Stealth in space is possible... but it will not resemble our conventional understanding of it.
We will now consider all elements discussed in previous parts of this series to paint a general picture of how stealth would be applied in a plausible setting.
First of all, we must understand that stealth is not an absolute. That means that 'stealth' is actually a smooth transition between low and certain detection.
This leads to sorting a detected spacecraft into one of four categories:
We will now consider all elements discussed in previous parts of this series to paint a general picture of how stealth would be applied in a plausible setting.
First of all, we must understand that stealth is not an absolute. That means that 'stealth' is actually a smooth transition between low and certain detection.
This leads to sorting a detected spacecraft into one of four categories:
- Soft Detection
- Hard Detection
- Identification
- Target Lock
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| The F117 Nighthawk, designed for radar and infrared stealth. |
Soft Detect
In space, the spacecraft is fighting for its place among the meaningless static and noise generated and picked up by normal sensor operation. An insulated hull or cold-plate design does this by trying to match the background temperature of 3K as closely as possible. Directional radiators try to reduce their irradiance until they fall under the detection threshold of a sensor. Spacecraft on a departure burn try to hide in the brightness of a planetary background.
A soft detect happens when a spacecraft emits enough energy in the direction of a sensor that the signal generated rises above the noise floor. This sort of detection is generally the job of wide-angle scanners that sweep the entire sky, searching for above-average levels of photons.
Looking at a planet and measuring a spike in brightness, or watching empty space and detecting a handful of high-energy photons, will reveal that something is emitting energy. However, the same characteristics that allow a soft detect by a sensor prevent it from establishing a precise location or velocity of the emitter. They can only say that 'something in this direction is hotter than empty space'.
Cross-referencing the data from several sensor platforms can narrow down the location of the stealthed spacecraft, but it will still encompass billions of cubic kilometers.
Hard Detect
Once the wide-angle sensors have piked up a statistically significant signal, the defenders' next step is to try to obtain a hard detect.
A hard detect is a precise and certain localization of the stealthed spacecraft. This is achieved with narrow-angle sensors that focus on a small slice of the sky. Once they narrow down the source of the energy emissions to a small enough area, the amount of data obtained on the spacecraft rises quickly. You could reasonably say that the spacecraft is not 'stealthed' anymore.
By watching a time-lapse of the spacecraft's location, the velocity and heading can be obtained. Even more sensitive sensors can be set to track the spacecraft instead of scanning huge areas of the sky, leading to a 'hard detect'.
However, transitioning from soft to hard detection is not a simple feat. The wide-angle sensors and the soft detect only provide a cloud of likely positions of the stealthed spacecraft. Over time, the cloud becomes smaller and denser. A narrow-angle sensor would still have to be run over millions of cubic kilometers, if not billions, of potential positions before the emissions are caught in its field of view. This process can be lengthy, and months can be spent trying to chase down an accelerating spacecraft.
Our reference 1GW spacecraft with its cold 208K radiators and 'stealth' 151kW propulsion could change its position by up to 6.5 million kilometers in a single day. This is a volume of 1.15 million million billion cubic kilometers to hide in, even after a soft detect has been achieved.
In space, the spacecraft is fighting for its place among the meaningless static and noise generated and picked up by normal sensor operation. An insulated hull or cold-plate design does this by trying to match the background temperature of 3K as closely as possible. Directional radiators try to reduce their irradiance until they fall under the detection threshold of a sensor. Spacecraft on a departure burn try to hide in the brightness of a planetary background.
A soft detect happens when a spacecraft emits enough energy in the direction of a sensor that the signal generated rises above the noise floor. This sort of detection is generally the job of wide-angle scanners that sweep the entire sky, searching for above-average levels of photons.
Looking at a planet and measuring a spike in brightness, or watching empty space and detecting a handful of high-energy photons, will reveal that something is emitting energy. However, the same characteristics that allow a soft detect by a sensor prevent it from establishing a precise location or velocity of the emitter. They can only say that 'something in this direction is hotter than empty space'.
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| How the sensor data would likely look from one direction. Several directions give a 3D image. |
Hard Detect
Once the wide-angle sensors have piked up a statistically significant signal, the defenders' next step is to try to obtain a hard detect.
A hard detect is a precise and certain localization of the stealthed spacecraft. This is achieved with narrow-angle sensors that focus on a small slice of the sky. Once they narrow down the source of the energy emissions to a small enough area, the amount of data obtained on the spacecraft rises quickly. You could reasonably say that the spacecraft is not 'stealthed' anymore.
By watching a time-lapse of the spacecraft's location, the velocity and heading can be obtained. Even more sensitive sensors can be set to track the spacecraft instead of scanning huge areas of the sky, leading to a 'hard detect'.
However, transitioning from soft to hard detection is not a simple feat. The wide-angle sensors and the soft detect only provide a cloud of likely positions of the stealthed spacecraft. Over time, the cloud becomes smaller and denser. A narrow-angle sensor would still have to be run over millions of cubic kilometers, if not billions, of potential positions before the emissions are caught in its field of view. This process can be lengthy, and months can be spent trying to chase down an accelerating spacecraft.
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| A 10-degree vs 3-degree field of view comparison. |
Identification
After a hard detection has been achieved, and your spacecraft is being tracked with great accuracy, there are still ways to fool the sensors.
One method is to hide your spaceship inside a voluminous shroud. Once visual surveillance becomes available, you will be hard-pressed to hide the exact size of your radiators, the shape of your propulsion bell and the width of your primary laser lens... Hiding all this in a metamaterial cloak that shrouds or obscures the exact features of your spaceship probably won't hide your purpose (an attack fleet would probably be travelling along deltaV-expensive or otherwise unusual trajectories), but it will reduce the accuracy of your opponent's estimate on the composition and strength of your forces.
The downside is that if this technique is permanently deployed, it will interfere with your stealth (catches incoming sunlight and outgoing waste heat), and if deployable, requires you to know when a passive sensor has detected you... which is impossible.
Another option is to bundle several spaceships together. This way, your opponent's mass estimates cannot be relied on. Yet another is to place your radiators on extremely long booms, so that they do not correspond to the position of your spaceship. If they move or rotate, it will further confuse opponents into over or under-estimating your forces.
Trying to hide as a civilian vessel is a fantasy often perpetuated in science fiction. First of all, it is impossible to convince a space military force that a spaceship heading along an unusual trajectory, with an insulated hull and 'cold' radiators is anything but hostile. Secondly, civilian spaceships travelling at several kilometers per second are weapons of mass destruction in the wrong hand, so all will need to be equipped with transponders that continuously report on their positions from launch to destination. Your spaceship would have to build up an entire paperwork trail to be plausibly found at that location in space, and that fall into spy work outside the scope of this blog.
In any case, you would have to follow a trajectory that would take you straight through the most heavily defended volumes of space. Thirdly, a military spaceship will not be build like a civilian craft. For example, civilian craft might take the performance hit of using water as propellant, but military craft would require the higher performance of liquid hydrogen to catch up with targets. Their larger, hotter reactors and more powerful propulsion systems would create thermal signatures and exhaust trails that are quite different from those of civilian craft. The radiators would be quite different too. Trying to fit military systems inside a civilian craft will leave you with a spaceship that is hard-pressed to pass as a civilian craft, and would get torn to bits when facing a dedicated military opponent.
In practice, identification will be performed using active scanners. Once your position is established, the power output of a RADAR or LIDAR can be focused on your position for good return signals. This creates a requirement for a set of countermeasures quite different than those for thermal imaging.
RADAR countermeasures include radar-absorbent surfaces and cool-looking angular shapes. LIDAR defenses include meta-materials that can modify the light bounced off.
