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For Questions That Don't Merit Their Own Thread


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10 hours ago, Rutabaga22 said:

Wouldn't near C interstellar travel be deadly to a human?

The Gs of going near C would turn you into a spray of red, right? 

Shouldn't the Alcubierre Drive be the "Alcubierre Death Machine"?

100 km/h is certain death for an unprotected human. It's all about the vehicle :)

Under constant acceleration of 1 G you reach light speed in a little over a year. The G forces aren't really the hard part, it's the "constant acceleration" thing we need to figure out.

Alcubierre drives in theory could be safe to the occupants since they are in 'normal' space. However it would likely cause a particle 'bow wave' akin to a supernova on arrival, so whatever you decide to stop at will be fried to a cinder. So I vote in favour of your proposed name chance :D

 

 

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As the theory predicts that the Alcubierre  drive releases all impacted particles on shutdown, even its engaging would be a death sentence from the Pangalactic High Council High Court, for the whole star system extermination.

P.S.
Interesting, if this particle pack is enough dense, would the Alcubierre ship turn into a black hole on arrival.

Or at least would it cause a fusion explosion of the packed hydrogen nuclei and vaporize the ship.

Edited by kerbiloid
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11 hours ago, kerbiloid said:

P.S.
Interesting, if this particle pack is enough dense, would the Alcubierre ship turn into a black hole on arrival.

Quick Fermi estimation... I think the general rule of thumb is that space contains about 1 million particles per cubic meter. Let's say you travel 13.8 billion ly at most (because you want to see where you end up, even if what you see was 13.8 billion years ago >.<). That's 13.8*10^9 years * 365.25 days * 24 hours * 3600 seconds * 3*10^8 meter/second. What about your warp field's cross section? 10K sq.meter sounds nice, 100x100 meter, Jeb wants some proper shielding and parachutes after all, so you sweep up 10^4*10^6 particles per meter traveled. Molecular weight? Tiny of course, elemental particles, but hey let's say they're all water molecules because I happen to know 1 mole of water (6*10^23 molecules) is 18 grams. So the total mass you sweep up is 13.8*10^9*365.25*24*3600*3*10^8 * 10^4*10^6 * 0.018 / 6*10^23 makes about...

40*10^9 kg. 1 solar mass is in the order of 10^30 kg so I think we're safe from that at least. Then again, you might be creating primordial black holes... and maybe everything collapsing in on itself would actually be better than the alternative :D

 

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I love this conversation. Put in laymans terms the thought experiment that came up with the idea of the drive basically is.

If I discovered magic I could use it to create matter with negative mass that I could then use to treat space and the universe as if it is a 2 dimensional piece of paper, I could then gather up a large fold of this paper and slide it under the spacecraft I am using while keeping my craft perfectly in place. So I don't actually move my craft I move the entire universe. Thus not putting any acceleration forces on the craft and it's occupants.

The trouble is using this logic, you can't just affect a localised area of space around your craft, because once you treat space itself as something that can be compressed and released then it is all connected and everything in the universe gets affected. Crudely, if you ride a jet ski and suck in and expel water to propel yourself then you are creating a wake and changes in the water you are moving. In a river that gets absorbed by the banks. No such luck in space. planets and solar systems are just flotsam bobbing up and down in the ripple you create.

So don't worry about the devestation you create when you arrive. As soon as you started moving space you doomed everything else.

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11 hours ago, kerbiloid said:

The things are much worse, it varies by orders of magnitude.

https://en.wikipedia.org/wiki/Interstellar_medium#Interstellar_matter

That's about right then isn't it? The interstellar mediums (making up 99% plus of the volume) range from 10^-4 to 50 per cubic cm, which makes 100 particles to 50 million particles per cubic meter. That's inside the milky way galaxy, we're traveling across the universe here, 99.9999etc % of that is going to be intergalactic space which is much less dense, and we're averaging over the radius of the observable universe. So 1 million seems a nice ballpark figure, and probably a gross overestimation. It will do fine for a Fermi estimation, in fact 1000 would have been fine too, it doesn't matter all that much.

A black hole's event horizon is determined entirely by its mass and for a micro black hole these are absolutely tiny. r = 2GM/c^2, so our theoretical black hole's event horizon is going to have a radius of 2 * 6.67*10^-11 * 40*10^9 / 9*10^16 = approx 6*10^-17 meter or 0.6 attometer, that's about the size of a single quark. And that's going to be outside of our warp bubble after moving... (displacing?) a 13.8 billion ly distance, the furthest one could possibly travel, seems like that's not going to be an issue.

Also, IIRC Hawking radiation is inversely proportional to a black hole's mass, which is why these micro black holes should evaporate very quickly.

I'm not worried about black holes. We're still going to blow ourselves up some other way though, this is the KSP forum after all.

