On the evening of December 27, the Long March 5 remote three carrier rocket was successfully launched. Guo Wenbin/photo
Qian Xuesen, known as the father of China Aerospace, once said: If scientific experiments can be successful every time, then why experiment? After setbacks and failures, we will become smarter.
The "Phoenix Nirvana" trip of the Long March 5 is the best example at present.
Two years ago, the second launch of the Long March 5 was defeated. This news hung over the hearts of Chinese people like a haze, and once caused doubts. Today, the largest rocket in China has been reborn for more than 900 days, and it has gone out again.
On December 27th, the Long March 5 started its third flight at Wenchang Space Launch Site, accompanied by a roar that shook the mountains. A dazzling flame surrounded the big rocket and flew out of the sky. In the end, the mission was declared successful, and this big rocket was dormant for two years, and finally it was proud!
Behind the soaring, it can be described as "twists and turns". In the words of Long Lehao, academician of China Academy of Engineering and chief designer of Long March series rockets of the First Academy of China Aerospace Science and Technology Corporation, "Failure is almost success, and success is almost failure" — — Over the past two years, more than 900 days and nights, China astronauts dare not take it lightly every moment.
Soul-stirring 2 hours and 43 minutes
Long March 5 is a rocket destined to be extraordinary from birth, which has entrusted too many people’s dreams and long-cherished wishes. For a long time, when it comes to the development of a certain technology or a certain field in China, people have become accustomed to using "big but not strong" to describe it. But aerospace is breaking this statement, and the first punch to break this statement is the Long March 5 — — It is equivalent to the admission ticket of a "space power". Its development difficulty can be imagined.
As early as 1986, the demonstration of a new generation of launch vehicles was carried out in China. Since the mid-1990s, the research on a new generation of rocket engines has been put on the agenda. In 2016, a new generation of big rockets developed after 30 years of demonstration — — The first flight of Long March 5 was successful, which attracted much attention.
However, behind the success of the first flight, there was also an episode of "almost failure".
Hu Xudong was the commander of the first flight mission 01 of the Long March 5. He still remembers that it was November 3, 2016, and the launch time was postponed from 18: 00 to 20: 43. In the meantime, it experienced six suffocating time resets, and even faced the test that the launch mission was forced to cancel.
People who watched the launch thus remembered the special moment of "near misses" and gained a somewhat more intuitive understanding of this rocket, which kicked off the era of China Grand Carrier.
When the time was set back to 17: 30 on the same day, the atmosphere in the test hall suddenly became tense, and hundreds of scientific and technological personnel looked at the big screen together — — The rocket "has a fever" because the primary circulation precooling pump of the rocket can’t be started normally. At the moment, the temperature displayed on the big screen is 238K, which is much higher than the take-off standard of 110K … …
According to Hu Xudong’s recollection, at this time, the mission headquarters decided that if the pre-cooling effect of the engine could not meet the launch conditions by 19: 30, the propellant leakage procedure would be started and the launch mission would be cancelled.
At 19: 28, there were only two minutes left from the "bottom line", the engine temperature dropped to a predetermined value, and the rocket successfully "cooled down".
"Set the ignition time to 20: 40." Hu Xudong exhaled a sigh of relief greatly. However, even at the last minute before the launch, emergencies have occurred again and again.
At 20: 40, only one minute left before the final launch, Hu Xudong just issued the password of "1 minute preparation", and suddenly heard Wei Kang, the commander of the control system, issue "the most awesome password in China’s space history": "01, stop launching!"
"What’s the matter?"
At this moment, Hu Xudong involuntarily stood up and blurted out 1.
Ten seconds before the launch, Hu Xudong began to count down, and suddenly he received a request from Wei Kang "Please wait a moment".
"Stop the launch!" Hu Xudong stopped emission process, and once again organized the troubleshooting. The problem was finally solved.
The "ignition" password was finally issued and the rocket took off.
Behind the cheers, astronauts including Hu Xudong began to sort out and analyze the launch data, and they had to face 630,000 original data — — These are related to whether China Rocket can still "turn the corner" next time.
Guess the beginning but not the ending.
Long Lehao was on the scene for the first two launch missions of Long March 5. One of his obvious feelings is that although the first launch mission was successful, the "stumbling" three hours before takeoff seems to be more touching. He said: "This is inevitable. After all, this is a brand-new rocket and the situation is too complicated."
Accordingly, the second launch, for many people at the scene, "was originally very smooth." "Before taking off, it was not as thrilling as the Long March 5 Yaoyi (the first flight mission, reporter’s note, the same below)." Long Lehao said that the launch site of Yaoer was "much calmer" and "much better" in the first few minutes.
At that time, he was still thinking, "This may be the first tortuous experience, exposing some problems, and then doing a lot of improvement work, having experience and a relatively stable mentality."
Indeed, after the Long March 5 took off from Wenchang Space Launch Site for the second time, everything was normal in the first few minutes. But after flying for more than 300 seconds, the problem appeared.
"All of a sudden, the flight curve of [Long March 5] is not quite right … …” In the test hall of Wenchang Space Launch Site, Long Lehao saw from the big screen that the curve was not going up in their predetermined direction, but was "falling" down.
