👩🏿‍🤝‍👨🏾 🎯 🤜🏾 Space power 💅🏽 🏉 🈲

Half a century ago, the Soviet scientist Nikolai Kardashev formed a scale in which the level of development of civilization was determined by the amount of energy used. The approach is very logical - when mankind mastered the energy of horses, coal, oil and nuclear decay - each time it rose to a new level of power. Space exploration depends not only on the ability to put a satellite into orbit, but also on technologies that enable it to function. And providing spacecraft with energy is one of the most important facets of astronautics. What methods did people come up with?

Artist James Vaughan

Formulation of the problem

In the problem of power supply of a spacecraft, two criteria can be distinguished, which make it possible to visually distribute various approaches. It is power and duration. Indeed, it is logical that some technical solutions are used for the “many, but not for long” task, and others for “for decades, even if only a little.” If you take these criteria as the axis of the graph, you get the following picture:

Spacecraft Power Systems , David W. Miller, John Keesee

The first satellite went on a flight with charged silver-zinc batteries, which provided a “beep-beep” transmitter for 21 days. The solution was logical - the experimental solar panels were waiting in line at the D facility, which became Sputnik-3 (launched May 15, 1958). Silver-zinc batteries, due to their high energy density and high discharge currents, are widely used in astronautics, and their drawback is that the small number of recharge cycles is unimportant when the battery is used once. An interesting metamorphosis occurred with the Soyuz ship - the first ships flew with solar panels, on the 7K-T modification (Soyuz-10 - Soyuz-40, except for -13, -16, -19, -22) they were removed, leaving only batteries with a power reserve for two days, and with the next modification of “-TM” the solar panels were returned again and already permanently.Until now, batteries remain a rational solution for devices that will last no longer than a few days and do not require large amounts of electricity. Sometimes even non-rechargeable elements are put on the devices, for example, the MASCOT jumping probe, dropped from the interplanetary station Hayabusa-2 onto the Ryugu asteroid, used lithium-thionyl chloride elements, which lasted for 16 hours. But rechargeable elements are more common, it is more convenient to work with them, because, if necessary, they can be recharged before starting without disassembling the device. Due to its high characteristics, lithium-ion cells are now very widely used not only in household appliances, but also on spacecraft.which will work no longer than a few days and do not require large amounts of electricity. Sometimes even non-rechargeable elements are put on the devices, for example, the MASCOT jumping probe, dropped from the interplanetary station Hayabusa-2 onto the Ryugu asteroid, used lithium-thionyl chloride elements, which lasted for 16 hours. But rechargeable elements are more common, it is more convenient to work with them, because, if necessary, they can be recharged before starting without disassembling the device. Due to its high characteristics, lithium-ion cells are now very widely used not only in household appliances, but also on spacecraft.which will work no longer than a few days and do not require large amounts of electricity. Sometimes even non-rechargeable elements are put on the devices, for example, the MASCOT jumping probe, dropped from the interplanetary station Hayabusa-2 onto the Ryugu asteroid, used lithium-thionyl chloride elements, which lasted for 16 hours. But rechargeable elements are more common, it is more convenient to work with them, because, if necessary, they can be recharged before starting without disassembling the device. Due to its high characteristics, lithium-ion cells are now very widely used not only in household appliances, but also on spacecraft.used lithium thionyl chloride elements, which lasted for 16 hours. But rechargeable elements are more common, it is more convenient to work with them, because, if necessary, they can be recharged before starting without disassembling the device. Due to its high characteristics, lithium-ion cells are now very widely used not only in household appliances, but also on spacecraft.used lithium thionyl chloride elements, which lasted for 16 hours. But rechargeable elements are more common, it is more convenient to work with them, because, if necessary, they can be recharged before starting without disassembling the device. Due to its high characteristics, lithium-ion cells are now very widely used not only in household appliances, but also on spacecraft.

MASCOT Hayabusa-2

If energy is required a lot, but for a short time, it makes sense to use chemical sources. For example, on the space shuttles were the so-called APUs. Despite the completely identical name with the auxiliary power plant on airplanes, these were specific devices. Chemical fuel was burned in the combustion chamber (hydrazine-based fuel and nitrogen tetroxide), hot gas was supplied to the turbine, and its rotation created pressure in the shuttle's hydraulic system without intermediate conversion of energy into electricity. Hydraulics turned the control surfaces of the orbiter at the stages of launching into orbit and landing. It is curious that now the energy density of lithium-ion batteries has reached such values that the Electron launch vehicle has appeared,in which a turbopump unit (a device for supplying fuel to the engine) performing a similar function was replaced with an electric pump with a battery pack. Losses on a larger mass of batteries were compensated by the simplicity of development.

