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From Wikipedia:

Under RD AMROSS, Pratt & Whitney is licensed to produce the RD-180 in the United States. Originally, production of the RD-180 in the US was scheduled to begin in 2008, but this did not happen. According to a 2005 GAO Assessment of Selected Major Weapon Programs, Pratt & Whitney planned to start building the engine in the United States with a first military launch by 2012.[3] This, too, did not happen. In 2014, the Defense Department estimated that it would require approximately $1 billion and five years to begin US domestic manufacture of the RD-180 engine.[4]

From my understanding, Prat & Whitney have technical plans and documentation, why they still can't manage to produce engines independently?

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In something as complex as a rocket engine, there are specs and docs, and then there are things that only the people on the production line seem to know.

I recall an anecdote for the center body of some fighter jet, where they were having a problem separating the product from the mold. They called in an old timer who used to work on the line, and he explained that they had applied a thin coat of ranch dressing before starting as a lubricant. But it had never been documented, it was just how it was done.

Rocket engines are tricky beasts. The Russians have coatings and materials that are not available in the United States, which is one of the main complaints I have heard. Is it really a US based rocket engine if you buy all the components from Russia? So how many do you have to make inhouse? How far down the chain do you need to go? 100% US based? If so, then you have to start with making tools to make tools to make tools sort of things.

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  • $\begingroup$ Surely it isn't just the exact copy. Today new alloys, electronics, etc are available than before 30 years. $\endgroup$
    – mark.g
    May 31, 2016 at 17:43
  • $\begingroup$ @mark.g Every change you make opens you up to more testing and development. There are no drop in equivalents. Also this is a very extreme environment, where the very very specific material requirements are quite extreme and unique. $\endgroup$
    – geoffc
    May 31, 2016 at 17:45
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    $\begingroup$ Got a reference on that ranch dressing anecdote? That sounds hilarious and I'd like to read more! $\endgroup$
    – Ezra Bailey
    May 31, 2016 at 17:50
  • $\begingroup$ NO! It might have been the SR-71 since I remember Titatnium being involved, but it was just that, an anecdote. $\endgroup$
    – geoffc
    May 31, 2016 at 17:53
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    $\begingroup$ RD-180 uses an oxygen rich preburner, P&W might still not have the metallurgy to pull this off (RS-25 uses a fuel rich preburner because the US had no alloys suitable for an extermly hot, high pressure, oxygen rich environment back when it was developed). SpaceX developed a new alloy SX-500 for the oxygen rich preburner of Raptor engines, which might be usable. $\endgroup$
    – Georg Patscheider
    May 28, 2019 at 10:04

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