Japan’s Obayashi will have tiny cubsat test to learn about tethers for space elevators

Shizuoka University and contractor Obayashi aim to launch two small (10 sq cm) satellites connected by a 10-meter steel cable from the International Space Station. This small cube sat space tether step is a tiny step towards a larger vision of a space elevator. However, is mostly unrelated. It is in space but the tether material has nothing to do with what is needed for earth based space elevators.

The Obayahi space elevator is planned to be built by the year 2050 with a capacity to carry 100-ton climbers. It is composed of a 96,000-km carbon nanotube cable, a 400-m diameter floating Earth Port and a 12,500-ton counter-weight. They expect the space elevator to cost $9 billion.

Obayashi knows the current technology levels are not yet sufficient to realize the concept, but our plan is realistic, and is a stepping stone toward the construction of the space elevator.

The construction will be technically feasible with an assumed cable tensile strength of 150 GPa, it will take roughly 20 years to construct the cable [after the materials become available in the required multi-tons quantities], the impacts of wind or Coriolis force on cable displacement are small, and it is essential to fix one end of the cable to the earth’s surface, always applying pre-tension at the ground end. According to the plan, a 20-ton cable is deployed initially, and is reinforced 510 times by climbers up to 7,000 tons, ascending in succession over roughly 18 years. The facilities are then transported and constructed within one year.

Elon Musk does not want to be asked about space elevators until carbon nanotube or graphene structures can be built longer than a foot bridge

There have been analysis of super-long bridges that could be built with stronger materials. Currently the longest main span of a suspension bridge is 1991 meters. Stronger 10 GPa cables with 1-kilometer length would enable 6200 meter long bridge spans. This would be long enough for bridges across the straits of Gibraltar.

Strongest bulk tethers known to Nextbigfuture are 80 GPa which are 24 times stronger than Kevlar

There was a breakthrough in 2018 where carbon nanotube bundles have been made with 80 Gigapascals of strength. This will be strong enough for space elevators. However, production needs to move from tiny amounts in the lab to the 7000 tons needed for space elevators.

This was a 8X leap from the best materials in 2016.

In 2016, Jian Nong Wang and his colleagues made nanotubes with a process akin to glass blowing: Using a stream of nitrogen gas, they injected ethanol, with a small amount of ferrocene and thiophene added as catalysts, into a 50-mm-wide horizontal tube placed in furnace at 1,150–1,130 °C. They packed the nanotubes even more densely by pressing the film repeatedly between two rollers.

The resulting films had an average strength of 9.6 gigapascals. By comparison, the strength of nanotube films made so far has been around 2 GPa, while that for Kevlar fibers and commercially used carbon fibers is around 3.7 and 7 GPa, respectively. The films are four times as pliable as conventional carbon fibers, and can elongate by 8% on average as opposed to 2% for carbon fibers.

DRUM ROLL Spooling a cylinder of blown carbon nanotubes onto a rolling drum, researchers create a black film containing aligned, densely packed nanotubes (left). After being passed through a roller several times, the film becomes flatter and the nanotubes more densely packed (right). The film is exceptionally strong and ductile.
Credit: Nano Lett

This will mean rockets and spaceplanes that go at about Mach 8 will be able to rendezvous with rotovators. This will reduce the cost of putting things into orbit by about ten times.

There was a NASA study of hypersonic skyhooks that determined the best designs and the strength of materials needed. No show-stoppers were uncovered. However, the elements of the concept require further development and refinement and then actual implementation programs. They have to build and test hardware to make the engineering work reliably.

Depending upon the tether system design the tether being over two times stronger will reduce the weight of the needed tether by 5 to 20 times. Keeping the weight of the system about the same would allow a lower performance hypersonic vehicle to make a rendezvous. Something that say only went mach 8 instead of mach 15.

Obayashi wants to make a bunch of facilities on a space elevator

Other facilities include Martian/Lunar Gravity Centers, an Low Earth Orbit Gate, a Geostationary Earth Orbit Station, a Mars Gate and a Solar System Exploration Gate.

Obayashi wants to build a space elevator using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, connected by a cable from a platform on the sea to a satellite at 36,000 kilometers above Earth.

The elevator would be powered by an electric motor pulley.

The cars would travel at up to 200kph and arrive at the space station eight days after departure from Earth.

The cost of transport is expected to be about one-hundredth of that of the space shuttle.

Carbon nanotube is the most likely material to be used for the cables.


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