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Launch vehicles that use electric actuators for thrust vector or flight control require a safe, reliable and lightweight source of electrical power. Honeywell, working with NASA Glenn Research Center and Lockheed Martin Space Systems, has developed and successfully tested a turbine-driven electric power generation system which meets these needs. This Turbine Power Unit (TPU) uses hydrogen and oxygen propellants which react catalytically to drive a shaft-speed turboalternator mounted on foil bearings. A high-reactance permanent-magnet machine (HRPMM) was selected for this application. The power conditioning and control electronics can be located within the TPU housing and the hydrogen fuel can be used to pressurize the bearings and electronics and to regeneratively cool the machine. A brassboard unit incorporating many of these features was successfully tested at output power levels from 0 to 138 kilowatts (kW).

In association with NASA Glenn Research Center and Lockheed Martin Space Systems, Honeywell has developed and successfully tested an electric power generation system that uses non-toxic hydrogen and oxygen propellants that are reacted catalytically. The resulting fuel-rich gases drive a turbogenerator. Speed control of this system is challenging due to highly variable electric load profile. Discrete two-position valves were used to control the propellant flow for improved reliability compared to proportional valves. This “bang-bang” speed control method exhibits variation in turbine acceleration and deceleration with load. The control thresholds for the turbine speed are adjusted based on load so as to compensate for increased speed overshoot and undershoot.

Honeywell is working with Lockheed Martin and NASA to develop a lightweight, turbine-driven electric power generation system that offers greatly increased safety and reduced operating costs as compared to existing systems. The approach is to utilize a “bang-bang” speed control system with fuel-rich, catalytically-reacted hydrogen and oxygen propellants to drive a turbine and shaft-speed, high-reactance permanent-magnet generator. The rotating assembly is supported by gas-cooled “foil” bearings. The flight system is envisioned to be regeneratively cooled and have power conditioning and control electronics integrated within the pressurized turbogenerator housing. System definition and component development have been completed. “Brassboard” system testing is currently underway.

Two recent studies highlight the unique cooling requirements of Directed Energy Weapons (DEW) and identify methods to address these requirements. Both systems generate substantial heat loads, one requiring more than 1 MW of cooling. Furthermore, much of the heat is generated within a small volume, resulting in a high heat flux. Both spray cooling with ammonia and microchannel heat exchangers with de-ionized water or ammonia were considered. In each case it was determined that the ultimate heat sink would be the ambient air. In one study the heat transfer process was more challenging due to a relatively narrow allowable temperature range and a maximum allowable temperature near the ambient air temperature. Heat transfer options considered the use of a liquid loop with either direct ram air cooling, an air cycle cooling system, and a vapor cycle cooling system.