Early in the book: The first few years will enable 20ton payloads without humans [radiation tolerance an issue for the two week trip]... From Finding

Early in the book: The first few years will enable 20ton payloads without humans [radiation tolerance an issue for the two week trip]... From Finding 7-5: Radiation is not a problem for tether climbers, as the designers will incorporate this threat into the design requirements and ensure operational success through any radiation environment. Historic precedence supports this conclusion as the space community runs spacecraft in all regions where the space elevator will be operating. However, when people are included in the tether climb [after some years of robotic success], the radiation problem becomes an order of magnitude more difficult. There are many ways to reduce the radiation and shorten the trip, which will have to be incorporated when the human element is added. Although the authors envision eventually using the elevator for transporting humans, I don't see any discussion about how to speed up the trip or increase the shielding. There is a fairly long section on debris. The authors note that significant debris only exists in low earth orbit. They think the chance of collision is small, but large enough that the situation needs to be monitored. They think debris can be tracked and that if a collision were forecast, the cable could be moved. Also, they think space faring nations should be tasked with removing some of their junk from orbit.