Boom wants to start now. The Denver-based company’s goal is a 40-seat plane, flying at Mach 2.2, mostly at an altitude of 60,000 feet (comparable to the Concorde), with a round-trip ticket from London to New York costing $5,000, and the flight lasting only 204 minutes. Tokyo to San Francisco? Just $6,500, and less than 5 hours. Los Angeles to Sydney? $7,000, for a six-hour flight.