Hi Sawyer

We have discussed SEs but not in any great detail. There are dedicated Yahoo groups that discuss SE issues in detail and I don't think anyone here feels the issues are within their competence to talk about at length.

In summary the main issues, as garnered from Yahoo's Space Elevator Group, are...

(1) Cable strength - which isn't quite as fair away as you might think. There are a lot of terrestrial applications that will drive R&D forward. Another under-appreciated fact is that a Kevlar SE is feasible right now on the Moon. Jerome Pearson, one of the SE's discoverers, has discussed a Lunar SE in depth and is well worth reading.

(2) Elevator power - a big problem is that no current energy source can power an SE car all the way to GEO. No energy storage or power system has a low enough power-to-mass ratio that can run a car at the desired speeds. Conceivably a nuclear reactor driven car could do it, but it has a lot of problems. SO what is to be done? Current plans are for a power-beaming system using Free Electron Lasers to illuminated a specially designed solar panel on the car. This has a lot of problems, but none are showstoppers yet. Leaps forward in nuclear or solar technology could change the issue overnight. Personally I think inflatable solar concentrators would be superlative in performance above the atmosphere, but they do restrict an SE to daytime departures.

(3) Radiation Belts - a manned SE is even more difficult than a cargo system because the SE takes hours to traverse the high density regions of the Earth's radiation Belts. Shielding is possible, but imposes a huge mass penalty - preferably the shield should be as light as possible. Novel hydrogen-rich plastics might be the right solution but it needs research.

(4) Catastrophe avoidance - SEs represent a huge potential energy and if they were heavy their fall from near-orbit could be devastating. Brad Edwards has mitigated this issue by making the SE a thin, light ribbon which would deccelerate in Earth's atmosphere - if it fell. Since current SE designs are tension balanced the remaining portion above a break would lift into a higher orbit. Another problem is that massive failing SEs could wipe out any neighbouring SEs almost unavoidably. Defending SEs from failing kin is a major issue and yet to be resolved decisively. A lone SE would be worse than useless since it wouldn't deliver the economy promised and would be a space hazard.

The SE has a lot of promise. Partial SEs, rotating tethers and the like could go a long way towards providing access to space from Earth, but on smaller worlds like the Moon, Mars and the moons of the Jovians the full SE is achieveable with today's materials. It would provide economical surface/space access to dozens of worlds.

Adam