Sofia, the historic plane-borne telescope, lands for the last time

Sofia, the historic plane-borne telescope, lands for the last time

In the past eight years, a modified Boeing 747 made hundreds of flights on a single mission: to carry a 19-tonne, 2.5-meter telescope known as the Sofia, or Stratospheric Observatory for Infrared Astronomy . Flying a telescope on a jumbo jet offered a way to scan the sky at wavelengths that could not be seen from the ground, but the ticket was expensive. So yesterday, NASA and the German space agency grounded the mission. Its final flight landed early Thursday morning at NASA’s Armstrong Flight Research Center in the desert near Los Angeles.

Sofia was an innovative way to contemplate the infrared universe. Infrared light is essentially thermal radiation, but astronomers can’t probe cosmic objects like stars and dust-covered galaxies without water vapor in Earth’s atmosphere absorbing this light. This confuses attempts to observe these objects with telescopes built on top of mountains, such as observatories in Hawaii and Chile. But by hovering through the stratosphere, at an altitude of 40,000 feet or more, Sofia could fly above that water vapor and get a much better view.

“Nearly 50% of the energy in the universe comes out in the mid to far infrared. Sofia has played an important and unique role in her lifetime, probing this whole range of wavelengths, and we have been able to observe all kinds of phenomena that were otherwise invisible to other installations,” says Jim De Buizer, Sofia Senior Scientist at NASA Ames. Research Center in Mountain View, California.

De Buizer and Sofia’s team made a number of important astronomical discoveries, including measuring the cosmic magnetic fields permeating nearby galaxies, mapping the growth of massive stars, observing Pluto’s faint shadow when it passed in front of a distant star and even the discovery of water on the sunlit surface of the moon’s southern hemisphere. Data from Sofia’s latest flight will map stellar nebulae and help scientists study the magnetic fields of the starburst Sculptor galaxy.

But while flying a telescope in a jet is much cheaper than launching one aboard a spacecraft, like NASA’s Spitzer and Webb space telescopes and the European Space Agency’s Herschel space observatory, it’s still not cheap. There are costs for pilots, staff, engineers and mechanics, plus a series of repairs to the plane that had to be carried out in 2018. Sofia costs NASA around $85 million a year, a fraction important part of its astrophysical budget. And that’s actually only 80% 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 brought Sofia down.

“In the end, the project itself just wasn’t productive. You’re talking almost a Hubble cost to operations, but at a fraction of the science productivity,” says Casey Dreier, senior space policy adviser for the Planetary Society, a nonprofit research organization based in Pasadena, Calif.

It wasn’t the first time his budget had been questioned. In 2014, following debates over budget constraints and austerity measures, the Obama administration threatened to cut funding for Sofia, just 11 days after the telescope and plane went into service. But the US Congress chose to continue funding it. In 2019, after Sofia completed its primary mission, advancing projects that studied infrared nebulae, stars, and galaxies, Congress extended the project for three years, with the possibility of further extensions. Citing budget concerns, NASA proposed canceling the program in fiscal year 2021 and again each of the following two years. (Fiscal year 2023 begins tomorrow.)

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