COLORADO SPRINGS — Volunteers dressed in Christmas hats and military uniforms are taking calls from children around the world who want to know when Santa will be coming.

NORAD Tracks Santa, based at Colorado’s Peterson Air Force Base, says it uses infrared sensors from Rudolph’s nose to determine Santa’s location Monday and let callers know when they need to get to bed.

Canadian astronaut David Saint-Jacques tweeted that he is helping track Santa from the International Space Station.

The military says the program isn’t affected by the U.S. government shutdown since it is run by volunteers and funded by a previously approved defense budget.

The holiday tradition, now in its 63rd year, began after a child mistakenly called a Colorado command that monitored for signs of a nuclear attack, asking to speak to Santa.