Scene Description in my Book: you are the squadron leader of a fighter wing in the midst of a great space battle. Your carrier ship has been destroyed and your fleet is on the retreat; they are being pursued by enemy bombers with their own fighter escort. Your squad decide to make a last stand to buy time for the fleet to get away, so they engage. The ensuing battle is fierce your fighters take out many but the enemy outnumbers you. One by one your squad HM’s (heart monitors) flat line you are the last. A blast takes out the front window and the cold grip of space fills the cockpit, you luckily put your pressurized helmet on just in time. You fight on for glory for freedom, till death takes you…

So how long would the fighter pilot survive for if the enemy doesn’t kill him first?

Environment (Important): Battle takes place away from sun so radiation will not be too much of a problem. The pilot has a pressurized helmet with air, so the air won’t just tear his lungs apart (I think). He does not have a proper space suit just a full body Flight suit with its insulation, his suit is tightly connected to his helmet (so air decompression should not kill him).

I'm thinking that he will still be killed very quickly because space is cold very cold -270.45 Celsius, -454.81 Fahrenheit but wanted to ask anyway.

If you want me to add any more details just ask.

  • $\begingroup$ wearing an helmet when the body is covered in t-shirt and boxers is not going to help that much. Do you mind telling what is your pilot wearing on his body? $\endgroup$
    – L.Dutch
    Apr 20, 2018 at 5:24
  • 6
    $\begingroup$ Just some feedback for your story,not the question: Why the hell would your astronauts not wera proper spacesuits? This just makes no sense at all... $\endgroup$
    – dot_Sp0T
    Apr 20, 2018 at 5:29
  • 4
    $\begingroup$ So it looks like he won't be able to breathe at all. About a minute or so. @dot_Sp0T they don't wear spacesuits in Star Wars... I assume that is the ship is destroyed, you are supposed to die considering the damage done by these futuristic weapons. They don't expect pilots to survive. $\endgroup$
    – Vincent
    Apr 20, 2018 at 5:33
  • 2
    $\begingroup$ Space can be very cold, or it can be very hot. In fact, the ISS is both, at the same time (hot in the sun side, and cold in the shade). $\endgroup$
    – RonJohn
    Apr 20, 2018 at 6:44
  • 1
    $\begingroup$ Explosive decompression will not be stopped by a helmet alone. Some sort of space suit is needed, whether it's a mechanical couterrpressure suit or an airbag suit, as others have answered $\endgroup$
    – pojo-guy
    Apr 20, 2018 at 11:25

6 Answers 6


The pressurized helmet is actually just about the worst thing you could put on. He was better off without it.

Assume the helmet is pressurized to 14.7psi (atmospheric pressure at sea level. Also the pressurization level chosen for the ISS. For men, neck circumference average 19.5in which means the crossectional area of his neck is probably around 30 square inches. That means the helmet is pushing your soldier's head out of the helmet with about 450 pounds of force. If the helmet doesn't pop right off, it's going to do substantial damage to the neck muscles and spine. Also, that atmospheric pressure is going to rush into the lungs, causing substantial barotrauma. Divers know that an air embolism can occur in just 1 meter of water, which corresponds to about 1.5psi. The 14psi of air pressure rushing into the soldier's lungs will certainly do damage.

It'd be nice to say that the helmet just provides low pressure oxygen, minimizing barotrauma. However, the human body requires about 3psi of oxygen to function. Less than that, and you lose consciousness due to hypoxia. Breathing pure oxygen will help, but not enough to keep it below known barotrauma levels.

To resolve this, you could have your soldiers always wearing a space suit as a safety precaution. If the suit was similar to the BioSuit, you would be able to get away with arguing that the suit doesn't hamper movement in any way. These suits are designed with a great deal of ingenuity to ensure they keep the body from being subjected to the worst of the effects of vacuum. (Fascinatingly, they're air permeable. The skin can actually withstand the vacuum of space without too much trouble with a little restraint. It's the gross expansion of the body that causes problems. This means BioSuits permit cooling via sweat. Instead of evaporating into the air, the water evaporates into space!)


