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Post by cutterjohn on Dec 7, 2016 6:03:57 GMT
It's not as difficult as it sounds, the HST was able to spot a galaxy 1/25th of the Milky Way's size from 13.4 billion LYs away. Granted, at that distance there was a light lag of 13.4 billion years, but if we can snap a picture of something that far away, I think we can rather comfortably spot anything inside the Oort Cloud. We are also currently tracking almost 3,000 asteroids with a diameter of 30m or less as part of the Near Earth Object program, which we can see when they are illuminated by the sun and can otherwise be tracked with math. the Hubble telescope also weighs 11t and is 14m long, not to mention that the exposure times it uses to take 1 photo is in the order of hours or days, I don't know the exact details but the short exposure images are 37hours 10 minutes... (standard deep field : 37 hours, deep field : 23 days (what I think you were referring to) source:wiki) source: www.stsci.edu/hst/stis/software/planning/etc/etc.stsci.edu/etc/input/stis/imaging/ps: telescopes also look at bright objects, with high emission or reflection of light, everything a stealth ship won't be. Even then Pluto look more like a pixilated blob then a planet on most images 11t and 14m long are nothing in this game. There are ships several hundred meters long that mass kilotons, and stations much larger than that. You think the warring factions would have no intelligence gathering structures when they can build such massive structures in space? The fighting ship doesn't *need* to be equipped to do massive sweeps to find enemies, because they'd have massive radio and infrared telescopes doing that for them at strategic locations. Listening posts on moons and asteroids. Spy satellites. And plain old meat spies, such as at refueling stations. The game lets you make 47.2 meter diameter mirrors, mirrors every bit as good as telescope mirrors. That's the maximum size of mirror you can fit in the laser turrets. Hubbles mirror is 2.4 meter diameter. That's 1,748 m^2 of mirror that we can make in game, vs 4.5 m^2 for hubble. An exposure that takes ten minutes for hubble could be done in just a hair over 1.5 seconds with that 47.2 meter mirror. As far as radio telescopes... Hell, they could make one kilometers across with the construction technology they have. Space is certainly big. But you have no cover at all. Once you're found once, you're pretty much found for good. When you have milli-gs of acceleration, and millions of km of wide open territory to cover, you're not going to dash into hiding.
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Post by amimai on Dec 7, 2016 6:47:01 GMT
So you will be spending your military budget building 100 Hubble telescopes and defending them?
Ok that's fine...
Btw that still does not answer how your telescopes will see stealth ships that do not conveniently have reflective/emissive surfaces to spot...
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Post by newageofpower on Dec 7, 2016 7:53:06 GMT
So you will be spending your military budget building 100 Hubble telescopes and defending them? Ok that's fine... Btw that still does not answer how your telescopes will see stealth ships that do not conveniently have reflective/emissive surfaces to spot... Are you actually that stupid, or are you being deliberately obtuse? What has been said before: If a ship launches with a hot burn (i.e. almost fucking rocket in the game or IRL), you only need to spot the burn and then you can figure out where it's trajectory will take it. If it makes another burn to change the path, welp, that's another dead giveaway. The only combat spacecraft with realistic stealth (and even then, its highly conditional and extremely fragile against real warships) I've seen has been the Hydrogen Steamer.
