“You kind of design a plane around an engine rather than the other way around. Let me know when we can hear their engine.”

becomes clear all this remains theoretical for now. The Boom engineers have built a mock cockpit and passenger cabin out of cardboard and plywood. The black leather seats in the cabin came from OfficeMax, and Scholl asked his team to sit in them for a few hours each to experience what the plane will feel like. (It’s a bit cramped.) On the floor of the hangar, tape has been laid out to mimic the design of a one-third-scale plane, which Boom says it’ll build and fly by the end of next year.

The Concorde failed for a variety of reasons: expensive tickets, sonic booms that nixed overland travel, the slowdown in air travel after Sept. 11. In the years since, the other couple of efforts to build a supersonic commercial jet fizzled, and the conventional aerospace wisdom is that such projects are too expensive and risky. “Very few people really need to be somewhere in three hours,” says Jeremy Conrad, a former U.S. Air Force officer who runs hardware-focused venture firm Lemnos Labs. “And have you traveled international business class lately? It’s a great experience.”

Conrad says blustery Silicon Valley types often underestimate how tough it is to build aerospace hardware that tests the bounds of physics. There are some recent exceptions, though, most notably Elon Musk’s SpaceX and Jeff Bezos’s Blue Origin. Scholl and his team say a startup has the best shot at a project like theirs, because it can get going without loads of bureaucracy and with relatively little money. To date, Boom has raised $2.1 million and says that will last it through the development stage, though it’ll eventually take tens or hundreds of millions of dollars to take a plane to market.

Given the scale it’s planning, Boom may have a chance, says Richard Aboulafia, an aerospace consultant at Teal Group. “At 40 seats, that is kind of intriguing,” he says. “It’s possible that you would have enough routes with enough passengers to justify the development of this plane.” He’s more skeptical about the research and development costs. Boom says it’ll tweak offthe-shelf engines for supersonic flight, The bottom line Aerospace startup Boom is working on what it says will be a relatively cheap jet that can fly at Mach 2.2.

�Richard Aboulafia, aerospace consultant at Teal Group

In the U.S., the federal government oversees car safety, while states handle the drivers. That worked fine until the cars started becoming the drivers. The bellwether legal framework for fully self-driving cars is in the hands of the California Department of Motor Vehicles. The department’s draft rules,