 

8 hours ago, ColdJ said:

If I discovered magic I could use it to create matter with negative mass that I could then use to treat space and the universe as if it is a 2 dimensional piece of paper

I think there is actually a solution that doesn't require negative mass. Unfortunately, it requires negative energy... We never get a break do we :D

 

 

Edited by Beamer
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31 minutes ago, Beamer said:

That's about right then isn't it? The interstellar mediums (making up 99% plus of the volume) range from 10^-4 to 50 per cubic cm, which makes 100 particles to 50 million particles per cubic meter. That's inside the milky way galaxy, we're traveling across the universe here, 99.9999etc % of that is going to be intergalactic space which is much less dense, and we're averaging over the radius of the observable universe. So 1 million seems a nice ballpark figure, and probably a gross overestimation. It will do fine for a Fermi estimation, in fact 1000 would have been fine too, it doesn't matter all that much.

A driveway usually consists of absence of stones (stone vacuum), until the very first has been met.

The same with gas clouds.

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About how much of an early warning would Japan have of incoming ballistic missiles coming from 1000 km away?

I ask here as Google will not give a straight answer. The US would have 30 minutes or so thanks to early warning IR sats. But no else apart from Russia has these systems. France had the Spirale IR sats… for a brief period of time in 2009. Contrary to the misleading claims that Japan’s IGS sats can be used for “missile early warning”, this is only by looking for signs of missile deployment- not round the clock warning- not taking into account the existence of solid fuel missiles. It is unclear if US early warning info is transmitted to allies or not*.

This leaves them to rely on their radars for detecting incoming missiles. These radars have pretty poor range (within the context of BMEW), about 1000 kilometers max, but I would assume these would have worse range when it comes to targets from space.

This question arose as Japan’s PM announced his intention to have the government study the potential for construction of fallout shelters. Not only is the survivability of them questionable, but I wonder whether it is worth the cost if we are only going to get 1 minute-40 seconds of warning.

*I assume it is not clear because despite Wikipedia claiming DSP provided “timely warning” of launches during the Gulf War, Japan began sounding sirens only after a missile had splashed down recently.

Also this counts as a spaceflight related question, right?

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OK, so I'll take a shortcut instead of doing the math. The Iranian Qiam-1 (800 km) has a flight time of six minuteshttps://www.airandspaceforces.com/for-missile-warning-in-iraq-thank-the-space-force/ Out of these, it's going to spend at least three well above the horizon, so a little bit more than your assessment. However, we also know that the Soviets considered a five-minute warning to be unacceptably low.

52 minutes ago, SunlitZelkova said:

but I would assume these would have worse range when it comes to targets from space

Not really - the installations tend to be have capabilities well beyond medium orbit.

54 minutes ago, SunlitZelkova said:

Japan began sounding sirens only after a missile had splashed down recently

This bit usually is taken to be a damning factor for an air defense system.

55 minutes ago, SunlitZelkova said:

not taking into account the existence of solid fuel missiles

This bit irks me because one of the most hawkish things to have come out of Japan in recent years was a call for a regional-level missile strike capability because of a hypothetical situation when 'enemy' missiles are spotted on the launchpads and fueling. Given how long ago has the issue of making ampulized, storeable hypergols has been resolved, I'm sad to say some Japanese politicians seem to be stuck in the 1960s. The difference in time between liquids and solids is about 20 seconds, needed for the fuel to flow down the lines.

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1 hour ago, SunlitZelkova said:

About how much of an early warning would Japan have of incoming ballistic missiles coming from 1000 km away?

V-2 was 320 km / 5 min.
Pershing II had 2 500 km / 5..10 min.
Low-trajectory SLBM as well.

30 min is for ICBM. Japan has 5+ min from launch to hit.

1 hour ago, SunlitZelkova said:

But no else apart from Russia has these systems.

Israel has a lot of of them, for the rockets of any size and color.
Though, it's because they need to be warned about small 100+ mm rockets, when you can hide in any strong building, rather than about nukes.

Even if warn about the launch immediately, not a lot of things can be done in five minutes by random people.
It would take several minutes just to get out from a skyscraper.

Subway. Only subway.

Edited by kerbiloid
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4 hours ago, SunlitZelkova said:

About how much of an early warning would Japan have of incoming ballistic missiles coming from 1000 km away?

Don't want to start any arguments but, before considering your own capabilities, you also have to consider what the opposite side is launching: well, you know, something particularly fast with a strange-looking warhead.

Question: Do Japanese public spaces such as office buildings and shopping malls with underground parking underneath have designs for emergency air-raid shelters?

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2 hours ago, kerbiloid said:

30 min is for ICBM. Japan has 5+ min from launch to hit.