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Post by amimai on Dec 7, 2016 9:27:38 GMT
So you will be spending your military budget building 100 Hubble telescopes and defending them? Ok that's fine... Btw that still does not answer how your telescopes will see stealth ships that do not conveniently have reflective/emissive surfaces to spot... Are you actually that stupid, or are you being deliberately obtuse? What has been said before: If a ship launches with a hot burn (i.e. almost fucking rocket in the game or IRL), you only need to spot the burn and then you can figure out where it's trajectory will take it. If it makes another burn to change the path, welp, that's another dead giveaway. The only combat spacecraft with realistic stealth (and even then, its highly conditional and extremely fragile against real warships) I've seen has been the Hydrogen Steamer. no u... didn't you get the part about the 10 MINUTE EXPOSURE TIME? I don't now how up to date you are on your photography but that's really long, and would be utterly useless for getting direction or duration of anything... you know those artsy pictures you get of a highway filled with streaks from car headlights? that's the same effect, except the streaks from space ship burns would be at best about a mm in length, low resolution, and look more like a blob amongst a lot of similar blobs that are stars. the amount of time a burn would happen would be at best minute, more then likely seconds in length, even if by chance you have your telescope pointed in the right direction, at the right time, and you opened your shutter at the exact moment needed, you would still not capture anything because it would be too faint to detect against background or be so blurred due to under-exposure that it would be indistinguishable from random noise in the image. and before you start, Long range detection of non-emissive non-reflective objects in space is hard, we have a 1000s of telescopes pointed into space at the moment and we still probably would not spot a 1km wide asteroid on an impact course to earth unless we were really lucky... here is what it would look like IRL (do note this is the best image of the lot taken from earth to the ISS that is only 400km away) left : actual image(is it a bird? a plane? no its superman!) right : computer generated model because we actualy know what we were looking at in the first place
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Post by shurugal on Dec 7, 2016 14:46:06 GMT
okay, but we're not talking about a typical SLR personal camera with a wide-angle lense, sense a wide-angle lense is not a telescope. What angle of the sky is covered in a single exposure by a telescope capable of detecting the OMS plume of the space shuttle at 15Mm? I would be willing to bet a fair sum that it is a number expressed in radians or arcseconds, not degrees. I see what you are getting at. This particular IR camera used in the Atomic Rockets comes from the google groups discussion and the specifications are as follows: "Telescope - 2 meter aperture, f/2 optics. Dall-Kirkham folded Cassegrain, most likely, but with f/2 it isn't as vital as with some systems. Detector - Tektronix 2048 x 2048 pixel CCD array, 350-1000 nm response, 80% quantum efficiency, 27 um pixel size. Angular resolution - 0.0004 degrees (detector-limited) Field of view - 0.8 degrees Scan rate - 3600 seconds for full sky assumed, thus 0.7 seconds per FoV Detection Threshold - 2.5E-17 watts per square meter, at 1:1 Signal to Noise over zodiacal background and 1E-9/pixel false positive rate." I'm not going to pretend I understand all of this, but the numbers you are looking for is the angular resolution (.0004 degrees) and field of view (.8 degrees). Because the FoV is limited, the camera will take multiple exposures to capture the entire sky; at .7 seconds per exposure, it comes out to be about 3600 seconds for a full sky scan. Also, if I remember my metric prefixes correctly, 15 million km is 15 Gm. good catch on the prefixes, that was my fuxup. However, I don't believe that the time given for full sky scan is correct. If the field of view is .8 degrees, that means it only images ~.2 deg 2 at a time. since a full sphere is ~41k square degrees, that means you need a minimum of over 200k exposures, at .7 seconds per exposure, and assuming instantaneous traverse and stabilize for next shot, it would take 38 hours to do a full scan (if .8 is already in deg 2, that drops to 41k scans and 8 hours). If we factor in an overlap in each image of 10% (otherwise we risk missing things in the borders) that gives us ~41 hours for a full scan (9 hours, if i've misread the specs) now, for a range of the whole solar systems, that would be a useful scale, but with a detection range of only 15Gm for 'stealthy' emissions, that's only a tenth of an AU. of course, if we set several of these in LEO and have them only scan half the sky, they could usefully detect anything in earth-orbit. Expecting them to catch burns, however, is unrealistic. To reliably catch a burn, your coverage needs to update in shorter intervals than the burn will last. If we assume that average burn times for craft attempting to move stealthily are no more than 10 minutes in duration, then we need at least 250 of these sensors covering the same area of sky on a sequential scan path (55 if i misread), and even then we still only have a detection range of ~earth orbit, so anyone wanting to insert stealthily just needs to make their adjustments while still in deep interplanetary space. of course, my math could be a load of shit, but i don't think it is. I could have misinterpreted the FoV rating of that sensor, but even if I did, it only reduces the number of them needed to get continuous coverage. We're still talking about multi-million dollar sensor packages that are going to be an absolute -bitch- to maintain (and I should know, my day job is maintaining military sensor and network equipment).
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Post by lieste on Dec 7, 2016 15:04:40 GMT
Why do you calculate 0.8 deg into 0.2 deg^2? I'd expect something fairly close to 0.6 deg^2 and given how 'flat' 0.8 deg is actually almost identically to the square or 0.64 deg^2...
