For Questions That Don't Merit Their Own Thread

[K^2]

29 minutes ago, Hyperspace Industries said:

If you had a plasma magnet sail (which is not a light sail but rather a solar wind (charged particle) sail) and put it in an orbit inside the van Allen belts of earth, would the belts speed it up as with the solar wind, or would they make it orbit slower and fall back to earth?

Unless you re-orient your magnetic sail as you orbit around the planet, the average effect is just drag, slowly de-orbiting the craft. But the situation is exactly the same with a light sail. If you don't re-orient it, the average light pressure is just drag.

If you do adjust the sail orientation, you can use Van Allen belts for propulsion, but there is still more impulse in light pressure than charged particles, so you're still better off with a solar sail than a magnetic one.

Edited March 5, 2022 by K^2

[Hyperspace Industries]

Could you use a series of magnetic coils to accelerate solar wind like a mass driver or coil gun while having them create a rotating magnetic field (like a plasma magnet sail) which (exactly like a plasma magnet sail) uses the charged plasma to create a larger magnetic field which captures and throws even more solar wind plasma out the back as reaction mass?

 

(By the way, @K^2, while the solar wind has less impulse than light, the plasma magnet gets more twr, the reason why plasma magnets have much better twr than solar sails, and ion engines, is that the plasma makes more magnetic fields which make more magnetic fields allowing for a tiny, and super simple, coil fed with 10 kw of power to generate a 30 km or so (actually the size depends on the density of the solar wind so the field gets larger the farther away from the sun you are) magnetosphere that captures the solar wind. This sounds ridiculous but apparently the university of Washington did tests in a vacuum chamber and math and plasma sails work.)

Edited March 5, 2022 by Hyperspace Industries
of course, since we can never have anything perfect, the magnetic field is spherical, so no matter which way you point the sail it will always go the way the wind blows, so it's more of a balloon than a sail.

[DDE]

On 3/4/2022 at 11:44 PM, magnemoe said:

The problem with infantry in APC is that they are not infantry but passengers. Their main benefit is that you have an fast vehicle who is hard to ambush with machine guns or artillery who light skinned stuff like trucks is and also provides fire support. 
Now they also protect you from friendly fragments then you hitting targets, this works better with smart weapons as you can get much closer to the target so you hit an target with a bomb or two then kick in the door couple of seconds later, but walls does that too. 

More seriously, the Soviets did try to use "active seating" on the BMDs and BMP-3 to get the passengers to contribute to the vehicle's firepower via forward hull guns. This seems to have been an abortive branch.

[magnemoe]

35 minutes ago, DDE said:

More seriously, the Soviets did try to use "active seating" on the BMDs and BMP-3 to get the passengers to contribute to the vehicle's firepower via forward hull guns. This seems to have been an abortive branch.

6 or 7 is the current standard, 8 is the tanks, 4 and 5 also works if you want something lighter.   Gun ports does not make much sense if you have remote weapon systems outside of morale  
Infantry is kind of the an battleships destroyer screen in WW 1 for tanks, it does not work if you have an destroyer carrier who has to be armored as an battleship.
But infantry is slow and vulnerable so you want to speed them up and protect them. 

Obviously the war in Ukraine will affect this a lot as you have an war between two modern and skillful countries.
One thing is obvious the western weapons who is gifted and is most successful will be the most like the one Ukraine is using as in an Russian clone or something who is very easy to use. 

[DDE]

26 minutes ago, magnemoe said:

Gun ports does not make much sense if you have remote weapon systems outside of morale  

Try two forward hull guns.

The original point of the BMP-T was to spam RWS mounts to give all the "passengers" as many separate weapons as possible.

[steve9728]

1 hour ago, DDE said:

Try two forward hull guns

Or with ability to launch loitering munition

[K^2]

17 hours ago, Hyperspace Industries said:

Could you use a series of magnetic coils to accelerate solar wind like a mass driver or coil gun while having them create a rotating magnetic field (like a plasma magnet sail) which (exactly like a plasma magnet sail) uses the charged plasma to create a larger magnetic field which captures and throws even more solar wind plasma out the back as reaction mass?