Without a BioSuit or another properly designed space suit, your best option is actually to ditch the helmet and exhale. That minimizes barotrauma. In that case, you have about 15 seconds of consciousness. The vacuum of space in your lungs will literally rip the oxygen from your red blood cells. 15 seconds later, that deoxygenated blood reaches your brain, and you stop.

  • 5
    $\begingroup$ Technically the oxygen will jump from their blood cells into the vacuum, rather than the vacuum pulling anything. $\endgroup$
    – Tim B
    Apr 20, 2018 at 14:37
  • 2
    $\begingroup$ This is the perfect level of revolting, +1 $\endgroup$ Apr 20, 2018 at 14:43
  • $\begingroup$ I wonder why the BioSuit folks stuck a cheap off the shelf motorcycling spine protector on their high tech bespoke suit? Makes me wish we could get a closer look at the rest of the suit's construction. $\endgroup$
    – dwizum
    Apr 20, 2018 at 16:11
  • $\begingroup$ @dwizum I'd have to go through the resources I looked at when I first investigated it, but if memory serves, that spine protector is actually part of the breathing apparatus, and it's designed to help manage pressure in the suit as the lungs expand and contract. I remember there being a really cool breather apparatus that did brilliant things with pressure. Now if this picture happens to have a spine protector from a brand you recognize, it might be that this picture was from too early in the development process, and they simply needed a mock for the picture. $\endgroup$
    – Cort Ammon
    Apr 20, 2018 at 17:15
  • $\begingroup$ Or it might be that that was just the thing which cradles the actual backpack that holds onto the breathing apparatus. $\endgroup$
    – Cort Ammon
    Apr 20, 2018 at 17:16

On the contrary he's actually more likely to die from overheating, in a vacuum he's perfectly insulated from convection and thermal conduction so the only way for him to lose heat is by the emission of infrared radiation which would be too slow to disperse the heat generated by his metabolism and normal bodily functions.

I assume his suit is pressurized (or tight) otherwise the difference in pressure between his helmet and the rest of his body is going to do something horrible to him... I think the pressurized air in his helmet would force its way into his lungs and cause them to expand, possibly rupturing one or both of them, then if the pocket of air in his chest cavity is still expanding it could cause abdominal expansion, and if there's enough air in his helmet he might even vacate his bowls through his posterior.

Assuming he's in a pressurized suit he'll probably survive a few minutes before succumbing to carbon dioxide poisoning.

  • $\begingroup$ Very succinct answer! You might consider putting the helmet-pressure-baloons-chest death first, though, as it is the most immediate. $\endgroup$
    – bukwyrm
    Apr 20, 2018 at 10:25
  • 1
    $\begingroup$ +1 for mentioning the heat problem. That's a fact most people aren't aware of, since all we're told is "space is cold" $\endgroup$
    – thanby
    Apr 20, 2018 at 15:42

The pilot has a pressurized helmet with air, so the air won’t just tear his lungs apart (I think). He does not have a proper space suit just a full body Flight suit with its insulation, his suit is tightly connected to his helmet (so air decompression should not kill him).

It doesn't matter that he has a flight suit and helmet, since what's important is the air pressure around his whole body.


At most, an astronaut without a suit would last about 15 seconds before losing conciousness from lack of oxygen. (That's how long it would take the body to use up the oxygen left in the blood.) Of course, on Earth, you could hold your breath for several minutes without passing out. But that's not going to help in a vacuum. In fact, attempting to hold your breath is a sure way to a quick death. To make it for even a few seconds, Sunshine's Mace must have expelled the air from his lungs before he ventured into the starry void. If he hadn't, the vacuum would have caused that oxygen to expand and rupture his lung tissue, forcing fatal air bubbles into his blood vessels, and ultimately his heart and brain. Scuba divers are also at risk for air embolism; they're instructed not to hold their breath as they ascend from the deep sea.

