You don't need a full vaccum. Even half an atmosphere would greatly reduce air resistance and allow for 4x the velocity in 1 atm. Humans can survive (uncomfor

You don't need a full vaccum. Even half an atmosphere would greatly reduce air resistance and allow for 4x the velocity in 1 atm. Humans can survive (uncomfortably) at .5 atm and you eliminate the vacuum cannon problem simply by putting pressurization valves periodically throughout the tube.