Why stealth in space is still there
Hi, Habr! In this article I want to consider the topic is not too relevant in reality, but disturbing the minds of many amateurs (and, if I may say so) science fiction professionals - ways to hide in space, subject to the use of technology for the foreseeable future only.
There is a common opinion in the geek environmentthe fact that in any realistic science fiction setting of stealth in space can not be. The problem is that as soon as we are going to make a game or write a book with a pretense of realism, that is (according to popular opinion) without stealth in space, it turns out that fighting without this stealth is somewhat problematic - both participants in the battle can calculate its outcome in advance because then with full information. This forces the igrodels to either make KSPs with guns, or go to the space operator, and the writers to write not sci-fi proper action films, but spy novels, or again to go to the space operator.
And so, without stealth in space is bad. But maybe he is still there? After all, the article on “Nuclear missiles” is by definition not the ultimate truth, and we still have no practical experience of space warfare.
The following facts of objective reality speak against stealth in space:
And what can we do about it? The answer is under the cut.
By stealth, we mean the impossibility of identifying an object as representing a threat before our intelligence officers approach it at a distance of the same order as the firing contact distance. Because it is one thing when earthlings can follow the Martian fleet to near-earth telescopes at a distance of hundreds of millions of kilometers, and quite another to send spy probes to Mars, which can also shoot down, as in reality reconnaissance stratostats and shooting down reconnaissance - UAV.
The article “Atomic Missiles” states that false targets will not work, but the arguments are, to put it mildly, weak and not supported by calculations:
Consider a specific example. Suppose Ilon Mask did everything with the BFR and by the middle of the XXI century the Moon and Mars were already colonized and do not quite love each other and / or the Earth. Let us also assume that fundamental breakthroughs in rocket production did not happen and the main interplanetary transport is something like ITS from the presentation of 2016 (that is, the result of the upgrades of the BFR itself). The main means of warfare, respectively, is the same ITS, but loaded with various means of causing goodness and light to the Martian separatists or to the crawling earthlings, respectively.
Suppose the means of carrying good in one ITS will fit about 150 tons. Although planned 450 tons, and for departure from Earth orbit to Mars. By sacrificing the characteristic speed and choosing the appropriate base (Lagrange points, circumlunar orbit, elongated elliptical), you can increase the load capacity and up to a thousand tons. But for the evaluation from the top we take the most pessimistic case.
Peaceful Martiantractor transport worker displays a combat platform on the combat course
The price of the ITS orbital unit is estimated at $ 130 million for a tanker and $ 200 million for a ship. A tanker can be made indistinguishable from a ship in any possible telescope - just put solar batteries on the tanker, and the ship does not make the famous transparent window - neither of them clearly draws $ 70 million of difference (due to the more complex structure of the ship compared to the transporter) . But even if it suddenly pulls, the difference of 70 million is not fundamental against the background of prices for military equipment. So a hundred SM-3 rockets (the closest existing analogues of space-to-space rockets) with a mass of 150 tons will cost 1 billion 840 million dollars. Of course, rockets need a guidance system, but a telescope like “Kepler” weighs several tons, at a cost of the order of hundreds of millions of dollars.
But let's say we want to arm our combat ship not with disposable missiles, but with potentially reusable drones or manned fighters. As a weapon for our fighter take the kinetic gun "Volcano-Falanx." Just because the laser any more serially still not produce, and it is unlikely that their price will differ in the smaller side. $ 13 million for a 5 ton gun only . Suppose that a five-ton rocket unit for moving our guns in the future will cost not 20 million as it is now, but only 2 due to serial production, 15 ten-ton fighters will cost $ 225 million - already comparable with the price of ITS.
Here are only 200 million - this is on condition that we buy a new ITS from shipyards. What is not necessary at all - for a false purpose, you can and should take a used ship that has already managed to pay for its production carrying peaceful cargoes. For the tanker, a multiplicity of 100 flights is planned, for an interplanetary ship - 12 (the difference is due to the duration of the interplanetary flight), so the price of $ 20 million for voluntarily-forced buying up of ships in the “one flight before decommissioning” looks quite fair and does not cause the shipowner to want to mess with your native MCRN . And $ 20 million is a bit more expensive than one (!!!) space rocket and is comparable to the price of one fighter.
