How long can a human survive in outer space?

Outer space is an extremely hostile place. If you were to step outside a spacecraft, such as the International Space Station, or on a world with little or no atmosphere such as the moon or Mars without the protection of a space suit, then the following things would happen:

You would lose consciousness because there is no oxygen. This could occur in as little as 15 seconds.
Because there is no air pressure to keep your blood and body fluids in a liquid state, the fluids would "boil." Because the "boiling process" would cause them to lose heat energy rapidly, the fluids would freeze before they were evaporated totally (There is a cool display in San Francisco's science museum, The Exploratorium, that demonstrates this principle!). This process could take from 30 seconds to 1 minute. So, it was possible for astronaut David Bowman in "2001: A Space Odyssey" to survive when he ejected from the space pod into the airlock without a space helmet and repressurized the airlock within 30 seconds.
Your tissues (skin, heart, other internal organs) would expand because of the boiling fluids. However, they would not "explode" as depicted in some science fiction movies, such as "Total Recall."
You would face extreme changes in temperature: sunlight - 248 degrees Fahrenheit or 120 degrees Celsius;shade - minus 148 degrees Fahrenheit or minus 100 degrees Celsius
You would be exposed to various types of radiation (cosmic rays) or charged particles emitted from the sun (solar wind).
You could be hit by small particles of dust or rock that move at high speeds (micrometeoroids) or orbiting debris from satellites or spacecraft.

You would die quickly because of the first three things listed, probably in less than one minute. The movie "Mission to Mars" has a scene that realistically demonstrates what would happen if an astronaut's space suit were to rapidly lose pressure and be exposed to outer space. So to protect astronauts, NASA has developed elaborate space suits.

Here are some interesting links:

Survive Outer Space FAQ

How long can you survive in outer space?

Without a space suit, youâ€™d lose consciousness in about 15 seconds, die after 90 seconds and freeze solid within 12 to 26 hours.

Has anyone ever floated away in space?

Nobody has ever floated away and been lost in space, even though TV and film makes it seem like a more common issue. While the United States had some issues during the first spacewalk, astronauts go to great lengths to prevent themselves from becoming untethered.

How many dead bodies are in space?

In 1971, during the Soyuz 11 mission, three astronauts died due to an accidental decompression of their capsules. Astronauts Viktor Patsayev, Georgi Dobrovolski and Vladislav Volkov all passed away, but their bodies were brought back to Earth.

What does space smell like?

According to astronaut Thomas Jones, space faintly smells like a mix of sulphur, rum, seared steak and gunpowder. Tony Antonelli describes the odor as completely different than anything youâ€™ve ever smelled while other astronauts describe it as similar to raspberries.

How long is a day in outer space?

A day in outer space is 90 minutes long, which means that astronauts see around 16 sunsets per day. However, practically speaking, â€œdaysâ€ donâ€™t really exist in outer space; they only come into play when youâ€™re on a planet.