Tang Feng has no doubt that Dr. Schmitz's words can sometimes be used as truth as the world's top expert in the development of launch vehicles.

Dr. Schmitz took a sip of water and continued, "If Mr. Musk could give me an extra $300 million, oh no, $200 million in research and development, I could have developed my Grasshopper rocket a little more perfectly, not like the Falcon 9 is now." Although the Falcon 9 has successfully returned to the landing site, I think there is at least a 70% chance that the recovered first-stage core rocket will not be reusable. ”

Tang Feng asked curiously, "Doctor, how could you have such a judgment?" Isn't the rocket already successfully recovered? ”

"Hehe" Dr. Schmitz shook his head with a smile, "Don, rocket recovery is not a simple project, I have spent almost twelve years on this project, and of course I know what the problems of the current Falcon 9 are. Rocket launch is to go through the test of high temperature, high speed and high pressure, so the test of the rocket engine is the most stringent. As a reusable spacecraft, NASA's previously discontinued space shuttle has undoubtedly done its best, but even the space shuttle engine, the so-called SSME engine, was originally designed to be reused 100 times, although this design requirement has not been met, but the SSME engine of the five space shuttles used by the United States has only reached 55 times of reuse. ”

"The SSME engine has a vacuum thrust of 213 tons, a specific impulse of 452 seconds, and a thrust-to-weight ratio of 63 (rated thrust) / 68.5 (maximum thrust). The combustion chamber pressure of the SSME is as high as 20.7 megapascals, or 207 atmospheres, and the operating temperature of the combustion chamber is about 3,300 degrees, compared to the pre-turbine temperature of the best aero engines such as the F119, which is only 1,700 degrees. When the SSME engine is operating, the injector at the top of the combustion chamber injects 380.6 kg of oxidizer and 108.4 kg of pre-fired gas mixed with hydrogen and water and 12.6 kg of liquid hydrogen per second into the combustion chamber. In order to press a large amount of propellant into the combustion chamber. Its liquid hydrogen pump and liquid oxygen pump pressure speed are 34,311 rpm and 22,250 rpm respectively, plus the advance pressurization of the pre-pressure pump, so as to achieve unprecedented pressures of 33 megapascals and 33.2 megapascals. Tang, you may not understand this, the most advanced kind of 6-moving 2 CRH380A-trailer high-speed rail train developed by you Huaxia is 9,600 kilowatts, and the power of SSME's small turbopump is several times this power. ”

These data Tang Feng heard a little foggy. But in the end, Tang Feng understood this metaphor. He also didn't expect that the power of a small pressure pump was even greater than the power of the front of the high-speed rail train, which has to be said to be a quite shocking data.

Dr. Schmitz shrugged his shoulders and said, "That's the basic data for the SSME engine, but what is the data for the Falcon 9?" Compare and you will know what is the difference between the rocket engine of the Falcon 9 and the rocket body. ”

"At the time, when I was designing the Falcon 9, the first stage of the core rocket would separate at a speed of 6,000 km/h and at an altitude of 74 km, so it would be much less demanding to return from suborbital, but equally demanding on the engine and body. The Falcon 9 is powered by a Merlin engine with a thrust-to-weight ratio of around 150. That's more than twice as much as SSME. However, the combustion chamber pressure of the Merlin rocket engine is about 100 atmospheres, while the pressure of the kerosene pump and the liquid oxygen pump is as high as 140 atmospheres. The ground specific impulse of this liquid oxygen kerosene engine is generally only about 280 seconds, and the vacuum is only more than 300 seconds, which is far from the 366 seconds of the ground vacuum of 452 seconds of SSME, so in order to achieve reuse, we can only work the weight reduction of the arrow body. ”

Dr. Schmitz sighed, seemingly regretting the design. "It was because of the engine that I had to find a way to reduce the weight of the rocket body. The Falcon 9 first stage, including the engine, has a structure-to-mass ratio of more than 15. Or of the 390 tons of weight after filling, only 21 tons are the weight of the arrow body, which is much smaller than the mass of the egg shell in the egg, and this arrow body has to withstand nearly Mach 6 control, thrust reverse, re-entry, and fly hundreds of kilometers in the atmosphere and land safely, therefore. I don't think the most critical point that the Falcon 9 can be reused is the rocket body, which is too fragile."

Tang Feng finally understood the reason why Dr. Schmitz was not optimistic about the Falcon 9, according to Dr. Schmitz's statement, the rocket body of the Falcon 9 was too fragile.

"Doctor. So the 'Starry Sky One' rocket that we are about to experiment during the day today has avoided the problems you just mentioned? Tang Feng asked.

Dr. Schmitz smiled, nodded and said, "Tyrant, thanks to your strong support for this project, without your funding, the kind of recyclable rocket I dreamed of would have been in vain after all." That's right, Don, as early as when I was researching the Falcon rocket and the Grasshopper rocket, I once proposed a plan to Mr. Musk, you know, I have participated in the study of the launch vehicle with the largest take-off mass and thrust in the world, the finalization of the Soviets' Energia rocket, and I have also participated in the research and development of the engines of several space shuttles such as Columbia in the United States, and even led ESA to send their Ariane-5 rocket into space, so when I was developing the Falcon rocket under Musk, I once wanted to develop a rocket that can be recycled and reused, and can have a strong LEO capacity, so I gathered all the advantages of the rockets I participated in the development of and designed a launch vehicle that can be called an epoch-making launch vehicle, but unfortunately, Mr. Musk rejected my plan at that time because of financial reasons, because if this plan is to be implemented, the preliminary experimental cost alone will require at least 1.5 billion US dollars. Mr. Musk didn't have that funding, so the plan stayed in my design."

"But Don, your presence has finally made my long-standing dream come true. Ever since you asked me to lead the development of the new rocket last year, I have actually been building this launch vehicle for testing according to the design I had back then. Don, don't doubt my ability, after so many years of improvement, I am already close to 100% sure that this new launch vehicle can meet the recyclable and reusable standards in the design, because this is an epoch-making launch vehicle, and with it, you can have the whole of outer space! (To be continued.) )