Thanks for information, Its good to we have you here in this forum.
It has always been a question to me that if second stage of Safir is based R-27, so why thrust of its very low and isn't comparable to thrust of R-27(3.4 tons vs around 230 tons).
Now its interesting to see this small engine of SA-2 produces 3.4 tons of thrust too. You think why the thrust of second stage of Safir is so low, Can the 3.4 tons thrust that has been announced for thrust of second stage of Safir be misinformation?
Thank you for the kind words. This forum is one of the most informative and authentic to be found; all of its participants deserve credit. With regard to your question, I offer two points of possible interest. First, the Safir second stage appears to utilize the steering engines (thrust ~3.5tons) found on the Soviet R-27 missile, not the main engine (thrust ~23 tons). Note that the two steering engines, which are fed by a single pump, together generate about 3.5 tons. And seconed, while this thrust level is approximately the same as that produced by the SA-2 engine, the specific impulse (energy generated per unit mass of propellant burned) for the former is about 22% more than the latter. Thus the velocity change imparted to the satellite when using the R-27 steering engines is roughly 17-19% more than for the same second stage powered by the SA-2 engine. I ignore some minor factors, such as propellant density, burn time, etc; this is why the numbers listed (22% vs. 17-19%) are slightly different. In other words, if the second stage size remained the same, but an SA-2 engine were used in the Safir, the Omid and other satellites would not have achieved orbital velocities.
Finally, the SA-2 engine, as noted in my previous post uses TG-02 and AK-27 for its fuel and oxidizer; the R-27 steering engines employ UDMH and N2O2, which is more energetic. Hope this helps.....