Unrealistic SCI-FI metals

[Darth Wong]

I have never before seen someone actually claim that you want to help the enemy focus his weapon energy in one spot, and use a brittle form of armour to boot.

[Pu-239]

Anyone have any idea why titanium is used in the hull of the Alfa sub? I mean titanium is inferior to steel, and weight is not a concern for a sub.

[Darth Wong]

Anyone have any idea why titanium is used in the hull of the Alfa sub? I mean titanium is inferior to steel, and weight is not a concern for a sub.

Corrosion resistance in salt water, perhaps.

[Pu-239]

Aren't there easier ways to prevent corrosion? I mean if you can make something out of titanium, why not make it out of stainless steel?

BTW, isn't stainless inferior to carbon steel when it comes to heat treatment?

[SyntaxVorlon]

You have obviously never seriously studied failure mechanisms in engineered structures; you want to absorb and spread out energy.

Well duh! If this wasn't true you would not be shooting down my arguements so quickly!
Besides my high school's science dept. sucks donkey balls. Math dept. is pretty good, but my Chemistry teacher's primary teaching tools were '70's science videos.
Well I concede my arguements, most of them.

[The Duchess of Zeon]

Anyone have any idea why titanium is used in the hull of the Alfa sub? I mean titanium is inferior to steel, and weight is not a concern for a sub.

Corrosion resistance in salt water, perhaps.

Weight does matter on a submarine:

http://www.warships1.com/RUSssn19_Alfa_history.htm

[beyond hope]

If you had a way to produce enough and form it, how's diamond for a hull material? still prone to shattering?

[Darth Wong]

Diamond has cleavage planes and near-zero ductility. You would have to be seven kinds of insane to use diamond for any structural or armour application.

[GrandMasterTerwynn]

TAKE THIS ENGINEERS!

Oh, I can feel the jealousy :twisted:

Your puny landing scheme is no match for the power of a fully grown engineer!

http://personal.smartt.com/~sansell/images/ckt_chrg.jpg

Oh pshhhh, you call that a circuit diagram?

[GrandMasterTerwynn]

A 500 kT weapon is 2.1E15 J. At a range of, say, 400 metres, this is 1 GJ per square metre, which is enough to melt 0.1 metres off the armour. More realistically, it would vapourize a thinner layer violently off the surface and destroy all sensors, antennae, etc. This would not only blind the ship, but it would also produce a rocket-like propulsive effect and shove it away. The internal stresses produced by this acceleration could be seriously dangerous in their own right.

But not indefensible, nor beyond the limits of the future to find a counter against - At least within the realm of a couple hits (Obviously you'd roll the ship after one hit to offer your undamaged side).

How much radiation shielding would be needed, though? That's what might kill a chance of viably defending a vessel against that sort of detonation, the weight of the radiation shielding (Which would presumably be around a still-smaller pressure hull, than as a component of the armour hull - If the components between them could survive the dosage. If not, the weight is, of course, regrettably increased).

Well, in space combat, the best anti-radiation shielding is to have active countermeasures that stop your enemies weapons from exploding at point-blank ranges. No feasible amount of armor is going to stop a close multi-megaton nuke hit from turning a ship and her crew into debris and statistics.

[SWPIGWANG]

Hypervelocity assumes a sufficient fraction of c as to go far behind the technology we can feasably see, I think; and armour is melted today, without rendering such considerations in armour design less relevant. It's about more than material and thickness...

You don't necessarily need c fractional velocities to melt the armour, as DU projecties today have its outer most layer melted with the armor when it hits.

The problem is heat emission: spacecraft must radiate heat (IR) or they will roast. If there was a need, we could build--now--IR sensors good enough to detect a heat source on the scale of the Space Shuttle's OMS rockets at the distance between earth and mars.

YOU SERIOUS about the sensor!? *shocked* (how about search capcities...afterall there is alot of sky out there)

Well, you can always power down and coast....


Since I'm stupid, how does dislocations in metals help with strengh and is there other tricks of this kind we can play with other materials?

Uh, what would happen if laser hits high pressure gas stored in a fuel tank? Since any ship capable of going anywhere probably have something around 60 percent fuel at minmum with forseeable technology, unless it is things like sails and such....

[Vympel]

Weight does matter on a submarine:

http://www.warships1.com/RUSssn19_Alfa_history.htm

I should note that the Project 945 Sierra-class boats (still in service) had titanium hulls and were the ultimate Soviet 3rd generation submarine. However, they were seen as too expensive, so the more well known Project 971 Akula-class was designed- with steel hulls. The design was a 'close approximation' of Sierra-class capabilities.

Wonder how they did it.

[The Duchess of Zeon]

[
You don't necessarily need c fractional velocities to melt the armour, as DU projecties today have its outer most layer melted with the armor when it hits.

On a tank.

[Darth Wong]

Since I'm stupid, how does dislocations in metals help with strengh and is there other tricks of this kind we can play with other materials?

