Typical aerospace rocket engines use valves to control the flow and pressures of propellant and pressurants. These typical valves are designed to operate with a mechanical, electromechanical, or pneumatic operator. They all have at least one, and often multiple, penetrations from the fluid to the operator’s prime mover. The penetrations are sources for leaks, failures, and are often considered to be unreliable for use in single string systems. Therefore, the fluid system designer frequently will utilize several parallel path valves, effectively doubling the resources needed to accomplish the task. These redundant valves allow for isolation of the potentially leaking fluid penetrations. If the systems cannot afford the multiple path approach, then the valves are subjected to high levels of testing and quality control, or utilize bellows or other expensive and difficult to handle/design and costly features.
Magnetostrictive (MS) materials used in valves allow the valve to be opened, closed, or variably positioned by applying a magnetic field via a standard coil to the outside of the hermetically sealed envelope. Thus all moving parts are contained inside the welded pressure shell and no mechanical penetrations through the pressure shell are required. This eliminates the need for any mechanical seals to the atmosphere and also allows for a variable position valve using a variable current source into a driving coil. MS materials are insensitive to heat or cold and thus the valve can operate over a wide temperature range. The MS materials in the valve have fast response times and can operate up to 100 times faster than typical aerospace solenoid-driven valves.
An advanced MS regulator (MSR) was developed by combining MS-based sensors (MSS) with a MS-based valve (MSV). This innovative approach utilized the rapid response of the MSV to provide a regulator capable of controlling downstream pressures with minimal under or overshoot pressures. In addition, the components are lightweight, compact, highly precise, and can operate over a wide range of temperatures and pressures.
This MSR concept uses the MSV element, a MSS pressure transducer, and a servo-circuit to control the current to the valve coil. This all-electric design enables highly accurate and highly reactive regulation. As the current changes in the MSS, the servo-circuit adjusts the magnetic field strength to the MSV coil, causing the valve poppet to reposition and bring the pressure back to the setpoint.
The MSS pressure transducer uses a force-to-angle converter, which provides the magnetic flux angle of the field surrounding the magnetostrictive material as an analog of the force applied to the material. As a sensor, this property is utilized in a servo circuit to control the MSV in a closed loop system.
The MSV and MSR may also allow mixture ratios to be controlled both on a volume flow and a mass flow basis. Using the MSS to control the MSV, and open or close the flow area through the valve seat, permits the valve to serve as a mass or volume control device as well. The MSS performing a dual function then reduces the need for an additional flowmeter, thereby potentially reducing weight on the spacecraft.