Nuclear thermal propulsion

Recently more sophisticated models have been developed for describing the steady state vaporization behavior of U Zr C,./-8 and U Nb C, y9 in high temperature, high pressure H2. The principal purpose of these studies was to assess the performance of these fuel systems in nuclear thermal propulsion (NTP) applications using H2 propellant. Vaporization rates and melting temperatures may be the two primary processes that limit the operating temperature and lifetime of the structural and fissionable materials in NTP systems. When the atom fraction of U is <0.1, the... 

A further special area of propulsion systems is Chemical Thermal Propulsion (CTP). CTP is defined in contrast to STP (solar thermal propulsion) and NTP (nuclear thermal propulsion). In CTP, in a very exothermic chemical reaction in a closed system, heat but no pressure is generated since the products of the reaction are solid or liquid. The heat energy is then transferred to a liquid medium (the propellant) using a heat exchanger, which is responsible for the propulsion of for example, the torpedo. Suitable propellants are e.g. water (the torpedo can suck it in directly from its surroundsings) or H2 or He, due to their very low molecular or atomic masses. The basic principles of CTP can also be used in special heat generators. A good example for a chemical reaction which is suitable for CTP is the reaction of (non-toxic) SF6 (sulfur hexafluoride) with easily liquified lithium (m.p. 180 °C) ... 

Bennett, G., H. Finger, T. Miller, W. Robbins, and M. Klein. 1994. Prelude to the Future A Brief History of Nuclear Thermal Propulsion in the United States. Pp. 221-267 in A Critical Review of Space Nuclear Power and Propulsion, 1984-1993, edited by M. El-Genk. New York American Institute of Physics Press. 

NASA was also evaluating missions that require nuclear thermal propulsion (NTP) technology. However, NTP was never evaluated by the Naval Reactors Prime Contractor Team (NRPCT) as part of this project and it would likely require a significantly different design and may require some different technologies than the space nuclear power plant designs for electrical power generation. 

Direct heating thermal rockets are distinguished from heat transfer thermal rockets in that the energy transfer does not occur through a material wall. Such devices include the arcjet, which already has been mentioned, liquid and gaseous core nuclear rockets, and nuclear bomb propulsion. Most of the previous discussion applies directly to the selection of a propellant for an arcjet propulsion device. In reality even the arcjet performance is temperature limited--except in this case the propellant acts to heat the wall rather than the reverse. 

In a nuclear bomb propulsion device, the primary purpose of the propellant would be to absorb heat. To serve this purpose, the propellant would probably be chosen for its ablative properties. As a consequence of such thermal energy absorption, the ablative material would be expelled and in thus contributing to the thrust, may be considered to be a propellant. ... 

An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, or from the products of a chemical reaction involving explosive materials, or from a nuclear reaction which is uncontrolled. In order for an explosion to occur there must be a local accumulation of energy at the site of the explosion which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. 

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