Flights of spacecraft are associated with huge energy consumption. For example, the Soyuz launch vehicle, standing on the launch pad and ready to launch, weighs 307 tons, of which more than 270 tons are fuel, that is, the lion's share. The need to spend a crazy amount of energy on moving in outer space is largely due to the difficulties of mastering the far reaches of the solar system.
Unfortunately, a technical breakthrough in this area is not yet expected. The mass of fuel remains one of the key factors in planning space missions, and engineers take every opportunity to save fuel in order to extend the operation of the device. One way to save money is through gravitational maneuvers.
How to fly in space and what is gravity
The principle of moving the device in an airless space (an environment from which it is impossible to push off with either a screw or wheels, or anything else) is the same for all types of rocket engines made on Earth. This is jet thrust. Resists the power of a jet engine gravity. This battle with the laws of physics was won by Soviet scientists in 1957. For the first time in history, an apparatus made by human hands, having acquired the first cosmic speed (about 8 km / s), has become an artificial satellite of planet Earth.
In order to put the device weighing a little more than 80 kg into low Earth orbit, it took about 170 tons (that is how much the R-7 rocket, which delivered the satellite to orbit, weighed) iron, electronics, purified kerosene and liquid oxygen.
Of all the laws and principles of the universe, gravity is perhaps one of the main ones. It runs everything from the device of elementary particles, atoms, molecules to the movement of galaxies. It is also an obstacle to the development of outer space.
Not just fuel
Even before the launch of the first artificial Earth satellite, scientists clearly understood that not only an increase in the size of rockets and the power of their engines could be the key to success. The search for such tricks by researchers was prompted by the results of calculations and practical tests, which showed how costly fuel flights outside the earth's atmosphere. The first such decision for Soviet designers was the choice of the spaceport construction site.
We will explain. To become an artificial Earth satellite, a rocket needs to accelerate to 8 km / s. But our planet itself is in continuous motion. Any point located at the equator rotates at a speed of more than 460 meters per second. Thus, a missile entering an airless space in the area of zero parallel will in itself have almost half a kilometer free per second.
That is why in the wide open spaces of the USSR a narrower place was chosen (the daily rotation speed in Baikonur is about 280 m / s). An even more ambitious project aimed at reducing the influence of gravity on a booster rocket appeared in 1964. It became the first marine space center "San Marco", assembled by Italians from two drilling platforms and located at the equator. Later, this principle formed the basis of the Sea Launch international project, which successfully launches commercial satellites to this day.
Who was the first
And what about long-distance space missions? Scientists from the USSR were pioneers in using the gravity of space bodies to change the flight path. The reverse side of our natural satellite, as is known, was first photographed by the Soviet Luna-1 camera. It was important that after the moon’s flyby, the spacecraft could return to Earth so that it would face the northern hemisphere. After all, information (obtained images) had to be transmitted to people, and tracking stations, radio antenna dishes were located in the northern hemisphere.
Equally successfully managed to use gravitational maneuvers to change the trajectory of the spacecraft by American scientists. After flying near Venus, the interplanetary automatic ship Mariner 10 needed to reduce speed in order to transfer to a lower near-solar orbit and explore Mercury. Instead of using jet thrust for this maneuver, the speed of the vehicle was slowed by the gravitational field of Venus.
How it works
According to the law of universal gravitation, discovered and experimentally confirmed by Isaac Newton, all bodies with mass attract each other. The force of this attraction is easily measured and calculated. It depends both on the mass of both bodies and on the distance between them. The closer, the stronger. Moreover, with the bodies approaching each other, the force of attraction grows exponentially.
The figure shows how spacecraft flying near a large cosmic body (a planet) change their trajectory. Moreover, the movement rate of the apparatus at number 1, flying farthest from a massive object, changes very slightly. You can not say about the apparatus number 6. The planetoid changes its direction of flight dramatically.
What is a gravity sling. How does she act
The use of gravitational maneuvers allows not only to change the direction of the spacecraft, but also to adjust its speed.
The figure shows the trajectory of a spacecraft, usually used to accelerate it. The principle of operation of such a maneuver is simple: on a red-colored section of the trajectory, the apparatus seems to be catching up with a planet running away from it. A much more massive body, with the force of its attraction, carries away a smaller one, dispersing it.
By the way, not only spaceships are dispersed in this way. It is known that celestial bodies, not attached to stars, are walking around the galaxy with might and main. It can be both relatively small asteroids (one of which, by the way, is currently visiting the solar system), and planetoids of decent size. Astronomers believe that it is the gravitational sling, that is, the impact of a larger cosmic body, that ejects less massive objects beyond their systems, dooming them to eternal wanderings in the icy cold of empty space.
How to slow down
But, using gravitational maneuvers of spacecraft, one can not only accelerate, but also slow down their movement. The scheme of such braking is shown in the figure.
In the red part of the trajectory, the planet’s attraction, in contrast to the version with a gravitational sling, will slow down the movement of the device. After all, the vector of gravity and the direction of flight of the ship are opposite.
In what cases is it used? Mainly for the release of automatic interplanetary stations into the orbits of the studied planets, as well as for the study of the circumsolar regions. The fact is that when moving to the Sun or, for example, to the planet closest to the sun, Mercury, any device, if you do not apply measures to slow down, will be willy-nilly accelerated. Our star has incredible mass and tremendous force of attraction. The spacecraft, which has gained excessive speed, will not be able to enter the orbit of Mercury, the smallest planet in the solar family. The ship will simply slip past, the baby Mercury will not be able to pull it tight enough. For braking, you can use engines. But the flight path to the Sun with a gravitational maneuver, say near the Moon and then Venus, will minimize the use of rocket propulsion. This means that less fuel will be needed, and the released weight can be used to accommodate additional research equipment.
Get into the eye of a needle
If the first gravitational maneuvers were carried out timidly and indecisively, the routes of the last interplanetary space missions are almost always planned with gravitational adjustment. The thing is that now astrophysicists, thanks to the development of computer technology, as well as the availability of accurate data on the bodies of the solar system, primarily their mass and density, are more accurate calculations. And the gravitational maneuver must be calculated extremely accurately.
So, laying a trajectory farther from the planet than necessary is fraught with the fact that expensive equipment will fly completely not where it was planned. And underestimating the mass can even threaten a collision of the ship with the surface.
Maneuver champion
This, of course, can be considered the second spacecraft of the Voyager mission. Launched in 1977, the device currently leaves the limits of its native star system, retreating into the unknown.
During operation, the device was visited by Saturn, Jupiter, Uranus and Neptune. The gravity of the Sun acted on him throughout the flight, from which the ship gradually moved away. But, thanks to correctly calculated gravitational maneuvers, at each of the planets its speed did not decrease, but increased. For each planet studied, the route was built on the principle of a gravitational sling. Without the use of gravitational correction, Voyager could not have been sent so far.
In addition to the Voyagers, gravitational maneuvers were used to launch such well-known missions as Rosetta or New Horizons. So, “Rosetta”, before setting off in search of the comet Churyumov-Gerasimenko, made as many as 4 accelerating gravitational maneuvers near Earth and Mars.