On September 3, 2006, the European Space Agency’s SMART-1 spacecraft intentionally crashed into the moon as part of its mission objectives. SMART-1 was launched in 2003 and marked a milestone as the first European spacecraft to reach the moon. It was also the first mission under the Small Missions for Advanced Research in Technology program, which aimed to develop and test new spaceflight technologies using cost-effective spacecraft. The primary goal of SMART-1 was to demonstrate Solar Electric Primary Propulsion, a type of solar-powered electric engine. During its nearly two-year orbit around the moon, SMART-1 mapped the lunar surface, analyzed the moon’s mineral composition, and searched for signs of water ice. These efforts aimed to contribute to a better understanding of the moon’s geological history and origins. Originally scheduled to crash into the moon in September 2005, SMART-1’s mission was extended through a series of engine maneuvers. One maneuver that used up the spacecraft’s xenon fuel supply extended its operational life by several more weeks. On September 3, 2006, the moon’s gravity pulled SMART-1 out of orbit, and it crashed into the moon at a relatively slow speed of 4,473 mph (7,200 kph) in a region called the "Lake of Excellence." The impact was observed from Earth, with telescopes capturing the flash of the collision. It wasn’t until 2017 that NASA’s Lunar Reconnaissance Orbiter was able to spot the crater created by SMART-1’s impact. The spacecraft left behind a crater just over 13 feet (4 meters) wide and a gouge more than 65 feet (20 meters) long. The mission demonstrated the effectiveness of the solar electric ion engine, which used xenon gas as a propellant. At the time, SMART-1 was only the second spacecraft to test this technology, following NASA’s Deep Space 1. The European Space Agency hoped this mission would pave the way for more cost-effective and fuel-efficient exploration of the solar system. Today, September 3, 2026, marks a significant milestone as the BepiColombo mission to Mercury, a joint project between the European Space Agency and Japan, begins its arrival phase. The mission is releasing the combined orbiter ahead of entering Mercury’s orbit. The Mercury Transfer Module that carried the probes used a solar electric xenon propulsion system, similar to the one tested on SMART-1. This propulsion technology has also been used in other NASA missions, including the Psyche asteroid spacecraft, the Dawn asteroid mission, and the DART asteroid impact mission.