Heaters of engines

Spaceships need thrust and propulsion to reach space and also to change course in space. How do you free yourself from the Earth's gravity, what are the types of fuel that are useful in space and what do you do to keep the spacecraft on track? That's how you speed it up

Written by: Ariel Keres, young Galileo
If you like sci-fi movies about space adventures, you've probably noticed how easy it is to get around up there. It seems that the question of the propulsion of satellites or an interstellar vehicle in space is rather marginal in these films. In the "Star Trek" movies, for example, the members of the Enterprise crew jump from planet to planet with the help of "warp drive"; This allows them to move through space at a speed higher than the speed of light. In the movie "Interstellar", which was released in 2014, a "wormhole" is quite convincingly described - a kind of tunnel in space-time through which one can quickly pass from one part of the universe to another, which is thousands of light years away.

But we live in reality and not in a movie: superspace propulsion and wormholes are currently only theoretical assumptions, and there is no known way to use them for movement in space. The movie "Saving Mark Watney" that was released a few months ago is a bit more realistic: it deals with the survival of a man who is left alone on the planet Mars. Although the technology in the film is contemporary or almost contemporary, there are some more or less intentional inaccuracies in it - for example the length of the mission of Watney and his team. A mission to Mars is planned according to "launch windows". The launches will be carried out when the Earth and Mars are as close as possible to each other, according to their orbits around the Sun. Such an event occurs every 26 months, and therefore the people who reach the Red Planet will stay on it for about 500 days, and not 39 days as in the mission described in the film.

Although the propulsion capabilities developed by man are impressive, they still do not justify a stay on Mars for such a short time, considering the huge investment involved in the launch and relative to the benefit derived from such a short stay. Besides that, after a stay of less than six weeks, the return to the Earth, which is receding and going in its orbit, will also be very long because the spacecraft will have to "chase" it.

How do you feel in space?
As you probably understand by now, when it comes to changing direction or trajectory, navigation in space is a complicated and expensive matter - whether it's spacecrafts that reach great distances or whether it's satellites remaining near the Earth. The scientists, engineers and engine designers have been working for many years on planning and developing powerful engines that will also be light and fuel efficient. The following five questions examine how it is possible to reach space and change its direction and speed.

1 # I want to reach space. How do you do it?
If you throw a stone up, it will return to the ground after a short time because the earth pulls it by gravity (be careful not to hit your head). In order to fly into deep space and also to place satellites in orbit around the Earth, despite the force of gravity, an enormous propulsive force is required. "In order to reach space, launchers are needed - powerful aircraft that can reach very high speeds in order to overcome the Earth's gravity," explains Menachem Kidron, director of the Israel Space Agency. "In a ground launch, i.e. from land or ship, you start at zero speed and you have to reach a speed that will allow you to stay in orbit or escape - release from the Earth's gravity. The escape velocity, which enables flight into deep space, is 11.2 kilometers per second. When launched from an airplane, the initial speed of the airplane already exists, flying at an altitude of tens of kilometers. That's why we need engines with a lot of power." If you free yourself from the Earth's gravity, you can continue into deep space, let's say to the Moon or Mars.

2 # What will give me sufficient energy to free myself from the weight of the earth?
"Propulsion when leaving the Earth into space is done with the help of liquid fuel or solid fuel," says Kidron. "Each type of drive has advantages and disadvantages. In liquid fuel propulsion, very large launchers are used, in which oxygen and hydrogen 'meet' and create a lot of energy and tremendous thrust when they ignite. When the oxygen and hydrogen are burned, gases are created under enormous pressure; These come out of the back of the vehicle and propel the rocket or spacecraft into the sky. There is a tank of oxygen and a tank of hydrogen, and a system of pumps and pipes that flow them in optimal ratios. The hydrogen and oxygen are kept under very high pressure so that they remain in a liquid state. This method already worked with the launch of the first satellite - Sputnik - into space in 1957. Its advantage is the high energies it produces and the possibility to start and stop the flow of gases to the engine whenever you want. The launch was carried out in stages, from the big to the small. Only one engine would be a waste because it is very big and heavy. That's why each stage has its own engine, and each stage is easier than the previous stage. Throw away what has finished working and get rid of its weight. The disadvantage of driving with liquid fuel is that hydrogen and oxygen are flammable and very dangerous gases and must be well controlled, otherwise fatal accidents can happen."

