When people first began exploring space in the 1960s, a single pound of payload might cost up to $80,000 (adjusted for inflation).
The requirement to develop a new, expensive rocket for each launch was a major contributor to the high cost. That began to change when SpaceX began producing low-cost, reusable rockets, and the company is now ferrying customer payloads to LEO for as little as $1,300 per pound.
This is making space accessible to scientists, startups, and tourists who could not previously afford it, but the cheapest means to reach orbit may not even be a rocket at all – it may be an elevator.
The elevator in space
The seeds for a space elevator were planted in 1895 by Russian physicist Konstantin Tsiolkovsky, who published a paper thinking about the construction of a tower 22,000 miles high after witnessing the 1,000-foot-tall Eiffel Tower.
This would allow access to geostationary orbit, where things appear to remain fixed above the Earth’s surface, but Tsiolkovsky admitted that no material could hold the weight of such a structure.
A space elevator might make sending a payload to any Earth orbit as cheap as $100 per pound.
Soon after Sputnik, in 1959, Russian engineer Yuri N. Artsutanov proposed a solution: instead of building a space elevator from the ground up, start at the top.
He explicitly proposed putting a satellite in geostationary orbit and tethering it to the Earth’s equator. The satellite would ascend as the tether lowered. The tether would be kept taut once tethered to the Earth’s surface by a mix of gravitational and centrifugal forces.
We could then use electrically driven “climber” vehicles to deliver payloads to any Earth orbit. The Earth is at the bottom, a satellite is on top, and a rope with robots attached connects the two.
According to physicist Bradley Edwards, who examined the concept for NASA approximately 20 years ago, building a space elevator would cost $10 billion and take 15 years, but once operational, the cost of transferring a payload to any Earth orbit might be as low as $100 per pound.
“Once you lower the cost to almost a Fed-Ex level, it opens the door to a lot of people, a lot of countries, and a lot of companies getting involved in space,” Edwards told Space.com in 2005.
Aside from the economic benefits, a space elevator would be cleaner than utilizing rockets because there would be no fuel burning and no damaging environmental emissions, and the new transport system would not contribute to the problem of space trash to the same extent that expendable rockets do.
So, why haven’t we got one yet?
In his NASA paper, Edwards stated that all of the technology required to build a space elevator already existed, with the exception of the material required to build the tether, which must be light while also strong enough to survive all of the massive forces operating on it.
According to the paper, the right material — ultra-strong, ultra-tiny carbon “nanotubes” — would be ready in just two years.
“Steel isn’t strong enough, and neither are Kevlar, carbon fiber, spider silk, or any other material other than carbon nanotubes,” Edwards wrote. “Fortunately for us, carbon nanotube research is extremely hot right now, and it is quickly progressing toward commercial production.”
Unfortunately, he underestimated how difficult it would be to manufacture carbon nanotubes – no one has been able to grow one longer than 21 inches too far.
Further research into the material discovered that it also frays under tremendous stress, which means that even if we could make carbon nanotubes at the required lengths, they’d be at risk of snapping, damaging not only the space elevator but also endangering people on Earth.
Carbon nanotubes were the early favorite as a tether material for space elevators, but there are alternative options, including graphene, an essentially two-dimensional form of carbon that is already easier to scale up than nanotubes (though not easy).
In contrast to Edwards’ report, Johns Hopkins University academics Sean Sun and Dan Popescu believe Kevlar fibers may work if we repaired the tether on a regular basis, similar to how the human body heals its tendons.
“It would be possible to mathematically model the entire tether using sensors and artificially intelligent software to predict when, where, and how the fibers would break,” the researchers wrote in Aeon in 2018.
“When they did, speedy robotic climbers patrolling up and down the tether would replace them, adjusting the rate of maintenance and repair as needed — mimicking the sensitivity of biological processes,” they went on to say.
In the words of Zephyr Penoyre and Emily Sanford “It could be constructed from fibers that are already mass-produced… and relatively inexpensive.”
Astronomers from the University of Cambridge and Columbia University believe Kevlar might be used to build a space elevator if it were built from the moon rather than the Earth.
The Spaceline concept proposes that a rope tied to the moon’s surface may reach toward Earth’s geostationary orbit, held taut by the pull of our planet’s gravity. We could then utilize rockets to transport goods — and maybe humans — to solar-powered climber robots at the end of this 200,000-mile tether. The bots might then proceed up the line to the surface of the moon.
This would not eliminate the need for rockets to enter Earth’s orbit, but it would be a less expensive method of reaching the moon. According to the researchers, the forces acting on a lunar space elevator would not be as powerful as those acting on one extending from Earth’s surface, allowing up additional alternatives for tether materials.
“[T]he required material strength is far lower than that of an Earth-based elevator — and hence it might be created from fibers that are already mass-produced… “and reasonably priced,” they stated in a document posted on the preprint server arXiv.
China anticipates that its “Sky Ladder” will reduce the cost of sending people and products to the moon by 96%.
Meanwhile, some Chinese researchers aren’t giving up on the concept of using carbon nanotubes for a space elevator – in 2018, Tsinghua University claimed that they’d generated nanotubes strong enough for a tether.
The researchers are currently working on scaling up manufacturing, but in 2021, state-owned news source Xinhua produced a video presenting a concept named “Sky Ladder,” which would consist of space elevators above Earth and the moon.
After ascending the Earth-based space elevator, a capsule would fly to a space station connected to the moon-based one’s cable. If the initiative is successful — a big if — China estimates Sky Ladder will reduce the cost of carrying people and commodities to the moon by 96%.
In the 120 years since Tsiolkovsky saw the Eiffel Tower and imagined something much bigger, enormous progress has been achieved in finding materials with the qualities required for a space elevator. At this point, it appears likely that we will one day have a material that can be made at the scale required for a tether — but by then, the need for a space elevator may have vanished.
Several aerospace businesses are making headway with their own reusable rockets, and when they enter the market alongside SpaceX, launch prices may fall much lower.
Meanwhile, SpinLaunch, a California business, is creating a huge centrifuge to accelerate cargo into space, where much smaller rockets can propel them into orbit. If the company succeeds (another huge if), it claims the system will reduce the amount of fuel required to reach orbit by 70%.
Even if SpinLaunch does not take off, various groups are working on ecologically acceptable rocket fuels that emit significantly fewer (or no) hazardous pollutants. More effort will be required to efficiently scale up their production, but it will be a lot easier to overcome than creating a 22,000-mile elevator to space.