between 2 to 3 miles - this is diggable using modern mining techniques. It should also provide a permanent way for astronauts and space vehicles to enter outer space. A lot easier than firing rockets.
Under the Laws of Thermodynamics and GR, that's quite incredible. The FE would have to be unimaginably thick to prevent our feet from melting from the heat of the UA. Of course, we'll now hear special pleading that TD and GR don't apply to the FE and the UA for some convenient reasons.
Even conservative estimates of the energy needed for the UA to accelerate the FE for the next minute is much more than 10
1000 joules! Try standing just three miles over that for a while.