By Dr. Gary L. Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
This is the second of a five-part series on the dynamics of human spaceflight systems for interplanetary and deep space missions.
In part I, we examined the size and design elements of future manned spacecraft. Now we will look at the need for gravity aboard manned spacecraft, and how we might go about achieving artificial gravity in deep space.
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Gravity is an extremely important component to maintaining astronaut health. Research on past astronauts has shown conclusively that prolonged exposure to zero gravity, or microgravity, has a number of adverse health effects, including loss of bone density, muscle atrophy, and deterioration of bodily systems and organs.
Exercise and other preventative tactics can help to delay or minimize these afflictions, but completely nullifying them doesn’t appear to be possible at this time. Granted, some of our astronauts have stayed aboard the ISS for close to a year. Although they experienced these health degenerations, they ultimately recovered after returning to Earth and few had any serious lasting effects. So with that in mind, it is theoretically possible that humans could endure short trips in microgravity such as those that would be required to reach Mars or Venus.
To Go Farther than Mars or Venus Would Certainly Require a Form of Simulated Gravity
However, missions to go farther and longer would almost certainly require simulated gravity to avoid long-term and potentially irreparable damage to the astronauts’ health. There are two practical ways of simulating gravity: acceleration and centripetal force.
The acceleration method would require maintaining a consistent spacecraft acceleration of 1G (or 9.8 miles per second squared, m/s2) until the halfway point in the trip is reached. The space station would then need to turn itself around, so that the “floor” that the crew members stand on inside the spacecraft is oriented toward the destination. Then retro-rockets must be fired to decelerate at the same constant rate of 1G until the spacecraft reaches its destination, at which point its net velocity should be zero.
Using Acceleration, the Space Station Could Conceivably Be in Any Shape and Size
The advantage to the acceleration method is that the space station could conceivably be any desired shape or size. The disadvantage is that trip times, speeds, fuel consumption, and other variables are all confined to relatively fixed parameters in order to maintain the acceleration necessary to simulate Earth’s gravity.
Another drawback lies in limitations presented by the laws of the universe. One cannot accelerate infinitely, and as one accelerates the energy needed to go faster increases exponentially. The speed of light is an unreachable barrier as infinite energy would be required for such speed. However, this is not a problem that needs serious attention for most trips, as it would take a spaceship, accelerating at 1G, 30 million years to reach light speed. More on this topic in Part III.
The second method of simulating gravity is centripetal force, or in other words, through the use of a rotating spacecraft. This rotation creates a) centrifugal force that would push all objects within the space station outward, and b) centripetal force that counterbalances the force outward with resistance directed inward.
Rotating Spacecraft Offer Much Greater Freedom in Planning Trip Dynamics Like Speed
The advantage to using rotation to simulate gravity is that this space station motion could be independent or complementary to the acceleration and deceleration of the station itself during the trip. So there is much greater freedom in planning trip dynamics like speed, time, fuel, and so on. However, like the acceleration method, there are significant disadvantages to utilizing rotation to simulate gravity.
First, the space station can only be one shape: circular. This could be a ring or any cross-section of a cylinder, where the inside surface serves as the “floor” on which the crew stand when the centrifugal force pushes them outward (or “down” from their perspective inside the ship). The other key drawback is that the space station must be sufficiently large and rotating sufficiently fast to create the right amount of force that accurately approximates Earth gravity, but does not cause motion sickness in the crew.
Researchers don’t yet know even the minimum parameters for size and number of revolutions per minute (rpm) needed to comfortably simulate gravity in space this way. That’s because human bodies behave differently in space and the same conditions cannot be replicated perfectly on Earth.
However, estimates based on the information we have so far suggest that a ring-shaped space station would have to be at least 650 feet (200 meters) in diameter, and would have to be rotating at no less than one to three rpm to simulate 1G. Building a spacecraft of that size or larger with this kind of capability would be the most expensive project in history. So the subject of gravity remains a solvable, though extremely challenging problem.
In the next part, we’ll discuss different kinds of propulsion systems that might be used on future spacecraft to cross vast distances in reasonable amounts of time.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.