Robert W. Bussard proposed the Ramjet system in 1960.
The starship crew in Anderson's novel attempt to colonize a new planet by traveling to the starBeta Virginis. Robert W. Bussard had proposed a ramjet as the ship's mode of propulsion a decade earlier. Physicists have reexamined this unusual mechanism for travel through space in a new paper, and they have found the ramjet wanting. The authors concluded that the engineering challenges are currently insurmountable, and that it is feasible from a pure physics standpoint.
A ramjet is a jet engine. ramjet engines are lighter and simpler to operate than their turbojet counterparts, because the engine's forward motion exploits the engine's forward motion to compress incoming air without the need for compressors. A French inventor named ReneLorin received a patent in 1913 for his idea of a flying stovepipe, but he failed to build a viable prototype. Albert Fon was granted a German patent in 1932 for his ramjet propulsion unit, which he proposed to increase the range of gun-launched projectiles.
A basic ramjet has three components. The hot exhaust from the fuel flows through the nozzle. The ramjet engine can achieve a steady flow by ramming external air into the combustor with the forward speed of the vehicle being powered by it. Oxygen isn't needed on board. ramjets can only produce thrust if the vehicle is moving, so they need an assisted takeoff using rockets. ramjets are most useful for increasing the range of shells and for increasing the speed of missiles.
Simple ramjet operation with Mach numbers of flow shown.
Robert Bussard thought that the concept could be modified to help with interstellar travel. The basic premise of his 1960 paper is to use huge magnetic fields as a "ram scoop" to scoop up protons. The protons would be compressed until they produced thermonuclear fusion, and magnetic fields would then divert that energy into rocket exhaust to produce thrust. The greater the thrust, the higher the protons flow.
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Scientists discovered that there was a lower density of hydrogen outside of our solar system. John F. Fishback proposed a functional magnetic scoop field, taking into account factors such as radiation losses and the thermal distribution of the interstellar gas.
The cut-off speed was calculated by Fishback. The authors of this latest paper explained that the higher the magnetic field lines that focus them into the fusion reactor, the faster the ship. The stronger field causes higher mechanical stresses. Fishback concluded that a ramjet could only accelerate up to a certain threshold speed at which point it would have to slow down.
This latest paper examined Fishback's solution. Peter Schattschneider is a science fiction author and physicist at the Vienna University of Technology. There is a lot of hydrogen in the space. You could use the hydrogen in front of the spacecraft to run a fusion reactor and accelerate the craft with the help of the huge magnetic fields.
Fishback and his co-author Albert Jackson used software developed at TU Wien to calculate the magnetic fields in electron microscopy. Particle can be collected by a magnetic field and guided into a fusion reactor.
The authors found that a long magnetic coil was needed in order to achieve a thrust of 10 million newtons. The funnel has to be 4,000 kilometers in diameter. The authors concluded that it is very unlikely that Kardashev of type II could build magnetic ramjets. Humans on Earth have yet to attain a type I civilization.
The title of the book is Acta Astronautica, 2021. The article is titled "About DOIs."
