Why are there debris after a rocket is launched? How serious are the consequences if it falls to the ground?

In recent times, some foreign media have been constantly hyping up the issue of the wreckage of the Long March 5B Yao-3 rocket launched by my country, believing that the location of the wreckage is uncertain and there is a possibility that it will fall in a densely populated area and cause personal injury and property damage.

In response to this, China's Ministry of Foreign Affairs made it clear when answering reporters' questions that my country's rockets have been specially designed, and most of the components will be ablated and destroyed during the re-entry process. The probability of causing harm to aviation activities and the ground is extremely low. This is a method commonly used internationally.

At 1:45 a.m. on July 31, China Manned Space Agency released a message: the ink debris of China's Long March 5B carrier rocket has fallen, and the coordinates of the landing area are: 119 degrees east longitude and 9.1 degrees north latitude. This place is an uninhabited sea area, and there have been no reports of casualties or damage so far.

As a result, foreign media hype died down.

So, why do rockets have debris and how are they generally dealt with?

Traditional rockets are actually disposable vehicles that are discarded after sending cargo or spacecraft into orbit. For example, the Long March 5B Y3 launched on July 24 sent the 23.2-ton Wentian experimental module into orbit. The entire 800-ton rocket completed its mission, and most of the payload was fuel, which burned up, leaving the rest of the rocket shell and engine as wreckage.

The debris occurred and was handled in several stages.

First of all, right after the launch, we saw some white blocks falling in the video. These are the insulation layers covering the rocket fairing. They are insulation measures taken to ensure that the payload in the fairing is not damaged when there is a large temperature difference between day and night at the launch site.

These insulation layers are made of plastic foam and are designed to have a windward side. Once the rocket starts, as the vibration and speed increase, these foam insulation layers will fall off. These are the white fragments that people see falling in the video. These foams all fall in the launch area and will not cause any damage to people or property.

But this is not considered wreckage; it can only be considered a procedure or episode in the launch process, like the flowers scattered by the goddess when she ascends to heaven.

When a rocket takes off, it first burns the fuel in the boosters. After burning, the boosters are useless, so they are the first part of the rocket to become debris. For example, the four strapped boosters of the Long March 5B rocket burn out their fuel after burning for about 170 seconds, and then separate from the first stage of the rocket core and fall freely.

The rocket then flew out of the atmosphere, and the fairing became the second part of the rocket debris and fell off. The so-called fairing is the cover on the head of the rocket, which is one of the important components of the rocket. Due to the dense air on the earth, the payload will be affected by aerodynamic forces, aerodynamic heating, acoustic vibration, etc. during launch. The fairing is wrapped around the payload to protect it.

The rocket had already left the atmosphere more than 200 seconds after launch, at which point the fairing lost its function and was thrown off in two halves, falling toward the surface.

The above debris falls from a not-too-high altitude and will not be burned by the atmosphere, so larger debris fragments will fall and may cause damage to people and objects on the ground.

The debris dropped by rockets launched from inland launch sites, such as those launched from Jiuquan, Taiyuan, and Xichang in my country, usually falls on land, so it is necessary to take precautions in advance and do a good job of recovery afterwards. That is, to calculate the landing point carefully, evacuate the population and livestock there, find and recover the debris after it falls to the ground, and make compensation for the damaged property.

At coastal launch bases, such as the rockets launched from my country's Wenchang Launch Center, precise calculations and control will be carried out to allow the debris to fall into uninhabited high seas, and good notification and monitoring will be carried out to avoid causing injuries and international maritime disputes as much as possible.

The fairing of the Long 5B Yao-3 rocket that launched the Wentian experimental module was 5.2 meters in diameter and 20.5 meters long. It was jettisoned 224 seconds after launch, and the wreckage fell into the high seas near the Philippines without causing any damage. One piece of it drifted for many days and was salvaged by Filipino fishermen.

If the rocket is launching a manned spacecraft, an escape tower will be installed on the top of the rocket above the fairing. The escape tower is connected to the astronaut cabin in the fairing. Once an emergency occurs during the launch, the escape tower engine will ignite instantly, driving the astronaut cabin to quickly escape from the rocket. This ensures the safety of astronauts in rocket accidents.

The rocket will reach an altitude of about 40 kilometers about 120 seconds after launch. If everything goes well, the escape tower will be jettisoned. If there is a malfunction in the future, the crew cabin will start the tower-free escape mode in the high altitude where the air is thin. The escape tower will become debris and fall back to the earth. The treatment method is similar to the fairing debris. Shortly after the escape tower is jettisoned, the fairing will be jettisoned.

