In June, while beachgoers in Hawaii sit blissfully unaware, a flying saucer will descend over the island of Kauai. This is not a stunt for an alien invasion movie. NASA is gearing up to conduct the first test flight of a disk-shaped spacecraft designed to land heavy loads and, one day, people on Mars.
The Low-Density Supersonic Decelerator (LDSD) will be lofted into the stratosphere from the Navy's Pacific Missile Range Facility on Kauai. The inflatable technology is intended to help slow down vehicles after they enter the thin Martian atmosphere at supersonic speeds.
"It may seem obvious, but the difference between landing and crashing is stopping," says Allen Chen at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who oversaw the landing of the one-ton Curiosity rover in 2012. "We really only have two options for stopping at Mars: rockets and aerodynamic drag."
Until recently, NASA had used parachutes and air bags for most robotic landings on Mars, starting with the Viking mission in 1976. But the heavier the load, the harder it is to come in softly.
For the car-size Curiosity, NASA invented an ambitious system called the sky crane, which combined parachutes with landing gear powered by retro rockets that could lower the rover to the surface on tethers.
However, Curiosity pushed the weight limits of that technology, and human landings could require 100 tons per mission. Such weight can't be adequately slowed by parachutes in the Martian air, which is just 1 percent as dense as Earth's.
Rocket-powered landings are out of the question, too, as the atmosphere is still just thick enough to buffet incoming spacecraft with more turbulence than thrusters can accommodate.
The LDSD design solves this quandary by using a balloonlike decelerator and a giant parachute twice the size of Curiosity's. The decelerator would attach to the outer rim of a capsulelike entry vehicle. When the capsule is traveling about 2,700 mph, the device would rapidly inflate like a Hawaiian pufferfish to increase surface area. The added air resistance would slow the capsule down to about 1,500 mph, at which point the 110-foot parachute could safely deploy.
To simulate Mars's thin atmosphere on Earth, the team in Hawaii will first lift a test vehicle fitted with the LDSD system to about 23 miles above the Pacific Ocean using a high-altitude balloon. The craft will detach and fire a small rocket to reach a height of 34 miles.
As it falls back to Earth, the system will inflate, and moments later the parachute will fire. The saucer should gently splash down in open water.