Mike Houts

Phase 1 Space Fission Propulsion System Testing and Development Progress

Successful development of space fission systems requires an extensive program of affordable and realistic testing. In addition to tests related to design/development of the fission system, realistic testing of the actual flight unit must also be performed. If the system is designed to operate within established radiation damage and fuel bum up limits while simultaneously being designed to allow close simulation of heat from fission using resistance heaters, high confidence in fission system performance and lifetime can be attained through a series of non-nuclear tests. The Safe Affordable Fission Engine (SAFE) test series, whose ultimate goal is the demonstration of a 300 kW flight configuration system, has demonstrated that realistic testing can be performed using non-nuclear methods. This test series, carried out in collaboration with other NASA centers, other government agencies, industry, and universities, successfully completed a testing program with a 30 kWt core, Stirling engine, and ion engine configuration. Additionally, a 100 kWt core is in fabrication and appropriate test facilities are being reconfigured. This paper describes the current SAFE non-nuclear tests, which includes test article descriptions, test results and conclusions, and future test plans. INTRODUCTION AND BACKGROUND Successful development of space fission systems will require an extensive program of affordable and realistic testing. In addition to tests related to the design/development of the fission system, realistic testing of the actual flight unit must also be completed. Because heat from fission cannot be used for full-power testing of flight units (due to radiological activation), space fission systems must be designed such that heat from fission can be very closely mimicked by some other means. While some nuclear testing will be required, the system will ideally be optimized to allow maximum benefit from non-nuclear testing during the development phase. Non-nuclear tests are affordable and timely, and the cause of component and system failures can be quickly and accurately identified. The primary concern with non-nuclear tests is that nuclear effects are obviously not taken into account. To be most relevant, the system undergoing non-nuclear tests must thus be designed to operate well within demonstrated radiation damage and fuel burn up capabilities. In addition, the system must be designed such that minimal operations are required to move from non-nuclear testing mode to a fueled system operating on heat from fission. If the system is designed to operate within established radiation damage and fuel bum up limits while simultaneously being designed to allow close simulation of heat from fission using resistance heaters, high confidence in fission system performance and lifetime can be attained through a series of non-nuclear tests. Any subsequent operation of the system using heat from fission instead of resistance heaters would then be viewed much more as a demonstration than a test i.e. the probability of system failure from nuclear effects would be very low. These types of systems, along with any other nuclear propulsion system that can be tested with existing nuclear facilities, can be characterized as Phase 1 systems. https://ntrs.nasa.gov/search.jsp?R=20020050531 2020-01-31T05:03:31+00:00Z

Test Facilities in Support of High Power Electric Propulsion Systems

Successful development of space fission systems requires an extensive program of affordable and realistic testing. In addition to tests related to design/development of the fission system, realistic testing of the actual flight unit must also be performed. If the system is designed to operate within established radiation damage and fuel burn up limits while simultaneously being designed to allow close simulation of heat from fission using resistance heaters, high confidence in fission system performance and lifetime can be attained through non‐nuclear testing. Through demonstration of systems concepts (designed by DOE National Laboratories) in relevant environments, this philosophy has been demonstrated through hardware testing in the High Power Propulsion Thermal Simulator (HPPTS). The HPPTS is designed to enable very realistic non‐nuclear testing of space fission systems. Ongoing research at the HPPTS is geared towards facilitating research, development, system integration, and system utilization via co...

Hardware Based Technology Assessment in Support of Near-Term Space Fission Missions

Fission technology can enable rapid, affordable access to any point in the solar system. If fission propulsion systems are to be developed to their full potential; however, near‐term customers must be identified and initial fission systems successfully developed, launched, and utilized. Successful utilization will most likely occur if frequent, significant hardware‐based milestones can be achieved throughout the program. Achieving these milestones will depend on the capability to perform highly realistic non‐nuclear testing of nuclear systems. This paper discusses ongoing and potential research that could help achieve these milestones.

