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Post by Friendly Anon on Jun 13, 2016 12:13:20 GMT
This seems like a very interesting project. And clearly a lot of thought and even more math has been put into it. But I have some thoughts on some of the concepts that might offer a different perspective.
First, the stealth issue. Atomic Rockets as well as your blog rail against the very idea. Clearly, space is perfectly empty, and detection instruments perfectly accurate. Therefore stealth can't exist? Well I can think of several reasons that might be wrong. While an emission from a heavy duty rocket engine, large radiator panels, energy weapons etc. might seem hard to miss, spacecraft don't necessarily operate with very high energy outputs at all times. And while a dedicated scan of a specific part of the sky would probably reveal any relatively near objects in that part of the sky, the problem here is the same as it is for detecting dwarf stars, asteroids, SETI etc. It's a hell of a damn big sky, and there simply is no way to watch all of it.
Additionally space isn't exactly empty. Being in front of, or behind a large body such as a planet or the sun would probably be effective in masking or blocking entirely the signs of a ships presence. This would be especially true for a low orbit which is spent 50% directly in front of, and 50% obscured by the planet. If, on top of this emissions could be shielded from certain directions or otherwise directed, it would make it a lot more difficult to pick out the spacecraft. Stealth on earth doesn't mean "invisibility" either like a star trek cloak. It means "reduced observability". Any emission or radar reflection not in the direction of the enemy sensors is beneficial. An analogy to submarines may trigger some, but I think it's potentially a good one. Subs not only have to balance off masking their engine noise but also choose when to use active sonar. Jet engines on the f117 and f22 are shielded in such a way that IR does not escape at many angles of view. There's no particular reason these principles do not extend to space, to my mind.
The game Elite Dangerous, is an arcade space game no doubt. But it does have game mechanics that I think could reflect on a deeper truth. The ships can turn off their engines and radiators and coast on maneuvering thrusters to evade detection at range. Utilizing asteroids to break line of sight is also useful. Finally, they can dump heat into pellets and expel them in certain directions rather than relying on radiators to keep internal heat under control. In other words, the same basic principle of reducing and directing emissions and utilizing bodies to break or mask line of sight to sensors.
It also has an interesting concept of active radiators. There isn't a real world concept I know of, but it seems the individual parts to make it work do exist. Basically you can convert heat to electricity via steam dynamos. And electricity to radiation, via for example lasers or cyclotrons. That radiation could be pointed in a specific direction rather than emitted in all directions, further enabling the stealth concept. I don't know how effective such a system would be, probably nowhere near that shown in the game, but I think it's worth thinking about. Another idea that can arise from this is to point it deliberately at the enemy, basically transferring your excess heat to them. Or adding even more power to the emission deliberately. I can only imagine an enemy that faces a large amount of excess heat is going to make some very different choices from one that has a balanced heat budget.
Your selection of weapons seems well informed. But it strikes me that a few types that were being developed for example for use in the orion battleship have been missed. While I can understand casaba howitzers never (publically) functioned, and bomb pumped lasers suffered from very bad efficiency issues, it seems like particle beams ala teleforce would be very useful in space. Combining very high muzzle velocities, and low ammo weight with potentially enough force to easily cut through any armor that is reasonable to fit on a missile or spaceship.
I'm also wondering if armor that is shaped like a saw wave ( ^^^^^^^^^ ) would be useful. It seems to me if cylindrical and saw shaped armor was combined, an incoming projectile would always hit at least one of the plates at the worst angle. The surface area would also be increased, making it potentially more useful as a radiator, although I'm not sure this would be significant at all. Finally, the empty space inbetween the blades of the saw would break up armor piercing projectiles and missiles. Maybe this is a stupid idea. But shaped armor can do a lot to improve armor without increasing mass on earth. Why not in space?
That is all.
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Post by Friendly Anon on Jun 13, 2016 12:17:38 GMT
Oh, and I almost forgot, I didn't see you talk about radiation shielding for crews anywhere. It seems to be often taken for granted even in hard sci-fi. Presumably any long term spacecraft would need this, either a physical barrier (weighty) or be able to generate a magnetic field of its own. There was an estimate made of the weight of such a system and it came out much less than expected. So maybe it should be considered. Flares are no joke.
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Post by qswitched on Jun 14, 2016 0:55:24 GMT
Hello, welcome to the forum!
About radiation shielding, this is actually accounted for, and in ship design, you have to make sure your crew is shielded enough before you can fly, both from the reactors, and from external sources.
