Could someone provide a graph of speed vs mass of a typical spacecraft - say, Soyuz or Dragon, as it rises towards LEO? If not graph, then a single fixed point of mass at speed of 2 km/s will do.
A segment of this train might be used to propel vehicles to about 2 km/s. A branch in the track to separate "communal transport" from a NASA launch facility, a section with a fast-acting airlock, the vehicle exits the vacuum tube at a friendly angle upwards, engages rocket engines, crosses the atmosphere and enters the orbit. We gain 2 km/s at initial stage very cheaply, but we are limited by the dimensions and tolerances (like curve angles) of the communal part used primarily for plain human transport. This limits the amount of fuel we can fit in the launch vehicle, and as result puts a total cap on how much we can get to the orbit (if anything at all).
Additionally, would this mode of launch be viable at all?