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Post by shurugal on Dec 7, 2016 16:26:09 GMT
Why do you calculate 0.8 deg into 0.2 deg^2? I'd expect something fairly close to 0.6 deg^2 and given how 'flat' 0.8 deg is actually almost identically to the square or 0.64 deg^2...
the math for degrees of circular FoV of X angle to Deg2 should be Deg2= x2/pi
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Post by lieste on Dec 7, 2016 17:51:53 GMT
No it doesn't. When small enough to be considered flat it must approximate a circle. (i.e. pi*r^2 or pi*d^2/4)
This is 0.5 deg^2... but it is usual for a detector and the images captured to be rectangular rather than circular, so the 0.8 should either be the diagonal or the vertical/horizontal dimension.
It would IMO be most appropriate to use the vertical/horizontal orientation (~0.64 deg^2), rather than the diagonal measure (~0.32 deg^2), but all of these are much larger than 0.2 deg^2
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Post by shurugal on Dec 7, 2016 18:37:53 GMT
No it doesn't. When small enough to be considered flat it must approximate a circle. (i.e. pi*r^2 or pi*d^2/4) This is 0.5 deg^2... but it is usual for a detector and the images captured to be rectangular rather than circular, so the 0.8 should either be the diagonal or the vertical/horizontal dimension. It would IMO be most appropriate to use the vertical/horizontal orientation (~0.64 deg^2), rather than the diagonal measure (~0.32 deg^2), but all of these are much larger than 0.2 deg^2 good to know, i'll re-run the numbers using .64 deg 2. 41,252.9612 deg 2 in a full sphere yields 64458 scans with no overlap. With 10% overlap to prevent dead spots, 70904 scans. .7 seconds per exposure, zero reposition time, 49632.8 seconds for a full spherical exposure. assume sensor is in LEO and only scans 1/2 sphere: 6 hours, 53 minutes, 36.4 seconds to scan assigned area. assume enemy uses high-impulse short-duration burns to minimize exposure times and makes burns an average of 10 minutes. To achieve a high rate of detection, must scan the sky every 5 minutes. Require a cluster of 83 sensors to achieve 5-minute scan window to allow detection of burns. If we are only interested in detecting objects in the solar plane, 3 orbiting clusters will suffice. If we are worried about polar insertions, 3 more clusters in polar orbit. someone could probably devise a set of orbits similar to the GPS constellation that would put 3 sensors at the points of a triangular pyramid at any given time, but that would only increase the expense and complexity of the system. So, minimum number of sensors needed: 249. include constant polar coverage at 498. Detection range makes for only a mediocre early-warning system, but would probably be worth the expense to provide near real-time tracking of anything in earth/lunar orbits.
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Post by lieste on Dec 7, 2016 19:17:37 GMT
If a ship is stealthy it will burn very weakly, especially if using cool outgassing. If it burns powerfully then there will be considerable residual heat that will linger well beyond the burn duration.
A 10 minute stealthy burn is pointless - it will accomplish *almost* nothing and will need to be repeated a *very* large number of times to accomplish any trajectory adjustment. A brief hard burn will result in compromised IR stealth for many times the burn duration, and could be picked up on a wide area search of much lower sensitivity and much higher refresh rate which cues the high sensitivity/high resolution scanners to triangulate on the location of interest if an unidentified object (no need to twitch every time a known object performs a minor burn though).
Generally high performance engines can be burnt for short periods to accomplish trajectory changes, but are easy to track while doing it. Lower performance engines are burnt near continuously over days/weeks/months to accomplish an equivalent transition.
