For Questions That Don't Merit Their Own Thread

[Spacescifi]

If radiation pressure could be artificially increased (without simply shooting a massive amount of photons) how many times would you need to increase it to match the thrust of a spaceX booster?

A billion times? A trillion? Or a zillion?

And would not a single large rear nozzle be preferred over a cluster for the main engine?

The reason being that variations of flow inside the nozzle will not be a problem as the exhaust is lightspeed anyway... just with the force of it's momentum amplified so greatly that now the equivalent of an incandescent light is throwing out rocket level thrust.

The bigger nozzle the greater the maximum thrust you can get, which is effected also by how much light is being emitted.

Nonetheless, I expect the radiation pressure to be so greatly amplified that a nozzle of a given size with amplified radiation pressure shooting out will be on par for thrust with a chemical rocket.

The big advantage being that it can accelerate for far longer.... a torchship without the heat... only the thrust. Since the radiation pressure of the exhaust is so high that it does not require massive amounts of power to generate the light that is emitted, just what you would use if you were emitting light from electrically for a nozzle equal to a rocket nozzle.

Edited December 31, 2021 by Spacescifi

[JoeSchmuckatelli]

Apologies to Spacescifi - please answer his question if you are able.

 

Just wanted to share this - both because it's cool, and affected something near my old stomping grounds.  The failure of the Oroville Dam:

 

Also, how they fixed it:

 

 

FYI - this is the only dam in the US taller than the Hoover Dam

Edited December 31, 2021 by JoeSchmuckatelli

[Gargamel]

On 12/20/2021 at 10:04 PM, SunlitZelkova said:

Yes, most definitely. CIWS, at least the Phalanx, are already capable of handling 122mm and higher caliber artillery shells- certainly they can handle 356mm battleship shells. One would assume Russian and Chinese systems have similar performance.

Wait a sec.    In all my research, nothing indicates the Phalanx is suitable for anything faster or denser than an anti ship missile.    
 
The 18” inch (450mm) guns that reached deployment were tossing 1300kg Shells at almost Mach 3.   Hitting one of these beasts with 20mm Gatling gun is the definition of using a pea shooter.   
 

Even if the phalanx could track the shells, and it’s not unreasonable to expect it to be able to, hitting the target won’t do a bit of good. 
 

Naval artillery is not a precision shot, it’s more like a shotgun from afar.   They’ll launch a salvo of shots, and hope to catch the target in the middle of the spread.    So even if we continually hit the target with CWIS, at best it’ll have some minor affect of the trajectory, equally likely to knock a long shot onto target as to knock a shot off target.   And to be honest, given the short CWIS range and high speed of the shell, there won’t be enough rounds on target to actually make a difference.  
 

Unless you can point out some other sources that contradict this, no CWIS won’t stop a main naval artillery shell.   
 

But.... a battle ship would still lose to a modern cruiser or destroyer.    It has BVR weapons like anti ship missiles that a battle ship would have difficulty dealing with.   Even if their AA took them all out, the torpedos these cruisers/destroyers carry would destroy the battle ship as they are guided munitions and the battle ship has zero defense against a guided torpedo. 

[SOXBLOX]

https://www.quora.com/Could-a-Phalanx-CIWS-shoot-down-incoming-shells-from-an-Iowa-class-battleship

^ This says no. The actual impactor from Phalanx is 12mm in diameter, not 20. (It's a saboted round.) That's puny compared to the shell. If a modern ship were threatened by such guns, though, it could track the shells with its big radars and maneuver away from the impact zone.

Additionally, the ship could probably swat the shell out of the sky with guided missiles. More interesting is the Mk 45 5" gun found on USN and allied cruisers and destroyers. It can certainly engage air targets right now. If it were to use any of the guided shells developed for it, it could hit a 16" shell with ease. That would probably be enough punch to foul the shell's flight.

[DDE]

22 minutes ago, SOXBLOX said:

https://www.quora.com/Could-a-Phalanx-CIWS-shoot-down-incoming-shells-from-an-Iowa-class-battleship

^ This says no. The actual impactor from Phalanx is 12mm in diameter, not 20. (It's a saboted round.) That's puny compared to the shell. If a modern ship were threatened by such guns, though, it could track the shells with its big radars and maneuver away from the impact zone.

Additionally, the ship could probably swat the shell out of the sky with guided missiles. More interesting is the Mk 45 5" gun found on USN and allied cruisers and destroyers. It can certainly engage air targets right now. If it were to use any of the guided shells developed for it, it could hit a 16" shell with ease. That would probably be enough punch to foul the shell's flight.

There's another datapoint as well: the P-1000 cruise missile is ostensibly armored against 20 mm rounds.

