Orbital Sciences Corp.'s Antares rocket lifts off at Wallops Island, Va., in April of last year. The Antares uses a pair of Russian-made NK-33 rocket engines that Moscow says it will stop supplying for military launches. Steve Helber/AP hide caption

itoggle caption Steve Helber/AP

This artist's illustration shows what NuSTAR should look like in orbit after its 30-foot-long mast deployed. JPL-Caltech/NASA hide caption

itoggle caption JPL-Caltech/NASA