These techniques can help fool identification, but immediately flag your spaceship as a hostile target.
Target lock
So, your spaceship has been caught in a hard detect, has been identified and you are unlikely to escape the enemy's sensors for the foreseeable feature. Is that the end of your mission?
Hardly.
For the enemy to do anything, they must establish a much tighter feedback loop. A hard detect can be achieved with as little as two positive pings on a radar. Getting weapons systems to fire at you requires a way to report on your position, bearing, velocity and changes in those values with much less delay.
In some scenarios, this is trivial. Your spaceship might be quite visible on a radar, and your propulsion might be easily picked up after a narrow-angle sensor is told to follow you and report on changes in your vector regularly. In other scenarios, it might be very difficult. With countermeasures for active scanners and an undetectable propulsion system, a laser beam might not be able to follow you because of lightspeed lag, and you might accelerate out of the way of incoming missiles.
Now let's discuss further aspects of stealth.
After a hard detection has been achieved, and your spacecraft is being tracked with great accuracy, there are still ways to fool the sensors.
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| A Q-ship: The USS Anacapa hid guns behind hinged flaps |
The downside is that if this technique is permanently deployed, it will interfere with your stealth (catches incoming sunlight and outgoing waste heat), and if deployable, requires you to know when a passive sensor has detected you... which is impossible.
Another option is to bundle several spaceships together. This way, your opponent's mass estimates cannot be relied on. Yet another is to place your radiators on extremely long booms, so that they do not correspond to the position of your spaceship. If they move or rotate, it will further confuse opponents into over or under-estimating your forces.
Trying to hide as a civilian vessel is a fantasy often perpetuated in science fiction. First of all, it is impossible to convince a space military force that a spaceship heading along an unusual trajectory, with an insulated hull and 'cold' radiators is anything but hostile. Secondly, civilian spaceships travelling at several kilometers per second are weapons of mass destruction in the wrong hand, so all will need to be equipped with transponders that continuously report on their positions from launch to destination. Your spaceship would have to build up an entire paperwork trail to be plausibly found at that location in space, and that fall into spy work outside the scope of this blog.
In any case, you would have to follow a trajectory that would take you straight through the most heavily defended volumes of space. Thirdly, a military spaceship will not be build like a civilian craft. For example, civilian craft might take the performance hit of using water as propellant, but military craft would require the higher performance of liquid hydrogen to catch up with targets. Their larger, hotter reactors and more powerful propulsion systems would create thermal signatures and exhaust trails that are quite different from those of civilian craft. The radiators would be quite different too. Trying to fit military systems inside a civilian craft will leave you with a spaceship that is hard-pressed to pass as a civilian craft, and would get torn to bits when facing a dedicated military opponent.
In practice, identification will be performed using active scanners. Once your position is established, the power output of a RADAR or LIDAR can be focused on your position for good return signals. This creates a requirement for a set of countermeasures quite different than those for thermal imaging.
RADAR countermeasures include radar-absorbent surfaces and cool-looking angular shapes. LIDAR defenses include meta-materials that can modify the light bounced off.
These techniques can help fool identification, but immediately flag your spaceship as a hostile target.
Target lock
So, your spaceship has been caught in a hard detect, has been identified and you are unlikely to escape the enemy's sensors for the foreseeable feature. Is that the end of your mission?
Hardly.
For the enemy to do anything, they must establish a much tighter feedback loop. A hard detect can be achieved with as little as two positive pings on a radar. Getting weapons systems to fire at you requires a way to report on your position, bearing, velocity and changes in those values with much less delay.
In some scenarios, this is trivial. Your spaceship might be quite visible on a radar, and your propulsion might be easily picked up after a narrow-angle sensor is told to follow you and report on changes in your vector regularly. In other scenarios, it might be very difficult. With countermeasures for active scanners and an undetectable propulsion system, a laser beam might not be able to follow you because of lightspeed lag, and you might accelerate out of the way of incoming missiles.
Now let's discuss further aspects of stealth.
Strategic movement
Why bother with stealth at all?
Stealth on its own does not achieve anything. Your spaceships WILL be eventually detected, and the enemy will not jump in surprise. The thermal signatures increase in number, become statistically significant, are narrowed down then identified as spaceships, with sensors attached to track each of them days, weeks or months before the come close. So what's the point?
Stealth allows for strategic movement. If spaceships are launched on an 8 month trip, and are only detected in the last week, then you can launch multiple fleets from several directions, and have them insert into various orbits for a multi-pronged or staged attack, before any are detected.
Similarly, stealthed spaceships can choose to engage or break off from an upcoming encounter.
Stealth allows for first-attack advantage. In its purest form, a fleet can fire upon an opposing fleet twice its number, and immediately destroy half of it. This means that even if your are immediately spotted, identified and targeted after firing, you'll be able to wield a decisive advantage going into any engagement.
Stealth also ties into the capabilities off various weapons systems. If lasers are effective from a distance of 100000km, and you are spotted incoming from 80000km, then you can strike first. You can launch missiles from closer ranges, too. This means your missiles will not need as much deltaV to reach the target: as a result, they can be smaller, and you pack more of them into the same ship, which is important when facing laser defenses.
The home advantage
While this might not apply to all settings, the 'home advantage' is an important aspect of space war, and stealth plays a major role.
The 'home advantage' is an extension of how battles are won: an objective is set, and two opponents fight to complete it or stop the other from completing it.
In interplanetary space war, the attacking fleet's objective is to destroy all space defenses so it can move onto pressuring ground objectives. To do that, it approaches along a Hohmann trajectory, during which it drifts through space after a departure burn.
The second step of a Hohmann trajectory is an insertion burn. The attacking spaceships perform a retro-burn that puts them in orbit around the destination planet.
The spaceships defending the planet can win by destroying the incoming spacecraft. However, they can also perform their own departure burn, and attempt to meet the attacking fleet in deep space. If they can stop the attacking fleet from performing a retro-burn, they will force them to be flung back out into interplanetary space. This is a second win condition, and constitutes the home advantage.
In practice, the defenders don't really have to send out their own spaceships. They can shoot projectiles, launch missiles or send off drones into the path of the attacking fleet, and home to defeat them weeks or months before they approach the planet. If the attacking fleet is then too damaged to face the remaining defenders, or expends too much propellant dodging the projectiles and so on, then it will be forced to abort the mission and perform a fly-by.
Where does stealth come into play?
If the attacking fleet completely forgoes stealth, then the defenders will be able to fire projectiles and missiles at it for months. Sending a missile into the path of an incoming spacecraft is much cheaper and faster than sending another spaceship, so defenders will have a great advantage in terms of resources and efficiency.
With stealth, the attacking fleet is detected closer to the planet. This reduces the amount of weapons fire that it has to dodge, and considering the fact that a soft detect only gives a fuzzy location with lots of room to hide in, the defenders would have to shoot huge volumes of fire to hope to catch and destroy an attacking spaceship from far away.
With stealth and stealthy propulsion, the attacking fleet can come from a variety of trajectories that are close to the Hohmann trajectory, but can deviate by millions of kilometers from the most efficient route. This vastly reduces the 'home advantage' of defenders.
Worldbuilding
How stealth affects your setting depends on the technology level of the setting, its level of development and ultimately, where you want the balance to lie.
Remember, this is ToughSF, where we give options, not restrictions.
If you want to recreate submarine warfare in space, you can. Restrict the sensitivity of sensors, increase the effectiveness of stealth techniques and the mass devoted to them, and you'll have spaceships traversing the solar system unnoticed until they attack. You have to realize the consequences, though: If 'space submarines' are capable of invisibly launching missiles and streams of kinetic projectiles without being detected, then your opponents will try to counter it with more sensor platforms, and in return, you'll build sensor hunters to keep your 'space submarines' undetected and safe.
