Space tourism: Hundreds have already booked their tickets and begun training for a spectacular voyage

Glenn King is the director of spaceflight training at the National Aerospace Training and Research Center, a private company based in Pennsylvania which has already trained nearly 400 future Virgin Galactic passengers for their trips. The training program lasts two days which involves putting the trainee in a single-seat cockpit at the end of a 25-foot-long (eight-meter-long) arm and spinning them around to simulate gravitational force, or G force.

Some 600 people have booked flights on Virgin Galactic, the company owned by British billionaire Richard Branson (in pic), and thousands more are on a waiting list. The cost per flight? $200,000 to $250,000. Virgin Galactic hopes to take its first private astronaut on a suborbital flight in early 2022, with eventual plans for 400 trips a year. Blue Origin, owned by Amazon's Jeff Bezos, has not yet published prices or a calendar.

The US Federal Aviation Administration, which oversees the aviation industry, recommended in 2006 that future "commercial passengers" on suborbital flights fill out a "simple medical history questionnaire." Orbital flights which go further and last longer would require a more detailed form and blood tests, X-rays and urine specimens.

Orbital flights, which cost millions of dollars each, are envisioned by SpaceX, the company founded by billionaire Elon Musk, which has at least four planned over the coming years. The first launch of only civilians, baptized "Inspiration4," is scheduled to take place in September. The American billionaire Jared Isaacman has fully paid for a trip powered by a SpaceX Falcon 9 rocket that will take him and three passengers on a three-day flight in low Earth orbit.

In January 2022, the company Axiom Space plans to send a former astronaut and three newcomers to the International Space Station. It eventually plans trips to the ISS every six months. Seven "space tourists" visited the space station between 2001 and 2009.

A company called Space Adventures has partnered with SpaceX to send four customers in orbit around the Earth next year. A Japanese billionaire, Yusaku Maezawa (in pic), has reserved a flight on SpaceX's "Starship" in 2023 and is inviting eight other people to come along for the ride.

Difficult to say, said Robert Goehlich, an adjunct assistant professor at Embry-Riddle Aeronautical University Worldwide. "A new investor might accelerate any schedule," he said, "while an accident might decelerate any planning." Three major factors will need to come together: flights will have to be safe, profitable and environmentally friendly.