"China's self-developed Long March 10 rocket made its first flight on August 12 and failed in the second half of the mission."

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

Because most people understand that the Long March 10 neither exploded nor deflected, how could it fail? It's a success.

In a subsequent interview with Yun Hongjun, the chief engineer of Long March 10, the latter only said with tired eyes: "We are actively looking for the cause."

In fact, the team has preliminarily determined that the closure of the YF77 is a problem with the engine itself, and it has nothing to do with the arrow body, and it should be the business of the Sixth Academy.

Liu Minglu has flown back to Chang'an overnight, pulled out 4 YF77 prototypes from the factory at one time, and put them on the test bench for testing.

At 7 p.m. on August 13, Liu Minglu ordered with a gloomy face:

"The 5th 1000-second long test starts!"

An hour ago, the four engines had undergone a 500-second test run without any problems, but Liu Minglu immediately asked for the second, third, and fourth times, and the liquid hydrogen tanker was brought in as quickly as possible.

This time, after the No. 3 engine continued to run for 670 seconds, with a bang, the turbopump impeller at the core of the engine cracked, and the high-speed debris directly punched a large gap in the nozzle, and the engine stopped urgently.

Tests on the remaining two engines were also immediately suspended, and the cause was apparently found.

Liu Minglu just glanced at the wreckage of the engine from a distance, and knew that it was the problem he thought of.

High-thrust hydrogen-oxygen engines, it's still too difficult.

In the early 70s, the space agency changed the YF20 hydrogen-oxygen engine from the YF70, the main poison engine in service at that time, and the formalization was the subsequent YF73, with a four-combustion chamber of less than five tons of thrust;

This was followed by the YF75, with a single combustion chamber of 8 tons of thrust, which was used to make the upper stage for the Long March 3 series, and then the YF77 project was launched in 2002.

The vacuum thrust of YF77 is 70 tons, which is more than eight times that of YF75.

But 14 years of development and 50,000 seconds of testing convinced them that the YF77 was reliable enough, even if that number wasn't that much.

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

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

Liu Minglu was silent for a long time, and then let the remaining three engines undergo another 1,500-second ultra-long test.

After two successive attempts, the thrust of Engine 2 began to become unstable at 1020 seconds, its oxygen pump failed, making the fuel supply not continuous enough, and after several large fluctuations in thrust, the pale blue tail flame suddenly disappeared and Engine 2 stalled.

The failure of 4 engines and 2 obviously shows that the design of the YF77 is problematic rather than accidental.

Having never done such an ultra-long test before, and the most feared problem had not been discovered, it was finally revealed.

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

Academician She didn't even look at the few pieces of paper that were the same as turning his head, he pushed them aside casually, and pinched his hands to look at the two people in front of him who were obviously not resting.

"Sit, sit, and don't break the law and stand and do anything."

He got up himself and sat the two of them down, then went to make two cups of tea and moved the chair to sit down across from the couch.

"I made the basic configuration of the Long March 10, and the engine to be used has long been decided, so I can't blame you;

In 10 months, the Long March 10 rushed out and did not blow up the launch pad, even if it was successful, and the people of the whole country did not blame you, it has done a good job. ”

There really was no violent reaction from the people, and they didn't think it was very serious about the engine failure reported by the space agency.

Because in the eyes of 99% of people, since the rockets have not exploded since they have flown out of their field of vision, it is basically settled, and the rest are minor problems.

But Yun Hongjun obviously didn't think so: "No, it's all my responsibility, if there are astronauts who sit on it, I can come back if I am lucky, and if I am unlucky, I ...... if I am unlucky."

"The engine is our ......"

"Okay, I'm not here to hold you accountable, and I'm not here to ask you to write a review."

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

"It's only going to be in the archives, no one is going to look at it. I just want to ask you, do you have the confidence to solve these problems, in April 2017, can you complete the flight of the Yao-2 mission with a new generation of manned spacecraft?

Our priority remains to go to the moon! ”

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

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

This time the first flight only broke one YF77, so all the tests were completed, and the third level used two YF77s this time, but fortunately, there were no major problems.

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

Six YF77s, none of them can be broken 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, and it took 6 months for the Sixth Institute to solve this problem."

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

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

6 months may seem like a short time, but you must know that the YF77 started development 14 years ago.

"There's another way."

Yun Hongjun suddenly spoke:

"Xinyuan Company has two hydrogen and oxygen machines, H50 and H240, with a vacuum thrust of 50 tons and 340 tons respectively, which can be used directly without modification."

The naming convention of H50 and H240 is not the same, H50 is dedicated to vacuum, so the number is directly vacuum thrust; There are two versions of H240, the first stage version uses a sea level thrust of 240 tons, and the vacuum version, that is, the nozzle used by Xinyuan No. 2A and Xinyuan No. 3 is particularly large, with a vacuum thrust of 340 tons and a specific impulse of 466 seconds.

One H240 is completely on top of the four YF77s, two H50s can also replace two YF77s, although the thrust is slightly smaller, but the specific impulse reaches 459 seconds, better than the YF77's 432 seconds, the difference is not big, it can be used.

As for the H80 that Xinyuan still has, it is being tested at this time, so I don't know yet.

(End of chapter)