Iran demonstrated that it had mastered solid fuel rocket technology when it recently tested a solid fuel rocket motor for its Shahab 3 ballistic missile (which has a range of 1,700 kilometers). The solid fuel rocket technology, like the design of the Shahab 3 itself, probably came from North Korea. Iran has been a big customer of North Korean military technology for over two decades. North Korea mastered the difficult technology for manufacturing solid fuel rocket engines. Unlike liquid fuel rocket engines, solid fuel rockets are storable, more mobile and more reliable. They are also cheaper, once you know how to make the stuff.