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Since the beginning of the Space Age there have been several types of propulsion used for spacecraft. The first propulsion system used for any craft was solid fuel. However, with the advent of the liquid fuel rocket in the early twentieth century, the majority of space craft launched were powered by liquid state propulsion systems. However, this is not the complete picture. Propulsion also plays an important role long after a spacecraft leaves the Earth’s atmosphere. Due to the unique conditions of space propulsion plays various roles from helping artificial satellites with attitude control, to docking with space stations, and helping deep space probes maintain course. There is also the research being done to find more powerful and efficient propulsion systems that will make it possible to explore more of space in the future.
Currently the most dominant form of propulsion used in modern space programs is liquid fuel rockets. These engines rely on fuels, like oxygen, hydrogen, or hydrazine to create thrust and propel spacecraft to their designated locations. Solid fuel propulsion is another type used; however, this is now only found in use for booster rockets for craft like the U.S. space shuttle.
Further research into improving the efficiency of different propulsion systems has produced other interesting advances. One of them being put into use is the ion engine. Rather than use combusted fuel to create thrust, the ion engine use accelerated ionized gas or plasma. This system is more efficient in its use of propellant and is good for long voyages. For this reason it is used for satellites and probes sent out into space. The only downside is that ion engines don’t produce the same amount of thrust as conventional systems; however, that doesn’t diminish the important role they play. This helps satellites correct their orbital path to keep from crashing to Earth. They also help to keep space probes on course.
Scientists are still looking for new ways to propel spacecraft especially as space programs like NASA start looking to planning missions to Mars. Some of the ideas being considered represent using some of the most powerful sources of energy available. One idea being developed is a nuclear rocket. It works by using the heat of a nuclear reaction to heat a propellant gas to create thrust. This produces greater amounts of thrust than traditional propulsion systems, but there are issues with the high temperatures being produced melting the engine. Another option being considered is solar sails. The craft would use the concept of sail ships but instead of wind it would capture the energy particles of solar winds for propulsion.
Whatever new propulsion system is eventually adopted it will draw from the combined knowledge and research that has given us our modern space program.
IF you enjoyed this article there are several others on Universe Today that you might enjoy. First there is an interesting article about the Dawn Spacecraft. There is also another interesting article that talks more about Ion Engines.
There are also great resources on the web. There is an interesting article on the European Space Agency site about the benefits and limitations of electric propulsion. There is also another great article on the NASA website about VASIMIR, an experimental propulsion system using plasma.
You can also listen to Astronomy Cast to learn more about propulsion systems. Episode 145 on Interstellar travel is a good episode if you want to learn about new types of propulsion being considered.