Technicians work on Magnetoplasmadynamcis (MPD) plasma accelerator. James Hansen wrote in Spaceflight Revolution: "Beginning in the late 1950s, a small group of Langley researchers led by Robert V. Hess, an applied physicist from Austria who had come to work for the NACA in 1945, began pursuing two major variants of the Hall accelerator: the MPD arc and the so-called linear Hall accelerator. Through the 1960s, [Robert] Hess and his associates refined these versions of the plasma accelerator, thus making extensive experimental and theoretical studies of the physics and overall performance of their devices. Although they successfully demonstrated the efficiency of the MPD arc and linear Hall accelerator and made several important findings relating to the manner in which oscillations and instabilities in plasma could develop into turbulent flows, MPD researchers were never able to simulate reentry conditions or the interaction between the solar wind and the geomagnetosphere, and they would never realize meaningful applications in space propulsion. As was the case with the other MPD experimental facilities ..., the linear Hall-current accelerator possessed limitations that Hess and his colleagues could not eradicate. By the late 1960s, Hess and others in MPD shifted the focus of their work with these accelerators to the potential application of gas lasers.
