Just how high can you get for $200,000? If you pony up the money to the good folks at Virgin Galactic, you'll reach an altitude of approximately 68 miles (110 kilometers) above the surface of the Earth.

That's 6.2 miles (10 kilometers) above a boundary known as the Kármán line, where by most definitions the atmosphere ends and outer space begins.

These dizzying, suborbital heights have typically remained the domain of experimental aircraft such as NASA's X-15, which only ascended beyond the Kármán line twice. Virgin Galactic, however, plans to offer regular flights there aboard SpaceShipTwo.

“The vehicles have been designed to go a little bit higher than that," says Stephen Attenborough, commercial director for Virgin Galactic. “We may at some point be able to offer a slightly increased altitude or higher apogee for the flight, but the physics will tell you that the higher you go, the higher the g-forces are going to be on the way up and the way down."

In other words, approximately 68 miles is a perfect cruising altitude not only because it places SpaceShipTwo firmly in space, but also because going any higher would make the flight too rigorous for some prospective passengers.

After all, one of Virgin Galactic's core goals is to make spaceflight as inclusive as possible, despite reaching speeds of nearly four times the speed of sound. So far training exercises indicate that 93 percent of humans between the ages of 22 and 88 are fit enough to enjoy the ride.

And what a ride it's going to be.

What to Expect

So let's say you've purchased your golden ticket to space aboard SpaceShipTwo. What sort of experience can you expect? While it's easy to discount the whole venture as a pricey plane ride with a cool view, Virgin Galactic talks it up as a great deal more.

“We describe the whole experience as sensory overload," says Attenborough, “because each stage has its own dynamics that are very likely to be a great deal more intense than anything our passengers will ever have experienced before."

After two days of g-force and safety training, passengers will board SpaceShipTwo for the grand ascent. The jet-powered, all carbon composite Mothership WhiteKnightTwo will provide all the power for the first hour-long leg of the trip, hauling SpaceShipTwo up to an altitude of 50,000 feet (15 kilometers) like a turtle in an eagle's talons. At this point WhiteKnightTwo will release the spacecraft, allowing it to glide along serenely before igniting its powerful hybrid rocket engine.

“The environment inside the spacecraft changes pretty dramatically at that point, and you experience some very rapid acceleration," Attenborough says. “You accelerate close to four times the speed of sound, and that's going to happen in a relatively short period of time. You're talking about half a minute or so."

This is where the g-forces come into play, hitting passengers with a force that's three-and-a-half times greater than the pull of gravity on Earth. While quite a thrilling experience, most people should be able to cope with the stress quite comfortably.

Then things start getting cosmic. The view through SpaceShipTwo's large windows shifts from sky to starscape, and the profile of the planet comes into sharp contrast with the void. Then the engine cuts out, silence fills the cabin and the 3.5 g-force pull gives way to microgravity

“At that point passengers will get to leave their seats almost immediately and enjoy a few minutes of the weightless experience," Attenborough says. “We have a nice big cabin that's been deliberately designed to maximize the amount of space available, so people can float around and also enjoy the spectacular view.

SpaceShipTwo's windows are approximately twice the size of a normal commercial aviation window, but just how amazing will the view really be?

“We think it will be actually something of a transformative experience," says Virgin Galactic CEO George Whitesides. “Once the engine shuts off, the cabin will be devoid of any mechanical noise from the inside and any atmospheric sound from the outside, so people will be able to make a deep and organic connection with the universe and the planet. It should be an extraordinary moment."

When will flights begin?

Any discussion of Virgin Galactic inevitably comes back around to this question. The company tries to avoid such estimates, however, for a simple reason: When venturing into the intrinsically dangerous environment of space, safety comes first.

“We've had a philosophy from day one to choose the safest prototype technology and build the safest vehicle possible," Attenborough says. “The only way you can do that is by having a test flight program that is exhaustive and not constrained by time."

WhiteKnightTwo and SpaceShipTwo are already airborne, and Virgin Galactic expects the spaceship to take its first solo glide test fall 2010. If all goes well, subsequent tests will expand the envelope further and further toward FAA licensing and commercial operations.

“So we've been working on this project for over 5 years and I think we can now realistically say we're on the final stretch," Attenborough says, “but exactly how long that final stretch will be is still an unknown."

Image: SpaceShipTwo detached from WhiteKnightTwo in this artist's impression (Virgin Galactic)