NASA’s Science Mission Directorate is canceling the over-budget Gravity and Extreme Magnetism Small Explorer (GEMS) astrophysics mission, following the denial this week of an appeal from the Goddard Space Flight Center-led science team, the agency announced June 7.

Congress is being formally notified that the 2009 mission selection, capped at $119 million, not counting launch costs, is being canceled, says Paul Hertz, NASA’s astrophysics division director.

The decision followed an agency confirmation review decision to cancel GEMS, and the appeal confirming the project faces a 50% chance of exceeding the cap by $24-36 million, or 20-30%.

“One of the major contributors was the technology development in maturing the instrument technology so it would be ready for spaceflight,” Hertz said during a press briefing. “It has been more difficult and taken longer than originally estimated. That delayed their ability to get started on the rest of the planning and stretched out their schedule, resulting in cost growth.”

GEMS, which was targeted for a November 2014 launch, was intended to study the origin of polarized X-ray emissions in the strong magnetic fields around black holes, neutron stars and supernova remnants. Some of the nine-month mission’s scientific objectives will be picked up by NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, a mission scheduled for launch from the Marshall Islands aboard a Pegasus XL rocket on June 13.

Other objectives may be picked up by NASA’s contribution to Japan’s  Astro-H mission, which is also scheduled for a 2014 launch. In addition, the agency’s astrophysics division plans the selection of new Small Explorer missions next spring.

When NASA sought Small Explorer mission proposals in 2007, GEMS was to be capped at $105 million. The cap growth tracked inflation.

So far, the agency has committed $50 million to the project, including an estimated $13 million in closeout costs. Orbital Sciences Corp. had been selected for spacecraft design, fabrication and testing. Goddard was leading project management as well as providing the primary instrumentation — a dual telescope X-ray polarimeter. Though a launch vehicle has not been procured, the likely choice was in the Pegasus class, according to budget documentation.

The allocation of closeout expenses had not been determined, but Orbital Sciences does not appear to be the primary recipient, Hertz says.