Rocketdyne
The Rocketdyne Division was founded by North American Aviation (NAA) in 1955, and was later part of Rockwell International (1967-1996) and Boeing (1996-2005). In 2005, the Rocketdyne Division was sold to United Technologies Corporation, becoming Pratt & Whitney Rocketdyne as part of Pratt & Whitney. In 2013, Pratt & Whitney Rocketdyne was sold to GenCorp, which merged it with Aerojet to form Aerojet Rocketdyne.
Integrated Powerhead Demonstrator
Future engine development work beyond the powerhead demo was never funded by the US government, and neither Rocketdyne—nor later Aerojet Rocketdyne after a 2013 merger—chose to pursue such development with their own or other private funding.