Concerning stealth, Atomic Rockets has mentioned answers to most of your questions. As Atomic Rockets mentioned, you can scan the entire sky effectively in four hours under present day technology, so scanning time is not an issue.
Stealth on Earth is significantly easier, because the ambient air temperature is about 273 K, or room temperature. If you can keep yourself somewhat close to this temperature (such as by turning engines off), you can blend in much easier. In space, the ambient temperature is 3 K, or close to absolute zero, and it's extremely hard to cool your ship anywhere close to that. As Atomic Rockets mentioned, the tiny amount of heat that the maneuvering thrusters on the space shuttle emitted were detectable as far out as the asteroid belt! Radar is used on earth because detecting heat is only really viable at close ranges (like what homing missiles use) relative to the far-out radar ranges. Ultimately, stealth is very different on Earth. Underwater, it's even more stealthy, with water basically killing the range of nearly any kind of EM sensor, forcing you to use sonar instead.
The main issue is engine heat, and you either need to put out a ton of heat when moving, or take years/decades to get anywhere. If you want to play the long con and take years to get to your target, stealth might work for you, but operating a military campaign means you need reasonable travel times.
Decoys are also mentioned in Atomic Rockets, and how they need to be as massive as what they are decoying, otherwise a careful analysis will reveal them as a decoy. And if they're going to be just as massive, you might as well just get another ship anyways.
Hiding behind a planet or asteroid is the one effective way to have stealth in space, but a network of tiny satellites scattered across the solar system is a cheap way to counter this. Hundreds of little solar powered satellites constantly scanning the sky, and reporting back any anomalous heat sources.
About weapons, particle beams were considered, however literature is a little scant on weaponizing them. The USAF has apparently deployed one in low earth orbit within the last twenty years (though if successful, this is not clear), however the material remains classified. As you've probably found in the blog, the detail I put into the technologies is very high, and I only implement systems if there is a clear analysis of scaling laws, limitations, etc. I can't really find much on particle weapons in scientific literature because so much is classified unfortunately.
Sloped armor is used in game as mentioned in the blog, though it's not shaped like a saw, because each internal corner would be a weak point. It's a simple slope across the whole ship, and it's extremely effective. Missiles in space are actually extremely pointed, not for aerodynamics, but because the armor becomes heavily sloped against point defense fire.
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Post by Friendly Anon on Jun 14, 2016 10:28:58 GMT
Well you seem certain. But, in keeping with the spirit of discovery, why don't you try modelling sensor and emission reducing systems and see what happens? The sub analogy does work because yes, water blocks EM very well. But it also carries sound exceptionally well. So you do end up with a situation similar to space where the slightest peep from the engine will be detectable passively, at quite some range. And still they bother to try and mask the sounds. The other problem with the size of the sky isn't so much the scanning time. I mean GAIA is scanning the whole sky to immense detail in six hour revolutions. But processing that data to pick out useful information is going to take years and years.
As for the armor corners, that could indeed be an issue but sloped armor has certain designs to deal with that such as that found in the gaps between the abrams and merkava turrets and the body. A sine wave-ish or ( ◡◡◡◡◡◡◡ ) design could also be considered. I still don't know if it would be any good, but it seems like a hit from the side on a cylinder would be quite devastating without some slopes. Maybe it would be best used on the parts of the ship that are most likely to be exposed only from the side, and the cylinder design for facing the enemy.
I'll look forward to it either way.
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Post by withcarbos on Jun 15, 2016 12:07:25 GMT
GAIA is scanning the whole sky to immense detail in six hour revolutions. But processing that data to pick out useful information is going to take years and years. But you don't need to process all that much data: all you have to do is pick out any brilliant new stars with large proper motions relative to say Sirius or α Cen or Arcturus. Let the computer ignore anything else; what remains are spaceships (even with just life support active, habs are bright against the cosmic background).
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Post by qswitched on Jun 15, 2016 21:26:20 GMT
So I actually did model sensor systems early on in the project (at the beginning of the project, I was dead set on wanting stealth, too), but the results were dismal. I found a tiny 10 cm sensor could detect a spacecraft with engines off from across Jupiter's entire sphere of influence, which is generally the largest distance you'll ever see in terms of engagement. With engines on, that range became interplanetary. I explored a few radiator heat reduction techniques, like using a heat pump to run the radiators colder, but this required prohibitively large radiators, something absurd like kilometers of radiator for a ten meter long ship.
