Artificial gravity is the creation of an inertial force in a spacecraft, in order to emulate the force of gravity. This concept is often seen in but is not limited to science-fiction shows like "Star Trek", and researchers are currently working on methods to create artificial gravity in space.
Not only would the creation of artificial gravity simplify the next era of space exploration, making tasks more straightforward, but it would also be crucial for potential space tourism.
The effects of microgravity in space can actually be harmful to humans, so as we look at longer crewed missions, including journeying to Mars, artificial gravity could be essential to our astronauts' health.
Creating artificial gravity
In his 1905 theory of special relativity, Albert Einstein wrote that gravity and acceleration are actually indistinguishable. That means that in a rocket travelling at 31.19 feet per second (9.81 meters per second ) squared — the downward acceleration of gravity here on Earth — an astronaut would feel their body anchored to the floor just like it is on their home planet.
The problem is you can’t always be accelerating at this rate in space, especially in an orbiting space station. Fortunately, there is more than one form of acceleration — and by using centrifugal force we can generate something equivalent to gravity on Earth.
One possible way of creating artificial gravity in space is by utilizing a technology called an O’Neill cylinder. Named after the physicist who proposed them, Gerard O’Neill, this consists of a pair of massive cylinders that rotate in opposite directions, allowing them to be permanently directed toward the sun, replicating gravity.
Aside from being a long way from any kind of practical application, at 20 miles (32.2 kilometers) long and 4 miles (6.4 km) in diameter — designed to house several million people — O'Neill cylinders are way too big for most applications smaller than colonies in space.
Researchers at the University of Boulder Colorado have a smaller scale suggestion — rotating systems that could fit inside the rooms of spacecraft.
While this wouldn’t provide artificial gravity for the whole craft or station, it would enable space travellers to retreat to a specific area and spend some time experiencing a gravitational field more like that of Earth.
The system also uses centrifugal acceleration, replicating a gravitational field of 1G — the same as that on Earth — with astronauts lying down on a short-radius centrifuge for a quick spin.
Spinning astronauts might not be the ideal solution, however. As anyone who has ridden the teacups one too many times can tell you, this method comes with its own health effects.
Another potential design for creating artificial gravity is a long spinning stick-like vehicle around 328 feet (100 metres) across with a nuclear reactor on one end and a crew compartment on the other for journeys to Mars. However, these have had engineering issues preventing their application.
The health effects of microgravity
Establishing artificial gravity could be key to protecting the health of astronauts on long-term space missions. For five decades NASA’s Human Research Program (HRP) has studied the effects of microgravity on the human body.
They have found that deprived of the gravity of Earth weight-bearing bones lose on average 1 to 1.5% of mineral density every month of spaceflight. Muscle mass is lost more rapidly under microgravity conditions than on Earth.
In addition to these factors, during spaceflight, fluids in the human body can shift upwards putting pressure on the eyes that potentially lead to vision issues.
The Voyager space hotel
The Voyager space station is a planned rotating wheel space station set to begin construction in 2025. Pioneered by the Orbital Assembly Corporation (OAC) Voyager will differ from the International Space Station in two key ways; it will be open to the public, and it will have artificial gravity.
Placed in a low-Earth orbit, the space hotel will rotate rapidly enough to generate artificial gravity for its 400 occupants. If the station is completed as currently planned it will become the largest man-made structure ever placed into orbit.
The first steps of the project will include the creation of a prototype gravitational ring to improve that artificial gravity in space is viable. The 200-foot (61-meter) diameter ring will generate gravity equivalent to roughly 40% that of Earth's, or about the same as the gravity of Mars.
- NASA, "Artificial Gravity", March 2021.
- NASA, "The Human Body in Space", February 2021
- Theodore W. Hall, "Artificial Gravity in Theory and Practice", 46th International Conference on Environmental Systems, July 2016.
- National Space Society, "O’Neill Cylinder Space Settlement", accessed May 2022.
- National Space Society, "Stanford Torus Space Settlement", accessed May 2022.
- Orbital assembly, "The Space Gravity Experience Is Here", accessed May 2022.
- Nikolas Martelaro, "Powering the Stanford Torus", Stanford University, May 2017.