Need a moment of levity? Try watching movies astronauts falling on the moon. NASA shots of Apollo astronauts stumbling and bouncing in ponderous motion are incredibly believable.
For MIT engineers, the lunar mishaps also represent an opportunity for innovation.
“Astronauts are very physically capable, but they can struggle on the Moon, where the gravity is one-sixth that of Earth, but their inertia is still the same. Moreover, wearing a spacesuit is a significant burden and can restrict movement, says Harry Asada, a professor of mechanical engineering at MIT. “We want to provide astronauts with a safe way to get back on their feet if they fall.”
Asada and his colleagues are designing a pair of wearable robotic limbs that can physically support an astronaut and lift him back to his feet after a fall. The system, which scientists have dubbed Supernumerary Robotic Limbs, or “SuperLimbs,” is designed to slide out of a backpack that also houses the astronaut’s life support system, along with the controller and motors that power the limbs.
Scientists built a physical prototype, as well as a control system that steers the limbs based on feedback from the astronaut using it. The team tested an initial version on vigorous people who also volunteered to wear tight clothing similar to an astronaut’s spacesuit. When volunteers tried to get up from a sitting or lying position, with the support of SuperLimbs, they did it with less effort compared to when they had to recover on their own.
The MIT team predicts that SuperLimbs could physically assist astronauts after a fall while helping them conserve energy for other crucial tasks. The project could prove especially useful in the coming years with the launch of NASA’s Artemis mission, which plans to send astronauts back to the Moon for the first time in more than 50 years. Unlike the largely exploratory Apollo mission, Artemis astronauts will seek to build the first enduring lunar base – a physically demanding task that will require many extended extravehicular activities (EVAs).
“During the Apollo era, astronauts had an 80 percent fall rate when doing excavation or other tool work,” says team member and MIT graduate student Erik Ballesteros. “Artemis missions will actually focus on construction and excavation, so the risk of collapse is much higher. We think SuperLimbs can help them recover so they can be more productive and extend their EVA.
Asada, Ballesteros and their colleagues will present their project and research this week at the IEEE International Conference on Robotics and Automation (ICRA). Their co-authors are postdoc Sang-Yoep Lee of MIT and Kalind Carpenter of the Jet Propulsion Laboratory.
Taking a stand
The team’s project is the latest use of SuperLimbs, which Asada first developed about a decade ago and has since adapted to a range of applications, including assisting workers in aircraft manufacturing, construction and shipbuilding.
Recently, Asada and Ballesteros have been wondering whether SuperLimbs could help astronauts, especially since NASA plans to send astronauts back to the lunar surface.
“In communication with NASA, we learned that the issue of falling to the Moon is a serious risk,” Asada says. “We realized we could make some modifications to our design to help astronauts recover from falls and continue working.”
The team first took a step back to study how people naturally recover from falls. In the up-to-date study, they asked several vigorous volunteers to try to stand up straight after lying on their sides, fronts, and backs.
The researchers then looked at how the volunteers’ standing attempts changed when their movements were restricted, just as astronauts’ movements are restricted by most of their space suits. The team built a suit that mimicked the stiffness of time-honored spacesuits and asked volunteers to put it on before they tried again to get up from various fallen positions. The sequence of movements of the volunteers was similar, although it required much more effort compared to free trials.
The team mapped each volunteer’s movements as they stood up and found that each of them performed the same sequence of movements, moving from one position, or “landmark,” to the next in a predictable order.
“These ergonomic experiments helped us easily model how a human stands,” says Ballesteros. “We could postulate that about 80 percent of people behave in a similar way. We then designed a controller that took this trajectory into account.”
A helping hand
The team developed software that could generate the robot’s trajectory in a sequence that would support hold the human and get them back on their feet. They attached the controller to a hefty, stationary robotic arm, which they attached to a huge backpack. The researchers then attached the backpack to the bulky suit and helped the volunteers put the suit back on. They asked volunteers to lie on their back, front or side again, and then asked them to try to stand up while the robot sensed the person’s movements and adjusted to support them stand up.
Overall, the volunteers were able to stand steady with significantly less effort when they were assisted by the robot, compared to when they tried to stand alone while wearing a bulky suit.
“It feels like there’s an extra force moving with you,” says Ballesteros, who also tried the suit and arm support. “Imagine that you are carrying a backpack, someone grabs it by the top and pulls it up. Over time, it becomes natural.”
The experiments confirmed that the control system could effectively guide the robot to support a person get up after a fall. The researchers plan to pair the control system with the latest version of SuperLimbs, which consists of two multi-jointed robotic arms that can extend from a backpack. The backpack would also contain the robot’s battery and motors, as well as the astronaut’s ventilation system.
“We designed these robotic arms based on AI search and design optimization to look for designs for classic robotic manipulators with some engineering constraints,” says Ballesteros. “We analyzed many designs and looked for one that uses the least amount of energy to lift a person. This version of SuperLimbs is a product of that process.”
Over the summer, Ballesteros will build the full SuperLimbs system at NASA’s Jet Propulsion Laboratory, where he plans to streamline the design and minimize the weight of its parts and engines using advanced, lightweight materials. Next, he hopes to connect the limbs to astronaut suits and test them in low-gravity simulators to one day support astronauts on future missions to the Moon and Mars.
“Wearing a space suit can be physically taxing,” notes Asada. “Robotic systems can help reduce this burden and help astronauts be more productive during missions.”
This research was supported in part by NASA.