Do I think stealth is impossible? No. But extremely expensive, difficult, and likely requiring technologies beyond plausible near future tech? Yes. In the future, we may very well see stealthy spacecrafts, but under current technologies, trying to make it work is extremely difficult, and not worth the time and effort.
It should be noted that we already do have stealth drives in some capacity, in the form of reactionless drives, solar sails and the like. But their drawback is their mediocre speed (yearlong journeys or more). And hiding the heat signature of the radiators is still an issue (not an impossible obstacle, but still very difficult and expensive, again).
About sloped armor, when you run the numbers, the additional mass of jagged or high surface area armor ends up performing the same as simply adding the mass as a flat plate. Note that the Abrams or Merkava both have smooth slopes on the turret and main body.
Also, the ships in Children of a Dead Earth usually have a tapered cylinder rather than a regular cylinder, which does alleviate the issue of getting hit head on. The taper makes it very awkward to find the exact point perpendicular to the sloped armor.
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Post by apophys on Jul 28, 2016 17:07:05 GMT
Why do you prefer methane over decane? From the stats you mentioned, decane looks significantly denser while having similar thrust characteristics. Also, a few questions regarding hull armor: - Would it be possible to use the armor itself as a giant main radiator (embedded inside the main armor, or inside the whipple shield)? I can't imagine the piping & coolant being prohibitively extra mass compared to the material it replaces, nor causing too much structural weakness, and the loss in cooling efficiency by having only one direction of radiation should be more than countered by the surface area. Because if that would work, it might allow for significantly higher energy use in the weapons (specifically thinking spinal-mount coilguns). - I notice your cylinder armor is perfectly round, with several cylindrical propellant tanks inside. Is this just for ease of modeling? It wastes a (small) bit of mass as opposed to going straight across from the tangent points on those propellant tanks. I basically mean making a prism with rounded edges, like this: - Building on the above: How about a rounded rhombic prism for a broadside ship (4 cylindrical propellant tanks with the same hexagonal packing, wrapped together in armor)? Looks like a smaller profile and much better angled armor (30 degrees, largely) than a cylinder, with still fine mass and structural stability.
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Post by qswitched on Jul 30, 2016 17:07:08 GMT
Some of the ship designs do use decane instead of methane. It ends up being a little under twice the density of methane, while yielding about 1 km/s less exhaust velocity. It's a bit of a toss up which is ultimately better, which is why both were used for various ship designs. Ultimately, methane ends up somewhat cheaper, so most of the designs used that.
Using the armor as a giant radiator has a huge number of issues. One is that you'll likely have to get rid of the Whipple Shield, because the radiators for most nuclear reactors run much hotter than the melting point. Alternatively, you need much more expensive materials, which is at odds with the point of the Whipple Shield. Regardless, the Whipple Shield is often the first thing to go in combat, which means if they are your radiators, they'll get shot immediately. This same sort of issue occurs with your main armor as well. If you put your coolant pipes near the surface of the armor, they'll work best, but they'll also get damaged as soon as you suffer hits. If your coolant pipes are at the back of the armor, they'll survive damage much longer, but the heat transfer across the armor will be abysmal, and your radiator efficiency will suffer immensely (especially if you're talking 10+ cm of armor that the heat needs to transfer across).
In the same vein, even if the pipes are near the back of the armor, damage to the front of the armor often causes spallations and other damage all throughout the bulkhead. This means any damage at all has the possibility of wrecking your coolant pipes. Generally, separate radiators have the advantage of being smaller, and can be aimed edge-on at the enemy to reduce their cross section, and thus, greatly reduce the enemy's ability to hit them.
But the biggest issue is that material strength decreases with temperature. If the bulkhead cooling your reactor is 1200 K, you have a giant, glaring weak point on your ship, sure to attract all sorts of fire.
A tighter armor cross section would save on mass for sure. It is a bit tricky, however, because the propellant tanks and the compartments in general vary with differing shapes along the length of the ship. For instance, going from six tanks to four (which is fairly common), would require geometric discontinuities between the sections which might be minor weak points.
About the angled armor, a full cylinder would have the best slope, as only a small section would be close to 0 degrees. With the rounded prisms, anytime the enemy is side-on, a full section of the ship is close to 0 degrees. And when the enemy is barraging your ship with thousands of projectiles, having such a large weak spot is a problem. Even if it means the adjacent sections are better armored, having one section which is poorly armored is a problem, as armor is usually only as good as it's weakest point.
