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## PowerPedia:Spacecraft propulsion

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Spacecraft propulsion is used to change the velocity of There was an error working with the wiki: Code[1].

All current spacecraft use chemical rocket (There was an error working with the wiki: Code[2] or There was an error working with the wiki: Code[3]) for launch, though some (such as the There was an error working with the wiki: Code[4]. Most satellites have simple reliable chemical rockets (often There was an error working with the wiki: Code[42]s) or There was an error working with the wiki: Code[43]s to keep their station, although some use There was an error working with the wiki: Code[44]s for There was an error working with the wiki: Code[45]. Newer geo-orbiting spacecraft are starting to use electric propulsion for north-south stationkeeping. Interplanetary vehicles mostly use chemical rockets as well, although a few have experimentally used There was an error working with the wiki: Code[46]s with some success (a form of electric propulsion).

#### The necessity for propulsion systems

Artificial satellites must be There was an error working with the wiki: Code[5] into There was an error working with the wiki: Code[6] object of interest. They are also subject to There was an error working with the wiki: Code[7] from the thin There was an error working with the wiki: Code[8], so that to stay in orbit for a long period of time some form of propulsion is occasionally necessary to make small corrections (There was an error working with the wiki: Code[47]). Many satellites need to be moved from one orbit to another from time to time, and this also requires propulsion. When a satellite has exhausted its ability to adjust its orbit, its useful life is over.

Spacecraft designed to travel further also need propulsion methods. They need to be launched out of the Earth's atmosphere just as satellites do. Once there, they need to leave orbit and move around.

For There was an error working with the wiki: Code[9] along its orbit. The simplest fuel-efficient means to move from one circular orbit to another is with a There was an error working with the wiki: Code[48]: the spacecraft begins in a roughly circular orbit around the Sun. A short period of There was an error working with the wiki: Code[49] in the direction of motion accelerates or decelerates the spacecraft into an elliptical orbit around the Sun which is tangential to its previous orbit and also to the orbit of its destination. The spacecraft falls freely along this elliptical orbit until it reaches its destination, where another short period of thrust accelerates or decelerates it to match the orbit of its destination. Special methods such as There was an error working with the wiki: Code[50] are sometimes used for this final

Some spacecraft propulsion methods such as There was an error working with the wiki: Code[51]s provide very low but inexhaustible thrust an interplanetary vehicle using one of these methods would follow a rather different trajectory, either constantly thrusting against its direction of motion in order to decrease its distance from the Sun or constantly thrusting along its direction of motion to increase its distance from the Sun.

Spacecraft for There was an error working with the wiki: Code[52] also need propulsion methods. No such spacecraft has yet been built, but many designs have been discussed. Since interstellar distances are very great, a tremendous velocity is needed to get a spacecraft to its destination in a reasonable amount of time. Acquiring such a velocity on launch and getting rid of it on arrival will be a formidable challenge for spacecraft designers.

#### Effectiveness of propulsion systems

When in space, the purpose of a propulsion system is to change the velocity v of a spacecraft. Since this is more difficult for more massive spacecraft, designers generally discuss There was an error working with the wiki: Code[53], mv. The amount of change in momentum is called There was an error working with the wiki: Code[54]. So the goal of a propulsion method in space is to create an impulse.

When launching a spacecraft from the Earth, a propulsion method must overcome a higher There was an error working with the wiki: Code[10] pull to provide a net positive acceleration. In orbit, the spacecraft tangential velocity provides a centrifugal force that counterweighs the gravity pull at a given path (which is actually the orbit path) so that any additional impulse even very tiny will result in a change in the orbit path.

The rate of change of velocity is called There was an error working with the wiki: Code[55], and the rate of change of momentum is called Force. To reach a given velocity, one can apply a small acceleration over a long period of time, or one can apply a large acceleration over a short time. Similarly, one can achieve a given impulse with a large force over a short time or a small force over a long time. This means that for maneuvering in space, a propulsion method that produces tiny accelerations but runs for a long time can produce the same impulse as a propulsion method that produces large accelerations for a short time. When launching from a planet, tiny accelerations cannot overcome the planet's gravitational pull and so cannot be used.

