[r9etb]

The Venture Star and its new engine would have improve spaceflight but would have eliminated the external flight by being a single stage to orbit!

The problem with Single Stage to Orbit is that you've got to drag that big-ass fuel tank around all the time, which requires a bigger tank, which is heavier, which requires a bigger tank, and so on....

The mathematics of staging are compelling.

[Young Werther]

The problem was weight. It wouldn't be the first time tha weight problems would need to be addressed. The program was cancelled by NASA and a next generation engine was put on the shelf.

The linear spike engine was unique in that its thurst remained constant from ground launch to orbit insertion. This engine should be first in line for future launch vehicles and the bell shaped engine should be put on the shelf.