The Human Body in Space: Distinguishing Fact from Fiction (2013) | Hacker News Reader

The Human Body in Space: Distinguishing Fact from Fiction (2013)

sitn.hms.harvard.edu

I just finished listening to the Audible narration of the excellent Project Hail Mary [1] book by Andy Weir. It explores quite a few of these issues, including the cosmic radiation one. Highly recommended!

[1] https://www.andyweirauthor.com/books/project-hail-mary

The Expanse handles this stuff much better than other shows, as has been noted many times. As entertaining as it is, For All Mankind gets things very wrong in a lot of cases and falls prey to a lot of the 'space tropes' that plague sci-fi. And I certainly don't expect hard sci-fi realism everywhere, but in something like For All Mankind, which is supposed to exist in an alternate timeline but be firmly planted in the real world, it's jarring. When it's in something like the movie Event Horizon I really don't care about realism.

In one episode Naomi inhales in just before exposure to the vacuum - it would have been fatal according to the article.

In the book she exhales: "She pushed her jaw forward in a yawn, opening her throat and her Eustachian tubes. Cyn yelped as she hit OPEN OUTER DOOR. Air tugged at her once, hard, as it evacuated. Adrenaline flooded her blood as she was assaulted invisibly on every square centimeter of flesh. The breath in her lungs rushed out of her, trying to pull her lungs along with it.[...] With her lungs empty, there was no reserve. She wasn’t holding her breath, surviving off the gas held inside her. Someone could hold their breath for a couple minutes. In the vacuum, she could make it maybe fifteen seconds unaided.

Corey, James S.A.. Nemesis Games (The Expanse) (p. 425). Orbit. Kindle Edition.

Nice to know that the author got it right in the book.

If you're referring to the scene where she deliberately exits an airlock, then she actually exhaled whereas the other person with her did not and died.

(Purposely being vague to avoiding spoiling anyone on this great series)

Yes, that one.

I rewatched this moment on Prime and I remembered it correctly. While she exhales after last words slowly, she inhales sharply before pressing the button.

I remember it probably because I watch everything with subtitles on and that was written. I now watched it without to avoid being biased and it still holds.

In addition she was exposed to the vacuum about 40 seconds before using the shot.

What you really want is something like the Sturm Invocation from Charles Sheffield.

I just watched the scene in For All Mankind with the astronauts/lunar surface/duct tape and it seemed to match this article. Which aspects of For All Mankind are you referencing that got it wrong?

The duct tape scene is not right, there is a youtube video [0] from a physicist and astronomer that explains pressure suits (which the duct tape would provide). He surmised that they had a minimum of a minute to do their work, and certainly wouldn't have been leaking blood all over the place.

The other trope that For All Mankind really fumbled on was the decompression of the space station (I'm avoiding spoilers for those that don't know why). It followed the trope of massive amounts of air continuously rushing out of the station when that can only happen when there is a massive amount of air available to continuously feed the decompression. In reality, it would be a short rush of air to vacuum as the window was large enough for most to escape very quickly.

[0]: https://www.youtube.com/watch?v=pdoMOXvqjbY

> Because thermal radiation (the heat of the stove that you can feel from a distance, or from the Sun’s rays) becomes the predominant process for heat transfer, one might feel slightly warm if directly exposed to the Sun’s radiation, or slightly cool if shaded from sunlight, where the person’s own body will radiate away heat.

Since the body also produces heat, would you even feel cool when shaded? If body heat generation outpaces radiation then I think you'd feel warm. Wikipedia puts the energy radiated out as about 2000kcals per day, or right around a human would produce from metabolism. So I guess it basically balances out.

https://en.wikipedia.org/wiki/Black-body_radiation#Human-bod...

Evaporation from your pores will still cool you a bit, as the water takes heat away with it when it leaves you.

Reading this, I learned that the 'Exposed To Space' stuff that happens in The Expanse (TV show - I've not read the books) is pretty much spot on.

This article is from 2013, but since 2019, there's been active research in things like latent herpes reactivation, which could have implications for long duration spaceflight.

https://www.frontiersin.org/articles/10.3389/fmicb.2019.0001...

The big question for a Mars expedition is where between 1G and 0G Mars's .4G is for your body. We really need centrifuges in space to start studying this before it becomes something astronauts are depending on.

This should be tagged 2013.

I came here just now thinking it was a new article. I actually found it by way of Google a couple months ago after watching a certain episode of The Expanse.

Plus there could also be the psychological effects of possibly being isolated and confined in a small floating tin can.

IIRC Nasa put out a bunch of RFPs last year for studying, identifying, and alleviating that exact problem.

Imagine if they tried to cram a bunch of people in a literal metal tube with no windows and send them to the bottom of the ocean for months as a time. How could anyone be stupid enough to think that would work?

Make the transit ship spin. Surround the habitable parts with water and other materials. It’s so simple but nobody seems to be aware that these are solved problems.

> It’s so simple but nobody seems to be aware that these are solved problems.

It isnt reasonable to assume napkin solutions are "so simple" in practice or have not been considered. There are plenty of people smarter than either of us that look at these problems.

The problem isn’t the smart people who look at these problems. It’s the collective behavior of the masses to have amnesia about basic physics.

Maybe the problem is people filling air with pseudo-scientific BS all the time, for instance, i dunno, Scientology?

I’m not a Scientologist.

Lots of people have thought of similar things. I know I have read scifi which uses water for shielding but I can't think of a specific name.

