Katy Perry Seen Rehearsing for 'Lifetimes' Tour in Sneak Peek Video

Katy Perry's getting ready to take her fans through a series of lifetimes ... 'cause she's rehearsing for her upcoming tour -- and, TMZ has exclusive video of the practice.

The singer-songwriter -- who is set to embark on her "Lifetimes" Tour later this month -- spent the first couple weeks of April rehearsing for the concert series ... using an arena in Ontario, California to get ready.

We're told Katy was very nice and professional with the staff who work at the arena ... and, check out the clip for yourself -- tons of futuristic lights and a huge infinity symbol literally taking center stage.

It's hard to see exactly what's happening ... but, it looks like Katy and her backup dancers are walking the length of the symbol -- a huge spotlight following them along as they go.

Worth noting ... all these videos were taken before Katy went to space -- when she revealed a setlist written on the back of a butterfly-shaped piece of paper to the camera.

Many online have been clowning Katy and the rest of the all-female Blue Origin flight for their trip to space ... especially a moment after they touched back down to Earth when Katy literally got down on her knees and smooched the ground -- after just 11 minutes in the air.