Similarly, you can try to find a sweet spot that gives stealthy spaceships some level of effectiveness, but make the requirements great enough that fleets are regularly composed of both stealthy and unstealthy spaceships. For example, you might build a setting where the solar system has been explored and settled for a long time, and tension between the warring parties have been building up gradually. Sensor platforms will litter the solar system, above, below and around your planet. In such a situation, the only way to escape detection is with a 'hydrogen steamer' - a spaceship with large volumes of liquid hydrogen that it boils off to reduce its emissions to zero. However, such a spaceship could not compete with armored, high-powered warships in direct combat. As a result, you'll build some of both.
Sensors are what really make or break stealth.
If you want spaceships to accelerate into faster trajectories than multi-month Hohmann missions, then you'll need directional stealth: cold plates, angled radiators and so on. For that to work, you'll need the enemy's sensors concentrated into one area of the sky - so maybe during peacetime, opposing factions will spend their military budget creating spaceships equipped with powerful sensors, LIDARS and small lasers. Their only job is to hunt down enemy sensor platforms and shoot them down at the start of the war, paving the way for the main fleet to attack undetected.
Replacement sensors take time to reach the far-away but advantageous watchpoints, and those who try to do it quickly will be detected, so as the war goes on, sensors will be concentrated near the enemy, where they can be replaced faster than they can be shot down.
Similarly, you've justified a 'destroyer' class, a 'cruiser' class and a 'submarine' class, allowing you to use all the naval tropes scifi is famous for.
Or instead, military spaceships could spend their entire time tailing each other. If one fleet breaks off and enters an attack trajectory, the tailing fleet will attack it well within detection range. To complicate things, you can have a fleet of stealthed ships tailing the visible fleet tailing your visible fleet, with the opponent's stealth fleet trying to hunt it down at the same time....
On the opposite end of the spectrum, you can apply stealth techniques to the sensor platforms and make the impracticably well hidden. In a setting where you'll always get detected, there is no need for stealth. Since it is cheaper to shoot down a spaceship than to build one, the defenders might simply build orbital defenses to counter fleets rather than using their own. The attackers would then trade in their fleets for massive, interplanetary lasers that require re-focusing mirror drones that are also much cheaper than spaceships, and easier to hide too....
In conclusion, you cannot ignore stealth in space as being possible. If will affect how your fleet is build up, how spaceships look like and even the grand military strategy pursued by opposing factions. At the very least, you must give strong arguments as to why it is not feasible and even then, consider the fact that like many modern military technologies (tank armor, air drones, aircraft carrier fleets...) it will enter into cycles of development and proliferation that have to be matched or countered.
Why bother with stealth at all?
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| Movement of the WWI Baltic fleet across the globe |
Stealth allows for strategic movement. If spaceships are launched on an 8 month trip, and are only detected in the last week, then you can launch multiple fleets from several directions, and have them insert into various orbits for a multi-pronged or staged attack, before any are detected.
Similarly, stealthed spaceships can choose to engage or break off from an upcoming encounter.
Stealth allows for first-attack advantage. In its purest form, a fleet can fire upon an opposing fleet twice its number, and immediately destroy half of it. This means that even if your are immediately spotted, identified and targeted after firing, you'll be able to wield a decisive advantage going into any engagement.
Stealth also ties into the capabilities off various weapons systems. If lasers are effective from a distance of 100000km, and you are spotted incoming from 80000km, then you can strike first. You can launch missiles from closer ranges, too. This means your missiles will not need as much deltaV to reach the target: as a result, they can be smaller, and you pack more of them into the same ship, which is important when facing laser defenses.
The home advantage
While this might not apply to all settings, the 'home advantage' is an important aspect of space war, and stealth plays a major role.
The 'home advantage' is an extension of how battles are won: an objective is set, and two opponents fight to complete it or stop the other from completing it.
In interplanetary space war, the attacking fleet's objective is to destroy all space defenses so it can move onto pressuring ground objectives. To do that, it approaches along a Hohmann trajectory, during which it drifts through space after a departure burn.
The second step of a Hohmann trajectory is an insertion burn. The attacking spaceships perform a retro-burn that puts them in orbit around the destination planet.
The spaceships defending the planet can win by destroying the incoming spacecraft. However, they can also perform their own departure burn, and attempt to meet the attacking fleet in deep space. If they can stop the attacking fleet from performing a retro-burn, they will force them to be flung back out into interplanetary space. This is a second win condition, and constitutes the home advantage.
In practice, the defenders don't really have to send out their own spaceships. They can shoot projectiles, launch missiles or send off drones into the path of the attacking fleet, and home to defeat them weeks or months before they approach the planet. If the attacking fleet is then too damaged to face the remaining defenders, or expends too much propellant dodging the projectiles and so on, then it will be forced to abort the mission and perform a fly-by.
 |
| Not-to-scale diagram of home advantage. Defenders can shoot along the transfer trajectory. |
If the attacking fleet completely forgoes stealth, then the defenders will be able to fire projectiles and missiles at it for months. Sending a missile into the path of an incoming spacecraft is much cheaper and faster than sending another spaceship, so defenders will have a great advantage in terms of resources and efficiency.
With stealth, the attacking fleet is detected closer to the planet. This reduces the amount of weapons fire that it has to dodge, and considering the fact that a soft detect only gives a fuzzy location with lots of room to hide in, the defenders would have to shoot huge volumes of fire to hope to catch and destroy an attacking spaceship from far away.
With stealth and stealthy propulsion, the attacking fleet can come from a variety of trajectories that are close to the Hohmann trajectory, but can deviate by millions of kilometers from the most efficient route. This vastly reduces the 'home advantage' of defenders.
Worldbuilding
How stealth affects your setting depends on the technology level of the setting, its level of development and ultimately, where you want the balance to lie.
Remember, this is ToughSF, where we give options, not restrictions.
 |
| Submarine launching ICBMs |
Similarly, you can try to find a sweet spot that gives stealthy spaceships some level of effectiveness, but make the requirements great enough that fleets are regularly composed of both stealthy and unstealthy spaceships. For example, you might build a setting where the solar system has been explored and settled for a long time, and tension between the warring parties have been building up gradually. Sensor platforms will litter the solar system, above, below and around your planet. In such a situation, the only way to escape detection is with a 'hydrogen steamer' - a spaceship with large volumes of liquid hydrogen that it boils off to reduce its emissions to zero. However, such a spaceship could not compete with armored, high-powered warships in direct combat. As a result, you'll build some of both.
Sensors are what really make or break stealth.
If you want spaceships to accelerate into faster trajectories than multi-month Hohmann missions, then you'll need directional stealth: cold plates, angled radiators and so on. For that to work, you'll need the enemy's sensors concentrated into one area of the sky - so maybe during peacetime, opposing factions will spend their military budget creating spaceships equipped with powerful sensors, LIDARS and small lasers. Their only job is to hunt down enemy sensor platforms and shoot them down at the start of the war, paving the way for the main fleet to attack undetected.
Replacement sensors take time to reach the far-away but advantageous watchpoints, and those who try to do it quickly will be detected, so as the war goes on, sensors will be concentrated near the enemy, where they can be replaced faster than they can be shot down.
Similarly, you've justified a 'destroyer' class, a 'cruiser' class and a 'submarine' class, allowing you to use all the naval tropes scifi is famous for.
Or instead, military spaceships could spend their entire time tailing each other. If one fleet breaks off and enters an attack trajectory, the tailing fleet will attack it well within detection range. To complicate things, you can have a fleet of stealthed ships tailing the visible fleet tailing your visible fleet, with the opponent's stealth fleet trying to hunt it down at the same time....
