Two different curvatures are used on the Vanguard concentrator. Tracking is by an innovative exocentric gimbal mechanism that reduces torque requirements and provides rapid emergency detracking. Its four cylinders are parallel and arranged in a square. They are interconnected through the heater, regenerator, and cooler and use double-acting pistons. This is often called the Siemens arrangement.
Engine power is controlled by varying the pressure of the working gas.
Many small-diameter heater tubes arranged in a conical geometry inside a cavity absorb the concentrated sunlight and transfer heat directly to the hydrogen working gas in the engine. Shown in Figure 2-2, six of these systems were produced and installed at sites around the United States for operational testing. Facets have one of five different curvatures, depending on their location on the dish. These facets are attached and aligned in the factory. The mirror support frame is slotted at the bottom so the power conversion unit can be lowered for servicing.