What caused controversy and was hyped by foreign media this time was the wreckage of the final stage rocket.

The final stage rocket refers to the last stage of the rocket that carries the payload. This stage of the rocket flies the highest and reaches the fastest speed. Generally, the final stage rocket completes its mission only after sending the "guest" to orbit. After that, the rocket is separated from the spacecraft, satellite or equipment being transported.

The Long March 5B Yao 3 rocket is a one-and-a-half-stage rocket. The half stage refers to the four boosters that contribute 90% of the thrust, pushing the rocket off the ground and into the atmosphere. After burning the fuel and separating, the core stage is responsible for accelerating the Wentian laboratory module to the first cosmic speed of 7.9 kilometers per second and sending it to the space station orbit about 400 kilometers above the ground, and the mission is completed.

After completing its mission, the core first stage rocket will separate from the Wentian Experimental Module and become an uncontrolled wreckage. This "wreckage" is 33.16 meters high, 5 meters in diameter, and weighs 21.6 tons. Although the huge wreckage has lost its power, it will still fly at an inertial speed of 7.9 kilometers per second.

In low-Earth orbit, although it is a high vacuum, there are still extremely rarefied atmospheric molecules. Frictional resistance will gradually slow down the debris, and under the pull of the Earth's gravity, it will gradually reduce its altitude and eventually fall down. As the altitude decreases and enters the dense atmosphere, the temperature of the rocket debris can reach one or two thousand degrees due to high-speed friction with the atmosphere. Most of it will be burned, but a small part of the debris that cannot be completely burned will still fall to the surface of the Earth.

So, when and where did the debris fall to the ground? Will it cause damage to people and property? This is the focus of recent doubts and speculation by some institutions and foreign media.

In fact, the world has long had a practice regarding the safety of rocket debris re-entering the atmosphere. my country also attaches great importance to it and has taken two main measures: first, the debris was passivated; second, the movement of the rocket debris was closely monitored and four orbital reports were issued.

The so-called passivation treatment is to "drain" the remaining high-pressure gas, fuel, and electricity by program control before the wreckage re-enters the atmosphere, so as to avoid an explosion under high temperature and high pressure during the fall, leaving more and more scattered fragments and forming a larger impact range.

Under the close monitoring and reporting of the Chinese space agency, the core stage debris of the Long March 5B Yao 3 rocket fell into the atmosphere in the early morning of July 31 after traveling in space for a week, igniting a magnificent spark in the sky. After most of it burned, some fragments fell into the uninhabited sea. The dust settled, and all kinds of doubts and hype came to an abrupt end.

How much do you know about incidents of rocket debris injuring people and damaging property?

In human space exploration, there will always be sacrifices. However, casualties occur more often when rocket launches fail. Such injuries and sacrifices have occurred both in China and abroad, so I won’t mention them here. However, since there are debris after the rocket launch, these debris will fall to the ground, and injuries will always occur, but injuries are still very rare.

This is because the Earth is so large that even though there are more than seven billion people, the population is still very sparse compared to the Earth's surface area. The Earth's surface area is 510 million square kilometers, which means there is one person per 70,000 square meters.

Of course, the population is not evenly scattered over these areas. There are densely populated areas and uninhabited areas, and uninhabited areas account for the vast majority of the earth's area. For example, the ocean occupies 70% of the earth's surface area. Therefore, under normal circumstances, the wreckage falls in uninhabited areas.

But with so many launches, there will always be some that fall into populated areas, especially boosters and first-stage rockets, which are abandoned shortly after launch. However, the debris handling procedures are extremely standardized and strict, and the drop point will be calculated in advance and personnel will be organized for evacuation. Therefore, even if it falls into a densely populated area, it will only damage some facilities without harming people or livestock.

Therefore, rocket debris falling to the ground happens from time to time, both in China and abroad, but injuries are rare. However, as more and more space launches are carried out, more and more debris will fall. Will this pose a greater threat to humans? I think this situation will not only not happen, but will also decrease.

Because, with the continuous progress and development of human science and technology, the way of rocket launch is also constantly improving, and rocket recovery technology is also constantly improving. For example, Musk's Space Exploration Technology Company (SpaceX) rocket recovery technology has gradually matured, which not only greatly reduces the harm of debris, but also allows rockets to be reused, greatly reducing launch costs.

It is reported that my country's rocket recovery technology has also made progress. In the future, the Long March 8 rocket will carry out a test of recovering the core first stage rocket and booster as a whole. Therefore, as the level of human civilization continues to improve, the number of rocket debris damage incidents will continue to decrease.

What do you think about this? Welcome to discuss and comment.

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