Nerva

Scientists worked on a new rocket engine.

This engine used heat to push. Most rockets use a chemical mix to burn. This one used a small reactor instead. The reactor makes a lot of heat.

This heat warms up a gas. The warm gas pushes the rocket up. It can be much better than old engines. It could even help people reach Mars. The engines were tested, but they never flew.

They were very strong and ready for space.

NERVA was a special rocket engine program.

It ran for about twenty years. NASA and the AEC worked together on it. Most rockets use a chemical mix to make power. NERVA used a nuclear reactor instead. This reactor is a part that makes heat.

This way of working is very strong. It can be much better than chemical engines.

The engine uses a gas called hydrogen. The gas is kept very cold in a tank. A pump pushes the gas into the reactor. The reactor makes the gas very hot. The hot gas then pushes out of the engine. This push helps the rocket move through space.

Scientists used graphite to build the reactor. Graphite is a material that stays strong when hot. They also made a shield to block radiation. Radiation is a type of energy from the reactor. The shield used a mix called BATH. This mix kept people and parts safe. NERVA was a success, but it never flew in space.

NERVA was a huge project to build a new kind of rocket engine.

It stood for the Nuclear Engine for Rocket Vehicle Application. This program ran for about twenty years. It was a joint effort between NASA and the Atomic Energy Commission. The goal was to create a technology base for space missions. Scientists wanted to see if nuclear power could help us travel through space.

Most rockets use chemical reactions to create power. NERVA worked in a different way. It used a nuclear reactor to create heat. This heat was used to warm up a liquid fuel. The most common fuel used was hydrogen. Because hydrogen has a low molecular mass, it works very well. A pump moves the cold liquid hydrogen into the reactor. The reactor makes the hydrogen extremely hot. This hot gas then shoots out of a nozzle to create thrust.

People had thought about nuclear rockets for a long time. During World War II, scientists like Stan Ulam and Frederick Reines talked about these ideas. In 1946, Ulam and C. J. Everett wrote a paper about using atomic bombs for propulsion. Later, in 1953, Robert W. Bussard wrote a detailed study on the topic. By 1955, a committee led by Mark Mills recommended that development should move forward. The work began under the name Project Rover at the Los Alamos Scientific Laboratory.

Building these engines was a very hard job. Engineers had to find materials that would not melt or break. They chose uranium-235 for the fuel in the reactor. They also chose graphite for the structure of the reactor. Graphite is great because it actually gets stronger as it gets hot. To keep the engine safe, they made a special radiation shield. This shield was a mixture called BATH. It used boron carbide, aluminum, and titanium hydride to block radiation.

NERVA was a very successful program. It met or even went past its original goals. By the end of 1968, the XE engine was ready for a human mission to Mars. The engines were built with parts that were ready to fly. However, the program was cancelled by President Richard Nixon in 1973. This means the NERVA engines never actually flew in space. Even so, they proved that nuclear thermal rockets are a reliable tool for exploring the stars.

The Nuclear Engine for Rocket Vehicle Application, known as NERVA, was a major development program for nuclear thermal rocket engines. This project lasted for roughly twenty years. It was a joint effort between the Atomic Energy Commission (AEC) and the National Aeronautics and Space Administration (NASA). The program was managed by the Space Nuclear Propulsion Office (SNPO) until it ended in January 1973. The main goal was to build a technology base for nuclear rocket systems. Scientists wanted to design propulsion systems for future space missions.

Nuclear thermal rockets work differently than the chemical rockets we use today. Conventional rockets create thrust through a chemical reaction. This reaction produces heat, which makes a fluid expand and escape through a nozzle. NERVA used a nuclear reactor to provide that heat instead. Because nuclear reactions are much more powerful than chemical ones, a small reactor can replace large amounts of chemicals. This allows the engine to be much more efficient. In fact, these engines aim for at least twice the specific impulse of a chemical engine.

To make the engine work, engineers had to manage many complex steps. First, they had to store a working mass, usually liquid hydrogen, in a large tank. Because hydrogen must stay extremely cold, it is kept in liquid form below 20 Kelvin. A turbopump then moves this liquid hydrogen into the reactor. Inside the reactor, the hydrogen is heated to about 2,700 Kelvin. As the hydrogen heats up, it expands rapidly. This hot gas is then pushed out of the rocket nozzle to create thrust.

Designing the reactor required choosing very specific materials. For the fuel, engineers chose uranium-235. They rejected plutonium because it forms compounds too easily and cannot reach high enough temperatures. For the reactor structure, they chose graphite. Graphite was a great choice because it is inexpensive and actually gets stronger at temperatures up to 2,800 Kelvin. To control the reactor's power, they used control drums. These drums were coated with a neutron moderator on one side and a neutron poison, called boron, on the other.

Safety was a major priority during the development process. The engine emitted intense neutron and photon radiation. To protect people and other parts of a spacecraft, engineers developed a radiation shield. They created a material called BATH. This was a mixture of boron carbide, aluminum, and titanium hydride. The titanium hydride acts as a neutron moderator, while the boron carbide absorbs neutrons. This material was very strong and could withstand high temperatures.

The history of these ideas began long before NERVA. During World War II, scientists at the Los Alamos Laboratory speculated about nuclear rockets. In 1946, Stan Ulam and C. J. Everett wrote a paper about using atomic bombs for propulsion. In 1953, physicist Robert W. Bussard wrote a detailed study on nuclear energy for rocket propulsion. By 1955, a committee led by Mark Mills recommended moving forward with development. This led to Project Rover at the Los Alamos Scientific Laboratory. Project Rover eventually became the foundation for the NERVA program.

NERVA was considered a highly successful program because it met its goals. It proved that nuclear thermal rockets were a reliable tool for space exploration. By the end of 1968, the XE engine was deemed ready for a human mission to Mars. The engines were built with components that were flight-certified. However, the program was cancelled by President Richard Nixon in 1973. Because of this cancellation, the NERVA engines never actually flew in space.