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Post by shurugal on Dec 7, 2016 23:10:40 GMT
If a ship is stealthy it will burn very weakly, especially if using cool outgassing. If it burns powerfully then there will be considerable residual heat that will linger well beyond the burn duration. A 10 minute stealthy burn is pointless - it will accomplish *almost* nothing and will need to be repeated a *very* large number of times to accomplish any trajectory adjustment. A brief hard burn will result in compromised IR stealth for many times the burn duration, and could be picked up on a wide area search of much lower sensitivity and much higher refresh rate which cues the high sensitivity/high resolution scanners to triangulate on the location of interest if an unidentified object (no need to twitch every time a known object performs a minor burn though). Generally high performance engines can be burnt for short periods to accomplish trajectory changes, but are easy to track while doing it. Lower performance engines are burnt near continuously over days/weeks/months to accomplish an equivalent transition. I said nothing about a ten-minute stealthy burn. Running stealthy low-impulse burns only makes sense in deep interplanetary space where you will get the most bang for your dV. As you draw within sensor range, it makes far more sense to fire high-impulse, short-duration burns to try and fall into gaps in sensor sweeps. An exhaust plume travelling at ~5 km/s will spread out fast enough that it will cool down to background levels in a few minutes at most, thanks to Boyle's Law. If we only used one sensor sweeping half the sky every 7 hours, then in the average of 3.5 hours between burn and sweep, the exhaust plume will have moved 63Mm from the point of the burn, and will have lost all heat. Even if you catch the plume 5 minutes after the burn, it still will have moved 1.5Mm. You could still trace it back to the point of origin, but if the burn was enough to make a significant shift in orbit, then by the time you trace the gasses back to their points of origin, calculate the old trajectory, and then make a guess at what the new one could be (remember, you might be able to see how much gas was expelled and how fast it is going, but you don't know the mass of what it was pushing, so you can't calculate acceleration), the ship could have travelled tens of Mm, and could be hundreds of km away from your predicted trajectory. I think this is where our disconnect is. Hot burns are easy to track. But to track a burn, you have to already know where it is. To catch a burn that you don't know about before time, you have to be scanning the sky in intervals less than the duration of the burn. You could use a system that takes 7 hours to sweep half the sky to track things all day, but you need to be sweeping the sky much, much more often if you expect to catch an unknown object burning.
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Post by newageofpower on Dec 7, 2016 23:43:32 GMT
I said nothing about a ten-minute stealthy burn. Running stealthy low-impulse burns only makes sense in deep interplanetary space where you will get the most bang for your dV. As you draw within sensor range, it makes far more sense to fire high-impulse, short-duration burns to try and fall into gaps in sensor sweeps. An exhaust plume travelling at ~5 km/s will spread out fast enough that it will cool down to background levels in a few minutes at most, thanks to Boyle's Law. If we only used one sensor sweeping half the sky every 7 hours, then in the average of 3.5 hours between burn and sweep, the exhaust plume will have moved 63Mm from the point of the burn, and will have lost all heat. Even if you catch the plume 5 minutes after the burn, it still will have moved 1.5Mm. You could still trace it back to the point of origin, but if the burn was enough to make a significant shift in orbit, then by the time you trace the gasses back to their points of origin, calculate the old trajectory, and then make a guess at what the new one could be (remember, you might be able to see how much gas was expelled and how fast it is going, but you don't know the mass of what it was pushing, so you can't calculate acceleration), the ship could have travelled tens of Mm, and could be hundreds of km away from your predicted trajectory. Why would you ever only use one sensor? Once you can see how much gas was expelled (and at what energies) you then see how long the burn was for. I think this is where our disconnect is. Hot burns are easy to track. But to track a burn, you have to already know where it is. To catch a burn that you don't know about before time, you have to be scanning the sky in intervals less than the duration of the burn. You could use a system that takes 7 hours to sweep half the sky to track things all day, but you need to be sweeping the sky much, much more often if you expect to catch an unknown object burning. Again, why would you ever only use a single sensor system?
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Post by shurugal on Dec 8, 2016 0:39:17 GMT
I said nothing about a ten-minute stealthy burn. Running stealthy low-impulse burns only makes sense in deep interplanetary space where you will get the most bang for your dV. As you draw within sensor range, it makes far more sense to fire high-impulse, short-duration burns to try and fall into gaps in sensor sweeps. An exhaust plume travelling at ~5 km/s will spread out fast enough that it will cool down to background levels in a few minutes at most, thanks to Boyle's Law. If we only used one sensor sweeping half the sky every 7 hours, then in the average of 3.5 hours between burn and sweep, the exhaust plume will have moved 63Mm from the point of the burn, and will have lost all heat. Even if you catch the plume 5 minutes after the burn, it still will have moved 1.5Mm. You could still trace it back to the point of origin, but if the burn was enough to make a significant shift in orbit, then by the time you trace the gasses back to their points of origin, calculate the old trajectory, and then make a guess at what the