The sub-scale prototype of a supersonic passenger jet that will eventually, succeed the iconic BAC Concorde is set for first flight in 2021. Leading the way towards the historic resurrection of trans-Atlantic supersonic air travel is an American startup, Boom Technology, Inc. founded in 2014 and based in Denver, Colorado.

The company said its "XB-1 Baby Boom," which is a one-third-scale supersonic demonstrator of the actual jet will be rolled out on October 7. Test flights of the XB-1 will demonstrate and prove key technologies such as advanced carbon fiber composite construction and computer-optimized high-efficiency aerodynamics.

"XB-1 is the first step in bringing supersonic travel back to the world," said Boom Technology founder and CEO Blake Scholl in a statement. "Flights at twice the speed mean we can travel twice as far -- bringing more people, places, and cultures into our lives."

Scholl described XB-1 as history's fastest privately developed aircraft. Results of the XB-1 test program will allow Boom Technology to fine-tune the design for full-size supersonic transport (SST) passenger plane.

Baby Boom flight tests will pave the way for the ultimate introduction of the "Boom Overture" supersonic passenger jet. Overture will be capable of speeds up to Mach 2.2 (2,300 km/h). It will have a range of 8,300 kilometers and will be capable of carrying anywhere from 55 to 75 passengers and crew.

Overture is set for introduction in 2025 or 2027. Passenger flights are expected to begin in 2030. Each SST is expected to cost $200 million.

Boom Technology plans to price its transatlantic roundtrips at around $5,000 a seat, which is about the price of an ordinary business class. It estimates fares for the Overture will be 75 percent lower than the Concorde

A supersonic flight from New York to London in a Boom Overture should take only three hours. This trip takes close to seven hours on an ordinary passenger jet.

"We've learned that the demand for supersonic has grown even faster than we anticipated," said Scholl. He also said Boom Technology is working to ensure the supersonic future is safe and environmentally and economically sustainable.

Boom Technology already has at least $6 billion worth of pre-orders for 76 Overtures. Buyers include Virgin Galactic and Japan Airlines Co Ltd.  The latter has pre-orders for 20 Overtures. It invested $10 million in Boom Technology in 2017.

In June 2017, Virgin Galactic, which was founded by Sir Richard Branson said it signed an option to buy 10 SSTs from Boom Technology for $2 billion. Virgin Galactic's spacecraft arm, The Spaceship Company, is assisting with the design and development of the prototype jetliner.

Concorde last flew in 2003. In its 27 years of service, it set transatlantic flight speed records that still stand. The legendary jetliner was laid low by a combination of factors, including expensive airfares and a downturn in the aviation industry following the terrorist attacks of September 11, 2001, in the United States.