Over the past eight years, a modified Boeing 747 jetliner has flown hundreds of flights on a unique mission: carrying a 19-ton telescope known as Sofia, or the Stratospheric Observatory for Infrared Astronomy. Flying a telescope on a jumbo jet offered a way to peer into the heavens at wavelengths that could not be glimpsed from the ground. Sofia was an innovative way to gaze at the infrared universe. Infrared light is essentially heat radiation, but astronomers can't probe cosmic objects like dust-enshrouded stars and galaxies without the water vapour in Earth's atmosphere absorbing that light. That confounds attempts to observe those objects with telescopes built on mountaintops, like the observatories in Hawaii and Chile. But by soaring through the stratosphere, at an elevation of 40,000 feet or higher, Sofia could fly above that water vapour and get a much better view. The Sofia team have made a number of significant astronomical discoveries, including measuring cosmic magnetic fields permeating nearby galaxies, charting the growth of massive stars, and even discovering water on the sunlit surface of the moon's Southern Hemisphere. The data from Sofia's final flight will map stellar nebulas and help scientists study the magnetic fields of the Sculptor starburst galaxy. But while flying a telescope in a jet is much less expensive than launching one aboard a spacecraft, it's still not cheap. There are costs for the pilots, staff, engineers, and mechanics — plus a round of repairs to the aircraft that had to be made in 2018. Sofia costs NASA about $85 million per year, and that's actually only 80 percent of the funding it needs: NASA's German counterparts provided the rest. It was ultimately the mission's high operating costs, relative to its scientific output, that took Sofia down.