Riding the wind of rebirth

"To put it another way, the Long March 3B rocket can now carry any type of satellite in the world, right?" Yang He asked.

Indeed, this is the case. It wasn't until 2019 that China designed the Shijian-20 satellite, which weighed eight tons. And it wasn't until five years later, in 2023, that Jupiter, the largest satellite ever built, broke the nine-ton mark and was launched by the Falcon Heavy rocket.

By then, China will also have its own heavy-lift launch vehicle for transporting space station modules—the Long March 5B, with a formidable carrying capacity of 22 tons.

The Long March 5B is also a clustered rocket. Although 90% of its design is new technology, its technical approach is consistent with that of the Long March 2E, Long March 3A, and Long March 3B.

Therefore, Zhou Zhi is very proud of China's aerospace technology, saying, "That's the idea. And it's not just that. I'm afraid the Long March 3B will be able to meet the launch requirements for satellites for many years to come."

Of course, rocket design is not simply about increasing size, fuel, and payload capacity. The entire rocket consists of the rocket body structure, propulsion system, control system, telemetry system, external measurement and safety system, propellant management and attitude control system during the coasting phase, cryogenic propellant utilization system, separation system, and auxiliary systems. Each system is a highly complex and precise high-tech research field, and it is also a symbol of a country's comprehensive national strength and technological accumulation. This is the true "pearl of industry".

Zhou Zhi is actually an outsider to these things, but because he has been paying attention to his project for a long time, his understanding of rockets is much better than that of his peers.

Therefore, he could easily recount many details, which broadened the horizons of his friends and left them in awe.

For example, the Long March 3B can perform missions with various orbital requirements and can also meet the requirements for payload attitude adjustment, reorientation, and spin-up. It can even provide various types of fairings according to different user needs. It can be said that it has implemented the business practice of "the customer is king" to a great extent, and it is indeed a rocket designed to meet the needs of commercial launch missions.

For example, Zhou Zhi also told his friends that the rocket's attitude is actually controlled by the four liquid-fueled engines, each with a thrust of 75 tons, installed on the first core stage. Each engine not only provides power, but its nozzle can also swing unidirectionally by a maximum angle of 10 degrees under the drive of a servo mechanism to control the rocket's flight attitude.

The booster nozzles do not have this function, but each booster is equipped with a tail fin at the rear to stabilize its attitude.

The part that Zhou Zhi understood most deeply was the part hidden inside the fairing, the most important of which was the star-rocket interface.

"The so-called satellite-rocket interface is the part where the lower frame of the satellite connects to the upper frame of the rocket's payload support. The satellite and the rocket are locked together by straps," Elbow explained. "The Long March 3B rocket can provide various mechanical interfaces, generally providing standard mechanical interfaces. However, our mission this time is very special, so we are using a special interface."

"The strapping integrates multiple functions such as satellite-rocket connection, unlocking, release, and measurement. It separates the traditional satellite-rocket connection part into a module with various interfaces reserved. By using strapping of different diameters, it can be adapted to satellites of different weights. By designing this as a standard and modular system, forming a design standard, satellite-rocket matching can be carried out conveniently and quickly."

"Next, I'd like to ask you a question. Our upcoming Xingqing-1 satellite is actually only a medium-sized satellite, so why do we need to use a heavy-lift launch vehicle like the Long March 3B to carry out the mission? Also, why do we need to use special adapter tape to adapt to our Xingqing satellite?"

"Your question is way too technical. I refuse to answer it," Yan Xiao protested.

Everyone agreed that this question was indeed quite technical and not something they could answer.

“I think there must be multiple satellites installed inside the rocket's fairing right now.” He Shiqing looked at the towering Long March 3B rocket. “Since they are medium-sized satellites, the weight of a single satellite certainly wouldn't require the Long March 3B to launch. Therefore, to reach the weight needed for the Long March 3B to launch, it can only be done by combining multiple satellites.” “Also, because it's a multi-satellite launch, the connection between the satellites and the rocket is naturally much more complex than a single-satellite launch, so only special strapping can be used.”

"Absolutely right!" Zhou Zhihe clapped his hands with poetic enthusiasm: "See? This problem is actually not difficult at all. The key is whether you like to use your brain!"

"Speaking of which, we should all have thought of this," Feng Xueshan laughed. "Actually, it's the only possibility!"

“Yes, mainly because we’ve all stopped thinking hard enough,” Yan Xiao laughed. “No wonder Shi Qing has always been a top student.”

“I’m not afraid of being laughed at by Xiao Miao and Zhouzi for saying this in front of them,” He Shiqing said with a smile.

As everyone toured the base, they listened to Zhou Zhi's explanations. Sometimes, even if Zhou Zhi didn't know about a particular piece of equipment or venue, they could ask the accompanying soldiers for details.

For example, there is a railway line under each launch tower, which is used to transport the rocket launch platform.

The rocket was transported to the base by train. After final assembly on the assembly platform at the base, the platform and the rocket standing on it were moved by rail to the launch pad and secured, and then fuel loading began.

“Speaking of fuel loading is also a very interesting topic,” Zhou Zhi said with a smile. “It also fully demonstrates how much effort scientists put into rocket launches.”

"Most of the existing main liquid rocket fuels are binary, consisting of a reducing agent and an oxidizer. Therefore, a liquid rocket must have two tanks, one for storing the reducing agent and the other for storing the corresponding oxidizer."

"Regarding the quality of fuel, there is a parameter called 'specific impulse,' which is a velocity change formula. It is related to the mass of the rocket at liftoff, the mass remaining after complete combustion of the stage, and the rocket's exhaust velocity. The higher the specific impulse, the stronger the rocket's carrying capacity and the better its performance."

"But considering only specific impulse is not enough. For example, the fuel combination with the highest specific impulse in commonly used rocket engines is liquid hydrogen and liquid oxygen, whose specific impulse is unparalleled compared to other fuels."

"However, it also has many problems. First of all, the storage conditions are quite demanding. Liquid hydrogen has a boiling point of only 20K, while liquid oxygen has a boiling point of 90K and a freezing point of 50K. In other words, if liquid hydrogen and liquid oxygen are stored at the same temperature, the liquid oxygen will freeze. Therefore, the rocket's cooling system cannot be just one set; the two must be stored at different temperatures, which requires a lot of money."

"The addition of this expensive cooling system increases the cost of the rocket. Moreover, although liquid hydrogen has a high specific impulse, its density is too low, even less than that of water. Therefore, to hold enough liquid hydrogen for flight, the storage tank needs to be much larger. As a result, all rockets that use liquid hydrogen and liquid oxygen as their main propulsion system have one characteristic: they are fat. The most representative example is the 'big orange tank' in the middle of the US Space Shuttle, which is super big."

The TV commercials for Tang are still running. It's basically a powder made from orange flavoring and sugar, which can be mixed to create an orange-flavored drink. Because it was supposedly originally a beverage used by astronauts and was considered a "high-tech product," it sold incredibly well in the domestic market. In CCTV commercials, the Tang packaging was often accompanied by scenes of space shuttles slowly ascending into the sky with huge flames. That distinctive big orange can is indeed unforgettable. (End of Chapter)