Another challenge is coordinating operations across the lunar surface with those in orbit and back at Earth, which requires a system of standardized time.
For example, clocks on the Moon tick slightly faster than those on Earth due to the weaker gravitational pull experienced at the Moon’s surface.
Their approach involves applying relativistic principles used for Earth and adapting them to the Moon’s environment, including: Weaker gravity on the Moon leads to a faster tick rate for lunar clocks than Earth clocks.
Local gravitational anomalies, known as mascons, subtly influence the Moon’s gravitational field and, thus, the flow of time.
In addition to mapping the lunar surface, the twin satellites also mapped the Moon’s gravitational field in fine detail.
Some very ambitious plans for the future of humanity in space are being developed by NASA, other space agencies, and the commercial space industry. According to these plans, permanent infrastructure will be built on and around the Moon to support a long-term human presence, including scientific, commercial, and research activities. The first crewed missions to Mars are also demanded, along with the establishment of surface habitats that will enable follow-up trips. There are numerous obstacles to these plans, from technical and logistical problems to concerns about human safety and health.
Coordinating operations on the lunar surface with those in orbit and back at Earth presents another difficulty, necessitating the use of a standardized time system. A group of NASA researchers recently created a new lunar time system for all lunar assets as well as those in cis-lunar space. They suggest that relativistic time transformations—more commonly referred to as “time dilation”—be the basis of this system. By resolving disparities brought on by varying gravitational potentials and relative motion, such a system will enable coordination and efficient timekeeping on the Moon.
Slava G. conducted the research. James G. Turyshev. Dale H. Williams. Four research scientists from NASA’s Jet Propulsion Laboratory (JPL) are Boggs and Ryan S. Park. Their paper, “Relativistic Time Transformations Between the Solar System Barycenter, Earth, and Moon,” was just preprinted online and is presently undergoing review before being published in the journal Physical Review D.
Lorentz Transformations and Einstein’s Special Theory of Relativity (SR) predicted relativistic time transformations (RTT), which explain how time slows for the observer as their reference frame accelerates. Einstein demonstrated that acceleration and gravity are nearly the same and that time flow varies with the strength of the gravitational field when he expanded SR to include gravity in his General Relativity (GR) theory. Spacecraft operating beyond Earth are subject to acceleration, microgravity, and lower gravity, which poses a challenge for space exploration.
RTT will become a significant factor when humans start conducting long-term operations on the Moon, Turyshev told Universe Today in an email.
Time flows differently depending on motion and gravitational potential, which is taken into account by [RTT]. Because of the weaker gravitational pull at the Moon’s surface, for instance, clocks there tick a little faster than those on Earth. When coordinating space missions, even a small timing error can result in significant positional inaccuracies or communication delays, making these differences, which are on the order of microseconds per day, significant. Time is of the essence in space exploration. Different time scales have distinct functions based on the frame of reference. “.”.
Three main timescales that are relevant were identified by the team in their paper. They consist of:.
With adjustments for Earth’s gravitational potential, Terrestrial Time (TT) is the timescale used for Earth-based systems. It represents time at mean sea level.
Barycentric Coordinate Time (TCB) is the time coordinate that is centered at the barycenter of the Solar System in the Barycentric Celestial Reference System (BCRS). Both gravitational potentials and body motion with respect to the barycenter cause relativistic effects, which is why TCB is crucial for high-precision modeling of celestial mechanics and dynamics.
Derived from TCB, Barycentric Dynamical Time (TDB) is adjusted to run at the same average rate as Terrestrial Time (TT). This adjustment ensures that ephemerides stay consistent with Earth-based observations over extended periods of time by preventing a long-term secular drift with respect to TT.
“Relativistic adjustments establish a connection between these time scales, guaranteeing reliable timekeeping for communication, planetary ephemerides, and spacecraft navigation,” Turyshev continued. Without these adjustments, even at comparatively short distances, spacecraft trajectories and mission timings would soon become unreliable. “.”.
Numerous components of NASA’s Artemis Program are active in cislunar space and on the lunar surface in the vicinity of the south pole. These include the Lunar Gateway in orbit, several Human Landing Systems (HLSs), and the Artemis Base Camp, which will include the Foundation Surface Habitat (FSH), the Habitable Mobility Platform (HMP), and the Lunar Terrain Vehicle (LTV). A Moon Village with various power, transportation, and in-situ resource utilization (ISRU) components is also planned by the ESA.
