A climber capsule ascends a tether anchored to Earth's surface, extending past geostationary orbit (~35,786 km altitude) where a counterweight keeps the cable taut via centrifugal force. Climbers grip the cable mechanically and would take roughly a week to reach GEO at speeds around 200 km/h. The core engineering barrier is tensile strength-to-weight ratio: the cable must withstand roughly 30-120 GPa of stress, far beyond steel or Kevlar, which is why carbon nanotubes or graphene are the usual proposed materials. Cable tension peaks near the GEO point, where the pull of gravity below balances the outward centrifugal force above.
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