Nuclear Thermal Rocket - History

History

Although engineering studies of all of these designs were made, only the solid-core engine was ever built. Development of such engines started under the aegis of the Atomic Energy Commission in 1955 as Project Rover, with work on a suitable reactor starting at Los Alamos National Laboratory and Area 25 in the Nevada Test Site. Four basic designs came from this project: KIWI, Phoebus, Pewee and the Nuclear Furnace. Twenty rockets were tested.

When NASA was formed in 1958, it was given authority over all non-nuclear aspects of the Rover program. In order for NASA to cooperate with the AEC, the Space Nuclear Propulsion Office was created at the same time. In 1961, the NERVA program (Nuclear Engine for Rocket Vehicle Applications) was created. Marshall Space Flight Center had been increasingly using KIWI for mission planning, and NERVA was formed to formalize the entry of nuclear thermal rocket engines into space exploration. Unlike the AEC work, which was intended to study the reactor design itself, NERVA's goal was to produce a real engine that could be deployed on space missions. A 75,000 lbf (334 kN) thrust baseline NERVA design was based on the KIWI B4 series, and was considered for some time as the upper stages for the Saturn V, in place of the J-2s that were actually flown.

Although the Kiwi/Phoebus/NERVA designs were the only ones to be tested in any substantial program, a number of other solid-core engines were also studied to some degree. The Small Nuclear Rocket Engine, or SNRE, was designed at the Los Alamos National Laboratory (LANL) for upper stage use, both on unmanned launchers as well as the Space Shuttle. It featured a split-nozzle that could be rotated to the side, allowing it to take up less room in the Shuttle cargo bay. The design provided 73 kN of thrust and operated at a specific impulse of 875 seconds (8.58 kN·s/kg), and it was planned to increase this to 975 with fairly basic upgrades. This allowed it to achieve a mass fraction of about 0.74, comparing with 0.86 for the SSME, one of the best conventional engines.

A related design that saw some work, but never made it to the prototype stage, was Dumbo. Dumbo was similar to KIWI/NERVA in concept, but used more advanced construction techniques to lower the weight of the reactor. The Dumbo reactor consisted of several large tubes (more like barrels) which were in turn constructed of stacked plates of corrugated material. The corrugations were lined up so that the resulting stack had channels running from the inside to the outside. Some of these channels were filled with uranium fuel, others with a moderator, and some were left open as a gas channel. Hydrogen was pumped into the middle of the tube, and would be heated by the fuel as it travelled through the channels as it worked its way to the outside. The resulting system was lighter than a conventional design for any particular amount of fuel. The project developed some initial reactor designs and appeared to be feasible.

More recently an advanced engine design was studied under Project Timberwind, under the aegis of the Strategic Defense Initiative ("Star Wars"), which was later expanded into a larger design in the Space Thermal Nuclear Propulsion (STNP) program. Advances in high-temperature metals, computer modelling and nuclear engineering in general resulted in dramatically improved performance. While the NERVA engine was projected to weigh about 6,803 kg, the final STNP offered just over 1/3 the thrust from an engine of only 1,650 kg by improving the I to between 930 and 1000 seconds.

In January 2012, the propulsion group for Project Icarus began a technology development project, known as Project Bifrost, under the auspices of Icarus Interstellar and General Propulsion Sciences, to develop an NTR propulsion system, initially aimed at interplanetary missions.