02-05-2011, 02:45 PM
Presented by:
Thomas Rand-Nash
[attachment=13249]
The Space Elevator
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
The Ribbon
The Anchors
The Climbers
The Power
The Ribbon: Design
The Ribbon: Construction
Initial production takes place on earth
Aligned nanotubes are epoxyed into sheets, which are then combined (reinforced)
Climbers have a similar system on-board to build tether
Why Carbon Nanotubes?
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
Measuring Tensile Strength
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
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
Deformation
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
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
The Anchors
The space anchor will consist of the spent launch vehicle
The Earth anchor will consist of a mobile sea platform 1500 miles from the Galapagos islands
The Climbers
Initial ~200 climbers used to build nano-ribbon
Later used as launch vehicles for payloads from 20,000- 1,000,000 kg, at velocities up to 200km/hr
Climbers powered by electron laser & photovoltaic cells, with power requirements of 1.4-120MW
The Power
Free-electron lasers used to deliver power
Adaptive Optics on Hobby-Eberly telescope used to focus Earth-based beams, (25cm spot @ 1,000km altitude)
Reduced power delivered at high altitudes compensated by reduced gravitational force on climber, (~0.1g)
Major Hurdles
Ribbon Construction
Atmospheric:
Lightning
High Winds
Atomic Oxygen
Orbital:
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 60-100km
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 500-1700km
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 1-10cm objects coming on-line
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
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.'"
Thomas Rand-Nash
[attachment=13249]
The Space Elevator
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
The Ribbon
The Anchors
The Climbers
The Power
The Ribbon: Design
The Ribbon: Construction
Initial production takes place on earth
Aligned nanotubes are epoxyed into sheets, which are then combined (reinforced)
Climbers have a similar system on-board to build tether
Why Carbon Nanotubes?
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
Measuring Tensile Strength
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
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
Deformation
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
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
The Anchors
The space anchor will consist of the spent launch vehicle
The Earth anchor will consist of a mobile sea platform 1500 miles from the Galapagos islands
The Climbers
Initial ~200 climbers used to build nano-ribbon
Later used as launch vehicles for payloads from 20,000- 1,000,000 kg, at velocities up to 200km/hr
Climbers powered by electron laser & photovoltaic cells, with power requirements of 1.4-120MW
The Power
Free-electron lasers used to deliver power
Adaptive Optics on Hobby-Eberly telescope used to focus Earth-based beams, (25cm spot @ 1,000km altitude)
Reduced power delivered at high altitudes compensated by reduced gravitational force on climber, (~0.1g)
Major Hurdles
Ribbon Construction
Atmospheric:
Lightning
High Winds
Atomic Oxygen
Orbital:
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 60-100km
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 500-1700km
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 1-10cm objects coming on-line
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
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.'"
