Space Towers

Long ago kings and empires often signaled their power via impressive buildings, such as temples, cathedrals, and pyramids.   Today, cities and corporations often similarly signal via big skyscrapers, bridges, and ships.  But for nations, the fraction of  wealth spent on a single showy construction has dramatically decreased.  Space programs serve a similar function, but don’t leave such huge monuments to admire.

A new Acta Astronautica article suggests this trend may reverse.  New Scientist reports:

A giant inflatable tower could carry people to the edge of space without the need for a rocket, and could be completed much sooner than a cable-based space elevator, its proponents claim. … The team envisages assembling the structure from a series of modules constructed from Kevlar-polyethylene composite tubes made rigid by inflating them with a lightweight gas such as helium.

To test the idea, they built a 7-metre scale model made up of six modules.  … The team [also mathematically] modelled a 15-kilometre tower made up of 100 modules, each one 150 metres tall and 230 metres in diameter, built from inflatable tubes 2 metres across. Quine estimates it would weigh about 800,000 tonnes when pressurised – around twice the weight of the world’s largest supertanker. “Twenty kilometres up is about as dark as outer space. You can see about 600 kilometres in any direction.”

The analysis in the tech paper is solid, if preliminary.  This seems doable now. (Quotes from the paper are below.) My immediate reaction was tech lust and pride: “COOL!”  Once upon a time I would have celebrated the social value of such innovations, but now I understand that while innovation in general should be praised, we probably waste too much on showy but not especially useful monuments like this.

Yes, it could be used for tourism, to reduce the cost of spaceflight, and for geoengineering, but those probably won’t cover its costs.  I’m proud my culture seems able to do such a thing, but I’ll admit my gain may come at the expense of others who look worse by comparison.  Those quotes from the paper:

We propose an alternative device to provide access to the near space and space environments that utilizes a self-supporting core structure. The structure provides a fixed link between ground and near space locations enabling the transportation of equipment, personnel and other objects or people to platforms or pods above the surface of the Earth for the purpose of scientific research, communications and tourism. The device may be assembled from the surface upwards, avoiding difficult and expensive in-orbit construction. The space-elevator tower can provide access to lower altitude regions and can also be scaled to access altitudes above 15 km, or the typical ceiling altitude for commercial aviation. The approach may be further scaled to provide direct access to altitudes above 200 km and with the gravitation potential of Low Earth Orbit without the technical challenges associated with constructing a cable at least 35,000 km long. The elevator platforms also have significant advantages over orbiting satellite platforms. Geographically fixed but providing access to regions of space closer to the surface than geostationary orbit, elevator platforms provide the ideal means to communicate over a wide area and to conduct remote sensing and tourism activities. As a tourist destination, the elevator platforms provide stations located at fixed attitudes from the surface for observation. The elevator platforms provide the means to access safely a region of space with a view extending hundreds of kilometers. …

Consider an example core-structure design for an Earth-based elevator to access near space at 20 km altitude. Advantageously, to access orbit, the elevator could be constructed at 5 km altitude in one of four regions on the equator. The core would be required to span a further 15 km altitude. Based on Elevator B, a suitable structure comprises of gas cells with constant wall thickness 1.2 cm arranged in a torus of inner diameter 228 m and outer diameter 230 m. Fabricated from Boron, a 15 km elevator structure can be supported by 150 bar hydrogen gas. Approximating the structure as two concentric cylinders, the mass of the structure is 6.5×10^8kg, and the mass of the pressurization gas needed is 1.4×10^8kg. Other core designs may be analyzed by comparison with the two-cylinder design and by appropriate adjustment for the amount of wall material utilized.

Constructed at 5 km altitude, the structure would have a buoyant mass of 3.1×10^6kg giving a total mass of 7.8×10^8kg. The load capacity of the structure, in excess of that needed to support itself, is 3.1×10^8kg of force equivalent. The critical buckling load at the top is 4.1×10^9N, and at the center of gravity (located at 7.3 km up the core) the critical load is 1.6×10^9N, which exceeds significantly the dead weight load of the building, including the mass of the gas, indicating that the core would be structurally stable and able to support the raising of payloads of mass in excess of 10^6 kg. By further tapering the wall thickness, further design margin may be obtained by lowering the center of gravity and reducing the structural mass, or taller structures may be constructed. Alternatively, the core diameters can be tapered to increase the structural stiffness in the base, although the variation of core diameter may be undesirable for mounting elevator machinery. Additionally, the core can be segmented and pressurized equivalently without inducing an imbalance of support forces between segment walls. …

Consider a highly simplified scenario where a single stage-to-orbit rocket is launched to a typical circular orbital height of 120 km. … Comparing initial to final rocket-mass ratios, the elevator launch at 20 km is shown to be 26% more efficient than the equivalent ground launch.

Added 13June: If you search for “Space Tower” you’ll see Alexander Bolonkin has published over a half dozen times (eg 1 2 3) on inflatable space towers since 2002.  But the Acta Astronautica article doesn’t cite him at all.  Suspicious.

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