His mind is tight: the flight curve falls, which means that the rocket is gradually losing thrust. If the thrust is not enough, the rocket will have no acceleration and will not be able to overcome the gravity field.
"At that time, I had a presentiment that ‘ It’s over ’ This launch is going to fail … …” Long Lehao said.
The measuring hall was silent.
A monitoring team member at the scene told reporters that their hearts, like the flight curve on the big screen, "kept falling", and many people silently shed tears.
That night, Xinhua News Agency released the news of mission failure.
"This result is what no one wants to see." Long Lehao said that he soon told himself that the failure of scientific experiments was inevitable. What we need to do now is how to find out the cause of the failure as soon as possible, take measures, try to go around as soon as possible, and prove once again that our rocket is trustworthy with practical actions.
That night, when Long Lehao left the test hall, he didn’t have much communication with the space junior on the spot. But he believes that these young astronauts have the ability to withstand the pressure. "Now it does seem that they are not overwhelmed by difficulties — — Get down and still stand up! " Long Lehao said.
What’s the problem with the engine again?
On April 16, 2018, the National Space Administration released the investigation on the failure of the Long March 5 remote rocket, which mentioned that the Long March 5 remote rocket suddenly failed when it flew to 346 seconds.
The cause of the failure is that the turbine exhaust device of the first unit of the core-stage liquid hydrogen and liquid oxygen engine is abnormal in the local structure under the complex mechanical and thermal environment, and the engine thrust drops sharply instantly, resulting in the failure of the launch mission.
Engine is also an engine. Yes, this word, which once stung the Chinese people’s key technology in the aviation field, has become a stumbling block in the aerospace field this time.
A big rocket is naturally inseparable from a big thrust, and a big thrust is inseparable from the development motivation. Before the Long March 5, the maximum thrust of a single rocket engine in active service in China was only about 70 tons, so it was "inadequate" to launch a very large spacecraft.
A new type of high thrust engine came into being. According to Zhou Limin, secretary of the Party Committee of the Sixth Academy of China Aerospace Science and Technology Corporation, after 15 years of unremitting research, eight newly developed 120-ton liquid oxygen kerosene engines were assembled on the four boosters of the Long March 5, and four newly developed hydrogen-oxygen engines were assembled on the first-class and second-class rockets.
He has an image saying that developing an engine is as difficult as climbing Mount Everest. "Some foreign experts say that even if we design it, we can’t make it." Among them, the hydrogen-oxygen engine that failed in the remote second mission is even more difficult.
Zhou Limin still remembers that in the face of brand-new engines, the research team began to tackle scientific and technological problems day and night, and dozens of new materials and more than 100 new processes were overcome one by one. However, the starting of the engine has become the biggest obstacle.
He said that in the starting stage, the whole engine is in an unstable dynamic process, because the speed changes from a static state to tens of thousands of revolutions, and the temperature changes from a low temperature state to a high temperature state. Our control sequence is controlled in milliseconds, and any action that is not well coordinated and fails to achieve the expected result may lead to failure.
At first, the development team was hit hard. After the prototype of the engine used in the first flight of Long March 5 was developed, its test results failed four times in a row: two starting explosions and two burning gas systems.
Zhou Limin said that these have dealt a great blow to the confidence of the entire research and development team and design team. "Many people dream of the explosion scene in their dreams, and they can’t eat or sleep well."
Find out the "devil" and destroy the "enemy"
And these are just the "pains" that China astronauts encountered in the engine development stage. After the failure of the Long March 5 Tele-2 mission, the pressure faced by these people became even greater, and they even called the faulty engine problem "the devil".
A test team member of the Sixth Academy of China Aerospace Science and Technology Corporation told the reporter that in order to find out the "devil" and destroy the "enemy", the development team has suffered unprecedented hardships, hardships, twists and turns and doubts in the past two years. The experience of tempering, struggling, struggling and tackling key problems is also rare in the history of development. Especially those "demons" who are hidden deep, the tension and complexity of the battle are unprecedented.
“‘ Devil ’ It pops up from time to time, blinding the development team’s sight, and even pushing them into the endless abyss of opaque. However, the development team was not intimidated by the darkness and was not defeated. " Zhou Limin said.
According to the statistics of the Sixth Academy of China Aerospace Science and Technology Corporation, in the second and third quarters of 2019 alone, the development teams of 11 hydrogen-oxygen engines in Beijing of the Academy worked overtime for 23,000 hours, and finally found out the "devil" hidden in the engine and eliminated the "enemy" who was recalcitrant, eliminating hidden dangers and eliminating faults.
Li Dong, the chief designer of the Long March 5 rocket, told the reporter that after the failure of the Long March 5 rocket, after more than 100 days of troubleshooting and positioning, and more than 180 days of experimental verification, the reason for the failure was finally confirmed. After that, according to the conclusion of fault investigation, the development team improved the design of the first-stage hydrogen-oxygen engine, and adopted corresponding improvement measures from the aspects of structure, materials and technology, which improved the adaptability to the flight environment.