On the opposite end of the spectrum, you can apply stealth techniques to the sensor platforms and make the impracticably well hidden. In a setting where you'll always get detected, there is no need for stealth. Since it is cheaper to shoot down a spaceship than to build one, the defenders might simply build orbital defenses to counter fleets rather than using their own. The attackers would then trade in their fleets for massive, interplanetary lasers that require re-focusing mirror drones that are also much cheaper than spaceships, and easier to hide too....
In conclusion, you cannot ignore stealth in space as being possible. If will affect how your fleet is build up, how spaceships look like and even the grand military strategy pursued by opposing factions. At the very least, you must give strong arguments as to why it is not feasible and even then, consider the fact that like many modern military technologies (tank armor, air drones, aircraft carrier fleets...) it will enter into cycles of development and proliferation that have to be matched or countered.
The space warfare in Aliens universe is stealthy kinda like this. I mean, like "almost submarines".
ReplyDeleteIs this the end of Stealth is possible series? That was one of best explainations of how would space stealth would work, thanks for your work!
Yes, the last part. You are welcome.
DeleteThis series only considered 'hard sf' methods for achieving stealth. There are many fictional ways to achieve pseudostealth.
Yeah, there are plenty of them, hyperspace, cloaking devices, directing heat into other dimension... In the Aliens universe "Sulaco" warship has got cooling towers like power plants in real world... But they work only in atmosphere :p
DeleteWhat are your plans for next posts?
Probably piracy in space and laser webs.
DeleteIf you can stealth missiles to even a small degree then you have a way to square the circle that concerns how to keep back salvoes for future engagements. Less missiles can be used to slip through defences, instead of swamping them with your entire reserve.
ReplyDeleteYou might even be able to toss them into the path of an unsuspecting constellation, requiring less propellant and thus more of the small-but-many warheads you mention here.
Done right, stealth in space is not just a strategic utility, but an excellent logistical tool as well.
Good point. I hadn't thought of using stealth beyond applications in combat.
DeleteI did though mention stealthed projectiles as a requirement for the 'slow projectile' tactics discussed in the Electric Cannon two-part post.
A short note on detection: there is a physical limit to the amount of resolution possible, even with the highest tech, narrowest field sensors. Spacial resolution is dependent upon angular resolution. This latter is determined by the base-length of an array (or any single sensor) and the wavelength(s) of the energy emissions detected. A detector ar array with a baseline of 300m, such as the Arecibo observatory, provides a resolution for visible light wavelengths of 0.001 arc seconds. At 1 AU, this would provide a spatial resolution of 300m length (90 000 m^2 area) per pixel. In order to reduce this to a resolution on the order of 1 m^2 at 1 AU, you would need an array baseline of 1 000 000 km (I forget if I was still basing this on visible spectrum, or if I was including IR spectrum when I researched this figure).
ReplyDeleteHow do virtual telescopes (interferometers) affect this requirement.
DeleteIn discussions with astronomers on Google+, a prevailing idea is that after initial detection using CCDs, the area the spaceship is in will always be narrowed down eventually to a Hard detect level of precision.
The baseline requirements are a physical absolute. When I refer to an "array", however, I am refering to the interferometric telescopes that you meantion. Interferometric telescopes allow you to save mass (and money) by creating a virtual aperture, or baseline. If you have two puny 5mm telescopes, one located on the Earth and the other on the moon, you will have the same reolution as a single giant telescope with a 364 000 km aperture. You won't be able to detect much of anything, but anything you DO detect ill have quite good resolution (rough guestimate: 10m^2 at 1 AU, visible spectrum). The actual sensitivity of the array, however, is pretty much exactly as good as the total apperture area of the array's constituents. Your two 5mm telescopes will give you the sensitivity of about a single 7mm telescope.
DeleteInitial detection will not always lead to a hard detect. If you have an initial detection relying on a scanning array (say the 4hr scan time suggested by K. Burnside, cited by Atomic Rockets), and/or if the initial detection relies on a time exposure, it might be possible to detect a trace on one scan, but then thee might be zero trace on the next several scans. Intermittant burn times, especially randomly timed and/or short burst duration, can take advantage of such time lapse or scanned detections. If you DO manage to repeat a detection, it can be several pixels away from the first. If you only have one vessel, thise might be enough for a preliminary track (if you are lucky). But if you have several vessls conducting manoeuvers this way, it maight be impossible to determine which repeats correspond with which vessels (especially if they change course), or even if you are tracking a vessel rather than a few large asteroids randomly reflecting sunlight.
If, however, you have a realtime detector that is imaging the same area of space for a significant amount of time, then, yes, even though you don't have good resolution, you should be able to get a hard lock. The problem here is that if you lose trace (intermittent burns), there is no guarantee that the vessel will not make an undetectable low level burn that takes it on a completely different course.
In short, for most objects, the astronomers would be quite correct. It does not take excellent resolution to achieve a hard detect (you might find, however, that the big asteroid you are tracking is actually 10 big asteroids). The astronomers would be incorrect, however, in some dealings with objects that are making intentional efforts NOT to be detected. Notably, determining the mass and velocity of a vessel by analysing the characteristics of the exhaust plume in order to determine the thrust would definitely NOT be possible without at least TWO arrays, each with at least a 1 000 000 km baseline... and even then might not be possible if it can make an undetectable burn.
Thanks! I'm really loving the information you're contributing. Would you mind if I collected and re-shared your writing on Google+?
DeleteI did some searching on the differences between sensitivity and resolution and what they mean for telescopes, and if I understand it correctly, resolution is being able to locate a signal within a smaller and smaller portion of the sky, and sensitivity is being able to detect a smaller and smaller change in the signal.
Ian Mallet commented on the performance of binary detectors, that are basically photon traps that are triggered when a threshold is reached. Modern CCD sensors are extremely sensitive (10^-9Watts or better) under optimal conditions. Hence, the assertion that every spaceship, whether following a soft detect, a random search or simply probabilistic scans, will trip a few pixels on a binary detector somewhere, leading to a hazy cloud of detections along its trajectory.
I agree with the remainder of your post.
Sharing would be fine with me. Full disclosure: I am not an expert, just someone who does a lot of reading and research. I am particularly interested in physics and applied sciences research papers; as well as military tactics, strategy, planning, construction, and design.
DeleteYou essentially have the right idea regarding resolution and sensitivity.
Emission flux is inversely squared with the distance. If the distance increases by a factor of 10^3, the flux willbe decreased to 10^-6. If you have an emitter with an effective flux of 1kW at 1m, at 1000 km your CCD with a 10^-9W sensitivity and a 1m aperture would no longer be able to detect the signal. At 1 000 000 km the same CCD will require a combined actual detector area of 1 000 000 m^2 to receive a signal from a 1 kW emitter. It would need a 1000 m^2 aperture to receive a signal from a 1GW emitter at the same distance. On the other hand, most CCDs are actually much more sensative than this.
Another issue is that it is not enough to detect the signal. It is even more a matter of receiving enough of a signal for it to be significantly greater than background noise. Such background noise includes the 3°K background radiation; stellar, galactic, and other astronomical radiation; random solar illumination (reflection) off of small asteroidal masses; intrference from anything in between the detector and the emitter, such as any atmospheric particles, solar wind, cometary debris, interplanetary dust, etc; 'legitimate' space traffic; interplanetary radio trafic; etc.
