Traditional rockets can be intimidatingly risky, complex and expensive. This essay explores alternative non-rocket launch possibilities that may be cheaper and safer.
Konstantin Tsiolkovsky first proposed the concept of a space elevator in 1805. It is envisioned as a cable that stretches from the surface of the Earth to a height of around 100,000 km. A spacecraft can climb up the cable and pick up speed due to the tangential velocity of the cable. The higher the spacecraft climbs, the greater its velocity will be, as tangential velocity increases proportionally with distance from the surface. Spacecrafts can thus attain velocities high enough to reach anywhere between Mercury and Jupiter without a drop of fuel. In addition, there will be fewer engineering constraints on the spacecraft since it doesn’t need to have a combustion chamber or even be able to withstand extremely high temperatures and pressures like chemical rockets do. The elevator will also make space access cheap and easy. This could help kickstart industries like space mining and space tourism, making it a promising discovery.
However, building such a tall structure requires a material with an extremely high tensile strength. While carbon nanotubes with sufficient tensile strength do exist, the longest carbon nanotube today is half a meter long, not the required 100,000 kilometres. Once built, the elevator can lower launch costs and be used for harvesting solar energy from space, starting space mining operations, or even colonizing other planets. But since there is no compelling incentive to do any of these things, and since the set-up costs of the elevator are on the order of tens of billions of dollars, financing its construction seems difficult.
A more feasible alternative to the space elevator is the sky-hook. A sky-hook is designed as a tall tower that orbits the Earth. The bottom half of the sky-hook will be moving slower than the orbital velocity at its altitude, and the top-half will be moving faster. A spacecraft launched from Earth can accelerate to match velocities with the bottom of the hook. The hook can then grab the spacecraft out of the air and the spacecraft can slide up the sky-hook tower and pick up speed the same way a climber picks up speed by ascending the space elevator cable. Since the spacecraft only has to match velocities with the bottom of the hook instead of accelerating all the way to some orbital velocity, it can carry less fuel. Furthermore, proposed sky-hook designs such as Boeing’s HASTOL are on the order of hundreds of kilometres long, not a hundred thousand kilometres like the space elevator. Hence they can be built with existing materials such as steel.
But the construction of a sky-hook will require launching hundreds of thousands of kilograms worth of materials into space. The current rocket-launching infrastructure is woefully inadequate to support such a large-scale construction project. As with the elevator, there will also be large set-up costs. Thus obtaining financing seems equally unlikely even if the engineering challenges were overcome.
Another non-rocket launch option in space towers. The concept involves suspending a huge track or runway on top of 80 to 120 km tall ‘space’ towers. These towers will be able to stand several kilometres tall by using something called active support, as opposed to passive support used by traditional buildings. Spacecraft can then accelerate down that runway to orbital or escape velocities, the same way aeroplanes accelerate down run-ways before take-off. Since the spacecraft will have a run-way to push off to gain speed, it doesn’t need to carry fuel, thus significantly lowering fuel and launch costs.
However, just like with sky-hooks, an engineering feat of this scale has never been attempted before. The tallest building today is less than a kilometre tall. Furthermore, the concept of active support has never been used to construct buildings, so a lot of research and development on active support and the construction of megastructures would need to be done before these space towers can be erected.
There is a common theme to the disadvantages of the non-rocket alternatives discussed so far. Firstly, although space-enthusiasts vehemently disagree, there is no immediate and compelling economic incentive to build them. Although easy access to space will open up several lucrative opportunities, from solar power systems to lunar and asteroid mining to space tourism, one will have to wait several decades after the first elevator or sky-hook is built to reap benefits from such opportunities. Hence nobody is willing to foot the massive set-up costs of these technologies today.
Moreover, such construction projects are also risky. We lack the experience to confidently carry-out large-scale engineering projects in space, and although many detailed studies exploring the space elevator, skyhooks, space towers, and other rocket alternatives have been conducted, there is a serious deficit in engineering know-how and industrial capacity that must be filled before these rocket alternatives can be seriously considered.
The current prospects for rocket alternatives seem grim. But the Space Age is characterized by its ability to do the impossible. Every Space Age triumph, from Sputnik to Apollo 11 to New Horizons seemed impossible at the time. While rocket alternatives seem like a long shot today, the previous successes of the Space Age should convince us not to abandon them in their infancy.
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This is so informative and enlightening.. great going!!!