(By the way, @K^2, while the solar wind has less impulse than light, the plasma magnet gets more twr, the reason why plasma magnets have much better twr than solar sails, and ion engines, is that the plasma makes more magnetic fields which make more magnetic fields allowing for a tiny, and super simple, coil fed with 10 kw of power to generate a 30 km or so (actually the size depends on the density of the solar wind so the field gets larger the farther away from the sun you are) magnetosphere that captures the solar wind. This sounds ridiculous but apparently the university of Washington did tests in a vacuum chamber and math and plasma sails work.)

That's an interesting idea. The relevant magnetoplasmadynamics is way over my head, though.  It is plausible that if the sail works as you describe, modulating the magnetic field in a clever way will allow you to get more impulse out of the same plasma at a cost of a higher energy drain, which is what you're looking for. But I don't have the background to even say if it's possible, let alone analyze the energy efficiency of such setup.

If you are really interested, my recommendation would be to see who the main author on the original paper is, find their university e-mail address, and just e-mail them this question. If they don't reply, try one of their graduate research assistants instead. They might have already considered it and possibly even ran simulations of it.

[Hyperspace Industries]

On 3/6/2022 at 9:34 AM, K^2 said:

That's an interesting idea. The relevant magnetoplasmadynamics is way over my head, though.  It is plausible that if the sail works as you describe, modulating the magnetic field in a clever way will allow you to get more impulse out of the same plasma at a cost of a higher energy drain, which is what you're looking for. But I don't have the background to even say if it's possible, let alone analyze the energy efficiency of such setup.

 Thanks! That's probably the biggest compliment I've gotten in a while. 

If I may ask, posit that we were capable of accelerating the charged particles that way, how fast could we reasonably get them going?

By the way, the main benefit of this would actually not be thrust, but rather steering. The classic sail version gets more than enough thrust for pretty much every place where the solar wind is strong enough for it to work, but, since the field is spherical and kilometers wide, the only way to go anywhere else than directly away from the sun is to put two magnets tens of kilometers away from each other. The goal with this is to be able to have a sanely sized drive which can thrust in more useful directions, in this case by accelerating charged particles in the opposite direction.

 

Edit:

It seems that this drive is impossible, or at least impractical.  It seems that every single thing about plasma magnet propulsion forgot one thing mentioned on the side in the original paper, The thing takes 1.5 YEARS to get the magnetic field going!

Edited March 7, 2022 by Hyperspace Industries
Disproved myself.

[monophonic]

On 3/4/2022 at 10:44 PM, magnemoe said:

You run out of active defenses long before an 40 mm gun run out of ammo even if you could intercept them all however.

There is a reason most APS only carry enough ammunition for 2-4 engagements. The APS destroying the incoming projectile does not completely vaporize it. The remains of the destroyed weapon rain on the tank and mounted equipment - such as the APS itself. They tend to not get more intercepts done before the shrapnel rain breaks them up.

On 3/4/2022 at 6:06 PM, TheSaint said:

(TBH, I think this is exactly where the US Army is right now. They've spent the last 20 years focused on asymmetric warfare, so their AFV development has been focused on LAVs and MRAPs; vehicles which work great in an environment which has completely uncontested airspace and no opposing AFV elements. And I think they got a huge wake-up call last week. But I digress.) 

Last week is certainly a big wake-up call, but at least some in the US Army have been awake before. I know they have been training with a friendly nation on how to employ said light formations (Stryker battalion on at least one exercise) against armored peer opponent. And learn they have.

On 3/4/2022 at 6:06 PM, TheSaint said:

Also, the entire point of the discussion was what would happen if armor-based active defense systems rendered low-velocity anti-tank weapons, such as ATGMs or RPGs, obsolete. What are your drones and air strikes firing? (And, TBH, this is kinda half counterpoint and half serious question. What would they be firing? I don't think a recoilless round would be fast enough to defeat a mature active defense system. I guess everything would just be BBBRRRRTTTT from there on out?)

And, again, there are no perfect solutions. If they create a new defense, a new offense will be created to defeat it. Then someone creates a new defense to defeat that. The point is that I don't think the heavily-armored, high-velocity main gun MBT is going away anytime soon.

RPG-30 fires a small precursor projectile to trigger the APS and allow the main projectile get through before the APS is ready to engage again. Some top attack missiles (like NLAW and TOW-2B) use EFPs (explosive formed penetrators) to attack the roof of the tank. Some anti-armor munitions (SADARM, SMArt, BONUS, Sensor Fuzed Weapon) use the same possibly from considerable altitude. At least SADARM and SFW have been used operationally with success in the 2003 invasion of Iraq. You are absolutely right about the incessant race between the weapon and counter-weapon. MBT like the manned fighter jet has been announced dead several times yet both still form the backbone of any competent armed force.

