At what altitude are the satellites flying, the orbit calculation, the speed and direction of movement

Just as the seats in the theater allow a different look at the view, different orbits of satellites give perspective, each of which has its purpose. Some seem to be hanging over a point of the surface, they provide a constant view of one side of the Earth, while others are circling around our planet, sweeping over many places in a day.

Types of orbits

At what altitude do the satellites fly? There are 3 types of near-earth orbits: high, medium and low. On the highest, most remote from the surface, as a rule, there are many weather and some communication satellites. Satellites rotating in the medium earth orbit include navigation and special, designed to monitor a particular region. Most scientific spacecraft, including NASA's Earth Observation System fleet, are in low orbit.

The speed of their movement depends on how high the satellites are flying. As we get closer to the Earth, gravity becomes stronger, and motion accelerates. For example, the NASA Aqua satellite takes about 99 minutes to fly around our planet at an altitude of about 705 km, and a meteorological device remote to 35,786 km from the surface will need 23 hours, 56 minutes and 4 seconds. At a distance of 384,403 km from the center of the Earth, the Moon completes one revolution in 28 days.

Aerodynamic paradox

The change in the altitude of the satellite also changes its speed in orbit. There is a paradox here. If the satellite operator wants to increase its speed, it can not just start the engines for acceleration. This will increase the orbit (and altitude), which will lead to a decrease in speed. Instead, start the engines in the direction opposite to the direction of motion of the satellite, that is, perform an action that would slow down the moving vehicle on Earth. This action will move it below, which will increase the speed.

Characteristics of orbits

In addition to altitude, the path of the satellite movement is characterized by eccentricity and inclination. The first relates to the shape of the orbit. A satellite with a low eccentricity moves along a trajectory close to circular. The eccentric orbit has the shape of an ellipse. The distance from the spacecraft to the Earth depends on its position.

The inclination is the angle of the orbit with respect to the equator. The satellite, which rotates directly above the equator, has a zero slope. If the spacecraft passes over the northern and southern poles (geographical, not magnetic), its slope is 90 °.

All together - height, eccentricity and inclination - determine the motion of the satellite and how the Earth will look from its point of view.

High Earth

When the satellite reaches exactly 42164 km from the center of the Earth (about 36 thousand km from the surface), it enters the zone where its orbit corresponds to the rotation of our planet. Since the apparatus moves at the same speed as the Earth, that is, its period of revolution is 24 hours, it seems that it remains in place over a single longitude, although it can drift from north to south. This special high orbit is called geosynchronous.

The satellite moves in a circular orbit just above the equator (eccentricity and inclination are zero) and relative to the Earth stands still. It is always located above the same point on its surface.

The geostationary orbit is extremely valuable for weather monitoring, since satellites on it provide a constant view of the same surface area. Every few minutes, meteorological instruments such as GOES provide information on clouds, water vapor and winds, and this constant flow of information serves as a basis for monitoring and forecasting weather.

In addition, geostationary devices can be useful for communication (telephony, television, radio). GOES satellites provide the operation of a search and rescue beacon used to assist in the search for ships and aircraft in distress.

Finally, many of Earth's high Earth orbit satellites monitor solar activity and monitor levels of magnetic field and radiation.

Calculating the altitude of GSO

The centripetal force F _ц = (M ₁ v ² ) / R acts on the satellite and the gravitational force F _т = (GM ₁ M ₂ ) / R ² . Since these forces are the same, you can equalize the right parts and cut them by the mass M ₁ . As a result, we get the equality v ² = (GM ² ) / R. Hence the velocity v = ((GM ₂ ) / R) ^1/2

Since the geostationary orbit is a circle of length 2πr, the orbital velocity is v = 2πR / T.

Hence, R ³ = T ² GM / (4π ² ).

Since T = 8.64 × 10 ⁴ s, G = 6.673 × 10 ^-11 N · m ² / kg ² , M = 5.98 × 10 ²⁴ Kg, then R = 4.23x10 ⁷ m. If you subtract from R the radius of the Earth, equal to 6.38 x 10 ⁶ m, you can find out at what altitude the satellites fly over one point of the surface - 3.59x10 ⁷ M.

The Lagrange points

Other remarkable orbits are the Lagrangian points, where the gravitational force of the Earth is compensated by the gravity of the Sun. Everything that is there, is equally attracted to these heavenly bodies and rotates with our planet around the star.

Of the five Lagrange points in the Sun-Earth system, only the last two, called L4 and L5, are stable. In the rest the companion is like a ball balancing on the top of a steep hill: any slight perturbation will push it out. To remain in a balanced state, spacecraft here need to be constantly adjusted. At the last two points of Lagrange, the satellites are likened to a ball in a ball: even after a strong perturbation they will return back.

L1 is located between the Earth and the Sun, allows the satellites in it to have a constant view of our luminary. The SOHO Solar Observatory, NASA's satellite and the European Space Agency are following the Sun from the first point of Lagrange, 1.5 million kilometers from our planet.

L2 is located at the same distance from the Earth, but is behind it. Satellites in this place require only one heat shield to protect themselves from the light and heat of the Sun. This is a good place for space telescopes used to study the nature of the universe by observing the background of microwave radiation.

The third point of Lagrange is located opposite the Earth on the other side of the Sun, so that the star is always between it and our planet. The satellite in this position will not have the opportunity to communicate with the Earth.

