Artemis II astronauts attend a call with Canadian children inside the spacecraft on Thursday on their way to the Moon.

HOUSTON — Now more than halfway to the moon, the Artemis II astronauts prepared for their historic lunar mission to push deeper into space than the Apollo astronauts.

The downside is their toilet is on the blink again.

The three US and one Canadian astronauts are set to reach their destination on Monday. It is the first moon-bound crew in more than 53 years, picking up where NASA's Apollo program left off.

The mission control has instructed the astronauts to break out more of the backup urine collection bags. The "lunar loo" malfunctioned following Wednesday's liftoff and has been hit-and-miss ever since.

Engineers suspect ice may be blocking the line that is preventing urine from completely flushing overboard.

John Honeycutt, chair of the mission management team, said it is human nature to be interested in the space commode, and even though it is "in a good state right now", he'd like it to be working at 100 percent.

"They're OK," he said of the astronauts. "They trained to manage through the situation."

Artemis II is poised to set a distance record for humans, traveling more than 400,000 kilometers from Earth before hanging a U-turn behind the moon and heading home without stopping or entering lunar orbit. The record is currently held by Apollo 13.

The Canadian Space Agency celebrated the country's role in the mission, speaking from Quebec with astronaut Jeremy Hansen as he headed toward his lunar rendezvous. Hansen is the first non-US citizen to fly to the moon.

Hansen, Victor Glover, Reid Wiseman and Christina Koch are the world's first lunar astronauts since Apollo 17's crew of three in 1972. Koch and Glover are the first female and first black astronauts to the moon, respectively.

Their nearly 10-day mission — ending with a Pacific splashdown on April 10 — is the first step in NASA's bold plans for a sustainable moon base. The space agency is aiming for a landing by two astronauts near the lunar south pole in 2028.