The Compton Gamma Ray Observatory, with a mass of nearly seventeen tons, was the most massive space telescope ever launched. This meant that, when its orbit degraded and it re-entered the atmosphere, large pieces of metal were likely to survive and crash-land onto Earth’s surface. When the CGRO’s orbital navigation and control systems began to degrade, NASA officials decided it was too risky to lose complete control of where the pieces might land. On June 4, 2000, CGRO was steered carefully into the atmosphere and successfully de-orbited over the South Pacific, where the pieces fell harmlessly into the ocean.