Only a handful of decades ago, a group of very smart scientists figured that if they crammed a giant metal barrel full of explosive chemicals and bolted on a little compartment for people or cargo, they could light the fuse and use the resulting explosion to propel the stuff into outer space. They called this assembly a “space rocket,” and aside from a few dozen catastrophic failures, the idea has been working swimmingly ever since. Unfortunately, moving stuff into space with rockets isn’t particularly economical, costing about $10,000 per pound even when the assembly doesn’t blow up. A single launch of the reusable US space shuttle costs roughly $500 million in total.
The problem is that the Earth’s escape velocity (the speed required to escape Earth’s gravity) is so bloody high. A rocket, which often weighs tens of thousands of pounds, must push that enormous weight up to about 25,200 miles per hour, and sustain such speeds for several minutes. The rocket must carry so much fuel to sustain these speeds that the fuel makes up a significant portion of the vehicle’s weight, meaning that much of the fuel is spent lifting the rest of the fuel off the ground.
Because there has been no alternative (aside from avoiding outer space altogether), humankind has been stuck with this method of Earth egress for as long as such efforts have been undertaken. Many clever people have contemplated the idea of a tower or cable that can reach into Earth’s orbit and ferry people and cargo into space and back with much less energy, but when knowledgeable persons took to scribbling out the calculations, they found that the tower was physically impossible, and that the strongest material known to man was only half the strength necessary to make a cable reaching into space. But all of that changed in 1991, when carbon nanotubes came along and offered a possible solution.
Carbon nanotubes are made from the same carbon atoms that make up diamonds, but arranged in long, hollow, tube-like molecules. The molecular bonds in these molecules give the structures incredible tensile strength, and some degree of flexibility. A single molecule, though 50,000 times thinner than a human hair, can be theoretically made into a nanotube of any length. A number of these nanotubes can then be compressed into an extremely sturdy wire; enough to withstand the pressure needed for a space elevator.
The space elevator concept is relatively straightforward… it consists of a long carbon nanotube cable with one end attached to a fixed point on the Earth (or on an ocean-going platform), and the other end extending well beyond geosynchronous orbit. The centrifugal force caused by the Earth’s rotation would keep the cable taut, and thereby maintain the elevator’s fixed position. Large, tram-like elevator cars would then use electric motors to move themselves up the cable, and be accelerated as the Earth’s centrifugal force begins to propel them. After dropping off their payload in orbit, they could slowly descend in a similar fashion.
Despite the straightforward concept, construction of the elevator will be an engineering feat if it ever comes to fruition. It will require technologies that do not exist today, and some creative problem solving. For instance, as of this writing, the longest nanotubes to be developed are measured in centimeters, and a space elevator cable would need to be about 62,000 miles long. But researches all over the globe are addressing the problems, and despite the hurdles, optimistic estimates put a working space elevator in action as early as 2018. Although the project would cost several billions of dollars, it would reduce the stuff-to-orbit cost from $10,000/pound to less than $400/pound, so it should pay for itself in about a decade.
Researchers also need to anticipate and plan for what might go wrong with a space elevator. The airspace surrounding the elevator would need to be kept entirely clear of aircraft, lest a collision destroy the aircraft and compromise the integrity of the elevator. Satellites would also pose a hazard, since on a long enough timeline, all non-synchronous satellites will eventually reach a collision state with the elevator unless they are redirected. There are also natural factors, such as meteoroids and micrometeorites; ice formation on the cable; lightning and wind.
If the space elevator were to break near the Earth, the elevator would become unstable, and raise to a higher orbit. If it were to break nearer the top, the top section would raise to a higher orbit, and what cabling didn’t burn up in re-entry would theoretically drift to the Earth with all the force of a falling sheet of paper, given the cable’s light weight and flat, ribbon-like design. Any elevator cars would require an emergency descent system in the event of an emergency, perhaps using a system of parachutes.
NASA is currently exploring the possibility of a space elevator, and has identified several areas of critical research before one might be made feasible and practical. A space elevator has long been the stuff of science fiction, but with the discovery and development of carbon nanotubes, it may just be the primary vehicle to space in the coming decades.