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
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.
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.