Yes, I meant that. I flip flopped on how to format this so the numbers are all over the place (like the 1000km missile but 1000km range radar) :confused:

2 hours ago, kerbiloid said:

Subway. Only subway.

It has been theorized that Tokyo could firestorm. There is lots of flammable material on buildings intended for thermal control/energy efficiency.

Some speculations on nuclear war claim fallout shelters will simply save lives but I have seen at least one early 1960s take from some professor claiming these- from subway to basement- would end up much like the basements of Dresden and Tokyo and asphyxiate people.

3 hours ago, DDE said:

This bit usually is taken to be a damning factor for an air defense system.

Yep. The talk of early warning and sheltering is pretty bizarre considering even Britain, as far away as it was from the western USSR, was generally seen as doomed to little to no warning in media (Threads and When the Wind Blows feature nuclear detonations within seconds of the characters receiving a warning) and government policy (letters of last resort - I’d assume this meant they didn’t expect to be around to order retaliation).

The irony of it all is that these fallout shelters being discussed in Japan aren’t just for common people, they are intended to keep the entire government functioning, probably including the 100+ member National Diet.

3 hours ago, DDE said:

This bit irks me because one of the most hawkish things to have come out of Japan in recent years was a call for a regional-level missile strike capability because of a hypothetical situation when 'enemy' missiles are spotted on the launchpads and fueling. Given how long ago has the issue of making ampulized, storeable hypergols has been resolved, I'm sad to say some Japanese politicians seem to be stuck in the 1960s. The difference in time between liquids and solids is about 20 seconds, needed for the fuel to flow down the lines.

IKR.

But given the Izumo class helicopter carriers were built with a flight deck capable of accommodating the F-35B takeoff and landing despite promises that they would never be deployed on such ships, I think something else may be afoot here.

———

So getting back to something closer to science…

How fast do people run on average when running for their lives?

I have only found one article with no source claiming 12mph/19kmh, or about 300 meters in one minute.

Which is a lot more than I thought, but that doesn’t take into account running over people who have fallen or the bottleneck at the entrance to a shelter, or people shoving you back to get ahead of you.

Japan is known for public orderliness in crisis but I can’t see how lining up and calmly filing into a shelter is going to work, when there is a minute and half or so until the missile hits- although people are so oblivious to the actual severity of the danger there I would not be surprised if people did calmly file in expecting 10 minutes or so of evacuation time, only to get vaporized or blasted.

But IIRC MythBusters tested the “everybody just cram into the airplane” method of airliner boarding and it kind of worked, right? So maybe we will be ok, right? :(

1 minute ago, steve9728 said:

Don't want to start any arguments but, before considering your own capabilities, you also have to consider what the opposite side is launching: well, you know, something particularly fast with a strange-looking warhead.

Question: Do Japanese public spaces such as office buildings and shopping malls with underground parking underneath have designs for emergency air-raid shelters?

No. There is little to no concept of civil defence there, in stark contrast to South Korea. It’s silly considering how strong natural disaster preparedness is.

My question was related to civilians sheltering rather than getting retaliatory missiles off.

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6 minutes ago, SunlitZelkova said:

No. There is little to no concept of civil defence there, in stark contrast to South Korea. It’s silly considering how strong natural disaster preparedness is.

My question was related to civilians sheltering rather than getting retaliatory missiles off.

Yeah, that's what I am meaning too. According to my experience travelling in Japan, I can hardly imagine the panic of those five minutes, especially in the cities. Hope for world peace

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3 minutes ago, SunlitZelkova said:

Some speculations on nuclear war claim fallout shelters will simply save lives but I have seen at least one early 1960s take from some professor claiming these- from subway to basement- would end up much like the basements of Dresden and Tokyo and asphyxiate people.

Crude free-standing shelters in Hiroshima and Nagasaki were considered stunningly effective at mitigaging everything except follow-up fallout damage.

5 minutes ago, SunlitZelkova said:

The talk of early warning and sheltering is pretty bizarre considering even Britain, as far away as it was from the western USSR, was generally seen as doomed to little to no warning

A strong counterexample is Sweden. Not sure what they were counting on, but they were counting on the level of 65k bunkers.

https://archive.md/br8hA

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1 hour ago, SunlitZelkova said:

Tokyo

https://ru-m-wikipedia-org.translate.goog/wiki/Геофронт?_x_tr_sl=ru&_x_tr_tl=en&_x_tr_hl=ru&_x_tr_pto=wapp

(It's strange but the wiki article doesn't have an English version.)

Also, the classics.

https://fallout.fandom.com/wiki/Pulowski_Preservation_shelter

https://evangelion.fandom.com/wiki/GeoFront

 

Spoiler

 


 

1 hour ago, SunlitZelkova said:

How fast do people run on average when running for their lives?