The law of There was an error working with the wiki: Code[56] means that in order for a propulsion method to change the momentum of a space craft it must change the momentum of something else as well. A few designs take advantage of things like magnetic fields or light pressure in order to change the spacecraft's momentum, but in free space the rocket must bring along some mass to accelerate away in order to push itself forward. Such mass is called reaction mass.

In order for a rocket to work, it needs two things: reaction mass and energy. The impulse provided by launching a particle of reaction mass having mass m at velocity v is mv. But this particle has kinetic energy mv2/2, which must come from somewhere. In a conventional There was an error working with the wiki: Code[11], the fuel is burned, providing the energy, and the reaction products are allowed to flow out the back, providing the reaction mass. In an There was an error working with the wiki: Code[57], electricity is used to accelerate ions out the back. Here some other source must provide the electrical energy (perhaps a There was an error working with the wiki: Code[58] or a There was an error working with the wiki: Code[59]) while the ions provide the reaction mass.

When discussing the efficiency of a propulsion system, designers often focus on effectively using the reaction mass. Reaction mass must be carried along with the rocket and is irretrievably consumed when used. One way of measuring the amount of impulse that can be obtained from a fixed amount of reaction mass is the There was an error working with the wiki: Code[12], the acceleration due to gravity on the Earth's surface (I_{sp} g = v_{e}).

A rocket with a high exhaust velocity can achieve the same impulse with less reaction mass. However, the energy required for that impulse is proportional to the square of the exhaust velocity, so that more mass-efficient engines require much more energy. This is a problem if the engine is to provide a large amount of thrust. To generate a large amount of impulse per second, it must use a large amount of energy per second. So highly efficient engines require enormous amounts of energy per second to produce high thrusts. As a result, most high-efficiency engine designs also provide very low thrust.

##### Calculations

Burning the entire usable propellant of a spacecraft through the engines in a straight line in free space would produce a net velocity change to the vehicle this number is termed 'There was an error working with the wiki: Code[60]'.

The total \Delta v of a vehicle can be calculated using the rocket equation, where M is the mass of fuel (or rather the mass of propellant), P is the mass of the payload (including the rocket structure), and v_e is the velocity of the rocket exhaust. This is known as the There was an error working with the wiki: Code[61]:

: \Delta V = -v_e \ln \left(\frac{P}{M+P}\right)

For historical reasons, as discussed above, v_e is sometimes written as

: v_e = I_{sp} g_{o}

where I_{sp} is the There was an error working with the wiki: Code[62] of the rocket, measured in seconds, and g_{o} is the There was an error working with the wiki: Code[63] at sea level.

For a long voyage, the majority of the spacecraft's mass may be reaction mass. Since a rocket must carry all its reaction mass with it, most of the first reaction mass goes towards accelerating reaction mass rather than payload. If we have a payload of mass P, the spacecraft needs to change its velocity by

\Delta v, and the rocket engine has exhaust velocity ve, then the mass M of reaction mass which is needed can be calculated using the rocket equation and the formula for I_{sp}

: M = P \left(e^{\Delta v/v_e}-1\right)

For \Delta v much smaller than ve, this equation is roughly linear, and little reaction mass is needed. If \Delta v is comparable to ve, then there needs to be about twice as much fuel as combined payload and structure (which includes engines, fuel tanks, and so on). Beyond this, the growth is exponential speeds much higher than the exhaust velocity require very high ratios of fuel mass to payload and structural mass.

In order to achieve this, some amount of energy must go into accelerating the reaction mass. Every engine will waste some energy, but even assuming 100% efficiency, the engine will need energy amounting to

:\frac{1}{2} Mv_e^2

Comparing the rocket equation (which shows how much energy ends up in the final vehicle) and the above equation (which shows the total energy required) shows that even with 100% engine efficiency, certainly not all energy supplied ends up in the vehicle - some of it, indeed usually most of it, ends up as kinetic energy of the exhaust.

For a mission, for example, when launching from or landing on a planet, the effects of gravitational attraction and any atmospheric drag must be overcome by using fuel. It is typical to combine the effects of these and other effects into an effective mission There was an error working with the wiki: Code[64]. For example a launch mission to low Earth orbit requires about 9.3-10 km/s delta-v. These mission delta-vs are typically numerically integrated on a computer.

