Orbital maneuver

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In space, orbital maneuvers (otherwise known as burn ) is the use of propulsion systems to change the orbits of spacecraft. For far-flung spacecraft from Earth (such as those in orbit around the Sun), an orbital maneuver is called an in-space maneuver (DSM) .

The remaining flights, especially in transfer orbit, are called sliding .

Video Orbital maneuver

General

Rocket equation

The Tsiolkovsky rocket equation , or the ideal rocket equation is a useful equation for considering vehicles that follow the basic principles of a rocket: where a device that can apply acceleration to itself (Encouragement) by issuing part of its mass at high speed and moving due to the conservation of momentum. In particular, it is a mathematical equation that connects delta-v (changes in the maximum speed of a rocket if no other external force acts) with the effective exhaust velocity and the start and end mass of the rocket (or other reaction machine.)

Untuk manuver has been established (atau perjalanan yang melibatkan sejumlah manuver has been installed):

${\ displaystyle \ Delta v = v _ {\ text {e}} \ ln {\ frac {m_ {0}} {m_ {1}}} } Â Â$

dimana:

${\ displaystyle m_ {0}} Â$ adalah total massa awal, termasuk propelan,

${\ displaystyle m_ {1}} Â Â$ adalah total massa akhir,

${\ displaystyle v _ {\ text {e}}} Â$ adalah kecepatan buang efektif ( ${\ displaystyle v _ {\ text {e}} = Saya _ {\ text {sp}} \ cdot g_ {0}} Â$ di mana ${\ displaystyle I _ {\ text {sp}}} Â Â$ adalah impuls spesifik yang dinyatakan sebagai periode waktu dan ${\ displaystyle g_ {0}} Â$ adalah constant gravitation),

${\ displaystyle \ Delta v \} Â Â$ adalah delta-v - perubahan maximum kecepha kendaraan (tanpa gaya eksternal yang bekerja).

Delta-v

Perubahan yang diterapkan dalam kecepatan setiap manuver disebut sebagai delta-v ( ${\ displaystyle \ Delta \ mathbf {v} \,}  ÂÂ$ ).

Anggaran Delta-v

The total delta-v for all and every maneuver is estimated for the mission and is referred to as delta-v budget. With a good approximation of delta-v budget designers can estimate the fuel for the load requirements of the spacecraft using a rocket equation.

Impulsive maneuvers

An "impulsive maneuver" is a mathematical model of maneuvering as an instantaneous change in the speed of the spacecraft (large and/or direction) as illustrated in figure 1. This is the case of the limit of the burn to produce a certain amount of delta-v, tends to zero.

In the physical world there is no sudden change in speed as this will require "unlimited power" applied during "very short time" but as a mathematical model in many cases describes the effect of maneuvering in orbit very well.

The off-set velocity velocity after the actual burning end of the velocity velocity at the same time is generated from the theoretical impulsive maneuver only due to the generally small difference in gravitational forces along the two-lane (red and black lines in figure 1).

In the planning stages the space mission designer first approximates the orbital changes they mean by using impulsive maneuvers that greatly reduce the complexity of finding the correct orbital transition.

Applying a low boost for longer periods

Applying a low impulse for a longer period of time is referred to as non-impulsive maneuvers (where 'non-impulsive' refers to maneuver not being a short period of time rather than not involving Impulse - change of momentum, which obviously must happen).

Another term is limited burns, where the word "limited" is used to mean "nonzero", or practically, again: in longer periods.

For some space missions, such as those that include meeting rooms, high-fidelity models of trajectories are required to fulfill mission objectives. Counting the "limited" wound requires a detailed model of the spacecraft and its plunger. The most important of the details include: mass, center of mass, moment of inertia, thruster position, thrust vector, thrust curve, specific impulse, pushroid pushed offset, and fuel consumption.

Assists

Oberth effect

In astronotics, the Oberth effect is where the use of rocket engines when traveling at high speed produces far more beneficial energy than low speed. The Oberth effect occurs because the propellant has more usable energy (because its kinetic energy is above its chemical potential) and it turns out that the vehicle is capable of using this kinetic energy to produce more mechanical energy. Named after Hermann Oberth, an Austro-Hungarian-born German physicist, and founder of modern rocketry, which seems to first describe its effect.

The Oberth effect is used in flyby powered or Oberth maneuver where impulse applications, usually from the use of rocket engines, are close to the body of gravity (where gravity is low, and its speed is high) provides more change in kinetic energy and final velocity (ie higher specific energy) than the same impulse that is applied further from the body to the same initial orbit.

Since the Oberth maneuver occurs in very limited time (while still at low altitude), to produce high impulses, the machine must always achieve a high boost (impulse by time definition multiplied by thrust). Thus the Oberth effect is much less useful for low thrust engines, such as ion boosters.

Historically, this lack of understanding of these effects led researchers to conclude that interplanetary travel would require a very impractical amount of propellant, because without it, it would require enormous amounts of energy.

Gravity help

In orbital mechanics and aerospace techniques, snapshot gravity , gravity aid maneuvers , or swing-by is the use of relative motion and gravity of a planet or object another space to change the path and speed of the spacecraft, usually to save propellant, time, and cost. Gravity assistance can be used to speed up, slow down and/or redirect the spacecraft path.

"Help" is provided by the movement (orbital angular momentum) of the body that does gravity when pulling on the spacecraft. This technique was first proposed as a mid-way maneuver in 1961, and is used by interplanetary probes from Mariner 10 and so on, including two probe fly Voyager by Jupiter and Saturn.

