Atmospheric and Space Questions...

[Spacescifi]

Atmosphere Question: Correct me if wrong, but it is my understanding that even if an object is heat resistant enough not to ablate during reentry, the air running into it at the front would still glow and become plasma because of friction and compression from not being able to get out the way fast enough.

Not sure if a fireball with a tail would still form if the object is not ablating.

My guess is maybe, but it will be less bright and shorter than if it were from the object actually ablating.

Space Question: I could not enjoy Guardians of The Galaxy 3 because it seemed too... immature.

Worst of all, Star Lord's near death scene turned my suspension of disbelief right off... since he beginscto freeze solid within moments of being exposed to vacuum in outer space, and a tree's limbs that grow out to catch him also freeze solid and break like ice from apparent amazing coldness of fictionap vacuum.

So my question is this... space vacuum does not feel cold does it?

If anything your eyes would feel hot since they would begin to boil from the lack of air as the liquid on them turns to gas.

And that is besides the fact that heat is hard to loose in space since vacuum does not conduct heat through touch, only by radiation, and the human body is never hot enough to glow without a person already being dead, so that's not a way to loose heat fast either.

So my guess? Space would not feel cold, your body temperature would not change, but could feel hotter from the sun's rays hitting you eith no atmospheric filter, also your eyes and tongue would both feel hot as the liquid boiled off them.

 

So instead of freezing within moments, Star Lord would be in pain trying to cover his eyes and mouth before he lost consciousness.

 

Thoughts?

[Shpaget]

Water boiling from exposure to vacuum does not make it feel hot. It actualy cools down (which is the source of comically fast freezing in vacuum trope in fiction), but as you noted a lot slower than depicted in the movie. It is possible to freeze water by exposing it to vacuum, but it takes time.

Exposure to vacuum leads to a quick loss of consciousness (in about 15 seconds, or the time it takes for the deoxygenated blood in lungs to reach the brain). Death is quick to follow.

[FleshJeb]

9 minutes ago, Shpaget said:

Exposure to vacuum leads to a quick loss of consciousness (in about 15 seconds, or the time it takes for the deoxygenated blood in lungs to reach the brain). Death is quick to follow.

I've never bought that explanation. Surely you can hold your breath in vacuum just/nearly as well as you can on Earth. A couple of minutes with prep time is no issue. And your tissue should be easily strong enough to handle a one atm differential. So it must be another mechanism. Could it be rapid, whole-body vasodilation causing loss of blood pressure and consciousness? I don't know how strong the physiology is behind vasoconstriction, but we know it regularly handles swings on the order of 100mmHg (1 atm = 760mmHg). It stands to reason that one could get absolutely ripped on stimulants or other vasoconstricting drugs, and extend vacuum consciousness for a lot longer. Al Pacino in spaaaaaaccceee.

[kerbiloid]

31 minutes ago, FleshJeb said:

Surely you can hold your breath in vacuum just/nearly as well as you can on Earth.

The lungs would explode. You should exhale first. And with empty lungs it's less than a minute.

Also, the limbs start popping at 10..12 km, so the blood vessels become obstructed.

Actually, you have only the oxygen which is already in your brain.

15 seconds is the brain reserve time, with or without the air.

[KSK]

Everyone else seems to have the space question in hand, so I’ll have a crack at the atmospheric one.

As I understand it, you’re broadly correct about how and why the air turns into plasma. How long and bright the plasma is for ablative vs non ablative heat shields, I’m not sure about.

My guess is that most of the light comes from the plasma rather than the radiating heat shield - not least because the vapour from the ablating shield will contribute to that plasma.

There’s probably some footage of testing PICA-X tiles or whatever they used for the Shuttle tiles, on the internet somewhere. That should give you some idea of what they look like during reentry.

 

[Shpaget]

3 hours ago, FleshJeb said:

Surely you can hold your breath in vacuum just/nearly as well as you can on Earth.

You most certainly can not. Your lungs would need to contain one atmosphere of pressure difference. The limit on human physiology is about one tenth of that, something you can test by trying to blow a column of water up a hose and see how high you can make it go.  Your target is 10 meters; I'd be surprised if you can manage more than one.

And don't call me Shirley.

[kerbiloid]

1 hour ago, KSK said:

How long and bright the plasma is for ablative vs non ablative heat shields, I’m not sure about.

My guess is that most of the light comes from the plasma rather than the radiating heat shield - not least because the vapour from the ablating shield will contribute to that plasma.

The Earth uniform atmosphere height is 7.99 km.

So, by diving vertically, the craft would pierce a 8 km thick layer of sea level air.

The aerobraking trajectory is:

Spoiler

So, while aerobraking, the craft will pass 100 km vertically and 500..1000 km horizontally.

So, its full distance will be 5..10 times longer than that, something about 50+ km of the uniform sea level air.

It's  ~= 50 000 * 1.225 ~= 60 t of air per 1 m2 of the craft cross-section.

As the ablator mass per 1 m2 is negligible, compared to that, the fiery tail depends only on the heated air.

[magnemoe]

7 hours ago, kerbiloid said:

The Earth uniform atmosphere height is 7.99 km.

So, by diving vertically, the craft would pierce a 8 km thick layer of sea level air.

The aerobraking trajectory is:

  Hide contents

So, while aerobraking, the craft will pass 100 km vertically and 500..1000 km horizontally.

So, its full distance will be 5..10 times longer than that, something about 50+ km of the uniform sea level air.

It's  ~= 50 000 * 1.225 ~= 60 t of air per 1 m2 of the craft cross-section.

As the ablator mass per 1 m2 is negligible, compared to that, the fiery tail depends only on the heated air.

Ty for that diagram, I assume its mostly  the same for all capsules. Assume winged crafts would have an more shallow profile also the discarded parts would be different. 
The solar panels on the service module give me some scares. KSP  1,  was entering Eve atmosphere and dropped the interplanetary stuff like nuclear engines radiators and solar panels for the transfer. Drag slowed the module down until the solar panels and radiators  broke and the module went past at high speed and some meters away  

[kerbiloid]

27 minutes ago, magnemoe said:

Assume winged crafts would have an more shallow profile also the discarded parts would be different. 

The military fetish number for shuttles and gliders since 1950s is ~2 000 km maneuver (rounded to miles).

The HTV-2 glider has performed a 2 000 km flight with S-maneuver.

[Spacescifi]

The big question is... how does outer space vacuum feel to the exposed human body?

I think it would feel awfully empty. You may see a few flashes from cosmic rays passing through you before passing out.

I doubt it feels cold, since there is nothing to shed body heat quickly.

Ears tend to make a popping sound when air presssure changes, and I expect it to be painful even if you hear nothing in space.

So basically a painful or unpleasant 15 seconds before passing out in space.

Spoiler

I originally asked these questions to see what it would feel like for Superman/Supergirl to fly through space.

There are differences of course... but some things remain the same like:

1. Won't feel cold.

2. Won't hear anything in deep space (ignoring comic books and TV shows and movies where they ignored this.

Differences: In low orbit where there is minimal atmosphere Superman/Supergirl can still hear everything on planet Earth. In addition to hearing a mess of sound all at once, they can use telescopic vision to zoom in on points of interest and also hear it as if they were there. They can even  combine this with X-ray vision to "hear" through walls.

The only reason they could hear at all is because their superhearing is ridiculously powerful, and if they are within anything conducts sound around them, they can hear due to super sensitive and super ranged snd focused hearing.