Kids. They are slow runners.
(Adults fast walk ~2 m/s, fast run ~6 m/s, so about 3 m/s without kids.)
But the vault entrance capacity is limited, so the faster the people can run, the stronger is throng at the doors.

Also we should take into account that any proper public shelter must have two sequential doors, a strong and pressure external and a pressure internal, and they should be closed one by one, not at once.
If things run well, just for double protection.
If things run realistically, see the Doomsday (2008) gates closing scene for visualisation. 
The crowd is storming the primary gate while they are closing, some stick crushed between the gate leaves. When the primary gates arer closed, the secondary gates start closing, and those who had passed through the primary, quickly get in, so the secondary gates are not blocked semi-opened with bodies.
Of course, in the movie there were gates in a wall, not pressurized, but the principle stays same.

So, you need to have enough time between the alarm sound and the second gates having been closed, and this takes several minutes depending on the gates construction.
Also, once you run an alarm, there will be panic crowd blocking the street, so the administration wouldn't be able to escape from city by roads.
This means that even if an ICBM launch is detected, several minutes will be spent on confirmation and so, next several minutes on the commandment evacuation, and you have, say fifteen min for alarming and hiding.
So, if the gates need five minutes to make the entrance fully closed, and there should be a safety interval of, say, five minutes, to do it before the possible shockwave comes, you have only five minutes to give the street people after the alarm sound before you start closing the gates.
5 min = 300 s = about half-mile of zigzag run to join the crowd at the gates. So, it's mostly hiding the the folds of the local urban terrain is left, at the opposite side from the potential GZ.
Obviously, no other option in case of the 5 min missile flight time, unless a shelter is right at hands.
The bright side: beyond the 1..2 km radius (which is anyway deadly), the fallout is ~45° narrow, so they have 7/8 chances to appear outside of strong fallout.

1 hour ago, DDE said:

Sweden

And Finland.

https://www.cnbc.com/2022/05/17/finland-has-civil-shelters-capable-of-withstanding-a-nuclear-attack.html

Edited by kerbiloid
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8 hours ago, SunlitZelkova said:

potential for construction of fallout shelters. Not only is the survivability of them questionable, but I wonder whether it is worth the cost if we are only going to get 1 minute-40 seconds of warning

In no particular order:

Moscow's metro stations are deep underground for a reason.  

Assess the threat.  NK launching one (or 5) nukes at Japan is very different from the MAD scenario where RU launches the vast majority of its arsenal to kill the West and its Allies. A 15kt weapon is a neighborhood killer.  If you are not in the exact part of Tokyo... You are likely fine. 

Most people won't need to worry about the fallout.  The biggest risk is ingesting the heavy metal / radioactive dust and Japan has lots of masks (N-95 is all you need). 

The biggest risk is the breakdown of the logistics system - but if it were only one bomb, you would treat it like a regional natural disaster. 

(Side note) Did you ever look at the Ventura County, CA Nuke Safety guide? https://www.google.com/url?sa=t&source=web&rct=j&url=https://s29710.pcdn.co/wp-content/uploads/2018/05/VC-Nuclear-Safety-18pp-Education-Guide-Downloadable-FINAL.pdf&ved=2ahUKEwjB2IGA9un6AhXMjIkEHWhzCAkQFnoECBsQAQ&usg=AOvVaw1TSd_62zTvRvimK9GFOXeT. It's not bad. 

Several countries give the US places to use to watch for CN/RU nukes - the presumption is that they are also beneficiaries of the early warning.  Unfortunately, bureaucracy may not give you much time, anyway. 

 

 

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1 hour ago, JoeSchmuckatelli said:

Moscow's metro stations are deep underground for a reason.  

Keep in mind that the good folks at Bunker 703 say that the Metro was mainly a shelter-in-olace option. The blast doors were to be closed down at the first sight of an attack. Not many chances for anyone topside, although I know of dedicated surface evacuattion entrances added by some factories as cost-cutting measures.

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8 hours ago, JoeSchmuckatelli said:

I did not. Thanks!

8 hours ago, JoeSchmuckatelli said:

A 15kt weapon is a neighborhood killer.

They have ones in the 100 kiloton+ range too. I think the bigger ones would be for cities and smaller ones reserved for things like air bases and ports.

They could use multiple ones too. The US did a study in the late 40s, estimating it would take 40x (!) Fat Man sized weapons to destroy Moscow. This is probably why one of the loadouts for the B-36 was 4x Mk 4 bombs (modernized, production Fat Man).

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On 10/16/2022 at 5:00 AM, Beamer said:

Under constant acceleration of 1 G you reach light speed in a little over a year. The G forces aren't really the hard part, it's the "constant acceleration" thing we need to figure out.

Isn't there some weird stuff about reaching C requiring infinite energy though?

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