Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

Original Article ↗ Hacker News Discussion ↗

Feasibility & Materials

  • Many see the concept as “neat but not possible” with current materials; especially a 200 km superconducting loop is viewed as far beyond today’s engineering.
  • Critical gaps: long, defect‑free carbon nanotube (CNT) fibers; high‑temperature superconductors with high current density; structural materials that can survive radiation, micrometeorites, and thermal extremes over decades.
  • Some think advances in superconducting tapes and nanomaterials since 2001 help, but nowhere near what a full system would need.

Cooling and Superconductors

  • Maintaining liquid‑helium temperatures along 200 km is seen as a major challenge.
  • Shading isn’t enough: Earth and Sun fill almost the entire sky, so passive deep‑cryogenic cooling is considered impossible.
  • Discussion of NbTi (sub‑10 K, ~10 T), iron‑pnictide / FeSe‑class high‑Tc materials, and possibly using liquid nitrogen instead of hydrogen; consensus: promising lab tech, not yet scalable to elevator size.

Orbital Mechanics and the 200 km Limit

  • This design tops out at 200 km and has no gravitational counterweight, so it does not by itself provide orbital velocity.
  • Climbing it only adds a few m/s of tangential speed—orders of magnitude too little; payloads still need rockets or electromagnetic acceleration at the top.
  • Some confusion over whether Earth’s rotation via magnetic coupling could supply more momentum; others point to the paper itself, which explicitly requires extra propulsion.

Electrical and Magnetic Effects on Tethers

  • Past tether missions (e.g., TSS‑1R) saw currents far above predictions and electrical discharges that broke the tether.
  • Participants expect a real elevator to be a giant conductor/static accumulator, making grounding, charge management, and electrical robustness nontrivial.

Failure Modes and Safety

  • Debate over how dangerous a broken tether is:
    • One side: huge velocities, whip‑like behavior, catastrophic impacts, popular fiction scenarios.
    • Other side: ultra‑light, thin tether would have low terminal velocity, flutter down, and be more nuisance than extinction event.
    • Payloads could be designed for safe reentry or water impact, and segmented “explosive” disconnection is proposed.

Economics and Use Cases

  • Strong skepticism that a trillion‑plus‑dollar structure would beat rockets or mass drivers economically, even if technically possible.
  • Others argue asteroid or lunar mining, plus avoiding terrestrial mining externalities, could justify the cost, though commodity price collapse is a concern.
  • A counterpoint: if such materials existed cheaply, terrestrial megaprojects would likely consume them before a space elevator.

Alternative Launch Concepts

  • Multiple competing or complementary ideas discussed:
    • Launch loop and space fountain (dynamic momentum support instead of static magnetic levitation).
    • Mass drivers / railguns, especially at high altitude to reduce drag; 8 km/s railguns are considered theoretically scalable but harsh on payloads.
    • Light‑gas guns for small payloads.
    • Skyhook concepts that can work with current materials, relying on orbital tethers.
    • Laser launch, large balloons plus railguns, and conventional hydrogen‑oxygen rockets, with reminders that orbital energy is mostly in speed, not height.

Carbon Nanotubes and Intermediate Markets

  • CNTs are highlighted as crucial but limited to roughly “foot‑length” continuous fibers today.
  • Question raised: what mid‑scale markets could monetize progress toward longer CNTs?
  • Suggestions: any use needing very strong “medium‑length” cables or everyday materials that benefit incrementally as practical lengths increase.

Historical and Conceptual Context

  • This proposal is linked to earlier work on magnetically confined kinetic energy storage rings (MCKESR), where magnetic forces, not material strength, provide centripetal force.
  • Alternating‑gradient magnetic stabilization is mentioned as a conceptual precursor, borrowed from particle accelerators.
  • Some see mass drivers and related concepts as more physics‑ and economics‑favored than full elevators, particularly given progress in superconducting tapes and hyperloop‑like tech.