Nanothread breakthrough could make cosmic elevators a reality
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Dreams of taking an elevator into space have just been given a boost after researchers created ultra-thin, super-strong nanothreads made from diamonds.
The threads are made up of a long, thin strand of carbon atoms arranged in the same way as the inside of a diamond.
The discovery could finally be the breakthrough needed to hoist and support cosmic elevators that would transport people into the atmosphere.
Dreams of taking an elevator into space have just been given a boost after researchers created ultra-thin, super-strong nanothreads (artist's impression pictured) made from diamonds
The research was carried out by John Badding, a professor of chemistry at Penn State University, and the findings are published in the journal Nature Materials.
'From a fundamental-science point of view, our discovery is intriguing because the threads we formed have a structure that has never been seen before,' Professor Badding said.
The core of the nanothreads that Professor Badding's team made is a long, thin strand of carbon atoms arranged like the fundamental unit of a diamond's structure.
CREATING DIAMOND NANOTHREADS
The core of the nanothreads is a long, thin strand of carbon atoms arranged like the inside of a diamond.
The team used the large high-pressure Paris-Edinburgh device at Oak Ridge National Laboratory to compress a 0.2inch (6mm) wide amount of benzene.
This molecule is a flat ring containing six carbon atoms and six hydrogen atoms.
The resulting diamond-core nanothread is surrounded by a halo of hydrogen atoms.
During the compression process, the flat benzene molecules stack together, bend, and break apart.
Then, as the researchers slowly release the pressure, the atoms reconnect in an entirely different yet very orderly way.
The result is a structure that has carbon in the tetrahedral configuration of diamond with hydrogens hanging out to the side and each tetrahedron bonded with another to form a long, thin, nanothread.
Diamonds feature zig-zag 'cyclohexane' rings of six carbon atoms bound together, in which each carbon is surrounded by others in the strong triangular-pyramid shape of a tetrahedron.
'It is as if an incredible jeweller has strung together the smallest possible diamonds into a long miniature necklace,' Professor Badding added.
'Because this thread is diamond at heart, we expect that it will prove to be extraordinarily stiff, extraordinarily strong, and extraordinarily useful.'
'One of our wildest dreams for the nanomaterials we are developing is that they could be used to make the super-strong, lightweight cables that would make possible the construction of a "space elevator", which so far has existed only as a science-fiction idea.'
The team's discovery comes after nearly a century of attempts by other labs to compress separate carbon-containing molecules, such as liquid benzene, into an ordered, diamond-like nanomaterial.
'We used the large high-pressure Paris-Edinburgh device at Oak Ridge National Laboratory to compress a 0.2inch (6mm) wide amount of benzene - a gigantic amount compared with previous experiments,' said Malcolm Guthrie of the Carnegie Institution for Science, a co-author of the research paper.
'We discovered that slowly releasing the pressure after sufficient compression at normal room temperature gave the carbon atoms the time they needed to react with each other and to link up in a highly ordered chain of single-file carbon tetrahedrons, forming these diamond-core nanothreads.'
Engineer Peter Debney recently proposed a space elevator in which a cable would be lowered from a satellite in geostationary orbit. A counterweight would balance the system (pictured). Debney warned current materials aren't strong enough for this system - but Professor Badding's diamond-like structure could change this
Professor Badding describes the thread's width as 'phenomenally small, only a few atoms across', hundreds of thousands of times smaller than an optical fibre, which is much thinner than the average human hair.
Professor Badding described the thread's (illustrated) width as 'phenomenally small, only a few atoms across'
Parts of these first diamond nanothreads appear to be somewhat less than perfect, so improving their structure is a continuing goal of Professor Badding's research.
The first references to an elevator that could transport people into space was made in 1895 by Konstantin Tsiolkovsky.
His proposal was for a free-standing tower reaching from the surface of Earth to the height of geostationary orbit.
In 1975 American scientist, Jerome Pearson, designed a system with a cable which would be thickest at the geostationary orbit, where the tension was greatest.
He suggested using a counterweight that would be extended out to 89,000 miles (144,000km) - almost half the distance to the moon.
In 1979, the idea of space elevators became more mainstream after they features in Arthur C. Clarke's novel, The Fountains of Paradise.
More recently, engineer Peter Debney proposed a theory that borrows the methods by which cathedrals control their centre of gravity - by tapering at the top.
But until now, there have been few materials strong enough, or that can be manufactured in sufficient quantities, to create a cable long enough to reach.
When building any tall structure - from gothic cathedrals to skyscrapers, and eventually a space elevator - the sturdiness and balance comes from its centre of gravity.
All tall buildings, from gothic cathedrals to skyscrapers, stay upright because their centre of gravity is as low as possible. The centre of gravity determines balance, for example. This graphic shows that by digging deep foundations, and securing them with piles of metal and a concrete raft, this centre is underground
This is the same theory that applies to all tall and 'super-tall' buildings.
