The idea of a sailing spaceship is gaining momentum. The new versions promise tremendous speed
Aharon Hauptman
Imaging photographs: NASA, University of Washington
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A magnetic "bubble" surrounds a spaceship. Under the influence of electrically charged particles of the solar wind, the bubble will be able to accelerate the spacecraft to a speed of about 100 km per second. Right: a sail spacecraft, one of NASA's designs. Does not need fuel to accelerate.
The idea of propelling a spaceship with a sail is not new. Even more than 400 years ago, the astronomer Johannes Kepler dreamed of sailing ships that would sail with the force of "heavenly gusts" into space. In the fifties and sixties of the 20th century, the idea was revived in many science fiction stories and scientific articles. Developments currently being carried out in the research laboratories may lead to the realization of the dream perhaps already in the next decade.
The idea is simple: when light rays hit a reflective surface (let's say a large mirror), the reflected photons ("particles" of light) exert a force on the surface. Power means acceleration, so a mirror attached to the spacecraft will essentially be a kind of sail, and the spacecraft will accelerate similar to the way a sailboat or a kite is accelerated, as a result of the gust of wind. When you think about it, the words "spaceship" suddenly take on a real meaning.
The great advantage of a sailing spacecraft is that it does not need fuel to accelerate, at least as long as the light reaches it. And a small but constant acceleration is enough to accumulate, within a few months, enormous speeds that cannot be achieved with any conventional means of propulsion. Speed is the key to travel through space to truly enormous distances - to the edge of the solar system, not to mention beyond it.
In the story "The Wind Blowing from the Sun" (from 1963), the science fiction writer Arthur C. Clark imagined an international competition of "space sails". And this is how one of the spaceships was described there: "If they took all the sails of the tea ships that ever ran in the waters of China, and sewed them into one huge sheet - it could not compare to the single sail that the spaceship spread against the sun. And yet the sail was not much firmer than a soap-bubble; Those five square kilometers of aluminum-coated plastic were only millionths of a centimeter thick." (Translated by Yoram Rappaport, Masada Publishing House 1972).
But if the idea of the space sail is simple, its realization is not. This is a sail that measures hundreds of meters (up to tens of kilometers, according to certain designs) and is thin. This requires very strong, lightweight, heat-resistant materials, as well as a sophisticated retirement mechanism. The engineering difficulties caused NASA to abandon the idea in the 70s, but in recent years it has been revived. The great progress in the development of very strong and light composite materials raised hopes, and indeed, one of the materials tested for this purpose is very reminiscent of Clark's description: carbon fibers coated with an amazingly thin layer of aluminum, only a few tens of atoms thick. Such a thin foil can be stored in a small box and spread out in space to an area the size of a football field.
As the idea gained traction, more elaborate versions of it were proposed. For example, a futuristic version that is not satisfied with sunlight but offers the use of light beams from powerful laser devices, which will be located at "strategic" points in space, possibly on other planets. A combination of a giant sail and a concentrated beam of light should give the spaceship propulsion power for vast distances, perhaps far beyond the solar system.
But recently a much more innovative idea was proposed: a sail-less spacecraft. A team of scientists from the University of Washington, led by Dr. Robert Wingley, is working vigorously on "mini-magnetospheric plasma propulsion", or M2P2 for short. According to this idea, the spacecraft will be wrapped in a kind of giant magnetic bubble, which will function like a sail, as a result of the interaction between the magnetic field and particles which are continuously emitted from the sun. The idea sounds complicated, but it is based on quite simple physics. The real "wind" blowing from the sun (in addition to light radiation, which is not exactly "wind") is a stream of electrically charged subatomic particles, which "blow" everywhere at speeds of up to 1,000 km per second, to enormous distances from the sun. The meeting between an electric charge and a magnetic field creates a force that can be used as an impulse that accelerates the spaceship.
When the idea was proposed a few years ago, it turned out that in order to implement it, the spacecraft would have to be wrapped in such a strong magnetic field that this is impractical (at least until superconducting materials are developed). But Dr. Wingley and his men showed that a huge, weak magnetic field can achieve the same force as a smaller but stronger field. They also showed that it is possible to create such a weak magnetic field with the help of a conducting coil containing an amazingly small amount (40 kg) of plasma (ionized gas). With the help of this facility (a laboratory model of which has already been built), they claim, it is possible to "inflate" a magnetic bubble with a diameter of 40 km and this will capture a sufficient number of solar wind particles that will allow it to function as a gigantic sail.
In this way, the light solar wind will be able to accelerate spacecraft to speeds of about 100 km per second. Such a spaceship will indeed be hopelessly slow compared to the speed of light - the dream of the dreamers of intergalactic journeys - but it will be much faster than any spaceship built so far; And it will be the practical solution for journeys to the outskirts of the solar system.
The idea, which was presented only recently at a scientific conference, seemed to NASA to be so practical that the agency allocated a respectable research grant to Dr. Wingley's team to continue developing the idea. (Details can be found Site.
A compilation of Dr. Aharon Hauptman's articles on the Hidan website
{Appeared in Haaretz newspaper, 19/10/2000}
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