What is the purpose of this move with frequent changes in the orbits of US satellites?

Just a warning.

The horizontal velocity of a satellite flight is called the first cosmic velocity, that is, the orbital velocity. As long as the satellite gains this horizontal velocity, it does not need to be repowered to fly around the earth. At this time, the flight trajectory of the satellite is called the satellite orbit.

If we think of the Earth's sphere surrounded by satellites as a homogeneous sphere, its gravitational field is the central force field, and its center of mass is the center of gravity. Then, in order to make the artificial earth satellite (referred to as the satellite) move in a circular motion in this central force field, in layman's terms, it is necessary to make the force (centrifugal inertia) formed by the acceleration of the satellite's flight just cancel (balance) the gravitational force. The orbital plane of the satellite passes through the center of the Earth.

If the velocity is slightly greater, an elliptical orbit is formed, and if the escape velocity is reached, it is a parabolic orbit, at which point it will fly around the Sun and become an artificial planet; If it reaches the third cosmic velocity, it will be in a hyperbolic orbit, flying around the center of the Milky Way like the Sun.

As far as artificial earth satellites are concerned, their orbits are divided into low and high orbits according to their altitude, and forward and retrograde orbits according to the direction of the Earth's rotation. There are some orbits of special significance, such as equatorial orbit, geosynchronous orbit, geostationary orbit, polar orbit and sun-synchronous orbit.

The shape and size of the satellite orbit are determined by the major and minor axes, while the intersection angle, perigee amplitude and orbital inclination I determine the orientation of the orbit in space. These five parameters are called satellite orbit elements (number of roots). Sometimes the perigee time TP is also added, which is collectively referred to as the six elements.

With these six elements, it is possible to know the position of the satellite in space at any given moment.

Six elements of satellite orbit: long axis, minor axis, intersection angle, perigee amplitude angle, orbital inclination angle I, and perigee time TP.

There is no clear demarcation boundary between high and low orbits, and satellite orbits several hundred kilometers above the ground are generally called low Earth orbits.

The orbital inclination is zero, and the orbital plane coincides with the Earth's equatorial plane. This type of orbit is called an equatorial orbit.

When the orbit altitude is 35,786 kilometers, the orbit period of the satellite is the same as the rotation period of the earth, and this kind of orbit is called geosynchronous orbit; If the inclination angle of the geosynchronous orbit is zero, then the satellite is just above the earth's equator, flying around the earth at the same angular speed as the earth's rotation, and from the ground, it seems to be stationary, this kind of satellite orbit is called geostationary orbit, which is a special case of geosynchronous orbit. There is only one geostationary orbit.

When the orbital inclination angle is 90 degrees, the orbital plane passes through the earth's poles, and this kind of orbit is called polar orbit.

If the direction of rotation and angular velocity of the orbital plane of a satellite around the Earth's axis of rotation are the same as the direction and angular velocity of the Earth's revolution around the Sun, its orbit is called a sun-synchronous orbit. The sun-synchronous orbit is retrograde with an inclination of more than 90 degrees.

The Russian side said that this was a dangerous signal, and the United States was issuing a warning.

The move of the US military satellite has an obvious purpose and is a danger signal, which has caused major security risks to the safety of satellites in orbit in various countries around the world.

At present, the vast majority of global geosynchronous orbit satellites are used for civilian use, such as meteorology, navigation, and disaster warning, and so on, and very few are used for military purposes.

This is to show off to other countries how superb their technology is and how advanced their technology is.

Russia's automated early warning system for dangerous situations around the earth has found that the ultimate purpose of their massive maneuvers is to encircle and monitor for a long time a number of targets classified as advanced threats by the United States.

Show off your beautiful skills. I want others to know how strong he is. I also want to check the basic whereabouts of each person returning home through satellites.

You've all guessed wrong, I think the machine is aging and broken.

There is no point in showing off, actual combat drills are the real purpose, think about the European satellite system, and I dare not think about war.

He's warning his opponent how strong he is.

This is a warning to other countries that this is their territory.

This means that the United States can attack other satellites it wants to destroy at any time with a first-class satellite, which is similar to a military exercise, showing its muscles.

This is the Americans rehearsing space attack satellites**, and we have to beware of it.

The United States is pretending to be a calf, and the official performance was very good, but in the end a donkey rolled around.

Apparently preparing for anti-satellite.

It is used to deter other countries.

Meaning, you guys are a little pediatrician who is in sync, and watch my magic makeover.

