Innovative Nuclear Space Power
and Propulsion Institute
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Innovative Nuclear Space Power and Propulsion Institute |
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Why Nuclear Thermal Propulsion?
Nuclear
Thermal Propulsion
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Why Nuclear Thermal Propulsion?
Because of its high performance potential, nuclear thermal propulsion (NTP) could be utilized for manned missions and cargo transport to the moon or mars, unmanned explorations of the outer planets, and earth orbit transfers of satellites.
Nuclear propulsion can provide a greater specific impulse (Isp) to reduce the time for a manned mission to Mars from 600 days to about 200 days. In reducing this time, nuclear propulsion will reduce the risk to astronauts from cosmic radiation to say nothing of the other health and psychological benefits from shorter mission times.
Transit Times for Mars Long Duration Missions
All Chemical Propulsion (specific impulse = 475s) vs. Nuclear Thermal Propulsion (specific impulse = 925s)
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Figure 1: Comparison of transit times for a long duration mars mission using either chemical or nuclear propulsion systems. (America at the Threshold, Synthesis Group Reports, US GPO, 1991) |
Transit Times for Mars Short Duration Missions
All Chemical Propulsion (specific impulse = 475s) vs. Nuclear Thermal Propulsion (specific impulse = 925s)
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Fig. 2: Comparison of mission duration times for a 30 day mars surface mission using either chemical or nuclear propulsion systems. (America at the Threshold, Synthesis Group Reports, US GPO, 1991) |
High performance space nuclear reactors for power and/or propulsion present a unique and challenging set of materials engineering requirements. To understand these requirements, it is instructive to examine the factors that contribute to nuclear rocket performance. Specific impulse (Isp) is used to measure performance and is defined as thrust divided by propellant mass flow rate (see Eq. 1).
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1) where, |
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Fig. 3: Nuclear thermal rocket engine (Koenig, 86) |
A nuclear thermal rocket operates by the same basic principles as chemical rockets--namely the expansion of hot gas (propellant) through a rocket nozzle to provide thrust. As shown in Figure 3, the propellant flows through coolant channels of the solid-fuel reactor core where it is heated to very high temperatures (>3000 K proposed for pseudo-ternary carbides). To achieve high performance (as measured by Eq. 1), the fuel is required to operate at very high temperatures. Hydrogen has been used as a propellant during all rocket reactor tests and is preferred because it has the lowest molecular weight. However, hot hydrogen can react with the fuel resulting in corrosion and mass loss. Furthermore, mission cost constraints require a compact, lightweight reactor necessitating high power densities (high neutron flux) with associated radiation damage and increased susceptibility to fracture. |
