Cabin position
What the cabin experiences
Net gravity (gravity minus the centrifugal effect of Earth's spin). It crosses zero at geostationary altitude; beyond it, things are flung outward.
Tether design
Uniform-stress tether results
Cross-section grows from the anchor to its maximum at GEO, then shrinks toward the counterweight. The taper depends only on specific strength (strength ÷ density).
Climb profile
Energy, power & time
Mechanical power needed at constant speed. It is highest at the base and falls to zero at GEO; above GEO the climber must brake, and that energy can be recovered.
Debris impact resilience
Impact risk
The flux default is illustrative only. For real design work, take the flux for the relevant debris size and altitude band from ESA MASTER or NASA ORDEM. The model assumes each impact severs at most one strand (strands spaced wider than the debris) and that damage arrives randomly (Poisson).
Corrosion: atomic oxygen erosion
Oxide coatings (e.g. SiO₂, Al₂O₃) can cut polymer erosion by orders of magnitude if they stay crack-free.
Surface loss
Atomic oxygen matters mainly from ~200 to ~700 km, and fluence swings widely with the solar cycle. Uses the design life set above.
Communication backup system
Example paths: fibre embedded in the tether, free-space laser link, RF (S/X-band), satellite relay, and a low-rate emergency beacon.
Link availability
Getting it up there: seed ribbon and bootstrap
Nobody launches the finished tether. A thin "seed" ribbon is launched to geostationary orbit, unreeled down to Earth and up to a counterweight at the same time, then thickened by climbers that each lay a new strip alongside.
- LaunchSeed ribbon, reel and deployer go up in pieces and are assembled at GEO.
- UnreelRibbon pays out down and up together, so the centre of mass stays at GEO.
- AnchorThe lower end is caught and fixed to an ocean platform at the equator.
- ThickenClimbers ride up laying fresh ribbon, then stay at the top as counterweight.
Material
Seed ribbon
Launch
Thickening
Seed, launches & build-up
Tether capacity after each climber trip (log scale). Each trip adds ribbon in proportion to what the tether can already carry, so growth is exponential: early trips add grams of capacity, late trips add tonnes.
Material comparison at this safety factor and seed load
Model & assumptions
Constants
Simplifications
- Spherical, point-mass Earth; no oblateness (J2), Moon or Sun perturbations.
- Rotating-frame potential: Φ(r) = −GM/r − ½ω²r². Energies and taper come from differences in Φ.
- Tether is an ideal uniform-stress design: A(r) = A₀·exp[(Φ(r) − Φ(R))·ρ/σallow].
- Coriolis forces during climbing, tether oscillation, and wind loads are not modelled.
- Release outcomes assume the payload leaves with the tether's local speed ωr, purely horizontal.
- Deployment follows the seed-ribbon approach (Edwards, 2000s): seed mass and counterweight scale linearly with the first climber's load. Deployer overhead is applied to the ribbon only. Each climber's total mass equals the tether's current capacity; its ribbon share adds capacity and its body stays at the top as counterweight. Unreeling dynamics, orbital assembly and anchoring are not modelled.
Reality checks
- A practical tether needs a specific strength of roughly 20+ MYuri (taper under ~10). Only nanotube and graphene materials at near-theoretical strength reach this, and they have not yet been made at kilometre lengths.
- Spider silk is extraordinarily tough, but its specific strength (~1 MYuri) is far too low to carry load here. In a hybrid design it is best treated as a sensing, optical or cladding layer, not the structural core.
- Quantum entanglement cannot carry signals faster than light. Quantum links add security (key distribution), not speed; the GEO round trip is always at least ~0.24 s by any route.
- Energy figures cover lifting only. They exclude the capital cost of the tether, climbers and power-beaming systems.
Educational physics model — not an engineering certification.