Your analysis of military vs civilian vessels is not entirely valid. Stealth is founded as much (if not more) on behaviour as it is on tech. Yes, a military vessel will probably have higher performance than civilian vessels as a rule (this will NOT be a universal, since some civilian organisations will pay a premium for faster delivery), but military vessels will seldom be running at their highest performance levels. In stealth operations, military vessels will be matching the performance characteristics of civilian vessels as closely as possible. In many cases, the a stealth vessel or craft will actually UNDERperform civilian vessels, even at their maximum performnce (this is the case of the F-117, for example, which is incapable of anything near mach 1).
ReplyDeleteFurthermore, strategic stealth missions might actually incorporate civilian vessels and missions. For example, a civilian transport might include a weapons shipment. The launch of a civilian communications array might have a software patch that monitors and collects all communications for analysis by espionaage networks. A science station might be equipped with a weapons array. Probes built for tracking asteroids and analysing them for mining operations could be fitted with hardware and/or software patches to collect stragtegic data. Etc.
'Behavious' reliant stealth falls under spywork and statecraft, which was intentionally left out of the discussion. Your other points are valid.
DeleteWell, my point was that all stealth is behaviour reliant, but I can see where some of the specific examples might be considered more as "spywork". On the other hand, stealth is an important tool in spywork, and has been used more by spies than "legitimate" military. The important feature defining stealth is less about not being detected than it is about not being noticed.
DeleteAgreed. Although stealth is most *effective* when used as an enabler for a first strike capability.
DeleteOne of the biggest oversight on the part of Atomic Rockets is that they fail to consider the sheer bulk of space traffic. It is not enough to detect presence. You must also sort through the data to detect unusual activity on the part of that pressence. This means that the activity of ALL detection must be analysed over a frame of time to sort out usual from unusual, and then unusual from potentially agressive.
ReplyDeleteThis is even more difficult if you only have intermittent contacts. Such intermittent contacts would be unavoidable in high traffic zones.
Finally, there will not only be legitimate civilian activity, but legitimate military activity as well. Are those battleships attacking? Or are they merely conducting harmless training exercises? Is that fast moving craft attacking? Or is it an emergency response unit?
I believe that any mature spacefaring civilization will enforce a 'full-transparency' tactic of handling traffic. Every spaceship has to have an active transponder that reports its position and vectors, and malfunctioning/out of place/non-responsive spacecraft are by default flagged as dangerous at best, hostile at worst.
DeleteThis is because, as mentioned, any civilian spacecraft can become kiloton yield weapon when impacting an airless moon or asteroid habitat. An analogy would be every single aircarft today carrying a nuclear reactor by default. I also believe that computational capacity will outstrip space traffic for many decades to comes.
I also has to consider the fact that the settings being developed by autnors and game designers are vast and varied. Some are classic invasion stories set in the very near future, so the limitations of physical telescopes are crucial to identifying a far away target. Others have a solar system bustling with activity, and sensors literally dotted around planets and along interplanetary routes, above and along the planetary plane. I have to keep by conclusions non-restrictive, so more 'you could's than 'you cannots's.
Such a full transparency policy might actually be rather problematic. First, all the transponder signals add to the noise, making it even more difficult to detect the traffic flying without transponders. Second, enforcement could tie up all of your interception forces, reducing your ability to respond to real hazards. Third, transponder signals are easily manipulated (that is, it is easy to provide a false transponder signal that could hide a hostile mission); even if it makes localising a target easier in 3D, it can make it more difficult to determine the real intent of that target. Fourth, it is not so easy to justify at interplanetary distances, because any threat would be at least several days away, and probably several months away. I could really only image such signals being justified once you enter certain "flight zones"... say 1 000 000 km from a planet.
DeleteIn any case, any such measure in effect would be null and void once hostilities start; and if war is declared, not only will this policy not be enforced, such transponders would actually be forbidden because it could illuminate nearby military traffic (this is the reason that black outs were imposed in uch of Europe during WWII).
There is always a level of flexibility. Many of the arguments will be determined by the environment the author sets out for their sci fi universe. You have valid points there. I was basing an argument more for current trends and possibilities in our actual solar system.
The entire "there ain't no stealth in space" mantra flies out the window if a civilisation has not developed radio imagery. Some stealth might be possible because the current military tech tends to send out one kind of signature, so all detector tech looks for that signature and ignores everything else as civilian (this is the case with "low observable" RADAR... most military frequencies use a specific band for RADAR, and so all RADAR detectors look for this band; thus some "low observable" RADARs are built to use frequencies outside of this band).
Awesome posts! they shine a new light on the whole stealth in space segment, some parts are in my Opinion rather controversial like the Atmosphere brake and alike but in the big picture its very well done. I have some questions:
ReplyDelete-Could one also use Nuclear warheads as warheads on a Stealth missiles, I know that the decay of the Fissile material creates quite some heat making it harder to hide. Same with Casaba Howitzers.
-Can one use a Asteroid as a kind of spaceship for stealth, presumably made of Ice as a Heatsink.
-Metamaterials: They are amazing, I don't know how one could possibly spot something covered in it when LIDAR is completly out of the game.
-What about mines? Covering them in metamaterial would make them nearly invisbile. Presumably Kirklin type.
-For Stealth missile, what about two-stages? First stage is a hot high Delta-v engine with high thrust giving a nice amount of Velocity and a second-stage covered is a Vantablack/Meta covered warhead having a cold gas thruster for guiding.
Thank you! I'm glad to find you reading the rest of the blog.
DeleteTechnically, stealth through aerobraking is already implemented in Manoeuvrable Re-Entry bodies for nuclear warheads. They can accelerate over 10G in the upper atmosphere, turning too fast and hard for ground stations to track them... but that's a special case.
-Stealth warheads work best with Casaba Howitzers. The range they get out of a small package means they can stay far away from their targets and increase their stealthiness. Radioactivity of a rather stable isotope such as U-238 should be undetectable at thousands of kilometers distance. Fusion versions are silent.
-Asteroids are generally rather spherical, so they receive a lot of sunlight. This makes them very hard to cool down to undetectable levels. It is very likely that all asteroids of useful size are mapped and tracked strictly before military operations are even considered. Because they are hard to move as well, they become the equivalent of trying to hide an island from Radar. Do-able, but what's the point? Everyone knows its still there.
-Metamaterials are the FUTURE. They still do have restrictions, however. Vantablack radiates just like everything else when heated. If you shine a bright laser on it, it will become very visible, and I doubt any stealth system meant to handle sunlight and stray radar bounces can hide itself from intense laser beams.
-Mines are only as useful as their orbit. Sitting in deep space, they have next to no chance of ever hitting anything.
-That's a good design for a stealth missile, yes. It works best for long range firing to give the cold stage more time to move out of the predicted path.
I read already quite a lot from your blogs, but that was some time ago before i knew that the whole Tough SF segment was only written by your hand. Want to comment your posts about Lasers Net/web and the problem series when i learned a bit more about Photonics. Could take a few days
DeleteOff-topic Can it be that you are an Particle beam weapon fan? The article on reddit in 2016 and your name. Matter beam, A beam made out of matter. A particle beam
Stealth Warheads: But don't you have to cool down the Pu-239 core on the warhead? You really don't want that your warhead get thermal expansion or worse. Other than that, Stealth Warhead could bring the small casaba back howitzer from the dead. Fired from point blank they would be quite devastating.
"Want to comment your posts about Lasers Net/web and the problem series when i learned a bit more about Photonics. Could take a few days"
DeleteBad idea! Ask from the source!
"Off-topic Can it be that you are an Particle beam weapon fan? The article on reddit in 2016 and your name. Matter beam, A beam made out of matter. A particle beam"
Yes, yes and yes. I've always found particle beams to be fascinating, both as propulsion, weapon and a tool for scifi settings.
Stealth warhead: It is assumed that the cold 'tip' is insulated from the hot booster stage. Also, you only really need to keep the skin cold. The plutonium interior can be kept a casual room temperature while the skin is flushed with liquid hydrogen.
