Uninformed, yes :( . There are theoretical limits for how high Isp - the specific impulse, defined as how much thrust, in, say, pounds of force, you can get fr

Uninformed, yes :( . There are theoretical limits for how high Isp - the specific impulse, defined as how much thrust, in, say, pounds of force, you can get from a unit of fuel flow, going into the engine, in, say, pounds of mass per second. The engines created in '60s are already rather close to that theoretical limit - so saying that you can do much better just because decades has passed is similar to saying "well, surely we had SR-71 flying back in '70s already - by today we ought to have all civil aviation routinely doing at least Mach 2". So - no, it's pretty hard, including for fundamental reasons, to make engines much better that NK-33 by Isp. And that parameter is of paramount importance for a rocket engine. Mind you, this is still not the only parameter. After all, you probably care a lot about economic efficiency. Elon Musk seems to understand that pretty well - and SpaceX engines, while lacking technically, could be in a much better position economically. Next, you're right that design and manufacturing aren't standing still. Both control of materials parameters and the ability to convert the raw material into an engineered device substantially rose - talking about, say, 3D printing engines or parts, which happens rather frequently now, but didn't in '70s. So it's a complicated matter. However, NK-33 still have good technical parameters, and were bought inexpensively - in '90s, when Russia was severely starved for cash. Why not to use something which is already there, and not expensive? That's quite a rational decision Orbital - and Aerojet before them - took. Regarding the second part, about storage. Surely this is unprecedented case. That's why the engines were tested - many times, both in Russia and in USA, and also analysed, trying to predict how several decades of storage could affect engines. The results were apparently positive - of course you and I don't have the original raw data which was used to make that decision. But don't think the engines just were, say, buried underground; their storage history is roughly known and isn't that different from other products of heavy machinery industry. So I think Elon is habitually being overreacting in regard to Orbital usage of those engines. May be it has something to do with Elon's unsuccessful attempts to strike a deal with Russian space industry back when SpaceX was really young - or may be it's just a tradition for him, Elon sometimes says something out of proportions, even though SpaceX real - smaller - results are undeniable. Elon misses the point - it's only for uninformed the phrase "rocket engines made in USSR 40 years ago" would mean "unacceptable variant". George Sutton, author of "History of Liquid Propellant Rocket Engines" mentions that USSR spent far more towards rocket engine research than all other countries combined, and NK-33 is one of the serious achievements of Soviet rocket school. Don't discount something off hand just because it's old and foreign.