Watch JPL Engineers Put a Mars Lander’s Legs to the Test

Montalvo called out a 3-2-1 countdown, and the lander swooped down with a bang, slamming into the guardrail. When the team studied the high-speed video later, they were surprised to find a perceptible wobble in one of the leg’s main struts. Increase the lander’s size, and this wobble would be even more noticeable. In response, stronger flight struts will be designed to handle those forces.

The team has also tested the lander’s “load limiters” – steel rods connecting its chassis to its legs. When the legs move during touchdown, the rods are forced to bend, absorbing some impact. The limiters were used on past landers like InSight, but they’re bigger on this prototype and will be even bigger on the final design.

“You’d never be able to bend these steel rods with just your hands,” Montalvo said. “It’s pretty insane seeing just how much force goes into them, bending them nearly in half after a drop.”

Testing of the lander’s full-size foot pads has been taking place in a box filled with 10,000 pounds (4,536 kilograms) of powdery, Mars-like soil. About 16 inches (41 centimeters) in diameter, the flat, round footpad attaches to an assembly with nearly a half-ton of iron weight plates.

Patrick DeGrosse, the test bed lead, kept watch during one test as the lander foot plunged into the soil, leaving a deep indentation while tossing a cloud of dust. The impact shook the walls of the building. Afterward, high-speed cameras showed how energy radiated out from the pad.

“We don’t want the lander’s feet to sink so far that the bottom of the lander hits the surface,” DeGrosse said. “And we want to make sure the lander is very even on the surface. It needs to be sturdy, because the lander is also a platform for the rocket to lift off from.”

After each test, DeGrosse rebuilds the soil bed 4 inches at a time, tamping down the material to make sure it’s compressed the way scientists expect it to be on Mars. The conditions also need to be consistent for the team to understand how the footpad interacts with the soil. So DeGrosse repeats this time-consuming process four times a month.

“You have to rebuild Mars multiples times to do this test,” he said.