This explains why a rocket works in space but a turbine engine or a propeller does not work. There are two main categories of rocket engines; liquid rockets and solid rockets. In a liquid rocket, the propellants , the fuel and the oxidizer, are stored separately as liquids and are pumped into the combustion chamber of the nozzle where burning occurs. In a solid rocket, the propellants are mixed together and packed into a solid cylinder.
Under normal temperature conditions, the propellants do not burn; but they will burn when exposed to a source of heat provided by an igniter. Once the burning starts, it proceeds until all the propellant is exhausted.
With a liquid rocket, you can stop the thrust by turning off the flow of propellants; but with a solid rocket, you have to destroy the casing to stop the engine.
More fuel means more weight, which adds to the cost of a mission. To save on money when shooting for far-away planets such as Jupiter, some spacecraft whip around a planet say, Venus and use its gravity to get a speed boost.
This shortens the time it takes to get to other destinations. A large fraction of the rocket engines in use today are chemical rockets; that is, they obtain the energy needed to generate thrust by chemical reactions to create a hot gas that is expanded to produce thrust.
A significant limitation of chemical propulsion is that it has a relatively low specific impulse, which is the ratio of the thrust produced to the mass of propellant needed at a certain rate of flow.
Historically, these propellants have not been applied beyond upper stages. Furthermore, numerous concepts for advanced propulsion technologies, such as electric propulsion, are commonly used for station keeping on commercial communications satellites and for prime propulsion on some scientific space missions because they have significantly higher values of specific impulse. However, they generally have very small values of thrust and therefore must be operated for long durations to provide the total impulse required by a mission.
Julian Dimitrov, Herts. Reaction forces do indeed work in a vacuum. Spacecraft are usually equipped with a reaction control system RCS. These are typically located in specific locations around the exterior of the spacecraft to allow for its orientation to be changed. Often, spacecraft also have a larger main rocket engine that is used to raise or lower its orbit or change its orbital plane, known as vectoring. Imagine two astronauts floating next to one another inside the spacecraft.
If one astronaut were to push the other, both astronauts would move away from their original positions in opposing directions at the same speed assuming they were of the same mass. When an RCS thruster or main engine is ignited, the resultant gas is forced at very high speed out of the engine bell or thruster. The movement of this gas from the spacecraft is what provides the reaction force to propel it in the opposite direction. Once a roll, pitch or yaw manoeuvre has been initiated by burning an RCS thruster, the spacecraft will continue to move along the axis of the thruster even after it stops its burn.
Already a subscriber? Want more? More From Discover. Recommendations From Our Store. Stay Curious. View our privacy policy. Website Accessibility.
0コメント