Suppose we want to send a 10,000 kg space probe to Mars. The required \Delta v from There was an error working with the wiki: Code[13] is approximately 3000 m/s, using a There was an error working with the wiki: Code[65]. (A manned probe would need to take a faster route and use more fuel). For the sake of argument, let us say that the following thrusters may be used:

{| border="1" cellpadding="4" cellspacing="0" style="margin: 0.5em 1em 0.5em 0 background: #f9f9f9 border: 1px #aaa solid border-collapse: collapse font-size: 95% text-align:right"

|Engine

|There was an error working with the wiki: Code[14](m/s)

|Specific impulse(s)

|Fuel mass(kg)

|Energy required(GJ)

|Energy per kgof propellant

|minimum powerper N of thrust

|-

|There was an error working with the wiki: Code[66]

|1,000

|100

|190,000

|95

|500 kJ

|0.5 kW

|-

|There was an error working with the wiki: Code[67]

|5,000

|500

|8,200

|103

|12.6 MJ

|2.5 kW

|-

|There was an error working with the wiki: Code[68]

|50,000

|5,000

|620

|775

|1.25 GJ

|25 kW

|-

|There was an error working with the wiki: Code[15]

|300,000

|30,000

|100

|4,500

|45 GJ

|150 kW

|}

Observe that the more fuel-efficient engines can use far less fuel its mass is almost negligible (relative to the mass of the payload and the engine itself) for some of the engines. However, note also that these require a large total amount of energy. For earth launch engines require a thrust to weight ratio of much more than unity. To do this they would have to be supplied with Gigawatts of power — equivalent to a major metropolitan Electricity generation. This would need to be carried on the vehicle, which is clearly impractical.

Instead, a much smaller, less powerful generator may be included which will take much longer to generate the total energy needed. This lower power is only sufficient to accelerate a tiny amount of fuel per second, but over long periods the velocity will be finally achieved. For example. it took the There was an error working with the wiki: Code[69] more than a year to reach the Moon, while with a chemical rocket it takes a few days. Because the ion drive needs much less fuel, the total launched mass is usually lower, which typically results in a lower overall cost.

Interestingly, for a mission delta-v, there is a fixed I_{sp} that minimises the overall energy used by the rocket. This comes to an exhaust velocity of about ? of the mission delta-v (see also There was an error working with the wiki: Code[16]). Drives such as VASIMR, and to a lesser extent other Ion thrusters have exhaust velocities that can be enormously higher than this ideal, and thus end up powersource limited and give very low thrust. Where the vehicle performance is power limited, e.g. if Solar power or nuclear power is used, then in the case of a large v_{e} the maximum acceleration is inversely proportional to it. Hence the time to reach a required delta-v is proportional to v_{e}. Thus the latter should not be too large.

#### Propulsion methods

Propulsion methods can be classified based on their means of accelerating the reaction mass. There are also some special methods for launches, planetary arrivals, and landings.

##### Rocket engines

A There was an error working with the wiki: Code[70] is a reaction engine that can be used for spacecraft propulsion as well as terrestrial uses, such as missiles. Rocket engines take their reaction mass from one or more tanks and form it into a jet, obtaining thrust in accordance with Newton's third law. Most rocket engines are internal combustion engines, although non combusting forms exist.

Most rocket engines are Internal combustion engine There was an error working with the wiki: Code[17]. This bell-shaped nozzle is what gives a rocket engine its characteristic shape. The effect of the nozzle is to dramatically accelerate the mass, converting most of the thermal energy into kinetic energy. Exhaust speeds as high as 10 times the speed of sound at sea level are not uncommon.

Rockets emitting plasma can potentially carry out reactions inside a There was an error working with the wiki: Code[71] and release the plasma via a There was an error working with the wiki: Code[72], so that no solid matter need come in contact with the plasma. Of course, the machinery to do this is complex, but research into There was an error working with the wiki: Code[73] has developed methods, some of which have been used in speculative propulsion systems.