Additionally, China and Russia are planning the International Lunar Research Station (ILRS), a lunar habitat centered on the Moon’s south pole. This station might have an orbital component, a surface component (perhaps in a lava tube), and additional components resembling the Artemis Base Camp and Moon Village, according to several statements. Interests in commercial space, such as mining, harvesting, and even tourism, will follow and parallel these. The Moon’s orbit around the Earth means that these operations must, of course, stay in communication with mission control.
Determining a specific Lunar Time (LT) scale and a Luni-centric Coordinate Reference System (LCRS) is crucial as lunar exploration picks up speed, according to Turyshev. He and his associates therefore created a TL scale to guarantee accurate timekeeping for operations on and near the Moon. Their approach involves applying relativistic principles used for Earth and adapting them to the Moon’s environment, including:.
Because of the Moon’s lower gravity, lunar clocks tick more quickly than Earth clocks.
Periodic time variations are introduced by the Moon’s orbit around the Sun and Earth.
Time is subtly affected by local gravitational anomalies called mascons, which affect the Moon’s gravitational field.
“Our results indicate that lunar time is approximately 56 microseconds ahead of Earth time every day, with additional periodic variations due to the Moon’s orbit,” Turyshev said. Over a span of roughly 27–55 days, these periodic oscillations occur with an amplitude of about 0–47 microseconds. “”.
Turyshev and his group used high-precision data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission, which involved two satellites that collected lunar observations from 2011 to 2021, to infer these changes. The twin satellites created a detailed map of the Moon’s gravitational field in addition to its surface. Measurements from Lunar Laser Ranging (LLR) experiments, which determine the Earth-Moon distance with millimeter-level accuracy, were added to this. Turyshev said.
We used this information to model the orbital dynamics and gravitational potential of the Moon, guaranteeing sub-nanosecond accuracy in the ensuing time transformations. Key constants, similar to those used for time systems based on Earth, were introduced to describe the transformations. These limitations are the most important ones.
In order to compensate for the combined gravitational and rotational potential at the selenoid level, LL stands for the average rate of time transformation between the Moon’s center and surface.
LM adjusts for the average rate of time transformation between Barycentric Coordinate Time (TCB) and Lunar Time (TL), much like LB does for Earth.
LH, which stands for the long-term average of the Moon’s total orbital energy as it revolves around the barycenter of the solar system. It includes contributions from gravitational interactions with the Sun and planets and defines the rate difference between TCB and the luni-centric coordinate system time (TCL).
According to the Geocentric Celestial Reference System (GCRS), LEM is the long-term average of the Moon’s total orbital energy during its orbit around the Earth.
PEM produces time-dependent oscillations by taking into consideration periodic relativistic corrections brought on by the Moon’s elliptical orbit and gravitational perturbations from the Sun and planets.
Our extremely precise lunar timekeeping system is based on these changes, and it is essential for mission planning and operations in the future. “.”.
According to Turyshev and his colleagues’ paper, establishing a single lunar time system is crucial for mission success for a number of reasons. These consist of:.
Accurate Landing and Navigation: From orbiters to landers and rovers, synchronized timekeeping will guarantee accurate positioning and lower the possibility of mistakes during crucial mission phases as many missions aim for the lunar surface.
Smooth Communication: To prevent communication lags and guarantee the proper sequence of data transfer, activities involving Earth, orbiters, and lunar bases must be coordinated with regular time synchronization.
Collaborative Science: Large-scale investigations of lunar geology, seismic activity, and gravitational anomalies are supported by the accurate sharing and comparison of data between missions carried out by various space agencies and organizations thanks to a common time standard.
Autonomous Operations: As lunar missions become more complex and long-term, a specific lunar time system will enable bases and spacecraft to function without relying on Earth-based timekeeping when Earth is not visible.
To become an interplanetary species, humanity must adapt in many ways, including new timekeeping systems. In this century, as human presence on the moon increases and becomes permanent, a coordinated system of lunar time will become more and more significant. When regular crewed missions to Mars start, similar steps will need to be taken, and those efforts have already started in earnest! For more information, see the Darian Calendar and Mars Coordinated Time (MCT).
