ATRX

ATRX is a Northern Virginia-based aerospace company founded by Virgin Galactic alumni developing the Hummingbird, a single-stage-to-orbit (SSTO) space plane with horizontal takeoff and horizontal landing (HTHL) that would take off from a conventional runway, reach orbit, and return to land like an aircraft — eliminating the expendable launch infrastructure required by vertical-launch rockets.

The Hummingbird uses an Air-Turbo-Ramjet (ATR) propulsion cycle that transitions from air-breathing turbine mode at subsonic speeds through ramjet combustion in the supersonic regime to rocket combustion above the atmosphere, aiming to capture the fuel efficiency of jet engines during the dense-atmosphere phase of ascent where rocket engines are least efficient. This combined-cycle approach is the central engineering bet behind SSTO spaceplanes: using ambient air as oxidizer for the first portion of the flight dramatically reduces the oxidizer mass a vehicle must carry, which is typically 70-80% of a chemical rocket's propellant mass.

ATRX participated in the Techstars Space 2024 accelerator cohort, gaining mentorship from defense and space industry advisors while securing early-stage capital. The company's Virgin Galactic founding team brings direct experience with rocket-powered spaceplanes (SpaceShipTwo/VSS Unity), composite airframe manufacturing, and FAA/AST commercial launch licensing — though transitioning from suborbital to orbital HTHL requires solving propulsion integration challenges that have eluded government programs including NASP (National Aerospace Plane) and HOTOL.

ATRX competes in the SSTO/spaceplane niche with Reaction Engines (SABRE precooled engine, UK), Hermeus (hypersonic aircraft), and SpacePlane Inc., all pursuing variants of the same dream of aircraft-like orbital access.