Halfway to space in the skies above Hawaii, NASA successfully tested its Low-Density Supersonic Decelerator, a vehicle equipped with new technology for ferrying heavy payloads to Mars. A massive balloon lifted the saucer-shaped vehicle from a naval base in Kauai at 11:45 a.m. (Pacific) on Saturday morning, and it splashed down three hours later in the salty Pacific.
"It worked beautifully," Mark Adler, the project manager from NASA's Jet Propulsion Laboratory, told reporters Sunday morning from the Pacific Missile Range Facility. "The test was 100% successful."
NASA's primary goal was to evaluate whether shooting the vehicle into Earth's stratosphere with a rocket strapped to its back could reasonably simulate the conditions a spaceship might face entering Mars' atmosphere from outer space.
They also needed to confirm that they could successfully monitor the experiment and capture data during the flight that will enable them to improve LDSD's design in the future. On Sunday, the scientists headed to the base's port to meet the boats that recovered the balloon, the vehicle, its black box and its parachute.
The team will spend the next weeks and months inspecting the vehicle and digging through gigabytes of data recorded during the LDSD's short voyage to understand exactly what went right and what did not.
At the climax of Saturday's flight, preliminary measurements confirmed that the spaceship screamed through the thin air at Mach 4, four times the speed of sound — the supersonic velocity Adler's team sought to achieve.
This means they will be able to use the same testing infrastructure next year for more rigorous evaluations of the LDSD's inflatable doughnut, known as a SIAD (Supersonic Inflatable Aerodynamic Decelerator), and its parachute, the elements of its design actually responsible for deceleration. The team tested the SIAD and the parachute on Saturday, although Adler says this was for "extra credit."
They already know from video footage taken by cameras on the vehicle that while the SIAD seemed to perform "flawlessly," according to mission principal investigator Ian Clark, the parachute did not deploy correctly. With the chute only partially inflated, the LDSD slammed into the ocean at speeds estimated around 20 to 30 mph, Clark said at the news conference. The vehicle looks to have survived intact.
Clark and Adler knew well before the balloon launch that the parachute could be a problem. Clark, who specializes in entry, descent and landing technologies such as supersonic parachutes, explained why: "They're tantalizing in that you think you can understand them." But the complex physics that govern how they unfurl can confound even the careful calculations of rocket scientists, he said.
Engineers like Clark want badly to understand them because they provide an unrivaled amount of resistance for their weight; a 200-pound chute can produce 120,000 pounds of drag.
"Take 200 pounds of rocket fuel, or anything else, you are not going to get that much deceleration," Clark said.
But they are devious.
For LDSD's 100-foot-diameter chute to open properly, hundreds of thin nylon strings, rated for different strengths, must break at precisely the right time in precisely the right order.
"It's a really complicated process," Adler said. "It's like this jellyfish that's trying to turn into a parachute."
The bulk of the material is plain old rip-stop nylon ("stuff you can buy at JoAnn Fabrics," Clark said) held together by a strong Kevlar skeleton. Uncompressed, the chute easily fills a wooden shipping create. On the LDSD, the chute gets crammed into a small canister, packed by a hydraulic press until the fabric reaches the density of oak wood.
Deploying the chute on the LDSD presents an additional challenge because there is a rocket engine sitting right where the chute should be. This was installed for tests on Earth and would not be needed on a vehicle sent to Mars.
Clark and the team came up with a creative solution to work around this, employing another technology, like the SIAD, long forgotten in the archives. They installed an acorn-shaped balloon called a "trailing ballute" (a name combining "balloon" and "parachute") that yanks the real chute out of the vehicle so that it can open unencumbered.
In yesterday's test, the ballute worked well, releasing the parachute at the right time, but the chute itself malfunctioned. In Earth's thick atmosphere, the SIAD provided enough resistance to continue slowing down the vehicle, Clark said at the conference. But in Mars' much thinner atmosphere, a spaceship would need the extra resistance to bring a heavy load from Mach 2.5 — its speed after the SIAD inflates — to speeds at which equipment and possibly people could safely land.
Working out these kinks will require Clark and the team to keep brainstorming and conducting ground tests, like those they have done at the China Lake Naval Air Weapons Station in China Lake, shown in this video.
They have until next summer to master the dynamics of the parachute, when they'll return to Hawaii for two more tests, these focused explicitly on the decelerators. If all goes well then, NASA will be one step closer to a new way of landing bigger, better missions on Mars.