Yes, the concept of a 24-hour day is still used as a reference for timekeeping in space missions. Despite experiencing different day-night cycles, astronauts on the International Space Station (ISS) and other space missions follow a schedule based on a 24-hour day.

To maintain a sense of routine and consistency, mission controllers on Earth synchronize the astronauts’ activities and rest periods with a 24-hour schedule. This helps regulate their sleep-wake cycles and provides a sense of normalcy in an environment where they may witness multiple sunrises and sunsets within a 24-hour period.

However, it’s important to note that the actual day-night cycle experienced by astronauts in space is different from that on Earth. As the ISS orbits the Earth, it completes roughly 16 orbits in a 24-hour period, resulting in multiple cycles of sunlight and darkness. Astronauts may experience around 16 sunrises and sunsets every day, leading to unique challenges in terms of maintaining sleep patterns and adapting to the changing lighting conditions.

Despite these differences, using a 24-hour day as a reference for timekeeping helps astronauts synchronize their activities with mission control, plan experiments, coordinate with ground teams, and maintain a sense of routine and time structure throughout their mission.