Casaba Howitzers aren't really dead... the megaton version might mass about a ton, maybe 3 tons with the solid rocket motor and cold-flush skin. A liquid booster brings the missile mass to 10 tons. A 100GJ railgun pushes it to 4.5km/s, the booster adds another 5km/s, and the solid motor gives it another 3km/s of tracking capability.
For that mass investment, it gets the range of a laser a thousand times heavier and much more visible and vulnerable to counter-attack.
"could bring the SMALL casaba back howitzer from the dead." The one which destroys 273mm (I think) at 10km distance. I hope you didn't get the impression that I think that Casabas are bad, I love them.
DeleteYour numbers about the railgun gave me a deja-vu, the Energy is just a bit to high for my pessimistic view on hypothetical/theoretical weapon systems (rather want to see that your weapon is better than you though it was). 100GJ would require multiple 100MW reactors to charge for multiple seconds. And storing so much energy is very hard. Although there are Superconducting storage rings.
Yes, yes. That's how i imagined my Missile. First-stage some high energy used from 100-10x the Detection range. The second stage is just a Warhead in either Vantablack or Metamaterials (Depends on your time frame of the scenario) with four or more small thrusters that cross. They use their really small delta-v budget to re-correct their path. And to rotate.just Up-down left-right in in between. Making it as small as possible using a 5kt Warhead. Detonate it at maybe 5km distance and see your enemy get ripped apart by your Particle beam shotgun.
And Once again.... the penultimate part of the Casaba post describes that one can use magnets for better focus and an Electron beam to neutralize the Ionized Carbon and hydrogen atoms. Could this also be used as a Anti-shield tactic?
Also posted on some other blogs. Electric Cannons II and solution ..... long range, do you have to manually check your posts for comments thought?
I don't think it would a bad idea. I always want to have some "basic" knowledge (under basic i mean able to discuss with Luke about complex Laser physics, other than that It might worth looking at your posts i liked them all to this point. Is it more a physics/math post or a "How would it look like" post?).
I think they're just plain scary. Mishandled, from a worldbuilding point of view, they open the door to 'bigger is better' snipefests where 100 ton advanced Casaba Howitzers vaporize warships from 0.5 (futuristic) to 10+ (focused) million kilometers... the exact situation I try to avoid with lasers in the first place.
DeleteThe numbers/performance of weapon systems is really up to you. You might want a near future setting with 100MJ railguns and chemical missiles, or instead an advanced near-soft-scifi setting with nuclear-pumped plasma railguns and solar-system spanning x-ray laser beams.
Generating gigawatts of power isn't actually very hard. Storing it can be done with flywheels or SMES.
Focusing a casaba howitzer beam is a method of increasing range, but it does not add to the beam's momentum. Focusing it doesn't help it punch through magnetic shields. If the shields are really worrisome, then maybe heavier atoms, such as mercury or iron, can be used instead of plastics. They'd have much worse velocity (2-5 times lower) but the particles will be 4 to 25 times heavier.
The beam's momentum will be up to 5 times higher. Its charge-to-mass ratio, another important factor, would be massively lower, making it quite insensitive to magnetic fields.
I get the comment notifications in my email. I try to respond to each and every comment, and clean up some spam and deleted comments, but if there are too many, I might miss some.
I always try to cater to those who want the maths and those who just like hearing the concepts and worldbuilding, so you are likely to find both. If you still find something confusing, don't fear: ask me directly and I'll explain everything.
*sigh* Third time a charm. I don't talk about momentum. I talk about the Electron beam. Which is meant to neutralize the Plasma from the Casaba Howitzer as you described. The magnets are meant to be powered by the heat of the detonation, the magnets just use their magnetic fields to focus the positive charge plasma, then the plasma is hit by an electron beam which add electrons to the ions back again and neutralize and de-ionize them. A mass spectrometer in reverse, focusing a particle beam into a tight beam and let it pass a electron shower.
DeleteSMES? Superconductive magnet storage? I thought they have a low energy density. Requiring hundred of tons for a hundred giga joule pulse.
And I remembered now why I decided rail/coil missiles wouldn't be that great. If you have High-tech drives with 50km/s Delta-v for your missiles 5km/s extra delta-v isn't really worth having hundred tons of capacitor on a ship. Every gram counts.
Didn't really read that much stories where Casaba Howitzers where in, but if both sides have them wouldn't it create a MAD scenario? Did that ever happened? You always have to keep in mind that the enemy might revenge their capital ship. Just what happened in WW2 with the HMS Hood and the Bismarck.
Also they might be too good. If their is a cheaper alternative to kill an enemy you would choose it over a Lance.
Btw. Do you have a short nickname for Casaba Howitzers?
Also do you know where i could find some advanced physics? Nuclear, Photonic, Quantum?
Ah, and sorry for spamming your email. I think at this point nearly a third of the comments on Nuclear Lance are from me :)
I'm sorry!
DeleteJust to make sure this time, you are asking if the electron beam, meant to neutralize the casaba howitzer beam, can be used as an anti-shield device?
If that is the question, then no. The electron beam in this case is meant to correct tiny excesses in positive charge that come from hydrogen ions (protons) being accelerated to high velocities than the heavy carbon and oxygen or others. It is very weak and adds very little electrons in total.
SMES: Currently, they can reach 40kJ/kg. The main ways to increase this value is by reducing the cooling requirements and to increase the strength of the physical bonds that keep the magnetic loop from splitting apart. Using carbon-based materials, such as carbon nanotubes, the mechanical limit on capacitors is 40-50MJ/kg. However, if the two plates of a capacitor get too close or are damaged, they literally explode. Flywheels might be safer.
High deltaV missiles usually means the same propulsion technology can be used in the targets they chase. Due to scaling savings, a larger rocket can generally accelerate better than a smaller rocket with the same deltaV, so the initial boost might be the only way for a small missile to catch up with a large target... but that's a difference conversation.
Casaba Howitzers are very rare in SciFi. They were actually a classified piece of technology will still do not have much details on. I imagine a setting where Casaba Howitzers are common has a consequence of First Look - First Strike- First Kill scenarios: any detected spaceship is zapped by a plasma beam, so everyone hides like rats in a hole and is very scared to do anything.
I don't have a nickname :/ Some commenters just write CHs.
Advanced physics aren't 'found', silly! :D They're explored by trawling through wikipedia, watching Kurzgesagt and Isaac Arthur and reading AskScience threads on Reddit!
Don't worry, it's not spam: you ask interesting questions, and I enjoy answering comments on my blog!
Nickname:You don't have a nickname? million-fold energy difference is one thing, but a missing nickname...
DeleteFinally: Yes that was what i meant and thank you, now i understand its just to eliminate Electrostatic blooming. I don't know what Electrostatic blooming exactly is but i think is means that the positive charged ions in the plasma repel each other because they have the same electromagnetic charge. Just like trying to press neodym magnets together with facing the both the same pole (And then violently rotate and slam together thus breaking...)
High Dv: Yes i agree on the High delta-v word building element. But I already considered that argument. The higher Dv drives everyone has the more insignificant the railmissiles initial velocity means.
SMES: On a other post you gave a 40MJ/ton figure which sounded horrible to. But 400MJ/ton sounds acceptable for big weapon systems.
Advanced Science: Kurzgesagt? Awesome channel love them, but i wouldn't consider them advanced physics or even remotely close to that. Wikipedia Articles? Done that few years ago, Last post i remember reading back then was Strange matter. Isaac Arthur? I will check him out. AskSciene? Not very often on there should change it.
