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Affordable Development and Demonstration of a Small NTR Engine and Stage: How Small is Big Enough?The Nuclear Thermal Rocket (NTR) derives its energy from fission of uranium-235 atoms contained within fuel elements that comprise the engine's reactor core. It generates high thrust and has a specific impulse potential of approximately 900 seconds - a 100% increase over today's best chemical rockets. The Nuclear Thermal Propulsion (NTP) project, funded by NASA's AES program, includes five key task activities: (1) Recapture, demonstration, and validation of heritage graphite composite (GC) fuel (selected as the "Lead Fuel" option); (2) Engine Conceptual Design; (3) Operating Requirements Definition; (4) Identification of Affordable Options for Ground Testing; and (5) Formulation of an Affordable Development Strategy. During FY'14, a preliminary DDT&E plan and schedule for NTP development was outlined by GRC, DOE and industry that involved significant system-level demonstration projects that included GTD tests at the NNSS, followed by a FTD mission. To reduce cost for the GTD tests and FTD mission, small NTR engines, in either the 7.5 or 16.5 klbf thrust class, were considered. Both engine options used GC fuel and a "common" fuel element (FE) design. The small approximately 7.5 klbf "criticality-limited" engine produces approximately 157 megawatts of thermal power (MWt) and its core is configured with parallel rows of hexagonal-shaped FEs and tie tubes (TTs) with a FE to TT ratio of approximately 1:1. The larger approximately 16.5 klbf Small Nuclear Rocket Engine (SNRE), developed by LANL at the end of the Rover program, produces approximately 367 MWt and has a FE to TT ratio of approximately 2:1. Although both engines use a common 35 inch (approximately 89 cm) long FE, the SNRE's larger diameter core contains approximately 300 more FEs needed to produce an additional 210 MWt of power. To reduce the cost of the FTD mission, a simple "1-burn" lunar flyby mission was considered to reduce the LH2 propellant loading, the stage size and complexity. Use of existing and flight proven liquid rocket and stage hardware (e.g., from the RL10B-2 engine and Delta Cryogenic Second Stage) was also maximized to further aid affordability. This paper examines the pros and cons of using these two small engine options, including their potential to support future human exploration missions to the Moon, near Earth asteroids, and Mars, and recommends a preferred size. It also provides a preliminary assessment of the key activities, development options, and schedule required to affordably build, ground test and fly a small NTR engine and stage within a 10-year timeframe.
Document ID
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Borowski, Stanley K.
(NASA Glenn Research Center Cleveland, OH United States)
Sefcik, Robert J.
(NASA Glenn Research Center Cleveland, OH United States)
Fittje, James E.
(Vantage Partners, LLC Brook Park, OH, United States)
McCurdy, David R.
(Vantage Partners, LLC Brook Park, OH, United States)
Qualls, Arthur L.
(Oak Ridge National Lab. TN, United States)
Schnitzler, Bruce G.
(Oak Ridge National Lab. TN, United States)
Werner, James E.
(Idaho National Lab. Idaho Falls, ID, United States)
Weitzberg (Abraham)
(DOE Consultant Woodland Hills, CA, United States)
Joyner, Claude R.
(Aerojet Rocketdyne, Inc. West Palm Beach, FL, )
Date Acquired
December 15, 2015
Publication Date
September 1, 2015
Subject Category
Spacecraft Propulsion And Power
Spacecraft Design, Testing And Performance
Report/Patent Number
AIAA Paper 2015-4524
Meeting Information
Meeting: Space 2015
Location: Pasadena, CA
Country: United States
Start Date: August 31, 2015
End Date: September 2, 2015
Sponsors: American Inst. of Aeronautics and Astronautics
Funding Number(s)
WBS: WBS 279585.
Distribution Limits
Public Use Permitted.
Spacecraft design
Lunar flyby mission
Nuclear rocket engines
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