A saucer-shaped NASA vehicle testing new technology for Mars landings made a successful rocket ride over the Pacific on Saturday, but its massive descent parachute only partially unfurled.

The Low Density Supersonic Decelerator was lifted by balloon 120,000 feet into the air from the Hawaiian island of Kauai. The vehicle then rocketed even higher before deploying a novel inflatable braking system. But cheers rapidly died as a gigantic chute designed to slow its fall to splashdown in the ocean emerged tangled.

Still, NASA officials said it's a pretty good test of technology that might one day be used to deliver heavy spacecraft — and eventually astronauts — to Mars.

NASA planned a news conference on the flight Sunday.

Since the twin Viking spacecraft landed on the red planet in 1976, NASA has relied on the same parachute design to slow landers and rovers after piercing through the thin Martian atmosphere.

NASA-Mars Test

This image provided by NASA shows the saucer-shaped vehicle, which carries an enormous parachute, as it rises into the upper atmospher suspended beneath a high-altitude balloon. The technology could be used to land on Mars. (NASA/Associated Press)

The $150-million US experimental flight tested a novel vehicle and a giant parachute designed to deliver heavier spacecraft and eventually astronauts. Despite small problems including the giant parachute not deploying fully, NASA deemed the mission a success.

"What we just saw was a really good test," said NASA engineer Dan Coatta with the Jet Propulsion Laboratory in Pasadena, Calif.

Viewers around the world with an internet connection followed portions of the mission in real time thanks to cameras on board the vehicle that beamed back low-resolution footage.

After taking off at 11:40 a.m. PT from the Pacific Missile Range Facility on the Hawaiian island of Kauai, the balloon boosted the disc-shaped vehicle over the Pacific. Its rocket motor then ignited, carrying the vehicle to more than 50 kilometres high at supersonic speeds.

The environment at that altitude is similar to the thin Martian atmosphere. As the vehicle prepared to drop back the Earth, a tube around it expanded like a Hawaiian puffer fish, creating atmospheric drag to dramatically slow it down from Mach 4, or four times the speed of sound.

Then the parachute unfurled — if only partially — and guided the vehicle to an ocean splashdown about three hours later. At 33 metres in diameter, the parachute is twice as big as the one that carried the one-ton Curiosity rover through the Martian atmosphere in 2011.

Coatta said engineers won't look at the parachute problem as a failure, but as a way to learn more and apply that knowledge during future tests.

"In a way, that's a more valuable experience for us than if everything had gone exactly according to plan," he said.

A ship was sent to recover a "black box" designed to float after separating from the vehicle. Outfitted with a GPS beacon, the box contains the crucial flight data that scientists are eager to analyze.

"That's really the treasure trove of all the details," Coatta said. "Pressure, temperature, force, high-definition video: All those measurements that are really key to us to understanding exactly what happens throughout this test."

The test was postponed six times because of high winds. Conditions needed to be calm so the balloon wouldn't stray into no-fly zones.

Engineers planned to conduct several more flights next year before deciding whether to fly the vehicle and parachute on a future Mars mission.

"We want to test them here where it's cheaper before we send it to Mars to make sure that it's going to work there," project manager Mark Adler of the Jet Propulsion Laboratory told reporters in Kauai in early June.

The technology envelope needs to be pushed or else humanity won't be able to fly beyond the International Space Station in low-Earth orbit, said Michael Gazarik, head of space technology at NASA headquarters.

Technology development "is the surest path to Mars," Gazarik said at the briefing.