New Delhi, July 3 -- WASHINGTON - NASA's third attempt to launch the robotic spacecraft that would push its Neil Gehrels Swift Observatory to a higher orbit ended on the ground Thursday when engineers detected an anomaly with the Pegasus XL rocket, the last of its kind, that had been set to carry the rescue vehicle into orbit from Kwajalein Atoll in the Marshall Islands.

NASA's mission to rescue the Neil Gehrels Swift Observatory from orbital decay has been postponed three consecutive times since late June, twice for weather and on Thursday for what the agency described only as a "launch vehicle issue." No new attempt date has been announced. Teams are reviewing data from Thursday's aborted countdown before committing to another.

The se...