Riding the wind of rebirth

"This is an excellent satellite platform, characterized by its large capacity, long lifespan, high versatility, and high reliability. It is also the first time that our country has introduced the concept of 'modularization' in satellite design. In other words, we only need to use the same platform and add various special-purpose performance modules in the future to turn it into a variety of specialized satellites. This will save a lot of satellite design time."

"This launch used several technologies that were being used for the first time in the world, or that were being practiced in space for the first time."

"For example, for inter-satellite communication, we use high-frequency laser communication technology."

"Optical communication has advantages such as large bandwidth and strong anti-interference ability, making it suitable for high-speed transmission of massive amounts of data between satellites. However, it has extremely high requirements for satellite pointing accuracy and stability, and the technology is difficult to implement. Microwave communication technology is more mature, has good pointing fault tolerance, and is more flexible in system design and implementation, but its bandwidth is relatively limited due to spectrum resources."

"Another, more important reason is that the allocation of spectrum resources is in the hands of foreigners. The International Radio Association is responsible for receiving applications and allocating them, which creates many obstacles for us."

"Therefore, as long as the two issues of pointing and stability are resolved, optical communication is actually more advantageous in inter-satellite link applications."

"The satellite backbone network we require has a transmission rate in the terabyte range. This data transmission volume far exceeds that of all current terrestrial communication transmission equipment. Only optical communication can achieve this."

"Another advantage is that space is a vacuum environment, so there is no signal attenuation problem caused by the scattering of microparticles in the atmosphere."

"The problem of satellite pointing accuracy is solved by adjusting the satellite's attitude. Adjusting the attitude naturally requires energy. And satellites in space, whether they use batteries or gas, will always face the problem of energy depletion."

"To solve this problem, we adopted an important invention—ion propulsion technology."

"The principle of ion propulsion technology is actually very simple. It uses solar panels on satellites to absorb solar energy and convert it into electrical energy. The electrical energy then acts on the working fluid of the ion generator, causing it to release ions. Electromagnetic coils then constrain and orient the ions, causing them to be released in the desired direction, thus generating a force opposite to the direction of release."

"This force is very small, only enough to push an A4 sheet of paper. However, there is no atmospheric interference in space, and the solar panels can generate a large amount of electricity per unit. Therefore, we can design more ion thrusters to generate greater thrust."

"Furthermore, since satellites float in space in a relatively stationary state without any source of resistance, even a tiny force is enough to make them move, and if the acceleration is maintained for a sufficient time, they can still reach extremely high speeds."

“Using this feature, we can also enable satellites to change orbits. That is, when one of the five geostationary high-orbit satellites has a problem and cannot work, we can select one of the ten medium-orbit satellites, initiate the orbit relocation procedure, and send it to fly 15,000 kilometers to geostationary high orbit to take over the work of the decommissioned satellite.”

"Because the working time of the working medium released by ions, such as xenon, is extremely long, the working time of an ion electric propulsion engine can be guaranteed to be tens of thousands of hours or more. The lifespan of the engine exceeds the lifespan of the satellite itself. Therefore, this kind of engine can fully and reliably serve as a power source within the lifespan of the satellite."

The students listened with great interest. In a world without resistance, applying a continuous, minimal force—equivalent to blowing an A4 sheet of paper—to a satellite weighing tons on the ground would allow it to begin moving and overcome gravity to accelerate. Even if this acceleration is extremely small, given enough time, it would eventually give the satellite an extremely high speed, allowing it to traverse distances of tens of thousands of kilometers and reach another orbit.

"Now that we've solved the power problem, the next step is to address the issues of steering accuracy and stability."

"Laser is like a lighthouse. Although it has virtually no attenuation in space and can be received by satellites at extremely far distances, there is an important problem: it is different from signals that propagate in wave patterns. It is point-like. Receiving satellite signals is like a sailboat on the ocean. To receive the lighthouse's information, you first need to be able to find the lighthouse."

"This technology is called light source traction stabilization technology," Zhou Zhi continued. "It's quite simple. The optical equipment is mounted on a gimbal similar to a gyroscope, which can be automatically adjusted. The adjustment method is to design a light spot collection head that can run on a spherical surface and design an electric target. After the collection head receives the laser, it will act in the opposite direction based on the displacement of the laser on the electric target when the satellite moves relative to it, thus reducing such motion."

"The purpose of this device is to ensure that no matter how the satellite moves, the laser signal acquisition end on the satellite is always accurately aligned with the light source of another satellite, so as to ensure that the communication link is not interrupted."

"This movement only requires an internal motor to drive the balance through the interaction between the gimbal and the base. It is an internal force system, so there is no need to use the ion electric propulsion engine as an external force system, which can extend the overall life of the ion electric propulsion engine."

"Theoretically speaking, three geostationary satellites located above the equator, each covering an angle of 162 degrees and spaced 120 degrees apart, can cover the entire surface of the world except for the poles. This principle is called the 'minimum number of satellites for global communication' principle, which is also the core foundation of satellite communication systems."

"But our requirements are higher. We will use four satellites in geostationary orbit at high altitude to form a 'translation zone,' similar to the way light moves up and down in the tropics. By using a shift system, we will ensure that the signal coverage of the geostationary satellites includes both poles, so as to generate as many signal coverage areas as possible. This will allow more low-orbit satellites and ground stations to participate in inter-satellite and satellite-to-ground communication."

"At the same time, there is another satellite permanently stationed in our country's airspace, which serves as a redundant backup satellite and also provides greater load offloading capacity for domestic satellite communications, sharing some of the tasks of the on-duty satellites."

“Once the principles are explained, the rest is simple,” Zhou Zhi said. “The coverage area of ​​the ten medium-orbit satellites is not large. Each of them has its own satellite region. For communication needs within the same satellite region that require crossing two or three ground stations, they are relayed through a single satellite.”

"If they are adjacent star sectors, the medium-Earth orbit satellites will relay the signal themselves."

"If you need to cross two or three satellite regions, you would need to relay multiple times if you rely on medium-Earth orbit satellites. In this case, high-Earth orbit satellites would take on the relay task."

"Of course, this is just a very simple example. In actual relay missions, the situation is more complicated. For example, there is no ground station on the ocean, and the ship directly sends the signal to the medium-Earth orbit satellite for transmission."

"Regardless of the actual transmission link, it follows one principle: the principle of least relay. Our network can guarantee that two people at any location on Earth can establish a communication connection through a maximum of only four satellites." (End of Chapter)