Still, the planet would have to have measures in place for that... and the TL would need to be high enough... and the countermeasure would have to be fast enough... and someone would have to have been looking in that direction at the right time.
The ultimate weapon
- Thread starter Carlobrand
- Start date
Still, the planet would have to have measures in place for that... and the TL would need to be high enough... and the countermeasure would have to be fast enough... and someone would have to have been looking in that direction at the right time.
I think a robust enough defense system would have detection in all directions. A vessel accelerating towards relativistic speeds would be visible from the moment it started to move past a significant velocity. And, unlike an asteroid, it's acceleration would be steady, and its course would be noticeable, calling attention to itself.
But, as per the previous posts, it's up to the REF to determine the outcome of your game.
Just on a gut level I think it unlikely.
christopher.boote
SOC-12
Actually, there is in the MT OTU
Densitometers
Gravity is detected instantaneously (as far as we know) and is not subject to light speed lag
So a planetary defence densitometer combined with a deep sited meson gun can detect and hit things light minutes out
SF fiction to the contrary notwithstandfing, changes in gravity propagates at the speed of light.
Hans
But, what TL are those? (And you would need multiple densitometers and meson sites, otherwise the far side of the planet could still be attacked. Of course, that side mightn't be populated.)
They're presumed to travel at light speed, but it's not something that's readily tested. Testied it has been, however, and the news is funky... There's a published paper that notes that the evidence points to speed of Gravity being effectively infinite (Flandern, 1998, republished at: http://metaresearch.org/cosmology/speed_of_gravity.asp ).
Keep in mind, past about 10 LS, you're pretty much on passives only anyway, thanks to the inverse square law, and the need to not make the system melt its own controls...
And the absolute energy in solar return between 1000LS and 2000LS isn't really going to be that much in terms of a ship, even at 0.5 C.
If it's approaching dead on, it simply gets brighter. It could be mistaken for a nova or supernova. If it's crossing the sensor, it may be moving to fast for the comparator to make it out as a valid signal, presuming it instead two separate short term contacts.
The angle of approach potentially makes the difference between the detection being referred to defense or astrometrics.
Keep in mind: passives detect "in field objects" by their motion. A scope in space is going to get literally thousands of objects as bright or brighter than a capital ship at 2 AU... let alone a limited signature high-STL "planet killing bullet." They do this by one of several means.
Method 1: Blink Comparator. Take two shots of the same field from the same point. Cancel out anything that didn't move. (This can be done by digital subtraction, or by literally blinking two images on one screen back and forth.) No matter the speed, the object coming straight towards the scope is just a dot for most of the trip... and one that might show up as a faint ring, or might be canceled out.
False positives include close but slow and dim objects,
Method 2: Stereooptic Parallax. Take two images at once from different points of the same deep field. ID all the items by matched signatures (usually spectrographic); anything which is different is closer than the parallax measure's limit; with a 1" of arc accuracy, your "distance" is 1 parsec for a 2 AU baseline separation. Anything closer than your spearation and measurement accuracy's limit distance can be distance determined from the "apparent movement" (parallax). This only finds a location for objects, and is calculation intensive. False positives are non-threat objects which may have had sudden brightness changes resulting in anomalous signatures
Method 3: Parallax on blink. Take two canceled blink images. Then run the parallax calcs on just those objects which moved. Gives you a good 3D location and speed plot. Reduces the parallax calcs.
False positives will be few... but false negatives will be many. Objects moving directly at one scope will appear only in one camera, and may be considered noise.
Can also be done with interferometry.
Method 4: long stable exposure. Set up a stable exposure. Anything with apparent motion appears as a streak. Deep field alignment means this is going to pick up anything with significant apparent motion. But it won't give range.
Method 5: long stable vs reference short exposure. Cancel out the deep field by using a short exposure negative as a mask on the long stable exposure. Makes it easier to see the movement, by reducing the noise. Still doesn't give distance, only the apparent motion of the objects detected. If your reference is old enough, however, it can pick up a new object readily, even at low motion.
Intentional False negative obtainable by picking a bright stable referent, and coming in on a direct line from it to target.
False positives can include close small dim objects.
Method 6: Parallax version of method 5. (Method 4 produces too much to calculate by comparison.) Use your masked views, from the two cameras, and parallax calc on all the signature traces. With sufficient separation, you'll get some apparent motion on anything headed for one or the other. This isn't done yet because of the issue of the field itself not being stable from ground based scopes. I've seen it done with bullets, however, in experimental footage from DARPA released to the media... not good enough to take out the bullets, but the sniper only gets ONE burst.
