Transcript The Space Elevator

The Space Elevator
Thomas Rand-Nash
University of California, Berkeley
Physics 138
Summary
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The History
Why Do It?
How Could it be Done?
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The Ribbon
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Carbon Nanotubes, A Summary
Anchors
Climbers
Power
Some Problems and Proposed Solutions
The Future
The History
1960: Artsutanov, a Russian scientist first
suggests the concept in a technical journal
1966-1975: Isaacs and Pearson calculate specifics
of what would be required
1979: Authur Clarke, in Fountains of Paradise
describes a long filament lowered from
geosynchronous orbit, and used to hoist
objects from the surface
1999: Nasa holds first workshop on space
elevators
2001: Bradley Edwards receives NAIC funding
for Phase I space elevator mock-up
Why Build It?
Current:
$$$: Space Shuttle Missions
cost an average of
$500,000,000 or
$7,440/lb.
Elevator:
The projected 10 yr cost of
the elevator is $40B
(est. 500 missions)
Future “missions” require no
propellant, the major
cost of rocket missions
Current:
Riding on a continuous and
giant explosion is
extraordinarily
dangerous, as is re-entry
(Challenger, Columbia).
Elevator:
No human risk, missions are
unmanned.
How Could It Be Done?
The Components
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The Ribbon
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The Anchors
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The Climbers
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The Power
The Ribbon: Design
The Ribbon: Construction
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Initial production
takes place on earth
Aligned nanotubes
are epoxyed into
sheets, which are
then combined
(reinforced)
Climbers have a
similar system onboard to build tether
Why Carbon Nanotubes?
1)
2)
3)
Nanotubes: The Basics
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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The Chiral Vector R = na1 + ma2,
(where a1 , a2 are the primitive
lattice vectors and n,m are
integers) with wrapping angle 
connects atoms at A and B. The
length of R is the circumference of
the nanotube, and is created as A
is rolled into B. The direction of
the resulting tube axis vector will
be perpendicular to R.
Possible structures of nanotubes
can be formed corresponding to
wrapping angles 0≤≤30, (n,m)
m≤n.
Chirality
The values of n and
m determine the
chirality, or "twist" of
the nanotube. The
chirality in turn affects
the conductance of
the nanotube, it's
density, lattice
structure and
therefore, mechanical
properties.
Strain
a) “Transverse” strain finds
a natural release in a
bond rotation of 90° for
the armchair tube,
thereby elongating the
tube and releasing
excess strain energy.
Defect is formed, which
leads to non-elastic
behavior
b) “Longitudinal” strain
induces a 60° rotation in
the zig-zag tube. Less
tube elongation
therefore more resistant
to defect formation
Inelastic behavior
Quic kTime™ and a
TIFF ( Unc ompres s ed) dec ompr es s or
are needed to s ee this pic ture.
Measuring Tensile Strength
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CNT’s are connected
to the SEM tip via
either “nano-welding”
or Van der Waal
bonding
Individual CNT’s are
stretched until
breakage, or
deformed to
determine elasticity
Tensile Strength/Young’s Modulus
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Values for Y were
obtained by linear-fit
to the stress/strain
data points
Y ranged from
320-1470TPa
Strength values range
from 13-52GPa (vs.
63GPa needed for
elevator)
Elasticity
Qui ckTime™ and a
Motion JPEG B decompressor
are needed to see this pictur e.
Qui ckTime™ and a
Motion JPEG B decompressor
are needed to see this pictur e.
Deformation
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Tubes undergo abrupt shape shift under stress, emitting
phonons, or crunching. These correspond to
singularities in the stress/strain curves
Tubes bounce back from stress to reform original shape
Hole Propagation
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Tiny imperfections in
ordinary materials amplify
stress locally.
As load is applied, these
amplifiers pull and break
apart the adjacent
chemical bonds
In nanotubes, the
coupling between tubes is
very weak (VdW).
Therefore, a break in one
tube doesn’t affect
surrounding tube, and
hole propagation ends
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
The Anchors
a)
b)
The space anchor will consist of the spent launch
vehicle
b) The Earth anchor will consist of a mobile sea platform
1500 miles from the Galapagos islands
a)
The Climbers
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Initial ~200 climbers used to build nano-ribbon
Later used as launch vehicles for payloads from 20,0001,000,000 kg, at velocities up to 200km/hr
Climbers powered by electron laser & photovoltaic cells,
with power requirements of 1.4-120MW
The Power
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Free-electron lasers used
to deliver power
Adaptive Optics on
Hobby-Eberly telescope
used to focus Earthbased beams, (25cm spot
@ 1,000km altitude)
Reduced power delivered
at high altitudes
compensated by reduced
gravitational force on
climber, (~0.1g)
Major Hurdles
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Ribbon Construction
Atmospheric:
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Orbital:
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Lightning
High Winds
Atomic Oxygen
Meteors
Low orbit object
Ribbon Breakage
Sufficient Ribbons
Problems:
Nanotubes must be defect
free and straight
The epoxy must be strong
yet flexible, burn up at a
several hundred Kelvin,
and cure relatively quickly
The length of the finished
cable is 91,000km, and
nanotubes are cm in
length
Large scale behavior of
nanotubes unknown
Solutions:
Nanotubes are grown
aligned, and defects
can be controlled in
current production
methods, (spark gap)
The ribbon can be
produced in small
length bundles and
then connected
Atmospheric Oxygen 60100km
Threat:
Extremely corrosive, will
etch ribbon epoxy and
possibly nanotubes
Solution:
Coat ribbon with Gold or
Aluminum which have
resisted etching in these
atmospheric conditions,
(NASA’s Long Duration
Exposure Facility)
Low Orbit Objects 5001700km
Threat:
108,000 (>1cm) objects with
enough velocity to sever
or critically damage
tether. Strikes could occur
~every 14 hours
Solution:
Tracking systems for objects
>10cm already in place,
sea platform will move
tether to avoid
Tracking systems for 110cm objects coming online
Meteors
Threat:
Pretty obvious
Solution:
Va der Waal forces between
nanotubes limit the
damaged area
Low meteor flux, & small
probability of large
(>1cm) impacts
Climbers will be capable of
repairing ribbon
continuously
Lightning
Threat:
Ribbon has lower resistivity
than surrounding air,
lighting will prefer this
path.
Solutions:
Platform lies in a region of
very low lightning
activity
Platform is mobile, and can
move tether out of the
way of incoming storms
High Winds
Threat:
32m/s wind velocity will
induce enough drag to
destroy tether
Solution:
Winds at platform location
consistently below critical
velocity
Width of tether will be
adjusted to minimize wind
loading
The Future
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As of 2004, carbon nanotubes are more
expensive than gold. Future supply increase will
lower this price
Technology to “spin” Van der Waal bonded
nano-yarn has begun.
Edwards completed Phase II planning in 2004,
with funding from NASA’s institute for advanced
concepts
However, many properties of nanotubes still
remain to be tested, frictional, collisional, etc.
Third Space Elevator Conference is held to
discuss advances on the concept
Fully operational elevator could be built within 15
years.
Some Parting Words..
David Smitherman of NASA/Marshall's Advanced
Projects Office has compiled plans for such an elevator
that could turn science fiction into reality. His publication,
"Space Elevators: An Advanced Earth-Space
Infrastructure for the New Millennium", is based on
findings from a space infrastructure conference held at
the Marshall Space Flight Center last year. The
workshop included scientists and engineers from
government and industry representing various fields
such as structures, space tethers, materials, and
Earth/space environments."This is no longer science
fiction," said Smitherman. "We came out of the workshop
saying, 'We may very well be able to do this.'"