Fuel cells

Space shuttle fuel cell

If the duration of a space flight does not exceed two to three weeks, then, especially for manned spacecraft, the so-called fuel cells become very attractive. As you know, hydrogen burns in oxygen with the release of a huge amount of heat, and rocket engines using this are among the most efficient. And the ability to directly receive electricity from a combination of hydrogen and oxygen has generated sources of electricity, which, by the way, are used not only in astronautics.

A fuel cell works as follows: hydrogen enters the anode, becomes a positively charged ion and gives off an electron. At the cathode, hydrogen ions receive electrons, combine with oxygen molecules and form water.

By connecting several cells and supplying more components, it is easy to obtain a high power fuel cell. And the water released as a result of work can be used for the needs of the crew. The combination of properties determined the choice of fuel cells for the Apollo ships (and, by the way, for the lunar versions of the Unions, they too were originally chosen), shuttles and Buran.

It is worth noting that fuel cells can theoretically be reversible, dissociating water for hydrogen and oxygen, storing electricity and working, in fact, like a battery, but in practice such solutions in astronautics are not yet in demand.

Named sun

Life on Earth is impossible without solar energy - plants grow in the light, and energy goes further along the food chain. And for astronautics, the Sun immediately became regarded as an accessible and free source. The first satellites with solar panels, Vanguard-1 (USA) and “Sputnik-3” (USSR), went on a flight already in 1958.

The beauty of solar panels is the direct conversion of light into electricity - photons falling on semiconductors directly cause the movement of electrons. By connecting the cells in series and in parallel, the required voltage and current values can be obtained.

In space conditions, the compactness of solar panels is very important, for example, the huge “wings” of the ISS are made of very thin panels, which were folded in the transport position with an accordion.

Video disclosure of ISS panels

Until now, solar panels remain the best option if it is necessary to supply spacecraft with energy for years. But, of course, they, like any other solution, have their drawbacks.

First of all, in low Earth orbit, the satellite will constantly go into the shadow of the Earth, and it is necessary to supplement the panels with batteries so that the power supply is continuous. Batteries and the additional area of solar panels for charging them on the sunny side of the orbit significantly increase the mass of the satellite’s electrical system.

Further, the power of solar radiation obeys the inverse square law: Jupiter is 5 times farther than the Earth, but in its orbit a spacecraft with the same solar panels will receive 25 times less electricity.

Solar panels are gradually degrading under conditions of cosmic radiation, so their area should be calculated with a margin for long missions.

A linear increase in the mass of solar panels with an increase in the required power at some point makes them too heavy compared to other systems.

Alternative to batteries

If you read Nurbey Gulia’s wonderful book “In Search of an Energy Capsule”, you may remember that after a long search for the ideal battery, he settled on the flywheels modified for safe destruction. Now with the successes of lithium-ion batteries, this topic is less interesting, but experiments on storing energy in an untwisted flywheel were also carried out in space. In the early 21st century, Honeywell conducted experiments with flywheels, accumulators. Theoretically, this direction can also be interesting because flywheels are used in the satellite’s orientation system, and it is possible to combine modes of maintaining the required position in space and storing energy.

Concentrate it

Even at the stage of developing the concept, it was obvious that the Freedom station (after numerous changes implemented as the ISS) would need a lot of electricity. And the calculations of 1989 showed that the solar collector will be able to save from 3 to 4 billion dollars (6-8 billion in today's prices) in comparison with the power supply only from solar panels. What are these designs?

One of Freedom's earliest designs. Hexagon

constructions around the edges are solar concentrators. Mirrors form a paraboloid that collects sunlight on a receiver located in focus. In it, the coolant boils, the gas turns the turbine, which generates electricity. The panel next to it is a heat radiator in which the coolant condenses back into the liquid.

Unfortunately, the design, like many ideas for the Freedom station, fell victim to budget cuts, and the ISS uses only solar panels, so we can’t in practice find out if the cost savings were met. It is worth noting that solar collectors are also used on Earth, but they are distributed in the simplest form without concentrating mirrors - their drives greatly increase the cost.

Heat and electricity

When the Sun shines brightly overhead, one cannot believe in cosmic cold. Indeed, on the lit side of the moon, the temperature rises above 100 ° C. But on a moonlit night, the surface cools below -100 ° C. On Mars, the average temperature is around -60 ° C. And in the orbit of Jupiter, as we have said, the Sun gives only 1/25 of what goes to the Earth. And, fortunately for planet rovers and interplanetary stations, there is an option in which the spacecraft’s heating and power supply are conveniently provided.

As you know, the same substance can have many isotopes - atoms, differing only in the number of neutrons in the nucleus. And there are both stable and isotopes decaying at different speeds. Having picked up an element with a convenient half-life, you can use it as an energy source.

One of the most popular isotopes is ²³⁸ Pu (plutonium-238). One gram of pure plutonium-238 generates approximately 0.5 watts of heat, and a half-life of 87.7 years means that there will be enough energy for a long time.

