it only takes 10 min to assemble the device, and its small footprint allows it to be transported inside a spacecraft. Its functioning is based mainly on plastic sleeves that carry water to the seedlings and provide them with the necessary nutrients. When creating the modules, an external composter was also added so that human feces could be processed into fertilizer for plants and which would be responsible for water filtration [47]. Below is a diagram (Figure 1) that shows the functioning of this system and the  [78,43]). relationships between the individual components of the modules. The life support system described above could also have a positive effect on the mental health of astronauts. Many years of research have provided evidence that caring for plants and staying among greenery play an important role in mental relaxation [48]. Lack of long-term contact with nature would raise the risk of increased aggression and depression in spacecraft travelers. This problem has been known for a long time [49]. The need to surround oneself with nature was already discussed in Ancient Egypt. It was then that horticultural therapy was established. It is a method aimed at improving mental health, adapting to environmental changes and managing stress by spending time among plants [50]. Another positive effect of contact with flora is related to the production of phytoncides by plants. These are substances that have a bacteriostatic effect. At the same time, they contain tetracyclines, so they significantly affect the quality of air that could potentially be inhaled by astronauts. This, in turn, could have a beneficial effect on the respiratory system [51].

Bioprinting
Another idea for producing food during space flights is related to the use of bioengineering methods. The combination of biotechnology, nanotechnology and biomedical engineering has contributed in recent years to the development of bioprinting. It is a technique that consists of creating tissue or food from biological inks, most often made from plants. There are five different methods in this technology: (a) extrusion, (b) stereolithography, (c) inkjet, (d) laser-assisted and (e) microvalve-based bioprinting [52]. In the first one, pressure is applied to the material; stereo-lithography is based on the photopolymerization process; the next one requires the use of a special ink; another possibility is to use a laser beam that controls the movement of particles in solution; the last option is based on the use of a special mechanism that dispenses liquids by closing and opening a small valve [53]. Bioprinting is a method that is gaining increasing popularity. It is predicted that the international market related to this technology will grow by as much as 38.5% by 2023 [54]. In any case, it is worth considering whether this invention could also be used during space travel. The North American Space Agency (NASA) [55][56][57] already had such an idea in 2013. At the time, Systems and Materials Research Corporation (SMRC) proposed to produce food for astronauts using 3D printing. By this means, edible structures with the appropriate texture of protein, starch and fat would be created, which would be complemented by micronutrients, taste and aroma from the inks. As transporting liquid inks would not be profitable (they would quickly break), it was assumed that astronauts would store tasteless macronutrients (starch, protein, etc.) in the form of a powder, and would add oil or water in the right proportions only once in a 3D printer. The printer would be primarily responsible for selecting the ratio of dry to wet ingredients, because failure to deliver the precise amount may result in toxicity of the ingredients and their rapid degradation. In addition, the food printer allows a slow cooking process, which further adds to the appeal of the meals given that astronauts have limited access to kitchen appliances. Another advantage of using bioprinting in space is also the fact that, in the case of zero gravity, it may be more effective than on Earth. Currently, one of the problems is obtaining sufficiently strong structures that will not create the so-called 'puddle' [58] under the influence of gravity. Nevertheless, as gravity is reduced during space travel, this problem does not occur [59].

Laboratory meat
During spaceflight, access to farm animals, and thus meat, is very limited. Although the laboratory meat technology has been studied for years, this year it gained particular popularity, thanks to the first opening in 2020 of the first restaurant (in Israel and Singapore), where this product is served to customers. It is believed that in vitro meat could also be given to the first colonizers of the Red Planet. Previously, it was presumed that future inhabitants of Mars would be forced to switch to a vegetarian diet. The technological breakthrough makes it very possible that it will not be a necessity at all. The 3D printer gives us the ability to 'print' meat products previously grown using in vitro fertilization. Thus, this review will discuss the problem of farmed meat, which has recently become an increasingly popular product. The combination of 3D printer technology with the idea of 'farmed meat' can bring promising results. Such a process started with the collection of animal stem cells and mixing them in a bioreactor (e.g. with cyanobacteria) [60], which enables their growth. Then, in 3D printing, the production of stem cells would be transformed into animal products.
NASA and Aleph Farms tried to implement the abovementioned method over a year ago. On September 26th, 2019, tests were carried out using in vitro meat and 3D printers developed by 3D Bioprinting Solutions at the International Space Station. It was then possible to produce a piece of cow's muscle tissue [61]. It is believed that the idea of printing meat could gain the approval not only of astronauts and future colonizers of Mars but also of the inhabitants of Earth. The biggest advantage of the project is the fact that it allows creating wholesome meat products without the need to kill animals, and thus solves the ethical problems related to this topic. NASA's research on in vitro meat produced in 3D printers is the best proof that all projects related to space exploration can also benefit people living on Earth.

