In space travel, the first step is always the most expensive, but why blast-off in a rocket if you can catch a ride on a space elevator? Canadian space firm Thoth Technology has received a US patent for an elevator to take spacecraft and astronauts at least part way into space. If it’s ever built, the 20 km (12.4 mi) high Thothx inflatable space tower holds the promise of reducing launch costs by 30 percent in terms of fuel, and may even replace some classes of satellites.
Space travel is a field that is rich in paradoxes. Even though the cosmos stretches out tens of billions of light years away from us, it’s covering the first 100 km (62 mi) that mark the official boundary of space that presents the most difficult and expensive challenge for current technology.
Today, getting any higher than 50 km (31 mi) requires rocketry, but rockets are incredibly inefficient. Not only do they need to carry enough fuel to get a payload into orbit, but they also need fuel to carry the fuel to carry the fuel. Then, of course, there’s the problem of atmospheric drag which means expending even more fuel.
Over the past century, scientists and engineers have come up with many ways of overcoming these limitations. They’ve moved launch sites to the equator to take advantage of the velocity of the Earth’s rotation, they’ve tried launching rockets from balloons, and explored various catapult devices. However, one of the most efficient (at least, on paper) is also one that seems like pure fiction: a space elevator.
First proposed by Russian space pioneer Konstantin Tsiolkovsky in 1909 and popularized by Sir Arthur C Clarke in his novel The Fountains of Paradise, the space elevator is exactly what it sounds like. It’s an elevator that can carry passengers and cargo from the Earth’s surface and into geosynchronous orbit about 36, 000 km (22, 000 mi) up.
Such a cosmic lift would move payloads much more efficiently at an estimated cost of US$220 per kg ($100 per lb), which is a considerable saving on present costs of $25, 000 per kg ($11, 000 per lb). An elevator system would also have other advantages, such as being geographically fixed, and being able to carry out many of the functions of a satellite.
Unfortunately, current designs for space elevators are well beyond our ability to construct. They would need a tower or cable reaching up to geosynchronous orbit and another cable stretching thousands of miles beyond, with a counterbalance the size of an asteroid at the end to help hold up the structure.
Worse, no material exists out of which the elevator could be made and still support its own weight, though carbon nanotubes, boron nitride nanotubes, and diamond nanothreads have all been suggested.
The more modest design of the Thothx tower aims to get around these limitations.
According to the patent granted on July 21, the Thothx tower would be only 20 km (12.4 mi) high and about 230 m (755 ft) in diameter. Topped with a deck or decks, it could launch satellite payloads from the deck or pods attached to the tower. While 20 km may not seem like much compared to 36, 000 km, it’s still 20 times higher than any other manmade structure and high enough to shave a third off of launching costs.
The tower itself would be made of reinforced inflatable sections with an interior elevator tower made of multiple, extruded, pneumatically-reinforced segments. This forms an inner wall to the inflatable sections and a hollow middle for the elevator car. It also acts as a framework for raising decks, stabilizers, and other building components.
So wouldn’t a giant inflatable tower flop in the wind unless it was tied down? The Thothx tower would be much too high for guy wires, so the company has proposed using a series of flywheels to provide dynamic stability, and to act as compressors to pressurize the tower. By adjusting pressure and spin, the flywheels can compensate for any bending of the tower and keep it fixed over its footprint.
As to the elevating component, the patent proposes that pressurized cars would run in the core or climb up the outside of the shaft like a mechanical spider, as a cable wouldn’t be able to support its own weight without breaking.
The main function of Thothx would be for launching spacecraft, with the top of the tower acting as a launch pad for single stage to orbit rockets, landings, refueling, and relaunchings. In addition, the tower could be used for scientific research, communications, tourism, remote sensing, and mounting wind generators. Smaller, temporary towers (25 to 150 m) could also be used for providing large areas with communications and remote sensing.
“Landing on a barge at sea level is a great demonstration, but landing at 12 miles above sea level will make space flight more like taking a passenger jet, ” says Thoth President and CEO, Caroline Roberts, in a reference to the powered landing system being tested for the SpaceX Falcon 9.