NASA engineers in Hawaii readied a 3.5-ton flying saucer-shaped test vehicle for a 23-mile-high balloon ride Saturday, followed by a rocket-powered climb an additional 11 miles for a high-speed flight through the extreme upper atmosphere to test an inflatable entry body and a huge supersonic parachute for eventual use at Mars.

Artist's concept of the Low-Density Supersonic Decelerator. Credit: NASA

Flying at four times the speed of sound in the thin air near the edge of space, the test vehicle was expected to experience conditions similar to what a spacecraft would find plunging into the atmosphere of Mars prior to landing.

The heaviest spacecraft ever sent to the surface of Mars -- NASA's Mars Science Laboratory, or Curiosity rover -- tipped the scales at about one ton. To get heavier robots to the surface, and eventual crewed spacecraft that could weigh 20 tons or more, NASA must develop better atmospheric braking systems.

Enter the Low-Density Supersonic Decelerator, or LDSD, the first of at least three test vehicles to fly in a $200 million research program aimed at developing new technologies for future Mars missions.

The first test vehicle's high-altitude balloon was scheduled for launch from the U.S. Navy's Pacific Missile Range Facility on Kauai, Hawaii, between 2:15 p.m. and 3 p.m. EDT. Initial attempts to launch the craft earlier this month were blocked by the weather, but officials said late Friday that forecasters expected acceptable conditions Saturday.

"Landing on Mars is an extremely challenging thing to do," said Ian Clark, LDSD principal investigator at the Jet Propulsion Laboratory in Pasadena, Calif. "The atmosphere is extremely thin, it's about 1 percent the density of Earth's atmosphere. That means you need very large devices to react against the atmosphere to create the drag that we use to slow the vehicles down as they enter the atmosphere.

"If you want to land things that are even heavier than the Mars Science Laboratory, if you want to land several tons -- and as you cast your eyes to the horizon and you think about landing humans on the surface of Mars, missions that will be 10 to 15 tons, 20 tons or more -- you're going to need extremely large drag devices to slow those vehicles down. We don't have those currently, and that's what LDSD is developing."

The test vehicle features two new technologies. The first is an inflatable torus around a traditional heat shield known as the Supersonic Inflatable Aerodynamic Decelerator, or SIAD, that gives the test vehicle the general shape of a flying saucer. The second new technology is a huge parachute, the largest ever designed to deploy at more than twice the speed of sound.

The LDSD test flight sequence. See larger image. Credit: NASA

A giant balloon measuring 460 feet across and nearly 400 feet tall when filled with 34 million cubic feet of helium was expected to carry the LDSD vehicle to an altitude of 120,000 feet, or about 23 miles, after launch from Kauai.

At that point, the LDSD was to be released. After small rocket motors fire to spin the vehicle up for stability, an ATK Star 48 solid-fuel rocket motor was programmed to ignite to accelerate the test article and boost it an additional 11 miles to some 180,000 feet, or 34 miles.

Flying at more than four times the speed of sound, the flight plan called for the heavily instrumented SIAD torus to inflate, expanding the diameter of the entry vehicle from about 15.4 feet to 19.7 feet. After slowing to about 2.5 times the speed of sound, the parachute was expected to unfurl to a diameter of 110 feet, quickly slowing the craft even more.

"What we're trying to do is replicate the environment in which these technologies would be used," Clark said. "That means replicating the atmosphere, in particular the density of the atmosphere, which at Mars is extremely thin. To find (those conditions) we have to go halfway to the edge of space, or about 180,000 feet here on Earth, to test these devices. And we have to go several times the speed of sound."

Four Go-Pro video cameras were on board to provide realtime coverage of the SIAD inflation and parachute deploy. Video from higher resolution cameras will be stored on board and recovered after the test vehicle splashes down in the Pacific Ocean at the end of its flight.

Mission duration, from balloon launch to splashdown, was expected to be about three hours.

"This is our first experimental test flight of this vehicle that is designed to carry the SIAD and the parachute to the proper conditions very high in Earth's atmosphere and very fast so that it looks like, to these articles, that they're flying at Mars," said Mark Adler, LDSD project manager at JPL. "So we test them in those conditions at full scale to make sure they're going to work at Mars."

The SIAD torus initially was tested at the Naval Air Weapons Station at China Lake, Calif., using a rocket sled to accelerate the device to several hundred miles per hour. To test the parachute, a long cable was connected, fed through a pulley system and attached to a rocket sled. The parachute then was released from a helicopter, the rocket sled was fired up and the parachute was pulled toward the ground with a force equivalent to about 100,000 pounds of drag.

The Low-Density Supersonic Decelerator includes a saucer-shaped decelerator and a new supersonic parachute. Credit: NASA

"Our objectives for this first flight are to launch it from here, get the balloon off and out over the water, to get it up to altitude where we can drop the vehicle and conduct this powered flight and get the data back from it to see how it works," said Adler.

He stressed the test flight was just that, a test flight, and any number of things could go wrong. But "if we fire that motor and we get data back from it, that is a great day. That way we can learn exactly what happened and understand what to do for our next flights."

Two more LDSD vehicles are being built for "flights of record" next summer.

"We've been there before, eight successful landings on the surface of Mars, the United States leads in this area," said Mike Gazarik, director of space technology development at NASA Headquarters. "It's one of the more difficult challenges.

"When we look at the Curiosity rover, which landed two years ago, it's about a metric ton on the surface of Mars. We know that for exploration, for future robotic exploration, for future human exploration, we need more than that. ... And so for us, it's the challenges of Mars -- how do we get there, how do we land there, how do we live there, how do we leave there?"

The Low-Density Supersonic Decelerator "focuses on that very difficult challenge of landing there."

"We need to test and we need to learn," Gazarik said. "And we need to do it quickly and efficiently. ... It's about more mass, going to more elevations on the surface of Mars and landing more accurately."