Similarly, according to this
document for launching appliances and embarkation ladders on modern ocean going ships will have a factor of safety of 4.5 on davits and winch structural members, and 6 on "falls, suspension chains, links and blocks". As such, a facrtor of safety of 1.4 would potentially be very low for something like a space elevator tether which could potentially cause a large amount of dmae if it were to break somewehere along its length aloowing its lower part to fall to the ground.
Yes, the failure mode of an elevator is ugly. It's probably going to need shearing charges built in at 100km and in a lot of places between there and the surface as well.
Thing to remember about safety factors is the relative masses involved. On the davits etc, the mass of the cables is a small fraction of the mass the cables are supporting, so you need a pretty huge safety factor to account for the large mass getting accelerated.
On an orbital elevator, however, that's inverted. How much does 36,000km of tether mass? What % of the tether mass is one of those trains? I'd be surprised if the trains and cargo exceed 1% of the tether mass. Crud, I'd be surprised if the trains exceeded 0.01% of tether mass!
As a side note, I've read a long time ago that the max speed of a train going up the beanstalk is only 200-300kph
even in vacuum due to vibrational limits, so there's not much
additional load inflicted by the trains accelerating and decelerating. Remember, we're talking probably 2000 tons of train going up and coming down, times 5 trains on the beanstalk
each direction, and having at least 4 tracks going all the way up. Why 5 trains each direction? So that one train leaves each day. What's in the train going up? People, food, water, parts for whatever spacecraft are getting assembled up top, probably some air. What's in the train going down? People, refined metals from asteroids, trash, and possibly organic waste (sewage) to use for fertilizer. You'd generally try to keep the upload and download roughly equal in mass, but it's not
absolutely necessary. Makes powering the trains easier, though.
So despite having 10,000 tons of trains going up the beanstalk and another 10,000 tons going down, the 4 sets of tracks alone are going to weigh in the neighborhood of 20
million tons (70kg/m). Not the tethers. The tracks the trains use. The tethers will need to support that much weight.
