The Space Elevator Thomas Rand-Nash University of California, Berkeley Physics 138

Summary  The History  Why Do It?  How Could it be Done?  The Ribbon  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 suggests the concept in a technical journal : Isaacs and Pearson calculate specifics of what would be required of what would be required 1979: Authur Clarke, in Fountains of Paradise describes a long filament lowered from describes a long filament lowered from geosynchronous orbit, and used to hoist geosynchronous orbit, and used to hoist objects from the surface objects from the surface 1999: Nasa holds first workshop on space elevators elevators 2001: Bradley Edwards receives NAIC funding for Phase I space elevator mock-up for Phase I space elevator mock-up

Why Build It? Current: 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? 1) 2) 3)

 The Chiral Vector R = na 1 + ma 2, (where a 1, a 2 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. Nanotubes: The Basics

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 TPa  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 a) 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) b)

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 MW

The Power  Free-electron lasers used to deliver power  Adaptive Optics on Hobby-Eberly telescope used to focus Earth- based beams, (25cm 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 km 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 km 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. 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.'" 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.'"