End-to-End Demonstrator of the Safe Affordable Fission Engine (SAFE) 30: Power Conversion and Ion Engine Operation

The Safe Affordable Fission Engine (SAFE) test series addresses Phase 1 Space Fission Systems issues in particular non-nuclear testing and system integration issues leading to the testing and non-nuclear demonstration of a 400-kW fully integrated flight unit. The first part of the SAFE 30 test series demonstrated operation of the simulated nuclear core and heat pipe system. Experimental data acquired in a number of different test scenarios will validate existing computational models, demonstrated system flexibility (fast start-ups, multiple start-ups/shut downs), simulate predictable failure modes and operating environments. The objective of the second part is to demonstrate an integrated propulsion system consisting of a core, conversion system and a thruster where the system converts thermal heat into jet power. This end-to-end system demonstration sets a precedent for ground testing of nuclear electric propulsion systems. The paper describes the SAFE 30 end-to-end system demonstration and its subsystems.

Results of a first generation least expensive approach to fission module tests: Non-nuclear testing of a fission system

The use of resistance heaters to simulate heat from fission allows extensive development of fission systems to be performed in non-nuclear test facilities, saving time and money. Resistance heated tests on the Module Unfueled Thermal-hydraulic Test (MUTT) article has been performed at the Marshall Space Flight Center. This paper discusses the results of these experiments to date, and describes the additional testing that will be performed. Recommendations related to the design of testable space fission power and propulsion systems are made.

Realistic development and testing of fission systems at a non-nuclear testing facility

The use of resistance heaters to simulate heat from fission allows extensive development of fission systems to be performed in non-nuclear test facilities, saving time and money. Resistance heated tests on a module has been performed at the Marshall Space Flight Center in the Propellant Energy Source Testbed (PEST). This paper discusses the experimental facilities and equipment used for performing resistance heated tests. Recommendations are made for improving non-nuclear test facilities and equipment for simulated testing of nuclear systems.

Non‐Nuclear NEP System Testing

The Safe Affordable Fission Engine (SAFE) test series addresses Phase 1 Space Fission Systems issues in particular non‐nuclear testing and system integration issues leading to the testing and non‐nuclear demonstration of a 400‐kW fully integrated flight unit. The first part of the SAFE 30 test series demonstrated operation of the simulated nuclear core and heat pipe system. Experimental data acquired in a number of different test scenarios will validate existing computational models, demonstrated system flexibility (fast start‐ups, multiple start‐ups/shut downs), simulate predictable failure modes and operating environments. The objective of the second part is to demonstrate an integrated propulsion system consisting of a core, conversion system and a thruster where the system converts thermal heat into jet power. This end‐to‐end system demonstration sets a precedent for ground testing of nuclear electric propulsion systems. The paper describes the SAFE 30 end‐to‐end system demonstration and its subsystems.

Progress in hardware development for the SAFE heatpipe reactor system

Advanced Methods & Materials Company (AMM) previously fabricated the stainless steel modules for the SAFE 30 system. These earlier modules consisting of five fuel pins surrounding a heat pipe, were brazed together using a tricusp insert in the gaps between tubes to ensure maximum braze coverage. It was decided that if possible the next generations of modules, both stainless steel and refractory alloy, would be diffusion bonded together using a Hot Issostatic Pressing (HIP) process. This process was very successfully used in producing the bonded rhenium Nb-lZr fuel cladding and the heat exchanger for the SP-100 Nuclear Space System Ref. 1 & 2. In addition AMM have since refined the technology enabling them to produce very high temperature rocket thrust chambers. Despite this background the complex geometry required for the SAFE module was quite challenging. It was necessary to develop a method which could be applied for both stainless steel and refractory alloy systems. In addition the interstices between ...

Results of 30 kWt Safe Affordable Fission Engine (SAFE-30) primary heat transport testing

The use of resistance heaters to simulate heat from fission allows extensive development of fission systems to be performed in non-nuclear test facilities, saving time and money. Resistance heated tests on the Safe Affordable Fission Engine—30 kilowatt (SAFE30) test article are being performed at the Marshall Space Flight Center. This paper discusses the results of these experiments to date, and describes the additional testing that will be performed. Recommendations related to the design of testable space fission power and propulsion systems are made.

Options for development of space fission propulsion systems

Fission technology can enable rapid, affordable access to any point in the solar system. Potential fission-based transportation options include high specific power continuous impulse propulsion systems and bimodal nuclear thermal rockets. Despite their tremendous potential for enhancing or enabling deep space and planetary missions, to date space fission systems have only been used in Earth orbit. The first step towards utilizing advanced fission propulsion systems is development of a safe, near-term, affordable fission system that can enhance or enable near-term missions of interest. An evolutionary approach for developing space fission propulsion systems is proposed.