Classic rocket engines produce a high temperature, There was an error working with the wiki: Code[18]. The effect of the nozzle is to dramatically accelerate the mass, converting most of the thermal energy into kinetic energy. The large bell or cone shaped expansion nozzle gives a rocket engine its characteristic shape. Exhaust speeds as high as 10 times the speed of sound at sea level are not uncommon.

Part of the rocket engine's thrust comes from the gas pressure inside the combustion chamber but the majority comes from the pressure against the inside of the expansion nozzle. Inside the combustion chamber the gas produces a similar force against all the sides of the combustion chamber but the throat gives no force producing an unopposed resultant force from the diametrically opposite end of the chamber. As the gases (There was an error working with the wiki: Code[19]) expand inside the nozzle they press against the bell's walls forcing the rocket engine in one direction, and accelerating the gases in the opposite direction.

For optimum performance hot gas is used because it maximises the speed of sound at the throat-for aerodynamic reasons the flow goes sonic ("chokes") at the throat, so the highest speed there is desirable. By comparison, at room temperature the speed of sound in air is about 340m/s, the speed of sound in the hot gas of a rocket engine can be over 1700m/s.

The expansion part of the rocket nozzle then multiplies the speed of the flow by a further factor, typically between 1.5 and 4 times, giving a highly collimated exhaust jet. The speed ratio of a rocket nozzle is mostly determined by its area expansion ratio&mdashthe ratio of the area of the throat to the area at the exit, but details of the gas properties are also important. Larger ratio nozzles are more massive and bulkier, but they are able to extract more heat from the combustion gases, which become lower in pressure and colder, but also faster.

A significant complication arises when launching a vehicle from the Earth's surface as the ambient atmospheric pressure changes with altitude. For maximum performance it turns out that the pressure of the gas leaving a rocket nozzle should be the same as ambient pressure if lower the vehicle will be slowed by the difference in pressure between the top of the engine and the exit, if higher then this represents pressure that the bell has not turned into thrust. To achieve this ideal, the diameter of the nozzle would need to increase with altitude, which is difficult to arrange. A compromise nozzle is generally used and some percentage reduction in performance occurs. To improve on this, various exotic nozzle designs such as the There was an error working with the wiki: Code[20] have been proposed, each having some way to adapt to changing ambient air pressure and each allowing the gas to expand further against the nozzle giving extra thrust at higher altitude.

##### Airbreathing engines for launch

Studies generally show that conventional air-breathing engines, such as There was an error working with the wiki: Code[74] or There was an error working with the wiki: Code[75] are basically too heavy (have too low a thrust/weight ratio) to give any significant performance improvement when installed on a launch vehicle. However, they can be used on a separate lift vehicle (e.g. There was an error working with the wiki: Code[76], There was an error working with the wiki: Code[77] and There was an error working with the wiki: Code[78]). On the other hand, very lightweight or very high speed engines have been proposed that take advantage of the air during ascent:

There was an error working with the wiki: Code[79]

There was an error working with the wiki: Code[80]

There was an error working with the wiki: Code[81]

There was an error working with the wiki: Code[82]s

A Jet engine is an engine that discharges a fast moving jet of fluid to generate thrust in accordance with Newton's third law of motion. This broad definition of jet engines includes turbojets, turbofans, rockets and ramjets and water jets, but in common usage, the term generally refers to a gas turbine used to produce a jet of high speed exhaust gases for special propulsive purposes.

Engines that may need to operate at low hypersonic speeds could theoretically have much higher performance if a heat exchanger is used to cool the incoming air. The low temperature allows lighter materials to be used and combustors run at their maximum speeds (ordinarily, fuel flow must be reduced to prevent the turbines from melting, but doing so greatly reduces thrust) This leads to plausible designs like There was an error working with the wiki: Code[83], that might permit single-stage-to-orbit. The Skylon Spaceplane, and There was an error working with the wiki: Code[84], that might permit jet engines to be used as boosters for space vehicles.

##### Electromagnetic acceleration of reaction mass

Rather than relying on high temperature and There was an error working with the wiki: Code[21] forces to accelerate the reaction mass directly. Usually the reaction mass is a stream of Ions. Such an engine requires electric power to run, and high exhaust velocities require large amounts of energy.

