An alternative method that might eliminate some of these problems is “simulated gravity,” which uses a spinning structure to create centrifugal force that would have the same effect on the body as gravity would.
Whether or not this would solve the problems caused by lack of gravity remains to be seen. Still, NASA seems keen on the idea — to the tune of a $600,000 NASA Innovative Advanced Concepts (NIAC) Phase II grant to a team from Carnegie Mellon University (CMU) and the University of Washington (UW) who is looking to develop a structure that can simulate full Earth gravity and be launched in a single rocket.
The project in question is “Kilometer-Scale Space Structure from a Single Launch,” which was initially admitted to the NIAC program last year. Over the past year, they successfully completed a Phase I project where they “analyze[d] a mission concept analogous to the Lunar Gateway” that could deploy into a kilometer-long structure. Having met NASA’s expectations as part of that program, the team, headed by professor Zac Manchester of CMU and Jeffery Lipton of UW, were recently accepted as 2022 NIAC fellows.
This isn’t the first NIAC project addressing the idea of large structures in space, though. NextBigFuture reported in 2021 on around a dozen NIAC funded projects that would take advantage of new metamaterials to dramatically expand their size once in space. NASA isn’t alone in their support either — China’s National Science Foundation has supported efforts to develop a kilometer-sized object to the tune of $2.3 million.
Such large structures need large investment, but they also have large potential benefits. There are two options to reach Earth’s gravity using centrifugal forces. Either spin really, really fast, or have a really, really big axis of rotation. Unfortunately, humans, being the squishy bags of water that they are, don’t really like to spin super fast for long periods, as anyone who has ever gotten sick on a carnival ride can tell you. Science puts that rotational speed limit for discomfort at around 3 RPM. So, to rotate at less than 3 RPM and still have the benefit of a full Earth’s worth of simulated gravity, the structure itself must be a kilometer long.
Fitting that much material in a single rocket launch so far has proven impossible. But, Dr. Manchester and his team think they have found a potential solution to the impossible problem — a “high-expansion-ratio deployable structure” or HERDS. HERDS themselves utilize two novel mechanical innovations — shearing auxetics and branched scissor mechanisms.
Shearing auxetics are a novel type of metamaterial that will expand when pulled in a chiral pattern. The level of chirality can also control the stiffness of the material. They seem to be gaining traction in robotic applications as linear actuators and grippers, but their use case in space has yet to be proven.
YouTube video showing shearing auxetics in action. Credit – Lillian Chin YouTube Channel
Branched scissor mechanisms are another way to deploy a larger structure from a compact one. Originally developed by YouTuber and artist Henry Segerman, branched scissor mechanisms snap into much larger structures from more compact ones. You can even buy a demo kid yourself from Shapeways, but once again, the structures haven’t yet been used in space.
A video showcasing branched scissor mechanisms. Credit – Henry Segerman
Ideally, one or both of these systems would work to create the structure of a kilometer-scale space habitat capable of rotating at a speed that would sufficiently simulate Earth’s gravity. Drs. Manchester, Lipton, and their team think they can utilize these technologies to create tubular structures that can expand up to 150 times their size when packaged in a rocket fairing. That’s an ambitious goal, but they have the time and some funding to work on it. At the end of the two-year NIAC study period, if the idea is well fleshed out enough, these new technologies might even have time to be integrated into the plans for the Lunar Gateway.