Maps Orbital maneuver

Transferring orbit

Insertion of orbit is a general term for maneuvering that is more than just a small correction. It can be used for maneuvering to convert transfer orbits or climbing orbits into stable ones, but also to convert stable orbits into offspring: insertion of descent orbit . Also the term orbit injection is used, mainly to convert a stable orbit into a transfer orbit, ie. trans-lunar injection (TLI), trans-Mars injection (TMI) and trans-Earth injection (TEI).

Hohmann transfer

In orbital mechanics, Hohmann orbit transfer is an elliptical orbit that is used to transfer between two circular orbits of different heights, in the same plane.

The orbital maneuver to transfer Hohmann uses two machine impulses that move the spacecraft to and from the transfer orbit. This maneuver is named after Walter Hohmann, a German scientist who published a description in his 1925 book Die Erreichbarkeit der HimmelskÃÆ'¶rper ( Accessibility of the Celestial Body ). Hohmann was influenced by the German science fiction writer Kurd LaÃÆ'Ÿwitz and his book in 1897, Two Planets .

Bi-ellipse transfer

In the astronautics and aerospace techniques, bi-ellipsip transfer is an orbital transfer maneuvering the spacecraft from one orbit to another orbit and in some situations requires less delta-v than Hohmann's transfer maneuver.

Transfer bi-elips terdiri dari dua setengah orbit elips. Dari orbit awal, delta-v diterapkan mendorong pesawat ruang angkasa ke orbit transfer pertama dengan apoapsis di beberapa titik ${\ displaystyle r_ {b}}  ÂÂ$ menjauh dari badan pusat. Pada titik ini, delta-v kedua diterapkan mengirim pesawat ruang angkasa ke orbit elips kedua dengan periapsis pada radius orbit yang diinginkan, di mana delta-v ketiga dilakukan, menyuntikkan pesawat ruang angkasa ke orbit yang diinginkan.

While they require one more engine burning than the Hohmann transfer and generally require greater travel time, some bi-elliptical transfers require a lower amount of total delta-v than the Hohmann transfer when the initial semi-major axis end-ratio is 11.94 or larger, depending on the selected semi-major axis.

The idea of ​​a bi-elliptical transfer path was first published by Ary Sternfeld in 1934.

Low energy transfer

A low energy transfer , or low energy path, is an in-space route that allows the spacecraft to alter its orbit using very little fuel. These routes work on Earth-Moon systems as well as in other systems, such as traveling between Jupiter satellites. The weakness of the trajectory is that they take longer to complete than higher energy transfer (more fuel) such as the Hohmann orbit transfer.

Low energy transfer is also known as the path of weak stability limits, or ballistic trajectory.

Low energy transfer follows a special path in space, sometimes referred to as the Interplanetary Transport Network. Following this path allows long distances to pass for a little delta-v expenditure.

Orbital slope change

Orbital slope change is an orbital maneuver aimed at changing the orbital orbital tendencies of the body. This maneuver is also known as a change in the orbital plane when the orbital field is tipped. This maneuver requires changes in the velocity velocity of the orbital (delta v) on the orbital node (ie the point at which the desired orbital intersection is intersect, the orbital node line is determined by the junction of the two orbital planes).

In general, changing trends can require multiple delta-v to take place, and most mission planners try to avoid it whenever possible to save fuel. This is usually achieved by launching the spacecraft directly to the desired slope, or as close as possible to minimize any necessary tilt changes during the life span of the spacecraft.

The maximum efficiency of slope change is achieved in apoapsis, (or apogee), where the orbital velocity ${\ displaystyle v \,}$ is the lowest. In some cases, it may require less delta v to raise satellites into higher orbits, change the orbital plane in higher apogee, and then lower the satellite to its original height.

Trajectory of Constant-Thrust

The constant-thrust path and the constant acceleration path involve the spacecraft firing the engine in constant prolonged combustion. In the case of barriers where high vehicle acceleration is compared to local gravitational acceleration, spacecraft spots go directly to the target (taking into account the target movement), and keep accelerating constantly under high pressure until it reaches its target. In the case of this high thrust, the trajectory is approaching a straight line. If it is required that the spacecraft meet the target, rather than flyby, the spacecraft must reverse its orientation on the way, and reduce the rest of its path.

In a constant thrust trajectory, vehicle acceleration increases during the thrusting period, as fuel use means the vehicle mass decreases. If, instead of a constant push, the vehicle has a constant acceleration, the engine impulse must decrease during the trajectory.

This trajectory requires the spacecraft to maintain high acceleration for long periods of time. For interplanetary transfers, it may take days, weeks or months of constant thrust. As a result, there are currently no available spacecraft propulsion systems capable of using this trajectory. It has been suggested that some nuclear form (fission or fusion based) or an antimatter-powered rocket will be capable of this trajectory.

More practically, this type of maneuver is used in low thrust maneuvers, for example with an ion machine, Hall effect machine, and others. This type of machine has a very high specific impulse (fuel efficiency) but is currently only available with very low absolute thrust.

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Rendezvous and docking

Orbit phasing

In astrodynamics orbital phasing is the time-space adjustment of spacecraft positions along its orbit, usually described as adjusting the true anomaly of orbiting spacecraft.

Space rendezvous and docking

rendezvous space is an orbital maneuver in which two spacecraft, one of which is often a space station, arrive in the same orbit and approach to very close distances (eg in visual contact). Rendezvous requires an exact match of the orbital velocity of the two spacecraft, allowing them to remain at a constant distance through the orbit station maintainers. Rendezvous may or may not be followed by docking or anchored, a procedure that brings the spacecraft into physical contact and makes connections between them.

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See also

• Crash avoidance (spaceship)
• In-room propulsion technology
• Clohessy-Wiltshire equation for co-orbit analysis

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References

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External links

• Handbook Automated Rendezvous and Docking of Spacecraft by Wigbert Fehse

Source of the article : Wikipedia