Keep in mind also: short field scopes only have a few degrees field of view. As in, typically under 2°; deep field scopes have fields of view measured in low double digit arc seconds. So, a spherical search needs over 10000 images. (four square degrees per image presumed for this calc gives 10,314... it will be more, actually...) per sweep, and needs to sweep twice to detect motion on passives, tho' red/blue shifting can imply speed. If each sweep image takes 0.1 sec, and you have 100 scopes assigned the task, you can get one every 10 sec. Which will detect those fast moving things you've been on about... but not the slow moving stuff. False positives include close but slow and dim objects,
Method 2: Stereooptic Parallax. Take two images at once from different points of the same deep field. ID all the items by matched signatures (usually spectrographic); anything which is different is closer than the parallax measure's limit; with a 1" of arc accuracy, your "distance" is 1 parsec for a 2 AU baseline separation. Anything closer than your spearation and measurement accuracy's limit distance can be distance determined from the "apparent movement" (parallax). This only finds a location for objects, and is calculation intensive. False positives are non-threat objects which may have had sudden brightness changes resulting in anomalous signatures
Method 3: Parallax on blink. Take two canceled blink images. Then run the parallax calcs on just those objects which moved. Gives you a good 3D location and speed plot. Reduces the parallax calcs.
False positives will be few... but false negatives will be many. Objects moving directly at one scope will appear only in one camera, and may be considered noise.
Can also be done with interferometry.
Method 4: long stable exposure. Set up a stable exposure. Anything with apparent motion appears as a streak. Deep field alignment means this is going to pick up anything with significant apparent motion. But it won't give range.
Method 5: long stable vs reference short exposure. Cancel out the deep field by using a short exposure negative as a mask on the long stable exposure. Makes it easier to see the movement, by reducing the noise. Still doesn't give distance, only the apparent motion of the objects detected. If your reference is old enough, however, it can pick up a new object readily, even at low motion.
Intentional False negative obtainable by picking a bright stable referent, and coming in on a direct line from it to target.
False positives can include close small dim objects.
Method 6: Parallax version of method 5. (Method 4 produces too much to calculate by comparison.) Use your masked views, from the two cameras, and parallax calc on all the signature traces. With sufficient separation, you'll get some apparent motion on anything headed for one or the other. This isn't done yet because of the issue of the field itself not being stable from ground based scopes. I've seen it done with bullets, however, in experimental footage from DARPA released to the media... not good enough to take out the bullets, but the sniper only gets ONE burst.
Keep in mind also: signal intensity is a function of duration of exposure, distance, and strength of source (including, for passives, distance from actual source, actual source's strength, and detected objects size and albedo in the relevant wavelengths). Signal sensitivity is a function of the sensor, the size of the aperture and (if any) reflectors.
Almost all detection requires apparent motion to not be questionable/confusable. And if you're going to hit a planet after jumping, you need to be far enough out to correct for the jump's inaccuracy, and fast enough to not be stoppable.
The more apparent motion, the better - but that means sensors distant from the potential target, and that means slower response and ranging times, and fewer surveys per unit time.
Major systems ApCon probably has 3 to 6 arrays of 15° scopes in high orbits, and automated onboard blink comparator processing... but those arrays will still need to have at least 234 units to do continuous sky survey... and probably won't be good for more than a few light minutes. (Wide field also means poor angular resolution, and thus short ranges.)
Active sensors have MUCH better chances of detection, better distance discrimination (due to a controlled and calibrated signal strength) can be used for velocity detection with a single ping (tho it still takes two to get accurate course), and much shorter range. Tho 30° FoV actives are much more common than for passives.
O
Omnivore
Guest
Aramis, you are awesome! Now could you explain that in detail? :devil:
Seriously, great info. I'm wondering though if, in the special case of watching for relativistic inbounds, could you not detect blueshift during a long exposure to flag possibles? Assuming it is still accelerating that is.
Seriously, great info. I'm wondering though if, in the special case of watching for relativistic inbounds, could you not detect blueshift during a long exposure to flag possibles? Assuming it is still accelerating that is.
Doesn't anything that moves towards you get blue-shifted, whether it is accelerating or not?