By creating strong, far-reaching foundations deep into the Earth, the centre of gravity is shifted from above the ground, to below it.
Structural engineer Peter Debney, from Arup told MailOnline: 'The gravity we experience here on the Earth's surface is the result of two components.
'The first is our distance from the centre of the Earth, that is, the Earth's centre of gravity.
'As the Earth is not actually a sphere, the spin of the Earth causes there to be more material at the Equator and less at the poles, this means the Equatorial radius is higher than the Polar one.
'Thus the force of gravity is least at the Equator and maximum at the North and South Poles.'
In addition to that, Debney explained that because the Earth is spinning, there is a centrifugal force acting on everything, which is maximum at the Equator and zero at the poles.
HOW WOULD THE LIFT WORK?
Engineer Peter Debney proposes a system that uses the principles from gothic cathedral and skyscraper architecture to create a space elevator.
He claims firms could lower a cable from a satellite that is say in geostationary orbit above the Earth.
A counterweight, such as a suitably-sized asteroid, would be used at the other end of the cable to balance the system.
The cable would need to be made of graphene, or carbon nanotubes, because these materials are capable of holding heavier loads and bearing their own weight more effectively.
By anchoring the cable at the Equator, the gravitational acceleration on the system would be at a minimum.
The elevator itself would then extend from low to high Earth orbit, and would be kept taught by tidal forces.
The cable would taper, to adjust the centre of mass, but from the top down, rather than the bottom up, as seen in pyramids and spires.
'Combine these two effects together and the effective gravitational acceleration is least at the Equator, and maximum at the poles.'
He continued: 'If the centrifugal force from the Earth's rotation offsets the force of gravity; what happens when you get higher up a tall building?
'The first effect is that gravity is reduced as you are now further from the centre of gravity, and the second is that centrifugal force increases.
'There will, therefore, come a point when the centrifugal force exactly cancels out gravity.
'If you are on the Equator, this occurs at a height of approximately 18,000 km.
'This height is commonly known as the geostationary orbit, because if you position a satellite at this altitude over the equator and give it the right velocity, it will orbit within a 24-hour period, and remain over a fixed point on the Earth.'
Debney said the solution is to place a satellite in geostationary orbit, and lower a cable from it to the ground.
But, he continued, as soon as the cable lowers, it changes the centre of gravity of the satellite, placing it at a lower orbit and causing it to move relative to the ground.
To keep the whole thing in orbit, Debney added a cable would then also need to be extended up at the same time, to keep the system balanced.
Because this would make a nonlinear system, the cable would need to extend out almost twice as far as it is brought down.
The alternative is to use a counterweight, such as a suitably sized asteroid, beyond geostationary to balance the cable and save the excessive length.
The cable would also need to be made of a material that can hold its own weight at such heavy loads, such as graphene or carbon nanotubes.
This is where Professor Badding's diamond-like materials would come into play.
Tokyo-based company Obayashi Corporation announced plans to build an operational space elevator by 2050, (concept image pictured). It uses similar technology proposed by Debney, and seen in supertall buildings
The same principle applies to buoys (pictured). The taller they are, the stronger the counterweight needs to be to keep it afloat. Both buoys, and spires on churches, taper towards the top to reduce the load on the materials beneath it, more evenly distribute the weight, and reduce the wind resistance
Although the lift would cause the weight to distribute, the cable would be able to maintain being top heavy, in the same way Seattle's Space Needle, (pictured) does, due to the lower centre of gravity
Graphene has a breaking length of 3,568 km, but because breaking length assumes a constant force of gravity, and at that altitude the force is lower, this allows for extra length.
Debney continued that the space elevator cable will instead need to be a ribbon that tapers.
Just as the pyramids and spires of a cathedral taper towards the top to support the weight efficiently - the cable would need to taper towards the ground.
'It is almost certain that early versions of the space elevator will not reach the ground but instead extend from low to high Earth orbit,' said Debney.
'These will be kept taught by the tidal forces induced by the two ends orbiting at different altitudes: low orbits move at a higher angular velocity than high orbits.
'Curiously, despite the high orbits having a lower angular velocity, they have a higher tangential velocity, which means that if you want to go round the Earth slower you need to speed up.'
The accidental damage risks of installing a space elevator include space debris and micrometeorites, but the width of the ribbon cable, according to Debney, would minimise the risk from these impacts.
The risk from the falling cable is less than might be considered, too, as the ribbon would be 'both light and have a reasonable air resistance'.
Any cable falling from this height should burn up before reaching the ground and studies have shown that the whiplash effect experienced by upper parts of the cable are likely to snap sections and put them into orbit for recovery later.
Japanese construction firm Obayashi recently said it will have an elevator to space in operation by 2050.
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