NASA’s Saturn V Improvement Studies: Paving the Way for Future Heavy-Lift Capabilities

In the mid-1960s, as the Apollo program was in full swing, NASA was already looking ahead to the future of heavy-lift launch vehicles. The Saturn V, the most powerful rocket ever built at the time, was the backbone of the lunar missions. However, NASA recognized that to enable more ambitious missions beyond Apollo, the Saturn V would need to be upgraded and improved. To this end, a series of Saturn V Improvement Studies was conducted from June 1964 to April 1965, with the goal of determining the growth potential of the Saturn V and comparing alternative methods for increasing its payload capacity.

Study Objectives and Approach

The primary objective of the Saturn V Improvement Studies was to investigate potential modified stage designs for use in a Modified Launch Vehicle (MLV) version of the Saturn V. The studies aimed to define in detail the design, performance, and resource requirements for various MLV-Saturn V configurations.

At the outset of the studies, no specific mission requirements existed for an improved launch vehicle, as no missions beyond Apollo had been formally assigned. Therefore, the approach taken was to establish the earliest practical vehicle configuration that could be achieved, and then map out evolutionary steps to the “ultimate” practical configuration within the defined study constraints. These constraints included using expected near-term engine improvements and staying within existing facility limitations.

The modified stage designs considered were intended for launch vehicles operating in the 1970s, after the conclusion of the initially planned 15-flight Saturn V program. The studies looked at a range of changes that could be made to each stage, as well as different combinations of modified stages, to increase the Saturn V’s performance.

Uprating Techniques Considered

Several key techniques were identified for significantly increasing the Saturn V’s payload capacity:

First Stage (S-IC) Uprating

• Increasing the number of engines
• Uprating the F-1 engine
• Using toroidal-aerospike F-1 engines
• Using high-energy propellants (e.g. fluorine-oxygen)
• Increasing propellant loading
• Adding solid or liquid rocket boosters

Second Stage (S-II) Uprating

• Increasing the number of J-2 engines
• Uprating the J-2 engine
• Using toroidal-aerospike J-2 engines
• Using high-energy propellants
• Increasing propellant loading

Third Stage (S-IVB) Uprating

• Uprating the J-2 engine
• Using a new high-pressure engine (HG-3)
• Using toroidal-aerospike J-2 engines
• Using high-energy propellants
• Increasing propellant loading

Initial NASA in-house studies in early 1964 examined various configurations employing these uprating techniques. Concepts from other sources such as contractors were also considered. Ultimately, configurations were selected for the contractor studies that were deemed the most practical and representative options within the study constraints. Only concepts offering payload gains of 10% or more were carried forward.

Improved Propulsion

A key focus of the improvement studies was increasing the performance and thrust of the Saturn V’s propulsion systems. The studies assumed the use of an uprated F-1 first stage engine, a new high-pressure HG-3 engine for the upper stages, and the introduction of large solid rocket motors.

The uprated F-1, assumed to be available for the MLV vehicles, offered higher thrust than the standard F-1 used on the Saturn V. The HG-3 was a conceptual new upper stage engine that would operate at higher chamber pressure than the J-2 to increase thrust and specific impulse.

For the parallel solid motor integration studies, large 120-inch diameter solid rocket motors were baselined. These motors, notionally designed by United Technology Corporation, were designated UA-1205.

An uprated version of the J-2, the Saturn V’s upper stage engine, was initially not considered in the contractor studies. Early analysis indicated that a 10% increase in J-2 thrust would yield only a 4% payload gain, which was not deemed sufficient to warrant detailed investigation. However, later engine studies showed that the J-2 could potentially be uprated to 250,000 lbf thrust. NASA elected to revisit the use of uprated J-2 and J-2T (toroidal-aerospike) engines in subsequent in-house analyses.

