For Questions That Don't Merit Their Own Thread

[K^2]

Just now, kerbiloid said:

The gravity is not a significant actor on such short distances which 99% of the human science deals with.

I mean, we have measurements at a somewhat larger scales. I've alluded to measurements from neutron star binaries. The famous example is Hulse-Taylor binary. And now we're getting good results from gravitational wave observatories which pick up events involving somewhat larger objects. So we're pretty well covered on scales from particle interactions all the way up to something the size of a star system.

But yeah, that's still absolute peanuts compared to vast intergalactic spaces, let alone the scale of the observable universe. 

23 minutes ago, kerbiloid said:

So, the field theory, and especially the gravitation played a very little role in the modern science building until last several decades.
And even if it got reveled that the Earth is flat and covered with a crystal dome, 99% of science would not be affected at all.

I'd argue you would have to explain why the theory works. General Relativity replaced Newtonian Gravity because the former explained why gravity is approximately MG/R². The field theory model of GR replaced the original, geometrical formulation, because it showed that the Einstein Field Equations are just equations of motion for the mean field theory of the Poincare group. We still don't know how to turn it into a working theory of quantum gravity, but having the mean field is adequate for us to confirm that whatever that quantum gravity is, it works like we expect gravity to work on human scale - and this includes purely relativistic effects, like the gravitational time dilation of GPS satellite clocks.

So if we somehow came about and saw that the field theory just doesn't work in some cases, we'd need to know why, because otherwise we wouldn't know the limitations of it. We wouldn't know where we can and cannot apply the theory. It's not like we'd stop using practical aspects of it wherever it worked. We still use Newtonian gravity just fine, and we'll keep using GR for GPS satellites even if we somehow found out it's bogus, sure. But as far as the science of it goes, we'd be back to square one. And we'd be back to square one on a lot of science. At least, until we figure out what went wrong with our understanding.

[kerbiloid]

9 minutes ago, K^2 said:

So if we somehow came about and saw that the field theory just doesn't work in some cases, we'd need to know why, because otherwise we wouldn't know the limitations of it.

The general relativity theory is based on postulates, which were postulated without explanations.

This doesn't make any problem in its practical use.

[K^2]

45 minutes ago, kerbiloid said:

The general relativity theory is based on postulates, which were postulated without explanations.

This doesn't make any problem in its practical use

Practical use in engineering and building on top of it to expand our understanding aren't the same thing. We still use Newtonian gravity where practical, because we know its limitations. If I need to estimate a period of a satellite orbiting a massive body, for example, I know when I can use 2 pi sqrt(a³/MG) and when I have to factor in GR - I have to look at what the Schwarzschild radius is for that MG and use that as a guide. So if I'm doing research on exoplanets, I'm safe. I don't care about GR, I can keep using Newton. If I want to look at how accretion disk forms around a black hole, I probably have to go to GR. But that safety is there precisely because we understand how one theory supersedes the other and the precise conditions for it.

If we find that the underlying principles behind field theory are wrong, then so is GR. And while we can keep using it in contexts where we already were using it, like the aforementioned GPS. But if we want to make new discoveries with it, we have to know where it breaks down. We know we can keep using it to talk about periods of neutron stars, for example, because we have confirmation on this. But can we keep using it to describe physics inside a neutron star? Can we trust GR on physics we can't otherwise probe directly? Right now, we have no reason not to. We can still put an asterisk next to finding, saying, "Assuming gravity works," but it's useful to us.

If we find a new theory that replaces what we understand now, great. But if we don't, we're stuck. There is no point in doing an estimate on the maximum mass of a neutron star and comparing it to data if we can't trust the theory behind the estimates. It immediately shifts all of our priorities and goals as far as fundamental sciences are concerned.

P.S. I just want to clarify, our modern understanding of General Relativity is very different from Einstein's. Einstein took some assumptions about acceleration, geometry of space-time, and some postulates about stress-energy, and derived the equations from it. It's a bit like dimensional analysis - you get a result, but you don't have a deeper understanding of why that works. Modern understanding is based on symmetries, and while there is still a postulate at the root of it - that space-time is locally Minkowski, and space is locally invariant in translations, rotations, time, and boost - the rest follows. We no longer have to assume that gravity is caused by stress-energy, it's derived as the "charge" of the gauge field, etc.