However, water isn't light. According to this post on stack exchange it would take something like 330,000kg of water to shield a crew. Getting that into orbit is a big task.

Does something have better shielding mass ratio? But water itself can be more useful perhaps.

It’s just money.

You need a pretty big ship to do that fast enough for Earth gravity and not have the astronauts nauseous all the time. You could use a tether but NASA has had problems with tethers in the past and is a bit shy about them.

You don't need Earth gravity. All the problems with bone loss and ailments are from microgravity. I can't find any studies on reduced gravity (it would be really hard to test), but there's no reason to assume that something like half a gravity + exercise and supplements wouldn't significantly reduce health issues.

What’s the minimum radius?

Prior to Starship, just getting large enough structures and mass into space has been the limiting factor. There is a minimum diameter for spin gravity to avoid disorienting vestibular side-effects. Spinning two spacecraft attached by a tether might work for short-term use cases, but I don't know how feasible it is to keep that stable for months or years. Transporting adequate volumes of water shielding is probably infeasible for SpaceX's planned Mars mission profile:

- you need 1 meter of water shielding to reduce radiation to safe levels[0]

- each cubic meter of water is 1 metric ton

- Starship's circumference is ~28 meters

Assuming you only shield 4 meters of the length of the ship, not counting the top and bottom cross sections of the cylinder, you've already blown past the 100T payload capacity of Starship.

[0]: https://space.stackexchange.com/a/1826

You can use multiple deliveries when water is added in orbit.

Yes, that works fine for a space station, but not so much for a rocket that needs to accelerate and decelerate it on a trip to Mars (and back).

Especially for such rocket because you may need also additional fueling.

Starship already requires in-orbit fueling to fully refill its tanks for the outbound journey to Mars when loaded to its 100T payload limit. It cannot carry additional fuel to accelerate and decelerate another 100T+ of water shielding. SpaceX currently plans that Starship will return to Earth from the Martian surface without in-orbit refueling. I don't know the payload capacity for that trip offhand, but again water shielding would exceed the 100T mark and it would be an incredible amount of added complexity to do in-orbit refueling there with the limited fuel generation infrastructure.

Multiple launches. Assemble and fuel a big spinning water bottle in orbit. Maybe tether maybe not. Spin up and establish cycle orbit. Done. Basic physics and orbital mechanics.

https://en.m.wikipedia.org/wiki/Mars_cycler

Actually, assemble multiple water-filled cylinders in earth orbit and then put those in staggered cycle orbits. Power requirements are low so all you’d need is a regular engine with a large fuel tank.

Once those are in cycle orbit you now have giant water cylinders that you can catch every once in a while to ride to earth/Mars. Forever. With a tiny energy budget for corrections. Just wait till one passes by and slip your vessel inside it. Man I am good.

Since it's basic physics, how much power do you think is required to spin a cubic meter of water at 1g centrifugal force? How much energy is required to do that for a year?

I'm pretty sure it's lots :) I think that we just haven't figured out how to do this, so the "obvious" solution is not on the table (yet).

You should learn basic physics before you presume to know it...

It’s not a question of power. You could could get it spinning quickly or slowly with high or low power respectively but the question you are trying to ask it how much energy is required. The amount of energy to get the thing spinning is the same no matter what. And once you get it spinning, you’re done. It will keep spinning. I think there is a certain law that pertains to that. Something to do with fig newtons.

The amount of energy that is required is trivial compared to the other energy budgets. And it would be spun up at low power over the course of hours or days.

In the movie Men Behind the Sun they show the japanse putting people in vacuum chambers and literally shit their guts

since two of the three methods of heat transfer (conduction and convection)

This always drives me nuts. Convection is conduction, just in a fluid. Conduction and radiation are two entirely different physical processes.

Doesn't convection also require movement of the fluid? Under gravity convection works by changes in density when the fluid is heated (e.g. hot air rises). This movement of the fluid provides an extra component beyond regular conduction. The movement of the fluid transfers heat away.

In low g environments, convection due to density changes doesn't happen (hot air does not rise) which means heat pools around bodies at rest.

Edit: after reading the article a bit, i see that you were quoting a section that ends with "...(conduction and convection) cannot occur without matter." Which does make the distinction the author was making a little more less useful. However lack of convection is an issue inside the space station where fans must be installed to keep air from pooling around heat sources like lights and human bodies.

I think the distinguishing difference between conduction in a fluid and convection is that the fluid "leaves" and takes away the heat.

Well, not exactly.

Conduction means you touch something and that something slowly gets hotter and conducts heat away from your body. You can calculate how fast the energy is transferred based on properties of the material and geometry of objects and their interface.

Convection means you touch something and that something is constantly being replaced. You can't use the formula for conduction here.

In case of convection, the basic mechanism of energy being moved has nothing to do with conduction, rather with movement (replacement) of the material that takes away the heat.

How is moving heat by moving the material and moving heat by letting it to dissipate through stationary material not two different processes?

Actually conduction is radiation at the atomic level. If you bring either point up in a conversation which is understood to be about macroscopic physics though you're really just being an ass.

I thought conduction propagated as phonons rather than photons.

But I guess the particle interaction comes from photon exchange, on the other hand the frequencies are different enough I think you can safely call it a different thing (like how UV and AM radio are different.)

Thermal conduction is carried out with phonons and free electrons. It has a finite range. It is fundamentally distinct from thermal radiation which is propagated by photons with an infinite range.

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