O
Omnivore
Guest
Yes but if it was accelerating toward you and was relativistic, there are, I believe two artifacts you might be able to detect. One is the blueshift of the black body radiation and exhaust plume, the other is the change in blueshift as it accelerated. The last might be too slim to detect, but I bet that exhaust plume will be way out of norm at a significant fraction of light speed.
I think that's all assuming you're using active fire control where, with current technology, you need returns. Admittedly that's what I used in my example, but I always figure a defense network would have a bunch of passive detection suites networked together, and each one would have a level of sensitivity that could discern what was what. Then from that, like a submarine or jetfighter, you'd go active, paint the target, and slam it.
Passive sonar, or a photosensitive equivalent, would constantly track that target's signature. Discerning what it was would be another matter, but if it adjusts course, or suddenly makes a correctional burn, that's something that the software's going to pick up and say "Hey, look, here's a potential problem" to the operators. At the very least it's going to be marked as Contact-Alpha, as opposed to Object-Omega that swirls around Efate every 200 years.
Once you can do that, and I think the tech level for the Imperium easily makes this feasible, then, again, spotting and slapping some D in front of the attacker becomes academic (assuming appropriate forces).
Now, if you're actively looking for the thing, and don't know where it is, or not even a good idea, then yeah, you're going to have problems finding it.
But even then it's all dependent on your REF's interpretation of technology. I used a radar example, but maybe there's super advanced sensors a-la pick your sci-fi show of choice, that can spot and separate information for the operator; again, i.e. this here's a rock, but this here's a spaceship...and it has guns.
Just my take.
*EDIT*
I'd address some of your tech points, but I'm on lunch break.
Last edited:
Yes. The amount of blue shift is dependent upon relative speed. A changing blue shift is indicative of acceleration.
BG, the biggest hurdle is PURELY the physics involved. For the kinds of distances needed, you need either huge sensors (for getting wide FOV) or massive redundancy (to get coverage with narrow FOV), due to the absolutely miniscule singal strengths involved.
The best sensor spectra for detecting ships are going to be IR in the ranges emitted by blackbody radiation at 260-320 kelvins (habitats), and 1000-3000 kelvins (Radiators). These are areas where they are bright objects in a relatively dark background. (Unfortunately, these are also part of stellar spectral emissions.) The next best detection passive is in the local star's brightest emmission bands.
Neither of these have wide FoV cameras with significant sensitivity; wide FoV and sensitive detectors gives mediocre signal; narrow FoV and those same, or somewhat less sensitive detectors, gives much higher signal pickup.
Moreover IR has the advantage that it's nearly physically impossible to shield a ship from being a blackbody source with a total strength below the lowest of engine idle, habitat, or 0.1kW per person.
The best sensor spectra for detecting ships are going to be IR in the ranges emitted by blackbody radiation at 260-320 kelvins (habitats), and 1000-3000 kelvins (Radiators). These are areas where they are bright objects in a relatively dark background. (Unfortunately, these are also part of stellar spectral emissions.) The next best detection passive is in the local star's brightest emmission bands.
Neither of these have wide FoV cameras with significant sensitivity; wide FoV and sensitive detectors gives mediocre signal; narrow FoV and those same, or somewhat less sensitive detectors, gives much higher signal pickup.
Moreover IR has the advantage that it's nearly physically impossible to shield a ship from being a blackbody source with a total strength below the lowest of engine idle, habitat, or 0.1kW per person.
Interesting you should be talking about IR just now. I was giving the long range detection issue some thought: the fact that the game presents "interplanetary range" passive EMS systems which can only accurately detect ships at a range of a couple of light-seconds - "accurately" being defined under the game rules as giving you displacement, power, type and an accurate enough fix to try for a lock with your pin-point sensors. Otherwise the target shows as basically a "something" somewhere in a 25 thousand kilometer wide sphere (well, square) of space.
Issue came up with respect to ships going for Oort cloud fuel sources, and whether there was any way to detect them. That got me to thinking about this situation. Let's assume for a moment that "interplanetary range" passive EMS systems are in fact interplanetary range - they can detect some hint of something out as far as 1 AU (~150 million kilometers). "Something" in this case is likely heat: I can maintain radio silence, keep my radar off, paint the hull black and do nothing but fly, but my scout's plant is putting out from 500 to 800 megawatts (depending on the rules system), my ship is using that power, and most of it (that part that isn't actually making me go faster) is eventually going to end up leaving my ship as heat - or else I cook myself well-done rather quickly.
