Nuclear rockets

One day, we will not be content to send more probes that fly fast planets outside solar system: we want to visit with spacecraft capable of putting into orbit around them to take down robots their moons, and even bring back some rock samples. We want to send astronauts to their fascinating satellite, believed that some contain abundant liquid water, a fundamental condition to harbor life as we know it.

For such missions, nuclear fission seems more appropriate than chemical combustion. Chemical rockets are useful, but the relatively small amount of energy they provide for a given mass of fuel is limited.

With chemical propulsion, only a small spaceship that uses several "audiences" gravitational planets can reach distant planets. To take advantage of these extra gravitational maneuvers, the designers of tasks must wait "windows" launch short periods during which you can launch a spacecraft to planets positioned so that its speed in close race near to the distant celestial bodies.

The ejection velocities of the combustion gases are not sufficient enough to accelerate the rocket. The best chemical rockets, which used the reaction between hydrogen and oxygen, accelerate the vessels leaving the Earth's orbit to ten kilometers per second maximum.

In contrast, nuclear rockets would contact accelerations of 22 kilometers per second. We reach Saturn in just three years instead of seven, and no gravity assist. Nuclear rockets are safe and clean: a nuclear rocket does not need to be very radioactive at launch. The spacecraft with nuclear reactors, would be launched by a conventional chemical rocket. Once the payload to an altitude of about 800 km, it would drive the nuclear reactor.

IN A COMPACT NUCLEAR ENGINE, 37 cells chaufferaient hydrogen. Flowing through the element, the latter would vaporize between the rollers of nuclear fuel (light brown). Five sheets of the metal matrix of the roller is shown in detail on the left.The heated gas is then engulf into a central channel and emerge at the bottom of the element creating thrust.

The construction of a rocket engine Nuclear fission is possible: with my colleagues, we designed a compact nuclear rocket engine that could be built in six or seven years, at a cost of 3.5 to 5 billion francs. The costs of developing the engine would be offset by savings on future launch costs, because a nuclear spacecraft does not need to carry a large mass of propellant chemicals, so you could use small launchers, as Ariane 4.

Nuclear rockets are not new. In the late 1980s, the U.S. Department of Defense had a nuclear thermal propulsion program space. Its objective was the development of a nuclear engine light and compact for defense applications, such as injection of heavy payloads to high Earth orbit. The cornerstone of this project was a particle bed reactor, where the fuel consisted of small particles of uranium carbide packed, covered with zirconium carbide. Work on the reactor aborted before the construction of a flight model, but the engineers had shown a model of low power that the concept was feasible.

In our project, the nuclear fuel reactor would be in the form of perforated metal sheets, wrapped like a roll with jam, with a hollow center (see figure above). Envelope of lithium 7 surround roll fuel and slow the neutrons emitted by nuclear fission would occur within the fuel. Refrigerant (liquid hydrogen) would flow from the outside of the roll inward, vaporizing rapidly as it ├ęchaufferait and it would sink to the center. Gas heated to about 2700 degrees pass at high speed through a channel along the central axis of the roll and would be ejected by a small jet.

Such a system would benefit from the presence of hydrogen in the solar system. Thus, as the nuclear fuel lasts, a vehicle propelled by nuclear power could in theory go around the solar system in 10 or 15 years, by replenishing hydrogen if necessary. A spaceship could evolve for months in the atmospheres of Jupiter, Saturn, Uranus or Neptune, collecting detailed data on their composition or climate. A vehicle may also visit Europe, Titan or Pluto collecting rock samples, and full remake hydrogen hydrolyzing water from the melted ice.

Its reactor is started as far from Earth, a spacecraft would be safer than nuclear probes some exploration of deep space, equipped with chemical thrusters. The edge of the solar system, the sun's rays are too weak to provide the necessary electrical energy instruments spacecraft. That is why they generally work with plutonium 238, which is highly radioactive even at launch. In contrast, a probe nuclear propulsion, the instruments are powered by the engine that provides the thrust. In addition, the amount of radioactive waste produced is negligible (of the order of a gram to a mission in deep space).

With only chemical rockets, our ability to explore the outer planets and their satellites is limited. In the near future, nuclear rockets can only provide us with the power, reliability and flexibility needed to expand our knowledge of the outer Solar System.

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