Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

laser.
    Furthermore, the system would eventually pay for itself. If it can launch half a million spacecraft per year, the fees from these launches could easily pay for the operating costs as well as its development costs. Dyson, however, realizes that this dream is many decades into the future. The basic research on these huge lasers requires funding far beyond that of a university. Unless the research is underwritten by a large corporation or by the government, the laser propulsion system will never be built.
    Here is where the X Prize may help. I once spoke with Peter Diamandis, who created the X Prize back in 1996, and he was well aware of the limitations of chemical rockets. Even SpaceShipTwo, he admitted to me, faced the problem that chemical rockets are an expensive way to escape the earth’s gravity. As a consequence, a future X Prize will be given to someone who can create a rocket propelled by a beam of energy. (But instead of using a laser beam, it would use a similar source of electromagnetic energy, a microwave beam.) The publicity of the X Prize and the lure of a multimillion-dollar prize might be enough to spark interest among entrepreneurs and inventors to create nonchemical rockets, such as the microwave rocket.
    There are other experimental rocket designs, but they involve different risks. One possibility is the gas gun, which fires projectiles out of a huge gun, somewhat similar to the rocket in Jules Verne’s novel
From the Earth to the Moon.
Verne’s rocket, however, would never fly, because gunpowder cannot shoot a projectile to 25,000 miles per hour, the velocity necessary to escape the earth’s gravity. The gas gun, by contrast, uses high-pressure gas in a long tube to blast projectiles at high velocities. The late Abraham Hertzberg at the University of Washington in Seattle built a gun prototype that is four inches in diameter and thirty feet long. The gas inside the gun isa mixture of methane and air pressurized to twenty-five times atmospheric pressure. When the gas is ignited, the payload rides along the explosion at a remarkable 30,000 g’s, an acceleration so great that it can flatten most metallic objects.
    Hertzberg has proven that the gas gun can work. But to launch a payload into outer space, the tube must be much longer, about 750 feet, and must use different gases along the trajectory. Up to five different stages with different gases must be used to propel the payload to escape velocity.
    The gas gun’s launch costs may be even lower than those of the laser propulsion system. However, it is much too dangerous to launch humans in this way; only solid payloads that can withstand the intense acceleration will be launched.
    A third experimental design is the slingatron, which, like a ball on a string, whirls payloads in a circle and then slings them into the air.
    A prototype was built by Derek Tidman, who constructed a tabletop model that could hurl an object to 300 feet per second in a few seconds. The slingatron consists of a doughnut-shaped tube three feet in diameter. The tubing itself is one inch in diameter and contains a small steel ball. As the ball rolls around the tube, small motors push the ball so it moves increasingly fast.
    A real slingatron that can hurl a payload into outer space must be significantly larger—hundreds or thousands of feet in diameter, capable of pumping energy into the ball until it reaches a speed of 7 miles per second. The ball would leave the slingatron with an acceleration of 1,000 g’s, still enough to flatten most objects. There are many technical questions that have to be solved, the most important being the friction between the ball and the tube, which must be minimal.
    All three of these designs will take decades to perfect, but only if funds from government or private industry are provided. Otherwise, these prototypes will always remain on the drawing board.

FAR FUTURE (2070 TO 2100)
    SPACE ELEVATOR
    By the end of this century, nanotechnology might even make possible the fabled space elevator. Like Jack and the beanstalk, we might be able to climbinto the clouds and beyond. We would enter an elevator, push the up button, and then ascend along a carbon nanotube fiber that is thousands of miles long. This could turn the economics of space travel upside down.
    Back in 1895, Russian physicist Konstantin Tsiolkovsky was inspired by the building of the Eiffel Tower, then the tallest structure of its kind in the world. He asked himself a