For these drives it turns out that to a reasonable approximation fuel use, energetic efficiency and thrust are all inversely proportional to exhaust velocity. Their very high exhaust velocity means they require huge amounts of energy and thus with practical powersources provide low thrust, but use hardly any fuel.

For some missions, Solar energy may be sufficient, and has very often been used, but for others nuclear energy will be necessary engines drawing their power from a nuclear source are called There was an error working with the wiki: Code[85]s.

With any current source of power, chemical, nuclear or solar, the maximum amount of power that can be generated greatly limits the maximum amount of thrust that can be produced to a small value. Power generation also adds significant mass to the spacecraft, and ultimately the weight of the power source limits the performance of the vehicle. Current nuclear power generators are approximately half the weight of solar panels per watt of energy supplied, at terrestrial distances from the Sun. Chemical power generators are not used due to the far lower total available energy. Beamed power to the spacecraft shows potential.

The dissipation of waste heat from the powerplant may make any propulsion system requiring a separate power source infeasible for interstellar travel.

Some electromagnetic methods:

There was an error working with the wiki: Code[86]

There was an error working with the wiki: Code[87]

There was an error working with the wiki: Code[88]

There was an error working with the wiki: Code[89]

There was an error working with the wiki: Code[90]

There was an error working with the wiki: Code[91] (acceleration by electromagnetic forces emits plasma)

There was an error working with the wiki: Code[92]

There was an error working with the wiki: Code[93]

There was an error working with the wiki: Code[94]

There was an error working with the wiki: Code[95]s (for propulsion)

##### Systems without reaction mass carried within the spacecraft

The There was an error working with the wiki: Code[22] of There was an error working with the wiki: Code[96] states that any engine which uses no reaction mass cannot move the center of mass of a spaceship (changing orientation, on the other hand, is possible). But space is not empty, especially space inside the Solar System there are gravitation fields, Magnetic fields, There was an error working with the wiki: Code[97] and solar radiation. Various propulsion methods try to take advantage of these. However, since these phenomena are diffuse in nature, corresponding propulsion structures need to be proportionately large.

Space drives that need no (or little) reaction mass:

There was an error working with the wiki: Code[98]

There was an error working with the wiki: Code[99]s

There was an error working with the wiki: Code[100]s

There was an error working with the wiki: Code[101]

For changing the orientation of a satellite or other space vehicle, There was an error working with the wiki: Code[102] does not pose a similar constraint. Thus many satellites use There was an error working with the wiki: Code[103]s to control their orientations. These cannot be the only system for controlling satellite orientation, as the angular momentum built up due to torques from external forces such as solar, magnetic or tidal forces eventually needs to be "bled off" using a secondary system.

##### Launch mechanisms

High thrust is of vital importance for Earth launch, thrust has to be greater than weight (see also There was an error working with the wiki: Code[104]). Many of the propulsion methods above give a thrust/weight ratio of much less than 1, and so cannot be used for launch.

Exhaust toxicity or other side effects can also have detrimental effects on the environment the spacecraft is launching from, ruling out other propulsion methods, such as most nuclear engines, at least for use from the Earths surface.

Therefore, all current spacecraft use chemical rocket engines (There was an error working with the wiki: Code[23] or There was an error working with the wiki: Code[24]) for launch.

One advantage that spacecraft have in launch is the availability of infrastructure on the ground to assist them. Proposed ground-assisted launch mechanisms include:

There was an error working with the wiki: Code[105]

There was an error working with the wiki: Code[106]

There was an error working with the wiki: Code[107]

There was an error working with the wiki: Code[108]

There was an error working with the wiki: Code[25] (There was an error working with the wiki: Code[109], There was an error working with the wiki: Code[110])

There was an error working with the wiki: Code[111] (There was an error working with the wiki: Code[112], There was an error working with the wiki: Code[113])

There was an error working with the wiki: Code[114] (There was an error working with the wiki: Code[115])

##### Planetary arrival and landing

When a vehicle is to enter orbit around its destination planet, or when it is to land, it must adjust its velocity. This can be done using all the methods listed above (provided they can generate a high enough thrust), but there are a few methods that can take advantage of planetary atmospheres and/or surfaces.