[SOXBLOX]

4 hours ago, DDE said:

There's another datapoint as well: the P-1000 cruise missile is ostensibly armored against 20 mm rounds.

Well, it uses active radar guidance for terminal flight, so the radome is unarmored, at least...

[kerbiloid]

It sucks to use round prjectiles in XXI.

They have invented conical ones long ago.

[magnemoe]

17 hours ago, SOXBLOX said:

https://www.quora.com/Could-a-Phalanx-CIWS-shoot-down-incoming-shells-from-an-Iowa-class-battleship

^ This says no. The actual impactor from Phalanx is 12mm in diameter, not 20. (It's a saboted round.) That's puny compared to the shell. If a modern ship were threatened by such guns, though, it could track the shells with its big radars and maneuver away from the impact zone.

Additionally, the ship could probably swat the shell out of the sky with guided missiles. More interesting is the Mk 45 5" gun found on USN and allied cruisers and destroyers. It can certainly engage air targets right now. If it were to use any of the guided shells developed for it, it could hit a 16" shell with ease. That would probably be enough punch to foul the shell's flight.

Now the battleship would fire high explosive shells not armor piercing ones unless the other ship was armored like an battleship. The armor piercing shells are unlikely to arm unless they hit something very solid like an large engine block. On the other hand I doubt the Phalanx rounds are armor piercing either so they have no chance penetrating the still many cm thick casing who an anti tank round might do. 
And changing direction then you get fired on is as old as long range gunfire, you turn then you see the flash. It works better on an smaller and more maneuverable ship and is the limit of usable gun range in ship to ship combat, as the range closes the travel time gets shorter.

Not heard about guided AA shells but it sounds like an smart idea if they get it to work. With dumb shells it will work just like 5" gun AA back in WW 2 but with better computers. 

[SOXBLOX]

4 hours ago, magnemoe said:

Now the battleship would fire high explosive shells not armor piercing ones unless the other ship was armored like an battleship. The armor piercing shells are unlikely to arm unless they hit something very solid like an large engine block. On the other hand I doubt the Phalanx rounds are armor piercing either so they have no chance penetrating the still many cm thick casing who an anti tank round might do. 
And changing direction then you get fired on is as old as long range gunfire, you turn then you see the flash. It works better on an smaller and more maneuverable ship and is the limit of usable gun range in ship to ship combat, as the range closes the travel time gets shorter.

Not heard about guided AA shells but it sounds like an smart idea if they get it to work. With dumb shells it will work just like 5" gun AA back in WW 2 but with better computers. 

Phalanx rounds are armor-piercing. They're made of either tungsten or depleted uranium.

You're also right about the turning to avoid being hit thing. But obviously, modern warships will have the advantage in sensor suites, so they'll do better especially in night actions.

The guided projectiles work just fine. They're just expensive, and haven't been deployed yet. Here's a piece on one in the anti-air role during a test last year two years ago. https://www.thedrive.com/the-war-zone/36345/mq-9-reaper-howitzer-rocket-toting-f-16-all-shoot-down-mock-cruise-missiles-in-huge-test

[magnemoe]

2 hours ago, SOXBLOX said:

Phalanx rounds are armor-piercing. They're made of either tungsten or depleted uranium.

You're also right about the turning to avoid being hit thing. But obviously, modern warships will have the advantage in sensor suites, so they'll do better especially in night actions.

The guided projectiles work just fine. They're just expensive, and haven't been deployed yet. Here's a piece on one in the anti-air role during a test last year two years ago. https://www.thedrive.com/the-war-zone/36345/mq-9-reaper-howitzer-rocket-toting-f-16-all-shoot-down-mock-cruise-missiles-in-huge-test

Why armor piercing? you are firing at thin skinned missiles? Only real use is if you hit an solid fuel rocket at an sharp angle.

That shell would interesting for warships who has limited room for missiles. And I imagine making an railgun shell smart would be harder. 
Even harder than LEGO electronic. Had an teacher doing some work for LEGO electronic. They found that the static from dragging lego on an carped could produced so much static it would blow EMP proof military spec electronic all the time. They solved it by one layers of discharge triggers on the IC, another outside and an 3rd for the surrounding stuff. I imagine the current generated in wires in an railgun shell will be way worse  

[SOXBLOX]

2 hours ago, magnemoe said:

Why armor piercing? you are firing at thin skinned missiles? Only real use is if you hit an solid fuel rocket at an sharp angle.

