The Gravity and Extreme Magnetism Small Explorer mission, or GEMS for short, was supposed to blast off in 2014 to study black holes and neutron stars. But external reviews found the project would likely come in considerably over budget.



GEMS was selected under a strict cost cap, NASA officials said, unlike the price-busting James Webb Space Telescope to be launched in 2018.



"That cost cap is a very important aspect of the development of the project," said Paul Hertz, director of NASA's astrophysics division. Webb "is different."



Billions over budget and years behind schedule, Webb is NASA's largest science project and considered the successor to Hubble Space Telescope. Both Webb and GEMS are managed by Goddard Space Flight Center in Greenbelt, Md.

Adjusted for inflation, GEMS was supposed to hold at $119 million, not counting the rocket, but independent reviews estimated the final cost at 20 percent to 30 percent above that, Hertz said.

Hertz said in a news conference that the technology needed for the instrument took longer to develop than expected, and that drove up the price.

It will cost NASA an estimated $13 million to close out the project, Hertz said. After adding in the money already spent on GEMS, the final tab for the space agency will be $50 million.

No rocket had yet been purchased for the mission, and the telescope itself had not yet been built.

A number of existing observatories can address some of GEMS' science questions, Hertz said, including the NuStar telescope due to lift off next week from Kwajalein Atoll in the Pacific.