Noel Vasquez / Getty Images

Ashton Kutcher, seen here at a Los Angeles Lakers basketball game in February, is the 500th customer to sign up for a Virgin Galactic suborbital spaceflight.

Virgin Galactic says uber-celebrity Ashton Kutcher is the company's 500th customer to sign up for a suborbital trip into outer space.

"I gave Ashton a quick call to congratulate and welcome him," Virgin Galactic's billionaire founder, Richard Branson, said today in a blog post announcing that Kutcher was coming on board. "He is as thrilled as we are at the prospect of being among the first to cross the final frontier (and back!) with us and to experience the magic of space for himself."

Kutcher, who got his start in television on "That '70s Show" and is now one of the stars of the highly rated sitcom "Two and a Half Men," is said to have a net worth of around $140 million. So the $200,000 fare for a ride on Virgin Galactic's SpaceShipTwo rocket plane, also known as the VSS Enterprise, shouldn't break the bank. He's as well-known for his online presence (with 9.8 million Twitter followers) and his gossip-column appeal (due to last year's breakup with Demi Moore) as he is for his filmography.

All this makes him arguably the highest-profile prospective spaceflier confirmed to be on Virgin Galactic's list — although Tom Hanks, Katy Perry, Brad Pitt and Angelina Jolie are reportedly on the list as well. Beyonce and Jay-Z are among other celebs considering a flight. The stars are reportedly all paying their own way, except for physicist Stephen Hawking, who is receiving a free ride courtesy of Branson.

For Stephen Attenborough, Virgin Galactic's commercial director, getting to the 500-passenger point is as big a milestone as getting Ashton Kutcher to sign on. "It's great to get to No. 500," he told me.

It's way too early to put Kutcher's flight on the calendar. SpaceShipTwo is still in the midst of free-glide flight tests, with rocket-powered test flights expected to begin this year. Last year, Branson said he was holding out hope that he and members of his family will be able to take a ride into space as this year's Christmas present. That suggests 2013 could mark the start of commercial service, although Virgin Galactic and its partners at California-based Scaled Composites say the schedule is totally dependent on the outcome of tests at the Mojave Air and Space Port.

The current plan calls for commercial flight operations to be based at Spaceport America in New Mexico. SpaceShipTwo, which is capable of carrying six passengers and two pilots, would be linked up to its wide-winged WhiteKnightTwo carrier airplane and brought up to an altitude of 50,000 feet. At that height, SpaceShipTwo would drop from its mothership and turn on its hybrid rocket engine. The blast would take the craft beyond 62 miles (100 kilometers), the internationally accepted boundary of outer space — a commanding height from which Kutcher and his fellow passengers could see the arc of planet Earth and the dark sky of space above.

There'd be a few minutes of weightlessness, and then the passengers would return to their seats for the descent. After weathering up to 6 G's of acceleration, the fliers would glide down to the landing — and get their astronaut wings back at Spaceport America.

Attenborough said Virgin Galactic is already giving a lot of thought to determining who would fly when. One of the factors in the formula would give priority to customers "roughly in the order that they signed up," he said, but the schedulers also would consider customer preferences and the possibility of achieving firsts in spaceflight (for example, ahem, first prime-time TV star in space). "We're expecting to be able to keep everyone happy," Attenborough told me. 

How long do you think it'll be before Kutcher is clicking his camera on the final frontier? And do you suppose there'll be a deal to document everything for reality TV? Feel free to weigh in with your comments below.

More about celebrity spaceflight:

• Fly Justin Bieber into space, scientist says
• Bunnies in jetpacks? It's Playboy Club in space!
• Director James Cameron targets spaceflight
• Celebrities in space?

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.