That shell would interesting for warships who has limited room for missiles. And I imagine making an railgun shell smart would be harder. 
Even harder than LEGO electronic. Had an teacher doing some work for LEGO electronic. They found that the static from dragging lego on an carped could produced so much static it would blow EMP proof military spec electronic all the time. They solved it by one layers of discharge triggers on the IC, another outside and an 3rd for the surrounding stuff. I imagine the current generated in wires in an railgun shell will be way worse  

Phalanx also engages small boats, helicopters, low-flying aircraft, drones, bombs, etc. I think armor-piercing rounds are the best across these different use cases.

The HVP (guided shell) is all about magazine depth and cost effectiveness. The idea is for it to be a complete supplement to missile systems. The Army plans to fire it from the M109 in an air, ballistic, and cruise missile defense role (think THAAD plus a mid-range air-defense system) and the Navy can use it against just about anything.

As for the effects on the electronics, remember that it's a saboted round. It has a lot of extra protection while in the barrel. I imagine there's some sort of insulation between the sabot and the shell...

Edited January 3, 2022 by SOXBLOX

[JoeSchmuckatelli]

Just for fun, I looked up energy density of potential rocket fuels.   (Pardon the source, again it's idle interest, not a research paper) Energy density - Wikipedia

Hydrogen has everything beat by a mile.

Some of the smart folks here have explained that 'hydrogen doesn't like to behave' - meaning it escapes containment fairly easily.  The next two, Diobrane and Beryllium have been looked at as rocket propellant.  Diobrane is apparently nasty and also does not like to play nice (destroys containment system & escapes).  But Beryllium apparently is used.  I'm guessing for RCS?

So - beryllium has about 12 mj/kg more energy than methane... why don't we hear more about it as a potential fuel for rockets?

[magnemoe]

12 minutes ago, JoeSchmuckatelli said:

Just for fun, I looked up energy density of potential rocket fuels.   (Pardon the source, again it's idle interest, not a research paper) Energy density - Wikipedia

Hydrogen has everything beat by a mile.

Some of the smart folks here have explained that 'hydrogen doesn't like to behave' - meaning it escapes containment fairly easily.  The next two, Diobrane and Beryllium have been looked at as rocket propellant.  Diobrane is apparently nasty and also does not like to play nice (destroys containment system & escapes).  But Beryllium apparently is used.  I'm guessing for RCS?

So - beryllium has about 12 mj/kg more energy than methane... why don't we hear more about it as a potential fuel for rockets?

Usually energy density in volume is not that relevant for rockets, yes hydrogen has an downside here in that it has an so low density you have to use many times larger tanks. 
Its energy to weight and ISP is best for all chemical fuels however. 

For missiles energy density in volume is more interesting more so if you are restricted in size because of bomb bays or launch tubes. Heavy materials has low ISP but they have high trust. Now using heavy metal is mostly an bad idea as they are tend to be very toxic, think the low ISP and that you still have to carry the heavy missiles make it unpractical. 
 

[Jacke]

A rough rule-of-thumb is that the cost of a given launch vehicle is roughly proportional to its volume.  This makes low density fuels like LH2 not that good an idea for the first stage.  The high Isp of LH2+LOX and the lesser volume differences of making the upper stages use the low density LH2 makes it good for upper stages, where reducing boil-off becomes important.

[JoeSchmuckatelli]

1 hour ago, magnemoe said:

energy density in volume

Going to expose some more ignorance - b/c I thought we were talking power/weight... and you bring up ISP (which I've always thought of as efficiency).

 

I read mj/kg as a simple measure of energy per kilogram, thinking that if we can't use hydrolox engines b/c the hydrogen misbehaves, the next best thing would be to use another, alternative high-density fuel as a first stage.  Hence beryllium.   Again, thinking that if beryllium can be used in a rocket and has more energy density than methane... why not use it as a first stage given that it gets 12 mj/kg more than methane.   (meaning, to my mind, more oomph for the same weight.

 

So - clearly I'm missing something critical.

[Jacke]

Welp, from my recall of my several reads of Ignition!, I know enough to stay away from the boranes.  And I know beryllium is very toxic.  And fluorine is enough to drive you back to use storeables.

So it's either storeables or LOX with RP1, LMETH, or LH2.  Honestly, it's not worth pursuing others.  Need more Isp, go for ion, plasma, or nuclear drives.

[JoeSchmuckatelli]

4 minutes ago, Jacke said:

several reads of Ignition!,

Thanks for the link!  I now have something new to read!

[DDE]

8 minutes ago, JoeSchmuckatelli said:

Thanks for the link!  I now have something new to read!

