An Air Force satellite used for highly protected communications has survived 39 days of extreme temperatures, keeping it on track for a 2019 launch.

That news come from Lockheed Martin, the prime contractor on the Air Force’s $15 billion Advanced Extremely High Frequency program.

The fifth satellite in the current generation, known as AEHF-5, passed Thermal Vacuum Chamber (TVAC) testing, used to recreate the conditions the satellite will operate under in space. The satellite also completed acoustic testing that simulates the vibrations caused by high intensity, low frequency sound waves experienced during rocket propulsion.

“TVAC and acoustic tests are critical milestones in the production cycle of a satellite, where we have one shot to get it right, so we take every precaution to ensure the vehicle is ready for the harsh space environment,” said Michael Cacheiro, Lockheed’s vice president for protected communications said in a May 21 statement. “The team and the satellite performed flawlessly, and AEHF-5 is now in system level testing.”

AEHF satellites are critical to the United States and its international allies, such as Canada and the United Kingdom. The jam-resistant system provides global, survivable and protected communication between strategic commanders and tactical warfighters operating in all domains.

Lockheed Martin is currently under contract to deliver six AEHF satellites. AEHF-4 is set to launch on a United Launch Alliance Atlas V from Cape Canaveral later this year.

AEHF-4 will complete the minimum constellation of satellites needed to bring global Extended Data Rate (XDR) connectivity online. According to Cachiero, XDR provides roughly 10 times more communications throughput than the Air Force’s legacy satellite systems.