Star Wars, pre-war rehearsals.

It's showing off to other countries how advanced their technology is.

The process of autonomously changing the orbit of a satellite while it is in orbit is called orbit change. The satellite orbit is elliptical, and the method of saving rocket fuel can be launched to a large elliptical orbit first, and when the satellite is at apogee, the attitude on the satellite adjusts the rocket ignition, so that the orbit of the satellite becomes the required height. The orbit change can be multiple times, which requires an accurate calculation of the time of the satellite's orbit change, which is controlled by ground commands.

Due to the gravitational pull of the Earth, the orbits of artificial satellites and spacecraft (including space stations) will descend at a rate of about 100 meters per day. This will affect the normal operation of artificial satellites and spacecraft (including space stations). In the process of orbit operation, it is often necessary to change orbits.

In addition to avoiding the damage caused by "space junk", the main purpose of orbit change is to ensure the life of its operation.

The centripetal force required for an artificial satellite moving in a uniform circular motion around the Earth is provided by gravitational force. After the orbital radius r is determined, the corresponding linear velocity, period, and centripetal acceleration of the satellite are also determined. If the mass of the satellite is also determined, once the satellite changes its orbit, that is, the orbital radius r changes, the above physical quantities will change accordingly.

In the same way, as long as one of the above physical quantities changes, the others must also change.

The principle of satellite orbit change is actually to start several small rockets on the satellite to drive the satellite to a new orbit (adjust attitude). Therefore, the life of the satellite actually depends on the fuel situation of these small rockets, and when the fuel of the small rockets runs out, there is no way to adjust the attitude of the satellite, and the satellite can only be scrapped. Even if all the equipment on the satellite is in good condition, it can only be scrapped.

The purpose of the Orbital Express project is to verify the technical feasibility of spaceborne robots to maintain satellites in orbit, and to demonstrate and verify the operations of on-orbit interactive docking, on-orbit maintenance and device update. According to NASA, the purpose of the Orbital Express program is to validate space technologies such as satellite rendezvous, capture, docking, repair, and refueling to support future commercial, civil, and defense space programs in a broader range of fields, and to "provide support for key technologies for future U.S. space capabilities to replace astronauts in space operations for decades to come."

Specifically, the United States expects to acquire new space operational capabilities through the validation project, including refueling satellites to enable them to maneuver to increase coverage, changing the time of flight over targets and increasing the survivability of satellites, extending their lifespans, repairing satellites in orbit, replacing faulty components, updating system components, adjusting the structure of the satellites, enabling post-launch technical upgrades without the need to launch new satellites: space resource protection or the deployment of specialized satellites for space inspections, It can improve the performance of satellites in orbit while reducing the life cycle cost of their branches, and provide technical reserves for other orbit maintenance tasks.

In addition to civilian and commercial space activities, the "orbital" express program will enable satellites to support important national defense missions and trigger a new round of revolution in the field of space operations. For example, by maneuvering to avoid collisions with space debris or other objects, to change the orbit of reconnaissance satellites and to observe ground targets, to counter camouflage activities on the ground, and so on.

I think there are two main points:

First, in terms of orbital inclination, the orbital inclination of Landsat 1-3 is 99°, which is close to that of polar-orbiting satellites, which can ensure that the images obtained by satellites can cover the whole world. It's another kind of extreme case, for example, parallel to the equator (which is the case with many meteorological satellites, such as China's Fengyun series), which may not be able to obtain images of the world.

Second, its orbit is a sun-synchronous orbit, and the angular velocity of the orbital plane of the satellite around the earth is consistent with the angular velocity of the earth around the sun, so that the satellite is in the light side of the earth, a local time (9:30:00) through the equator, eliminating the change in spectral radiation caused by the angle of incidence of the sun.

Note: Now I have two points in mind. After thinking about it later, LZ also learned remote sensing?

Communicate a lot

First of all, the orbit of satellites in the sky is a balancing process.

So the orbital height will be different due to the different speeds.

Satellite docking is mainly to make the launch task that cannot be completed at one time when the load is too large, which is divided into multiple times and completed through docking.

Satellite docking is actually difficult, because the speed changes, the orbit altitude changes, so the docking is actually a collision in the process of orbit lifting or descending, but the relative speed is not large.

Satellites change orbit through the acceleration generated by their own thrusters, usually at the perigee or apogee of the orbit.

There are three basic maneuvers that can be used to change the track: (1) changing the shape or size of the track within the track plane; (2) Passed the change.

