A space bridge (space elevator) is a tether anchored on the equator, held taut by a counterweight beyond geostationary orbit whose outward centrifugal pull balances Earth's gravity on the cable. A climber rides the cable using motors, not rockets.
T(r) ≈ T_base + m_payload·g(r) − m_payload·ω²r
T_base ∝ M_counterweight·ω²·r_cw − ∫ λ(r) g(r) dr
margin = (T_limit − T(r)) / T_limit
- Climber speed — how fast the payload crawls up the tether toward the geostationary anchor.
- Counterweight mass — bigger mass beyond GEO increases outward centrifugal tension, keeping the cable taut.
- Cable strength limit — the maximum tension the tether material can bear before the safety margin turns negative (failure).
- Payload mass — heavier climbers add more local tension as they ascend through the gravity well.
Real-world application: this is the physics behind proposed space elevator concepts (carbon-nanotube or diamond-nanothread tethers) that could replace rockets for lifting cargo to geostationary orbit at a fraction of the energy cost.