Materials
Unlike earth-anchored space elevators, the materials for lunar space elevators won’t require a lot of strength. Lunar elevators can be made with materials available today. Carbon nanotubes aren’t required to build the structure. This would make it possible to build the elevator much sooner, since available carbon nanotube materials in sufficient quantities are still years away.
One material that has great potential is M5 fiber. This is a synthetic fiber that is lighter than Kevlar or Spectra. According to Pearson, Levin, Oldson, and Wykes in their article The Lunar Space Elevator, an M5 ribbon 30 mm wide and 0.023 mm thick, would be able to support 2000 kg on the lunar surface (2005). It would also be able to hold 100 cargo vehicles, each with a mass of 580 kg, evenly spaced along the length of the elevator. Other materials that could be used are T1000G carbon fiber, Spectra 200, or Zylon. All of these materials have breaking lengths of several hundred kilometers under 1g.
| Material | Density ρ kg/m3 |
Stress Limit σ GPa |
Breaking height (h = σ/ρg, km) |
|---|---|---|---|
| Single-wall carbon nanotubes (laboratory measurements) | 2266 | 50 | 2200 |
| Toray Carbon fiber (T1000G) | 1810 | 6.4 | 361 |
| Aramid, Ltd. polybenzoxazole fiber (Zylon PBO) | 1560 | 5.8 | 379 |
| Honeywell extended chain polyethylene fiber (Spectra 2000) | 970 | 3.0 | 316 |
| Magellan honeycomb polymer M5 (with planned values) | 1700 | 5.7(9.5) | 342(570) |
| DuPont Aramid fiber (Kevlar 49) | 1440 | 3.6 | 255 |
| Glass fibre (Ref Specific strength) | 2600 | 3.4 | 133 |
The materials will be used to build the ribbons which will connect from the L1 or L2 balance points to the surface of the moon. The ribbons would be used by the robotic climbing vehicle to get from the surface into orbit. The vehicles would be slow, compared to chemical rockets, but it is a good speed for transferring cargo.
The ribbons are going to be prone to damage by micrometeoroids from space so one way to improve their survivability is to make a multi-ribbon system instead of one. They will have interconnections at regular intervals, so that if one section is damaged, the parallel sections would carry the load until robotic vehicles can come and replace the missing ribbon. The interconnections would be spaced about 100 km apart, which is small enough to allow a robotic climber to carry the mass of the replacement 100 km of ribbon.
Read more about this topic: Lunar Space Elevator
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