|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
|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
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.