Invictus Spaceplane
You can add the European Space Agency to those working on a commercially viable spaceplane. Dubbed Invictus, the program is led by Frazer-Nash, in collaboration with Spirit AeroSystems, Cranfield University, and Reaction Engines Ltd. The concept plane will use Reaction's pre-cooler technology to overcome the shock heating that occurs at hypersonic speeds, allowing it to deploy existing jet engine architecture to take off like a plane and reach orbit like a rocket. Should they reach their goals, the concept will be flying at Mach 5 speeds — over 50% faster than the SR-71 Blackbird — by early 2031.