Why we haven't built a space elevator yet
In short: The rocket equation imposes a heavy tax on space travel, making current launch costs extremely high. To bypass these limits, engineers have proposed diverse alternatives like orbital rings, space fountains, and mass drivers. These non-rocket systems aim to provide initial velocity, potentially lowering costs to levels that enable large-scale colonization.
Current space launch costs are prohibitively high, ranging from $2,500 to $25,000 per kilogram to reach low Earth orbit. Because of the exponential nature of the rocket equation, even small gains in initial velocity from non-rocket methods could drastically lower the cost of space missions. If costs could drop to hundreds of dollars per kilogram, large-scale projects like space-based solar power or terraforming Mars would become feasible.
One primary concept is the space elevator: a ribbon-like cable anchored to Earth and extending past geosynchronous orbit (approximately 35,999 kilometers). At this height, centrifugal force keeps the cable taut, allowing vehicles to climb to orbit without rockets. However, current materials lack the strength-to-density ratio to support such a structure on Earth. While materials like Kevlar could work for elevators on the Moon or Mars, Earth-based designs require theoretical materials like carbon nanotubes or boron nitride nanotubes.
Other alternatives include 'space fountains,' which use a tall tower and projected pellets to hold the structure aloft, and 'orbital rings'—rotating cables in low Earth orbit with hanging tethers. There are also 'mass drivers' (or space guns) that use linear motors or explosives to accelerate payloads along tracks. While these could potentially launch cargo for as little as $40 per kilogram, the extreme G-forces often limit them to freight rather than human passengers.
Finally, 'endo-atmospheric tethers' offer a way to transfer kinetic energy from large, slow aircraft to smaller, high-speed vehicles. By using aerodynamics or centripetal action, these systems can propel payloads to hypersonic speeds without exotic propulsion. These diverse theories aim to move the heavy lifting of space travel from the launchpad to the ground or the atmosphere.
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Sources
- Summary by Intellect · source: Non-rocket spacelaunch
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