Very theoretically, enemy reconnaissance can track the ship’s “individual characteristics of the radiation spectrum”. But even in such a (as shown below, fantastic) situation, it is possible to arrange a “space thimble” using used ships and as carriers of weapons (and which of the ships are loaded with missiles and drones to the enemy is not necessary to know). Yes, the Space Fleet flying exclusively on used ships looks like a template - but the fighters for the independence of the colonies have had to turn around at all times.
And this is not at all a disguise for a peace ship, which could have negative diplomatic consequences. The space fleet honestly buys used ships, it simply does not recognize which ship it carries missiles and drones, and not ballast.
The above is probably true for any realistic scenario of interplanetary conflict in the near future. To clash in space - you need to colonize it at the beginning. And for this you need cheap interplanetary transport. And if the military does not use this transport from the principle - these are no longer the laws of the nature of the problem, but only those military ones. In addition, the “space thimble” method is designed for the enemy to look at any of our troughs in a very multispectral camera, and even with a quality of at least 4K, and therefore the simulator should have the same shape, dimensions and engines as the simulated one. But such a scenario is in fact doubtful.
The theoretical limit of the angular resolution of any telescope is very simple.
where R is the minimum angular resolution in radians, D is the aperture in meters, lam is the working length of the wave in them. For very small angles R can be considered the ratio of the distance to the observed object to the minimum distinguishable distance on it. It is easy to make sure that for the meter aperture and micrometer wavelength (near IR) the spatial resolution for a thousand kilometers will be just a meter. Well, if we try to look in a similar telescope for a hundred million kilometers (the distance between Mars and Earth at the moment of not great opposition), we will have a pixel with a size of 100 kilometers. Or we need a miracle telescope with a hundred-kilometer mirror in order to maintain a resolution of one meter.
This thing has only a 130-meter aperture.
Many readers immediately thought about optical interferometers. Yes, they have a shoulder length in the formula for spatial resolution instead of an aperture. Here only that length of a shoulder needs to be maintained with an error of smaller half of working wavelength. So the option "just take two space telescopes" does not fit - the shoulder should be hard. But even a rigid shoulder with a length of a hundred kilometers will "walk" because of the uneven thermal loads. For the same reason, nothing will come of the idea of a thin-film hundred-kilometer mirror.
In addition, deciding to save on the area of the mirror, we will save on photosensitivity. And you can not save on it. At a distance of the same 100 million kilometers, a spherically symmetrical object radiating at a wavelength of 1 micron with a power of 1 MW will produce 80 photons per square meter per second. Once again, eighty photons. To obtain any intelligible image, you will need to either increase the shutter speed to a few hundred seconds, or increase the area. And it provided that the matrix catches individual photons.
Ceres from the point of view of the telescope. Hubble. Pixel width - 30 kilometers
So. For a detailed observation of the enemy ship at interplanetary distances, we need a monstrous interferometer with mirrors of tens of meters, at least a kilometer-long rigid shoulder and an ultrasensitive matrix cooled to almost absolute zero. And this miracle of technology still can not do anything with the tactics of the “space thimble”. And not only.
The Cosmic Thimble was based on the fact that not a single telescope would be able to look under the casing of an interplanetary ship. But what if instead of a hold or a cargo container with its not-so-large volume to use alarge thin-film bag of soot or dust? As a result, enemy reconnaissance will have information about the presence in space of dozens of artificial dust nebulae, but there will be no information about their contents until someone has physically combed each nebula.
Suppose the size of soot particles in our cloud is 10 microns. The ratio of the mass / cross section of the particle will be about 20 grams per square meter. In Earth orbit, the pressure of sunlight on a black surface is 5.6 μN / m2. Thus, near the Earth, the sunlight will displace our smoke screen with an acceleration of 0.2 millimeters per second per second, which is quite possible to compensate for with the engines of the fleet hiding.