An astronaut who fell unconscious from lack of oxygen would last for a few minutes more before dying from asphyxiation or the effects of the pressure reduction. Ebullism would result in the formation of bubbles in the moisture found in the eyes, mouth, and skin tissue. One NASA test subject who survived a 1965 accident in which he was exposed to near-vacuum conditions felt the saliva on his tongue begin to boil before he lost consciousness after 14 seconds.


A blast takes out the front window... - if you're OK with having a 'blast' in vacuum take out the front window of a combat spaceship, without vaporizing, blinding or frying the pilot (or incapacitating the ship or its controls) - then this sounds like Star Wars-style sci-fi i.e. World War II in space or rather "space". If your readers aren't bothered by all the other physically and technically implausible elements, won't they prefer a technically unrealistic but vividly described and emotionally fulfilling scene? So do what fits your universe and your story. If your pilot needs to survive, say his "flight suit" is designed to keep him alive in vacuum for hours (while still being light, flexible and stylish) so he can be rescued after a depressurization event. If your pilot needs to die soon, just say how cold he felt as his consciousness slipped away. Whatever.

  • 1
    $\begingroup$ Thats a very valid point. Whatever crashed his front window most likely crashed him as well. $\endgroup$ Apr 20, 2018 at 18:56

first lets deal with what happens without the helmet. No temprature is not a factor there is not enough time for it to matter.

According to NASA studies using dogs and chimpanzees after about 15 seconds the body will begin to bloat as if the the entire body is swelling up after an injury (really your fluids are cold boiling), this continues until they look more like a human balloon,and quickly limits movement. they will also poop, vomit, and piss themselves due to the gas pressure in the bowels, this material has a tendency to freeze on the outside of the body. Primates survived for several minutes, regaining full function within hours if pressurized, but lost consciousness within 11 seconds.

Now what the helmet does.

Helmet with seal and air supply

The helmet may be more problem than advantage, if the helmet is continuing to add pressure to the body, trying to reach equilibrium, it will keep inflating the body until something gives. before then the pressure rise in the throat will cut off circulation to the brain and you will loose consciousness ins around 15-30 seconds. (it takes 10-11 seconds without the helmet) So at least you will not be conscious when you eventually pop. Of course the only way the helmet could be sealed is if it was sealed to the neck so tightly it would actually cut off circulation on its own in which cases you have strangulation and nothing to do with space.

Normal flight helmet

If the helmet is like a normal flight helmet however there is no good seal, so gasses will just escape around the edges giving a best a few more seconds of consciousness (~15 seconds total) as it did with Jim LeBlanc when his suit ruptured. They will suffocate. This is actually the best option if prolonged consciousness is your goal.

Source dogs

Source chimps


Given your environment, I think it all depends on how many air it has in the helmet and, less important, on how fast/slow it dissipate his body heat.

Assuming, like you do and can be true, that the suit is robust enough to not explode once in the vacuum and then there is not the problem with the depressurizing, all depends on how good is the insulation of the suit is.

If is not very good, your pilot will begin to suffer hypothermia once your body temperature is lower than 32/35 °C, you are dead once is lower than 20 °C (but you will be unconscious below 20/28 °C).

On the other hand, if it is really good, your pilot can start to suffer from hyperthermia, but this not seems to be a problem in this scenario, since anyway you probably are not going to live enough time.

Personally I think that in any case your pilot will battle with hypothermia, no insulation is perfect, so he will gradually lose body heat, with a good insulation it can last for a couple of hours (perhaps).

But then you must consider the air reserve. Since it is not a pressurized suite, the only air he has was the one in the helmet, so I'd say that this will be enough for some minutes (15 max if he is very good in controlling respiration and panic) and after that he will be unconscious and them he will die from asphyxiation.

  • $\begingroup$ You don't freeze in space. There is nothing there that could transport the temperature away from you. $\endgroup$ Apr 20, 2018 at 18:55
  • $\begingroup$ You don't dissipate convecting, but one way or another your body radiate heat if it you are not facing the heat source, and the OP stated that the pilot is not near a star. (that is the way the satellites and more generally the any actual space craft dissipate its heat) $\endgroup$
    – Gianluca
    Apr 20, 2018 at 20:12

Not the answer you're looking for? Browse other questions tagged .