There was a large thread about this yesterday, speculating about what it is:
https://news.ycombinator.com/item?id=5796880
I think a "launch loop" is consistent with all of Musk's statements (and nothing else is):
https://news.ycombinator.com/item?id=5796880
I think a "launch loop" is consistent with all of Musk's statements (and nothing else is):
+ "provides a relatively low 3g acceleration"
+ "for safety and astrodynamic reasons, launch loops are intended to be installed over an ocean near the equator, well away from habitation"
etc.
Some of the enormous advantages of HSR are the ease with which it can be seamlessly be integrated into urban infrastructure, its ability to directly serve city cores, the low trip overhead for passengers (30s from local subway train to HSR seat!, no advance reservations necessary), the ease with which it can serve multiple markets with a single trip (because the cost/overhead of an intermediate stop is quite low), and its high energy efficiency.
This make it quite different from air travel, and launch loops are more like extreme versions of air-travel in many ways (though without the flexible routing of airplanes, apparently).