There was an error working with the wiki: Code[26] and There was an error working with the wiki: Code[27].

There was an error working with the wiki: Code[28] by There was an error working with the wiki: Code[116] and There was an error working with the wiki: Code[117] upon lunar return were aerocapture maneuvers, since they turned a hyperbolic orbit into an elliptical orbit. On these missions, since there was no attempt to raise the perigee after the aerocapture, the resulting orbit still intersected the atmosphere, and re-entry occurred at the next perigee.

There was an error working with the wiki: Code[29].

There was an error working with the wiki: Code[118]s can soften the final landing.

There was an error working with the wiki: Code[119], or stopping by simply smashing into the target, is usually done by accident. However, it may be done deliberately with the probe expected to survive (see, for example, There was an error working with the wiki: Code[120]). Very sturdy probes and low approach velocities are required.

There was an error working with the wiki: Code[121]s can also be used to carry a probe onward to other destinations.

##### Methods requiring new principles of physics

In addition, a variety of hypothetical propulsion techniques have been considered that would require entirely new principles of physics to realize. To date, such methods are highly speculative and include:

There was an error working with the wiki: Code[30]

There was an error working with the wiki: Code[31]

There was an error working with the wiki: Code[32]

There was an error working with the wiki: Code[33]

There was an error working with the wiki: Code[122] (Warp drive)

There was an error working with the wiki: Code[34]

There was an error working with the wiki: Code[123]s (impossible to build with current technology)

Antigravity (true antigravity is currently theoretically impossible)

There was an error working with the wiki: Code[124]s (theoretically impossible)

There was an error working with the wiki: Code[125]

#### Table of methods and their specific impulse

Below is a summary of some of the more popular, proven technologies, followed by increasingly speculative methods.

Three numbers are shown. The first is the There was an error working with the wiki: Code[35]: the equivalent speed that the propellant leaves the vehicle. This is not necessarily the most important characteristic of the propulsion method, thrust and power consumption and other factors can be, however:

if the delta-v is much more than the exhaust velocity, then exorbitant amounts of fuel are necessary (see the section on calculations, above)

if it is much more than the delta-v, then, proportionally more energy is needed if the power is limited, as with solar energy, this means that the journey takes a proportionally longer time

The second and third are the typical amounts of thrust and the typical burn times of the method. Outside a gravitational potential small amounts of thrust applied over a long period will give the same effect as large amounts of thrust over a short period. (This result does not apply when the object is significantly influenced by gravity.)

{| border="0" cellspacing="0" cellpadding="2"

|+ Propulsion methods

|-

!Method !!There was an error working with the wiki: Code[36](m/s)!!There was an error working with the wiki: Code[126](N)!!Duration

|-

|- style="background-color: lightgray"

!Propulsion methods in current use || || ||

|-

|align="right"|There was an error working with the wiki: Code[127] || 1,000 - 4,000 || 103 - 107 || minutes

|-

|align="right"|There was an error working with the wiki: Code[128] || 1,500 - 4,200 || || minutes

|-

|align="right"|There was an error working with the wiki: Code[129] || 1,000 - 3,000 || 0.1 - 100 || milliseconds - minutes

|-

|align="right"|There was an error working with the wiki: Code[130] || 1,000 - 4,700 || 0.1 - 107 || minutes

|-

|align="right"|There was an error working with the wiki: Code[131] || 2,500 - 4,500 || || minutes

|-

|align="right"|There was an error working with the wiki: Code[132] || 2,000 - 6,000 || 10-2 - 10 || minutes

|-

|align="right"|There was an error working with the wiki: Code[133] || 4,000 - 12,000 || 10-2 - 10 || minutes

|-

|align="right"|There was an error working with the wiki: Code[134] (HET) || 8,000 - 50,000 || 10-3 - 10 || months

|-

|align="right"|There was an error working with the wiki: Code[135] || 15,000 - 80,000 || 10-3 - 10 || months

|-

|align="right"|There was an error working with the wiki: Code[136] (FEEP) || 100,000 - 130,000 || 10-6 - 10-3 || weeks

|-

|align="right"|There was an error working with the wiki: Code[137] (MPD) || 20,000 - 100,000 || 100 || weeks

|-

|align="right"|There was an error working with the wiki: Code[138] (PPT) || || ||

|-

|align="right"|There was an error working with the wiki: Code[139] (PIT) || 50,000 || 20 || months

|-

|align="right"|There was an error working with the wiki: Code[140]

|colspan="3" align="center"|As electric propulsion method used

|-

|align="right"|There was an error working with the wiki: Code[141] || N/A || 1 - 1012 || minutes

|- style="background-color: lightgray"