It's hard to explain lattice mechanics without diagrams. As for your second question, there are vast numbers of tricks we can use to play with material strength, but there are limits to what you can accomplish.

[Enlightenment]

You're right, passive stealth is out, but there are other forms of stealth - for instance the French are working on active stealth devices and those may hold promise for dealing with spoofing heat detection, at least good enough to prevent it from being used for missile targeting.

You're not understanding.

Spacecraft must radiate heat to remain at an operating temperature low enough that their components don't melt. In an atmosphere and on the ground, heat emissions can be hidden by designing heat diffusion systems that reduce the thermal signature to something near the ambient background temperature.

In space, the ambient background temperature (cosmic background radiation) is at 4 degrees kelvin. It's not possible for the heat generated by a multimegawatt powerplant to be channeled through radiators large enough that the emissions are not detectably above the cosmic background. Active countermeasures cannot help and more than 'active countermeasures' could prevent a large nuclear pile embedded in a block of ice from melting its way out.

The ideal missile seeker would be imaging IR sensor and spectrometer backed by signal processing logic and a fairly simple guidance package designed to home in on the programmed IR source with the right emission profile. Short of exploiting software bugs or cost-cutting defects in the missile, the best way for a target to avoid one of these things would be to burn out the missile seeker with a laser and get out of the hulk's way.

Missiles and lasers both, probably. Possibly also particle beams depending on what we're talking about in terms of technology level. One interesting idea, perhaps, would be the use of railguns to accelerate flechettes for point defence - That might be where they're viable, perhaps? Just a random thought.

Unguided projectiles are of dubious use at interplanetary space combat ranges. We're talking light seconds to light days here. Gun-derivatives as we know them are pretty much non starters for anything greater than knife-fight ranges.



As a reference source, you might want to look through Google Groups for the various space combat threads that have been posted into rec.arts.sf.science in the past five years or so. All this stuff has been hashed out in great detail in threads that have gone on for hundreds of posts, complete with math, references, and back-of-the-envelope designs. Feel free to drop in to the current space combat thread, too.

Google groups general overview of space combat threads

Current ongoing space combat thread

Usenet. It's more than just ASVS.

[Enlightenment]

YOU SERIOUS about the sensor!? *shocked* (how about search capcities...afterall there is alot of sky out there)

Well, you can always power down and coast....

Details

Lots of interesting reading in the rest of the thread, too.

Coasting helps, yes, but sooner or later you're going to be given away by the fact that your crew module must be at ~300K to keep the crew alive.

Uh, what would happen if laser hits high pressure gas stored in a fuel tank?

The fuel tank will violently disassemble itself. This is the published kill mechinism used by the USAF ABL.

Since any ship capable of going anywhere probably have something around 60 percent fuel at minmum with forseeable technology

60 percent fuel would be incredible with forseeable technology. Try more like six times more fuel than payload and structure.

[SWPIGWANG]

In space, the ambient background temperature (cosmic background radiation) is at 4 degrees kelvin. It's not possible for the heat generated by a multimegawatt powerplant to be channeled through radiators large enough that the emissions are not detectably above the cosmic background. Active countermeasures cannot help and more than 'active countermeasures' could prevent a large nuclear pile embedded in a block of ice from melting its way out.

But we can channel the direction of the radiation by freezing the direction facing the opponenet with a simple refrigerator and channel the waste heat to another facing. Who cares if you are a IR flashlight that lights up the sky as long as the beam doesn't cross pathes with the enemy sensor.

[Darth Wong]

But we can channel the direction of the radiation by freezing the direction facing the opponenet with a simple refrigerator and channel the waste heat to another facing. Who cares if you are a IR flashlight that lights up the sky as long as the beam doesn't cross pathes with the enemy sensor.

Beware tactics and technologies that are dependent upon fighting just one enemy whose happens to be conveniently facing your cold side. What if he has spotters, drones, sensor buoys, more than one ship, etc? And do you realize that the refridgeration would increase the overall heat output of the ship?

[SWPIGWANG]

Not if I have a perfect heat engine

Well, some stealth tricks is better than no stealth tricks.

[Warspite]

Anyone have any idea why titanium is used in the hull of the Alfa sub? I mean titanium is inferior to steel, and weight is not a concern for a sub.

Titanium is non-magnetic, defeating the purpose of Magnetic Anomaly Detectors, and a sub can dive deeper... Of course, it's a mother to weld, and costs an entire year's budget, but, hey, we don't have those problems in comunism, right?
The same results can be achieved with high strenght steel, at much cheaper prices, and with good quality control.

And weight is always a concern when building a vessel, the engines have more mass to push around, the loading on the structures will be higher, and sea is a dynamic enviroment, creating dynamic loads that will cause higher stresses, than for a lighter vessel. As for submarines, a higher weight, means a higher mass, a higher engine output to achieve a certain speed, bigger pumps... Oh, oh... Noise... Ooops.

