Space explained
Deep Space Exploration: Astronaut Training and Earth's Center of Mass
Both paths are indispensable to advancing NASA's deep space exploration goals.
In brief
NASA is preparing future astronauts with rigorous training for Moon and Mars missions while simultaneously refining measurements of Earth's center of mass. These micro-movements of our planet are crucial for space navigation, showing how precise Earth science underpins human space exploration.
Key points
- The 2025 NASA astronaut class is completing a two-year training program for lunar and Martian missions, including geology, flight and survival training.
- Earth's center of mass shifts seasonally by a few millimeters due to redistribution of water, ice and air, affecting satellite navigation.
- A new JPL-guided technique improves precision in measuring these shifts by combining GPS and satellite orbital data.
- Snow accumulation and monsoon rains cause specific center-of-mass shifts, such as the 3 millimeters toward the North Pole in March due to snow.
- Positioning accuracy, derived from understanding terrestrial reference systems, is essential for global logistics and future space missions.
- The GRACE-FO missions and the upcoming GRACE-C extend data collection to monitor gravitational fluctuations and support long-term space exploration.
Humanity constantly looks beyond its borders, driven by an unquenchable thirst for discovery. This ambition appears both in the rigor of human preparation and in the meticulous scientific analysis of our own planet. The path toward deeper space exploration is complex. It includes missions to the Moon and to Mars. It is an interweaving of intensive astronaut training and Earth science.
Humanity constantly looks beyond its borders, driven by an unquenchable thirst for discovery.
Human Preparation for Deep Space Exploration
The 2025 astronaut candidate class consists of ten individuals. They are halfway through a two-year training program. This takes place at NASA’s Johnson Space Center in Houston. Their goal is to acquire the skills needed for future missions that will take them to low Earth orbit, the Moon and, ultimately, Mars. This rigorous training is a long-term investment in human capabilities to face unknown environments.
An essential part of this path concerns the study of geology. The candidates have attended classroom courses and field exercises. The exercises took place in New Mexico and in Iceland. They have worked alongside Artemis astronauts and mission support teams. There they practiced geological observations, sampling with tools, navigation and teamwork, all skills that will translate directly to Artemis lunar missions. The ability to orient oneself on an alien surface requires a deep understanding of reference systems, a need that echoes in Earth science.
In addition to geology, the training includes flying. They fly on NASA WB-57 high-altitude research aircraft and T-38 supersonic jets. This serves to hone piloting skills and build confidence. The candidates spend time in altitude chambers. They simulate conditions from sea level to near vacuum. This familiarizes them with high-altitude and space-like environments. Survival training in water and intensive Russian language lessons are also integral parts of the curriculum, preparing astronauts for remote scenarios and international collaboration.
The Dynamic Heart of Our Planet
While the astronauts prepare to leave Earth, a team of scientists monitors Earth’s center of mass. This is the heart of our planet. The team is led by NASA’s Jet Propulsion Laboratory in California. This crucial reference point, although it moves only by fractions of an inch, is fundamental for satellite navigation and elevation measurements. Its precision is a quiet prerequisite for every space exploration adventure.
Earth is not a rigid body; the seasonal redistribution of water, ice and air causes continual oscillations of its center of mass relative to its geometric center. The last two international estimates, from 2017 and 2023, differed by 7 millimeters, a discrepancy almost equal to the movement itself. This variability requires ever more accurate measurement methods to ensure global positioning systems remain reliable.
To reduce this uncertainty, geoscientist Donald Argus developed a new technique based on ultra-precise satellite tracking. This innovative methodology combines GPS tracking and orbital data from multiple low Earth orbit satellites. It overcomes the limits of the earlier LAGEOS 1 and 2 satellites. The latter are 408-kilogram “disco ball” satellites studded with retroreflectors. They were launched in 1976 and 1992. Ground stations in more than twenty countries track them with laser precision.
Seasonal Oscillations and Their Impact
The study revealed seasonal oscillations of Earth’s center of mass. These are attributable to the oceans, the atmosphere and continental water. Continental water includes land ice, snow, lake and river water, soil moisture and groundwater. For example, snow accumulation in North America and Eurasia peaks in March. This shifts the center of mass by about 3 millimeters. It moves it toward the North Pole. A month later, in April, rainfall in the Amazon River basin moves the center of mass. This water reaches some 2,400 gigatonnes. It shifts the center of mass by 2.2 millimeters toward South America.
These mass calculations are consistent with observations from the GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) mission, launched in 2018. This mission, composed of twin satellites, maps monthly fluctuations in Earth’s gravitational field, driven primarily by the movement of water mass. The collected data are vital for monitoring our planet and for refining climate models.
Between August and October, the oceans swell due to ice melt and rainfall, shifting Earth’s center of mass toward the southern Pacific Ocean. The Pacific Ocean is so vast that its mass variations dominate those of the other oceans. Cold, dense winter air also helps tip the balance, for example over Arabia, Asia and northern Africa around December 21 each year.
The Synergy for the Future Beyond Low Earth Orbit
Accuracy in monitoring Earth’s center of mass has implications far beyond pure scientific research. Felix Landerer, a coauthor of the study, emphasized a point. Understanding these movements is essential, though “tiny.” It is crucial for the accurate positioning measurements on which the modern world relies. These advanced systems directly benefit global logistics and precision agriculture, but they also underpin the space navigation that will guide astronauts.
The next GRACE-Continuity (GRACE-C) mission, planned for launch in late 2028, will extend the GRACE data record for nearly twenty-five years. This long-term commitment to Earth science aligns perfectly with NASA’s vision of sustaining a long-term human presence beyond low Earth orbit. The convergence between meticulous Earth science and rigorous astronaut training is.
The astronaut candidates are preparing to graduate in 2027. They will join NASA’s active corps. Ultimately, their complete training and the ongoing research are two sides of the same coin. Both paths are indispensable to advancing NASA’s deep space exploration goals. They enable humanity to venture ever farther, supported by a solid scientific foundation and cutting-edge human capabilities.
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