# For Questions That Don't Merit Their Own Thread

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I don't think I've posted in this thread in a very long time so sorry if I'm doing this wrong, but:

Is there any way I can calculate how fast a small planet's atmosphere will be lost over geological timescales, and at what rate the planet's surface pressure will decrease? Assuming that it's just barely below the threshold of permanently maintaining an atmosphere of Oxygen and Nitrogen.

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Main contribution to atmosphere loss is usually due to solar winds, which are difficult to model, particularly so if the planet has a magnetic field. There are probably some empirical models out there, but I can't think of any simple estimates from first principles.

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5 hours ago, ChrisSpace said:

calculate how fast a small planet's atmosphere will be lost

A great compendium of space formulas is on

English transgooglation:

(The formulas are visible in Chrome but not in old Firefox)

***

(Not a native speaker, so some terms may sound weird in amateur translation)

Page 28 and bound ones:

***

First, define the temperature of your planet exosphere, Texosphere , K
Earth  ~1 500 K  at ~500..1000 km altitude.
Jupiter 1 100 K
Saturn and Uranus 800 K.
Neptune 750 K.

***

Roughly you can estimate it by the star UV luminosity,

Select your star spectral class and corresponding ratio of UV in its luminosity:

Star class UV ratio
A0 0.45
F0 0.21
F5 0.15
G0 0.08
G2 (incl. Sun) 0.07
G5 0.06
K0 0.04
K5 0.02
M0 0.01
M5 0
brown dwarves and other rubbish 0

Texosphere , K ~= 1 500 K * (sqrt(StarUVratio / SunUVRatio) / (PlanetaryOrbitRadius, AU))0.21 .

Say, if there was an F5 star instead of the Sun, then for Mars we get: Texo ~= 1 500 * ( sqrt(0.15 / 0.07) / 1.524) 0.21 ~= 1487 K.

So, actually the exosphere temperature is more or less same, just take the ready-to-use values from above.

***

Calculate the RootMeanSquareSpeed of gas

RootMeanSquareSpeed of gas=  sqrt(3 R Texosphere / MolarMass)

MolarMass:  O2 = 0.032 kg/mol,. N2 = 0.028 kg/mol,  average air = 0.029 kg/mol

R = 8.31441 J / (mol*K)

So, for the Earth conditions,
RootMeanSquareSpeed of gas=  sqrt(3 * 8.31441 * 1500 /  0.029) ~= 1850 m/s

***

EscapeSpeed of the planet = sqrt(2 G M / r)  ~= 11 200 m/s for the Earth.

(or ~3 700 m/s for Kerbin)

***

Conditions of gas retention  by a planet:

EscapeSpeed / RootMeanSquareSpeed

>= 6.0  Stable atmosphere.
~ 5.0  the gas escapes in several hundred million years.
~ 4.0  the gas escapes in several thousand years.

For the Earth = 11 200 / 1 850 ~= 6.0, stable atmosphere.

For the Kerbin= 3 700 / 1 850 ~= 2, the atmosphere will dissipate very quickly.

***
Rough estimation, Jeans's formula:

DissipationTime ~= ( RootMeanSquareSpeed 3 / (2 * GravityAcceleration2  * PlanetRadius) ) * exp(3 * GravityAcceleration  * PlanetRadius / RootMeanSquareSpeed 2 ).

So,
Earth
DissipationTime ~= ( 1850 3 / (2 * 9.812 * 6.371*106) ) * exp(3 * 9.81 * 6.371*106 / 1850 2 ) ~= ( 6.33*109 / (1.23*109) ) * exp(1.875*108 / (3.42*106)) ~= 5.15 * exp(54.8) ~= 3.24*1024 s ~= 1000 qdrln yr, i.e. "almost infinite".

Kerbin
DissipationTime ~= ( 1850 3 / (2 * 9.812 * 6*105) ) * exp(3 * 9.81 * 6*105 / 1850 2 ) ~= ( 6.33*109 / (1.155*108) ) * exp(1.766*107 / (3.42*106)) ~= 54.8 * exp(5.16) ~= 104 s  i.e. "almost immediately".

(Interesting fact: the Earth and Kerbin values (5.16 and 54.8) are incidentally equal but occupy opposite places, lol)

Actually, the formula gives obviously just a qualitative evaluation for such extreme cases as Earth and Kerbin.

***

Roughly, a planet, can hold a gas with MolarMass, kg/mol.

