This is NASA's Low-Density Supersonic Decelerator, or 'Giant Flying Saucer' to you and us.
So what is it? Well it's actually a giant air brake, or at least parts of it are. The LDSD is a prototype lander that will test out NASA's new braking methods for landing on other planets.
At present we rely on a number of fairly crude techniques that include huge parachutes, strong reinforced landing gear that can survive heavy impacts and of course braking thrusters.
The thrusters in particular are effective, but heavy, and expensive. To try and mitigate some of that cost and weight, the LDSD will trial a number of new techniques including more efficient parachutes, inflatable skirts which drastically increase the surface area, thus increasing drag.
NASA's going to be sending the LDSD into near-Earth orbit in June where it'll then turn it right back around and send it plummeting towards the Earth.