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Record 8 of 416
Analysis of a Radioisotope Thermal Rocket Engine
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Author and Affiliation:
Machado-Rodriguez, Jonathan P.(Puerto Rico Univ., Mayaguez, Puerto Rico)
Landis, Geoffrey A.(NASA Glenn Research Center, Cleveland, OH, United States)
Abstract: The Triton Hopper is a concept for a global hopper vehicle which uses a radioisotope rocket engine and In-situ propellant acquisition to explore the surface of Neptune's moon, Triton. The current Triton Hopper concept stores heated Nitrogen in a spherical tank to be used as the propellant. The aim of the research was to investigate the benefits of storing propellant at ambient temperature and heating it through the use of a thermal block during engine operation, as opposed to storing gas at a high temperature. Lithium, Lithium Fluoride and Beryllium were considered as possible materials for the thermal block. A heat energy analysis indicated that a lithium thermal mass would provide the highest heat energy for a temperature change from 900 Celsius to -100 Celsius. A heat transfer analysis was performed for Nitrogen at -100 Celsius flowing through 1000 passages inside a 1kg lithium thermal block at a temperature of 900 Celsius. The system was analyzed as turbulent flow through a tube with constant surface temperature. The analysis indicated that the propellant reached a maximum temperature of 877 Celsius before entering the nozzle. At this exit temperature, the average specific impulse [I(sub sp)] of the engine was determined to be 157s. Previous studies for the stored heated gas concept suggest that the engine would have an average I(sub sp) of approximately 52s. Thus, the use of a thermal block concept results in a 200 percent engine performance increase. In addition, a tank sizing study was performed to determine if the concept is feasible in terms of mass requirements. The mass for a spherical carbon fiber COPV storing 35kg of nitrogen at an initial temperature of -100 Celsius and a pressure of 1000psia, was determined to be 7.2kg. The specific impulse analysis indicated that the maximum engine performance is obtained for a mass ratio of 5kg of Nitrogen per every 1kg of lithium thermal mass. Thus for 35kg of Nitrogen the total thermal mass would be 7kg. This brings the total mass of the system to 49.2.kg which is less than the 56kg landing payload capacity of the Triton Hopper. Finally, an insulation analysis using 10mm of MLI insulation indicated that a total of 22 watts of heat are lost to the environment. With the heat loss known, the power required to heat the thermal mass to 900 Celsius in 24 days was determined to be 2.15 watts. The study's results allowed us to conclude that the thermal mass concept is the better option due to the performance increase provided, the low power requirement and its compliance with the landing mass requirement of the Triton Hopper.
Publication Date: Apr 28, 2016
Document ID:
20170010715
(Acquired Nov 16, 2017)
Subject Category: SPACECRAFT DESIGN, TESTING AND PERFORMANCE; SPACECRAFT PROPULSION AND POWER; FLUID MECHANICS AND THERMODYNAMICS; STATISTICS AND PROBABILITY; LUNAR AND PLANETARY SCIENCE AND EXPLORATION
Report/Patent Number: GRC-E-DAA-TN33703
Document Type: Conference Paper
Meeting Information: Annual AIAA science and Technology (SciTech) Forum and Exposition 2017; 9-13 Jan. 2017; Grapevine, TX; United States
Meeting Sponsor: American Inst. of Aeronautics and Astronautics; Reston, VA, United States
Contract/Grant/Task Num: NNX13AJ40A; WBS 371544.01.04.04
Financial Sponsor: NASA Glenn Research Center; Cleveland, OH, United States
Description: 19p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Public use permitted
NASA Terms: TRITON; RADIOISOTOPE POWER SYSTEMS; IN SITU RESOURCE UTILIZATION; NEPTUNE (PLANET); SPHERICAL TANKS; PROPELLANT STORAGE; LITHIUM; SPECIFIC IMPULSE; MASS RATIOS; PAYLOADS; THERMAL ENERGY; CONVECTIVE HEAT TRANSFER; CARBON FIBERS; TURBULENT FLOW; SURFACE TEMPERATURE; EXHAUST VELOCITY
Other Descriptors: TRITON HOPPER; RADIOISOTOPE; HYBRID ROCKET
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