Comet HLLV
The Comet HLLV was a proposed super heavy-lift launch vehicle designed for NASA's First Lunar Outpost program, which was in the design phase from 1992-1993 under the Space Exploration Initiative. It was a Saturn V-derived launch vehicle with modernized engines, stretched fuel tanks, and strap-on boosters. Its main goal was to support the First Lunar Outpost program and future human mission to Mars. It was designed to be inexpensive and simple while relying on existing technology to lower development costs. Design. The Comet would have been capable of putting 254.4 tons into low  Earth orbit and 97.6 tons to trans-lunar injection, roughly twice that of the Saturn V, making it one of the largest rockets ever designed in terms of payload. The vehicle resembled a Saturn V, but with engines updated to the F-1A and J-2S, stretched first and second stages, and new side boosters. Each of the two side boosters had two F-1A engines. Development costs were expected to be modest due to reliance on Apollo-era technology. A nuclear-powered variant of the third stage, with two 222.5-kN engines, was also considered. It would have reduced the rocket's  size, but at a predicted development cost of $2 billion over a chemical-only design. The nuclear option was planned to be developed later to support crewed Mars missions. To this end, NASA's Lewis Research Center established a Nuclear Systems Office to develop and test a fully functional nuclear engine by 2005. NLS derived launch vehicle. An alternate version of the launcher based on the then-in-development National Launch System was proposed. NASA's Marshall Spaceflight Center looked into the Comet rocket or a possible configuration with four F-1A boosters added to the basic 2-stage NLS  vehicle. The main expected advantage was that the vehicle could rely on technology currently flying rather than having to resurrect 20 year old technology and manufacturing equipment.