After uniting a balloon, rocket and parachute, NASA engineers are lookiing to Mother Nature for the high altitude wind tunnel that will help them devise the technologies needed to reach the Martian surface with more massive payloads and eventually humans.
Artist's illustration of the Low Density Supersonic Decelerator Technology Mission as it races into the stratosphere. NASA
Engineers from the Jet Propulsion Laboratory and elsewhere within NASA have gathered at the U.S. Navy's Pacific Missile Range Facility on the island of Kaua'i in Hawaii for the balloon launch of the Low Density Supersonic Decelerator Technology Demonstration Mission. After rising to 120,000 feet over the Pacific Ocean, the 6,900 pound saucer shaped LDSD payload -- the Supersonic Inflatable Aerodynamic Decelerator and a high strength parachute -- drop away from the launch balloon with a solid rocket motor that will accelerate the SIAD to an altitude of 180,000 feet and Mach 4 velocity.
The atmosphere at those altitudes is thin and suitably Martian like for the speeding 15 1/2 foot wide SIAD to expand on command to 20 feet and begin to slow with atmospheric drag and as though it were delivering not one, but two of NASA's one ton Curiosity rovers to the surface of the red planet. With SIAD slowing to 2 1/2 times the speed of sound, three minutes after the balloon release, a single 100 foot wide supersonic parachute will deploy -- pulled from its restraints by a ballute -- to lower the test hardware to the ocean's surface.
Once set for Tuesday, then Thursday, the three hour flight test may unfold on Saturday - if the weather and winds to push the 856 foot tall balloon and its 6,900 pound test vehicle away from Kaua'i are suitable. The Navy range, though, is available through June 14.
Since 1976 and the successful landings of NASA's twin Viking probes on Mars, NASA has relied on the same supersonic parachute design as part of the challenging entry, descent and landing (EDL) strategy needed to bring scientific probes to the surface intact. Curiosity, at just over 2,000 pounds, pressed the boundaries of that capability as it descended to the floor of Gusev crater in August 2012 in the landing phase under the wing of NASA’s “sky crane.”
Earlier this week, the National Research Council ranked EDL with in-space power and propulsion and overcoming the health hazards of radiation as the top technical challenges confronting those attempting to shape the human exploration of Mars.
A human mission would require as much as 40 tons of landed hardware, a capability NASA's Space Technology Mission Directorate is attempting to address with LDSD this year and a scaled up, more extensible 8 meter version of the Kevlar SIAD and parachutes next year.
"We've been living on the shoulders of the giants who developed EDL technologies decades ago," said Michael Gazarik, the directorate's associate administrator, earlier this week. "It's about more mass, going to higher elevations on the surface of Mars and landing more accurately. We need to test. We need to learn, and we need to do it quickly and efficiently. That's why we are here."
Preliminary testing of the system components began last year at the Naval Air Weapons Station China Lake in California in a bid to characterize the SIAD inflator with a rocket sled moving at several hundred miles per hour in near sea level atmospheric densities. But the engineering effort must look to the top of the stratosphere if it wants to achieve a Mars-like response.
"We'd love to test in a wind tunnel, but unfortunately, there are no wind tunnels in the world large enough and with the conditions we need for these tests," said JPL's Ian Clark, the LDSD principal investigator. "There are a lot of questions: How do these things deploy? How do they inflate? Will they be strong enough to survive the environment of Mars? How will they behave aerodynamically? What is the performance?"
Eager enough, the test team has nonetheless cautioned followers the Pacific "shakeout" test outcome is uncertain. Even the loss of the spacecraft, though, would just set the table for a pair of test runs already scheduled for next summer.
"If we can fire that (rocket) motor and get data back from it, that's a great day," said Mark Adler, the JPL's LDSD project manager, of the post-balloon phase of the flight test. "That way we can understand what to do for the next flight."