3 # Liquid fuel can be dangerous. Does he have a replacement?
"Another possibility for propulsion in space is the use of solid fuel," says Menachem Kidron. "Solid fuel is a type of polymer (a substance made of huge molecules that are made up of repeating structural units, like a chain made of beads) that is mixed with granules of an oxidizing agent. Everything together looks a bit like rubber - a viscous material. The advantages of the solid fuel are many: it produces more energy per unit volume, it is less flammable than the liquid fuel and less dangerous than it, and it requires much less pipes and pumps, which means much less weight. The solid fuel is very effective when you need strong and immediate acceleration. Its disadvantage is that it is impossible to stop the operation after it has started and then start it again, so the entire process, and in fact the entire journey into space, must be planned in advance." The space shuttles, for example, used liquid fuel as well as solid fuel.

4 # How do you keep track in space?
So we managed to mobilize (with the help of liquid fuel, solid fuel or both) a strong thrust that launched us into space. A little more acceleration, and here we are - we have placed our satellite in its orbit. But the satellite may lower slowly and eventually crash. A satellite needs the ability to regulate its trajectory, otherwise it will not be possible to use it for a long time. How do you keep it on track up there?
"Satellites sometimes have to move from a high orbit to a low orbit, correct an orbit or turn around so that they face the sun," explains Kidron. "The means of propulsion are chemical and electrical. In space you don't need a strong thrust because there is no resistance. Chemical propulsion is done using hydrazine - a liquid substance that is a compound of nitrogen and hydrogen - and creates thrust. An electric drive is an engine that uses xenon gas that is injected into an electric field. The gas atoms are turned into ions (electrically charged particles) and you get plasma. The ions of the gas are pushed out and provide thrust. The advantage of such engines is that they are small and light, and this allows more research and commercial equipment to be placed on the satellite. Their disadvantage is little drive, and thus moving from one place to another may take a long time," says Kidron. The Israeli-French Venus satellite, which will be launched into space in 2016, will use this propulsion method in space.

5 # Are there other options for propulsion in space?
In recent years, certain projects have begun to use a solar sail. A solar sail is a huge surface (its length can reach half a kilometer) that spreads out in space. The sun's radiation pushes him like a wind pushes a sailboat. Such sails provide a very low, but inexhaustible thrust. The disadvantage is the need to launch the spacecraft or the satellite with the solar sail folded inside it, so the sail must be very light and thin. It must also be strong - because all kinds of particles moving around in space can damage it and destroy it. Apart from that, the sun's radiation comes from only one direction, so even the vehicle powered by a solar sail will be able to move in only one direction - from the sun onwards.

In the near future (perhaps as early as this year, 2016), magneto-plasma drive motors with a variable specific impulse - or VASIMR for short - will be put into use, and have been under development for many years. Such an engine is based on the use of radio waves to ionize and heat excess gas, and accelerates the hot product to the exhaust nozzle using strong magnetic fields (heating using radio waves is somewhat similar to the operation of the microwave in your home). If this reminds you of the ion propulsion method mentioned in Kidron's words, you are right - except that, unlike normal ion propulsion, Vasimer propulsion is supposed to achieve a much stronger thrust; This would translate to a very high speed of flight in space. Other advantages of this type of engine are good control of thrust strengths and low wear, i.e. higher durability than that of contemporary ion engines. The Vazimer engine has no pumps, pipes and moving parts, and is therefore lighter, and therefore easier to maneuver. Its disadvantages are a low thrust-to-weight ratio. Apart from that, it is necessary to control the strong magnetic fields and the great heat generated in them. The problems that Wazimer engines pose to scientists will probably necessitate the installation of small nuclear reactors on spacecraft powered by these engines. And yet, perhaps we are finally faced with the solution for a short trip to Mars, including a stay of less than 39 days, and thus it will be possible to save Mark Watney not only in the movie, but also in reality.

Leads:
Unlike a normal ion drive, the Wasimer drive should achieve a strong thrust; This would translate to a very high speed of flight in space. Other advantages of this type of engine are good control of the thrust strengths and low wear, which means higher durability than that of contemporary ion engines
The advantages of the solid fuel are many: it produces more energy per unit volume, it is less flammable and less dangerous, and it requires much less pipes and pumps, which means much less weight. The solid fuel is very effective when you need strong and immediate acceleration. Its disadvantage is that you cannot stop the operation after it has started and then start it again

Did you know?
Worm Hole: is an assumed physical phenomenon that results from the calculations of general relativity and quantum mechanics. The wormhole - a kind of tunnel in the universe - may connect two points distant from each other in space-time. The scientists believe that if a wormhole did form, it is not large enough for the passage of atoms, and therefore the plans to transport spaceships through it are probably a bit exaggerated.

The article was published in the January issue of Young Galileo – Monthly for curious children

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