So amateur cosmonaut Mark Shuttleworth has discovered during his first few days on humankind's most remote outpost, 250 miles above Earth's surface. The 28-year-old South African is the world's second "space tourist," and he blasted off from Russia on a ten-day mission last Thursday. However, Shuttleworth reports that backache isn't so bad when you get to see 15 sunrises and sunsets each day, as the space station cruises in its high-speed orbit around Earth.

How does one get to be an amateur cosmonaut? A few extra million dollars to spend is a good start. Shuttleworth spent eight months training in Star City, Russia, to prepare for the trip which is reportedly costing him $20 million. "I have always dreamed of space as a platform for inspiration, education, and technology, and am working to realize that dream for South Africa," he says. The young man made millions by selling his Internet security company, Thawte, in 1999; he's now spending a small portion of his fortune on the trip of a lifetime, something he's dreamed about since childhood.

While he bought his own ticket, Shuttleworth is not just sitting back and enjoying the ride. He is conducting many experiments during the voyage, giving South African scientists their first chance to work with data from a space traveler (cosmonaut or astronaut). And while some members of the press have denounced the experiments as a ploy to give Shuttleworth's mission an air of legitimacy it doesn't deserve (SpaceDaily.com calls it "an expensive science kit"), Shuttleworth insists that he and his collaborators have serious scientific objectives. Indeed, one of the experiments Shuttleworth is conducting is related to one of Africa's — and the world's — gravest problems: AIDS. During his time on the International Space Station, Shuttleworth will attempt to grow crystals of HIV virus proteins. It's hoped that the research will help South African scientists learn more about HIV and develop drugs to counteract its effects.

Shuttleworth is the second private citizen to pay for his own ticket to space. Last April, 60-year-old Dennis Tito paid $20 million for a eight-day trip; he had wanted to go to space ever since his days working as a NASA engineer. Both Shuttleworth's and Tito's trips were organized through a United States company called Space Adventures, which negotiated their contracts with Russian space agencies. Space Adventures calls itself "the world's leading space tourism company."

While NASA has questioned the wisdom of sending private citizens into space, the Russians see it as a way of keeping them in the space business when funds are low. They are planning to take the next space tourist aloft in October. Lance Bass of 'N Sync has applied for the ticket. If the 22-year-old Mr. Bass gets on board the Soyuz capsule in October, he'll be the first entertainer to go into space.

• If this talk of ejecting a member of 'N Sync into space has given you the space travel bug, you can get further information on taking a space tour of your own from Space Adventures.
• Update, May 1: CNN reports that Mark Shuttleworth says his trip is "worth every penny." Read an interview with Shuttleworth on the space station from CNN.com.

A commercial flight from New York to Los Angeles typically cruises 34,000 feet (about 6.5 miles) above Earth's surface. Passengers on the C-21 will climb almost ten times higher than that to an altitude of about 62 miles, right where the hazy blue of Earth's atmosphere dissolves into the inky blackness of space. And while the largest commercial jets carry about 500 passengers, the C-21 will have just two passengers aboard.

You may even be able to go for free — if you've got enough air miles. US Airways has joined forces with Space Adventures to enable passengers to use their frequent flyer miles to purchase tickets to space. (Or you can earn up to 250,000 miles by purchasing a ticket for a ride on the C-21.) "We are proud to have US Airways as Space Adventures' official domestic airline," said Eric Anderson, President and CEO of Space Adventures. "We look forward to taking their passengers farther and higher than they have ever gone before."

You'll have to wait a while before going farther and higher than ever before, though. So far, Space Adventures only has a life-size model of the C-21, which they unveiled last month. They expect that the first spacecraft will take passengers up in 2005. According to the company, one hundred eager would-be space travelers have already bought tickets for a ride on the spacecraft that hasn't yet been built.

• Find out more about using frequent flyer miles for a trip to space at USAirways.com.
• The C-21 will have a "parabolic" flight path — in other words, it will be in the shape of a parabola or large curve (picture the flight path of a football kicked high into the air). You can learn more about parabolas from Destination Math.

Sailing to Mars
Buzz Aldrin, the second man to walk on the Moon, is a long-time fan of space tourism. Aldrin climbed out of Apollo 11 hot on the heels of Neil Armstrong in 1969. Now, at the age of 72, Aldrin is working on a new project that could put more of his fellow humans in space — namely, on journeys to one of our most fascinating neighbors, Mars.

Aldrin is an engineer by training. Together with scientists from Purdue University, the Massachusetts Institute of Technology, and the University of Texas, Aldrin is designing spacecrafts that would perpetually cruise between Earth and Mars. These crafts, known as "cyclers," would ferry people and supplies between the two planets, enabling humans to colonize Mars — something that has long been dreamed about in science fiction. "Some day, people will be going to Mars on a regular basis," says team member James Longuski, a professor at Purdue. "Most people are convinced that we are going to do this; the only question is when."

The average distance between Mars and Earth is 48 million miles. To get a sense of just how far this is, try doing the following calculation:

• Given that there are 2,500 miles between New York and Los Angeles, how many times would you have to travel from NY to LA and back to cover the same distance?

It sounds like a trip that would require a lot of fuel. According to the engineers, the cyclers may have a natural, renewable "fuel" supply: from the gravitational forces of the Sun, the planets, and their moons.

As a spacecraft travels close to a planet, its flight path is bent, causing it to whip around the planet and significantly increasing its speed (it's as if the planet's gravity gives the passing spacecraft a kick into space). This is the "slingshot" trajectory that you may have seen in movies. It's not just science fiction: it might help us get to Mars with very little fuel on board, in a journey that would take as little as six to eight months.

When the cycler flies by Earth, it will traveling at a speed of about 13,000 miles per hour. Space taxis will be needed to bring people from the surface of the planet to intercept the cycler. "This is sort of like a bus that doesn't stop," Longuski says. "When it comes by, you have to run alongside of it and grab on."

Aldrin and his group think that the first cycler could be on its way by as soon as 2018. So, if you're in middle school now, you could be taking a trip to Mars by the time you're in your thirties. (It seems a long way off now, but it's closer than you think!)

Fasten your seatbelts and make sure your seatback is in its upright position. Your flight to space may be departing soon.

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