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Space Elevator based on flaw tolerant mega cable may be possible! – Results from the 2nd International Conference on Space Elevator and Carbon Nanotube Tether Design in Luxembourg
 
Luxembourg, Dec 14, 2008. The European Spaceward Association (short: EuroSpaceward) has just held its 2nd International Conference on Space Elevator and Carbon Nanotube (CNT) Tether Design. Bringing together world renowned experts on the space elevator system and on CNT fibre research this event again has turned out as being a pace maker in Europe on cross-fertilization between extreme space engineering, nanotechnology and power beaming.
Scientists, engineers, entrepreneurs as well as representatives from space agencies and industry from the USA, Canada, Japan and Europe presented and discussed the latest achievements on their research work and possible implications for related business projects.
The conference started with an introduction by Markus Klettner on the environmental necessity to open up the ostensibly perceived closed ecologic and economic system on Earth by a large scale expansion of mankind into outer space in order to guarantee a long term survival of our species. In this context Prof. Charles Cockell from the Open University in Milton Keynes and author of the book Space on Earth – Saving Our World by Seeking Others’ spoke about the need to unite environmentalists and space explorers. In his words ‘environmentalists are highly ambitious space explorers who have chosen to look after the life support systems of the Earth’. Solar power satellites, HE3 mining of the moon and favourable sinks in space like the sun that easily convert toxic and nuclear waste in energy are a potential green perspective of a society able to bridge the gravity well by space elevator or other low cost, environmental friendly and safe space transportation means, for instance the envisioned Japanese Space Train.
 
 
Prof. Cockell sees the advantages and the potential danger when limitless resources in form of energy and raw materials are made available to inhabitants of the Earth: all acquire a high standard of living and consumption tails off. Industries are moved into space, with the Earth becoming an oasis, forever freed of industrial pollution hazardous to its biosphere. However a possible threat that will have to be mastered: once consumption expands to fit the unlimited available resources the high rate of consumption and waste built up may cause a new environmental crisis if there is little incentive to remove waste products from space resources back into space!

According to Andreas Hein, Technical University of Munich as well founder and former project manager of the WARR (Scientific Workgroup for Rocketry and Astronautics) Space Elevator Team, the characteristics of the space elevator may result in a cost reduction of more than 60% for space travels. In addition, significant lower insurance fees, higher reliability and in-time services could be advantages as well. Andreas Hein is sceptical about fostering mining of near Earth resources by space elevator. However, he envisions its potential capabilities and benefits for nuclear waste disposal and triggering LEO space tourism.

Dr. Brad Edwards, President of EuroSpaceward, emphasized in his talk on the state-of-the-art of Space Elevator research that the advance in the past 10 years has been such that the current primary hurdles are financial and political. With these two hurdles addressed the technical work can be completed and the first space elevator can be built”. This may sound optimistic, since the CNT fibre production technology to fabricate a mega cable of 36.000 km or even 100.000 km at a minimum strength of 60 GPa is at the moment still missing as the conference clearly highlighted. However, Prof. Windle’s research team at the University of Cambridge seems to lead the way towards super strong tethers. As Cambridge researcher Dr. Marcelo Motta pointed out they are currently able to produce almost cm long individual macroscopic CNT threads with tensile strength of up to 9 N/tex which compares to about 9 GPa at the given density of their material. Scaling up the Cambridge laboratory process to industrial production and spinning these threads, ropes and cables with 10 GPa should be soon feasible. As a possible next step Dr. Motta announced the likely participation of the Cambridge team in the coming Strong Tether Challenge hosted by NASA/Spaceward in 2009, as explained by Dr. Bryan Laubscher of Odysseus Technologies.

 
 
The long awaited presentation by Prof. Nicola Pugno from Politecnico di Torino, Italy, on the role of defects in the design of a space elevator cable brought clarifications on the thermo dynamical limits of designing such a super strong mega cable. According to Prof. Pugno, even applying healing processes fabricated pure CNT cables will never be without defects. Based on quantized fracture mechanics already an exceptional small defect like a single nano pin hole caused by a missing carbon atom in the hexagonal molecule of a CNT results in a strength reduction of about 20% from the theoretical value for the single nanotube! Extrapolating this to the mega cable of the space elevator, where larger nano holes and nano cracks are unavoidable the actually achievable strength is about one third of the theoretical strength. Assuming a theoretical strength of 100 GPa for a mega tether this means an actual value of 30 GPa with an upper thermo dynamical limit at 45 GPa. Following Prof. Pugno’s proposal efforts should focus on designing a system with a flaw tolerant mega cable of 10 GPa which should be practical on the multi scale. Implications for the design of the space elevator system are an increased taper ratio and mass of the tether, reducing payload capacity.

