A thin film deposition system includes a vacuum-preloaded gas bearing deposition head positioned in an external environment. The deposition head has a vertically-oriented output face including a plurality of source openings through which gaseous materials are supplied and one or more exhaust openings. An exhaust pressure at the exhaust openings is less than an ambient pressure, and a source pressure at the source openings is greater than the exhaust pressure, with the pressure at the outermost source openings being greater than the ambient pressure. A substrate positioner applies a vertical force onto a substrate unit, the vertical force passing through a center of gravity of the substrate unit. A motion control system moves the substrate positioner, thereby moving the substrate unit relative to the output face in an in-track direction without constraining the motion of the substrate unit in a direction normal to the output face of the deposition head.