In January of 2004, President Bush outlined a new, bold vision for U.S. Space Exploration. The goal of this vision is to help the US improve in scientific, security and economic areas. As a result, the general public has shown renewed interest in the space program, especially human exploration. Mankind has often dreamed of traveling into space beyond the moon. It aspires to fly manned missions to Mars, and hopefully, to the outer planets. This is a goal that began to see new public interest as a result of the Mars Pathfinder Mission Mars Pathfinder Mission and the 1984 discovery in Antarctica of the Martian meteorite ALH84001, which hints at the possibility of fossils existing on Mars. In order to accomplish the goals of human exploration to other bodies, more advanced propulsion technologies need to be further developed. In support of the Space Exploration Vision, Project Prometheus has been formed to study the application and flight of a nuclear reactor in space. As a result, Nuclear Thermal Rockets might be the propulsion we use to fulfill these human exploration dreams.

A Nuclear Thermal Rocket (NTR) creates thrust by heating and expanding a working fluid, such as hydrogen, a fusion fuel, in a nuclear reactor. An NTR engine has twice the efficiency of the best chemical engines due to the high energy level produced by the nuclear reactions when compared to the combustion in chemical thrusters. Consequently, NTR engines have an advantage over chemical engines when we compare the amount of energy available per unit mass of fuel. Thus, NTR engines produce a higher specific impulse (ISP) than current technology chemical rockets. The specific impulse of a rocket is improved by using a lower molecular weight exhaust. The exhaust of chemical rockets are constrained by the chemical reaction, but in an NTR, the heat source is not based on the propellant, so an NTR can use a low molecular weight propellant, such as hydrogen, to improve performance. The high specific impulse (Isp) levels of an NTR rocket offer opportunities for missions with shorter trip times and greater payloads that those that can be accomplished using only chemical propulsion. Keep in mind that this is at the cost of an increased system weight to accommodate an NTR power plant. An NTR is attractive for many high-energy missions because of its high thrust to weight ratios of the power plant and engines. NTR propulsion systems are referred to as high thrust when compared other advanced propulsion systems such as electrical propulsion. Current advanced NTR propulsion system designs under consideration include straight NTR, Bimodal, and Tri-modal with LOX augmented thrust. The reactor used in an NTR vehicle operating in the “Bimodal” mode, can be used to create electrical power when not being used to produce thrust. A Tri-modal system includes an afterburner-style operation cycle in which liquid oxygen (LOX) is injected into the nozzle for increased thrust (and therefore, lower Isp). Nuclear Thermal Rocket Propulsion is not a new technology. NTR dates back to the NERVA program in the 1960s. The NERVA engine was a solid-core design, which is the traditional and simplest design to make. Other advanced design concepts include a liquid-core and a gas-core reactor.

7820 Participation

7820/ Space Mission Design Branch performs Mission and Systems analysis on Nuclear Thermal Rocket concepts used for missions to Mars, Near Earth Orbiting (NEO) Asteroids and other bodies within and outside the solar system. With our in-house analysis capabilities, we can apply NTR system models and optimize ballistic trajectories to Mars and other planetary or sub-planetary bodies. When system models are unavailable, we develop those elements necessary to model a complete NTR vehicle. Our work also includes performing mass (e.g. payload) optimization studies for delivering the heaviest payload possible to Mars or other target body destination. We perform conceptual design (CAD modeling) and some structural analysis of the NTR spacecraft itself. We have been and still contribute as integral parts of architecture studies into the application of NTR propulsion systems to future human and robotic NASA missions.

Other Links of Interest to NTP

• Life on Mars
• Lunar mission applications of LOX augmentation
• LOX Information
• The HEDS homepage at NASA Headquarters
• Visualization of an NTR three-burn escape from Earth to Mars created by summer intern, Emily Condit, summer 1999, using Satellite Toolkit (www.stk.com ). To view click here.

Points of Contact

7820

Melissa McGuire (Melissa.McGuire@grc.nasa.gov)

Len Dudzinski (Leonard.Dudzinski@grc.nasa.gov)

GRC Resident Expert

Stan Borowski (Stanley.K.Borowski@grc.nasa.gov) Biography

HTML Contributions

Corinne Kellerman Summer Intern '04

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