MolarMass, mol ~= 450 * Texosphere, K / (GravityAcceleration, m/s2 * PlanetRadius, m)

I.e.
Earth: 450 * 1 500 / (9.81 * 6.371*106) ~= 0.01 kg/mol, neon or heavier.
Kerbin: 450 * 1 500 / (9.81 * 6*105) ~= 0.115 kg/mol, almost nothing in significant amount.

***

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11 hours ago, ChrisSpace said:

I don't think I've posted in this thread in a very long time so sorry if I'm doing this wrong, but:

Is there any way I can calculate how fast a small planet's atmosphere will be lost over geological timescales, and at what rate the planet's surface pressure will decrease? Assuming that it's just barely below the threshold of permanently maintaining an atmosphere of Oxygen and Nitrogen.

I'm not the math guy you might be hoping to hear from; but I've read a bit on this... and the consensus I've gathered is that planetary atmosphere is very little understood.

As @K^2 wrote, solar winds are the likeliest culprit in reducing atmosphere, and having a strong magnetic field is the likeliest method of protecting that atmosphere - but the 'regeneration' rate is also barely understood.  Volcanic activity (as an example), and other off-gassing processes (chemical and biological) can add atmosphere back - and at a rate we don't yet know how to calculate.  With so few examples and the wild differences between the planets and moons we can see and have visited... I'm left with the impression that despite our best efforts -- we're still guessing as to the answer.

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Still trying to realise what does the name of the automatic re-docking manipulator on the Russian orbital station modules mean, "Ляппа" / "Lyappa".

Spoiler

There is no such word in Russian, and it sounds rather childish or folkish for such serious thing, like "a silly thingie that spills".

It also unlikely "la(mbda)" + "(k)appa".

***

But today I've read the moderators' "Overlapping threads are merged", and got a new idea.

Wiktionary tells that "lapper" is "One who wraps or folds."

Maybe "lyappa" is actually "lapper" / "lappah", jockingly copypasted from English?

Can the thing on the photo be a "lapper" in English, as it laps on the the counterpart module grappling fixture, and then laps the docked module on its top?

***

Someone's animation:

("Load 25 images more", till such animations

Spoiler

)

Edited by kerbiloid
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Re: Albedo and Reflected Light...

From what I know about shadows in space - they should be clearly defined and nearly absolutely dark (given that there is no atmosphere to scatter light).  Sunlight in space (afaik) is almost blisteringly white.

...brings up the question: what about the light reflected back by the earth?

Does the 'blue' of the ocean cast a blue-shifted reflected glow upon the shaded side of the ISS or other satellites?

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On 11/11/2020 at 9:41 AM, ChrisSpace said:

any way I can calculate how fast a small planet's atmosphere will be lost over geological timescales, and at what rate the planet's surface pressure will decrease?

A simpler use-case might simply be something to do with the percentage of gasses that are beyond escape velocity given the Maxwell-Boltzmann distribution at a given atmospheric height, density and temperature.

______________

Anyway, for my own question :

I didn't know that FAA certifies space launches in the US. I thought that sure they must have something to do with NOTAMS and stuff, but seems like it's a lot more involved than I thought...

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12 hours ago, YNM said:

I didn't know that FAA certifies space launches in the US. I thought that sure they must have something to do with NOTAMS and stuff, but seems like it's a lot more involved than I thought...

Anything designed for controlled flight is an aircraft according to FAA rules. Moreover, everything above 18,000 feet and up to 60,000 feet is class A controlled airspace, meaning that you cannot fly through it without permission from the ATC. And the only way you'll be allowed in class A is if you are either flying a certified aircraft with a tail number and a flight plan or you have filed for and were granted an exception to allow you use of class A airspace.

I doubt that any rocket has ever had an airworthiness certificate and a registered tail number. I imagine, at most, they'd be registered as experimental aircraft. In that case, you would absolutely need to file for an exception to be allowed to climb to 60,000 feet, and FAA has right to approve or reject it on case-by-case basis.

Military launches can bypass all of that bureaucracy, of course. And I believe, there is a simplified path for getting permission for high altitude amateur rocket launches, so long as you have membership with one of rocketry associations in the US.

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How many of you knew this?

---

Way back in the day, my favorite video game was MechWarrior 2, which I played on a Dell Dimension XPS with a 66MHz Pentium and a 3DFx Voodoo graphics card (which, I am proud to say, I installed myself)  Thus began a long hobby of computer building.  To this day, the Dell is the only non-laptop I've purchased.

Of the Mechs in the game, my favorites were the "Chicken Leg" mechs... which reminded me of what I (and I'm going to goon this up) remember seeing on Battletech / Macross on after-school TV in the 80s.  The Chicken Leg mechs were so unlike anything I remember seeing anywhere (except maybe Star Wars - but those did not strike the chord that the Anime series did).  I even remember playing the pen and paper version of MechWarrior - where I favored the Chicken Leg mechs (the name of which escapes me).