Maybe i have a unique perception of "Advanced Physics" heck, I am on some posts about Nuclear Directed Energy Weapons, meanwhile my class mates struggle to understand the Ohm Law.
Ah, Thank you, nice to write with someone who has an aproval from Atomic Rockets.
Nickname: Technically, Casaba Howitzer is a code name for the project, itself an offshoot of Project Orion for nuclear pulsed propulsion.
DeleteElectrostatic bloom: two main ways particle beams spread. The first is electrostatic forces that repel same-charged particles. It is mostly eliminated in a well neutralized beam. The second is thermal bloom. Like a gas, the particles move in all directions due to their temperature. In relativistic beams, time dilation is so strong that particles seem to spread more slowly than they should.
High DeltaV: Not necessarily! DeltaV is not the only factor in a chase between a missile and a warship. If it were the case, fighter jets would escape all missiles easily. The missile has to only accelerate faster than its target to catch up, meaning it has to put on more deltaV than the target *over the course of an intercept*, not but the end of the burn. A high thrust, low deltaV missile can catch a low thrust high deltaV warship if fired from a certain distance. This is especially apparent when comparing chemical or nuclear-thermal rockets to nuclear-electric rockets.
Advanced science: You wanted to find science - Kurzgesagt only mentions scientific concepts briefly, but its your job to explore them further. Its a good starting point. For example, you could watch this recent video: https://www.youtube.com/watch?v=qsN1LglrX9s.
Are you intrigued by the idea of black, cold balls of iron, the ultimate fate of ultra-stable stars? So was I! Before the video, as I asked this question on Google+ to an astronomer: https://plus.google.com/+MatterBeamTSF/posts/6YhGhTpLHhP
Look at the incredible responses!
But, don't forget sight of the essentials. Ohm might be boring and classroom physics might feel limited, but they get you through your exams and help you make less basic mistakes when reading up on more advanced concepts. Look at me: I'm still learning, and I still make a lot of mistakes.
You're welcome!
Nickname: Yeah, the only thing i ever heard of the lead scientist on the project was about why they named the space ultimate weapon, "A weapon you only have to fire once". After a melon sort.
DeleteHigh Dv: Yes, Delta change v vector/velocity. Change in Velocity. See, as you said in most scenarios low Dv high thrust missiles are superior than high Dv low thrust missiles. And a railmissile only adds to your Delta-v.
Already watched the Vid, as far I know White Dwarf are the remaining iron core of star. Multiple hundred million kelvin hot. And due to their high density and size they can remain very hot over very long periods in order of 1e11 years / ten times the age of the universe.
Ultimate fate? Heat death, but you made me curious about your G+ post.
I don't have a problem about class physics or school in general, other than being a pretty bad system from Objective standpoint at the moment. Feels nice to help others and sometimes to correct the teachers about outdated information. Or in the case about Ohm Law asking with Superconductors which have no resistance thus should have infinite current . Ohm Law only applies in daily environment but it doesn't work in extreme cases. But it is interesting seeing the second best person in physics reading g/cm³ as "gram divided by centimeter small 3".
For the question: What about Laser cooling the black dwarf? Its often utilised to achieve temperature near zero. A photon with a specific wavelength is shot at the atoms. And the Atoms re-radiate light. But the special thing is. The re-radiated light has more energy than in the first place. Thus energy must have been removed from the atom.
Deletehttps://en.wikipedia.org/wiki/Laser_cooling
Remember that you can only cool the surface down. But if the layers have high thermal differences thermal exchange should be accelerated. Inner layers 450K outer layers 3K.
And I have a questions about Worldbuilding in this topic here:
DeleteWould it make sense calling Stealth missiles torpedos? I know that "torpedo" is often used for missiles with low acceleration, Dv, "slow". But won't it make more sense to use it for Stealth missiles? Torpedos are mainly used by submarines which are known for their stealth capabilities in fiction. Red October for example.
Other topic: Quantum dots, I saw a advertisement from Samsung few hours ago. QLED. The fact that quantum dots are now commercially available makes me wonder for the many applications they could have. Solar-pannels with over 50% efficiency , or high efficiency lasers and probably even stealth.
Torpedoes: Kind of hard to say. I've always thought of stealth projectiles as being mounted on the tip of a booster. It's more of a special warhead or a design feature that can be added in certain versions of a regular missile.
DeleteTorpedoes, at least in Atomic Rockets terminology, are missiles that use the same propulsion technology as their target and catch up with them by simply having better overall performance. A missile has much higher acceleration than its target, but not necessarily the same deltaV capacity.
Quantum dots: High-efficiency solar panels are a very good thing in the near future. However, solar power cannot reach the energy density and independence of nuclear power...
So no stealth missiles but stealth warheads? I am fine with that.
DeleteQunatum dots: I never said using them as a energy source for military spaceships would be plausible, considering that the further you away from the sun the less juice you get. But might have some minor applications like maybe stealth. If your spacesships wall are made out of Quantum dots they can convert a significant amount of light into energy, which would be instead wasted into heating the armor of your spaceship.
Question about Focused CH: If you have a range of 10 million kilometers but a beam velocity of 10 thousand kilometers per second. It would take 1000 seconds to reach its target, at that time the beam would have been spread out by thermal expansion. And the beam is like only 3% the speed of light. So relativistic time dilation is out of the game. Gamma factor is low.
Well, you can make the entire missile stealthy, but it would be very impractical.
DeleteQuantum dots: Sorry, I was working on the 50% efficiency remark.
As for quantum dots for stealth... well, how? The interesting property of quantum dots is that they allow for extremely small emitters that produce a clean-coloured light efficiently. The reverse is true: they can be tuned to absorb a specific wavelength of light efficiently. BUT - you'd need a set of quantum dots of different size for each wavelength you need absorbed. You'd need millions of sets for wavelengths ranging from radio to x-ray... they don't help with emitting your own signature either. Super-cooling them changes their properties.
Silly from me, considering that quantum dots must be designed for a specific wavelenght to be absorbed/emitted. The wide spectrum of solar radiation, short of LIDAR and other "space-radars" (not literally) a million layers from a hypothetical standpoint aren't that many. 3-5nm for quantum dots meaning a million would be a millimeter thick. From a practical one? Haha, no.
DeleteLike I said I am fine with that. Actually no, i am happy about that.
The two stage stealth missile i mentioned was exactly what you described.
A Hot "high" dv drive used outside the detection range. And the warhead with small directional thrusters. When i say high dv missile i mean high dv for a misile, not relative to a stellar spaceship. Also, high dv is important is important to a missile. If you and the enemy have 60km/s relative velocity and your missiles have "only" 50km/s Dv even the highest thrust won't let you catch it.
Again to your casaba range problem. A casaba still has the same ultimate enemy as lasers. Light lag or for Lance beam lag (?). Your focused Lance might be killing ships from 10 million kilometers in theory. But such a distance would mean 1000 second lag. Hundreds of million kelvin hot plasma would have expaned to a gigantic cloud at this point. And Lorentz factor is so small that we can ignore relativsm.
What do you think about my idea about Laser cooling for black dwarf dilema of yours, it is commonly used these days and doesn't require black holes and other type III technologies.
Yours sincerely.
The high temperature exhaust and the uncooled skin of the booster stage for a missile would be visible across the solar system. There is no 'detection range' for launching a missile.
ReplyDeleteSo, your target will know that something was launched, your will instead try to make your warhead survive point defenses. Can't shoot what you can't see.
A more apt tactic would be to launch the missile out of counter-fire range. You want to make sure that your booster stage will not be shot to pieces while it is highly visible.
Casaba Howitzers: all factors that affect spread are described by the beam angle. If it has a milliradian spread, then it will keep a milliradian spread as the beam cools through space. It doesn't start spreading faster over time.
