In late July 2017 Iran announced the successful second test launch of the Simorgh SLV (satellite launch vehicle). Within a week American intelligence officials revealed that while the Simorgh took off and disappeared from view of people on the ground without visible problem, as it approached the point, outside the atmosphere, where it would inset a satellite, the Simorgh malfunctioned and fell back to earth without accomplishing anything. Moreover American, South Korean and UN ballistic missile experts agree that the Simorgh appears to be based on the North Korean Unha SLV/ballistic missile design. Why do so many different sets of experts agree on what Simorgh actually is and its origins. That’s because Iran and North Korea have been trading weapons and weapons tech since the 1980s. After 2001 that relationship, never really publicized by either party, tried to disappear from public view. Simorgh/Unha is a good example of why disappearing has not worked.
Simorgh itself is an 87 ton two-stage liquid fuel rocket that can put satellites of up to 350 kg (770 pounds) into a LEO (low earth orbit) of 500 kilometers. The first test was in early 2016 and it was not successful. Iran says it plans to use Simorgh to put surveillance satellites into orbit. That was supposed to happen earlier in 2017 but apparently another test launch was considered necessary and since the second test also failed more are apparently on the way. The Simorgh appears to be stuck at the same stage of development as the North Korean Unha it is based on.
So much is known about Unha because in early 2017 a team of UN technical experts issued a report agreeing with South Korean allegations that North Korea was using foreign components and manufacturing equipment to build the Unha. South Korea knew this because they had obtained many components of an Unha rocket that had been launched but failed. The details were not revealed until later. That was because the Unha revelations were made by another unpublicized equipment failure in the February 2016 launch of a three stage Unha rocket. At the time this was described as part of the North Korean space program to put satellites into orbit.
The Unha equipment failure had to do with the explosive charges in the first and second stages (which fall back to earth largely intact). Many of these explosives did not go off. South Korea knew that tests of three stage ballistic missiles (that can be used to reach North America or put a satellite into orbit) provide the most recoverable parts. For years South Korea has been recovering many components of the large rockets because the first two stages fall back to earth in the ocean way offshore in international waters. This 2016 explosive bolt failure left a lot more components largely intact and as South Korean investigators sought to identify how (or where) they were manufactured. They discovered that many of the previously unidentifiable components (because of the self-destruct charges working) were made using more advanced manufacturing technology than what North Korea was supposed to have access to. Further digging revealed that the manufacturing equipment was of European origins but was exported to China, via a contract that clearly stated none of it was to be exported to North Korea. The UN investigators not only confirmed the South Korean allegations but were able to uncover even more details. The Chinese government was forced to admit that certain Chinese firms were defying Chinese sanctions and smuggling the technology and some of the needed software and raw materials to North Korea.
Before 2016 South Korean engineers concluded that the construction of the missile components retrieved appeared to be sloppy and there were some foreign components in the rocket but there was not enough recoverable evidence of anything more. Thus until 2016 the South Koreans concluded that the North Korean components and construction techniques were crude but effective, if not as reliable and efficient as Western or Russian designs. This is what Iran has done, on a larger scale (because of their oil wealth and access to more capable smuggling networks).
South Korean missile experts also concluded that physical evidence indicated North Korea had not developed any new ballistic missile technology, or even manufactured many new missile parts since at least 2012. That was when South Korea began to recover components of North Korea multi-stage ballistic missiles and examine them. By 2012 South Korea had developed technology and techniques to retrieve a lot of these components and have South Korean and foreign experts closely examine them. Initially South Korean engineers and scientists concluded that most of the components appear to have been made in North Korea. Moreover the longest range rockets were based on much older (1960s and 70s) technology and the design of the rocket engine was almost identical to one built in Iran. Many of the imported components of the missile were items that are not covered by sanctions, as they have many other industrial uses. The Iranian connection was long known as was North Korean access to older Russian rocket technology.
North Korea had carried out an impressive deception scheme that was largely undone by the failure of the self-destruct system for missile stages known to fall back into international waters where they could be recovered, even from great depths. This required someone willing to devote enough time, effort, technology and money to the effort. South Korea had all of those resources and was willing to share what they could with UN investigators who were now paying attention.
Another assist came from China getting angry at North Korea for defying demands that they cease their nuclear weapons program (which was also getting illegal foreign tech) and freely exploiting the corruption inside China. The Chinese government tended to leave Chinese companies alone if their illegal dealings were discreet and the firm was bringing new revenue to China. That has changed, at least for Chinese firms that left enough clues behind for foreign investigators to collect and put in front of senior Chinese officials.