Changing the orbital inclination angle to change the orbital plane; (3) When the inclination angle of the track is unchanged, the orbital plane is changed by rotating the orbital plane around the earth's axis.

1) Change the shape or size of the track within the track surface.

If a circular orbital satellite with an original orbital altitude of h suddenly increases the speed of the satellite at a certain point in the orbit δv (no change.

variable velocity direction), the satellite will not run faster in the original same orbit, but the original orbit will change in the same orbital plane.

It became an elliptical orbit (see Figure 1).

The perigee of the new orbit (the point at which the satellite is closest to the Earth) is located at the point where the velocity suddenly increases, while the altitude of this point remains at h. The main axis of an elliptical orbit always passes through the center of the earth, while the perigee and apogee of the new orbit are located at opposite ends of the main axis, respectively, and the height of the apogee of the orbit is greater than h and is determined by the value of δv.

If thrust is applied in the opposite direction of the satellite's motion, the speed of a satellite in circular orbit decreases at a certain point in the orbit, then this point.

It becomes the apogee of an elliptical orbit, and the height of the apogee is h, and the height of the perigee will be less than h.

More generally, for elliptical orbits, changing only the magnitude of its velocity without changing its direction creates another elliptical orbit.

Dao, which is an elliptical orbit of different shapes and orientations within the same orbital plane. The resulting orbital results depend on the delta v value and the change in velocity.

Where it happened. However, in two special cases, an elliptical orbit can be turned into a circular orbit, and the orbital height may have two values. At.

A certain number required to increase apogee velocity results in a circular orbit with a height equal to the apogee height of the elliptical orbit. Velocity at perigee decreases.

Less than a certain number of values required results in a circular orbit with a height equal to the perigee height of the elliptical orbit.

If you want to go from one circular orbit (from the center of the earth r1) to another circle orbit (from the center of the earth r2) that is not tangent to the same plane (assuming r2>r1), this can be done by two maneuvers above. It first accelerates in the R1 orbit to an elliptical orbit with a perigee of R1 and an apogee of R2, and then accelerates to an R2 orbit at apogee. The elliptical orbit used to change the orbit between two circular orbital changes is tangent to both circular orbits and is called a Hohmann orbital orbit.

2) Change the track surface by changing the track inclination.

The change of orbital inclination requires δ total velocity vector rotation of the satellite δ and the required δv can be obtained by adding the vector as:

2v sin（δθ/2）

3) Compound orbit change.

The above two methods are carried out at the same time, that is, through a single speed change, the inclination and shape of the track are changed at the same time.

According to the law of gravitation, mg=(gmm) (r2)=mv2 r

So decelerate when you ascend and accelerate when you descend.

Acceleration is not known. When the perigee of the elliptical orbit is tangent to the inner orbit, the velocity of the elliptical orbit is greater than the velocity of the circular orbit, so the radius of centrifugal motion increases. When the apogee of the elliptical orbit is tangent to the outer orbit, the velocity of the circular orbit is large, and the velocity of the elliptical orbit is small, so the radius of the pericentric motion decreases.

The satellite accelerates into far-earth orbit and decelerates into near-Earth. The velocity decreases after entering the far earth orbit and increases after entering the low earth orbit. The velocity obtained from the centripetal force formula and the gravitational force formula is proportional to gm r, i.e., inversely proportional to r.

The acceleration at the tangent point is the same, it refers to the centripetal acceleration produced by the gravitational force, since the gravitational force at the tangent point of the two orbits is the same, so the centripetal acceleration at the same point is unchanged. From (gmm) (r 2)=mv 2 r can obtain the expression v is gm r and then open a big number, it can be seen that the orbit radius increases and the velocity decreases, from the low orbit to the high orbit needs to ignite to increase the kinetic energy to increase the velocity, as long as the velocity increases, it will rise to a higher orbit and convert the kinetic energy into gravitational potential energy, so the running speed will be smaller when changing to a high orbit, but more gravitational potential energy will still increase its total energy, and finally reach a stable circular operation state of a higher orbit, At this time, the velocity is smaller than that of the low orbit, where the speed of the orbital radius increases and decreases, and the speed of the increase in the radius of the orbit refers to the speed of the circumferential operation of different orbits, and the speed of the ignition acceleration increases refers to the speed of the intermediate process of orbit change. If you change from high orbit to low orbit, it's the opposite!

It is inconvenient to explain it in detail with an illustration here, I hope it can help you!