The last Concorde may have completed travel in 2003 but that doesn’t mean supersonic travel came to an end entirely. Three aviation start-ups are hoping to bring Mach speed back by 2023—and plan to tackle the faults of the previous airplane. First, not all companies are planning to reach Mach 2 (as the Concorde did) but max out at Mach 1.1 to 1.8. Further, they’ll be more fuel-efficient (with two engines as opposed to four) and with a thinner nose, they should be able to reduce sonic booms. Read more about all three—one of which is referred to as the “direct descendant of the Concorde”—at the Wall Street Journal.