new one could be (remember, you might be able to see how much gas was expelled and how fast it is going, but you don't know the mass of what it was pushing, so you can't calculate acceleration), the ship could have travelled tens of Mm, and could be hundreds of km away from your predicted trajectory. Why would you ever only use one sensor? Once you can see how much gas was expelled (and at what energies) you then see how long the burn was for. I think this is where our disconnect is. Hot burns are easy to track. But to track a burn, you have to already know where it is. To catch a burn that you don't know about before time, you have to be scanning the sky in intervals less than the duration of the burn. You could use a system that takes 7 hours to sweep half the sky to track things all day, but you need to be sweeping the sky much, much more often if you expect to catch an unknown object burning. Again, why would you ever only use a single sensor system? read some of my previous posts, i never suggested using one sensor. I was stating that it would be absolutely necessary to use a cluster of at least 80 sensors of the type specified for each hemispherical sky section you wanted to scan. also: knowing the duration of the burn is irrelevant, you still don't know the mass of the ship making the burn, so you can only make a guess as to what acceleration the burn produced. Really, there are two key pieces of information missing: the first is the initial velocity of the contact. You can trace the exhaust plume back to the point where it forms a line (unless the burn was perfectly coaxial with the original path of travel, but then you have a nice arrow to follow), and then you will know where the ship was when it made the burn. But if you don't know the initial velocity of the ship, you won't be able to calculate the duration of the burn from the length of the streak. You also won't be able to know what the exit velocity of the exhaust was, because you won't know how much of its current motion is simply inertia from the ship. the second is the mass of the contact. Even if you know (or can reasonably assume) its starting velocity, without knowing how heavy it is, you won't know how much dV it just burned. You could infer its minimum mass from the fuel expended (IE, exhaust plume is X kilograms, so it must have a fuel tank with at least X capacity and an engine capable of delivering Y newtons on X fuel), but that only gives you one boundary for a range of possible new headings, and you have no idea where the other bound is because you do not know what the maximum mass could be. For all you know, Spaceball One could have just burned into orbit, because all you're looking at is a bunch of cold hydrogen. anyway, the point of all of this, is: Why would you ever only use one sensor?
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Post by cutterjohn on Dec 8, 2016 4:13:08 GMT
So you will be spending your military budget building 100 Hubble telescopes and defending them? Ok that's fine... Btw that still does not answer how your telescopes will see stealth ships that do not conveniently have reflective/emissive surfaces to spot... I watched them leaving port, obviously. Are you actually that stupid, or are you being deliberately obtuse? What has been said before: If a ship launches with a hot burn (i.e. almost fucking rocket in the game or IRL), you only need to spot the burn and then you can figure out where it's trajectory will take it. If it makes another burn to change the path, welp, that's another dead giveaway. The only combat spacecraft with realistic stealth (and even then, its highly conditional and extremely fragile against real warships) I've seen has been the Hydrogen Steamer. no u... didn't you get the part about the 10 MINUTE EXPOSURE TIME? I don't now how up to date you are on your photography but that's really long, and would be utterly useless for getting direction or duration of anything... you know those artsy pictures you get of a highway filled with streaks from car headlights? that's the same effect, except the streaks from space ship burns would be at best about a mm in length, low resolution, and look more like a blob amongst a lot of similar blobs that are stars. the amount of time a burn would happen would be at best minute, more then likely seconds in length, even if by chance you have your telescope pointed in the right direction, at the right time, and you opened your shutter at the exact moment needed, you would still not capture anything because it would be too faint to detect against background or be so blurred due to under-exposure that it would be indistinguishable from random noise in the image. and before you start, Long range detection of non-emissive non-reflective objects in space is hard, we have a 1000s of telescopes pointed into space at the moment and we still probably would not spot a 1km wide asteroid on an impact course to earth unless we were really lucky... here is what it would look like IRL (do note this is the best image of the lot taken from earth to the ISS that is only 400km away) left : actual image(is it a bird? a plane? no its superman!) right : computer generated model because we actualy know what we were looking at in the first place I already pointed out that we already make mirrors in the game that can take that 10 minute photograph in 1.5 seconds. And we have virtually no telescopes on earth looking in the infrared, since obviously earths atmosphere absorbs infrared. Everything emits in the infrared, rendering your 'non-emissive' moot. Your image is meaningless. 'Getting a good picture of' is not the same thing at all as 'detection'.
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Post by newageofpower on Dec 8, 2016 4:23:13 GMT
Problem is your engines will emit a ton more than 1 MW heat, unless you have a ridiculously low thrust... Use MPD? And have the sole weapon being stealth drone that also use MPD to launch missiles away from the main craft? ... I actually like this idea. Yes, magically generate all the electricity without emitting heat.
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