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Post by apophys on Jul 31, 2016 12:28:46 GMT
I assumed the radiator-armor could be easily sectioned and oversized to account for losing sections to damage. Material strength decreasing with temperature I didn't consider, though. Seems like the long thin radiator idea running the full length of the ship (perpendicular to the armor) is what I'll mostly use, then. About the angled armor, a full cylinder would have the best slope, as only a small section would be close to 0 degrees. With the rounded prisms, anytime the enemy is side-on, a full section of the ship is close to 0 degrees. Shouldn't it be possible to always roll the edge towards the enemy while in range of combat? Reaction wheels should be enough to roll. You even mention pointing radiators edge-on. Unless the case of having multiple enemies from multiple directions happens more often than I'm expecting. Thanks for the responses. I'm really looking forward to being able to test things ingame when it becomes available. Another thing I thought of: Would it be possible to make laser apertures of 100m or more with a thin umbrella mirror around the ship (aim by moving the ship itself, focus by deforming the umbrella)? I'm aware this would be an enormous target to shoot at, but the greater effective range of the laser could be worth it. Long-range artillery would allow kiting tactics, and thus the complete abandonment of armor. I was thinking a metal coating on a semi-rigid tensile membrane with tubular support structure (i.e. literally a shiny umbrella), but this might work too for much less mass: www.obs-hp.fr/www/preprints/pp136/PP136.HTML
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Post by qswitched on Aug 1, 2016 1:24:33 GMT
That's true about rolling, though reaction wheels are very poor for rotating an entire ship. For a reaction wheel to be effective, it needs to be of comparable mass of whatever it's rotating, which is why they're good for gun turrets, but not very good for an entire ship. Vernier thrusters are primarily what is used for rolling a ship.
Enemies from multiple directions is rare. However, a common case you have to worry about is drones coming in at low speed, which generally have the ability to attack from any direction, slowly circling your craft, or possibly splitting into multiple attack wings to get multiple attack directions.
About the laser apertures, the larger they get, the larger of a targeting cross section the ship/aperture becomes for the enemy. Projectile weapon range is dependent on many factors, but the biggest one is the enemy cross section. From what I've found, at certain sizes, the laser range gained from having larger and larger apertures increases slower than the range the enemy weapons gain from you increasing your size.
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Post by Friendly Anon on Sept 6, 2016 14:29:10 GMT
Ah, I see. I guess that makes some sense.
Well I guess if you can't see a good way it would work within your set limitations, then I guess that's that. But I can't help but feel that some significant element of tactical complexity that surely would be a factor in a real situation is missed.
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Post by Friendly Anon on Sept 6, 2016 14:30:03 GMT
Meant to quote "About sloped armor, when you run the numbers, the additional mass of jagged or high surface area armor ends up performing the same as simply adding the mass as a flat plate. Note that the Abrams or Merkava both have smooth slopes on the turret and main body."
Don't know what went wrong there.
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Post by wazzledazzle on Sept 6, 2016 15:04:58 GMT
The discussion just reminded me of heatsinks. As in, instead of shedding heat constantly through radiators, you pump it into a large amount of liquid and then vent it away into space. Obviously this doesn't allow for stealth, but it could allow firing more heat-inducing lasers without needing prohibitively large radiators. Of course, there's the drawback of the sinks being single-use.
Have you thought of implementing that, or is it something you researched and simply wasn't effective ? I'm curious, since those are featured in Attack Vector Tactical (hard-fi board game, though set farther in the future than CDE)
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Post by qswitched on Sept 6, 2016 17:43:30 GMT
I did do some research on heat sinks. The single-use nature heavily dissuaded me from persuing them further, given that you'd need very large "ammo" stores of coolant, costing a lot of one-off mass and volume. On the plus side, they could be hidden entirely within the spacecraft.
It seems to be a highly requested feature though, so it would definitely be a prime candidate for a future update.
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Post by Crazy Tom on Sept 6, 2016 20:06:01 GMT
I did do some research on heat sinks. The single-use nature heavily dissuaded me from persuing them further, given that you'd need very large "ammo" stores of coolant, costing a lot of one-off mass and volume. On the plus side, they could be hidden entirely within the spacecraft. It seems to be a highly requested feature though, so it would definitely be a prime candidate for a future update. Heat Sinks would be a godsend against missiles because they usually have short engagement windows and home on IR, so being able to retract them even for a minute or two would improve a craft's survivability by a lot. That way they can be reused by cooling them back down after the threat has passed.
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