Now, I originally postulated a start at 300 million miles - 2 AU, beyond the TL14 EMS system's game-stated range. Near as I can figure, from that distance, I look (very roughly) as "bright" in IR as an object re-radiating sunlight from about 300 thousand miles out (assuming a habitable world). As I get closer, I get brighter: 1 AU out, I'm 4 times brighter (I think - too many decades have passed between college physics and this moment) and I start being visible on the TL14 passive EMS. Or roughly thereabouts - perhaps only a battlewagon shows at that range and my scout needs to come in a bit more; basic idea still stands.
That is still way, way too far to pinpoint me or tell anything about me - but it's certainly enough to prompt a message to the oncoming man-made heat source: "Identify yourself, state your course, and why the heck are you flying so fast at us?" They can't be certain of my range except that I'm hotter than any natural phenomenon and only just now showed up on their sensors, so must be out roughly around an AU out - or else there is a VERY large heat source accelerating at them from a farther distance, which frankly doesn't bear thinking about.
(I'm thinking, based on the game mechanics ((a ship being lost somewhere in a 25,000 km square at a range of a couple light seconds)) that the sensors are only good for a couple of degrees of angle - in other words, at 1 AU, they can narrow me down to a volume of space roughly 6 million km across. Not sure that it means anything other than I shouldn't expect to get any laser communications.)
So, now they have "something" on passive EMS roughly an AU out, blue-shifted to a scary degree from their point of view, not responding to hails (what am I going to say that could possibly explain being precisely on target to impact the planet from that range - and accellerating), a bit over a half day from impact - and though they may not know my precise location and course, they can probably glean enough from a bit of observation to infer the potential for a rather unfortunate impending event.
Now their response is quite a bit simpler: have something fly out to meet me. Ideally two - one to get a firm fix on my course, the second farther back along my course to set up the attack solution based on data from the first. Doesn't have to be perfect, so long as it can bring me under fire a couple hours out. If they can throw enough firepower into me to shut down the drives, my calculations are thrown off and I miss. Okay, so they'll likely only have one shot at it. My effective agility is zero, and my effective computer rating might be zero as well, I think - we're asking my ship to detect and react effectively to missiles that have a closing velocity approaching 3000 kps at intercept, thanks to my own speed, so they're very likely to hit me as long as they can just put themselves in my path. Good time to bring out the nukes. Even if I've planned for that and had planned to coast in that final few hours so that crippling the drives wouldn't work, that bit of force applied at that range would still be enough to shove my glowing hulk out of its ideal path and into one that misses the target.
Large armored ships might be difficult to stop, but then large armored ships aren't real accessible to terrorists, and the governments who do have them aren't likely to spend them in suicide attacks that would outrage even their own people - not to mention finding a crew willing to take that ride. At least, not until well into the Imperial Collapse. For the typical ship a terrorist can get his hands on and fly alone or with minimal crew, your basic SDB or destroyer should carry enough firepower to do the trick.
Issue came up with respect to ships going for Oort cloud fuel sources, and whether there was any way to detect them. That got me to thinking about this situation. Let's assume for a moment that "interplanetary range" passive EMS systems are in fact interplanetary range - they can detect some hint of something out as far as 1 AU (~150 million kilometers). "Something" in this case is likely heat: I can maintain radio silence, keep my radar off, paint the hull black and do nothing but fly, but my scout's plant is putting out from 500 to 800 megawatts (depending on the rules system), my ship is using that power, and most of it (that part that isn't actually making me go faster) is eventually going to end up leaving my ship as heat - or else I cook myself well-done rather quickly.
Now, I originally postulated a start at 300 million miles - 2 AU, beyond the TL14 EMS system's game-stated range. Near as I can figure, from that distance, I look (very roughly) as "bright" in IR as an object re-radiating sunlight from about 300 thousand miles out (assuming a habitable world). As I get closer, I get brighter: 1 AU out, I'm 4 times brighter (I think - too many decades have passed between college physics and this moment) and I start being visible on the TL14 passive EMS. Or roughly thereabouts - perhaps only a battlewagon shows at that range and my scout needs to come in a bit more; basic idea still stands.
That is still way, way too far to pinpoint me or tell anything about me - but it's certainly enough to prompt a message to the oncoming man-made heat source: "Identify yourself, state your course, and why the heck are you flying so fast at us?" They can't be certain of my range except that I'm hotter than any natural phenomenon and only just now showed up on their sensors, so must be out roughly around an AU out - or else there is a VERY large heat source accelerating at them from a farther distance, which frankly doesn't bear thinking about.