Risk analysis of a flight to Mars
In addition to providing food security, space flight requires an analysis of potential sources of risk to the life and safety of human crews. The space flights performed so far have provided data on the accidents, their consequences, and possible ways of removing their consequences and preventing them in the future. The most well-known are: • On July 14th, 1970, a fuel tank explosion 320,000 km from Earth during the Apollo 13 mission resulted in aborting the mission to the moon and forced the return to Earth on a ballistic trajectory [62]. • On March 7th, 1985, a failure of the sun position sensor for solar batteries at the Salut 7 orbital station led to complete loss of voltage on board; after the sensor was repaired, the system was restored [63]. • On June 25th, 1997, the collision of the Progress ship with the Spiektr module of the Mir orbital station resulted in disconnection of the module on the locks, used only as a location for solar batteries [64]. • August 30th, 2018, unsealing on the Soyuz MS-09 at the ISS orbital station resulted from a hidden human error in the module production process [65].
Hence, the following adverse event scenarios in space flight are possible: • De-encapsulating of a segment or the whole -failure of the locks and transition links between the segments -collision with another object, large cross-sectional area • Fire in a segment or as a whole -short circuit -start of a fire • Electricity supply failure -short circuit -rupture of the supply line • Life support system failure -CO2 removal -air production • Failure of the water recovery and production system -component failure -clogged filters • Radiation -of the sun -from space It is essential to protect the spacecraft from cosmic radiation. It is indicated as the main source of damage at the molecular level in the human body [11,66].

Proposal for a radiological shield for a spacecraft
So far, space flights have been carried out in LEO-low orbit around the Earth. Only the Apollo missions, Apollo 8, 10, 11-17, have come near the moon. However, the stay time was too short to investigate the effect of radiation on the human body [75]. During flights on space stations, there have been several times when a coronal ejection in the sun made it necessary for crews to protect themselves from it. This was the case on March 13-14th, 1989 at the Mir station. It did not pose a threat to the international crew of Soyuz TM-7 according to Russian data [67], despite the fact that its orbit inclination was 51° [68]. However, there is some information that the wiring of electricity distribution at the station was replaced later [69]. A similar occurrence took place on January 20th, 2005, when the mass ejection from spot no. 720 on January 15-19 resulted in the refuge of the ISS crew in the Russian ROB module [83,70]. There is no information about damage to the electrical system of the station. A proposal of a shield is based on the use of a multi-layer cover. First, the outer layer must be resistant to collisions with particles with high kinetic energy or must act as a ballistic shield. The second, the middle one is meant to reduce the speed of the corpuscular radiation so that the inner one can slow it down and absorb it. For the construction of the outer layer, we can use the known depleted uranium, which is used, among others as armor in Abrams tanks [71]. It may also be another, newer material that will be invented in the future. Biphenyl can be used as the middle layer, which, being a multi-chain carbon compound [72], can act as a radiological shield according to NASA research [77], sketched in Figure 2. Lead can be used as the inner shield, which for many years has been the basic shield for all devices where radiation occurs.

Discussion
Astronautics is an interdisciplinary field, and many fields are involved in this research. The presented issues of a manned flight into the distant space indicate very complex problems that must be solved before the first flight. The issues raised in this paper require the development of several supporting techniques. The main goal is to ensure the safety of the crew. This can only be achieved by testing the reliability of individual components of the spacecraft system. For this purpose, we should conduct unmanned test flights of selected technical solutions in conditions similar to the space between Earth and Mars. Such a possibility is provided by a flight in orbit around the sun, similar to Earth's around the sun. The flight around the sun will allow the test vessel to move out of the Earth's magnetic field. We must be sure that the crew onboard the spacecraft will not be exposed to the risk of being irradiated, owing to the appropriate construction of the spacecraft body. Thus, it is possible to test solutions for securing renewable crops and to test the impact of the space environment without the protective magnetic field of the Earth on them. Although the presented solutions for feeding astronauts, such as bioprinting or laboratory meat, seem to have considerable development potential, only after testing will they be allowed to be used during long-term space flights. Without performing experiments (e.g. test flights), it can never be proven whether the presented technologies will function effectively in conditions different from Earth, including conditions of reduced gravity or increased radiation. The review also presents organisms such as insects, which, although not previously associated with food products, could also become nutritional food for astronauts after proper preparation. It remains uncertain, however, what the development of these organisms will look like in space, whether it will not be disturbed. Thus, thorough analyses are necessary before introducing them as food into the astronauts' diet, and test flights are the best way to check the effectiveness of these methods.

Conclusions
Flight to other planets is a great challenge for humanity and requires reliable preparation on our part. First, we must be sure that the crew onboard the spacecraft will not be exposed to the risk of being irradiated, and that they are protected due to the appropriate construction of the spacecraft body. Therefore, we cannot begin with it without proper testing of the proposed solutions for the expedition spacecraft. The test flight around the sun allows testing the technique and modern methods of food production. Thus, the first step taken to colonize Mars should therefore be un-manned test flights of selected technical solutions in conditions similar to the space between Earth and Mars. For this purpose, it is possible to indicate a flight in the orbit around the sun, similar to Earth's around the sun. This will allow the test vessel to move beyond the Earth's magnetic field. At the same time, it is possible to test solutions for securing renewable crops and food production onboard a spacecraft and to perform tests on the impact of the space environment on it. In addition, it is possible that the discoveries in the field of engineering, biotechnology and food science that we make in research related to space flight will also benefit people on Earth. The achievements to date give hope that a breakthrough in research related to the economic and safe production of food, as well as in works on protection against various types of dangerous radiation, will soon be achieved. To sum up, as of today, we can count on the proposed solutions, such as the consumption of insects and algae and the use of 3D printer technology, or radiation shields, which will pave the way for humanity to reach other planets.

Disclosure statement
The authors declare no conflict of interest.

Funding
The author(s) reported there is no funding associated with the work featured in this article.