The incident occurred in 1976 and is considered one of the most mysterious in the history of Black Mesa.
At 8:00 local time, testing of a new prototype air-to-air missile was scheduled to begin at Site Sigma on Beta Summit. However, scientists were moved experiment an hour later due to some problems.
According to the official version, the missile that was tested had too high values on the internal thermal imager. Therefore, it deviated from its course and exploded right near Beta Summit, trying to catch up with one of the satellites launched next to it.
The result was the destruction of Beta Summit almost to the ground and the death of most of the scientific personnel. Following the incident, the area was quarantined and closed to outsiders.