NASA's Voyager 1 and Voyager 2, launched in 1977, hold the distinction of being the oldest and most distant spacecraft still operational. These probes have uniquely transcended the boundaries of our solar system, marking a significant milestone in space exploration.

The original mission of the Voyager probes was to conduct a comprehensive survey of the outer planets, completing the ambitious Planetary Grand Tour. They successfully captured stunning images and collected valuable data about Jupiter, Saturn, Uranus, and Neptune, significantly enhancing our understanding of these celestial bodies.

Voyager 2, in particular, provided the first and only close-up observations of the icy giants, while Voyager 1 focused on Titan, Saturn's largest moon, revealing much about this enigmatic satellite.

After their primary planetary missions concluded, the Voyagers transitioned into a new phase of exploration. Having achieved escape velocity, both probes ventured into interstellar space--Voyager 1 in 2012 and Voyager 2 in 2018. This transition was marked by a notable shift in the data received, indicating a diminishing influence from the solar environment and an increasing interaction with the surrounding galactic medium.

Each Voyager spacecraft is equipped with Golden Records, which contain sounds and images meant to portray Earth's diversity and culture to any potential extraterrestrial life that may encounter them.

The longevity of the Voyager probes is primarily attributed to their nuclear power sources. While many space missions rely on solar panels, which become ineffective at greater distances from the sun, the Voyagers utilize radioisotope thermoelectric generators (RTGs) that generate power internally. Each RTG comprises plutonium-238, an isotope that decays over time, producing heat that is converted into electricity.

However, as the plutonium depletes, the energy output of the RTGs diminishes, signaling the gradual end of the probes' operational capabilities. Typically, these nuclear power systems have a maximum effective lifespan of about 60 years.

To preserve the remaining energy, NASA's mission team has begun to deactivate some instruments aboard the probes. For instance, Voyager 2's plasma science instrument was powered down recently to conserve energy, following a similar fate for Voyager 1's instrument in 2007 due to a malfunction. Currently, four instruments remain operational, including a magnetometer, which continues to gather data on the interstellar environment, such as cosmic rays and magnetic fields.

As the years progress, the depletion of energy resources will inevitably lead to the cessation of all probe functionalities. Although it is difficult to predict the exact timeline, both spacecraft are expected to reach this critical point within the next decade.

The Voyager missions have not only expanded our knowledge of the solar system but have also laid the groundwork for future interplanetary explorations. The data collected by these pioneering probes continues to influence and inspire subsequent missions aimed at further unraveling the mysteries of our universe.