Sep 052012
Before Challenger ruined all hope of the Space Shuttle achieving its intended goals, there were many, many ideas put forth to increase the capabilities of the STS. Numerous concepts dealt with increasing the propulsion system… increased thrust and/or increased fuel mass. One of the less obvious ideas: stuff a massively reworked Titan II first stage underneath the external tank. This would increase liftoff thrust, increasing payload delivered to orbit. While Martin Marietta put some effort behind the concept, I don’t think NASA ever really took it very seriously.
This is from a slide scanned at the NASA HQ archive.