The Need for “Artificial Gravity Health Centers” on the Moon
The four astronauts on Artemis II were in space for 9 days and did not suffer any significant medical problems from the low gravity environment that they experienced. But for space journeys lasting years, it is necessary to produce an analog of Earth’s gravity in order to protect astronaut health. Without gravity, bones lose mineral density at a rate of about 1.5% per month and muscles atrophy rapidly. Bodily fluids move towards the head, potentially causing eye damage and brain swelling.
There are two simple ways to produce artificial gravity. One is by accelerating astronauts on a rocket or any other propulsion system. The artificial linear acceleration would be indistinguishable from gravity for the passengers, for the same reason that gravity is not experienced in a free-falling elevator.
The challenge with this method is to have sufficient fuel for a prolonged acceleration phase. Steady acceleration at 1-gee for a full year brings a payload to the speed of light. This means that the required energy for a year-long journey equals the rest-mass of the payload. Chemical rocket fuel only converts a billionth of its rest mass to pure energy. Nuclear fusion of deuterium-tritium fuel converts 0.37% of the fuel rest mass to energy. In order to accelerate at 1-gee for a year and reach the speed of light, a rocket must carry anti-matter fuel that would annihilate a mass of matter comparable to that of the payload. CERN produces about a billionth of a gram of antimatter per year. To accelerate a lightweight 140-kilogram human at 1-gee for a full year would require CERN to produce antimatter for 140 trillion years, a period ten thousand times longer than the current age of the Universe.
The more practical method for generating artificial gravity is to spin a large structure so that the centripetal force would push passengers against the outer walls away from the rotation axis with a force that feels like gravity. This can be realized in a torus or a wheel-like structure or with two modules connected by a long tether and rotated around a common center.
To create the Earth-like gravity of 1-gee, equal to 9.8 meters per second squared, without causing dizziness for human passengers from high rotation speeds, the radius of the rotating structure needs to be larger than the Artemis II Space Launch System. A system with a radius of 100 meters needs to rotate three times per minute in order to generate a centripetal acceleration of 1-gee. A system with a radius of 1-kilometer needs about one rotation per minute. The centripetal acceleration scales as the radius divided by the square of the rotation-period.
The surface gravity on the Moon is 16.6% of the 1-gee on Earth. On Mars the value is 38% of gee. The health hazard for astronauts spending extended periods time on a permanent human base on the Moon needs more attention from NASA or space corporations like SpaceX or Blue Origins.
If humans will need to stay on the Moon or Mars for extended periods of time, one could imagine creating “artificial gravity health centers” for them, equipped with huge centrifuges measuring a kilometer in radius and rotating once per minute. Local residents will visit these rotating giant structures periodically to get the “1-gee experience” and rejuvenate their bodies. This is the kind of infrastructure that nobody talks about.
Other health risks on the Moon involve the exposure to energetic cosmic rays with 200 more radiation intensity than on Earth, enhancing the rates of cancer, central nervous system damage, and degenerative tissue effects. In addition, the lunar surface is covered with fine dust from asteroid impacts. Unlike dust on Earth, lunar dust was never eroded by wind or water, leaving it sharp like shattered glass.
There is no place like home.
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Progress report on my first bronze sculpture: “The Alien”
Five months ago, the accomplished artist Greg Wyatt gifted me two bronze sculptures of Galileo Galilei and 51 watercolors which transformed my Harvard office into a mini-museum. But Greg’s biggest gift was a chunk of plastelina for me to create an original sculpture, which I chose to name: “The Alien”.
In crafting this sculpture, I imagined what an ideal alien body might include, supplementing the human body with a third eye, a third leg, wings, and technological devices. I shipped my creation to Greg three months ago. By now, my sculpture progressed to the next phase and was cast in red wax.
Greg informed me of the wonderful news in an email and added that once the Alien sculpture is casted in bronze with a beautiful patina, he will make sure that it is mounted on an appropriate size cherrywood pedestal. I responded:
“Dear Greg,
This is amazing. The alien sculpture is becoming a reality. I will do my best to discover a real alien for comparison before the sculpture is cast in bronze.
With deep gratitude.
Avi”
Below are three perspectives of the red wax phase of the sculpture.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, former director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics (2005–2026), and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