!Currently feasible propulsion methods || || ||

|-

|align="right"|There was an error working with the wiki: Code[37]) || Indefinite

|-

|align="right"|There was an error working with the wiki: Code[142]s (for propulsion) || 30,000 - ? || 104 - 108 || months

|-

|align="right"|There was an error working with the wiki: Code[38] (Near term nuclear pulse propulsion) || 20,000 - 100,000 || 109 - 1012 || several days

|-

|align="right"|There was an error working with the wiki: Code[143] (VASIMR) || 10,000 - 300,000 || 40 - 1,200 || days - months

|-

|align="right"|There was an error working with the wiki: Code[144] || 9,000 || 105 || minutes

|-

|align="right"|There was an error working with the wiki: Code[145] || 7,000 - 12,000 || 1 - 100 || weeks

|-

|align="right"|There was an error working with the wiki: Code[146] || 7,000-8,000 || || months

|-

|align="right"|There was an error working with the wiki: Code[147] || 5,000 - 6,000 || || seconds-minutes

|-

|align="right"|There was an error working with the wiki: Code[148] || 4,500 || || seconds-minutes

|-

|align="right"|There was an error working with the wiki: Code[149] || 30,000/4,500 || || minutes

|-

|align="right"|There was an error working with the wiki: Code[150] || || ||

|- style="background-color: lightgray"

!Technologies requiring further research || || ||

|-

|align="right"|There was an error working with the wiki: Code[151]s || N/A || Indefinite || Indefinite

|-

|align="right"|There was an error working with the wiki: Code[152] || 200,000 || ~1 N/kW || months

|-

|align="right"|There was an error working with the wiki: Code[153] (There was an error working with the wiki: Code[154]' drive) || 20,000 - 1,000,000 || 109 - 1012 || half hour

|-

|align="right"|There was an error working with the wiki: Code[155] || 10,000 - 20,000 || 103 - 106 ||

|-

|align="right"|There was an error working with the wiki: Code[156] || 20,000 - 400,000 || || days-weeks

|-

|align="right"|There was an error working with the wiki: Code[157] || 100,000 || 103 - 107 || half hour

|-

|align="right"|There was an error working with the wiki: Code[158]

|colspan="3" align="center"|As propulsion method powered by beam

|-

|align="right"|There was an error working with the wiki: Code[159] || || ||

|-

|align="right"|There was an error working with the wiki: Code[160] || 10,000,000 || ||

|-

|align="right"|There was an error working with the wiki: Code[161] || 300,000,000 || 10-5 - 1 || years-decades

|- style="background-color: lightgray"

!Significantly beyond current engineering || || ||

|-

|align="right"|There was an error working with the wiki: Code[162] || 1,300,000-36,000,000 || ||

|-

|align="right"|There was an error working with the wiki: Code[163] || || ||

|-

|align="right"|There was an error working with the wiki: Code[164] || 10,000,000-100,000,000 || ||

|-

|align="right"|There was an error working with the wiki: Code[39] || || ||

|-

|align="right"|There was an error working with the wiki: Code[40]|| || ||

|}

General

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Low temperature

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Chemical heating

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Electric heating

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Solar heating

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Nuclear heating

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#### References and external links

NASA Beginner's Guide to Propulsion

NASA Breakthrough Propulsion Physics project

Rocket Propulsion

Journal of Advanced Theoretical Propulsion

Different Rockets

Spaceflight Propulsion - a detailed survey by Greg Goebel, in the public domain

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Directory:Propulsion

PowerPedia:Pulsed Plasma Thruster

PowerPedia:Jet Engine

Directory:UFOs

PowerPedia:UFO

Directory:Reverse Engineering UFO Craft