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Post by bigbombr on Aug 22, 2017 17:02:23 GMT
A laser rangefinder does the same thing as radar (bouncing off a target i mean, weakening quickly with range), only it has to be aimed at a target, instead of finding range for every object in a radius! In the military there is a distinction between acquisition and fire control. Acquisition devices have to try to catalogue every hostile in range, what they are, and where they are going. You could try to do that with IR and a laser rangefinder but it would take forever to keep pointing the laser at each possible target and back as their orbit changes and you have to determine it all over again in an endless cycle (and I still don't think heat gradients could be better than a 3d image) If laser rangefinders are longer range than radar for the same antenna size and weight, than they could definitely be used for fire control thou! Althou they would be more expensive too For finding targets at long range, IR seems to have the greatest range. A laser rangefinder with the same range as a tracking radar is probably smaller and cheaper, otherwise we wouldn't use laser range finders in either a military or scientific context. How many infantrymen carry a small rangefinder radar around? Because laser rangefinders are so much smaller and cheaper, you can have several of them. Radar searches in a cone, but isn't omnidirectional, so you'd need multiple of those too, considering light lag. As for why heat gradients on a 2D-image might (IMO) be more useful than a 3D-image for target identification: with whipple shields and hatches it's easy too hide what you're packing and what you're running, but entropy doesn't lie. Waste heat will tell you how much energy is used in which parts of the contact. A 2D picture is sufficient for identifying the guns on a warship. So, IMO, you'd use IR to find possible contacts, use detailed thermal imaging to determine position and ID of contacts, and use laser rangefinders to get their range and speed. This only needs to be done every once in a while, as you will see every time they make a burn. Radar might be a decent backup against small inert objects (like asteroids or projectiles), though reflection of and heating by sunlight might mean this is not necessary. This is the level of detail currently possible: i2.cdn.cnn.com/cnnnext/dam/assets/160823003713-f-35-fighter-jet-thermal-scan-jnd-orig-vstan-00003326-super-tease.jpg
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Post by princesskibble on Aug 22, 2017 17:29:27 GMT
A laser rangefinder with the same range as a tracking radar is probably smaller and cheaper, otherwise we wouldn't use laser range finders in either a military or scientific context. How many infantrymen carry a small rangefinder radar around? But even in places where lasers would seem optimal (SALH missiles as opposed to SARH) the military uses radar, which implies for short range(bombs, tank guns, and infantry weapns) lasers are useful, but for long range (missiles) they aren't. Because laser rangefinders are so much smaller and cheaper, you can have several of them. Radar searches in a cone, but isn't omnidirectional, so you'd need multiple of those too, considering light lag. Search radars steadily rotate to scan the sky every few seconds, and anyway laser rangefinders and radars are probably the same size because they are limited in range the exact same way So, IMO, you'd use IR to find possible contacts, use detailed thermal imaging to determine position and ID of contacts, and use laser rangefinders to get their range and speed. This only needs to be done every once in a while, as you will see every time they make a burn. But there may be hundreds of targets to track, each making small burns with RCS every few seconds!
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Post by bigbombr on Aug 22, 2017 17:49:12 GMT
But even in places where lasers would seem optimal (SALH missiles as opposed to SARH) the military uses radar, which implies for short range(bombs, tank guns, and infantry weapns) lasers are useful, but for long range (missiles) they aren't. Search radars steadily rotate to scan the sky every few seconds. But there may be hundreds of targets to track, each making small burns with RCS every few seconds! Long range radar use: On Earth, your detection range limit is often line of sight. Radar can bounce of the ionosphere, lasers can't. But radar range hits it limits despite this at a few hundred km. In space, this kind of range is useless. It's at least one, probably two to three orders of magnitude too short for space combat. Meaning you'd need 100 (10²) to 1000 000 (1000²) times as much power if you want radar to be useful at the appropriate ranges. Lasers spread their energy in a tighter cone, so they have a much greater range for the same power. Search radars steadily rotate: I specifically mentioned light lag, as this means you'll have to wait much longer for your return signal, so you're radar will turn much slower than on Earth, or you'll miss the return signal of long range signatures. Multiple fixed phased array radars spread over the hull giving full hemispherical coverage seem much better. This also saves considerably on mass, and means your radar system doesn't stick out from the hull and won't get lased ASAP. Many targets to track: Stationkeeping burns aren't every few seconds, and are only small nudges. Contacts will either burn briefly at predictable moments (how chemical rockets and NTR make an interbody trajectory) or gently for extended periods of time (Hall effect thruster or plasmadrives). Stationkeeping is both gentle and brief, and has a limited impact on trajectory. You use stationkeeping to maintain your orbit, not to fly like an aircraft. And using a laser rangefinder on a contact is only necessary when acquiring the exact trajectory of that contact. The broad course and range can be estimated by the thermal camera's. Lasing a contact at long range might be perceived as a threatening gesture, as you're implying you're acquiring a firing solution. You might use a laser rangefinder (or radar) during docking though.
