Lester L. Begg

Conceptual design of high power advanced low mass (HPALM) solar thermionic power system

The conceptual design of an innovative solar space power system based on thermionic conversion of heat to electricity is in progress. The system is particularly attractive for large power requirements (>20 kW). Solar energy is collected with an inflatable structure, which can be a parabolic reflector or a Fresnel lens or reflector. The solar flux is further concentrated with a secondary concentrator before entering the thermal receiver. The heat is converted to electricity directly by cylindrical inverted multicell (CIM) thermionic converters. Initial estimates of volume and mass yield a preliminary specific mass of /spl sim/80 W/kg and a preliminary specific stowed volume of /spl sim/40 kW/m/sup 3/.

Star‐C thermionic space nuclear power system

A 40 kWe Space Thermionic Advanced Reactor‐Compact (STAR‐C) system has been designed in response to evolving Air Force space power requirements. THe resulting nuclear power system is compact and has as overall system efficiency of 12.0%. The entire power conversion subsystem can be pre‐launch tested at its operating conditions, independently of the nuclear heat source. System mass, which includes the reactor power subsystem and shield, the control (PP&C) subsystem and the separation boom has been optimized to 2502 kg. The STAR‐C system has been designed to deliver 40.9 kWe at a reliability of 955 for 10 hears.

Conductively coupled multi-cell TFE with electric heating pretest ability

Problems associated with the development of a multi-cell thermionic fuel element (TFE) with ability of electric heating test are discussed. A conceptual design of such TFE with trilayer emitter stack is proposed. Trilayer emitter stack consists of a strong emitter fuel clad coated with a high temperature oxide ceramic. Emitter tungsten coatings applied to a ceramic and they separated one after another by insulated gaps. Modern materials that should be base to build this trilayer emitter are presented. Results of calculational investigations of TFE output parameters are included. Results of the preliminary test of TFE and it’s components are presented. It is shown that proposed TFE conceptual design from one side allows to provide high output parameters inherent to multi-cell design, and from other side to gain advantages of single cell TFE, such as TFE and reactor nuclear safety, reliability, work cost savings.

Technical Accomplishments of the Thermionic Fuel Element Verification Program

The Thermionic Fuel Element Verification Program (TFEVP) was created to demonstrate the technological readiness of a Thermionic Fuel Element (TFE) suitable for use as the basic element in a thermionic reactor having an electric power output in the 0.5‐ to 5‐MWe range and a full‐power life of seven years. The TFEVP has made significant progress in developing components capable of withstanding the required neutron fluence (4 × 1022 n/cm2, E > 0.1 MeV) and the required burnup (5.3%). Technology developed under the TFEVP also supports the 5‐ to 40‐ kWe thermionic systems currently of interest to the Strategic Defense Initiative Organization and the United States Air Force. The fast‐neutron flux in certain 5‐ to 40‐kWe systems is nearly an order of magnitude less than that in 0.5‐ to 5‐MWe systems. Component technology that has been developed for 0.5‐ to 5‐MWe systems will thus be suitable for use in long‐life, high‐performance, 5‐ to 40‐kWe systems. Components that are being developed by the TFEVP include ins...

Development and testing of conductively coupled multi-cell TFE components

The technology development and modeling results for conductively coupled multi-cell thermionic fuel element components are presented. Different design versions of the converter structural units are considered. The results of thermal test of the main converter components are presented.

Advanced radiator concepts feasibility demonstration

An innovative pumped loop concept for 600 K space power system radiators is under development utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time‐consuming coolant thawing during power startup. The melting/freezing process of Li in a NaK flow was studied experimentally to demonstrate the Li/NaK radiator feasibility during startup (thawing) and shutdown (cold‐trapping). Results of the vapor grown carbon fiber/composite thermal conductivity measurements are also presented.

Two-dimensional Simulation Of A Two-phase, Regenerative Pumped Radiator Loop Utilizing Direct Contact Heat Transfer With Phase Change

An innovative pumped loop concept for 600 K space power system radiators utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup, is under development. The heat transfer process with melting/freezing of Li in an NaK flow was studied through two-dimensional time-dependent numerical simulations to characterize and predict the Li/NaK radiator performance during startup (thawing) and shutdown (cold-trapping). Effects of system parameters and the criteria for the plugging domain are presented together with temperature distribution patterns in solid Li and subsequent melting surface profile variations in time.

LaserCom in UAS missions: benefits and operational aspects

Free Space Optical Communications (FSOC) is progressing continuously. With the successful in-orbit verification of a Laser Communication Terminal (LCT), the coherent homodyne BPSK scheme advanced to a standard for Free-Space Optical Communication (FSOC) which now prevails more and more. The LCT is located not only on satellites in Low Earth Orbit (LEO), with spacecrafts like ALPHASAT-TDP and the European Data Relay Satellite (EDRS) the LCT will also exist in Geosynchronous Orbit (GEO) in the near future. In other words, the LCT has reached its practical application. With existence of such space assets the time has come for other utilizations beyond that of establishing optical Inter-Satellite Links (ISL). Aeronautical applications, as for instance High Altitude Long Endurance (HALE) or Medium Altitude Long Endurance (MALE) Unmanned Aerial Systems (UAS) have to be addressed. Driving factors and advantages of FSOC in HALE/MALE UAS missions are highlighted. Numerous practice-related issues are described concerning the space segment, the aeronautical segment as well as the ground segment. The advantages for UAS missions are described resulting from the utilization of FSOC exclusively for wideband transmission of sensor data whereas vehicle Command and Control can be maintained as before via RF communication. Moreover, the paper discusses FSOC as enabler for the integration of air and space-based wideband Intelligence, Surveillance and Reconnaissance (ISR) systems into existent military command and control systems.

Thermionic converters with planar electrodes for solar power and propulsion systems

Different versions of thermionic converters (TICs), as well as modes of operation, are considered with an emphasis on solar power and propulsion systems. Output power parameters of the TICs operating in the ignited, Knudsen and quasivacuum modes of operation are presented. Comparison of these operation modes are performed. The main components of thermionic converters: electrodes; metal-ceramic seals; and spacing systems that ensure high performance and long life are discussed.

The thermionic fuel element verification program: Technical progress and future plans

The goal of the Thermionic Fuel Element Verification Program (TFEVP) is to demonstrate the technological readiness of a Thermionic Fuel Element (TFE) suitable for use as the basic element in a thermionic reactor having an electric power output in the 0.5‐ to 5‐MWe range and a full‐power life of seven years. The TFEVP has made significant progress in developing components capable of withstanding the required neutron fluence (4×1022 n/cm2, E≳0.1 MeV) and the required burnup (5.3%). Technology developed under the TFEVP also supports the 5‐ to 40‐kWe thermionic systems currently of interest to the Strategic Defense Initiative Organization and the United States Air Force. The fast‐neutron flux in certain 5‐ to 40‐kWe systems is up to a factor of five less than that in 0.5‐ to 5‐MWe system. Component technology that has been developed for 0.5‐ to 5‐MWe systems will thus be suitable for use in long‐life, high‐performance, 5‐ to 40‐kWe systems. Components that are being developed by the TFEVP include insulator se...