Configurations Studied

The contractor studies initially focused on four main MLV-Saturn V configurations:

1. MLV-Saturn V-1: Uprated first stage with five uprated F-1 engines, increased propellant capacity in all stages.
2. MLV-Saturn V-2: First stage with six standard F-1 engines, increased propellant capacity in all stages.
3. MLV-Saturn V-3: Uprated first stage with five uprated F-1 engines, second stage with four HG-3 engines, increased propellant capacity in all stages.
4. MLV-Saturn V-4(S): Uprated first stage with five uprated F-1 engines, four 120-inch solid rocket boosters attached to first stage, increased upper stage propellant capacity.

At the mid-term review, it was determined that the studies had progressed sufficiently that two additional configurations could be investigated:

5. MLV-Saturn V-1A: Variant of MLV-Saturn V-1 with HG-3 engines on second stage.
6. MLV-Saturn V-4(S)A: Variant of MLV-Saturn V-4(S) with six standard F-1 engines on first stage.

Modifications to the Saturn V’s Instrument Unit (IU) were not included in the initial studies. It was decided to first select the preferred overall vehicle configuration before studying IU changes.

Complementary In-House Studies

In parallel with the contractor efforts, NASA’s Marshall Space Flight Center (MSFC) conducted extensive in-house studies on alternative MLV-Saturn V configurations and uprating approaches. These studies aimed to provide a common basis for comparing the performance potential of different uprating philosophies.

The MSFC in-house studies focused primarily on estimating vehicle payload capability and did not involve detailed stage or vehicle design. They allowed NASA to rapidly explore a wider range of options than were feasible to cover in the contractor studies.

Other in-house analyses looked at the performance benefits of incorporating nuclear propulsion into the MLV-Saturn V. Nuclear thermal rocket stages, such as the conceptual RIFT (Reactor-In-Flight-Test) stage, offered the potential for significantly higher specific impulse compared to chemical rockets.

Study Results and Conclusions

The Saturn V Improvement Studies provided a wealth of data on the feasibility and expected performance of various MLV-Saturn V configurations. The studies indicated that uprating the Saturn V was a practical means to significantly increase its payload capacity. No insurmountable technical challenges were identified, and the uprated vehicles were found to be achievable using largely existing or near-term technology.

Configurations using uprated F-1 engines on the first stage and multiple J-2 or HG-3 engines on the second stage showed the most promise for increased payload capability within the study constraints. The addition of solid rocket boosters to the first stage also offered significant performance gains, but required more extensive vehicle and facility changes.

The studies concluded that MLV-Saturn V vehicles could be available in the early-to-mid 1970s, depending on the specific configuration and the development timelines for the upgraded engines and stages. Evolutionary uprating of the Saturn V was seen as an attractive path to enable more ambitious post-Apollo missions, including expanded lunar exploration and Mars expeditions.

Legacy and Implications

While the MLV-Saturn V configurations studied were never developed, the Saturn V Improvement Studies had a lasting impact on NASA’s thinking about heavy-lift launch vehicles. The studies demonstrated the feasibility and benefits of uprating the Saturn V, and provided a foundation for later conceptual vehicles like the Saturn MLV-V-4-260 and Nova designs.

Many of the uprating techniques considered, such as higher-thrust engines, solid rocket boosters, and high-energy upper stages, would eventually be applied to the Space Shuttle and later launch vehicles. The idea of using a series of evolutionary upgrades to incrementally increase capability, a key theme of the Saturn improvement studies, has been applied to vehicles like the Delta IV, Atlas V, and Falcon 9.

The Saturn V Improvement Studies also highlighted the importance of early planning and technology development for future launch vehicles. By starting the studies while the Apollo program was still underway, NASA was able to identify promising upgrade paths and key technology needs well in advance. This approach of anticipating future mission requirements and proactively developing enabling technologies continues to be a crucial aspect of NASA’s launch vehicle programs.

The Saturn V Improvement Studies were a vital early step in defining the post-Apollo future of heavy-lift launch vehicles. While the specific vehicles studied were never built, the knowledge gained and the analytical approaches developed laid the groundwork for NASA’s ongoing efforts to expand access to space and push the boundaries of exploration.