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Post by beta on Aug 22, 2017 18:33:26 GMT
There are methods where you can acquire a firing solution with purely passive IR systems ( en.wikipedia.org/wiki/Infra-red_search_and_track#Later_systems ) in the atmosphere, likely could do the same in space as apparent surface area and target motion analysis still work in space. It would likely be easier to jam a ranging attempt through pure passive IR. Either way, it would be awesome to have a detailed look into sensors and their countermeasures.
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Post by jtyotjotjipaefvj on Aug 22, 2017 18:39:31 GMT
Many targets to track: Stationkeeping burns aren't every few seconds, and are only small nudges. Contacts will either burn briefly at predictable moments (how chemical rockets and NTR make an interbody trajectory) or gently for extended periods of time (Hall effect thruster or plasmadrives). Stationkeeping is both gentle and brief, and has a limited impact on trajectory. You use stationkeeping to maintain your orbit, not to fly like an aircraft. And using a laser rangefinder on a contact is only necessary when acquiring the exact trajectory of that contact. The broad course and range can be estimated by the thermal camera's. Lasing a contact at long range might be perceived as a threatening gesture, as you're implying you're acquiring a firing solution. You might use a laser rangefinder (or radar) during docking though. We're talking about combat uses here though, right? You wouldn't want to glide along your orbit without burning in combat, you'd need to constantly change your trajectory or you're going to get hit by enemy fire. Besides that, you could deploy inert submunitions (eg. nukes with a simple proximity fuse) very stealthily. If the carrier just drops the munition and changes trajectory, you wouldn't be able to detect such a projectile using IR, since it'd be very close to ambient temperature. Radar might not be useful in long-range combat but I'd certainly see it being used for point-defence targeting, for example. In CoaDE, such submunitions will immediately get zapped by lasers at 1000km, but I don't think that's very realistic, especially not with just passive IR.
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Post by bigbombr on Aug 22, 2017 18:39:37 GMT
There are methods where you can acquire a firing solution with purely passive IR systems ( en.wikipedia.org/wiki/Infra-red_search_and_track#Later_systems ) in the atmosphere, likely could do the same in space as apparent surface area and target motion analysis still work in space. It would likely be easier to jam a ranging attempt through pure passive IR. Either way, it would be awesome to have a detailed look into sensors and their countermeasures. Even greatly simplified thermal or radar detection would be interesting.
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Post by Pttg on Aug 26, 2017 17:36:07 GMT
I am a little worried that it's been more than a month now since the last post by qswitched.
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Post by teeth on Aug 26, 2017 18:37:42 GMT
He does get on every now and then to like a few posts, but I don't understand why he hasn't posted. Usually he at least responds to bug reports.
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Post by aetreus on Aug 28, 2017 16:05:04 GMT
WRT radar, there's a number of important things people are missing. Radar isn't subject to an inverse-square relation, it's actually subject to an inverse hypercube relation(4th power). That means maximum radar range rises slowly with increasing power-aperature product, but also that RCS reduction has a much more gradual effect on radar ranges. Radar gives much, much more information on the target than passive IR. You can observe target range and importantly range rate, which gives you their precise orientation and motion, where IR just gives you bearings which are much harder to interpret into ranges.
RCS reduction techniques work, but less well than people think. Materials give some RCS reduction, but are actually quite heavy to be effective and don't generate a huge reduction in returns. Similarly shaping only goes so far- and because CoaDE ships can be observed from any orientation, while aircraft and ships generally only from a few, it is much harder to generate a broadly effective shaping for them. Even then size matters a lot still, a big target like a capital ship is not going to be able to hide itself from a powerful radar(and with a ship's cooling and power supplies, you can design some ABSURD radars) at combat ranges very well.