Edited February 17, 2023 by K^2

[JoeSchmuckatelli]

Are there any regulations about the interior dimensions of orbital habitats?  Seems to me that under 3m the person can reasonably expect to be able to self-recover / maintain contact with the craft and not be a danger to themselves or others.  But if the craft has any space bigger than 3m interior that someone could find themselves stuck in the middle and need assistance. 

Which returns us to the question - aside from common sense that we hope engineering and business have... Are there international regulations in effect for this stuff? 

[kerbiloid]

https://en.wikipedia.org/wiki/Loading_gauge

https://en.wikipedia.org/wiki/Intermodal_container

https://en.wikipedia.org/wiki/Vitruvian_Man

https://en.wikipedia.org/wiki/International_Docking_System_Standard

If a human gets stuck, it will take off a part of clothes and either throw it or use as lasso.

[darthgently]

Always carry your can of compressed air on your bat-belt when in habs big enough to be out of reach of walls.  Alternatively, pneumatically mobile bots could patrol the habs looking for crew needing rescue

[kerbiloid]

First try to stop motionless in that middle.

Spoiler

 

 

[Nuke]

muonium as rocket fuel. chemically behaves exactly like hydrogen, but without all the damn quarks. so its lighter. oh, and the nucleus is actually an anti-muon so keep normal muons away. so hard to produce. and its unstable.  but lets ignore all that. what kind of isp are we looking at?

Edited February 19, 2023 by Nuke

[kerbiloid]

But muons are very unstable.

[magnemoe]

18 hours ago, JoeSchmuckatelli said:

Are there any regulations about the interior dimensions of orbital habitats?  Seems to me that under 3m the person can reasonably expect to be able to self-recover / maintain contact with the craft and not be a danger to themselves or others.  But if the craft has any space bigger than 3m interior that someone could find themselves stuck in the middle and need assistance. 

Which returns us to the question - aside from common sense that we hope engineering and business have... Are there international regulations in effect for this stuff? 

No regulations, yes you have the common berthing adapter limits. Size of modules are also limited by fairing sizes so its hard to get large open spaces. Skylab wide because it was launched on an Saturn 5.
And we will get Sarship and other large rockets its limited need for large open rooms. First I see is zero g play for an hotel and here its part of the fun. Later on you will get stuff like dry docks for assembling or repairing stuff in atmosphere.  Here I assume it will be stuff for this, think scaffolding as you want to have something to push against. moving heavy elements. You can just put up some ropes so people drift around can grab, else steel plates around, an magnet and a string. 
 

[kerbiloid]

At least one way to reach the middle of the room and stay there in zero-g without drifting to any wall?

To move there, you need a push.

To stay there you need a retrograde push.

If you can make a retrograde push in the middle, then why not do it again to move?
And how can it zerize the velocity vector so precisely?

[darthgently]

2 hours ago, kerbiloid said:

At least one way to reach the middle of the room and stay there in zero-g without drifting to any wall?

To move there, you need a push.

To stay there you need a retrograde push.

If you can make a retrograde push in the middle, then why not do it again to move?
And how can it zerize the velocity vector so precisely?

Don't forget aero drag and the fact the station is adjusting attitude periodically which unless one is at CoM, could create relative translational velocities between person and walls

There is a non-zero chance that if one falls asleep without being properly stowed one could wake up stranded.  At least until station attitude control, or ventilation currents came to the rescue

Edited February 20, 2023 by darthgently

[kerbiloid]

24 minutes ago, darthgently said:

Don't forget aero drag

How can I forget it, when it stops me in the middle of the room when I'm trying to walk too fast.

25 minutes ago, darthgently said:

There is a non-zero chance that if one falls asleep without being properly stowed one could wake up stranded.  At least until station attitude control, or ventilation currents came to the rescue

1. Then he will drift in the direction of sleepy falling...

2... towards the ventilation fan.

[Terwin]

37 minutes ago, darthgently said:

There is a non-zero chance that if one falls asleep without being properly stowed one could wake up stranded.

Every human in space comes equipped with a pair of bellows attached to an adjustable nozzle and a pair of paddles.

So if needs be you could 'swim' or 'blow' your way towards a hand-hold.  Not that it would be fast, but it would work.

[AckSed]

1 hour ago, Terwin said:

Every human in space comes equipped with a pair of bellows attached to an adjustable nozzle and a pair of paddles.

So if needs be you could 'swim' or 'blow' your way towards a hand-hold.  Not that it would be fast, but it would work.