The cause of the failure was found, identified and improved. Everything seems so smooth.
However, new problems have come again.
The process of returning to zero is full of twists and turns
On November 30, 2018, the improved core-stage hydrogen-oxygen engine had problems during the long-distance test run.
Li Dong told reporters that this time the astronauts responded faster. According to the cause of the failure, the development team improved the local weak links of the engine and improved the dynamic strength margin of the structure.
On March 29, 2019, the zeroing work and improvement verification of engine test failure were all completed — — The two long-distance test runs passed successfully, and the second problem was solved in this way.
But soon, they ushered in the third "encounter."
On April 4, 2019, when the final assembly of the Long March 5 remote three rocket entered the final stage, an "abnormal vibration frequency" appeared in the process of analyzing the test data of a core-stage hydrogen-oxygen engine used for subsequent tasks.
It can be described as twists and turns, once again verifying that sentence: the road to scientific exploration has never been smooth.
"Without a trace of doubt!" Li Dong said that the developers followed the trail and found the crux of the problem — — The local structure of the engine is very sensitive to the complex mechanical and thermal environment, and it is easy to cause resonance. Once excited, it is not easy to decay.
In July 2019, the developers completed the structural improvement of the engine and completed more than a dozen large-scale ground tests.
At this point, the engine problem that has plagued the Long March 5 for more than two years has finally been investigated.
According to the statistics of the First Academy of China Aerospace Science and Technology Corporation, the Long March 5 was defeated by Yaoer on July 2, 2017 and successfully launched by Yaosan on December 27, 2019, which lasted for 908 days and carried out more than 40 key technical tests.
After 908 days and nights, I got up again after countless falls. And the biggest "hard bone" — — The hydrogen-oxygen engine has also completed the phoenix bath fire and nirvana rebirth in more than two years.
According to Long Lehao, more than 900 days, such an interval — — It is a long time in the history of the Long March rocket to go beyond the period of the follow-up flight after the mission fails. In his impression, there is not even a "return to zero" at such a long interval.
"We certainly hope that the interval will be shorter, but scientific research cannot change with subjective wishes." Long Lehao said that the failure of the Long March 5 rocket was due to the failure of a certain engine component under the interaction of complex mechanical and thermal environment — — This problem is deeply hidden, and it does not appear in most cases, but only occasionally. However, once it appears, it is a "disastrous result".
In his view, this "zeroing" finally caught this mischievous "devil", although it took a long time, it was worth it.
"We’re all suffocating."
In fact, it takes more than a few teams to find out the "devil" and "rebuild" the engine.
Yan Yong, deputy director of Beijing No.11 Institute of the Sixth Academy of China Aerospace Science and Technology Corporation, told the reporter that the failure to launch the Long March V Remote II rocket pushed the liquid power industry with the reputation of "golden power" to the forefront, and the failure of the first-class high-thrust hydrogen-oxygen rocket engine put the engine development team under tremendous pressure and test. With the help of the strength of the Group and the Sixth Hospital, the Institute has used all effective resources to carry out the zeroing work — — It can be said that this is a "national alliance" to tackle key technical problems.
"It’s the first time I’ve seen so many academicians get together!" Lv Wei, the quality supervisor of 11 universities in Beijing, said that he was most impressed by the evaluation. Twenty-five academicians and five university professors came to the site as invited experts to listen to the engine development work and put forward opinions and suggestions. Nearly 60 leading experts in the system also participated in the exchange and discussion.
In fact, after the failure of the mission two years ago, many people are also eager to try, looking forward to returning to the "battlefield" and showing their talents.
"If setbacks obscure the light of the road ahead, then use the unrepentant heart to light the fire at night!" Chen Jiwei, commander of the launching station system at Wenchang Space Launch Site, told the reporter that there was no frustration and discouragement, and everyone held their breath. All systems and posts rallied from scratch and immediately put themselves into the preparations for the rocket’s go-around.
Deduct the process again and again, anticipate and recall one by one, and operate the exercise again and again. The operation of the air compressor of a system in the station is not very stable, and the equipment manufacturer has repeatedly made dozens of improvement tests, but the problem still exists.
Many people have advised Chen Jiwei, "it’s not a restrictive factor, it’s almost enough." However, his answer is adamant. "The factors that affect the task must be solved without compromise!"
Today, the Long March V has finally won this "turn-over battle", and it has become the most iconic task of China Aerospace in 2019. This is not only because it determines the implementation of major engineering tasks such as the follow-up Chang ‘e V, manned space station and the first Mars exploration, but also because it presents the process of scientific experiments from failure to success to the public in such an intuitive way, which makes people feel moved and amazed.
In addition to Qian Xuesen’s sentence, Albert Einstein also had a "golden sentence" that was regarded as a standard by the scientific community. The general idea is that it is not a bad thing for a person to take detours and make mistakes on the road of scientific exploration, and it is not a shame. It is necessary to bravely admit and correct mistakes in practice.
Long March 5 did it. China astronauts did it.
China Youth Daily China Youth Network reporter Qiu Chenhui
