A Shuttle Derived Launch Vehicle concept studied by NASA in 1982. A predecessor to the Shuttle-C, this SDLV used a separable propulsion/Avionics module that would separate from the payload in orbit. The P/A module would re-enter and either land or splash down, to be recovered and reused. The payload shroud would be expended. Technically a better approach than Shuttle-C due to the re-use of the expensive bits, it was also a more expensive approach due to, well, the reuse of the expensive bits. Shuttle-C would attempt to be cost effective by using end-of-life SSMEs… engines that would have been thrown away anyway.