There are supply chain concerns here, of course.

If they go with the BE-3 instead of the RL-10 for ACES, they’ll be reliant entirely on Blue Origin for the engines on both stages of the Vulcan. One senses some discomfort at ULA at such a prospect.

But when you decline to build any of your engines in-house, these are the difficulties you can’t avoid.

Kirk: No need to post your comment twice. It did not appear because it included two urls, and such comments require my approval. Either be patience, or include only one url per comment.

Another recent revelation is that when Vulcan first flies (they say mid-2020), it will not be using the current 3.05 m diameter Centaur upper stage, but will instead use a 5.4 m diameter Centaur V, powered by four RL10 engines. That part really surprises me as the RL10 is rumored to be quite expensive, though Mr. Bruno said, “RL10 has had several updates, so it’s not a 1960s engine any more. The elegance of the expander cycle in LOX/LH2 definitely has appeal for its size class. (remembering that the cube-square law limits how big it can go). Aerojet has done really intriguing work in additive manufacturing and how that might be applied to RL10.” [2] so I wonder if some of its updates have target lowering its cost of manufacture.

Anyhow, the Centaur V sounds as if it is half-way between the current Centaur and the eventual ACES (Advanced Cryogenic Evolved Stage), lacking the ACES IVF (Integrated Vehicle Fluids) systems and MLI (Multi-Layer Insulation) which are required for extra-long duration missions and propellant depot operation. Mr. Bruno did say they have not yet decided if they will stick with the RL10 for ACES.

Another recent revelation is that when Vulcan first flies (they say mid-2020), it will not be using the current 3.05 m diameter Centaur upper stage, but will instead use a 5.4 m diameter Centaur V, powered by four RL10 engines. That part really surprises me as the RL10 is rumored to be quite expensive, though Mr. Bruno said, “RL10 has had several updates, so it’s not a 1960s engine any more. The elegance of the expander cycle in LOX/LH2 definitely has appeal for its size class. (remembering that the cube-square law limits how big it can go). Aerojet has done really intriguing work in additive manufacturing and how that might be applied to RL10.” [2] so I wonder if some of its updates have target lowering its cost of manufacture.

Anyhow, the Centaur V sounds as if it is half-way between the current Centaur and the eventual ACES (Advanced Cryogenic Evolved Stage), lacking the ACES IVF (Integrated Vehicle Fluids) systems and MLI (Multi-Layer Insulation) which are required for extra-long duration missions and propellant depot operation.