But preserving food is far from her only challenge. Douglas must also consider the nutritional value of the meals to ensure the astronauts stay healthy in orbit. One challenge is that vitamins in food degrade over time when exposed to oxygen, so packaging must be incredibly airtight. She also has to count calories. In the microgravity environment of the ship, an astronaut’s skeleton and muscles are no longer used to support their bodies, leading to a decrease in bone and muscle mass. To avoid this, astronauts regularly hit the space gym (treadmills, exercise bikes, and weight machines on board), but they need calorie-rich foods to compensate for these workouts.