This is NASA's latest project and it looks like a lot of fun. Built by the Jet Propulsion Laboratory at the US Naval Air Weapons Station at China Lake, California, this rocket sled on rails is designe "to replicate the forces a supersonic spacecraft would experience prior to landing."
It will allow NASA to test inflatable and parachute decelerators. Their researchers will then be able to "increase landed payload masses, improve landing accuracy and increase the altitude of safe landing-sites" prior to landing on Mars or other planets:
These new devices represent the first steps on the technology pathway to land humans, habitats and return rockets safely on Mars or other destinations.
I'm glad they are saying "other destinations". Also, I would be happy to pay money for a ride in one of these, followed by a jump in an ejection seat, James Bond style. [NASA]