Five reasons to put a space suit on when going on a space walk

Humans must wear space suits in the vacuum of space

             Photo by Valera Taljutov from FreeImages


Ever watched a sci-fi movie where a character takes off their helmet in space and their head instantly explodes?

Well, we all know that space is a hostile place and humans are not built to survive out there unaided. But how bad is it?

Here are five reasons to put a space suit on when going on a space walk.

  • Reason 1: the absence of the atmospheric pressure

The atmosphere around Earth provides us not only with precious gas mix to breath, but also with comfortable pressure.

Now, why is external pressure important? It’s because of the water! Water accounts for around 50% of our total body weight (usually more in men). Water is everywhere inside us: in the cells (including blood cells), tissues and organs. Liquid things, as we all know, boil and turn into vapor at certain temperatures. Water, for example, boils at 100 degrees at  “sea level”, i.e. at the atmospheric pressure of 1 atmosphere (or 101 325 Pa). But the higher above the sea level we are, the lower the atmospheric pressure is. And, as a consequence, the lower is the water’s boiling point. That’s the reason why you cannot make a decent cuppa up in the mountains – the boiling water is simply not hot enough. Now, there comes a point when water can boil at body temperature. The corresponding altitude is called the Armstrong limit and it is about 11-12 miles above the sea level. When there is no atmospheric pressure at all, i.e. we are in the vacuum of space, the exposed water boils straight away. Does that mean our blood and other fluids and tissues containing water will start boiling in the outer space immediately? No, only the exposed liquids, like saliva and tears. As for the other fluids, our body will keep “the stuff” inside pressurized. But the bubbles will start to form resulting in anything from swelling (bubbles under the skin) to bubbles in the bloodstream. This condition is known as ebullism.  Ebullism leads to injuries and can be fatal if not treated urgently.

  • Reason 2:  lack of oxygen to breath

This problem is the most obvious one. Let me ask you: how long can you hold your breath for? Comfortably- probably for about 30 seconds. Some people can hold their breath for several minutes. But that’s it.

In space you will have even less, about 15 seconds (see this source), before your body will spend all the oxygen and you will black out. Of course there will still be some air left in your lungs from that last breath you’ve taken, but that will be of no use. In fact, you  must do the most counterintuitive thing imaginable: BREATH IT OUT. Immediately! The lack of outside pressure in vacuum will cause the leftover air in your lungs to expand until…pop!

From the solar UV rays to the galactic cosmic rays, space radiation is all those hard rays that can damage our body cells and make them work the wrong way. If the UV rays will simply cause a massive sunburn, other kinds of radiation will make you sick and lead to serious diseases in the future. Provided you got away with your suit-free space walk in the first place.

  • Reason 4: cold. Or…is it really a problem?

The temperature of the Cosmic Microwave Background radiation that fills up space is 2.725 degrees Kelvin or -270.45 degrees Celsius. That’s as cold as it gets out there. But the good news is: if you find yourself in space without a suit, you will not freeze instantly in the shade. Nor will you be cooked in the direct sunlight. In the absence of any substance to pass your body heat to (such as air) you will only lose heat because of thermal radiation. But…Thermal radiation is quite slow. So, don’t worry, lots of other nasty things will happen to you in space before you finally freeze.

  • Reason 5: you cannot even call for help!

Remember, that sound is a wave. It requires a medium, like air or liquid, to propagate. In the vacuum of space there is no medium. Therefore even if you shout out “HELP” really loud, your fellow space walkers will not be able to hear you.


So let’s sum it up! You will not explode and your eyes will not pop out. Instead, you will swell, get a sunburn, pass out, suffocate and, eventually, freeze. Space trip, anyone?

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And best of luck with your space walk!