While DARPA’s Blackswift hypersonic , the dual mode turbojet/scramjet Falcon combined-cycle engine technology (FACET)soldiers on, (paid subscription required) and has actually successfully completed tests up to Mach 4 in a wind tunnel.

The technology used a turbojet to get to high supersonic speeds, at which point the scramjet kicks in, and the turbojet is cocooned, and it is supposed to take a vehicle to around Mach 6.

Additionally, the X-51A scramjet test vehicle has been moved to the Boeing plant at Huntington Beach, CA for structural tests.

It’s not as sophisticated as the FACET, it’s a pure scramjet, and boosted to speed by a rocket booster after being dropped by a B-52, and it’s rather crude, using existing equipment wherever possible, using a rocket booster from ATACMS, an existing fuel control system, and geriatric igniters from the TF-33 engine, along with using a rather heavy tungsten nose cone and ablative coatings elsewhere to deal with the heat.