What is a gravitational slingshot and how does it accelerate?
Gravitational slingshot is a special orbit that uses planetary gravity to accelerate, decelerate or change orbit. To achieve the goal of planetary gravity acceleration, several conditions must be met:
The probe and the planet must have relative speed.
The detector must have a precisely controlled orbit.
The former rules out the possibility of satellite accelerating around the earth, but you may be confused. The satellite moves around the earth close to the speed of the first universe. Why is there no relative speed? In fact, this is a complete misunderstanding. The satellite revolves around the earth only relative to the ground, and the relative speed with the earth is zero, so the relationship in this system cannot meet the first requirement.
How does the detector accelerate?
The angle and direction of the probe entering the planetary orbit determine whether it will accelerate or decelerate, which must be understood, because the gravitational slingshot can decelerate and change the orbital direction in addition to accelerating.
Acceleration: The direction of the detector leaving the planetary orbit is the same as that of the planetary orbit.
Deceleration: The detector leaves the planetary orbit in the opposite direction to the planetary orbit.
Orbit change is to design different orbits according to different needs.
The above picture is a schematic diagram of the acceleration and calculation process of gravity slingshot. In fact, the principle is easy to understand. We can simply explain that when the probe cuts into the planetary orbit, let the planetary gravity pull the probe to fly in the planetary orbit for a period of time, and then disengage when it accelerates to a sufficient speed.
When entering the planetary orbit, the speed will be higher and higher due to the gravity of the planet.
When escaping from the orbit of the planet, the speed will be slower and slower due to the gravity of the planet.
The two cancel each other out. We can simply understand that there is no speed loss when the probe enters the planetary orbit, but an extra planetary gravity drags the probe forward in the orbit, which increases the speed. Of course, this acceleration is based on reducing the revolution speed of the planet, but in fact, due to the great difference in mass between the two, the reduction of the revolution speed of the planet is ignored!
If it is difficult to understand, don't let the high-speed rail above throw tennis balls to help understand. This tennis ball will be bounced at twice the speed of the train+the original speed. Of course, the train speed will be reduced, but this value can also be ignored.
Application of gravity slingshot
It was the Soviet scientist Yuri who first proposed the gravitational slingshot? Condra Tucker proposed in his paper published in1918-1919 that a spacecraft can accelerate and decelerate between two planets by using the gravity and orbital speed of the planets.
1925 Friedrich? Zander also put forward a similar idea.
1959 Lunar No.3 probe was the first user of gravity slingshot, because the revolution speed (1.023km/s) of the Earth-Moon system can be used to accelerate or decelerate.
Mariner 1974 is the first probe to reach another planet by gravity slingshot. 1974 passed Venus on February 5th, and mariner 10 decelerated by gravity slingshot and flew to Mercury smoothly (mariner 10 was a flyby detector).
Voyager 1 and Voyager 2 are the ultimate applications of gravity slingshots, especially Voyager 2, because it completely exhausts the gravitational slingshot effect of celestial bodies in the solar system, from Jupiter to Pluto.
As mentioned above, satellites can't use the gravity slingshot of the earth to accelerate, so can't the earth accelerate? Not at all. When a probe out of the earth's orbit meets the earth in the orbit of revolution, the earth can also be used for gravitational slingshot acceleration.
Gravity slingshots are so easy to use, isn't there any disadvantage?
Gravitational slingshot is a free gas station for detectors, but it has a fatal disadvantage. For example, if planets are used to accelerate, it is not difficult to design an orbit through each planet, but it is extremely time-consuming. If you are in a hurry, you can only use it less or even not.
For example, Pluto's exploration of the new horizon only bounced once when it passed Jupiter, and then all the way to Pluto, and there was no time to wait for the gravitational slingshots of other planets to accelerate (because the orbits of planets are different, the orbits should be designed to run around each planet)
Of course, we believe that even in the future, rocket engines will still be useful without the help of gravity slingshots to accelerate. For example, using gravity slingshots to slow down when entering planetary orbit does not waste time, but also saves fuel. Why not use them?
Extreme application prospect of gravity slingshot
Maybe this is a question you haven't thought about. Double black holes are used to orbit each other to accelerate the spacecraft repeatedly until the spacecraft thinks that this speed is high enough, and then it is ignited at the top of the orbit to get rid of the gravitational slingshot of the black holes to accelerate the orbit.
This is an orbit called zoom-gyro, which can theoretically increase the speed of the spacecraft to near the speed of light. It looks like dancing with wolves, but in fact this black hole is much more cruel than wolves.
If the sun has a companion star, we might as well try to run in this way. However, the sun is a star. If the companion stars are too close, life will not be born, and it is meaningless to be too far away (the speed of circling each other is very slow). So two close black holes are obviously more suitable, but the nearest black hole to the earth is also 2800 light years, and it is not a double black hole. It seems a little difficult to find such a super gas station in the galaxy, or who dares to try it? In fact, as long as the orbit design is reasonable, the risk is not great, and there are various time delay effects, it may be possible to live for decades or even longer than others!