(FOX NEWS) — The Artemis II crew will experience a grueling return home once they re-enter Earth’s atmosphere, a former NASA astronaut said.

Col. Jeff Williams said the parachute sequence will be “pretty violent” until the main chutes open and the four astronauts splash down in the Pacific Ocean on Friday evening.

“I can tell you from my experience, that’s the longest… let’s say, minutes of your life—getting to that parachute opening,” Williams told “America Reports.”

The buildup of g-force will put immense pressure on the crew as they descend toward Earth, he said.

“You’re weightless until you enter the upper parts of the atmosphere, and then you start feeling just a little bit of an acceleration,” said Williams. “If you drop your pencil, instead of floating in front of you, it’ll start falling slowly, and then quicker and quicker. Then it builds up to those four Gs… so if you weigh 200 pounds, you feel like 800 pounds.”