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The Atlas III and V first stages were powered by NPO Energomash RD-180 engines, unlike the previous Atlas II which was powered by Rocketdyne RS-56 engines.

Why did Lockheed Martin switch to Russian engines? Were there technical advantages which outweighed the geopolitical challenges of relying on Russian space hardware? At the time of designing the Atlas III, were there “Made in America” candidates for the engines?

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    $\begingroup$ At the time, there were technical advantages and geopolitical advantages, not challenges. It was a win-win situation. $\endgroup$ Commented Oct 9, 2023 at 3:44
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    $\begingroup$ After the cold war, there's very few real geopolitical challenge in the field of civilian space technology. Buying from Russia doesn't necessarily mean depending on Russia. In this case it's quite the opposite: Russia became somewhat dependent on US to buy from them. $\endgroup$ Commented Oct 9, 2023 at 4:57
  • $\begingroup$ I recall at the time there was quite a lot of press/media attention about this, and the short was that the Russians had developed an engine (closed cycle?) that was reliable and performed well, something that the US companies had tried and failed to do, at the time. $\endgroup$ Commented Oct 9, 2023 at 6:57

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I recall a big brouhaha at the time, and there was a fair bit of coverage about why the US should suddenly start switching to a former enemy's engine.

TL;DR:

Sudden availability of technology that was hitherto unseen (working reliably) in the West, with unrivalled liquid-fuelled performance, at affordable prices, with the promise of handing over the tech and the paperwork, coupled with the need to keep this away from states such as North Korea, meant that this engine was the best on the available market at the time.

*Were there technical advantages which outweighed the geopolitical challenges of relying on Russian space hardware? At the time of designing the Atlas III, were there “Made in America” candidates for the engines?

The previous Atlas II was utilizing ICBM technology so Rocketdyne was asked to design a new engine system for the Atlas III then in development. The proposed cost was too high, triggering a search for an alternative.

The performance, and cost, of the RD-170, and the short scale development of this into the RD-180 meant that the latter was the cheaper, better performance route to take at a time when the US gov was also looking to keep post-Soviet tech away from North Korea and the open market.

ULA docs cover a bit of the history:

In the early 1990s the closed cycle, LOx rich, staged combustion technology rumored to exist in Russia was originally sought out by General Dynamics because engines of this kind would be able to provide a dramatic performance increase over available U.S. rocket technology.

Unlike its rocket building counterparts in the United States, Europe, China, and Japan, Russia was able to master a unique LOx rich closed cycle combustion technology which delivered a 25% performance increase.

To achieve this additional performance, staged combustion engine designs require a much better understanding of the combustion process and the stages of that process. The engine is the subsystem responsible for containing and controlling combustion. For a LOx rich process, where environments include much higher pressures and temperatures, it is imperative to be able to limit where these processes take place. The unique technology developed for the RD-180 sets it apart from its counterparts designed in the United States not from a combustion understanding standpoint but by the technology developed to mitigate combustion.

Extensive development was necessary to create the combustion devices, the preburner and the chambers, that were able to consistently control continuous throttle from 47% to 100%. This technology was developed by the Soviet Union beginning in the 1970s at the height of the space race, and required significant resources. Learning how to control this type of process meant burning up a lot of hardware. With the space race in full effect the Russian designers had unlimited resources. They were able to develop this unique design though a pragmatic hardware based approach where important design questions were resolved after full system tests.

After the fall of the Soviet Union, word of what the Russians had been able to accomplish made it into the global aerospace community and the technology was sought out by General Dynamics which later merged with Martin Marietta and eventually became Lockheed Martin. Twenty years after the technology had been developed it was still largely misunderstood by the global community and considered too risky.

There was skepticism in the reliability of the newly found Russian technology as it was such a departure from designs in use in the United States; the LOx rich staged combustion cycle engine, although it delivered performance improvements, was considered too risky not only in the U.S. but around the world. The staged combustion cycle must achieve far higher combustion pressures in the chamber than open cycles because the main combustion chamber receives high pressure gaseous oxygen directly from the turbine exhaust. The end result is higher performance however the reward comes with additional risk. For the RD-180, all of the oxygen flows through the preburner which drives the turbine. The gaseous oxygen that flows to the chamber requires much less energy to initiate a combustion process so the engine is more prone to consuming itself given an ignition source. NPO Energomash, the leading designer of engines in Russia, had gone through hundreds of designs, each an improvement on the last, to harness the power of LOx rich combustion. This required a very careful approach to how the fuel is burned in the preburner so that the temperature field is uniform. It also required improvements in materials and production techniques. They found a way to take the chamber pressures to new limits while protecting the internal components from fire risks. This required a new class of high temperature resistant stainless steel invented to cope with the risks of the LOx rich environment.

The RD-180 designed and built by NPO EM was specifically tailored for the Atlas launch vehicle. It is a two chamber derivative of the RD-170 which later evolved into the RD-171 and RD-171M.

http://www.ulalaunch.com/docs/default-source/evolution/rd-180-engine-an-established-record-of-performance-and-reliability-on-atlas-launch-vehicles.pdf

In 1997 Lockheed Martin established an agreement with NPO Energomash, the leading Russian developer of liquid propellant rocket engines, to purchase engines for Atlas launch vehicles. The Russian American collaboration required to make these flights successful has surmounted significant challenges and withstood the test of time. RD-180s are delivered to ULA, a 50/50 joint venture owned by Lockheed Martin and The Boeing Company, via an American Russian joint venture company RD AMROSS. RD AMROSS is a 50/50 joint venture between Pratt & Whitney Rocketdyne (PWR) and NPO Energomash (NPO EM). NPO EM is the designer and manufacturer of the RD180. PWR is the premier U.S. liquid rocket engine developer selected to collaborate with NPO EM in support of the RD-180 program. PWR and NPO EM both provide RD-180 integration and launch support services to ULA.

