A prototype inflatable braking system to land heavy payloads on Mars aced a debut test flight in June, but its supersonic parachute will need to be reshaped to better accommodate the turbulent airflow of rapid descent, NASA engineers said Friday.

NASA’s Low-Density Supersonic Decelerator (LDSD) rocketed to an altitude of 190,000 feet after being carried into the stratosphere by a massive helium balloon.

The thin air and low pressure at that altitude is as close as engineers can come to simulating flight in Mars’ atmosphere.

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The idea of the experiment was to accelerate the braking system to four times the speed of sound, which is roughly the speed that a spacecraft from Earth would hit the Martian atmosphere.

“Our main objective was to show that we can get this vehicle to altitude, that we can get it to conditions that the technologies will see when they actually fly at Mars,” LDSD project manager Mark Adler, with NASA’s Jet Propulsion Laboratory in Pasadena, Calif., told reporters at a press conference Friday.

Once in position, the vehicle inflated a doughnut-shaped air brake to increase its surface area and thus the amount of energy that could be dissipated by frictional heating during the fall through the atmosphere.

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That part of the test went better than expected, lead researcher Ian Clark, also with JPL, told reporters.

The structure inflated quickly and uniformly and managed to maintain its 20-foot diameter shape with only about 0.8 inches of deflection, which for an inflated structure is “pretty remarkable,” Clark said.

Problems began with the deployment of a supersonic parachute, which was quickly torn apart as it attempted to inflate while moving at  2,500 mph.

“We’ve  leaned that we have more to learn about supersonic parachute inflation,” Clark said. “There’s a lot of physics to this problem that we’re now getting new insights into.”

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For example, engineers now know that the parachute’s shape is more important than originally thought.

The parachute that flew in June was designed for drag and stability in sub-sonic, steady descent, Clark said.

“We didn’t have a lot of insight into the nature of supersonic parachute inflation,” he added.

Engineers plan two more test flights next summer from the U.S. Navy’s Pacific Missile Range Facility on Kauai, Hawaii.

“This flight was really just a shakeout flight,” Clark said.