THIS DAY IN SPACE

End of Rosetta Mission
On September 30, 2016, the European Space Agency’s Rosetta mission came to an end as the spacecraft deliberately crash-landed on Comet 67P/Churyumov–Gerasimenko. After orbiting and studying the comet for over two years, Rosetta's final descent was a planned maneuver to obtain close-up data of the surface before losing power as the comet moved away from the Sun. Launched in 2004, Rosetta made history in 2014 when it became the first spacecraft to orbit a comet, and it also deployed the lander Philae, which achieved the first soft landing on a cometary surface. During its mission, Rosetta provided groundbreaking insights into the composition and behavior of comets, including the detection of organic molecules, analysis of water isotopes, and real-time observations of a comet's evolution as it approached the Sun. The mission significantly advanced our understanding of how comets may have delivered water and prebiotic compounds to Earth. Rosetta's legacy endures as one of the most ambitious and scientifically rich missions in the history of space exploration.

Launch of NASA’s Transit 4B Satellite
On September 30, 1961, NASA launched Transit 4B, the first satellite to carry and test a radioisotope thermoelectric generator (RTG) as a power source in space. Built for the U.S. Navy’s Transit navigation system—an early precursor to GPS—Transit 4B was a navigation satellite that helped refine satellite-based geolocation for submarines and other military assets. The onboard RTG, called SNAP-3B, used the heat from decaying radioactive material to generate electricity, proving that nuclear power could be used to operate spacecraft over long durations and in environments where solar panels were ineffective. This successful demonstration paved the way for the use of RTGs in many deep-space missions, including the Voyager probes, Galileo, Cassini, and most recently, the Mars Perseverance rover. Transit 4B also continued the development of space-based positioning systems, helping to improve the reliability and precision of navigation technology. Its contributions were critical in both energy solutions for space and the evolution of global satellite navigation.