Astronomers are bracing for bad budgetary news about SOFIA, a modified 747 jetliner equipped with a state-of-the-art infrared telescope.

The joint U.S.-German project is several years behind schedule and digging into its operations budget as it limps toward a debut science flight now targeted for mid-2008.

Officials with the project fear NASA’s forthcoming 2007 budget request, due to be released Feb. 6, will contain no money for SOFIA, which stands for the Stratospheric Observatory for Infrared Astronomy.

David Black, president of the Universities Space Research Association — the Columbia, Md.-based private nonprofit awarded the SOFIA prime contract in December 1996 — said in an interview that word had reached him that NASA intends to put the airborne observatory on the chopping block in the months ahead.

“We haven’t been told anything official, but we have heard the same rumor,” Black said.

Word of an impending SOFIA cut already had reached Capitol Hill the week of Jan. 9, where staffers said science-minded members would take a dim view of terminating a program so far along in its development.

At a Jan. 11 SOFIA presentation here at the American Astronomical Society’s annual meeting, there was no mention of the budget ax some believe NASA is poised to drop on the program. Instead, SOFIA officials from both NASA and the Universities Space Research Association gave the 100 or so astronomers in attendance a forward-looking presentation on the status of the observatory’s development and the science SOFIA would be capable of doing once in the air.

Eric Becklin, the SOFIA chief scientist at the Universities Space Research Association, said during his presentation that SOFIA is 90 percent complete and on track to begin flight tests this autumn. The current schedule calls for installing SOFIA’s retractable door in 2007 followed by additional flight tests that would lead to the first science flights in 2008.

SOFIA was supposed to have been flying by now, taking astronomers and teachers up to the stratosphere several times a week to make observations of the infrared universe with the plane’s onboard 2.5-meter telescope and a changing suite of instruments.

Today, the modified Boeing 747 is still in Waco, Texas , its German-built telescope onboard but still awaiting instruments and other components, including a retractable door that will open once SOFIA is cruising at 14 kilometers — an altitude, SOFIA officials say, that puts the observatory above 99 percent of the water vapor in the Earth’s atmosphere that might obscure an instruments view of the stars.

SOFIA would be based out of NASA’s Ames Research Center in Moffett Field, Calif., where a hangar already has been modified to accommodate the aircraft. SOFIA also would conduct some flights in Germany, which is paying for about 20 percent of the project. The German space agency, DLR, built SOFIA’s 2.5-meter infrared telescope and has at least two instruments for the observatory in development.

NASA officials would not comment on what the future might hold in store for SOFIA. In written responses to questions submitted by Space News, NASA spokeswoman Erica Hupp said SOFIA’s original first science flight was to have occurred in October 2001. She said the schedule slips and cost growth in the development effort have been covered out of the program’s operations budget for the past four years. An independent program review planned for April, according to Hupp, will examine what NASA would have to spend to complete SOFIA and operate the flying observatory.

Congress approved a $48.3 million budget for SOFIA for 2006, Hupp said, noting that NASA has yet to send Congress an operating plan that details what NASA actually intends to spend on any given program or project this year.

Hupp could not say what NASA has spent to date on SOFIA, saying that an up-to-date cost estimate “has not been completed nor reviewed” by the agency’s Science Mission Directorate, which oversees the project.

One NASA SOFIA official said the agency has spent roughly $400 million on SOFIA.

Black said the U.S. contractor team has received and spent about $330 million. DLR, by Black’s estimate, has spent at least $100 million on the project.

Black acknowledged that SOFIA’s schedule has slipped as the program wrestled with telescope problems that have since been resolved and additional safety requirements imposed by NASA and the Federal Aviation Administration. Black said SOFIA’s technical hurdles have been cleared and the program’s problems today are entirely budgetary.

He said NASA “flatlined” the SOFIA budget a couple years ago, giving the project no choice but to slow down its march to completion.

For example, Black said delivery of a key component of SOFIA’s retractable door will not occur until mid-2007, because the program’s funding profile will not permit an earlier delivery.

He said additional money — perhaps $18 million in 2006 and $10 million in 2007 — could help the SOFIA program begin science flights perhaps six or seven months earlier than the July 2008 date team members have marked on their calendars.

Even if SOFIA were to achieve first light in January 2008, that still might be too late to achieve much overlap with NASA’s Spitzer Space Telescope, the infrared observatory launched in August 2003 on a nominal five-year mission. SOFIA’s capabilities are seen as complimentary to Spitzer’s and astronomers would like to have both telescopes in service at the same time. Recent projections show that the cryogen the Spitzer telescope relies on to cool its infrared sensors will be depleted sometime in 2008, causing the telescope to lose sensitivity, though not stop working.

About two years after SOFIA is slated to make its first science flight, the European Space Agency is due to launch the Herschel Space Observatory, a far-infrared space telescope built with NASA involvement.

Xander Tielens, the SOFIA project scientist at NASA Ames, said SOFIA’s wavelength coverage is unique, meaning no planned or existing infrared telescope will completely duplicate its capabilities.

A November 2004 Independent Science Operations Review ordered by NASA concluded that SOFIA is capable of achieving the type of “fundamental scientific impact that is usually associated with Great Observatories” at a fraction of what it costs to operate space telescopes like Hubble and the Chandra X-Ray Observatory. Still, the report also pointed out that delaying SOFIA’s first light beyond 2007 would come at the expense of some science objectives, by shortening the observatory’s overlap with Spitzer and putting it into competition for the astronomy community’s time, attention and resources as it gears up to start using Herschel come 2010.

Black said those two issues not withstanding, SOFIA is a valuable asset that promises to be performing valuable science long after Spitzer and Herschel are decommissioned. SOFIA is designed to operate 20 years with an evolving compliment of instruments.

“SOFIA will be the only game in town for the world’s far-infrared and sub-millimeter astronomers for the foreseeable future,” he said. “There are no other missions currently on the books that would fulfill that operation.”

Black predicted NASA could have a fight on its hands if it cuts a program as far along in development as SOFIA.

“If that is what comes out of the budget, I would be surprised if there wasn’t a substantial reaction from the astronomy community,” Black said. “If they are cutting SOFIA who knows what else is on the chopping block?”