To dock a spacecraft, a whole lot of drag is needed for decelerating from the high speed of atmospheric entry to the final stages of landing. Current decelerating technology dates back to NASA’s Viking Missions of the 1970s, and they were just recently used to deliver Curiosity to Mars. But larger spacecrafts hauling more massive loads are going to be need for longer, more advanced robotic and manned missions to Mars.
To safely land the crew and cargo, and to save on rocket propellant, NASA is advancing their used of drag for slow spacecrafts down. So, they built a saucer-shaped vehicle for landing heavy payloads, and they’ll be dropping it from a helium balloon this month as part of its first engineering shakeout flight.
Called the Low Density Supersonic Decelerator (LDSD), the rocket-powered flying saucer will be testing an inflatable decelerator and a supersonic parachute. The vehicle was built at NASA's Jet Propulsion Laboratory in Pasadena, California, and is currently housed in the Missile Assembly Building at the U.S. Navy's Pacific Missile Range Facility in Kaua‘i, Hawaii. A balloon will lift the vehicle to high altitudes, and then a rocket will take it even higher, at several times the speed of sound.
"We use a helium balloon -- that, when fully inflated, would fit snugly into Pasadena's Rose Bowl -- to lift our vehicle to 120,000 feet [36 kilometers]," JPL’s Mark Adler says in a news release. "From there we drop it for about one and a half seconds. After that, it's all about going higher and faster -- and then it's about putting on the brakes."
The timeline is tight. A fraction of a second after being dropped from the balloon, four small rocket motors will fire to spin up and gyroscopically stabilize the saucer. Then a half second later, a Star 48B long-nozzle, solid-fueled rocket engine will kick in with 17,500 pounds of thrust, sending the test vehicle to the edge of the stratosphere. In this picture, you can see the nozzle and the lower half of the Star-48 solid rocket motor (the dark objects in the middle, below the saucer).
"Our goal is to get to an altitude and velocity which simulates the kind of environment one of our vehicles would encounter when it would fly in the Martian atmosphere," JPL’s Ian Clark explains. The upper layers of Earth’s stratosphere are the most similar environment available to match the properties of the thin atmosphere of Mars. "We top out at about 180,000 feet [55 kilometers] and Mach 4. Then, as we slow down to Mach 3.8, we deploy the first of two new atmospheric braking systems."
Once in the stratosphere, the vehicle will deploy an inflatable 6-meter Kevlar tube around itself. The Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) is basically an inflatable doughnut that increases the vehicle's size and, as a result, its drag. That should quickly slow the vehicle down from Mach 3.8 to Mach 2.5, where the Supersonic Disk Sail Parachute first hits the supersonic flow. At 33.5 meters, it’s largest supersonic parachute ever flown. About 45 minutes after parachute deployment, the saucer is expected to make a controlled landing onto the Pacific Ocean off Hawaii.
The designs borrow from the same technique used by the Hawaiian pufferfish -- the ‘o‘opu hue -- to increase its size without adding mass: rapid inflation. The new drag devices can increase payload delivery to the surface of Mars from the current capability of 1.5 metric tons to 2 to 3 metric tons, depending on which inflatable decelerator is used in combination with the parachute (NASA is also developing an 8-meter decelerator, called SIAD-E).
The first launch opportunity was on June 3rd at 8:30 a.m. Hawaii Standard Time, but weather conditions prevented that from happening. Other potential launch dates include June 5, 7, 9, 11 and 14. Check here for updates. You can watch it all happen at NASA TV.