Something similar was used in the Gundam quote from which is taken as the title of the section. With the only difference that there was used a cold plasma from exotic elementary particles, which was completely weightless, was produced by thermonuclear reactors of ships in almost unlimited quantities, and finally was also hidden from radars. Soot against radar is useless, but there are other means against it. But the mass of soot can be a problem.
Twenty grams per square meter in the transition to a square kilometer turn into twenty tons. Suppose we want to cover a sphere with a diameter of 20 kilometers with soot so that the desired surface density is reached at a depth of 1 kilometer provided that the particles are evenly distributed. Those. at a carbon black density of 20 tons per cubic meter. We will need a little less than 84 kilotons of soot. Lot? Well, how to say - a similar amount of carbon is contained in a C-class asteroid with an average diameter of 20 meters. So, this method is quite suitable for covering the fleet base on those asteroids or near them.
Matilda is a typical C-class asteroid
And so, we flew to the enemy's planet when he did not wait for us using a “thimble” or artificial comets. What's next?
First of all, the same soot. For setting local dust curtains with a length of several kilometers, about a hundred tons of soot is enough - it will just fit into a transport worker playing the role of a false target. But in this situation, a “real” stealth is already possible - complete invisibility for enemy detection systems. The fact is that not the months of the flight, but tens of hours, separate us from the enemy, so that we can not radiate at all due to the release of heat into hydrogen snow.
Imagine a ship on the nose of which is a black-black tank with solid hydrogen. The specific heat of fusion of hydrogen is 59 kJ / kg. The solar constant in near-earth orbit is 1367 W / m2. Total tank length of 14.3 meters (length, taking into account the space for melted hydrogen) turned end to the Sun (ie, having a ton of hydrogen per meter of illuminated surface) will absorb sunlight while maintaining the melting point of that hydrogen for just under 12 hours. Heat generated by the crew and ship systems? Their contribution can be neglected for the same "Union" enough kilowatts per crew of three.
Of course, this method of hiding a ship only works during a ballistic flight. But the maneuver to reach the target can and should be carried out under the cover of the same soot.
A stealth fighter built using this technology using liquid engines can have the following characteristics:
Diameter - 2 meters
Length - 25 meters of which:
Hydrogen tank - 14.3 meters
Oxygen - 6 meters.
Rocket engine - 1 meter.
Control compartment and weapons - 3.7 meters.
Crew - 0-1 people.
Fuel mass - 22 tons.
The mass of tanks and the engine - 3 tons.
Mass of the control compartment - 2 tons.
The mass of weapons - 3 tons (missiles).
Initial mass - 30/27 tons (with and without weapons).
Final mass- 8/5 tons.
Flow rate - 4.3 km / s
Delta-Ve without weapons - 7.25 km / s.
Tactics of application - get out of the cargo hold of a chartered plane in the "international space" under cover of smoke curtains, roll up the target with accelerators, sneak up, launch missiles and leave without extra tricks.
And now the fighter on nuclear firing:
Diameter - 2 meters
Length - 20 meters of which:
Hydrogen tank - 14.3 meters
NRE with bioprotection - 2 meters.
Control compartment and weapons - 3.7 meters.
Crew - 0-1 people.
The mass of the working body - 3.14 tons.
Mass tanks and engine- 4 tons.
Mass of the control compartment - 2 tons.
Mass weapons - 3 tons.
Initial mass - 12.14 / 9.14 tons (with and without weapons).
The final mass is 9/6 tons (with and without weapons).
Flow rate - 9 km / s
Delta-Ve without weapons - 3.78 km / s.
Dry weight increased by a ton to account for biological protection. Delta-Ve slipped because the specific impulse of the solid-state NRE did not compensate for the dramatic decrease in the reactive mass and the addition of biological protection.
It is obvious that such a stealth fighter will be able to effectively attack only sedentary targets. For example, multikilometer interferometers for remote space detection.
