Originally Posted by
Flugplatz
I think that was part of the tech risk reduction for the X-33 as described. Seem to remember they couldn't get the thing from not leaking fuel or something
The composite tank was very challenging, with engineering conflicts that eventually caused Lockheed to switch to an aluminium design. Sadly that pretty much killed the SSTO capability of the X-33, metal was too heavy.
The sad result was the entire effort was cancelled, a major loss imho. It signaled the beginning of the era of stagnation in the US space program, decades of Titan and Delta launches with no expectations of anything better.