This is a Bell No. 2 rocket belt, also known as the Jet Pack or other terms. It is a small personal propulsion device strapped on the back and enables a person to fly short distances using low rocket power produced by a non-combusting gas.
The idea of the rocket belt appeared in "Buck Rogers" comic strips as early as 1929. Wendell Moore of Bell Aerosystems was the first to develop the invention in the mid-1950s. In the 1960s the U.S. military seriously studied the device as an aid to combat soldiers but found its short duration of just a few seconds too limited. Today, Jet Packs are mainly used for air shows, movie stunts or in football half-time shows and other events. This object was donated to the Smithsonian in 1973 by Bell Aerospace.