For space food, scientists can roughly divide it into seven categories: first, ready-to-eat food, that is, food that does not need to be processed and taken over; The second is rehydrated food, which belongs to freeze-dried food and needs to be eaten after adding water to restore the food to its original state; The third is heat-stable food, that is, soft-packed and hard-packed canned food after heating, sterilization and self-care; The fourth is frozen and refrigerated food, which is frozen on the ground and brought into space, and can be eaten after melting; Fifth, radiation food, food sterilized by radiation; The sixth is natural food, which has not been treated on the ground, such as fresh fruits, vegetables, bread, jam and so on. Seventh, rehydrated drinks, granular or soft solid drinks.

The selection of space food should follow the following basic principles: first, the nutritional structure should be suitable for the nature of astronauts' work and the nutrition should be comprehensive; Secondly, food quality standards are higher than national standards. In the case of meeting the standards, the key is to ensure the consistency of food quality and avoid problems after astronauts eat it; Third, food tastes like ordinary people; Finally, the food eaten by astronauts must be preserved for three days to track the astronauts' reaction after eating. In addition, space food must meet the requirements of astronauts' physiological changes under weightlessness, and can provide sufficient high-quality protein and calcium, as well as appropriate calcium-phosphorus ratio and vitamin D; The fat content of space food should not be too high at the beginning of flight, so as not to aggravate the symptoms of space motion sickness; In order to prevent the dysfunction of cardiovascular system, it is necessary to limit the supply of sodium and ensure the supply of potassium in space food. Collocation system

How to eat together and establish a diet system is also a very important issue. The diet system is a regulation to reasonably arrange the number of meals, the quantity and quality of food per meal and the interval between meals according to the life, work and exercise of astronauts, and it is also the basis for making daily recipes. For example, the Soviet salute space station stipulates 6: 4 meals a day, and the amount of food and calories per meal are nearly equal; The interval between meals is 3-5 hours; It takes 15~20 minutes to eat after exercise; Exercise or strenuous mental work must start after meals 1~ 1.5 hours. The United States adopts the system of three meals a day.

Space recipes must meet nutrition standards and astronauts' tastes and eating habits. There are generally two kinds of space recipes, one is universal and the other is personal hobby. In order to avoid monotony, the recipes used by the United States and Russia in space generally take 4-6 days as a cycle, and the food is not heavy except drinks every day in a cycle. For example, the general recipe of the American space shuttle is divided into three meals: A meal includes peaches, roast beef, scrambled eggs, pancakes, cocoa, orange juice drinks, vitamin tablets and coffee; Meal B includes mixed pork dishes, Turkish sausages, bread, bananas, almond biscuits and apple drinks. C There are shrimp, steak, rice, cauliflower, cocktail, pudding, grape juice drinks and ice cream. Judging from the types of these foods, their nutritional components are relatively complete and meet the nutritional standards of astronauts. Judging from the health status of astronauts who lived in the sky after the flight, no one was found to be malnourished. Although astronauts generally suffer from calcium deficiency and muscle atrophy during long-term space flight, this is only related to long-term weightlessness.