On 3/4/2022 at 7:25 PM, JoeSchmuckatelli said:

FWIW - "Javelin Cages" are now a thing.  Don't know yet if they work 

(My guess is 'Nope')

Your guess is correct. There is plenty of photographic evidence by now to prove it. Javelin - or any other top attack tandem HEAT weapon - will just punch through the "cage" with the precursor charge and pierce the thin roof armor with the primary charge. Even a single HEAT may actually have better penetration detonating at the cage rather than the armor surface. That's because a nose long enough for optimal stand-off distance would be cumbersomely long. An ERA tiling between the cage and the turret roof might change things a little - but is not a very good idea for other reasons, since the main route into and out of the tank is there.

On 3/6/2022 at 12:18 AM, magnemoe said:

6 or 7 is the current standard, 8 is the tanks, 4 and 5 also works if you want something lighter.   Gun ports does not make much sense if you have remote weapon systems outside of morale  
Infantry is kind of the an battleships destroyer screen in WW 1 for tanks, it does not work if you have an destroyer carrier who has to be armored as an battleship.
But infantry is slow and vulnerable so you want to speed them up and protect them. 

Battle carrier did not pan out in the maritime context and it is not optimal in the land context either. The solution is to operate your troop carrier as what it really is - a lightly protected battlefield taxi that dismounts its planes, eh, infantry out in a safe position. So 5 in that picture. 5/6 can work as long as you remember to dismount before contact with the enemy and operate the IFV as an assault gun during the combat. Never dismount under fire - unless you have been immobilized in which case its bailing out, not dismounting.

[SunlitZelkova]

On 3/4/2022 at 6:35 AM, JoeSchmuckatelli said:

So - if you posit an absence of a Cold War between the West and Soviets... What fills the vacuum? 

When looking at the absence of a WW2 - you have to ask whether Europe was willing to continue with the results of WW1... And do you need to change the ending of WW1 (plus the follow-on political and economic realities) to prevent WW2... And so what does that world look like? 

My alternate history/world is based on "people being better", some people here and there dying at a young age and thus not getting a chance to influence the world negatively, and a whole lot of miracles.

I would like to note that the reason we aren't living in a third world dystopia bathed in UV is because of one dude.

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

[Admiral Fluffy]

3 minutes ago, SunlitZelkova said:

I would like to note that the reason we aren't living in a third world dystopia bathed in UV is because of one dude.

Many thanks to that one guy.

[JoeSchmuckatelli]

A 'speed of light' question:

If the speed of light in air is different from the speed of light in water - does it speed back up once it leaves the water? 

 

Also, is the speed of light slower within the termination shock bubble of the solar system given the difference in stellar vs interstellar space? 

[StrandedonEarth]

10 minutes ago, JoeSchmuckatelli said:

A 'speed of light' question:

If the speed of light in air is different from the speed of light in water - does it speed back up once it leaves the water? 

 

Also, is the speed of light slower within the termination shock bubble of the solar system given the difference in stellar vs interstellar space? 

It would speed back up. In this situation it’s better to think of the speed of wave propagation, as opposed to particle speed. 

[JoeSchmuckatelli]

3 hours ago, StrandedonEarth said:

It would speed back up. In this situation it’s better to think of the speed of wave propagation, as opposed to particle speed. 

So - more like it's muted, but still the same sound?  Remove the 'muffling' influence and it regains its original volume?

Or - does it have a set amount of energy, and depending upon the media it will go the max speed at all times?

 

Are either of these decent analogies?

[K^2]

On 3/8/2022 at 8:17 PM, JoeSchmuckatelli said:

So - more like it's muted, but still the same sound?  Remove the 'muffling' influence and it regains its original volume?

The energy ("volume") and frequency ("pitch") remain the same. The only things that change as light passes through medium is the propagation speed and the wavelength.

The light still has all of its momentum, but you can think of it as if the medium is delaying the propagation.

[JoeSchmuckatelli]

I love human innovation... and while, here, we are most likely to talk about tokomaks or StarShips... this is cool:

 

Invented by an Indian farmer, it gives a little tech to a traditional, exceptionally physical method of harvesting tree nuts:

 

[DDE]

Dumb history question: in terms of shape rather than materials, when was this invented? Surely this isn't isn't high-tech, but Google is being uncooperative regarding ancient protective garmets.

