"The surface of the Earth is the shore of the cosmic ocean. On this shore, we have learned most of what we know. Recently we have waded our way out, maybe ankle deep, and the water seems inviting."

Those were the words of Carl Sagan back in 1980 on the PBS television show "Cosmos: A Personal Voyage." More than three decades have passed since the episode first broadcast, and for most of that time space travel has remained the exclusive domain of national space programs such as NASA or the European Space Agency (ESA).

Recently, private companies have begun to dip their toes in the cosmic ocean, too. The players range from economic titans like Richard Branson's Virgin Galactic to small, independent ventures questing after a Lunar X Prize.

What about you? Have we reached the point where regular folks can build their own homemade spacecraft? Or are we still confined to walk the shores?

What constitutes a spacecraft? By most definitions, it's a manned or unmanned vehicle designed to travel or function outside Earth's atmosphere. That's pretty good news for do-it-yourselfers with cosmic ambitions, because the minimum task boils down to sending a small device to a point approximately 62 miles (100 kilometers) above sea level. That point is also known as the Kármán line.

The border between atmosphere and space is far from set in stone -- or air. NASA and the United States Air Force, for instance, tend to identify the barrier at 50 miles (81 kilometers) [source: NASA]. If you were feeling particularly stingy, however, you could place the limits of Earth's atmosphere as high as 373 miles (600 kilometers) above sea level, where the outer limits of the thermosphere gradually terminate. Of course, this would make the International Space Station more of an upper atmosphere station, as it hangs out at roughly 220 miles (354 kilometers) above sea level.

So let's say you absolutely have to launch a small device into space as soon as possible. In order to send a payload to such a lofty altitude, you're going to want to turn to one of two propulsion methods: a balloon or a rocket.

Rockets pose a bit of a risk because, let's face it, everything from holiday fireworks to the Saturn Vs used in the Apollo missions are nothing short of controlled explosions. They depend on often dangerous and tightly controlled chemical components that combust to produce thrust. Dangers aside, the construction costs for such a spacecraft typically put the venture outside the range of the individual.

Blast off with a few do-it-yourself spacecraft next.