The fact that nuclear decay releases heat means that it must be somehow turned into electricity. For this, a thermocouple is most often used - two different metals fused together generate electricity when heating is uneven. The combination of an energy source in the form of decaying radioactive isotopes and thermoelectric converters gave the name “radioisotope thermoelectric generator” or RTG.

RTG scheme

RTGs are widely used in astronautics: they generated electricity for modules of scientific equipment left on the moon by Apollo astronauts, Soviet Lunokhods were heated by the decay of isotopes, Martian Viking stations worked on electricity from RTGs and traveled along Mars Curiosity. RTGs are a regular source of electricity for devices traveling to the external solar system - “Pioneers”, “Voyagers”, “New Horizons” and others.

RTGs are very convenient in that they do not require any control, do not have moving parts and are able to work for decades - the Voyagers have remained operational for more than forty years, despite the need to turn off part of the equipment due to reduced electricity generation. Unfortunately, they also have a drawback - low energy density (a powerful RTG will weigh too much) and the high price of fuel. The shutdown of plutonium-238 production in the USA and rising prices influenced the fact that the interplanetary station “Juno” went to Jupiter with huge solar panels.

Nuclear technologies are sure to raise safety issues, and RTGs have long had established technologies for its support. After 1964, when the accident of an American carrier rocket with a satellite powered by an RTG led to a noticeable increase in the radiation background throughout the planet, the RTGs were packed into capsules that could withstand a fall in the atmosphere, and subsequent accidents did not leave any noticeable marks.

The complexity of the transformations

A thermoelectric generator is not the only option for converting heat to electricity. In thermionic converters the cathode of a vacuum lamp is heated. Electrons “jump” to the anode, creating an electric current. Thermoelectric converters convert heat into infrared light, which is then converted into electricity similar to a solar panel. A thermoelectric converter based on alkali metals uses an electrolyte made from sodium and sulfur salts. The Stirling engine converts the temperature difference into motion, which is then converted into electricity by a generator.

Overhead reactors

Of all the controlled energy sources known to mankind, nuclear fuel has the highest density - one gram of uranium is capable of producing as much energy as 2 tons of oil or three tons of coal. Therefore, it is not surprising that nuclear reactors are a promising option when it is necessary to supply a large amount of energy to a spacecraft for a long time.

Left American SNAP, right Soviet "Buk"

Work on space reactors began back in the 1960s. The first to go into space was the American SNAP-10A, worked in orbit for 43 days and was shut down due to an accident not related to the reactor system. After that, the USSR took over. US-A satellites designed to track the movement of American aircraft carrier strike groups, Legenda targeting systems carried the Buk nuclear reactor on board to provide energy to the active radar system, and more than three dozen of them were launched. In the late 80s, the Topaz reactor flew into space two times, using less nuclear fuel and having greater efficiency - 150 kW of thermal power “Topaz” produced 6 kW electric versus 100 and 3 for Buk. This was achieved including the use of another energy converter - thermionic instead of thermoelectric.But after 1988, satellites with nuclear reactors on board no longer flew.

The revival of interest in nuclear reactors occurred in the 21st century. In the West, this is due to a decrease in stocks and an increase in the price of plutonium-238 for RTGs. In the USA, the Kilopower reactor is being developed, the task of which will become an analog of the RTG. An interesting feature is that the reactor is designed self-regulating and, after activation, like RTGs, does not require supervision. In Russia, a megawatt-class nuclear installation project is being developed. In combination with electric propulsion engines, a design with fundamentally new capabilities, a very efficient orbital tug, should be obtained.

Reactor safety is based on other principles than RTGs. Before starting, the reactor is clean (uranium is toxic, but it can be safely taken with gloves on), therefore, in case of an accident, on the contrary, gas generators are installed that reliably destroy it in dense layers of the atmosphere. But after switching on, dangerous isotopes begin to accumulate in the reactor, and Soviet US-A satellites in the event of an accident took the reactor to a high burial orbit. The muffled reactors still fly over our heads, but, given the lifetime of the orbits, the space scavengers of the future will sooner reach them and take them to useful resources than they will burn up in the atmosphere.

Cable Generator

As you know, the Earth has a magnetic field. It is already being used in spacecraft orientation systems, but there is another option. If you unwind a long cable, you can either get electricity by braking the device, or accelerate by passing current through the cable.

The forces acting on the satellite that released the conductive cable

So far, the idea of braking devices with cables to reduce the amount of space debris has received the most development, but it is technically possible to provide power to the satellite in this way, albeit not for a very long time.

Conclusion

Now the spacecraft power supply industry is actively developing. Solar panels and batteries are becoming more efficient, and the resumption of work on space nuclear reactors gives hope for the emergence of new powerful sources of electricity.

Material prepared for the portal "N + 1" .

Space power