A further possible constraint was depicted in the highly interesting lecture of Prof Vesselin Shanov’s from University of Cincinnati’s NanoWorld. He showed that pure CNT arrays unexpectedly stopped their growth in his Smart Materials Laboratory at approx 2 cm length; a fact which is inexplicable at the moment and that may show up limits in growing individual nanotubes to any length. However, according to Prof. Shanov hopes are there that this may be overcome.

 
 
Prof. Cécile Zakri described the production of CNT fibers and the mechanical properties achieved at her Centre de Recherche Paul Pascal in Bordeaux France. By spinning coagulated fibres upon injection of a CNT dispersion in the co-flowing stream of a PVA polymer solution

Prof. Zakri and her team yield continuous PVA-CNT fibres with a persistent high toughness expressed in a Young’s modulus of 120GPa as well as high electrical conductivity. Potential applications are already now: shape memory material, actuators and electrodes. Dr. Jerôme Guillot and Dr. Patrick Choquet from the Public Research Center Gabriel Lippmann in Luxembourg added a further interesting commercial application of CNT’s in the presentation of their research work: toxic gas sensing with hand held miniature devices.

Åge Riise from the European Space Agency’s ESOC, who’s been among the responsible of the 31 km long YES2 tether experiment flown in LEO space in September 2007 (see http://www.esa.int/SPECIALS/YES/index.html), presented the world’s first longitudinal wave climber LWC . Just by using a sanding machine, a 1.5m broomstick, simulating a tether, and 3 brushes attached to it by a clamp forming the vibration decoupled climber mock-up he demonstrated to the flabbergasted audience how an elevator car could ride to outer space on the high-speed longitudinal wave of an accordingly oscillated tether! (see excerpt of video clip below, showing the LWC in action; for a full coverage of the presentation please go to the download section) Download excerpt video clip
Current concepts however still favour energy supply by laser or microwave power beaming. Benoit Michel from Université Catholique de Louvain, Belgium, compared these two basic methods. His conclusion: space elevators will need to be powered by ground based visible light lasers combined with adaptive optics. Existing technologies seem to be mature enough to become usable for space elevator power beaming within 10 years.

Dr. Pierre Rochus, Deputy General Manager of Space Center Liège, covered the possible space applications of CNT and possible space qualification tests to be performed on Space Elevator climbers at his test facility in Belgium that is also used by the European Space Agency for satellite testing.

The space elevator is ideal for transporting equipment and material to space that is oversized, bulky or sensitive to vibrations typical for rockets. Its fitness to be used also for manned travel to space was examined at the conference by Dr. Brad Edwards, father of the modern space elevator concept. Dr. Edwards analysed the different scenarios, opportunities and limits of using the space elevator for transporting humans into space. He proposes that humans can safely use the space elevator when intrinsic, passive and/or active shielding against cosmic radiation are implemented when passing through the Van Allen radiation belts of the Earth. Intrinsic shielding is the self-shielding of the payload by itself and the climber mass. Active shielding involves producing a magnetic dipole around the climber to deflect the radiation. By applying these means a reduction of radiation exposure to tolerable values should be possible.

 
 
In a special artistic performance Lucia Prandi, from Modena Italy, interpreted how a conceptual artist perceives such a mega project. Recorded sounds of satellites tested in laboratories fired the imagination of participants.

The award ceremony on EuroSpaceward’s 1st children drawing contest on “imagine travelling by space elevator” carried out with the collaboration of the International St-George-School in Luxembourg and organized by Montse Ugalde highlighted one facet of EuroSpaceward’s mission: namely to create conscience in schools about the aspects of a possible future life concentrated in space and the usage of renewable solar energy from space in order to achieve a sustainable ecology, economy and biosphere on our planet Earth.

In the final outlook session of the conference Dir. Akira Tsuchida, JAXA Flight Director at Tsukuba Space Center of the Japanese experiment module Kibo of the International Space Station and Member of the Board of the Japan Space Elevator Association, set out the Japanese engagement in the space elevator endeavour. Though NASA, ESA and JAXA have currently still no roadmaps that include the space elevator the Japanese Ministry of Economy Trade and Industry (METI) has already realized the potential strategic value of this revolutionary space transportation system. In its long-term plan METI includes the space elevator and foresees CNT textiles with stretching strength of 10 GPa by 2018 and 100 GPa by 2026 that may serve as a space elevator ribbon. Remains the question how they think to be able to overcome the thermo dynamical limits postulated by Prof. Pugno for the mega cable?

John Winter and Dr. Edwards of EuroSpaceward closed the conference with an optimistic outlook on the dedication of the next US Administration under President Barack Obama toward a well funded space program that envisions a future in space in order to help solving our inherent burning problems on Earth, like the irreparable destruction of natural habitats, the depletion of valuable raw materials, the ever increasing need for energy, or the potential devastating climatic changes induced by a polluting world economy.

 
 

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