Martin H. Cooper

Fast Track'' nuclear thermal propulsion concept

The objective of the Space Exploration Initiative (‘‘America at the Threshold...,’’ 1991) is the exploration of Mars by man in the second decade of the 21st century. The NASA ‘‘Fast Track’’ approach (NASA‐LeRC Presentation, 1992) could accelerate the manned exploration of Mars to 2007. NERVA‐derived nuclear propulsion represents a viable near‐term technology approach to accomplish the accelerated schedule. Key milestones in the progression to the manned Mars mission are (1) demonstration of TRL‐6 for the man‐rateable system by 1999, (2) a robotic lunar mission by 2000, (3) the first cargo mission to Mars by 2005, and (4) the piloted Mars mission in 2007. The Rocketdyne‐Westinghouse concept for nuclear thermal propulsion to achieve these milestones combines the nuclear reactor technology of the Rover/NERVA programs and the state‐of‐the‐art hardware designs from hydrogen‐fueled rocket engine successes like the Space Shuttle Main Engine (SSME).

NERVA-derived rocket module for solar system exploration

A 50,000 pound thrust nuclear thermal rocket engine module concept based on Rover/NERVA technology is presented. Key engine features selected for reliability and safety have been integrated into this concept to provide 4.5 hours of full-thrust operation at a specific impulse of over 850 seconds. Those features include a single turbopump with an expander turbine, tank-head start in space, open-cycle decay heat removal with minimal loss of propellant, reactor cold end axial reflector, and tie tubes which are insulated end which are not used to provide turbine power. The tie tube configuration complements the open cycle decay heat removal concept. Retractable safety rods for water immersion subcriticality were considered and a design concept was developed. Other important safety issues were identified, and their method for accommodation in the design were considered for future implementation. 5 refs.

Nutherm: A small thermionic nuclear power source

NUTHERM is a 40 kWe space nuclear thermionic power supply with a design life of ten full power years. Thermionic conversion is achieved by Thermionic Heat Pipe Modules (THPM’s) located in a central cylindrical channel in each fuel assembly. Heat is transferred by thermal radiation from the fuel to the tungsten emitter and is removed by the molybdenum heat pipe, which also acts as the current collector. The core consists of 61 prismatic graphite‐UC (ZrC coated) fuel assemblies. Fifty‐seven fuel assemblies carry the THPM’s and four contain shutdown rods to prevent criticality in case of reentry and water immersion. A moveable beryllium reflector, which is split in the center with independent electric motor drives for each section, provides reactivity control. The payload is shielded by an optimized, conical, multilayer shield consisting of lithium hydride, boron carbide, stainless steel, and tungsten.