Lockheed Martin SR-72 "Darkstar".
documentedsource_actorPrivate Aerospace Contractors
Unclassified-concept (2013) unmanned Mach 5–6 hypersonic reconnaissance/strike aircraft — the 'Son of Blackbird' — using turbine-based combined-cycle (TBCC) propulsion. No prototype publicly confirmed.
Skunk Works has discussed the SR-72 since 2013 as an SR-71 successor. Planned TBCC engine blends a turbojet with a scramjet for runway-to-Mach-6 acceleration. In 2017 Rob Weiss said TBCC testing was done and an F-22-sized Flight Research Vehicle was near. Thermal management (>500°F surfaces) drives an unmanned design. As of 2026 no aircraft has been shown publicly; hundreds of millions in classified Skunk Works losses + Palmdale facility expansion are the circumstantial evidence it may exist. Reporting leans heavily on speculation.