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Post by cuddlefish on Aug 28, 2017 17:31:52 GMT
WRT radar, there's a number of important things people are missing. Radar isn't subject to an inverse-square relation, it's actually subject to an inverse hypercube relation(4th power). That means maximum radar range rises slowly with increasing power-aperature product, but also that RCS reduction has a much more gradual effect on radar ranges. Radar gives much, much more information on the target than passive IR. You can observe target range and importantly range rate, which gives you their precise orientation and motion, where IR just gives you bearings which are much harder to interpret into ranges. RCS reduction techniques work, but less well than people think. Materials give some RCS reduction, but are actually quite heavy to be effective and don't generate a huge reduction in returns. Similarly shaping only goes so far- and because CoaDE ships can be observed from any orientation, while aircraft and ships generally only from a few, it is much harder to generate a broadly effective shaping for them. Even then size matters a lot still, a big target like a capital ship is not going to be able to hide itself from a powerful radar(and with a ship's cooling and power supplies, you can design some ABSURD radars) at combat ranges very well. I'm now just imagining a ship with a multi-gigawatt RADAR array. SWACS?
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Post by RiftandRend on Aug 28, 2017 19:05:34 GMT
The main issue with radar is it's range to power ratios. I don't see it being more cost effective than IR+Laser Rangefinding at 10,000+ kilometer ranges where most of our combat takes place. An IR system can give you bearing data and a laser rangefinder can provide a range. Where radar would probably be more useful is in detecting cold and dark targets, but a LIDAR system can do that just as well for less cost and power requirements.
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Post by aetreus on Aug 28, 2017 23:14:14 GMT
The main issue with radar is it's range to power ratios. I don't see it being more cost effective than IR+Laser Rangefinding at 10,000+ kilometer ranges where most of our combat takes place. An IR system can give you bearing data and a laser rangefinder can provide a range. Where radar would probably be more useful is in detecting cold and dark targets, but a LIDAR system can do that just as well for less cost and power requirements. It's much easier to make a target "dark" to a visible/IR band laser than it is to make it radar-absorbent. Radar by its nature doesn't solely interact with the surface of the target, and even the best RAM materials don't have more than 10dB absorbtion over broad bands, no more than 20-30 over a narrow target band. Materials like carbon black or copper chromite match that performance across the entire visible/UV/IR bands, with reflectivity of 0.02-0.01(equivalent to -20 dB). Engineered materials can drive that down to something like -34, and applying a thin layer is all that's needed to counter a laser-based system.
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Post by Enderminion on Aug 28, 2017 23:20:48 GMT
The main issue with radar is it's range to power ratios. I don't see it being more cost effective than IR+Laser Rangefinding at 10,000+ kilometer ranges where most of our combat takes place. An IR system can give you bearing data and a laser rangefinder can provide a range. Where radar would probably be more useful is in detecting cold and dark targets, but a LIDAR system can do that just as well for less cost and power requirements. It's much easier to make a target "dark" to a visible/IR band laser than it is to make it radar-absorbent. Radar by its nature doesn't solely interact with the surface of the target, and even the best RAM materials don't have more than 10dB absorbtion over broad bands, no more than 20-30 over a narrow target band. Materials like carbon black or copper chromite match that performance across the entire visible/UV/IR bands, with reflectivity of 0.02-0.01(equivalent to -20 dB). Engineered materials can drive that down to something like -34, and applying a thin layer is all that's needed to counter a laser-based system. if your craft is battlefleet, then it has a nuclear reactor, even if you radiate heat away from me, I have microreconsats everywhere, looking everywhere, with IR cams
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Post by jtyotjotjipaefvj on Aug 28, 2017 23:53:44 GMT
It's much easier to make a target "dark" to a visible/IR band laser than it is to make it radar-absorbent. Radar by its nature doesn't solely interact with the surface of the target, and even the best RAM materials don't have more than 10dB absorbtion over broad bands, no more than 20-30 over a narrow target band. Materials like carbon black or copper chromite match that performance across the entire visible/UV/IR bands, with reflectivity of 0.02-0.01(equivalent to -20 dB). Engineered materials can drive that down to something like -34, and applying a thin layer is all that's needed to counter a laser-based system. if your craft is battlefleet, then it has a nuclear reactor, even if you radiate heat away from me, I have microreconsats everywhere, looking everywhere, with IR cams I have nanoreconsats that can detect your microsats from millions of miles away and disable them though. Now you need to use your ship's sensors.
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Post by Enderminion on Aug 29, 2017 0:17:50 GMT
if your craft is battlefleet, then it has a nuclear reactor, even if you radiate heat away from me, I have microreconsats everywhere, looking everywhere, with IR cams I have nanoreconsats that can detect your microsats from millions of miles away and disable them though. Now you need to use your ship's sensors. but I have picoreconsats that can detect your nanoreconsats from millions of megameters away and disable them though. ad infinitum
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