Bioenergetics is a study of the transformation and flow of energy in living organisms. It mainly investigates mitochondrial respiration and energy production in animal and plant cells, photosynthesis in plant chloroplasts, and nitrogen fixation. These processes are crucial for the biology of organisms on Earth, but also within the challenging environment of space travel. The main spaceflight hazards such as radiation, microgravity, and magnetic fields greatly affect the efficiency of bioenergetic processes, in consequence leading to various health impairments, decreased physiological performance and survival, cellular homeostasis dysregulation, oxidative stress, DNA damage, accelerated ageing, and several age-related diseases. All those impacts are associated with the loss of healthy mitochondrial function, which has been described as a hallmark spaceflight phenotype. Although preventative and countermeasure strategies are being developed, they are not yet successful. Moreover, the process of energy turnover from Solar light, H2O and CO2, into sugars and O2 in chloroplasts, and its subsequent utilization into CO2 and cellular energy in mitochondria, are crucial elements of every ecosystem on Earth. This process is also a foundation for developing the bio-regenerative life support systems for food and oxygen production in space travel. Furthermore, bioenergetics is crucial for the evolution and survival of organisms. However, the direction of adaptive phenotypic and genotypic changes arising under the challenging environment of long-term multigenerational spaceflight is currently unknown.