Other links:

The reason was simple... The engine was simply the best in the world. “There is nothing like the RD-180 available from U.S. or other western companies. It really is a very high quality engine,”

There was an added incentive to keep Russian engineers employed building these rockets for the U.S. market, and not supplying their know-how to North Korean or Iranian intercontinental ballistic missile programs

The deal to buy RD-180 rockets included a license to co-produce them domestically... But that never happened.

...a series of waivers and policy changes that resulted in the domestic version of the engine being pushed back indefinitely.

“The high cost and time involved in doing it, and the fact that the engines were readily available and relatively inexpensive, kept pushing back those plans,”

https://www.nationaldefensemagazine.org/articles/2014/7/1/2014july-costs-benefits-of-rd180-rocket-engine-replacement-program-debated

https://www.airforce-technology.com/features/featurerussian-rockets-the-us-governments-rd-180-conundrum-4325220/?cf-view

Although based on the NK-33, for the N1 variant, this was a pretty good documentary at the time, highlighting the situation that benefitted the West after the Cold War:

The 180 itself is derived from the RD-170, which at the time was the world's most powerful and heaviest liquid-fuel rocket engine in production. It was designed and produced in the Soviet Union by NPO Energomash for use with the Energia launch vehicle as strap-on boosters, a 1980s super-heavy lift launch vehicle. Energia was designed as part of the Buran program for a variety of payloads including the Buran spacecraft, with capacity to place about 100 tonnes in Low Earth orbit, up to 20 tonnes to geostationary orbit and up to 32 tonnes by translunar trajectory into lunar orbit.

Post-cancelation after only two flights and the dissolution of the Soviet Union, legacy of Energia/Buran project manifests itself most visibly in form of the RD-170 family of rocket engines, and the Zenit launcher, with the first stage roughly the same as one of the Energia first-stage boosters.

http://www.astronautix.com/r/rd-180.html

The engine, employing a LOX lead start, staged combustion cycle, and LOX rich turbine drive, delivered a 10 percent performance increase over then-operational US booster engines and provided clean, reusable operation.

Only the main turbo-pump assembly and boost pumps required development and they were scalable from the RD-120 and RD-170 engines. All other components were taken directly from the RD-170.

The RD-180 was developed in 42 months at a small fraction of the cost of a typical US new engine development.

Lockheed Martin chose the RD-180 engine for its Atlas V launch vehicle because of its proven track record of success (based on the flight history of its predecessor engine), performance, and lower cost.

The U.S. government was actively pursuing space cooperation with Russia in the 1990s and encouraged private-sector cooperation with Russia and other former Soviet Union states because of proliferation concerns.

In 1997, Florida-based Pratt & Whitney and NPO Energomash of Russia established the RD AMROSS LLC joint venture to produce the Russian RD-180 engine for the American market. Having partnered to sell other engine models, Pratt & Whitney and Energomash came together again to attempt to meet Lockheed Martin’s need for a new engine for its Atlas 3 and 5 vehicles with the RD-180 engine, then under development. Lockheed Martin selected the RD-180 as the first stage engine for its new Atlas models. Government policy, however, required that Lockheed Martin demonstrate the ability to manufacture RD-180s in the United States in order to avoid dependence on Russia to launch national security payloads.

Therefore, under the RD AMROSS partnership, Energomash would produce 101 RD-180 engines for the Atlas 3 and commercial launches on Atlas 5 at its Khimky plant in Russia, while Pratt & Whitney would build some two dozen more RD-180s in Florida to launch government payloads. Pratt & Whitney also contributed $25 million to Energomash for upgrades at the Khimky plant. The two companies are 50-50 partners in the joint venture.

https://www.globalsecurity.org/space/world/russia/rd-180.htm

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    $\begingroup$ not worth an edit, but the standard English spelling is apparently "brouhaha." I know a lot of silly things and do very well at bar trivia, but I was not aware of this until just now, so cheers $\endgroup$
    – Erin Anne
    Commented Oct 9, 2023 at 7:13
  • $\begingroup$ Haha, completely worth an edit, i was thinking is it this or is it that, i cant remember, and anyway i should be watching the road im driving on! Will edit when i can. I was very into the Soviet space program at the time, so this was big news $\endgroup$ Commented Oct 9, 2023 at 7:19
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    $\begingroup$ Good answer, but that first PR document...wow, the 3rd paragraph. Yes, if you're building an engine, it's important to control where combustion takes place. I think we can all agree with that one. $\endgroup$ Commented Oct 9, 2023 at 10:21
  • $\begingroup$ So, basically, if the Americans haven't bough it, Russia would have just sold it to someone else... $\endgroup$
    – vsz
    Commented Oct 9, 2023 at 11:03
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    $\begingroup$ That was the fear in the US. And, in reality, those days, the then Russian space program was looking at the edge of the toilet bowl, no money and all this tech (tech that many other people wanted). Things like this, the ISS with Clintons push, kinda saved them (both private and state co's) and injected hard cash. China by this stage was buying up tech for its space program restart too. $\endgroup$ Commented Oct 9, 2023 at 11:27

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