According to the document:
“This Phase I effort was intended to explore the Biefield-Brown effect, which allegedly converts electrostatic energy into a propulsive force. Activities under this program emphasized the experimental exploration of this electrostatic thrust-generation concept to verify its existence, to verify its operation in a vacuum, and to establish the magnitude of its thrust. To meet these goals an overall laboratory test configuration was designed and developed for quantifying the electrostatically induced propulsive forces on selected experimental devices.
This configuration utilized a vacuum chamber with a torsion fiber type measurement system for direct assessment of propulsive forces. Geometrical symmetries were incorporated in the design to minimize the influence of reaction forces which can arise from nearby bodies, including the walls of the vacuum chamber itself. Tests were conducted at atmospheric pressure and over a range of partial vacuum conditions. Direct experimental results indicate that when an electrostatic potential difference is applied between asymmetrical electrodes of an all metal test device, a residual propulsive force is generated and acts on the device. This residual force acts in the opposite direction to electrical wind forces and to the forces claimed to have been measured in a vacuum by T.T. Brown.”
21st Century Propulsion Concept, April 1988 (Veritay Technology, Inc.) [73 Pages, 3.7MB]