The Saturn MLV was a proposed concept family of rockets, intended as a follow-on to the Saturn V. MLV stands for "Modified Launch Vehicle".

Vehicle configurations representative of several alternative uprating methods were specified by the Marshall Space Flight Center for initial studies.

Proposed modifications
Thrust uprating and modifying of the five F-1 rocket engines used in the first S-IC stage, and corresponding increases in propellant tank capacities.
Addition of a sixth F-1 engine in the S-IC stage, as an alternative to engine uprating, plus increased propellant capacities.
Use of UA1205 solid rocket boosters derived from the Titan IIIC vehicle.
Additional J-2 engines in the S-II stage, ~131 s increased upper stage propellant capacities.
Improved or advanced upper stage engines, such as the HG-3, plus increased propellant capacities.
The baseline Saturn MLV would incorporate these changes from the Saturn V vehicle. The Saturn IC first stage would have been stretched 240 inches (610 cm) with 2,500,000 kg (5,600,000 lb) of propellant and five new F-1A engines; the S-II second stage would have been stretched 41 inches (100 cm) with 450,000 kg (1,000,000 lb) of propellant and five J-2 engines; the S-IVB third stage would have been strengthened, but with a standard 100,000 kg (230,000 lb) of propellant, and one J-2 engine. Nuclear propulsion in the third stage and toroidal J-2 engines in the second and third stages were also investigated.