How do nuclear-capable countries know if a rocket is an attack — or just something scientific?
Answer: The country firing the rocket is supposed to tell everyone that it is just science, not war.
In 1995, Norway did just that. They told everyone they were sending a rocket to explore the Northern Lights. One problem: The radar technicians in the newly formed Russia Federation (the Soviet Union having collapsed in 1991) didn't get the message. According to the Smithsonian Magazine, one night those technicians detected a fast rocket traveling 903 miles high, flying toward the Russian border.
Russian submarines were put on alert and the Russian President was notified. The Russian nuclear briefcase, holding the launch codes, was activated, the only known time that has occurred.
Fortunately, Russian President Boris Yeltsin concluded that, 10 minutes into its flight, the rocket was heading away from Russian airspace.
The entire incident was closed, along with the nuclear briefcase. American and Russian authorities then redesigned their notification and disclosure protocols.