There is a common opinion in the geek environmentthe fact that in any realistic science fiction setting of stealth in space can not be. The problem is that as soon as we are going to make a game or write a book with a pretense of realism, that is (according to popular opinion) without stealth in space, it turns out that fighting without this stealth is somewhat problematic - both participants in the battle can calculate its outcome in advance because then with full information. This forces the igrodels to either make KSPs with guns, or go to the space operator, and the writers to write not sci-fi proper action films, but spy novels, or again to go to the space operator.
And so, without stealth in space is bad. But maybe he is still there? After all, the article on “Nuclear missiles” is by definition not the ultimate truth, and we still have no practical experience of space warfare.
The following facts of objective reality speak against stealth in space:
- Vacuum has the highest possible transparency.
- The background either has a temperature of 4 K (relic radiation) or is predictable (stars).
- The ship inevitably radiates the heat produced inside it and reflects or re-radiates sunlight. Especially when maneuvering.
- The sensitivity of modern telescopes is enough to take a picture of the Voyager beyond the orbit of Pluto.
And what can we do about it? The answer is under the cut.
Agree on terms
By stealth, we mean the impossibility of identifying an object as representing a threat before our intelligence officers approach it at a distance of the same order as the firing contact distance. Because it is one thing when earthlings can follow the Martian fleet to near-earth telescopes at a distance of hundreds of millions of kilometers, and quite another to send spy probes to Mars, which can also shoot down, as in reality reconnaissance stratostats and shooting down reconnaissance - UAV.
I twist-twist want to confuse
The article “Atomic Missiles” states that false targets will not work, but the arguments are, to put it mildly, weak and not supported by calculations:
- A false goal should radiate in a manner similar to a true goal. This means that it should have the same energy source as on the object being covered.
- To work during acceleration, the LC must have the same mass and remote control as the real ship - otherwise the acceleration and radiation of the engines will not match each other.
- From the above, it is concluded that a false goal will be almost indistinguishable from the true price. What is strange, for already now the payload can be much more expensive than launching it into a target rocket orbit. In the future with the colonization of the Solar System, obviously, the rocket should be much cheaper than today, but everything else is not necessary.
Consider a specific example. Suppose Ilon Mask did everything with the BFR and by the middle of the XXI century the Moon and Mars were already colonized and do not quite love each other and / or the Earth. Let us also assume that fundamental breakthroughs in rocket production did not happen and the main interplanetary transport is something like ITS from the presentation of 2016 (that is, the result of the upgrades of the BFR itself). The main means of warfare, respectively, is the same ITS, but loaded with various means of causing goodness and light to the Martian separatists or to the crawling earthlings, respectively.
Suppose the means of carrying good in one ITS will fit about 150 tons. Although planned 450 tons, and for departure from Earth orbit to Mars. By sacrificing the characteristic speed and choosing the appropriate base (Lagrange points, circumlunar orbit, elongated elliptical), you can increase the load capacity and up to a thousand tons. But for the evaluation from the top we take the most pessimistic case.
Peaceful Martian
The price of the ITS orbital unit is estimated at $ 130 million for a tanker and $ 200 million for a ship. A tanker can be made indistinguishable from a ship in any possible telescope - just put solar batteries on the tanker, and the ship does not make the famous transparent window - neither of them clearly draws $ 70 million of difference (due to the more complex structure of the ship compared to the transporter) . But even if it suddenly pulls, the difference of 70 million is not fundamental against the background of prices for military equipment. So a hundred SM-3 rockets (the closest existing analogues of space-to-space rockets) with a mass of 150 tons will cost 1 billion 840 million dollars. Of course, rockets need a guidance system, but a telescope like “Kepler” weighs several tons, at a cost of the order of hundreds of millions of dollars.
But let's say we want to arm our combat ship not with disposable missiles, but with potentially reusable drones or manned fighters. As a weapon for our fighter take the kinetic gun "Volcano-Falanx." Just because the laser any more serially still not produce, and it is unlikely that their price will differ in the smaller side. $ 13 million for a 5 ton gun only . Suppose that a five-ton rocket unit for moving our guns in the future will cost not 20 million as it is now, but only 2 due to serial production, 15 ten-ton fighters will cost $ 225 million - already comparable with the price of ITS.
