Aerion Supersonic, which had plans to build silent business jets that would travel twice as fast as most commercial airplanes, is shutting down operations. First reported by Florida Today, Aerion, which had backing from Boeing, said it was unable to raise the money to build its AS2 supersonic jet.

“The AS2 supersonic business jet program meets all market, technical, regulatory and sustainability requirements and the market for a new supersonic segment of general aviation has been validated with $11.2 billion in sales backlog for the AS2,” the company said in an statement emailed to The Verge on Saturday.

“However, in the current financial environment, it has proven hugely challenging to close on the scheduled and necessary large new capital requirements to finalize the transition of the AS2 into production. Given these conditions the Aerion Corporation is now taking the appropriate steps in consideration of this ongoing financial environment.”

Aerion CEO Tom Vice said in January 2020 that the AS2 would likely cost about $4 billion for the company to develop, CNBC reported. At that time, it had already spent $1 billion to develop the AS2’s engine. And in April 2020, Florida Governor Ron DeSantis announced Aerion was relocating its headquarters from Reno, Nevada to Melbourne, Florida, at a plant to be built at Orlando Melbourne International Airport.

Earlier this year, Bloomberg reported Aerion was in talks to go public via a special purpose acquisition company, or SPAC. Those talks apparently did not come to fruition.

The company’s AS2 was intended to travel at around 1,000 miles per hour, and its patented “boomless cruise” technology would have allowed it to fly without creating a sonic boom. The company had planned to fly its first AS2 by 2024, and begin commercial flights by 2026.