1. Indian Institute of Technology Hyderabad THE SPACE ELEVATOR Aaditya Sapkal (ES12B1016)

2. The Components  The Ribbon  The Anchors  The Climbers  The Power

3. The Ribbon: Design

4. 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

5. Why Carbon Nanotubes? PropertySingle Walled Nanotubes Metal wires Tensile Strength45 billion pascalsHigh strength steel alloys break at about 2 billon pascal ResilienceCan be bent at large angles and restraightened without damage Metals and carbon fibers fracture at grain boundaries Temperature stability Stable upto 2800 degrees in vacuum, 750 degrees in air Metal wire in microchips melt at 600 to 1000 degrees C

6. 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

7. 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

8. 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)

9. Deployment

10. Major Hurdles  Ribbon Construction  Atmospheric: o Lightning o High Winds o Atomic Oxygen  Orbital: o Meteors o Low orbit object  Ribbon Breakage

11. Problems:Solutions: Sufficient Ribbons  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  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

12. Threat: Solution: Atmospheric Oxygen 60-100km  Extremely corrosive, will etch ribbon epoxy and possibly nanotubes  Coat ribbon with Gold or Aluminum which have resisted etching in these atmospheric conditions,(NASA’s Long Duration Exposure Facility

13. 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

14. 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

15. 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