| A rocket is a vehicle, missile or aircraft | | | | use steam rockets for interplanetary |
| which obtains thrust by the reaction to the | | | | transport using either nuclear or solar |
| ejection of fast moving fluid from within a | | | | heating as the power source to vaporize water |
| rocket engine. | | | | collected from around the solar system. |
| | | | |
| Overview | | | | Rockets where the heat is supplied from other |
| | | | than the propellant, such as steam rockets, |
| Uses | | | | are classed as external combustion engines. |
| | | | Other examples of external combustion rocket |
| In military use, rockets generally use solid | | | | engines include most designs for nuclear |
| propellant and are unguided. Rockets equipped | | | | powered rocket engines. Use of hydrogen as |
| with warheads (representing a form of | | | | the propellant for external combustion |
| missile) can be fired by ground-attack | | | | engines gives very high velocities. |
| aircraft at fixed targets such as buildings, | | | | |
| or can be launched by ground forces at other | | | | Rockets must be used when there is no other |
| ground targets. During the Vietnam era, there | | | | substance (land, water, or air) or force |
| were also air-launched unguided rockets that | | | | (gravity, magnetism, light) that a vehicle |
| carried a nuclear payload designed to attack | | | | may employ for propulsion, such as in space. |
| aircraft formations in flight. In military | | | | In these circumstances, it is necessary to |
| terminology, the word missile is often | | | | carry all the propellant to be used. |
| preferred over rocket when the weapon uses | | | | |
| either solid or liquid propellant, and has a | | | | Delta-v |
| guidance system. (This distinction generally | | | | |
| does not apply to civilian or orbital launch | | | | Delta-v is the theoretical total gain in |
| vehicles.) | | | | speed that a rocket can achieve without any |
| | | | external interference (without air drag or |
| Rockets remain the only way to leave the | | | | gravity or other forces). |
| Earth and are used to launch into orbit, to | | | | |
| rapidly accelerate vehicles, to change | | | | Due to their high exhaust velocity (mach |
| orbits, to de-orbit for landing, or for | | | | ~10+), rockets are particularly useful when |
| landing especially if there is no atmosphere, | | | | very high speeds are required, such as |
| e.g., for landing on the Moon, and sometimes | | | | orbital speed (mach 25). The speeds that a |
| to soften a hard parachute landing | | | | rocket vehicle can reach can be calculated by |
| immediately before touchdown (see Soyuz | | | | the rocket equation; which gives the speed |
| spacecraft). | | | | difference ("delta-v") in terms of the |
| | | | exhaust speed and ratio of initial mass to |
| Operation | | | | final mass ("mass ratio"). |
| | | | |
| In all rockets, the exhaust is formed from | | | | The mass ratios that can be achieved with a |
| propellant, which is carried within the | | | | single set of fixed rocket engines and |
| rocket prior to its release. Rocket thrust is | | | | tankage varies depends on acceleration |
| due to the action of accelerating the exhaust | | | | required, construction materials, tank |
| to very high speeds causing an equal and | | | | layout, engine type and propellants used, but |
| opposite reaction on the vehicle. | | | | for example the first stage of the Saturn V |
| | | | was able to achieved about a mass ratio of |
| Types | | | | 10. |
| | | | |
| There are many different types of rockets, | | | | Staging |
| and a comprehensive list can be found in | | | | |
| rocket engine  they range | | | | Often, the required velocity (delta-v) for a |
| in size from tiny models such as water | | | | mission is unattainable by any single rocket |
| rockets or small solid rockets that can be | | | | because the propellant, structure, guidance |
| purchased at a hobby store, to the enormous | | | | and engines weigh so much as to prevent the |
| Saturn V used for the Apollo program. | | | | mass ratio from being high enough. |
| | | | |
| Most current rockets are chemically powered | | | | This problem is frequently solved by staging |
| rockets (internal combustion engines) that | | | |  the rocket sheds excess |
| emit a hot exhaust gas. A chemical rocket | | | | weight (usually tankage and engines) during |
| engine can use solid propellant (see Space | | | | launch to reduce its weight and effectively |
| Shuttle's SRBs), liquid propellant (see Space | | | | increase its mass ratio. |
| shuttle main engine), or a hybrid mixture of | | | | |
| both. A chemical reaction is initiated | | | | Typically, the acceleration of a rocket |
| between the fuel and the oxidizer in the | | | | increases with time (if the thrust stays the |
| combustion chamber, and the resultant hot | | | | same) as the weight of the rocket decreases |
| gases accelerate out of a nozzle (or nozzles) | | | | as propellant is burned. Discontinuities in |
| at the rearward-facing end of the rocket. The | | | | acceleration will occur when stages burn out, |
| acceleration of these gases through the | | | | often starting at a lower acceleration with |
| engine exerts force ("thrust") on the | | | | each new stage firing. |
| combustion chamber and nozzle, propelling the | | | | |
| vehicle (in accordance with Newton's Third | | | | Vehicles |
| Law). See rocket engine for details. | | | | |
| | | | Rockets as a group have the highest thrust |
| Not all rockets use chemical reactions. Steam | | | | weight ratio of any type of engine; and this |
| rockets, for example, release superheated | | | | helps vehicles achieve a high mass ratios, |
| water through a nozzle where it instantly | | | | which improves the performance of flight. |
| flashes to high velocity steam, propelling | | | | |
| the rocket. The efficiency of steam as a | | | | Common mass ratios for vehicles are 20:1 for |
| rocket propellant is relatively low, but it | | | | dense propellants such as liquid oxygen and |
| is simple and reasonably safe, and the | | | | kerosene, 25:1 for dense monopropellants such |
| propellant is cheap and widely available. | | | | as hydrogen peroxide, and 10:1 for liquid |
| Most steam rockets have been used for | | | | oxygen and liquid hydrogen. However, mass |
| propelling land-based vehicles but a small | | | | ratio is highly dependent on many factors |
| steam rocket was tested in 2004 on board the | | | | such as the type of engine the vehicle uses |
| UK-DMC satellite. There are even proposals to | | | | and structural safety margins |