Lunar Time: The Timing Challenge of the New Era of Human Lunar Exploration

Tech 2024-08-02 13:45:36 Source: Network

Lunar Time: The Timing Challenge of the New Era of Human Lunar ExplorationAs humanity delves deeper into lunar exploration, the issue of time on the Moon has come to the forefront. Unlike the unified "Coordinated Universal Time" on Earth, a lunar time system has yet to be established, posing new challenges for long-term human activities on the Moon

Lunar Time: The Timing Challenge of the New Era of Human Lunar Exploration

As humanity delves deeper into lunar exploration, the issue of time on the Moon has come to the forefront. Unlike the unified "Coordinated Universal Time" on Earth, a lunar time system has yet to be established, posing new challenges for long-term human activities on the Moon.

Cosmic Mystery: Subtle Differences in the Flow of Time

Time, a seemingly intangible yet ubiquitous entity, has always been a constant theme of human contemplation. The subtle differences in its flow fascinate scientists even more.

Even before Einstein's theory of relativity, people realized that time is not absolute. Time flows faster at the top of a mountain than in a deep valley, a phenomenon known as time dilation due to the difference in gravitational fields. While this phenomenon has minimal direct impact on daily life, it cannot be ignored in the human quest for space exploration.

Lunar Time: A Sibling of Earth Time?

As human lunar exploration activities increase, establishing a time standard for the Moon has become an urgent need. NASA's latest calculations show that time on the lunar surface is 57.5 microseconds per Earth day faster than on the Earth's surface. This tiny difference, however, can have a significant impact over long periods of lunar exploration.

"Coordinated Lunar Time": A New Standard for Lunar Timekeeping

In April this year, the White House released a memorandum instructing NASA to work with other government agencies to establish "Coordinated Lunar Time" by the end of 2026. The memorandum outlines four key characteristics of "Coordinated Lunar Time":

1. Logical Traceability: Maintaining a logical connection with "Coordinated Universal Time" to facilitate time information conversion and comparison.

2. Precise Timing: Enabling precise recording of extremely short time intervals, meeting the growing demand for time accuracy in future lunar activities.

3. Self-Sufficiency: Operating independently in case of communication loss with Earth, ensuring that lunar activities are not affected by Earth signals.

4. Scalability: Providing guidance and reference for future human exploration of other celestial bodies, building a unified cosmic time system.

The Necessity of a Lunar Time System

Establishing a lunar time system is crucial for future human lunar activities. It not only ensures the accuracy of spacecraft communication, landing, and navigation, but also provides a reliable time reference for the construction of lunar bases, space stations, and other infrastructure.

As Xie Yi, a researcher at the Purple Mountain Observatory of the Chinese Academy of Sciences, pointed out, future lunar spaceports will need to inform passengers of the precise departure and arrival times of their spacecraft. At the same time, lunar time needs to be linked to Earth time to facilitate the coordination of personnel and resources between Earth and the Moon.

Earth Time: Humanity's Enduring Pursuit of Time

Humanity's pursuit of time accuracy has never ceased. In the early 20th century, Einstein's theory of relativity pushed the scientific world to new heights in the precise measurement of "seconds" in time.

General relativity states that the stronger the gravitational force, the slower time flows. Since the gravity on the Moon is only one-sixth that of Earth, time on the Moon is faster than on Earth, a consequence of time dilation.

To solve the time measurement challenges posed by relativity, scientists have deployed hundreds of atomic clocks around the world. These ultra-precise instruments, based on the principle of atomic vibrations, can capture every subtle change in the flow of time. By combining readings from atomic clocks around the world, scientists have derived "Coordinated Universal Time" and introduce "leap seconds" periodically to adjust for variations in Earth's rotation speed.

However, time calculation goes far beyond this. According to Einstein's special relativity, the faster a person or spacecraft moves, the slower time passes. Therefore, some spacecraft are equipped with their own clocks called crystal oscillators (shortened to "XO"). Even with XOs, time on spacecraft often needs to be synchronized with ground stations.

Lunar Time and Relativity: The Subtle Differences in Time

So, how do general relativity and special relativity affect the calculation of lunar time?

Xie Yi explains that if two clocks are placed on Earth and the Moon respectively, they will experience significantly different gravitational forces and motion states. Clocks on Earth are subject to stronger gravitational forces, and their speeds also differ significantly. This difference will cause a gradual deviation between the two clocks even if their readings are initially identical.

NASA has calculated the relative motion between the Moon, Earth, and the Sun, resulting in a difference of 57.5 microseconds per day. This means that after 50 years, astronauts on the Moon would be about one second younger than people on Earth.

This figure is calculated based on the principles of general relativity, taking into account the "drift" between ground and lunar time caused by gravitational differences and motion differences in general and special relativity.

Lunar Time: The Mystery of Cyclical Variations

Xie Yi's team's research has revealed that besides the daily difference between Earth and Moon time, there are also cyclical variations. This variation will have a significant impact on satellite navigation systems built by China around the Moon.

Lunar Timekeeping: Atomic Clocks vs Crystal Oscillators

So, which should we use for timekeeping: atomic clocks or crystal oscillators?

Cheryl Granlin of NASA Goddard Space Flight Center says that atomic clocks excel in long-term stability while crystal oscillators have an advantage in short-term stability. Scientists will continue to discuss and research this issue, ultimately choosing the most suitable timekeeping solution for the lunar environment.

Lunar Time: The Challenge of International Collaboration

The definition of lunar time will be jointly established by several institutions, including the International Bureau of Weights and Measures and the International Astronomical Union. Some discussions will be held in August.

Looking Ahead: The Establishment of a Lunar Time System

The establishment of a lunar time system is a significant step in humanity's exploration of the cosmos. It not only solves the challenges of timekeeping faced by humans during activities on the Moon but also provides valuable experience and insights for future human exploration of other celestial bodies.

With continuous technological advancements, humanity's understanding of time will continue to deepen, and the lunar time system will continually improve, laying a solid foundation for humanity's journey into the vastness of space.

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