Researchers have invented a new soft robotic device with eight tentacle arms that allows astronauts to grasp and service objects in space at a low cost and low risk.
The novel system, created at the University of Southern California, blends different types of adhesion to grasp objects without friction or gravity in the void of space. The device, with multiple arms, can make hard physical contact with objects in a way that minimizes debris produced by adhesion to those targets, keeping the cosmos cleaner and paving the way to building bigger systems in space. The patent application for this Reactive Electro-Adhesive Capture ClotH Mechanism (REACCH) was published by the U.S. Patent and Trademark Office on April 1.
Nature has millennia of experience creating systems that are adaptable and strong, so lead inventor and USC research professor David Barnhart thought it would be best to turn to biology for inspiration — and octopuses caught his attention. The undersea invertebrates are unique in their flexibility: On one occasion, a 600-pound octopus squeezed itself into a tube the size of a quarter. And flexibility is key for designing a capture device that can both expand to grasp different types of objects and contract for easy transportation on a spacecraft.
Such a device has to be able to withstand a huge amount of force in order to grasp a range of target objects, from small satellites to large rocket parts 10 times heavier than the device itself. Once again, octopuses are a great model. These mollusks have an impressive amount of strength, Barnhart told The Academic Times, as they "can use their tentacles to crack open clams, which are hard structural elements."
"The natural question is: How do we make an octopus in space?" he added.
Each of the eight arms of the capture device is flexible with two joints on either end, similar to how an octopus's arms can bend and retract. The tentacles are independently controlled in a method that makes gripping a target object much more precise. They first provide a shear force to make contact and then use a second shear force to oppose the first, grasping and holding an object in the microgravity of space – an environment different from any on Earth, even deep underwater.
Multiple sets of tiles layered on the tentacle arms can be adjusted to control the force applied to the object, similar to the suction cups on tentacles. The tiles also mimic nature, using a gecko-like adhesion to attract a force between molecules on contact. The weightlessness of outer space requires a unique approach, and these adhesive tiles combined with the tentacles' flexibility can solve a whole host of issues with current grasping methods, Barnhart explained.
"To date, every interaction between two free-flying objects in space has been very scripted, which means it was pre-designed to know where to attach" to other objects, Barnhart noted. "There are a lot of things that are not controlled in space, tumbling and mutating in a crazy fashion," he continued. REACCH has a unique ability to safely match the rotation of a target object in a safe manner, which is important for the safety of people on board a spacecraft.
In the patent application, the co-inventors noted that REACCH has an "ability to morph between pure compliance and pure control." Its flexibility to shift from adjusting an object to controlling it, by reaching a target and establishing a connection, is very unique. Switching between both types of contact allows the device to grip a spinning object with a low amount of risk. Current methods are high-risk and have a high potential cost, as maneuvering two objects that are floating and spinning at different rates in zero gravity requires a huge amount of precision. REACCH makes this process easier for astronauts and at the same time cuts down on the manpower needed for such an operation, rendering the novel method cheaper than any currently used in space.
After the target is secured, the device slowly pulls it closer to the spacecraft. Pulling an object too fast would cause the grip to slip, but moving slowly allows the REACCH to retrieve an object of practically any size. "As long as the acceleration is very low, the ability to hold on to something that has a different mass is resilient," Barnhart said. In this way, REACCH allows astronauts to modify elements in space, which Barnhart notes is "a capability that we don't have today."
"Traditional spacecrafts are built to fail. You send them out there and will never get them back, and people accept that," Barnhart said. But the ability to recycle rockets could be a game-changer, according to him — and according to Elon Musk, who stated that the cost of space travel could be lowered by up to 100 times if engineers figure out how to reuse rocket bodies. With the help of REACCH, astronauts can repair and replace current structures in space to extend their lifespans. Barnhart thinks this emerging field of space logistics is crucial, as new technology is required to assemble bigger space stations and rockets in the future.
Prior to his career at USC, Barnhart was a program manager at the Defense Advanced Research Projects Agency, which funded this patent application. He noted that his team is working on another project called Starfish, "following that same biological analogy in soft robotics. We're struggling to find a way to mimic this beautiful, complex, yet simple structure that nature gives us to apply to this unique problem in space of being able to grab anything." He mentioned that an earlier prototype of REACCH was structured in the shape of a blanket, but following nature's designs proved to be more effective for the team.
In the future, Barnhart said the "goal is to have others pick up the research and expand upon it, hopefully reaching somebody with REACCH" and inspiring new inventors. "One of the great things about space is that it is a global commons, and my hope is that all these new technologies can be shared internationally to accelerate innovation," he explained.
The application for this patent, "Multi-armed soft capture system," was filed Sept. 28 with the U.S. Patent and Trademark Office. It was published April 1 with the application number 17/035329. The earliest priority date was Sept. 26, 2019. The inventors of the pending patent are David Barnhart and Rebecca Rogers, University of Southern California.
Parola Analytics provided technical research for this story.