NASA's ACE satellite still monitoring solar wind 29 years after launch
NASA launched the Advanced Composition Explorer on August 25, 1997, to study energetic particles and the solar wind from the L1 Lagrange point. The spacecraft provides continuous space weather data, helping forecast geomagnetic storms that can affect satellites and power grids. After nearly three decades, ACE remains one of NASA's oldest operational sun-monitoring missions.
ACE was delivered to space aboard a Delta II rocket from Kennedy Space Center, then spent roughly three and a half months traveling to the L1 Lagrange point, a gravitational balance zone between Earth and the sun. Its nine primary instruments were 10 to 10,000 times more sensitive than any sensors previously flown in space.
The spacecraft provides continuous, round-the-clock monitoring of solar wind and charged particles, including galactic cosmic rays and interstellar material. Only one instrument, the Solar Energetic Particle Ionic Charge Analyzer, has failed since launch, ceasing operations in 2005. ACE remains operational alongside SOHO, which launched two years earlier in 1995, placing both among NASA's oldest active sun-watching missions.
ACE's remarkable longevity means society has come to depend on a spacecraft designed for a five-year mission as a key early-warning system for space weather. The geomagnetic storm forecasts derived from its data could help protect satellites, power grids, and communications networks from disruption. As ACE ages, its eventual failure may create a monitoring gap, though newer spacecraft could potentially assume its role. The mission's extended service demonstrates how long-term scientific investments can yield decades of practical benefits.