Willy Wonka approves this post. (Charlie and the Great Glass Elevator.)

[magnemoe]

6 hours ago, kerbiloid said:

At least one way to reach the middle of the room and stay there in zero-g without drifting to any wall?

To move there, you need a push.

To stay there you need a retrograde push.

If you can make a retrograde push in the middle, then why not do it again to move?
And how can it zerize the velocity vector so precisely?

Skylab astronauts managed to get stuck in the middle, I assume this is nothing to grab or kick off from or at least nothing obvious and no detectable velocity. Most likely they was moving away from the wall at less than an cm/second, found he could not grab it anymore and got a bit annoyed like if something rolls under the fridge. Having an string on some air vents would give you something to grab onto.  This is an viable solution to this issue. 
Down the line then we build mile sized stations with multiple spin habitats you can have the air ducts act and an public transport system. Yes some of that air will be used by stuff like toilets and space marine gyms  

[kerbiloid]

5 minutes ago, magnemoe said:

Skylab astronauts managed to get stuck in the middle

Without others' help? Is there a video?

***

The vent anyway pulls everything floating to the fan.

[magnemoe]

22 minutes ago, kerbiloid said:

Without others' help? Is there a video?

***

The vent anyway pulls everything floating to the fan.

Just stuff I read, and it was an none issue, memorable only as it was so weird and probably because astronauts know that it can be fatal on an eva. 
Some fans push, we tend to use fans to pull air out of bathrooms and stoves but AC and heaters with fans push, an pc cooling fan and an string would work fine. 

[AckSed]

I did not know the diameter of Skylab was that large. Makes me wonder what you could do with a 8 metre-wide hab (Starship 9-metre fairing plus walls with meteorite shielding, radiation shielding, life-support ductwork and all the rest).

Speaking of space stations, here's something I've always wondered: how does the ISS cope with the bits that fall off humans? I'm talking dead skin (that becomes dust), hair (that blocks filters) and especially skin grease. Is cleaning a part of their duties? Do they hoover daily? Who cleans the shower? Are the cargo capsules filled with hoover bags before it's disposed of?

[kerbiloid]

They use a vacuum cleaner for everything, and what is not caught, is collected in the fan duct and manually removed.

Also they use sticky things for hygiene, etc.

https://www.google.com/search?client=opera&q=samantha+cristoforetti+iss+tour&sourceid=opera&ie=UTF-8&oe=UTF-8

https://www.mvideo.ru/blog/pomogaem-razobratsya/byt-na-mks

ISS doesn't have a shower or a bath, only wet towels.

Every cargo ship bring a lot of disposable hygiene towels, clothes, napkins, wet and dry, which they use for hygiene and station cleaning.

[DDE]

Why is there still such an empahsis on looking for evidence of Martian water with Curiosity? I thiught it was a done deal a decade ago.

[AckSed]

Nah. It's like asking a geologist if they ever get tired of looking for hydration in rocks on other planets. The more evidence of water they find the more complete the picture they have of Mars' wet period.

[K^2]

2 hours ago, DDE said:

Why is there still such an empahsis on looking for evidence of Martian water with Curiosity? I thiught it was a done deal a decade ago.

As above, but also, water can exist in a lot of states. Some of these are simply traces of more abundant water in the past, which can establish both a firmer timeline of when the water disappeared off the surface and why, which is of obvious importance to us, humans. And yet another aspect of it is finding water that still in the state that might be useful to either some extant life on Mars that eluded our detection until now, or more likely and practically, for any future missions to Mars.

A common argument against habitation of Venusian clouds, for example, is lack of water vapor, but water locked in sulfuric acid is just as useful for a colony. You literally just need to heat the atmosphere to a few hundred °C, then cool it back down to extract water. On Mars, we're definitely out of luck with atmospheric water and water ice is heavily contaminated and locked away in hard to reach areas, but some hydrated rocks are just as good as liquid water if you have the right equipment to extract it. Finding a lot of water in the right type of rock could make the idea of sustaining a colony and even refueling rockets entirely with local resources a very plausible concept.

[kerbiloid]

They land the rover at the place called Jezero (from South-Slavic "Lake") because it's a dry lake, and start marvelling that it has water some time ago...

L - Logic.

Edited February 24, 2023 by kerbiloid

[tater]

Faust says there's a NOTAM for Space Operations at the Cape Sunday... except there are no launches scheduled.