The NASA Advanced Composition Explorer (ACE) has recently reached the venerable age of 15 in Earth's orbit. Launched on August 25, 1997, the spacecraft is scheduled to continue operations all the way through 2024.
ACE's main role is to measure potentially harmful radiations produced by the Sun, the solar system as a whole, and the Milky Way. It then relays its warnings to NASA, which distributes the data further.
The satellite launched aboard a Delta II delivery system. As it travels around the Sun, ACE constantly monitors space radiations. If a coronal mass ejection occurs, it can provide a warning up to 60 minutes in advance, which is enough for satellite and power grid operators to take protective actions.
Over the course of the mission, more than 140 science news items were released by the ACE Science Center, and in excess of 635 peer-reviewed papers published in respected journals.