“We didn’t design them to last 30 years or 40 years, we designed them not to fail,” John Casani, Voyager project manager from 1975 to 1977, says in a NASA statement.
In 2012, Voyager 1 became the first spacecraft to cross out of the heliosphere—a sort of bubble surrounding the solar system filled with the solar magnetic field and solar wind—making it the first spacecraft to enter interstellar space. Voyager 2 reached the cosmic milestone six years later.