When astronauts enter space, they are exposed to weightlessness. Physiological and psychological challenges are waiting ahead. They may have a puffy face and experience space motion sickness, cardiovascular deconditioning, muscle atrophy, and bone loss.

Moreover, long-term spaceflight has been shown to result in 83% of astronauts with post-flight orthostatic intolerance. For such problems, exercise countermeasures can be the primary approach to resolve these changes. Head-down bed rest (HDBR) simulates physiological effects in weightlessness and is widely used in countermeasure testing, and efficacy of exercise interventions has been widely studied in HDBR with different periods as well.

Usually, the long-term bed rest experiment is completed in stages, and a positive control of separated exercise countermeasures rarely tests at the same time in these experiments.

Like mariners of old, spacecraft steer by the stars—using combinations of telescopes, cameras and computers called startrackers to recognize stellar constellations to calculate their own position in space.