Pegasus II, also known as Thunderbolt, was an air-launched orbital rocket under development in 2012–2015 by Orbital Sciences Corporation for use by Stratolaunch Systems.[1]
The vehicle was to be carried by the Stratolaunch aircraft, developed by Scaled Composites, which is the world's largest aircraft by wingspan.[2][1] Originally designed with solid lower stages and a cryogenic upper stage, the Pegasus II design was subsequently modified in 2014 to exclusively use solid rocket motors.[3]
However, the failure of the design to meet the economic cost and revenue targets led to the design being "shelved" by Stratolaunch in May 2015. At the time, Stratolaunch "reopened the design plan and [was] evaluating over 70 different launch vehicle variants" for use on the Scaled Composites Stratolaunch.[4] In the end, no good economic case ever closed and Stratolaunch halted all work on their own family of air-launched rockets in January 2019.[5]
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