Month: September 2018

The space elevator is perhaps one of the most intriguing ideas for reaching space. It was first conceived as a thought experiment in 1895 by the grandfather of astronautics, Konstantin Tsiolkovsky. In it, he considered the building of a massive tower reaching up to geostationary orbit at 35,756 km (23,000 mi) above the surface of the Earth, and which at the top would have sufficient horizontal velocity to launch vehicles into orbit. The vehicles themselves would be carried aloft by elevators like the ones climbing the Eiffel Tower.

Tsoilkovsky knew the construction of such a tower would be next to impossible, there simply were no materials capable of withstanding the compressional pressures exerted the mass of such a tower as it was built upwards – nor are there today. However, in 1960, another Russian,  Yuri N. Artsutanov suggested that rather than building the elevator up from the ground, it could be built both down and out from geostationary orbit, using tension along the cable from its lower end and through the “counterweight” of the outward extent of its length to maintain is tautness and balance. Referring to the design as a “heavenly funicular”, Artsutanov estimated it would be capable of delivering up to 12,000 tonnes of payload to geostationary orbit per day.

Six years later, working entirely independently of Artsutanov, four American oceanographers – John Isaacs, Hugh Bradner, George Bachus and Allyn Vine (after whom the deep-ocean research submersible Alvin was named) – published their idea for a “sky hook” that essentially used the same approach: build a cable both “down” and “out” from a geostationary starting point. Their idea became the inspiration for Arthur C. Clarke’s 1979 novel The Fountains of Paradise, which did much to promote the idea of space elevators in the public mind.

Since then, the idea has received many re-visits, and has also given birth to a number of experiments and ideas for the use of tensile cables  – referred to as “tethers” for doing things like “lowering” experiments into the upper atmosphere for research (such ideas being tested during the space shuttle era) and for creating “artificial gravity” in spinning space vehicles travelling to Mars. A space elevator even appeared in Kim Stanley Robinson’s Mars trilogy as the means to get from orbit down to the surface of the planet. Today, the space elevator is the subject of study by the International Space Elevator Consortium (ISEC), which holds annual conferences on the subject and supports research programmes into space elevator concepts.

The appeal of space elevators  – if they can be built – is that they could deliver huge amounts of payload and manpower to orbit around Earth for a relatively low-cost when compared to using traditional rocket launches. And deliver them not just to geostationary orbit, but to other points above the surface of Earth, referred to as “way stations”.

For example, a “way-station” at around 420-450 km (262-281 mi) altitude would impart a horizontal velocity for vehicles “launched” from it to keep them in a low Earth orbit. similarly, a way station placed above the geostationary orbit point, at say 57,000 km (36,625 mi) would impart enough horizontal velocity to a vehicle “launched” from it that it could escape Earth on a flight to Mars.

But before this can happen, there are some significant issues to overcome. The “simplest” of these is that of finding a suitable anchor point on Earth.

To work at geostationary orbit, the primary station on an elevator would have to be positioned over the equator. The problem here is, an awful lot of the equator is ocean (78.7%), making the construction of such an anchor-point at best difficult. While the remainder of the equatorial region is over land, it brings with it the overheads of political haggling and leveraging to gain an anchor-point.

In The Fountains of Paradise, Arthur C. Clarke solved this problem by conveniently moving Sri Lanka (which he called by its ancient Greek name of Taprobane (Tap-ro-ban-EE) 1,000 km (625 mi) south of its current position to straddle the equator. Unfortunately, we can’t do that in the physical world.

The more significant issues, however, are exactly how to build the elevator tether and how to gradually and safely lower it through the denser part of Earth’s atmosphere, and without its “downward” mass simply ripping it apart before it can be anchored.

The most promising material for the tether construction is carbon nanotubes (CNTs). These are artificially “grown” structures with a number of unusual properties, one of which it their sheer strength: up to 10 times that of an equivalent steel cable, which comes at a fraction of a cable’s mass. CNTs have been known about for around 20 years and are seen as having a range of potential applications: construction, electronics, optics, nanotechnology, etc. However, there is one slight issue with their use in large-scale projects. So far, no-one has successfully “grown” a nanotube longer than 1.5 metres.

Even so, experimental cables have been lifted to altitudes of around 1 km (0.6 mi) using weather balloons and had scale “carriers” run up and down them to test how an elevator tether and its payload would react to the influence of wind and weather. Now, researchers at the Shizuoka University Faculty of Engineering are taking the practical research a step further, by deploying an experimental “space elevator” in space.

On Monday, September 7th, 2018, the  Kounotori-7 H-II Transfer Vehicle (HTV) resupply vehicle is due to be launched to the International Space Station (ISS). As a part of the six tonnes of supplies the vehicle will be carrying will be two small “cubesats” – satellites that are each just 10 cm (4 inches) on a side.

These will be deployed in space, connected by a 10 metre (33 ft) tether. Once the tether is under stable tension, a little electrically powered “car” will traverse it, marking the first time a vehicle has travelled along a tether in space. The test is intended to see how a space elevator tether might react to payloads moving along it in whilst in the “vacuum” of space, together with the stresses placed on it and its “anchor points”, etc.

It’s a small step along the way to establishing a space elevator, but the test will be watched with interest by Japan’s massive construction firm, Obayashi Corporation. In 2012, they announced they would have the world’s first space elevator operating by 2050. They are actively sponsoring research into CNT development, and believe the issues of growing long strands of CNTs and “knitting” them together into a tether will have been resolved by 2030.

Continue reading “Space Sunday: taking an elevator into space” →