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When people first started exploring space in the 1960s, it was expensive $80,000 (adjusted for inflation) put a A single pound Propulsion into low Earth orbit.
A major reason for this high cost is the need to build a new, expensive rocket for each launch. That really started to change when SpaceX started making cheap, reusable rockets, and today, the company carries customer payloads to LEO at a price. $1,300 per pound.
It makes space accessible to scientists, startups and tourists who couldn’t afford it before. Cheap The way to orbit might not be a rocket — it might be an elevator.
Space elevator
A Russian scientist first planted the seeds for the space elevator Konstantin Tsiolkovsky In 1895, after visiting the 1,000-foot-tall Eiffel Tower, he published a thesis on the construction of a structure. 22,000 miles High.
It would provide access to geostationary orbit, a height above the Earth’s surface where objects would appear stable, but Tsiolkovsky admitted that such a tower would not be able to support the weight.
A space elevator can bring up the cost of sending a payload Any Earth’s orbit is very low $100 per pound.
In 1959, after Sputnik, Russian engineer Yuri N. Artsutanov proposed a way around this problem: instead of building a space elevator from the ground up, start at the top.
More specifically, he suggested placing a satellite in geostationary orbit and dropping a tether from it below Earth’s equator. When the tether comes down, the satellite goes up. Once attached to the Earth’s surface, the tether is held taut due to a combination of gravitational and centrifugal forces.
Electrically powered „ascent” vehicles can be sent up and down the tether to deliver payloads to any Earth orbit.
According to Bradley Edwards, a physicist who researched the concept for NASA about 20 years ago, a space elevator would cost $10 billion to build and take 15 years, but once operational, the cost of sending a payload Any Earth’s orbit may be low $100 per pound.
„Once you get the cost down to almost a Fed-Ex kind of level, it opens the door for a lot of people, a lot of countries and a lot of companies to get involved in space,” Edwards said. told Space.com In 2005.
In addition to the economic benefits, the space elevator would be cleaner than using rockets—burning fuel, with no harmful greenhouse emissions—and the new transportation system would not contribute to the space junk problem. Degree of making expendable rockets.
So why don’t we have one more?
Tether problems
Edwards wrote in his report to NASA that all the technology needed to build a space elevator already existed. Besides The material required for tying the tether should be light but strong enough to withstand all the large forces acting on it.
The good news, according to the report, is that the perfect material — ultra-strong, ultra-small „nanotubes” of carbon — will be available within two years.
„[S]”Deal isn’t strong enough, Kevlar, carbon fiber, spider silk, or any material other than carbon nanotubes,” Edwards wrote. „Fortunately for us, carbon nanotube research is very hot right now, and it’s rapidly progressing toward commercial production.”
Unfortunately, he misjudged how difficult carbon nanotubes would be to synthesize—to date, no one has been able to grow them longer than that. 21 inches.
Further research into the material revealed that it would disintegrate under extreme pressure, meaning that even if we could make carbon nanotubes of the required length, they would be at risk. SnappingNot only destroys the space elevator, but also threatens life on Earth.
Looking ahead
Carbon nanotubes may have been an early frontrunner as a tether material for space elevators, but they exist Other optionsA two-dimensional form of carbon already exists, including graphene Easy to measure than nanotubes (though not yet Easy)
Contrary to Edwards’ report, Johns Hopkins University researchers Sean Sun and Dan Popescu say that Kevlar fibers. can Work – we must continue to do Adjust the tetherIn the same way the human body constantly repairs its tendons.
„Using sensors and artificially intelligent software, the entire tether can be mathematically modeled to predict when, where and how the strands will break,” the researchers say. wrote in Aeon In 2018.
„When they did, fast 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 continued.
„It can be made from fibers that are already mass-produced … and relatively cheap.”
Zephyr Benair & Emily Sandford
Astronomers at the University of Cambridge and Columbia University also think Kevlar could work for a space elevator — if it could be made from the moon rather than Earth.
They invite their opinion space line, and the idea is that a tether attached to the Moon’s surface can be extended toward Earth’s geostationary orbit, held tightly by our planet’s gravity. At the end of this 200,000+ mile-long tether the rockets could be used to deliver payloads — and potentially people — to solar-powered climbing robots. The bots can then travel up to the line on the lunar surface.
It doesn’t eliminate the need for rockets to enter Earth orbit, but it’s a cheaper way to get to the moon. The forces acting on a lunar space elevator may not be strong enough to extend from Earth’s surface, according to the researchers, opening up more options for tether materials.
„[T]The required strength of the material is much less than that of an Earth-based elevator – so it can be made from fibers that are already mass-produced … and relatively cheap,” they wrote. Paper Shared on the preprint server arXiv.
China predicts its „skyladder” will cut the cost of sending men and supplies to the moon by 96%.
Some Chinese researchers, meanwhile, haven’t given up on the idea of using carbon nanotubes for a space elevator – in 2018, a team from Tsinghua University revealed They created nanotubes that they say are strong enough for a tether.
Researchers are still working on ramping up production, but in 2021, state-owned news agency Xinhua released a video of what it calls a „skyladder” that features space elevators above Earth and the moon. .
After boarding an Earth-based space elevator, a capsule will fly to a space station attached to a Moon-based spacecraft. China predicts that if the project is stopped – and it is massive – it could cut the cost of sending men and supplies to the moon by 96%.
bottom line
In 120 years Tsiolkovsky contemplated the Eiffel Tower the way Great, great progress has been made in developing materials with the properties needed for space elevators. At this point, it looks like we may one day have a product that can be produced at the scale necessary for Tether — but by then, the need for a space elevator may have evaporated.
Several space companies are moving forward with their own reusable rockets, and as they join the market with SpaceX, competitive launch prices could drop further.
California startup SpinLaunch, meanwhile, is building a giant centrifuge to fly payloads into space, where much smaller rockets can propel them into orbit. If the company succeeds (another of those big ifs), it says it will reduce the amount of fuel needed to reach orbit by 70%.
Although SpinLaunch hasn’t gotten off the ground, several groups are forming Environmentally friendly rocket fuels It produces very little (or no) harmful emissions. It takes a lot of work to be efficient Increase their productivityBut overcoming that obstacle is much easier than building a 22,000-mile elevator to space.
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