The news sources say that this is not about the S-300 Favorit rocket launcher, but about S-400 or S-500 complexes or the latest developments of the military-industrial complex. However, relying on the facts, there is an opinion that we are talking about Topol-E - a modified Topol for experimental launches from Kapustin Yar according to Sary-Shagan, for various tests on new combat equipment (materials, automation, the units themselves) and missile defense. In this case, there was a rupture of a solid-fuel rocket engine. The most likely cause of the incident is the cracking of a solid rocket fuel charge. This phenomenon is most likely in old rockets.