synonymOrbit speed(Orbit speed) generally refers to the first cosmic speed (the object must reach the speed of circular motion when flying around the earth)
The first cosmic speed is divided into two nicknames:spacecraftMinimum launch speed, maximum running speed of spacecraft.In some problems, when a spacecraft runs at the first cosmic speed, it means that the spacecraft isearthSurface running.According to the mechanical theoryvone=7.9km/s。
Chinese name
First cosmic velocity
Foreign name
first cosmic velocity
Alias
Minimum launch speed of spacecraft、Maximum running speed of spacecraft、Orbit speed
First cosmic velocity refers to the movement of objects around the earth near the groundUniform circular motionSpeed of.
First cosmic velocity
The first cosmic speed is also called: the minimum launch speed of spacecraft, the maximum operating speed of spacecraft, and the surrounding speed.The first cosmic speed refers to the speed at which the artificial satellite moves in a uniform circle just close to the earth's surface. It is the maximum speed at which the artificial satellite rotates around the earth, and also the minimum launch speed at which it will never fall back to the earth.[3]
In some problems, when a spacecraft is running at the first cosmic speed, it means that the spacecraft is running along the earth's surface.According to the mechanical theoryvone=7.9 km/s.In fact, there is a dense atmosphere on the earth's surface, so it is impossible for a spacecraft to move in a circle close to the earth's surface. It must fly at an altitude of 150 kilometers to orbit the earthCircular motion。When the spacecraft operates at a high altitude hundreds of kilometers above the ground surface, the earth's gravity on the spacecraft is smaller than when it is on the ground, so its speed is slightly less thanvone。At this heightOrbit speedIs 7.8 km/s.
Derived formula
SolvedGM=V² r，takeRland=6.375×10sixm，Earth mass M=5.965 × 10 ^ 24kg,Universal gravitational constant6.67259 × 10 ^ - 11 m ^ 3/(kg · s ^ 2) is substituted and squaredv≈7.9km/s
Principles of Science
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First cosmic velocity
When the projectile is fired from the ground to a distance, the higher the velocity of the projectile, the farther the flight distance will be. When the velocity of the projectile reaches 7.9 km/s, the projectile will not fall back to the ground (regardless of the atmospheric effect), but will fly around the earth in a circle, which is the first cosmic speed.The first cosmic speed is also the speed at which man-made satellites orbit the earth near the ground“Uniform circular motion”Speed required.However, with the increase of altitude, the gravity of the earth decreases, and the flight speed required to fly around the earth also decreases. All spacecraft fly outside the atmosphere very high from the ground, so their flight speed is lower than that of the first universe.
When an artificial satellite makes a uniform circular motion around the earth near the ground (height ignored), its orbit radius is approximately equal to the earth radius R, its centripetal force is the universal gravitation of the earth on the satellite, and its centripetal acceleration is approximately equal to theGravitational acceleration。
Gravity on objects=Universal gravitation=The centripetal force of a spacecraft moving in a circle along the earth's surface.
application
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spacecraft
First cosmic velocity
Human beings want to launchArtificial earth satelliteOr launch an aircraft that has completed interstellar navigation, and it is necessary to get rid of the strong gravity of the earth, so how to get away from the earth?This will make the launch vehicle or artificial earth satellitespace shuttleorCarrier rocketWhat is the cosmic speed?It has several categories, which are described as follows:
The so-called cosmic speed is the speed needed to launch an aircraft from the surface of the earth. The aircraft will circle the earth, leave the earth and fly out of the solar systemMinimum speed, respectively called the first, secondThird cosmic speed。In the early days, people introduced the concept of three cosmic velocities in order to estimate the minimum energy required to overcome the gravity of the earth and the sun when exploring space routes.Assuming that the earth is a circle and there is no atmosphere around it, the lowest orbit that an object can move around the earth is a circular orbit with the same radius as the earth.At this time, the speed of the object is the first cosmic speed, which is about 7.9 km/s.After obtaining this horizontal velocity, the object can move around the earth without additional power.
First cosmic velocity
The objects on the earth will becomeMoving around the sunArtificialplanet, the minimum speed required isSecond cosmic speed。The speed of the second universe is 11.2 km/s, which is √ 2 times the speed of the first universe.The ground object can move along aparabolaOrbit away from Earth.Objects on the earth fly out of the solar systemThe minimum speed relative to the geocenter is called the third cosmic speed, which is 16.7 km/s.Objects on the ground can move along thehyperbolaOrbit away from the earth.When it reaches the distanceGeocentric930000 kilometers away, it is considered that it has been separated from the gravity of the earth, and then it will move under the action of the universal gravitation of the sun.The object's orbit relative to the sun is a parabola, and it will eventually leave the sungravitational fieldFly out of the solar system.Some special track speeds, such asOrbit speed、Disengagement speed, sometimes called the first and second cosmic velocities respectively.
