A) The technical attachment lists the lifespan as 5 to 7 years
B) It's a triple play of radically reduced launch costs, rapidly dropping space hardware costs thanks to growth in the market, and improving RF tech to greatly increase the bandwidth such a constellation can provide. Ubiquitous connectivity is a great example of a technology that's going to happen because of the high level industry trends. The interesting question is whether it will be a SpaceX constellation, OneWeb constellation, or an atmospheric solution like Google's Loon or Facebook's Aquila.
C) 4500 satellites is more than we currently have in LEO total. However, LEO is low enough that atmospheric drag deorbits idle satellites relatively quickly. SpaceX's constellation is designed to deorbit on its own after their 7 year life.
> It's a triple play of radically reduced launch costs
Which is a very recent phenomenon, and still not fully materializing – SpaceX' Falcon 9 already cut costs in half in its class without reusing anything. Actually reusable Falcon 9s and the planned competitor products will drive down costs further still.
Improvements in batteries and solar panels might be another aspect that might not be an advantage for SpaceX specifically (they're commodity devices that can be bought by anyone), but it might be part of the reason why it wasn't done sooner.
B) It's a triple play of radically reduced launch costs, rapidly dropping space hardware costs thanks to growth in the market, and improving RF tech to greatly increase the bandwidth such a constellation can provide. Ubiquitous connectivity is a great example of a technology that's going to happen because of the high level industry trends. The interesting question is whether it will be a SpaceX constellation, OneWeb constellation, or an atmospheric solution like Google's Loon or Facebook's Aquila.
C) 4500 satellites is more than we currently have in LEO total. However, LEO is low enough that atmospheric drag deorbits idle satellites relatively quickly. SpaceX's constellation is designed to deorbit on its own after their 7 year life.