The Low-Density Supersonic Decelerator Project will test inflatable decelerators and advanced parachutes in a series of rocket sled, wind tunnel, and rocket-powered flight tests to slow spacecraft prior to landing. This technology will allow NASA to increase landed payload masses, improve landing accuracy and increase the altitude of safe landing-sites. (NASA)
Rocket Sled Tests Are Technology Pathway to Safely Land Humans, Habitats and Cargo on Mars -- Mars Daily
Traveling 300 million miles through deep space to reach the planet Mars is difficult; successfully landing there is even harder. The process of entering the Red Planet's atmosphere and slowing down to land has been described as "six minutes of terror."
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 "only" 200 mph, but now there are only seconds left and the spacecraft is approximately 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.
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My Comment: We are still a long way from flying to Mars, but it is interesting to see how we are preparing for that eventual mission.