[JoeSchmuckatelli]

10 minutes ago, DDE said:

when was this invented?

Are you talking about the over-the-ears strapping?  Because people have been wrapping their faces to keep out dust/sun/ etc. for... ever?

[Gargamel]

The question and discussion about computer power supplies has been moved here:

 

[Guest]

On 3/10/2022 at 11:06 AM, JoeSchmuckatelli said:

I love human innovation... and while, here, we are most likely to talk about tokomaks or StarShips... this is cool:

 

Invented by an Indian farmer, it gives a little tech to a traditional, exceptionally physical method of harvesting tree nuts:

 

make my day, thanks!

[JoeSchmuckatelli]

Showing off a little USMC bias, I've often wondered which was the better aircraft: The Corsair or the Mustang.  Despite having looked this up previously, this is the first I've run across an 'official assessment'.

 

Quote

 

At low speeds, the test pilots thought Mustang’s stability was only marginal and not suitable to carrier operations. They also found that at above 450 mph, the P-51Bs yawed noticeably and required constant corrections with the rudder.

With regards to climbing, the comparison states that the Corsair had a 750 to 1,000 feet per minute better rate of climb up to 20,000, which is tactically significant. Above that, the Mustang had the advantage, however.

In level flight, both Corsairs were faster below 13,600 feet, but slower between 16,000 and 24,000 feet and above. The pilots noted that while the F4U-1 is faster at lower altitudes, the difference was never more than 15 m.p.h. Of the two Corsairs tested, the F4U-1A was noticeably slower than the F4U-1. No reason why was given.

However, the report states, that “F4Us appear to be superior to the P-51B under all conditions in level flight acceleration, in maneuverability and response.”

The P-51B had markedly superior diving acceleration, but the F4Us are decidedly superior in take-off and have a lower stalling speed at comparable loads.

Four sentences from the report summarize the findings of the pilots who flew both types.

The report states:

1. It is concluded that, in general:
2. There is little to choose between the P-51B and F4U-1 airplane in speed between sea level and 25,000 feet, and that above 25,000 feet, the P-51B is superior.
3. That the F4U-1 is everywhere considerably superior in climb, at any comparable loading and superior in all other performance elements except diving speed.
4. The F4U-1 is everywhere superior in maneuverability and response.
5. With equal endurance, the F4U carries about 86% more armament and that it is a better gun flatform.
6. In summary, the F4U-1 airplane appears to be the superior fighter for Naval or Marine employment, either land for ship-based except in the case where substantially all the fighting occurs above 25,000.

 

 

Enjoy: Mustang vs. Corsair – Inside the U.S. Navy’s 1944 Match-Up Between the Two Fighters - MilitaryHistoryNow.com

[mikegarrison]

On 3/10/2022 at 10:11 AM, DDE said:

Dumb history question: in terms of shape rather than materials, when was this invented? Surely this isn't isn't high-tech, but Google is being uncooperative regarding ancient protective garmets.

I'm pretty sure earrings were invented in pre-historic times.

[JoeSchmuckatelli]

12 minutes ago, mikegarrison said:

pretty sure earrings were invented in pre-historic times

Well played, sir 

[JoeSchmuckatelli]

This is cool:

In a sacred pool, researchers see reflections of Phoenicians' past (nbcnews.com)

[kerbiloid]

https://allabouteyes.com/see-past-fascinating-history-eyeglasses/

Quote

The technology might have remained stagnant for several centuries, because the next clear historical picture of spectacles comes during the 1700s. Glasses grew to be “hands free” with the development of temples to extend over the ears.

Perhaps the most famous of these more modern glasses include “Martin’s Margins,” spectacles developed by the inventor Benjamin Martin. These glasses are sold as collector’s items today, but they pioneered the pursuit for more accurate lens development and thinner lenses supported by durable frames.

NOTABLE DEVELOPMENTS

After the “over the ear” innovation, new developments with glasses began to speed up. Benjamin Franklin added to the versatility of glasses by inventing the bifocal lens, which allowed a person with both near and far-sighted affectation to use one pair of glasses instead of two. He did this at first by cutting lenses in half and putting them together into one frame.

So, only in 1700s they first realized that the ears are created to tie small things to them.