(I'm thinking, based on the game mechanics ((a ship being lost somewhere in a 25,000 km square at a range of a couple light seconds)) that the sensors are only good for a couple of degrees of angle - in other words, at 1 AU, they can narrow me down to a volume of space roughly 6 million km across. Not sure that it means anything other than I shouldn't expect to get any laser communications.)
So, now they have "something" on passive EMS roughly an AU out, blue-shifted to a scary degree from their point of view, not responding to hails (what am I going to say that could possibly explain being precisely on target to impact the planet from that range - and accellerating), a bit over a half day from impact - and though they may not know my precise location and course, they can probably glean enough from a bit of observation to infer the potential for a rather unfortunate impending event.
Now their response is quite a bit simpler: have something fly out to meet me. Ideally two - one to get a firm fix on my course, the second farther back along my course to set up the attack solution based on data from the first. Doesn't have to be perfect, so long as it can bring me under fire a couple hours out. If they can throw enough firepower into me to shut down the drives, my calculations are thrown off and I miss. Okay, so they'll likely only have one shot at it. My effective agility is zero, and my effective computer rating might be zero as well, I think - we're asking my ship to detect and react effectively to missiles that have a closing velocity approaching 3000 kps at intercept, thanks to my own speed, so they're very likely to hit me as long as they can just put themselves in my path. Good time to bring out the nukes. Even if I've planned for that and had planned to coast in that final few hours so that crippling the drives wouldn't work, that bit of force applied at that range would still be enough to shove my glowing hulk out of its ideal path and into one that misses the target.
Large armored ships might be difficult to stop, but then large armored ships aren't real accessible to terrorists, and the governments who do have them aren't likely to spend them in suicide attacks that would outrage even their own people - not to mention finding a crew willing to take that ride. At least, not until well into the Imperial Collapse. For the typical ship a terrorist can get his hands on and fly alone or with minimal crew, your basic SDB or destroyer should carry enough firepower to do the trick.
Well, I always saw it as this; in the days of gravitics, I could imagine a grav based sensor that is sensitive to puckers in space out to a certain range. That's your passive, and I'll bet it would be pretty darn accurate as well.
If you're using RADAR or LADAR or some other pinging technology, then, yeah, find a needle in a haystack would be easier than trying to scan 4-million cubic kilometers of space.
But, I'm a bit sleepy now.
Carry on
If you're using RADAR or LADAR or some other pinging technology, then, yeah, find a needle in a haystack would be easier than trying to scan 4-million cubic kilometers of space.
But, I'm a bit sleepy now.
Carry on
Isnt' a densitometer a type of grav-based sensor?
Don't forget, your reflective signature goes from 1/4*1/9 1x1/4 ... or 1/36 to 1/4, a multiplier of 9x... if the target world is orbiting at 1 AU, that is, and you're coming in almost opposed to the sun.
At the same time, your thermal emission signature climbs by a factor of 4.
At the same time, your thermal emission signature climbs by a factor of 4.
Well, I always saw it as this; in the days of gravitics, I could imagine a grav based sensor that is sensitive to puckers in space out to a certain range. That's your passive, and I'll bet it would be pretty darn accurate as well.
If you're using RADAR or LADAR or some other pinging technology, then, yeah, find a needle in a haystack would be easier than trying to scan 4-million cubic kilometers of space.
But, I'm a bit sleepy now.
Carry on
The canonical densitometers have ranges measure in single digit thousands of KM...
That's a problem. IF that's the case, then a speeding ship attack can indeed succeed.
Oh well.
Hopefully Wil's numbers have shown you all that - again - there is no all around satisfactory answer to the Traveller setting's near-c rock question.
As GMs, you simply need to pick an answer which will work for you and your group. For some of you one of the suggestions made here may be the answer you need. For most of you, however, the answer it to ignore the question entirely.
Threads like this one are only useful up to a certain point and, after that point is reached, threads like this a basically barren.
As GMs, you simply need to pick an answer which will work for you and your group. For some of you one of the suggestions made here may be the answer you need. For most of you, however, the answer it to ignore the question entirely.
Threads like this one are only useful up to a certain point and, after that point is reached, threads like this a basically barren.
Similar threads