How can we make the launch vehicle or space shuttle reach the speed of the universe? Theory and practice have proved that the speed of the rocket depends onrocket engineThe ratio of the jet speed to the mass of the rocket.The higher the jet speed of the engine, the higher the speed of the rocket;The greater the mass ratio of the rocket, the higher the speed the rocket can reach.
The mass ratio of a rocket is the ratio of the mass of the rocket at takeoff (including the mass of propellant) to the mass of the rocket at the time of engine shutdown (flameout) (the structural mass of the rocket, that is, the net weight).Therefore, a relatively large mass means that the structural mass of the rocket is small and it carries more propellant.Rocket can be divided into single stage and multi-stage, and multi-stage rocket can be divided into series, parallel series and series parallel combination. Generally speaking, the more rocket stages, the more itskinetic energyHowever, theoretical calculation and practical experience show that for every additional payload, the rocket needs to add more than 10 masses to bear. With the increase of the number of rocket stages, the lowest stage and subsequent stages become larger and larger, so that they cannot take off.Multi stage rockets generally do not exceed four stages.
Launch unmanned/manned space vehicles, interstellar travel vehicles, cargo ships and space stations.
Law of universal gravitation
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brief introduction
Newton
A law of interaction between objects, 1687NewtonFound.Any object has mutual attraction, and the force is equal to the mass of each objectPositive proportion, and the square of the distance between theminverse ratio。If m1. m2 is used to represent thequality, r represents the distance between them, then objects attract each other F=（Gmonemtwo）/r²，Gbe calledUniversal gravitational constant。Law of universal gravitationIt was published by Newton in 1687《Mathematical Principles of Natural Philosophy》First proposed in the book.Newton used the law of universal gravitation to explain not onlyplanetIt also points out that the satellites of Jupiter and Saturn have the same motion around the planet.He believes that the moon is not only attracted by the earth, but also by the sun, thus explaining what has long been discovered in the movement of the moonMean square error、a business travelEtc.In addition, he explainedCometThe motion orbit ofTidal phenomenon。Leverrier Successfully predicted and discovered according to the law of universal gravitationNeptune。After the emergence of the law of universal gravitation, the research on the motion of celestial bodies was formally established on the basis of mechanical theory, thus establishingCelestial mechanics。The magnitude of gravity between two objects andMass of objectThe product of is in direct proportion to the square of the distance between two objects, but has nothing to do with the chemical nature or physical state of the two objects and intermediary substances.
Expressed by formula
（G≈6.67×10-11N·mtwo/kgtwo）, can be read as F equals G times the square of M1M2 and R[1]
Including:
F: Gravity between two objects
G: Universal gravitational constant
mone: Mass of object 1
mtwo: Mass of object 2
R: Distance between two objects
Other cosmic velocities
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Second cosmic speed
Second cosmic speedvtwo。When the spacecraft exceeds the first cosmic speedvoneWhen it reaches a certain value, it will break away from the earth's gravitational field and become an artificial planet orbiting the sun. This speed is called the second cosmic speed, also calledEscape speed[2]。According to the mechanical theory, the second cosmic velocity can be calculatedvtwo=11.2 km/s.Since the moon is not beyond the scope of the earth's gravity, it is launched from the groundlunar probeThe initial speed of spacecraft shall not be less than 10.848 km/s.
Third cosmic speed
Third cosmic speedvthree。Launch spacecraft from the surface of the earth, fly out of the solar system, to the vastGalaxyThe minimum speed required for roaming in is called the third cosmic speed, also calledDisengagement speed[2]。According to the mechanical theory, the third cosmic velocity can be calculatedvthree=16.7 km/s.It should be noted that this is calculated when the spacecraft's orbit entry speed is consistent with the earth's revolution speedvthreeValue;If the direction is inconsistent, the required speed will be greater than 16.7 km/s.It can be said that the speed of spacecraft is the only factor to break away from the gravity of the earth and even the sun.
Fourth cosmic speed
It is predicted that when the object has a speed of 110~120km/s, it can leave the Milky Way and enterExtragalactic galaxyThis speed is calledFourth cosmic speed。
Fifth cosmic speed
It means that the spacecraft is launched from the earthLocal galaxy groupBecause the radius and mass of the local galaxy group do not have enough accurate data, it is impossible to estimate the data size.At present, scientists estimate that it is about 5 billion to 10 billion light years. According to this calculation, it should take 1500 to 2250km/s to fly away.
