Geekly Articles each Day

Real space battles in Children of a Dead Earth, part 1

The mainstream war games in space are multicolored pi-pip lasers, point-blank shooting, zero speed relative to absolute space, and other completely unrealistic things . Therefore, the Children of a Dead Earth simulator, which simulates battles on the currently available technologies, gives a completely unique experience. And besides, it’s just fun to play, he raises serious questions about how real wars can take place in the solar system, and has great educational value.


Battle in Mars orbit. Colored lines are not lasers, but tracers of railgun shells

Battlefield


Orbital mechanics for the unprepared person looks very incomprehensible. It is best perceived during the game, but it is advisable to give some basics in advance. First of all, the action will take place in the solar system, and any object will be in the orbit of any of its celestial bodies. What is an orbit? Speaking very simply and briefly, under the influence of the attraction of a heavy body, another body (satellite, ship, rocket, etc.) will move along a trajectory representing a conic section (circumference, ellipse, parabola, hyperbola) with a focus located in the center mass system, which in our case will be inside a heavy body. Several parameters define what this path will look like:


Another parameter is critical for all spacecraft. The reserve of the characteristic speed or delta-V is the amount by which the device can change the speed on its engines. For example, we have a chemical rocket engine and fuel at 2 km / s. We can spend them as we want - accelerating, slowing, changing the inclination of the orbit. When the delta-V is 0, we run out of fuel, and we can’t change our trajectory. The parameter is convenient because it does not care about the type of engine and fuel, and you can compare any devices.


The approximate values ​​of delta-V in m / s for flights between planets

Interestingly, in CoaDE, the delta-V supply of ships is usually less than what is required for a full-fledged flight between celestial bodies. It is assumed that the ships are flying with additional tanks, which are dropped before the start of the battle and are not visible in the game.


Calculation of the maneuver to intercept enemy groups in the orbit of Venus

The ship control interface is a bit like the Kerbal Space Program, but here ships are given commands, and they are maneuvering on their own.



For accurate calculation of the maneuver there is a very handy tool that switches the base body to display the trajectory. In the screenshot above, we aim at the meeting point, changing the base body from Venus to the enemy fleet. This feature is indispensable in complex missions.

In addition, there are several terms that are useful to know:


From the laws of orbital mechanics follow some unobvious features of the space battlefield:

  1. In order to join the battle, you must perform complex maneuvers to get closer to the enemy at a distance of your weapons. The opponent additionally complicates the task with his maneuvers.
  2. The one of the opponents, whose delta-V ends, loses the initiative, and the enemy with the remaining reserve of characteristic speed will determine the convergence characteristics. In general, the stationary target is completely helpless, because it can be fired from a great distance with absolute impunity.
  3. In orbit around a single celestial body, you can implement a wide variety of approaches for approaching, both with a minimum reciprocal speed on converging courses, and with a huge speed on intersecting or oncoming ones.
  4. The range of possible speeds of mutual convergence begins from the near-zero and can reach tens of kilometers per second. For example, with an economical, in terms of fuel consumption, the flight Earth-Mars, the final speed around Mars will be about 6 km / s. If you enter the opposite trajectory, the speed can reach 50 km / s (but such a trajectory will require> 30 km / s delta-V). On realistic technologies in the orbit of one celestial body, it is reasonable to expect a maximum convergence rate from near zero to several kilometers per second.
  5. The lighter the central body, the cheaper from the point of view of delta-V maneuvers. Around a light asteroid, you can easily turn around on the spot and start moving in the opposite direction, but on the orbit of a heavy planet of the same volume, delta-V is enough only to slightly change the parameters of the orbit.

Engines


Without the ability to change the orbit, it is impossible not only a space battle, but also any serious exploration of space. And changing the orbit is impossible without an engine. In the near future, the basis of space engines will be different designs with the release of reactive mass - solar and electromagnetic sails, as well as engines pushing off from the magnetic field of the planet, are too non-universal. The main characteristics for space engines are:


Chemical engine


The development of space itself began with chemical rocket engines. They have a low specific impulse and are now close to the physical limits of their effectiveness, but, due to their comparative simplicity and high yields relative to other types, they are the main engines of modern astronautics. The conquest of space requires a higher specific impulse, but these engines will not disappear completely.

In CoaDE, only liquid-propellant rocket engines with one or two components are presented so far, therefore we will consider only them in more detail. The principle of operation is relatively simple. In the combustion chamber, the fuel decomposes (if the component is one) or is burned by an oxidizing agent (if there are two components) with the release of a large amount of thermal energy. Transformed into a high-temperature gas, it enters the Laval nozzle, which converts the thermal energy of the gas into the kinetic energy of its rapid outflow.


