When astronauts spacewalk, it looks like they're floating serenely in the vacuum of space. The reality: they're hurtling at 17,220 mph inside bulky pressurized suits. Here's the lowdown on spacewalking, from how it's done to what it costs.

The technical name for a spacewalk is an EVA, or extra-vehicular activity, which would probably make for a great pick-up line next time you meet a hot astronaut. Since Alexei Leonov made the first spacewalk for the Soviet Union in 1965, 191 humans have ventured into space outside the confines of a craft (some of them were only partially outside). This number includes American astronauts who walked on the moon. Most spacewalks occur in orbit around the Earth or the moon, but a few on the Apollo missions were conducted in what NASA refers to as "deep space."

The first American spacewalker was Edward White, during the Gemini 4 mission in 1965, just a few months after Leonov. The photos of White floating in space tethered to his spaceship (bottom photo) virtually defined the 1960s popular image of space exploration. Like White's spacewalk, most EVAs are tethered. Since the tether carries oxygen and water to the astronaut, it allows the suit to be much less bulky.

Taking a Stroll in Low-Earth Orbit: The Truth About Spacewalks

Compare White's suit to the untethered one worn by astronaut Bruce McCandless in 1984. McCandless' suit not only had to include all of his life support systems, but he also had to wear the Manned Maneuvering Unit (MMU), which allowed him to propel himself in various directions using pressurized nitrogen. The MMU was retired and replaced by the smaller SAFER unit, (Simplified Aid for EVA Rescue), proving NASA's ability to push both the technological and acronymical envelopes.

The SAFER unit is used for certain emergency procedures, such as Stephen K. Robinson's EVA to the bottom of shuttle Discovery to remove some filler tiles that might have caused re-entry problems. They're also used for construction jobs in places the tether just won't reach.

In fact, most of the time when an astronaut spacewalks, he or she is putting in a few hours as an orbital construction worker. EVAs have been vital in the construction of the International Space Station, as well as making repairs to the Hubble Telescope and dealing with various mechanical problems that seem to crop up whenever a robotic arm is involved. The picture below comes from a NASA manual, and depicts a bag of tools designed for repairing the Hubble Space Telescope. I'm not sure what the Flash Gordon ray-guns are for.

Taking a Stroll in Low-Earth Orbit: The Truth About Spacewalks

Of course, NASA and the world's other space agencies don't send people on EVAs on a whim. It's dangerous work (although no one has ever died or been seriously injured on an EVA). Astronauts working on the ISS report an initial period of severe disorientation, as their perspective flips from "hand-stand" to "surfboard" and back repeatedly. The problem is, the abstract shape of the ISS doesn't give their brains any up or down cues to latch onto the way the space shuttle does.

Taking a Stroll in Low-Earth Orbit: The Truth About Spacewalks

Velocity is a big problem, mainly due to space junk. At over 17,000 mph, any impact is potentially deadly. A stray bolt from Skylab could strike you with more energy than a bullet, and even if it doesn't kill you outright, it could still tear a hole in your suit. Depressurization, loss of oxygen, and other generally irreversible difficulties immediately follow.

There's also radiation to worry about. With no atmosphere or heavy shielding, cosmic rays can build up dangerous rad levels pretty quickly. All EVA astronauts wear special MOSFET badges that continually monitor their radiation levels.

Finally, you could always get a bad case of the bends from working for up to eight hours in a pressurized suit. For some missions, astronauts "camp out" in the airlock, set to a lower air pressure. This flushes nitrogen from the blood and reduces the chances of later experiencing decompression sickness.

If all this hasn't scared you off, you could actually take a spacewalk yourself. Space Adventures, the company that lets insanely rich people take a ride on the ISS, will also let insanely rich people go on a 90-minute EVA adventure. It costs an extra $15 million and requires an extra month of training.

That actually seems like a fairly accurate estimation of the cost of a spacewalk. In 2004, when Russia had to use one of their Orlan suits to make some repairs left unfinished due to malfunctioning NASA gear, they charged NASA 500 hours of spacework, which experts estimated worked out to about $10 million. Since space agencies are not allowed to directly pay each other for work, they exchange work hours as currency. So basically, if NASA owes another country some money, our astronauts end up doing their homework for them.

Incorporating realistic spacewalks into science-fiction shouldn't be too difficult. Keep in mind that the suits are quite hard to move around in — astronauts are very sore after a long shift on an EVA, constantly pushing against the suit. It's one reason that female astronauts have been underrepresented among spacewalkers. From there, just ramp up the danger levels. Make the radiation deadlier, the high-velocity space debris more plentiful (possibly as a result of Kessler Syndrome). Maybe throw in some anaerobic space bacteria that will infect the astronaut if it gets in through a punctured suit. Or just go full Buck Rogers and have a laser battle combined with the weird choreography of a tethered spacewalk.