To skip right ahead: beryllium refuses to combust out of mercy for the people downstream of the exhaust

Quote

Another idea which didn't get anywhere, was that of a heterogeneous fuel — a suspension, or slurry, of a powdered metal, such as aluminum, in a liquid fuel such as gasoline. This had been suggested by several writers, among them Tsander in Russia and Sanger in Austria, and Heinz Mueller of BMW tried it out, using powdered aluminum or magnesium in diesel oil. The performance was very poor —the chamber pressure was 50 to 100 psi instead of the 300 they were shooting for —due to the incomplete combustion of the metal. But the other results were spectacular. The motor was fired in a horizontal position against an inclined wall to deflect the exhaust stream upwards. But the unburned metal particles settled down and decorated all the pine trees in the vicinity with a nice, shiny, silvery coating — very suitable for Christmas trees.

...

Then, once the fuel is in the motor — and I won't go into the problem of designing an injector which will disperse a gel properly — there's the problem of burning the aluminum. Unless the chamber temperature is well above the melting point of aluminum oxide (about 2050°) or, preferably above the considerably higher temperature at which it decomposes, the aluminum particle will simply coat itself with a layer of solid or liquid alumina, and refuse to burn to completion. When burned with N2O4 the chamber temperature is just about high enough to burn an aluminized gel properly. It's highly probable that combustion with nitric acid would be marginal, with a chamber temperature not quite high enough to make the metal burn to completion. (With a halogen oxidizer, such as ClF3, this particular problem doesn't arise, since AlF3 is a gas at the temperatures we're talking about.) And, naturally, the dense clouds of solid Al2O3 resulting from the combustion of an aluminized gel leave a very conspicuous exhaust trail.

...

The problems with beryllium-loaded gels are the same as those with aluminized ones, only more so, and with one or two peculiar to themselves. The exhausted BeO, of course, is violently poisonous, producing something resembling a galloping silicosis, but the most serious problem is in the combustion. Beryllium oxide melts at a considerably higher temperature than does aluminum oxide, and doesn't vaporize until the temperature is near 4000°, so that burning it is even more difficult than burning aluminum. Rosenberg, at Aerojet, burned a beryllium-hydrazine slurry ("Beryllizine") with hydrogen peroxide in 1965, and got a C* efficiency of some 70 percent, which indicated that none of the beryllium had burned. At Rocketdyne, they had the same experience with the combination. When Rosenberg used N2O4 as his oxidizer, his C* efficiency was some 85 percent, showing that some of the metal had burned. His performance was particularly bad at what should have been the optimum mixture ratio. Various expedients designed to improve combustion, such as vapor-coating the beryllium powder with chromium, didn't improve the situation appreciably.

Amusingly, I've come across a Soviet SLBM program that separately tried ClF5 and hydrazine-aluminum slurry. Fortunately, no-one told them to try both simultaneously.

Edited January 3, 2022 by DDE

[kerbiloid]

8 hours ago, DDE said:

Fortunately, no-one told them to try both simultaneously.

Until you just did...

[DDE]

Quote

The article then authoritatively states that “the spaceplane is capable of carrying an advanced imaging suite that features 1-meter-aperture adaptive optics with an integral sodium-ion-sensing laser. By compensating in real-time for atmospheric turbulence-caused aberrations sensed by the laser, the system is capable of acquiring very detailed images of ground targets or in-space objects, according to industry officials familiar with the package.” What “industry officials” and for what company? The author never names them. Furthermore, the characteristics of adaptive optics and laser guide stars are well known and have been used for ground-based telescopes for years. There are physical reasons why they will not work in the other direction.

(full article: https://thespacereview.com/article/576/2)

Why?

[JoeSchmuckatelli]

5 hours ago, DDE said:

article

Holy s-word... That's a lot of debunking! 

[kerbiloid]

5 hours ago, DDE said:

(full article: https://thespacereview.com/article/576/2)

Quote

Despite a lack of evidence that it ever existed, the supposed TR-3 Manta has attracted the attention of aviation enthusiasts, and Aviation Week. (credit: Adrian Mann)

Manta? Ok...

Spoiler

 

[DDE]

1 hour ago, JoeSchmuckatelli said:

Holy s-word... That's a lot of debunking! 

I believe I had to include the link, but I failed to find a polite way to warn everyine against clicking it.

[kerbiloid]

2 hours ago, DDE said:

but I failed to find a polite way to warn everyine against clicking it.

"All! Don't click this."

[wumpus]

20 hours ago, Jacke said:

Welp, from my recall of my several reads of Ignition!, I know enough to stay away from the boranes.  And I know beryllium is very toxic.  And fluorine is enough to drive you back to use storeables.

So it's either storeables or LOX with RP1, LMETH, or LH2.  Honestly, it's not worth pursuing others.  Need more Isp, go for ion, plasma, or nuclear drives.

Fun fact - the mirrors of the JWST are beryllium (covered with something non-reactive).  For when you really, really, want light weight (also helps if they aren't going to almost always be in a clean room or otherwise outside of an oxidizing atmosphere).