Here are only 200 million - this is on condition that we buy a new ITS from shipyards. What is not necessary at all - for a false purpose, you can and should take a used ship that has already managed to pay for its production carrying peaceful cargoes. For the tanker, a multiplicity of 100 flights is planned, for an interplanetary ship - 12 (the difference is due to the duration of the interplanetary flight), so the price of $ 20 million for voluntarily-forced buying up of ships in the “one flight before decommissioning” looks quite fair and does not cause the shipowner to want to mess with your native MCRN . And $ 20 million is a bit more expensive than one (!!!) space rocket and is comparable to the price of one fighter.
Very theoretically, enemy reconnaissance can track the ship’s “individual characteristics of the radiation spectrum”. But even in such a (as shown below, fantastic) situation, it is possible to arrange a “space thimble” using used ships and as carriers of weapons (and which of the ships are loaded with missiles and drones to the enemy is not necessary to know). Yes, the Space Fleet flying exclusively on used ships looks like a template - but the fighters for the independence of the colonies have had to turn around at all times.
And this is not at all a disguise for a peace ship, which could have negative diplomatic consequences. The space fleet honestly buys used ships, it simply does not recognize which ship it carries missiles and drones, and not ballast.
The above is probably true for any realistic scenario of interplanetary conflict in the near future. To clash in space - you need to colonize it at the beginning. And for this you need cheap interplanetary transport. And if the military does not use this transport from the principle - these are no longer the laws of the nature of the problem, but only those military ones. In addition, the “space thimble” method is designed for the enemy to look at any of our troughs in a very multispectral camera, and even with a quality of at least 4K, and therefore the simulator should have the same shape, dimensions and engines as the simulated one. But such a scenario is in fact doubtful.
Diffraction
The theoretical limit of the angular resolution of any telescope is very simple.
where R is the minimum angular resolution in radians, D is the aperture in meters, lam is the working length of the wave in them. For very small angles R can be considered the ratio of the distance to the observed object to the minimum distinguishable distance on it. It is easy to make sure that for the meter aperture and micrometer wavelength (near IR) the spatial resolution for a thousand kilometers will be just a meter. Well, if we try to look in a similar telescope for a hundred million kilometers (the distance between Mars and Earth at the moment of not great opposition), we will have a pixel with a size of 100 kilometers. Or we need a miracle telescope with a hundred-kilometer mirror in order to maintain a resolution of one meter.
This thing has only a 130-meter aperture.Many readers immediately thought about optical interferometers. Yes, they have a shoulder length in the formula for spatial resolution instead of an aperture. Here only that length of a shoulder needs to be maintained with an error of smaller half of working wavelength. So the option "just take two space telescopes" does not fit - the shoulder should be hard. But even a rigid shoulder with a length of a hundred kilometers will "walk" because of the uneven thermal loads. For the same reason, nothing will come of the idea of a thin-film hundred-kilometer mirror.
In addition, deciding to save on the area of the mirror, we will save on photosensitivity. And you can not save on it. At a distance of the same 100 million kilometers, a spherically symmetrical object radiating at a wavelength of 1 micron with a power of 1 MW will produce 80 photons per square meter per second. Once again, eighty photons. To obtain any intelligible image, you will need to either increase the shutter speed to a few hundred seconds, or increase the area. And it provided that the matrix catches individual photons.
Ceres from the point of view of the telescope. Hubble. Pixel width - 30 kilometers
So. For a detailed observation of the enemy ship at interplanetary distances, we need a monstrous interferometer with mirrors of tens of meters, at least a kilometer-long rigid shoulder and an ultrasensitive matrix cooled to almost absolute zero. And this miracle of technology still can not do anything with the tactics of the “space thimble”. And not only.
Minovsky particles, combat level!
The Cosmic Thimble was based on the fact that not a single telescope would be able to look under the casing of an interplanetary ship. But what if instead of a hold or a cargo container with its not-so-large volume to use a
Suppose the size of soot particles in our cloud is 10 microns. The ratio of the mass / cross section of the particle will be about 20 grams per square meter. In Earth orbit, the pressure of sunlight on a black surface is 5.6 μN / m2. Thus, near the Earth, the sunlight will displace our smoke screen with an acceleration of 0.2 millimeters per second per second, which is quite possible to compensate for with the engines of the fleet hiding.