So anyway, from that time - and really without thinking about it... I always assumed bird legs (including chickens) just had bent backwards legs -- i.e. the knee was backwards.

But ...

...it's not true.

Birds - including chickens - have a forward facing femur, just like (pretty much) every other terrestrial animal.  The knee is up close to the body, and what I always thought of as the knee - is actually the ankle.

Anyone else have this faulty 'understanding' of how bird legs worked?

(oh - and any responses / answer to my 'reflected light' question above?)

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Known for me since I tried to realize a horse kinematic model in schoolhood.

P.S.
So, to look like chickens chicks put heels under heels.

Edited by kerbiloid
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6 minutes ago, kerbiloid said:

Known for me since I tried to realize a horse kinematic model in schoolhood.

P.S.
So, to look like chickens chicks put heels under heels.

I've always known this about horses and dogs... but I assumed they were like that because they are mammals.  For what ever reason, I thought 'birds are different'

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2 hours ago, JoeSchmuckatelli said:

I've always known this about horses and dogs... but I assumed they were like that because they are mammals.  For what ever reason, I thought 'birds are different'

Chickens, dogs and horses has the standard leg model.

Humans, apes and elephants are the odd one as our ankles are at ground level at rest.
Chicken are a bit extreme having their knee that high, but cats also have their knee high,  looks like as animals get heavier they straighten their legs as in horses compared to cats.
So the mecwarior model does not have chicken legs.

And I say its an cool but stupid design, having the joint forward let you armor forward direction with an knee cap, bending backward you can not do that without limiting movement.

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What do you call a government that works by:

1. The country is ruled by king (if male) or queen (if female) from monarchy. A single noble family holds a central authority

2. If the current ruler dies or incapable of ruling anymore, the eldest descendant (male or female) take their place

3. The country is divided into several states with one state acting as central authority where the king/ queen lives and ruled the entire country and other states

4. The states are ruled by the descendants/ relatives of the family, each have their own jurisdiction and rules for their states, but all of them obey the central authority. The state's ruler also follows the central authority method of transfer of power (for example, if the king dies, the eldest son (let's say his name is A) of state X takes the throne and his son inherit the state X. If A dies, the next eldest member of state Y (lets say his/her name is B) takes the throne while B's son/ daughter inherit the state Y)

5. Each states are allowed to have their own military force that's commanded by the ruler of that state and central authority, but obey the latter if the orders from both sides are contradictory

6. Each states strives for the prosperity of their own people, but also required to contribute for the prosperity of the entire country (either by exporting goods for developing other states or helping them by sending military aid in times of war)

Note that said country is rather small in terms of habitable landmass. Most of the country consists of uninhabited mountain peaks with small amount of states (around 4-5 plus the central authority state)

Edited by ARS
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25 minutes ago, ARS said:

What do you call a government that works by:

1. The country is ruled by king (if male) or queen (if female) from monarchy. A single noble family holds a central authority

2. If the current ruler dies or incapable of ruling anymore, the eldest descendant (male or female) take their place

3. The country is divided into several states with one state acting as central authority where the king/ queen lives and ruled the entire country and other states

4. The states are ruled by the descendants/ relatives of the family, each have their own jurisdiction and rules for their states, but all of them obey the central authority. The state's ruler also follows the central authority method of transfer of power (for example, if the king dies, the eldest son (let's say his name is A) of state X takes the throne and his son inherit the state X. If A dies, the next eldest member of state Y (lets say his/her name is B) takes the throne while B's son/ daughter inherit the state Y)

5. Each states are allowed to have their own military force that's commanded by the ruler of that state and central authority, but obey the latter if the orders from both sides are contradictory

6. Each states strives for the prosperity of their own people, but also required to contribute for the prosperity of the entire country (either by exporting goods for developing other states or helping them by sending military aid in times of war)

Note that said country is rather small in terms of habitable landmass. Most of the country consists of uninhabited mountain peaks with small amount of states (around 4-5 plus the central authority state)

Classic 'high king' territory there

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Sounds like classic feudalism to me.

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Can a sufficiently powerful radar cause visible effects on a "glass cockpit"? Similarily, is there ultimately any truth to claims of the ability of humans to hear radio?

Looking for a way to describe being locked on by a stupidly powerful radar system.

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23 minutes ago, DDE said:

Can a sufficiently powerful radar cause visible effects on a "glass cockpit"? Similarily, is there ultimately any truth to claims of the ability of humans to hear radio?

