I ask you to build tractors, but you build rockets?

"The Long March 10 rocket independently developed by my country made its first flight on August 12, but failed in the second half of the mission."

When the headlines came out the next day, many viewers who watched the launch found it incredible.

Because according to most people's understanding, the Long March 10 neither exploded nor deflected, so how could it fail? It was obviously a success.

In a subsequent noon news interview with Yun Hongjun, the commander-in-chief of the Long March 10th, the latter just said with tired eyes: "We are actively looking for the cause."

In fact, the team has initially determined that the shutdown of the YF77 was a problem with the engine itself and had nothing to do with the rocket body. It should be a matter of the Sixth Institute.

Liu Minglu had already flown back to Chang'an overnight, pulled out four YF77 prototypes from the factory at once, and put them on the test bench for testing.

At 7 pm on August 13, Liu Minglu ordered with a gloomy face:

"The fifth 1,000-second test run begins!"

An hour ago, all four engines had gone through a 500-second test run, and there were no problems throughout the process. However, Liu Minglu immediately asked to organize the second, third, and fourth times, and mobilized the liquid hydrogen tanker as quickly as possible.

This time, after the No. 3 engine continued to run for 670 seconds, there was a loud explosion, and the turbine pump impeller at the core of the engine cracked. The high-speed running fragments directly punched a large gap in the nozzle, and the engine suddenly stalled.

Testing of the remaining two engines was immediately suspended, and the cause was apparently found.

Liu Minglu just took a look inside the engine wreckage from a distance and knew that it was the problem he had thought of.

The high-thrust hydrogen-oxygen engine is still too difficult.

In the early 1970s, the space agency modified the YF70 hydrogen-oxygen engine from the YF20, the main force engine currently in service at the time. It was formalized in the subsequent YF73, with four combustion chambers and less than five tons of thrust;

Then came the YF75, with a single combustion chamber and 8 tons of thrust, which was used as an upper stage for the Long March 3 series. Then in 2002, the YF77 project was launched.

The vacuum thrust of the YF77 is 70 tons, which is more than eight times that of the YF75. Such a large span, coupled with the fact that the hydrogen-oxygen engine is the most difficult type, caused many problems during the development process.

However, the 14-year development process and the cumulative test run of 50,000 seconds still convinced them that YF77 has sufficient reliability, even if this number is not actually much.

The cumulative test run time of the Aramco space shuttle main engine SSME exceeded 100,000 seconds before its first flight, so the experience of YF77 cannot be described as rich.

Moreover, due to the small size of liquid hydrogen molecules and extremely low temperature, the pipeline materials and processing requirements for liquid oxygen and liquid hydrogen engines are very high, which happens to be the weakness of the space agency in some aspects.

Liu Minglu was silent for a long time, and then asked the remaining three engines to conduct another 1,500-second long test run.

After two consecutive operations, the thrust of the No. 2 engine began to become unstable at 1020 seconds. Its oxygen pump failed, causing the fuel supply to be insufficiently continuous. After the thrust fluctuated greatly several times, the light blue The tail flame also suddenly disappeared, and the No. 2 engine stalled.

The failure of 2 of the 4 engines obviously shows that there is a problem with the design of the YF77 and it is not an accident.

Such an ultra-long test run has never been done before, and the most worrying problem has not been discovered. Now it has finally been revealed.

On the afternoon of the 14th, an accident investigation report of more than 4,000 pages jointly written by Yun Hongjun and Liu Minglu was placed in front of Academician She.

Academician She didn't even look at the piles of paper that looked like turning heads. He pushed them aside casually, held his hands and looked at the two people in front of him who were obviously not well rested.

"Sit down, sit down, it's not against the law, why are you standing there?"

He stood up and asked the two of them to sit down. Then he went to make two cups of tea, moved the chair to the opposite side of the sofa and sat down.

“I made the basic configuration of the Long March 10, and the engine to be used was already decided, so I can’t blame you;

In 10 months, it will be considered a success if the Long March 10 is launched without blowing up the launch pad, and the people of the country do not blame you, and have done a good job. "

There was indeed no violent reaction from the public, and the engine failure reported by the space agency was not considered serious.

Because in the eyes of 99% of people, since the rockets flew out of their sight without exploding, it basically counts as a success, and the rest are just minor problems.

But Yun Hongjun obviously didn't think so: "No, it's all my responsibility. If there are astronauts sitting on it, they are lucky enough to come back, but bad luck..."

"The engine is us..."

"Okay, I'm not here to make you take responsibility, nor am I here to ask you to write a self-criticism."

Academician She pointed to the thick pile of reports behind him:

"These things will only be in the archives, and no one will look at them. I just want to ask you, do you have the confidence to solve these problems? Can you complete the Yao-2 mission with a new generation of manned spacecraft in April 2017?"

Our first priority is still to land on the moon! "

The Long March 10's Yao-2 flight will send an unmanned manned spacecraft to the lunar orbit and back, and then the next time it will carry at least three astronauts for a fully realistic manned flight around the moon, and the next time it will land on the moon. It’s been months.

If there is a problem with the Yao-2 mission, the third mission will not be manned. This means that unless the fourth lunar flight is directly changed to a lunar landing, the date of the manned lunar landing will be postponed to 2019.

Only one YF77 was damaged during this first flight, so all tests were completed. Two YF77s were used in the third level this time. Fortunately, no major problems occurred.

But it is enough to show the importance of YF77 to Long March 10. Once the astronauts leave the atmosphere, whether the astronauts can safely complete the mission and return depends entirely on YF77.

Six YF77s, none of them can break down during the mission!

Liu Minglu clenched his fists and stood up:

"The main problem of YF77 is the problem of the turbine pump bearing and impeller. It took the Sixth Institute 6 months to solve this problem."

Six months to solve the problem, one month to test, and half a month to produce the Yao-2 rocket should be enough time.

Academician She nodded and did not blame why the 70-ton YF77 took so long. He was very clear about the difficulty of developing a hydrogen-oxygen engine, and the space agency had no previous experience.

Six months seems not a short time, but you must know that the development of YF77 started 14 years ago.

"There is another way."

Yun Hongjun suddenly spoke:

"Xinyuan Company has two hydrogen and oxygen machines, H50 and H240, with vacuum thrusts of 50 tons and 340 tons respectively. They can be used directly without changing the configuration."

The naming rules of H50 and H240 are different. H50 is dedicated to vacuum, so the number is directly the vacuum thrust; H240 has two versions, the version used in the first level has a sea level thrust of 240 tons, and the vacuum version is Xinyuan 2A and The nozzle used by Xinyuan 3 is specially enlarged, with a vacuum thrust of 340 tons and a specific impulse of 466 seconds.

One H240 can completely overtake four YF77s, and two H50s can also replace two YF77s. Although the thrust is slightly smaller, the specific impulse reaches 459 seconds, which is better than the YF77's 432 seconds. The difference is not big, and it can be used.

As for Xinyuan’s H80, it is currently undergoing testing so we don’t know yet.