https://en.wikipedia.org/wiki/Scramjet#Progress_in_the_2010s
Much of scramjet experimentation remains classified. Several groups, including the US Navy with the SCRAM engine between 1968 and 1974, and the Hyper-X program with the X-43A, have claimed successful demonstrations of scramjet technology. Since these results have not been published openly, they remain unverified and a final design method of scramjet engines still does not exist.The final application of a scramjet engine is likely to be in conjunction with engines which can operate outside the scramjet's operating range.[citation needed] Dual-mode scramjets combine subsonic combustion with supersonic combustion for operation at lower speeds, and rocket-based combined cycle (RBCC) engines supplement a traditional rocket's propulsion with a scramjet, allowing for additional oxidizer to be added to the scramjet flow. RBCCs offer a possibility to extend a scramjet's operating range to higher speeds or lower intake dynamic pressures than would otherwise be possible.
Scramjets might be able to accelerate from approximately Mach 5–7 to around somewhere between half of orbital speed and orbital speed (X-30 research suggested that Mach 17 might be the limit compared to an orbital speed of Mach 25, and other studies put the upper speed limit for a pure scramjet engine between Mach 10 and 25, depending on the assumptions made). Generally, another propulsion system (very typically, a rocket is proposed) is expected to be needed for the final acceleration into orbit. Since the delta-V is moderate and the payload fraction of scramjets high, lower performance rockets such as solids, hypergolics, or simple liquid fueled boosters might be acceptable.Theoretical projections place the top speed of a scramjet between Mach 12 (14,000 km/h; 8,400 mph) and Mach 24 (25,000 km/h; 16,000 mph).[44] For comparison, the orbital speed at 200 kilometres (120 mi) low earth orbit is 7.79 kilometres per second (28,000 km/h; 17,400 mph).[45]