Landing rovers and helicopters on Mars is a challenge. It’s even more challenging if you don’t have enough information about the loads on the parachutes during the descent to the surface. Researchers at NASA’s Armstrong Flight Research Center in Edwards, California, are experimenting with readily available, highly elastic sensors that can be attached to a parachute during testing to provide the missing data.
Knowing how the canopy material stretches during deployment can improve safety and performance by quantifying the fabric’s limits and improving existing computer models to create more reliable parachutes for tasks like landing astronauts on Earth or delivering scientific instruments and payloads to Mars. This is the work that Enhancing Parachutes by Instrumenting the Canopy, or EPIC, is pursuing to improve the ability to measure parachute tension.
“We want to prove which sensors will work in determining the load on the material of the parachute roof, without this being at the expense of this material,” says LJ Hantsche, project manager. NASA’s Space Technology Mission Directorate is funding the team’s work through the Early Career Initiative project.
The team started with 50 potential sensor candidates and narrowed down and tested 10 different types of sensors, including commercially available and developmental sensors. The team selected the three most promising sensors for further testing. These include a silicon-based sensor that works by measuring a change in the storage of electrical charge as the sensor is stretched. It is also easy to attach to data acquisition systems, Hantsche explained. The second sensor is a small, stretchable braided sensor that measures the change in electrical storage. The third sensor is made by printing a metallic ink onto a thin, flexible plastic.
Determining ways to attach each of the sensors to the canopy’s super-thin, slippery material was tricky, Hantsche said. Once the team figured out how to attach the sensors to the fabric, they were ready to begin testing.
“We started with uniaxial testing, where each end of the parachute material is secured and then pulled to failure,” she said. “The test is important because stretching the sensor causes the electrical response. Determining the correlation between strain and sensor response when it is on the fabric is one of our key measurement goals.”
This test phase was conducted in collaboration with NASA’s Jet Propulsion Laboratory in Pasadena, California. A fast version of this test, which simulates the speed of parachute deployment, was conducted at NASA’s Glenn Research Center in Cleveland.
The team used a bubble test for the sensors, which simulates testing a 3D parachute. It consists of the fabric sample and a silicone membrane sandwiched between a four-inch diameter ring and the test structure. When pressure is applied from the inside, the silicone membrane expands the fabric and the sensor into a bubble shape. The test is used to validate the performance of the sensor as it flexes and is compared to the other test results.
As the EPIC project nears completion, follow-up work may include temperature testing, developing the flight data acquisition system, determining if the sensor can be parachuted without adverse effects, and operating the system in flight. The EPIC team is also working with researchers at NASA’s Langley Research Center in Hampton, Virginia, to test their airborne sensors later this year using the center’s drone test, which involves dropping a capsule with a parachute.
In addition, the EPIC team is working with the Entry Systems Modeling Group at NASA’s Ames Research Center in California’s Silicon Valley to propose a comprehensive parachute project aimed at better understanding parachutes through modeling and flight testing. The joint NASA project could result in better parachutes that are safer and more reliable for the approaching era of exploration.