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The engine which powered the A-4/V-2 was brought back to the US as part of (I believe) Operation Paperclip, along with a couple of affiliated Nazis. The USSR effected a similar result with Operation Osoaviakhim. This engine, which burned a mix of water-diluted ethanol (for thrust augmentation & control of combustion temperatures) and LOX, ran its pumps on the hot steam & oxygen produced by the decomposition of high-test H2O2 over a silver (iirc) catalyst.

enter image description here

The basic design was adapted into the Rocketdyne A1 through A7 designs, which powered American rockets including Juno (launched Explorer I), Redstone (suborbital Mercury flights).

Over on the Soviet side it became reproduced as the domestic RD-101 through -103 and its derivatives are STILL USED (as of 2022) as the RD-107 and -108 series powering R-7-derived rockets including many of the flying Soyuzes.

It goes to say that the basic A-4 design was incredibly successful. But why was it so much better than its competition? Both the US & the USSR had contemporary domestic rocket programs, and some of them (eg, the XLR series which ended up becoming the LR79 family) were also incredibly successful.

Why was the A-4 engine family so successful?

Image source: Pinterest mystery meat

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    $\begingroup$ Nice picture! I haven't seen that one. Where did it come from? $\endgroup$ Jul 26, 2022 at 20:03
  • $\begingroup$ I catch your drift! $\endgroup$ Jul 27, 2022 at 7:51
  • $\begingroup$ It's an interesting question, it's probably off-topic as opinion based. At least part of the answer is that it was there, a lot more refined than the Soviet and US designs, and there was a pool of talent who knew how it worked. Also, there were many completed engines readily available for testing. $\endgroup$
    – GdD
    Jul 27, 2022 at 7:57
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    $\begingroup$ I don't think it's any more opinion based than any other history question. Yes, personal interpretation of the facts can vary but at the end of the day I'm looking for an empirical answer identifying a causal relationship between <something> & the popularity & longevity of these engines. I hope there can be an empirical answer at least for the US side, just because I hope a lot of the decision-making by NASA/NACA & possibly even the DoD or Rocketdyne is preserved somewhere. I don't know how to find that, however, so I'm turning to SE. $\endgroup$ Jul 27, 2022 at 18:59
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    $\begingroup$ You might be interested in this website: enginehistory.org/Rockets/RPE03/RPE03.shtml My take is that the US derivatives of the engine, even the very first one, were significantly different from the '39' model that powered the Nazi missile, so I'm not sure the premise of your question is correct. Since that's a matter of opinion, I'll just leave this as a comment rather than writing up an answer. $\endgroup$ Jul 28, 2022 at 11:40

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As noted in comments Organic Marble, there is not really a direct lineage from V2/A4 to current rockets in terms of hardware.

What did happen was a lot of learning. Designing a rocket involves things blowing up, which is dangerous and expensive so the fact that Germany had done hundreds of tests and thousands of weapons launches meant there was a vast resource of hardware(both flight and ground), documentation and people to build from.

While there were liquid fueled rocket programs by all nations (notably early JATO) the A4 was a complete and proven package massively larger than anything otherwise existing, with a track record and available in substantial numbers at low cost (to the allies at least).

Modifying a proven design is far easier than starting out, even if only because of all the meetings to make decisions avoided by saying 'copy what works'. Further if you have a working versions you can test sub elements of your new design even where some part of your own project is behind schedule rather than being held up by the slowest part.

It may also be significant that pre war there seems to have been some degree of scam/creative engineering in the rocket space (see 'Most Secret War -RV Jones and 'Ignition' by J Clark) which means claiming A4 linage added credibility/probability of approval but makes things confusing now.

So there was the American Hermes program that modified V2s, making domestic parts for them and building knowledge on ground handling, working with liquid oxygen and peroxide, designing science payloads and tracking them in flight/range safety. This lead to the civilian Bumper, working on two stage operation and payload development along with the military Navaho. Further work got the civilian Viking and the military Redstone missiles both still using the same propellant 'system' but with many minor upgrades, notably improved injectors moving from clustered chambers to a single one.

These in turn got the civilian Vanguard and military Atlas it is however questionable how much of the actual 'engine' was left at this point given the move to kerosene/LOX.

While liquid oxygen is still in use, the alcohol fuel, clustered combustion chamber, peroxide turbines, fuel injection for film cooling and injector system have all been overtaken by higher performance concepts.

What may be more significant is the ground equipment, people and infrastructure, notably the minitrack observation/tracking system that built out of flying the A4s and could then be re-used, so quite possible the 'most successful' part is the systems and people rather than the flying hardware.

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  • $\begingroup$ I would give the answer to this one just for its last sentence--excellent observation. However, there are some mistakes I can't quite look past. I am pretty sure (but not 100%) that the Viking project was homegrown--not an A-4 derivative. On the other hand, it was NAA/Rocketdyne which was contracted to study, clone, and derive a design from the A-4, leading to the Navaho/Juno/Jupiter/Redstone line of A-4-derived rocket motors. $\endgroup$ Aug 2, 2022 at 19:36
  • $\begingroup$ @AntonHengst - did not think to look at the military side that was running in parallel, updated to reflect - would suggest it does not change the central concept that the V2 was most important for being a 'worked example' that allowed other ideas to be tested rather than something that has a direct 'linage'. $\endgroup$ Aug 3, 2022 at 8:48

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