Halving Turbo Pump Costs Via Seal Simplifications

Purpose of Article IV:

In the last three articles, I have described an alternative to the current rocket engine shaft seal, highlighting the importance of physical simplicity. By reducing the number of parts needed in the Turbo Pump, the goal is to drive down the cost of rocket engines. This article describes the projected financial impact of such an invention.

A Turbo Pump’s seal system consists of:

• Wear ring seal (x1) — A type of seal which prevents the flow of a certain amount of fluid, but also bears the sideways loads of the shaft. They are generally manufactured as a single part
• Floating ring seal (x3) — A seal in the shape of a ring which is able to prevent a significant amount of leakage without compromising friction between the Turbo Pump body and the shaft. Assembled using 4 separate parts.
• Pressure labyrinth (x3) — A series of fins (blades) sticking out of the Turbo Pump that cuts into its corresponding “lining” when the Turbo Pump is active, so that there is minimal space in between the fins and the lining cut for gasses to leak through. Made using 2 parts.
• Segmented seal rings (x2) — A multi-segment ring with different rotating/oscillating parts to prevent flow. Made using 25 parts.
• Seal Housing (1x) — A series of parts used to secure the above segments to the body of the Turbo Pumps. It holds all these parts in place using 50 different shaped parts.

Considering that all of these parts are used in the specific quantities mentioned, we can estimate the total number of parts that exist as a consequence of the current shaft seal.

1 Wear Ring Seal * 1 part/Wear Ring Seal +
3 Floating Ring Seals * 4 parts/Floating Ring Seal +
3 Pressure Labyrinths * 2 parts/Pressure Labyrinth +
2 Segmented Seal Rings * 25 parts/Segmented Seal Rings +
1 Seal Housing * 50 parts/Seal Housing
= 120 parts in total

Other than the parts that are used for the shaft seal, there are approximately 50 parts that exist in order to keep the other compartments of the Turbo Pump running. These “other compartments” consist of the shaft, pump input/output entrances, load bearings etc.

The number of parts claimed in this article are not based on an official report, but rather on approximations that I calculated using multiple Turbo Pump diagrams, along with textbooks on rocket propulsion.

By dividing the number of parts saved by the total number of parts, it is understood that such an innovation can decrease the part number of a Turbo Pump by 70%.

Using that as a metric, we can predict the effect that this complexity reduction could have on the total cost of a Turbo Pump. If we decrease the number of parts by 70%, it is fair to project this as a 70% reduction in complexity. As discussed in the first article of this patent series, 80% of a Turbo Pump’s cost is directly dependent on the physical complexity (amount of parts). This mean that this innovation would get rid of 70% of that 80% originating from physical complexity. This would cut down the total cost of a Turbo Pump by

70% of 80%= 56% of the total cost

Let’s put that 56% into context of the Industry

• If we take the cost of a LOX/RP-1 Turbo Pump as $1.2 Million, agreeing with Barber Nichols’s assessment, we would save $648,000 per Turbo Pump. This means $6.5M saved per Falcon-9 rocket.
• SpaceX’s Starship has 33 engines. Each of these engines uses 2 Turbo Pumps, meaning that the Starship uses 66 Turbo Pumps. If we assume that the cost of a LOX/Methane Turbo Pump (the variant they use for the Starship) is similar to the cost of a LOX/RP-1 Turbo Pump, this innovation would save $42.7M per Starship.
• Elon Musk wanted to ramp up the Raptor Engine’s production up to 500 engines/year. Once this goal is a reality, SpaceX would be producing/purchasing 1000 Turbo Pumps for this plan alone. That is the equivalent of $650M saved annually for SpaceX’s production ramp-up.

Conclusion

There are opportunities to save large sums of money for Turbo Pump related corporations. This doesn’t have to mean only Space Companies, since there are Turbo Pumps used in sectors like jet engines. Decreasing the cost of Turbo Pumps by 54% can have many implications.