Orbital Sciences Corporation

The Pegasus is an air-launched rocket developed by Orbital Sciences Corporation (now part of Northrop Grumman Innovation Systems). Capable of carrying small payloads of up to 443 kilograms (977 lb) into low Earth orbit, the vehicle consists of three solid propellant stages and an optional monopropellant fourth stage. Pegasus is released from its carrier aircraft at approximately 40,000 ft (12,000 m), and its first stage has a wing and a tail to provide lift and attitude control while in the atmosphere.
The HAPS variant adds a Hydrazine Auxiliary Propulsion System maneuvering stage.

Pegasus XL HAPS Launch Schedule