Costly telescope-on-a-plane finally faces termination after years of problems

NASA and Germany’s space agency are permanently shutting down the Stratospheric Observatory for Infrared Astronomy (SOFIA), a telescope-on-a-plane that has been scrutinized for years for its high cost and low scientific output. Since 2014 the observatory has flown above the water vapour in Earth’s atmosphere to get an unobscured view of celestial objects and to gather data at infrared wavelengths.

Over the past several years, SOFIA has measured magnetic fields in galaxies¹, spotted water on sunlit portions of the Moon² and detected the first type of ion that formed in the Universe, helium hydride³. But it costs NASA around US$85 million a year to operate, which is nearly as much as the operational expenses for the Hubble Space Telescope. On 28 April, NASA and the German Space Agency, the two partners in SOFIA, announced they would shutter the observatory by 30 September.

The observatory’s high pricetag, combined with its relatively low scientific output, earned it a low ranking in the most recent decadal survey of the future of US astronomy and astrophysics. NASA cited the survey’s recommendation to shutter SOFIA — put forward by the astronomy community — in its decision. The observatory was originally meant to have a 20-year lifetime, but it will now be de-commissioned after only eight.

“It’s a very difficult decision, and certainly very painful for everyone who has worked on the mission,” says John O’Meara, chief scientist at the W. M. Keck Observatory in Kamuela, Hawaii, who has worked on long-term planning for US astronomy and astrophysics. But “it’s the right call”.

SOFIA costs more to run each year than many of NASA’s other astrophysics missions combined. The German Space Agency contributes another 20% in operating costs on top of NASA’s share. The observatory is expensive because it requires pilots and a staff to fly and fuel it.

‘Globally unique’

SOFIA is a Boeing 747 with a hole cut in its side to accommodate a 2.5-metre-wide, 17-tonne telescope, which peers out at the Universe as the plane flies at altitudes between about 11 and 14 kilometres. It has made approximately 800 science flights since it became operational in 2014. And it flies primarily from its home base in Palmdale, California, although it has also deployed to locations including Germany, Chile, and New Zealand — the latter to observe celestial objects that are visible only from the Southern Hemisphere.

SOFIA collects data that fill a gap between what is gathered by ground-based observatories and space-based infrared telescopes, such as the recently launched James Webb Space Telescope. It is the only observatory that can currently make observations at some far-infrared wavelengths. “SOFIA is globally unique,” said Walther Pelzer, head of the German Space Agency, in a statement announcing its closure.

Infrared observations allow SOFIA to make other unique observations, such as the detection of water on the sunlit Moon. “The shutdown is unfortunate for lunar science and exploration, as we have just begun mapping water on the Moon with SOFIA,” says Paul Lucey, a planetary scientist at the University of Hawaii at Manoa in Honolulu. “SOFIA’s capability is unique — there are no other observatories or spacecraft able to map the water molecule on the illuminated Moon.”

Under scrutiny

SOFIA’s scientific output has long been questioned. In 2019, five years after it began flying, a pair of NASA-commissioned reviews highlighted that the observatory had not resulted in large numbers of highly cited publications. In the first six years after starting operations, it produced 178 scientific papers, compared with more than 900 for Hubble over its first six years.

In response, SOFIA brought in a new director and ramped up its focus on scientific productivity. A December 2021 update on SOFIA’s website says that the observatory doubled its publications over the past three years, and that the decadal survey “placed SOFIA into a static box that misses the tremendous scientific growth SOFIA has experienced”.

Asked whether NASA had taken recent developments into account when making its decision, agency spokeswoman Alise Fisher pointed to the decadal survey, which states that it “found no evidence that SOFIA could, in fact, transition to a significantly more productive future”.

Charles Woodward, an astronomer at the University of Minnesota in Minneapolis, says that SOFIA’s closure has led to a feeling of “melancholy” among infrared astronomers, given that its productivity had been recently rising. “A significant portion of the community will think that SOFIA got the short end of the stick,” he says.

In recent years, several budget requests from US presidents have recommended terminating SOFIA. In all cases, Congress — usually led by House of Representatives minority leader Kevin McCarthy, who represents a district near Palmdale — provided funds to keep it going. The new decision might render Congressional wishes moot.

Between now and 30 September, SOFIA is scheduled to make its final observations, possibly including a deployment to New Zealand. NASA and the German Space Agency will then decommission the aeroplane.