[troutman]

https://www.space.com/11363-nasa-spa...versaries.html

In the 1980s, NASA and the Air Force collaborated on a highly secretive project known as the X-30 National Aerospace Plane (NASP). Due to the classified nature of the project, few details are known, but the concept was envisioned as a single-stage-to-orbit space plane. The program lasted over a decade, but technical hurdles and budgetary issues forced its eventual cancellation in 1993, before a prototype could be built.

Other test programs that fell short include the X-33, which was a joint development between NASA and Lockheed Martin in the mid-1990s. The X-33 suborbital space plane was planned as a technology demonstrator for Lockheed's proposed VentureStar orbital spacecraft.

"This was another space plane concept, a potential shuttle follow-on, in which NASA and Lockheed both put money," Launius said. "But it was underfunded and there wasn't the political support for it. They again ran into technical problems, and no one was willing to open a pocketbook to solve those, and that program was canceled as well."

Among other test programs, NASA experimented with a cargo-only version of the space shuttle, called Shuttle-C. This side-mounted carrier would be flown from the ground, unmanned, and used solely to ferry supplies into low-Earth orbit.

Spaceplanes: The return of the reusable spacecraft?
https://www.bbc.com/future/article/2...ble-spacecraft