Three months after announcing plans to ground the aircraft, NASA has declared the stratospheric observatory of infrared astronomy (SOFIA) operational after 18 years in development.

The astronomical observatory mounted on a Boeing 747SP has been gathering data since 2010, but was officially still listed in a prolonged developmental phase.

A NASA review of the programme on 29 May allowed SOFIA to pass a key decision point that formally transitions the programme into operational status.

“That’s the equivalent of a launch for a space mission,” says Paul Hertz, NASA’s astrophysics division director, in a statement released by the agency.

NASA also completed commissioning tests for the fifth instrument onboard SOFIA – the field-imaging far-infrared line spectrometer – in April. Commissioining flights for a sixth instrument – the echelon-cross echelle spectrograph – began afterward.

The main instrument onboard SOFIA is a 19t telescope that emerges from a cargo door that retracts into the cabin during flight. Problems installing the telescope and the door delayed the programme’s first flight from 2004 to 2010.

After years of delay and cost overruns, the programme is starting to gain operational momentum. SOFIA completed 14 flights and accumulated 100 science mission hours over a 30-day period from April to May.

The agency’s progress, however, may be coming too late. In March, the Obama Administration released a budget request for Fiscal 2015 that effectively ground SOFIA unless international partners, such as Germany, contribute more funding.

Appropriators in the House of Representatives voted to restore partial funding for the programme, but SOFIA’s future remains uncertain until a budget is passed later this year.