Gravity of the Situation: Time for the “G-whiz” Factor?

The emergence of private space stations is sparking renewed interest in harnessing centrifugal force to produce artificial gravity and make life in Earth orbit — or in transit to other worlds — far less deleterious to the human body.

Extended stays in microgravity have been linked to worsening eyesight, muscle loss, cardiovascular problems, and weakening bones, to list just a few examples. Therefore, finding ways to keep people healthy as they journey through the cosmos is of utmost importance, and several companies are now developing possible solutions.

For instance, there is Vast of Long Beach, California and its Haven-1 and Vast-1 missions. “By building artificial gravity habitats, we aim to create a more optimal environment for long-term stays in space,” states the company’s website. A large spinning structure in space “provides a pull that mimics the gravitational environment human bodies are accustomed to, thus reducing the detrimental physiological effects that extended stays in zero gravity cause.”

Seattle-based Gravitics also sees its StarMax building block space module as getting a leg up on imitating Earth’s gravity. “We’re growing the number of people living and working in space through human-centric space solutions,” states its website.

Luxury space outpost

Recently joining in on “G-whiz” space stations is Airbus, the European multinational aerospace corporation. Last month, it unveiled renderings and plans for LOOP, a multi-purpose orbital station.

As artwork goes, LOOP is an impressive space outpost. It consists of three levels: a habitation deck, a science deck, and a centrifuge that can create gravity conditions for onboard residents, thereby easing the stress of weightlessness on the human body.

Hurled into orbit in one piece via a super-heavy lift booster, Airbus LOOP, as viewed today, would be flexibly adapted to customer requirements, Jeremy Close, director of United Kingdom communications for Airbus Defense and Space, told SpaceRef. It is by no means certain, he said, that LOOP will actually contain a centrifuge.

Pain points

But Airbus architects decided to “think big” — as big as they possibly could, Close said.

“We wanted to address typical pain points of human spaceflight, and also think long-term,” Close said. The Airbus LOOP could potentially also serve as an element of interplanetary travel, he said, “hence, we included a centrifuge into the concept.”

The centrifuge could help reduce the stress that long-term stays in microgravity can have on the human body. “Placing the exercise bike there is an example, as exercising under gravity conditions would potentially be more effective than exercising in microgravity,” added Close.

Coping with the Coriolis effect

Also in spin up-mode is Above: Space Development Corporation of Huntsville, Alabama, which is eyeing space-based business parks with variable gravity. “We Provide Gravity” is a company mantra.

But one problem stemming from rotating spaceships is a strong Coriolis effect, or the merry-go-round-like force pulling away from a spinning center of mass. This can cause what’s called the Coriolis cross-coupled illusion, which results in disorientation and motion sickness.

Likening rotation and artificial gravity to overthrowing the “tyranny of the rocket equation” and taming the knowhow for powered escape into space, Tom Spilker, chief space systems architect for Above: Space says that encountering and countering the Coriolis effect is equally tyrannical.

Spilker is engaged in several initiatives, including the group’s Pioneer-class and Voyager-class space stations, to hasten the arrival of gravity-simulating habitation environments for leisure, commercial, and industrial activities.

How much artificial gravity?

In the future, Spilker added that research — likely carried out in low Earth orbit — will yield findings about how much artificial gravity is needed to be useful. A key question to tackle: What levels of artificial gravity are required to mitigate physiological effects?

“Currently, threshold gravity levels that avoid the various maladies brought on by microgravity are unknown and are the topics of basic research,” Spilker told SpaceRef. Unfortunately, that research is difficult to perform on Earth’s surface, or even in the brief periods of freefall afforded by parabolic aircraft flights.

With that knowledge in hand, Spilker told SpaceRef that space system architects, engineers, and physiologists will engage the Coriolis effect by coming up with designs that are “physically and economically feasible” without inducing “incapacitating levels of nausea and other effects of too-rapid rotation.”

Higher spin rates

Studying the idea of applying artificial gravity for space travel is Torin Clark, assistant professor in aerospace engineering sciences and biomedical engineering at the University of Colorado, Boulder.

One of the assumed limitations of short radius centrifugation, where one spins very fast, is that it tends to cause the aforementioned Coriolis effect-linked disorientation, Clark told SpaceRef.

Through incremental acclimation, Clark and colleagues found test subjects were able to eventually tolerate much higher spin rates. That translates into a far shorter radius centrifuge, roughly 6.5 feet (2 meters), which could fit within a room, rather than spinning the full habitat, he said.

Through a meta-analysis of previous studies using bed rest, Clark’s study team found that mitigation of physiological deconditioning of the human body is more effective when applied for longer and at higher g-levels.

The most commonly-used approach for intermittent centrifugation — done for 30 minutes to one hour per day at levels equating Earth’s gravity — is likely insufficient for preventing the bone loss and muscle loss that can result from life in microgravity, Clark said. “We suggest at least two hours, and maybe higher g-levels.”

Run the experiments

In terms of the future of artificial gravity, Clark said it is “tough to do” yet “likely necessary” for long-duration missions.

“We have never had a centrifuge in space that has been assessed as a countermeasure for physiological deconditioning,” Clark said. “But we know current countermeasures, such as exercise, are insufficient for all physiological systems.” And there may be further problems for missions of two-plus years in which deconditioned astronauts touch down far from Earth and don’t have the aid of ground support crews. “This motivates future ground-based and spaceflight research,” Clark added.

Similar in view is Dava Newman, Apollo Professor of Astronautics chair at the Massachusetts Institute of Technology in Cambridge, Massachusetts. As we prepare to go back to the Moon and plant footprints on Mars, Newman told SpaceRef, we need to understand how one-sixth gravity on the Moon or three-eighths gravity on Mars impacts the health and productivity of space travelers.

“We need to look at short arm centrifugation. Huge structures like in the 2001 movie, that’s great and engineers love it. But that’s not affordable. Let’s do what we can afford and do what we know about technologically,” said Newman, touting the advantage of using private space stations to support technology demonstrations.

“Let’s run the experiments and go beyond the power point charts,” Newman stated. “I’d actually love to have a centrifuge on the Moon so we can test out Mars gravity as well.”

Logical next step

Indeed, the dawning of private space stations is good news for such experimentation. Commercial space can accelerate the implementation of artificial gravity, said Jeffrey Sutton, Friedkin Professor and Founding Director of the Center for Space Medicine at Baylor College of Medicine in Houston, Texas.

“As we enter a new era of commercial space transport vehicles and space stations, along with a growing and diverse group of private space adventurers willing to participate in research studies on themselves, the opportunity is ripe to implement human-rated artificial gravity investigations in the space environment,” Sutton told SpaceRef. “A logical next step is to conduct this using a human-rated short-arm centrifuge,” he said.

Sutton pointed out that by taking that step, one could look in real-time at the potential benefits of using intermittent artificial gravity during a long-duration mission in low-Earth orbit. One would also be able to study real or potential negative effects, perhaps some of those being unanticipated, he said.

“Artificial gravity is difficult to implement, whether it be by rotating vehicle design or by flying a centrifuge,” Sutton concluded. “The operational need, feasibility, and efficacy can be debated at length on Earth, but until you actually subject individuals to artificial gravity in the space environment, the jury will remain out.”

Correction (5/25/2023): This article has been updated to correct Jeffrey Suttion’s professional title. SpaceRef regrets the error.