How do you balance the trade-offs between precision and complexity in timekeeping in space?

2 Why complexity matters

Complexity is the degree of difficulty or complication of a system or process. In timekeeping, complexity means how many factors or variables are involved in creating and maintaining a clock. Complexity is also important for space missions because it affects the reliability, flexibility, and scalability of clocks. For example, the International Atomic Time (TAI) is a complex system that combines the output of hundreds of atomic clocks around the world, using sophisticated algorithms and corrections to create a uniform and stable time scale. If the TAI system were not complex, it would not be able to cope with the variations and uncertainties of different clocks and locations.

3 How to balance precision and complexity

Balancing precision and complexity in timekeeping in space is a challenge that requires careful design, trade-offs, and adaptation. No single solution exists, but rather a range of options that depend on the purpose, context, and constraints of each mission. Several factors influence the balance, such as the type and quality of the clock. Quartz clocks are simple and cheap but less precise than atomic clocks, which are complex and expensive. The location and movement of the clock can also affect it; for instance, a clock on a low-Earth orbit satellite experiences more gravitational time dilation than one on a high-Earth orbit satellite, resulting in it running slower and needing more adjustment. Additionally, different clocks need different methods and frequencies of synchronization and coordination depending on their distance, communication, and reference. For example, a clock on a Mars rover needs to synchronize with a clock on a Mars orbiter, which needs to synchronize with a clock on Earth, which needs to synchronize with other clocks on Earth.

4 Examples of balancing precision and complexity

Space missions have implemented precision and complexity in timekeeping in various ways. For instance, the Apollo program used quartz clocks on the lunar module and command module that were synchronized with atomic clocks on Earth using radio signals. These quartz clocks were simple and reliable but less precise than the atomic clocks, resulting in discrepancies in the lunar landing and ascent times. The Deep Space Network (DSN) utilizes hydrogen maser clocks at its ground stations that are synchronized with each other and with TAI by very long baseline interferometry (VLBI). These hydrogen maser clocks are complex and precise yet sensitive and expensive, limiting their number and availability. The European Space Agency (ESA) has also developed a new type of atomic clock called the PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbite), which will be installed on the International Space Station (ISS) as part of the Atomic Clock Ensemble in Space (ACES) project. This PHARAO clock is designed to be more precise and stable than existing atomic clocks, while being more compact and robust, thus reducing its complexity and enhancing its adaptability.

5 Why balancing precision and complexity matters

Balancing precision and complexity in timekeeping in space matters because it affects the success and efficiency of space missions, as well as the advancement and understanding of science. By finding the optimal balance, space missions can achieve their goals and objectives, while minimizing their risks and costs. Moreover, by improving the precision and complexity of timekeeping in space, science can benefit from more accurate and consistent measurements, tests, and discoveries. For example, by using precise and complex clocks, scientists can test the predictions of relativity, measure the gravitational waves, and explore the origin and evolution of the universe.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?