Radioisotope Heat Source Research Articles

Thermal Preconditioning Utilizing a Radioisotope Heat Source

Gyroscopes and accelerometers used as sensors in inertial navigation systems have errors which change with temperature. In order to obtain adequate performance from these devices; precise, elevated (above ambient) temperatures are usually required to aid in maintaining close tolerances of temperature control. Most systems include electrical heaters on these sensors for this purpose. The time required for the sensors to reach operating temperature has been excessive, especially if the ambient temperature is low. Thermal preconditioning eliminates the warmup time by maintaining the entire inertial measurement unit (IMU) near the operating temperature of the sensors. This technique has not been practical in the past because continuous electrical power could not be provided and sources of portable power were not adequate to supply the heating requirements of large inertial systems. The size of inertial systems has been decreasing and the small systems can be kept near operating temperatures with less than 65 watts of thermal power even at low temperatures. A joint AEC/Air Force program to test the feasibility of using radioisotopes as heat sources to keep the inertial measurement unit at or near operating temperature was conducted. This paper discusses the design, operation and test of the thermal preconditioning unit utilizing a radioisotope heat source. Thermal and radiological safety aspects are also included in the discussion.

Analysis of a Radioisotope Thrustor-Auxiliary Power Unit

A major safety requirement imposed by the AEC on the utilization of radioisotopes as heat sources in direct cycle thrustors is that the fuel temperature will never exceed its melting temperature. This design condition implies low thrustor thermal efficiency. One promising concept for recovering some of this energy loss is a combined thrustor and thermoelectric generator.Analytical investigations indicate that this combined unit powered by four kilowatts of radioisotope heat source can produce typically 0.1 pound thrust at specific impulses greater than 750 seconds and an electrical power output of 50 watts. Under no propellant flow (zero thrust) conditions, the same unit can provide 150 watts of electric power.

Isotope-powered thermoelectric generator for Ripple I

The thermoelectric generator for Ripple I converts the energy from a radioisotope heat source into electrical energy by means of a small module having 36 p-and n-type Bi2Te3 thermoelements. This module is mounted to a plug assembly in such a way that any change or maintenance required can be done without elaborately shielded handling facilities. The power from the generator is fed to electronic amplifying equipment to power a xenon flashing light.

Radioisotope Fueled Thermionic Space Power Systems

In order to understand better the interacting variables of the radioisotope fuel properties and the operating conditions for thermionic converters a parametric study was made of the heat source and system variables. Fuel bodies and converters of various geometric shapes were studied with planar, cylindrical, and spherical emitter surfaces. The problems relating to radiological safety and shielding of the isotope fuel were reviewed. Cost and availability information was obtained for some of the more promising isotope fuels. The results of this study show that there is no completely ideal radioisotope heat source for thermionic space power systems and that the more promising isotope fuels will require important compromises between system specific weight, radiation shielding, system efficiency, and isotope containment to produce usable space power systems.