Aren't there easier ways to prevent corrosion? I mean if you can make something out of titanium, why not make it out of stainless steel?

BTW, isn't stainless inferior to carbon steel when it comes to heat treatment?

Let me say this first, it's impossible to totally prevent corrosion. Corrosion control on a ship is done mostly by two methods: painting (duh!) and in the propeller area, by applying zinc blocks sacrificial galvanic members, they corrode faster than steel, preventing corrosion of the hull and rudder. A discontinued method was to plug a generator to the hull and use the sea water as a conductor.
Paint is still the cheapest, and more pratical method, though.
But, allow me to say it again, it's impossible to prevent total corrosion.

Stainless steel his a non-magnetic metal, and corrosion resistant, not only to water, but also to a lot of diferent (and in most case, dangerous) substances. But, it's expensive as hell (grantedm less so than titanium), and requires special precautions when being welded, otherwise, you end up with two ruined plates. That doesn't prevent it's use in ship construction, though, but it's in more specialised areas, one example are the tanks of LNG's (liquified natural gas) and LPG's (liquified propane gas), they're usually spherical containers 20 metres high, carrying low temperature liquified gases.

Steel is beautifull!

[The Duchess of Zeon]

You're not understanding.

Spacecraft must radiate heat to remain at an operating temperature low enough that their components don't melt. In an atmosphere and on the ground, heat emissions can be hidden by designing heat diffusion systems that reduce the thermal signature to something near the ambient background temperature.

In space, the ambient background temperature (cosmic background radiation) is at 4 degrees kelvin. It's not possible for the heat generated by a multimegawatt powerplant to be channeled through radiators large enough that the emissions are not detectably above the cosmic background.

Oh, I do understand. It's just.. Hrmm. Couldn't you at least make the missile target the radiators? They'd presumably be relatively large structures and if the ship was built with an excess, the loss of one might be a severe problem (Especially if we're talking about a last-ditch way of keeping nukes away from the hull).

Active countermeasures cannot help and more than 'active countermeasures' could prevent a large nuclear pile embedded in a block of ice from melting its way out.

Well, of course active countermeasures can still be useful - All you need to do is create a heat source hot enough to confuse the seeker head away from the ship. That isn't impossible, though exactly how you make that cost effective is a viable question.

The ideal missile seeker would be imaging IR sensor and spectrometer backed by signal processing logic and a fairly simple guidance package designed to home in on the programmed IR source with the right emission profile.

Which could be replicated in a decoy.

Unguided projectiles are of dubious use at interplanetary space combat ranges. We're talking light seconds to light days here. Gun-derivatives as we know them are pretty much non starters for anything greater than knife-fight ranges.

Right, but defending against missiles you want a layered defence, which means the gun or something similiar would remain ideal for the purpose of providing the final layer in the defensive umbrella around a ship.

[The Duchess of Zeon]

I just thought of a possible armour that would be effective against nuclear devices:

ERA. Could you make Explosive Reactive Armour that would work in space? I'm not entirely sure of what that's going to do against an armed nuclear warhead, but even a partial yield detonation is better than a whole one, and I know that some nukes have survived quite a bit in an armed state.

[Warspite]

I just thought of a possible armour that would be effective against nuclear devices:

ERA. Could you make Explosive Reactive Armour that would work in space? I'm not entirely sure of what that's going to do against an armed nuclear warhead, but even a partial yield detonation is better than a whole one, and I know that some nukes have survived quite a bit in an armed state.

Reactive Armour only works by contact, and it's mainly efective against HEAT rounds, it could deflect flechettes, but that's still a very flimsy possibility. And what if it get's detonated by microasteroidal impact? One less chunk of armour to explode.
If the nuclear blast consists mainly of radiation, and detonates at a distance from the hull, then it's useless... Unless... How about a defensive aid that releases a very thick cloud of particles, between the hull and the nuclear blast? If it's detonated at distance, of course. Most of the detonation would be absorbed by this cloud, and possibly it could lessen the ablation effects of the blast.

[aerius]

BTW, isn't stainless inferior to carbon steel when it comes to heat treatment?

Not exactly, and it's more complicated than that. Generally you have a few things to play with in steel, hardness, toughness, corrosion resistance, and workability, and you can't gain in one area without losing in others. A stainless steel has far more corrosion resistance than a carbon steel, but it will be more brittle and harder to work with as a general rule. I could make a stainless that's as tough as a carbon steel, but it'll be softer, I could make it the same hardness and strength, but it'll be far more brittle. And no matter what I do it'll be a lot harder to work with and weld than a carbon steel.

[Darth Wong]

One of the coolest things about steel is all the myriad things you can do with it; soft steel, ultra-hard steel, super-tough steel, etc.

But as for DOZ's idea, I'd say a laser defense grid is the only real way to stop nukes in space: shoot 'em down before they hit you. A nuke won't detonate properly if it's destroyed; it has to go through a particular sequence of events to initiate the reaction.