The fourth and fifth points of Lagrange are extremely stable in the orbital trajectory of our planet at 60 ° ahead and behind the Earth.

Medium Earth orbit

Being closer to the Earth, the satellites move faster. There are two medium near-Earth orbits: half-synchronous and "Lightning".

At what altitude do satellites fly in a half-synchronous orbit? It is almost circular (low eccentricity) and is removed to a distance of 26,560 km from the center of the Earth (about 20,200 km above the surface). The satellite at this altitude makes a full turn in 12 hours. As it moves, the Earth rotates under it. In 24 hours it crosses 2 identical points on the equator. This orbit is consistent and very predictable. Used by Global Positioning System GPS.

Orbits "Lightning" (inclination 63.4 °) is used for observation in high latitudes. Geostationary satellites are tied to the equator, so they are not suitable for distant northern or southern regions. This orbit is very eccentric: the spacecraft moves along an elongated ellipse with the Earth located close to one edge. As the satellite accelerates under the action of gravity, it moves very fast when it is close to our planet. When removed, its speed slows down, so it spends more time at the top of the orbit at the farthest edge of the Earth, the distance to which can reach 40 thousand km. The period of revolution is 12 hours, but about two-thirds of this time the satellite spends over one hemisphere. Like a half-synchronous orbit, the satellite travels through the same path every 24 hours. It is used for communication in the far north or south.

Low Earth

Most scientific satellites, many meteorological and space stations are on an almost circular low earth orbit. Their inclination depends on what they are monitoring. TRMM was launched to monitor precipitation in the tropics, so it has a relatively low inclination (35 °), remaining near the equator.

Many of the satellites of the NASA observation system have an almost polar, highly inclined orbit. The spacecraft moves around the Earth from pole to pole with a period of 99 minutes. Half of the time it passes over the day side of our planet, and at the Pole passes to the night.

As the satellite moves, the Earth rotates beneath it. By the time the apparatus switches to the lighted area, it is above the area adjacent to the zone of its last orbit. Over a 24-hour period, polar satellites cover the greater part of the Earth twice: once in the daytime and once at night.

Solar synchronous orbit

Just as geosynchronous satellites should be above the equator, which allows them to stay above a single point, the polar orbits have the ability to stay in the same time. Their orbit is solar-synchronous - when crossing the equatorial spacecraft, the local solar time is always the same. For example, the Terra satellite crosses it over Brazil always at 10:30 in the morning. The next crossing in 99 mins over Ecuador or Colombia is also at 10:30 local time.

The solar-synchronous orbit is necessary for science, since it allows to keep the angle of sunlight falling on the Earth's surface, although it will vary depending on the season. This constancy means that scientists can compare the images of our planet one season of the year for several years without worrying about too much jumps in lighting that can create the illusion of change. Without a solar-synchronous orbit, it would be difficult to track them over time and gather the information needed to study climate change.

The path of the satellite here is very limited. If it is at an altitude of 100 km, the orbit must have a slope of 96 °. Any deviation will be unacceptable. Since the resistance of the atmosphere and the attraction force of the Sun and the Moon change the orbit of the apparatus, it must be regularly adjusted.

Launching: launching

Launching a satellite requires energy, the amount of which depends on the location of the launch site, the height and inclination of the future trajectory of its movement. To get to a remote orbit, you need to spend more energy. Satellites with a significant slope (for example, polar) are more energy-intensive than those that circulate above the equator. A rotation into the orbit with a low inclination is facilitated by the rotation of the Earth. The international space station is moving at an angle of 51.6397 °. This is necessary to make it easier for space shuttles and Russian missiles to reach it. The height of the ISS is 337-430 km. Polar satellites, on the other hand, do not receive help from the Earth's impulse, so they need more energy to climb the same distance.

Adjustment

After launching the satellite, it is necessary to make efforts to keep it in a certain orbit. Since the Earth is not an ideal sphere, its gravity is stronger in some places. This unevenness, along with the attraction of the Sun, the Moon and Jupiter (the most massive planet of the solar system), changes the inclination of the orbit. Throughout its lifetime, the position of GOES satellites was adjusted three or four times. NASA's low-orbiting vehicles should regulate their slope annually.

In addition, the atmosphere is affected by near-Earth satellites. The uppermost layers, though fairly sparse, exert strong enough resistance to draw them closer to the Earth. The action of gravity leads to the acceleration of satellites. Over time, they burn, spiraling lower and lower in the atmosphere, or fall to Earth.

Atmospheric resistance is stronger when the sun is active. Just as air in a balloon expands and rises when heated, the atmosphere rises and expands when the Sun gives it extra energy. The rarefied layers of the atmosphere rise, and their place is occupied by denser ones. Therefore, satellites on the Earth's orbit should change their position approximately four times a year to compensate for the resistance of the atmosphere. When the solar activity is maximal, the position of the apparatus must be adjusted every 2-3 weeks.

Space debris

The third reason forcing to change the orbit is space debris. One of the communication satellites Iridium collided with a dysfunctional Russian spacecraft. They broke up, forming a cloud of debris, consisting of more than 2500 parts. Each element was added to the database, which now has over 18,000 objects of technogenic origin.

NASA carefully tracks everything that may be in the way of the satellites, because because of space debris, it has already several times changed orbits.

The engineers of the Mission Control Center monitor the position of space debris and satellites, which can interfere with the movement and, as necessary, carefully plan the evasion maneuvers. The same team plans and maneuvers to adjust the slope and altitude of the satellite.