The combustion chamber and the Laval nozzle of the engine RD-107/108. On such fly Russian missiles “Union”

In real life, the components “liquid oxygen-kerosene” are popular because of the simplicity and high density of kerosene, “liquid oxygen - liquid hydrogen” due to high specific impulses (about 4.4 km / s) and “asymmetric dimethylhydrazine - nitrogen tetroxide” because it can be kept at room temperature for a very long time. The maximum achieved specific impulse of a chemical engine of 5.32 km / s was obtained using a three-component “lithium-fluorine-hydrogen” fuel, which is extremely inconvenient in practical use (lithium must be very hot, hydrogen must be cold, components cause corrosion of pipelines, and exhaust is toxic ).

In CoaDE, the most effective fuel pair will be “fluorine-hydrogen” (UI 4.6 km / s). In reality, no one will use it, because the exhaust of such an engine will be a very harmful for the environment hydrofluoric acid, but according to the plot of the game, the Earth has already come to an end, and the surviving remnants of humanity do not care about ecology. Also, CoaDE does not take into account the need for thermal protection of cryogenic tanks - liquid oxygen can be stored without insulation, but liquid hydrogen will evaporate too actively.


Chemical rocket engine design

The game takes into account the stoichiometric ratio (the ratio of fuel and oxidizer, allows you to either burn the fuel completely or have an excess of one of the components in the exhaust), the need to feed the components with a turbopump, cool the combustion chamber and the nozzle with one of the components (used in reality, otherwise the engine will simply melt ) and turn the engine to maneuver. The flexibility of the game designer allows you to create a variety of engines, suitable for a wide range of tasks, from large and efficient sustainer engines to compact orientation engines. Chemical engines in CoaDE are mainly used for rockets and drones.

Nuclear rocket


The heated gas for the Laval nozzle can be obtained not only by the chemical reaction of combustion. This task will perfectly cope with a nuclear reactor. Therefore, in the middle of the 20th century, experimental projects of RD-0410 and NERVA nuclear rocket engines began in the USSR and the USA.


NERVA in section

The principle of operation of a nuclear rocket engine is simple. A controlled nuclear reaction produces a lot of heat. A working fluid flows through the reactor, which heats up (while cooling the reactor) and is ejected through a nozzle. It follows from the specific impulse formula that the smaller the molecular weight of the working medium, the faster it will be ejected, and the more effective the engine will be. Therefore, in real projects, hydrogen was supposed to be used as a working medium. CoaDE, on the other hand, has a curious situation - the most efficient type of fuel is hydrogen deuteride - a molecule from one hydrogen atom and one deuterium atom (a hydrogen isotope with one neutron). Under conditions of high reactor temperature, the hydrogen deuteride will dissociate (the diatomic molecule will decompose into individual atoms), and the molecular weight will be less than that of the practically non-dissociating H2 reactor.

In real history, both projects have not progressed beyond testing, and the big news was the recent news about the development of a nuclear engine for the Russian Burevestnik cruise missile. In the game, they are one of the most suitable - the fact is that the specific impulse of a nuclear missile is about two times higher than that of a chemical rocket, and you can create a high-thrust engine without problems. And the problem of radioactive exhaust is not important when the ship flies outside the atmosphere.


Heavy shipboard nuclear cruising engine with a load of 120 tons and a specific impulse of 9.4 km / s

Electric Heated Rocket Engine


Another way to get hot gas is to use an electric heater. The advantage of this engine is that it can be used by any working fluid, up to the waste. The working fluid can be heated to a very high temperature, which makes it possible to obtain a high specific impulse, about twice as high as chemical rockets. The drawback of the circuit is that heating requires a lot of electricity (which means that the energy to be converted into energy in the reactor-heater system), and that the engine has little traction.


Tanks with butane and electric engine

In reality, engines of this type have been used extensively in astronautics for many years. A little traction is not a problem if the satellite is not actively maneuvering. But in CoaDE they occupy an auxiliary niche, being used on some ships as orientation engines.

Magnetoplasma engine


Although the Laval nozzle is a very efficient heat engine and has an efficiency of up to 70%, there are ways to eject the working fluid at much higher speeds. Electrical effects are used for this — the Coulomb force, the Hall effect, field emission, and others. Only one type is presented in CoaDE - magnetoplasma engines (MTD).



The photo above shows a working MTD. The pin in the center is the cathode (negative electrode), around it is a cylindrical anode (positive electrode). Between them flows ionized gas, which is accelerated by Lorentz force to very high speeds. The specific impulse of the MTD can reach tens of kilometers per second, but it has to be paid for by the fact that they consume up to several orders of magnitude more energy with a comparable with electric heating engines.


The specific impulse is 42 km / s, but consumes 10 megawatts and has a thrust of only 28 kg

In real cosmonautics, various types of electrojet engines are already widely used. They can not be put on a launch vehicle, but on the satellites there is quite enough traction in a few grams, provided that the engine will turn on for hours and days of continuous operation.

Nuclear impulse rocket


An interesting idea appeared in the middle of the 20th century. A huge amount of heat released by the atomic bomb can theoretically be used for movement. To do this, on the bomb itself, it is necessary to place a reserve of the working fluid that turns into an explosion into the plasma, and install a reflector plate on the ship that receives and absorbs the impact of the plasma.



