Mechanism to ensure safety of fission system during launch

Abstract

The potential for fission-based propulsion systems in opening the solar system to extensive exploration, development, and settlement has been recognized for decades. Work toward a first-generation flight demonstrator is underway at MSFC. Safety is one of the main concerns in the planning, development, and design of the system. The purpose of this research is to design, fabricate, and test a mechanism that will (1) enable complete separation of high reactivity worth nuclear fuel elements from the reactor core during launch and (2) enable reliable insertion of these elements into the core immediately prior to reactor startup. The mechanism will preclude any potential for inadvertent reactor startup during a launch accident. The mechanism thus represents one option for ensuring that the launch of space fission systems is fully safe. Early in the concept phase it became clear that there were many different ways to accomplish fuel separation followed by in-space insertion. The benefits of each method ultimately depended on the overall system (spacecraft or otherwise) design and the mission requirements or uses for the reactor. It became evident that since this information was not yet available the best solution would be to provide multiple designs and let the mission and spacecraft requirements dictate which design to use. With this in mind, two different in-space fueling methods were pursued with the available funding. The first method involves placing the nuclear fuel off axis and external to the fuel. The second method involves replacing some of the fuel with a neutron absorber until the reactor is ready to be fueled. Each method has its benefits and constraints that should be balanced with system and mission requirements.