Two NASA astronauts and an Italian flight engineer are sheltering in the space station’s Russian segment as mission control analyzes a possible leak of toxic ammonia coolant aboard the complex.

NASA and Boeing managers have again decided to extend the Starliner crew capsule’s stay at the International Space Station, passing up a June 26 re-entry to allow more time for analysis and testing to make sure helium leaks and thruster failures are fully understood, officials said late Friday.

The revised Atlas 5 rocket firing order includes two national security missions this summer before launching NASA’s daring asteroid sampler mission in September as originally planned.