In dynamics, it would look like this:



The principle of movement was successfully tested on a model with chemical explosives. In real history, the project fell victim to the 1963 nuclear test ban treaty and the fact that this mover was attempted to create a project of a warship, the astronomical value of which the politicians did not like. And it’s a pity - the theoretical specific impulse was at the level of tens of kilometers per second, and the thrust, too, had to be decent.



This is how one of the first projects of combat spacecraft in the history of mankind looked. Hundreds of nuclear warheads, howitzers firing marching charges, sea 127-mm and 30-mm guns were supposed to be on its arms. In CoaDE, this engine, unfortunately, is not yet represented.

Power industry


Different systems of a ship need electrical energy to function, and in space there are several ways to get it.

Solar batteries are very widely used now, but will only make sense in a situation of a future imaginary space conflict as an emergency option. First, they are large, fragile and produce little electricity. For example, MKS solar panels have a total area of ​​3200 m2, but produce no more than 120 kW. Secondly, the amount of energy coming from the Sun obeys the inverse square law, and, for example, in Jupiter’s orbit, which is five times farther from the Sun than the Earth, the same solar panel can produce 25 times less electricity. It is not surprising that they are not in CoaDE.

Fuel cells convert hydrogen and oxygen into water and electricity. This is very convenient for flights lasting 2-3 weeks, so they were put on the Apollo and Space Shuttles. But for the scenario of months-long flights, they are not suitable.

Radioisotope thermoelectric generators are actively used in modern cosmonautics where there are not enough solar batteries and long work is required. The principle of their work is very simple - an isotope with a short half-life, for example, plutonium-238, decays naturally, releasing heat that is supplied to the thermocouple - two metals that produce electricity on the temperature difference.



RTGs are good in that they can work for decades (and work, they have been operating on Voyagers for 40 years) and do not require any control, but have very low efficiency, require expensive fuel, and make sense only for low power. Real RTGs are usually no more powerful than hundreds of watts, in CoaDE, generators are no more powerful than tens of kilowatts, otherwise they become too heavy.


In CoaDE, RTG is separately designed, separately - radiators for heat dissipation

And only nuclear reactors can provide power levels and energy densities suitable for combat in space. In an extremely simplified form, they work like this: in the decay of some heavy atoms, neutrons are released. These neutrons can be sent to other atoms and cause their decay with the release of heat and new neutrons. Moving in the reactor absorbers and neutron reflectors, you can get a controlled nuclear reaction with the release of a huge amount of heat. Then this heat can be sent to some heat engine to convert it into electricity. There are many ways of converting - turbines, Stirling engines, thermoelectric, thermionic, thermophotovoltaic converters and others.


Kilopower Reactor Recently Tested

In real cosmonautics, atomic reactors were used in the USSR, which launched more than three dozen radar reconnaissance satellites with the BES-5 Buk nuclear reactor


Model of BES-5 “Buk”, on the left, reactor, on the right, heat exchange system radiators

With a mass of 900 kg "Buk" had a thermal power of 100 kW and an electric 3 kW. Later, in two flights, a Topaz-1 reactor with a thermal power of 150 kW and an electric 6 kW was tested.

In CoaDE, an atomic reactor is the main source of energy. Only a thermoelectric generator (thermocouple) is available as a heat engine. There are only two circuits in the reactor, in the first the coolant transfers heat from the reactor to the thermocouple, in the second it removes heat from the thermocouple to the radiator.



An interesting effect arises when manipulating the temperature at the outlet of the thermocouple. The greater the temperature difference, i.e. the lower the output temperature, the higher the efficiency of the thermocouple. But the lower the output temperature, the greater the area and mass of radiators required, because the efficiency of radiation of heat is proportional to the first degree of area, but the fourth degree of temperature. As a result, the output temperature below 1000 degrees Kelvin does not make sense - the radiators are becoming too heavy. And above 2500 K they cannot be made because even the most heat-resistant materials start to lose strength.

Thermoregulation




Pictured is the International Space Station. Red arrows indicate heat exchange system radiators. Their total area is about 470 m2, and they can take only 70 kW of heat, because they operate at a low temperature.



And this is one of the heaviest ships from the default set in CoaDE, on the left there are radiators of residential compartments operating at low temperatures and not luminous, on the right, radiators on silicon carbide shine brightly, removing heat from reactors and lasers and having a temperature above 1000 K.

But perhaps such large glowing panels will not be used in the future. In a real space program, active work is underway to create droplet radiators, where instead of a radiating surface, a stream of droplets of a minimally evaporating liquid under vacuum conditions flies between the generator and receiver. Such radiators are better because the flow of droplets has a much larger radiating surface, and the radiator will weigh several times less. Models have already been tested on the “World” and the ISS, and they may appear in space in the coming decades.


Photos of experiments with drip refrigerators in zero gravity

Weapons and armor - in the next section

Source: https://habr.com/ru/post/412121/

More articles:


All Articles