It is totally realistic. Russia was a big country and it had population to spare (lots of peasants). Official USSR statistics (which were only revealed in the 90s) show that there was a deficit of around 10 million in the census done in the early 40s compared to the early 30s
To make satellites, rockets and manufacture weapons, you can do it with terrorized slaves, not necessarily free people. In the early 40s, just before the war and until around 1942, all Russian Aerospace designers, including Korolev, were detained in Sharashkas (prison-research centers) run by the NKVD. All early-war combat aircraft of the USSR were designed in such prisons. Korolev lost almost all his teeth while in the Gulag.
After the war, the USSR (like the US) received a significant input of technology from Germany. All early Russian rockets (R-1 up to R-5) were basically improved and enlarged V-1s.
The nuclear know-how was spied from the Manhattan project. It is quite easy to design something like that when you know it has already been done (even if you don't have all the details).
Ok, so when you don't like it, it must be propaganda, right? But you never do any of that yourself, do you?
Unfortunately for you, the history of the Soviet Union is very well known today because, when it collapsed in 1991, all its archives were made public. The soviets were obsessive bureaucrats and, as such, kept meticulous files on everything; especially the OGPU/NKVD/KGB. As a result, the picture is quite clear.