Traveling 300 million miles to Mars is difficult, but successfully landing there is even harder. During the first four minutes of entry, friction with the atmosphere slows a spacecraft considerably. But at the end of this phase, the vehicle is still traveling at over 1,000 mph with only 100 seconds left before landing. Things need to happen in a hurry. A parachute opens to slow the spacecraft down to 200 mph, but there are only seconds left and the spacecraft is still 300 feet from the ground. From there, the spacecraft may use rockets to provide a gentle landing on the surface, airbags to cushion the impact of a free fall, or a combination of rockets and tethers to lower a rover to the surface.
To conduct advanced exploration missions in the future, NASA must advance deceleration technology to a new level of sophistication. Enter the Low-Density Supersonic Decelerator Project, a technology development and demonstration effort that will test inflatable decelerators and advanced parachutes in a series of rocket sled, wind tunnel, and rocket-powered flight tests.
The project includes three decelerators. Two are inflatable -- very large (20 feet and 26 feet in diameter, respectively), durable, balloon-like pressure vessels that inflate around the perimeter of the entry vehicle to enhance drag in the Martian atmosphere at supersonic speeds (greater than Mach 3.5) and slow the vehicle to Mach 2. The third device is a parachute measuring 110 feet in diameter that will further slow the entry vehicle from Mach 2, or nearly 1,100 mph, to less than 175 mph. All three devices will be the largest of their kind ever flown at such high supersonic speeds.
These kinds of devices are often tested in a wind tunnel prior to flight; however, the parachute is so large that it will not fit inside any existing wind tunnel and the inflatable decelerators are too large for current supersonic wind tunnels. Thus, a series of rocket sled tests will begin early next year at the U.S. Naval Air Weapons Station at China Lake to replicate the high aerodynamic forces each of these structures would experience during entry and descent at Mars. One set of tests will accelerate an aeroshell 15 feet in diameter to 300 mph in just a few seconds using a rocket sled.
The inflatable decelerator will then be deployed to simulate the stresses it would see during flight. Another set of tests will attach a parachute to the rocket sled to verify that the parachute will be able to withstand the forces expected during supersonic flight. The technology development effort will culminate in a series of flight tests, in which an Apollo-sized capsule is lifted to an altitude of 120,000 feet -- to simulate the thin Martian atmosphere -- using a balloon, and accelerated to Mach 4 using a rocket. The decelerator systems are then tested almost exactly as they would be used at Mars, enabling future missions to confidently use these technologies to land there.