As for ranges, well, a milliradian beam at 10 million km will cover an area 200km wide. However, the energy levels required to do any sort of damage at that range is stupidly high (thousand teratons yield or more). A microradian beam, achievable with magnetic focusing, only needs about 100 megaton yield as it spreads to 200m across instead.
Firing these beams along 3 axis means that they'll smack into the target head-on whichever direction it accelerates. This is important because even moderate accelerations can evade the beams. Setting up this 'beam trap' is best achieved with stealth warheads, that move slowly and cooly into position.
Laser cooling: only useful for cooling a small number of atoms (about a millionth trillions of a gram) from 1 kelvin temperatures to 0.0001 kelvin temperatures. It doesn't work on large numbers of atoms or higher temperatures.
Odd, i thought such hot gas would tend to expand, the rate at which it expands gets slower with time, as the heat lowers the rate at which it expands also lowers, Heat:Atomic vibrations (kinetic) turn their heat energy into kinetic energy of the expanding medium. Even cold gas expands in the vacuum of the space, due extreme pressure differential. But a cloud of expanding gas (Explosives) Also don't forms a spherical ball when it has some velocity but rather some sort of cloud (Isaac Arthur: Space warfare)
Delete-I once heard that a gas in form of a pancake expands into the form of a cigarette and a gas in form of cigarette expands into the one of a pancake. Flip-over effect was it called. In relation to CH, Is that true?
-"that move slowly and cooly into position." Is slowly really needed? If something nearly invisible is travelling 20km/s or 200m/s does it really do much of a difference? Or do you meant that is should be slow so it can move in position more accurately and easily?
The beam spread listed in the data I linked to was empirical: it came from test in real world situations. It includes all factors such as electrostatic repulsion and thermal expansion, even if we are unaware of them all.
DeleteThe pancake/cigarette explanation is for the effect the shape of the propellant plate has on the beam produced. The particles in the centre and the edge of a propellant plate are accelerated at different rates. Therefore, a flat wide plate that initially produces a pancake cloud actually stretches into a cylinder, while a long and narrow propellant plate spreads into a pancake cloud.
By moving slowly, I meant the distances involved and the low deltaV produced from cold engines makes it look like the warheads are crawling to their positions. This applies to any cloud of hot gas in vacuum.
-So, instead of expanding into the form of an pancake in the travelling time it expands into an very long and narrow cigarette? Well that answers my question. Casaba Howitzers would also make great psychological weapons, A high velocity plasma jet is hitting you in 10min and you can't do anything. That would also force most to hide, by using stealthier designs.
Delete-Is it coincidence that all your blogs play together so well?
Except the ones which addresses problems et cetera. Laser Weapon Web/Casaba Howitzers -> Stealth in space is possible e.g
-Being slow is a problem of pure stealth missiles, they have the pro of being completely stealthy but aren't a springchicken, what do you are expecting if your use of propulsion is just a fire extinguisher with a fancy name. Hybrid have the advantage that they are fast but the disadvantage is that the enemy knows that a missile has been launched. But the warhead is still nowhere to been, and cold if properly isulated with Aerogels for example.
The later doesn't have to deal with "crawling" because their thruster aren't for accelerating but to change its final position.
-Metamaterials: Do they work on nearly all light? Except Gamma rays of course. Because if the answer is "yes" why don't use it as Anti-laser armor? Or is there some critical photon number for Meta's?
-Yes, a world with long range, cheap Casaba Howitzers would lead to submarine-like chases across the solar system.
Delete-Its an impression mostly due to my linking blog posts together for the sake of completeness.
-The warhead is bathed in sunlight. Thermodynamics means that it heats up to 700K over time. It has to be actively cooled to remain undetected.
-The shorter the wavelength, the easier it is to prevent reflections. There is no known reflector for gamma rays. It is the reflections that provide data back to the sensor to reveal your position.
Absorbing the incoming energy, such as radio waves or sunlight, is critical to prevent reflections. Metamaterials can help with this.
However, these materials can only convert the energy into heat. This heat must be removed with active cooling or it will be re-radiated and detected.
Therefore, an anti-laser armor based on super-energy-absorbant metamaterials is pointless: it would just heat up and start melting faster than regular materials.
I've often heard that with Metamaterials you can decide what to do with the incoming electromagnetic radiation, Absorbing "perfectly" (1), Reflecting it "perfectly" (1), bending it.
Delete[1] Second Law of Thermodynamics.
Thank you for mentioning baseline and resolution of any sensor dealing with any sort of wave detection.
ReplyDeleteThanks also for the discussion.
This is something I posted to one of Isaac Arthur's discussion threads a few months back:
Wrt cold non-maneuvering warheads, I usually like to challenge the "no stealth in space" assertions that often get made. The concrete example I use is the Gallileo probe (which had a malfunctioning high-gain antenna): It used the low gain omnidirectional antenna to transmit to Earth, but in order for Earth to pick it out of the background at all, it required the entire deep space network working in concert (with it's Earth-diameter order baseline), with subcooled detectors. The transmission rate was down to bits per second. The Gallileo probe was transmitting omnidirectionally, and the only reason we could find it was because we knew exactly where it was going to be.
"No stealth in space" seems to be dogma to me (or at least, not universally applicable like it is treated). Sure, hot human containing maneuvering interplanetary craft are going to be hard to hide, but there are a great many engineering constraints to any given detector before "differentiable in principle from the uncluttered cosmic microwave background" becomes "detected". (Aperture, integration time, background clutter (of which there is plenty in the solar system), the fact that as a detector becomes more powerful, it becomes more directional and it has to be pointed at what it is trying to detect.) (There is an awful lot of junk in Earth orbit right now that we barely track.)
I could imagine warfare being conducted at a much lower technology level and speed using cold conical specularly reflective warheads that drift along normal solar orbits (10s of km/sec) and only maneuver when they start getting into planetary SOI ranges. It seems like Earth/Mars's best shot of detecting this sort of attack is being paranoid enough to closely monitor each other's orbits (with telescopes in each other's orbits - see the resolving power of Hubble wrt Mars from Earth - it isn't all that good) to detect the launching of the attack (and right before the attack hits).
Hello and welcome to ToughSF, eccentricorbit0.
DeleteThe Gallileo probe at Jupiter's distance was indeed only able to be tracked thanks to its low gain antenna. Had it not generated a radio signal, we would have been forced to rely on the infrared or optical signature, which would be much lower.
I agree with your assessment of the current 'common sense' understanding of "no stealth in space". I think it is mainly based on the fact that no real spacecraft design to date has ever made any effort to hide its signature. Even spy satellites today are merrily reflecting most of the sunlight they receive with their insulating coating, turning them into miniature stars in the sky.
Note that the large number of possible 'cold' thruster designs means that dedicated space warships can maneuver without producing a significant signature. The lowest tech examples are cold gas thrusters, with more advanced designs accelerating propellant to higher velocities without expending any hot gases (such as a railgun cooled by liquid hydrogen).
One counter I haven't covered much in the stealth in space series of blog posts is preventive laser illumination of the entire sky with a short-wavelength laser. While Vantablack can absorb most regular wavelengths (microwave, infrared, opticalm perhaps UV and some radio), it cannot handle X-rays. These X-rays will force the surface of a stealth spaceship to emit a distinctive signal through X-ray fluorescence. Whether X-ray lasers will become powerful enough to be used in this manner is debatable, but the possibility exists.
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ReplyDeleteEven cold gas expands in the vacuum of the space, due extreme pressure differential. But a cloud of expanding gas (Explosives) Also don't forms a spherical ball when it has some velocity but rather some sort of cloud (Isaac Arthur: Space warfare)
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