The new science lab for China's space station is set for launch on Sunday.
The Long March 5B rocket is set to launch at approximately 2:22 EDT (0622 GMT) Sunday from the Wenchang Space Center in China's southernmost province of Hainan Island.
The launch will mark the eighth flight of the Long March 5 rocket, the most powerful launcher in China's inventory.
The Long March 5B launcher has a low-Earth orbit lift capacity of about 55,000 pounds or 25 metric tons.
The gantry arms on Long March 5B's 300-foot-tall (92-meter) launch pad tower will open in the final phase of the countdown.
clearing the way for the heavy-lifter to take off from Wenchang and head east into the South China Sea.
In the final seconds before liftoff, sparkers on Long March 5b's main stage will fire to burn off hydrogen gas that has accumulated during the countdown.