Something similar was used in the Gundam quote from which is taken as the title of the section. With the only difference that there was used a cold plasma from exotic elementary particles, which was completely weightless, was produced by thermonuclear reactors of ships in almost unlimited quantities, and finally was also hidden from radars. Soot against radar is useless, but there are other means against it. But the mass of soot can be a problem.
Twenty grams per square meter in the transition to a square kilometer turn into twenty tons. Suppose we want to cover a sphere with a diameter of 20 kilometers with soot so that the desired surface density is reached at a depth of 1 kilometer provided that the particles are evenly distributed. Those. at a carbon black density of 20 tons per cubic meter. We will need a little less than 84 kilotons of soot. Lot? Well, how to say - a similar amount of carbon is contained in a C-class asteroid with an average diameter of 20 meters. So, this method is quite suitable for covering the fleet base on those asteroids or near them.
Matilda is a typical C-class asteroid
Tactical stealth
And so, we flew to the enemy's planet when he did not wait for us using a “thimble” or artificial comets. What's next?
First of all, the same soot. For setting local dust curtains with a length of several kilometers, about a hundred tons of soot is enough - it will just fit into a transport worker playing the role of a false target. But in this situation, a “real” stealth is already possible - complete invisibility for enemy detection systems. The fact is that not the months of the flight, but tens of hours, separate us from the enemy, so that we can not radiate at all due to the release of heat into hydrogen snow.
Imagine a ship on the nose of which is a black-black tank with solid hydrogen. The specific heat of fusion of hydrogen is 59 kJ / kg. The solar constant in near-earth orbit is 1367 W / m2. Total tank length of 14.3 meters (length, taking into account the space for melted hydrogen) turned end to the Sun (ie, having a ton of hydrogen per meter of illuminated surface) will absorb sunlight while maintaining the melting point of that hydrogen for just under 12 hours. Heat generated by the crew and ship systems? Their contribution can be neglected for the same "Union" enough kilowatts per crew of three.
Of course, this method of hiding a ship only works during a ballistic flight. But the maneuver to reach the target can and should be carried out under the cover of the same soot.
A stealth fighter built using this technology using liquid engines can have the following characteristics:
Diameter - 2 meters
Length - 25 meters of which:
Hydrogen tank - 14.3 meters
Oxygen - 6 meters.
Rocket engine - 1 meter.
Control compartment and weapons - 3.7 meters.
Crew - 0-1 people.
Fuel mass - 22 tons.
The mass of tanks and the engine - 3 tons.
Mass of the control compartment - 2 tons.
The mass of weapons - 3 tons (missiles).
Initial mass - 30/27 tons (with and without weapons).
Final mass- 8/5 tons.
Flow rate - 4.3 km / s
Delta-Ve without weapons - 7.25 km / s.
Tactics of application - get out of the cargo hold of a chartered plane in the "international space" under cover of smoke curtains, roll up the target with accelerators, sneak up, launch missiles and leave without extra tricks.
And now the fighter on nuclear firing:
Diameter - 2 meters
Length - 20 meters of which:
Hydrogen tank - 14.3 meters
NRE with bioprotection - 2 meters.
Control compartment and weapons - 3.7 meters.
Crew - 0-1 people.
The mass of the working body - 3.14 tons.
Mass tanks and engine- 4 tons.
Mass of the control compartment - 2 tons.
Mass weapons - 3 tons.
Initial mass - 12.14 / 9.14 tons (with and without weapons).
The final mass is 9/6 tons (with and without weapons).
Flow rate - 9 km / s
Delta-Ve without weapons - 3.78 km / s.
Dry weight increased by a ton to account for biological protection. Delta-Ve slipped because the specific impulse of the solid-state NRE did not compensate for the dramatic decrease in the reactive mass and the addition of biological protection.
It is obvious that such a stealth fighter will be able to effectively attack only sedentary targets. For example, multikilometer interferometers for remote space detection.