Looking for a way to describe being locked on by a stupidly powerful radar system.

I don't think the radar locks onto you - rather the system reads the return from the stupidly powerful radar and calculates the intercept for the weapon system

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48 minutes ago, DDE said:

Similarily, is there ultimately any truth to claims of the ability of humans to hear radio?

Back in the day when most radio was amplitude-modulated, and people had tooth fillings made with metal alloys, it's possible that some people were able to pick up radio with their teeth. Certain oxides that can form from metals in fillings of mid-century dentists work like semiconductor under the right conditions, and that can make a diode in your tooth with adjacent crown, for example, which will act as antenna of a simple detector radio. That might let you feel the signal when you are close to the transmitter. I don't think there is any possible way for you to actually hear the sound, but if the station is playing a song with familiar beat, you might be able to recognize it and think you hear it.

There is a lot of conjecture in this, and I'm not aware of any case being properly documented by a physician, but it's the only variant on this story that seems plausible. As in, it absolutely could have happened, but I can't say for sure if it has.

I don't think anything like this can happen with modern radar. Even if people still used these kinds of materials for dental work, the frequency is too high for a simple detector like this to produce even a pain sensation. Unless the beam is powerful enough to literally start cooking your skin, I can't think of any way you'd feel it. And that is possible with power of a long range active radar, but you have to be standing within meters of the dish.

As for picking it up in glass, I don't think it will screw with any modern nav-aids or any other electronics. So unless you have a dedicated RWR, I don't think there's any chance of you becoming aware. If you do happen to be flying a plane equipped with RWR, which would pretty much make it a military plane, then you'll know that there is radar trained on you because the RWR will be making a ruckus with buzzers and blinking all sorts of warning lights, telling you to get the hell out of Dodge.

Edit: I'm just now realizing I'm not sure how RWR behaves with friendly radar. I assume the simple and most useful way would be for it to give you a warning on a new source, then shut up once it does the IFF handshake, but with older systems that might still have produced a new bleep on each sweep, since tracking location of sources is somewhat sophisticated.

Edited by K^2
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The superpowerful radar should melt the  foiled chocolate in the survival kit, so the pilot would feel a warm thick mess underneath, try it and ensure it's sweet.

Edited by kerbiloid
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7 hours ago, K^2 said:

Unless the beam is powerful enough to literally start cooking your skin, I can't think of any way you'd feel it. And that is possible with power of a long range active radar, but you have to be standing within meters of the dish.

Actually, from the descriptions of "radar trauma" I hear, it goes staright to the bladder and the eyeballs... but it could be the wrong frequency.

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6 hours ago, DDE said:

Actually, from the descriptions of "radar trauma" I hear, it goes staright to the bladder and the eyeballs... but it could be the wrong frequency.

The trick when microwaving liquid is to stir, otherwise you can get hot spots

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14 hours ago, kerbiloid said:

The superpowerful radar should melt the  foiled chocolate in the survival kit, so the pilot would feel a warm thick mess underneath, try it and ensure it's sweet.

Warship radars and some other radar systems are known to kill birds but that is on very close range, you don't want your radar frequency who get absorbed by water anyway.
Understand radars on modern planes like the F-22 can be used like an soft EMP, it overload the sensors and you will get errors in the sensor and control wiring unless well shielded.
Now  this might be just for trolling during peace time, but overloading sensors is old.

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41 minutes ago, magnemoe said:

Understand radars on modern planes like the F-22 can be used like an soft EMP, it overload the sensors and you will get errors in the sensor and control wiring unless well shielded.

I know, and that's what I'm looking for, just cranked up to dozens of megawatts.

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What's the best guidance systems used on missiles for space battles? Especially the one that takes place in-orbit of a planet? Could normal missile guidance be used normally? (Infrared, heatseeking, radar-guided, laser-guided etc.)

Edited by ARS
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48 minutes ago, ARS said:

What's the best guidance systems used on missiles for space battles? Especially the one that takes place in-orbit of a planet? Could normal missile guidance be used normally? (Infrared, heatseeking, radar-guided, laser-guided etc.)

Think both radar and IR would work, later might get issues in some cases.
Main difrence is that I think most air to air missiles uses fins to steer, this will not work in space.
Another issue is that most anti air missiles are solid fuel with an limited range, you want to do this different in space.

Simplest would be an solid first stage and and second stage with rcs and an monoprop engine for correction burns. This is a bit like the anti ballistic missile version of the standard missile upper stage.
Probably a bit larger warhead, no reason to use explosives unless you orbits are pretty similar as the impact has more kinetic energy than tnt.

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