Chapter 424 Determining the next direction

Hu Lai frowned, a little surprised.

All along, in his impression, domestic rocket engine technology is still very powerful.

Although commercial rockets are not good enough, the Long March system launch vehicle used by the national team over the years has still successfully launched various satellites, large and small, into the sky, and even the "Zhurong probe" was sent to Mars.

But I didn't expect it.

Today, Pang Panglong suddenly told him that the main reason why "recyclable rocket technology" cannot be realized at present is because the performance of domestic rocket engines is insufficient.

This... is really unexpected.

He looked at Pang Pang Long and calmed down, ready to listen carefully to Pang Pang Long's introduction.

"Old Pang, please explain it carefully."

Pang Panglong took the teacup handed over by Director Zhang and said without restraint:

"Boss, when talking about rocket engines, we must first talk about the overall launch vehicle."

"Let me take our country's largest heavy-lift launch vehicle, the Long March 5, as an example."

"Now the Long March 5 has achieved a carrying capacity of 25 tons in low-Earth orbit and 14 tons in geosynchronous orbit. It sounds like the carrying capacity of 20 tons is not much, right? But what many people don't know is..."

"In order to achieve this 25-ton carrying capacity, the take-off mass of the Long March 5 has reached an astonishing 869 tons!"

"In other words, when the Long March 5 rocket is actually ignited and launched, it has to push not only the 25-ton payload, but also its own weight of more than 800 tons!"

More than 800 tons!

Hu Lai was a little surprised by Pang Pang Long's first words.

Before this, he did not have a detailed understanding of the take-off mass of the launch vehicle. When Pang Panglong said this, he couldn't help but nodded slightly.

"More than eight hundred tons, the thrust required is indeed quite a lot!"

"That's right."

Pang Pang Long glanced at Hu Lai.

Seeing that Mr. Hu was very interested, he introduced more diligently.

"Boss, we who have studied junior high school physics all know that when an object moves from rest to motion, the initial thrust required is definitely the largest."

"Especially for something like the Long March 5, which has a take-off mass of up to 870 tons and takes off vertically. If it wants to start from a stationary state and constantly overcome the earth's gravity to accelerate upward to do work, it requires huge kinetic energy."

"if……"

"I said that if you were to design the Long March 5, what kind of engine would you choose within the 'Karman Line', that is, the distance from ignition in a static state until it reaches the atmosphere?"

What kind of engine?

Faced with Pang Panglong's question, Hu Lai thought for a moment and then said hesitantly:

"Of course, it is necessary to install high-thrust rocket engines on the Long March 5. If one is not enough, then two will be used. In short, it will provide sufficient power for it to fly first, so that it can gain a certain speed and rush out of the atmosphere!"

As soon as he finished speaking, Pang Panglong immediately showed a smile on his face and said:

"That's right, boss!"

"Whether it was the Soviet Union in the past or us now, we all adopted this method."

"The Long March 5 uses two 60-ton high-impulse hydrogen-oxygen engines 'YF-77' as the main thrust, plus eight 120-ton high-thrust 'YF-100' liquid oxygen kerosene engines.

Four thrusters."

"A total of two engines and four thrusters are bundled together to form a first-stage rocket, helping the Long March 5 successfully enter the 'Karman Line'!"

"Anyway, once it enters the 'Karman Line', the first-stage rocket will separate, and the mission of the first-stage rocket will be completed!"

Hu Lai nodded.

But at this moment, Pang Panglong suddenly changed the subject and said:

"certainly!"

"If it is a normal launch, there is no problem with this combination. Anyway, as long as the rocket is sent to the 'Karman Line', the mission is completed."

"However, once rocket recovery technology is involved, such a combination becomes problematic."

oh?

Hu Lai's expression lit up, waiting for Pang Panglong to continue speaking.

"There are two main reasons."

"First one: As you said just now, boss, in order to cope with the take-off weight of more than 800 tons, it is necessary to use a high-thrust engine. It can be said that the bigger the better."

"but……"

"In the actual process, from the time the rocket is launched to when the rocket reaches the 'Karman Line' and completes separation, the fuel in the entire first-stage rocket will basically be exhausted. At this time, the weight of the first-stage rocket is actually less than 10 times the weight of the original take-off.

%.”

"That means an awkward question."

"The weight of the 'first-stage rocket' has been greatly reduced and the mass is too light. Once the engine is ignited and pushed back, the high-thrust engine we use will have excess thrust. Even the minimum thrust of the engine will prevent the 'first-stage rocket' from falling down at all.

.”

Hu Lai was stunned and immediately understood what Pang Pang Long meant.

If the self-weight of the recovered first-stage rocket is 10 and the engine thrust is also 10, then the gravity can be offset just enough to allow the first-stage rocket to land smoothly.

If the rocket's dead weight is 10 and the engine thrust is 12, then if you find the right time, you will have a chance to land smoothly and recover.

But if the rocket's dead weight is 10 and the engine thrust is 20 or even 50, then the thrust of the engine will inevitably make the rocket fly into the sky again.

In other words, the best situation is to make the engine thrust equal to the falling potential energy of the rocket falling.

Then the problem comes...

If the engine thrust is reduced, how can the take-off weight of 870 tons get into the sky?

He shook his head, not expecting such a problem.

At this time, even Director Zhang on the side couldn't help but frowned and couldn't help but ask:

“So now that Mask’s SpeakX company has solved this problem, how did they solve it?”

Pang Panglong took a sip of tea and moistened his throat.

“SpeacX’s Falcon 9 uses their independently developed ‘Merlin engine’.”

"Their thinking is different from ours. We used two large specific impulse hydrogen-oxygen engines YF-77 to try our best to increase the speed, while they used nine Merlin engines in parallel."

"When ascending, the nine engines are fully powered. When landing, eight engines are shut down and one engine is working. At the same time, the working small engine is throttled to reduce the thrust. This just offsets the weight of the rocket's descent, thus achieving a smooth recovery."

oh?!

Nine engines in parallel?

After hearing the explanation, Director Zhang couldn't help but sigh.

“I have to say, SpeakX still has something to offer.”

After saying that, he looked at Pang Panglong again and said with a smile:

"But Lao Pang, there is no way to solve this problem, right?"

"According to what you said, the weight of the first-stage rocket is too light, so how about increasing its weight, for example, by allocating more fuel during recovery?"

"..."

Pang Panglong was silent for a while and looked at Lao Zhang.

"Old Zhang, the astronauts have thought of every solution you can think of."

"Actually, this is the second point I want to make. Compared with the first point, this point is an issue we urgently need to face."

"I just introduced that the Long March 5 uses two large hydrogen-oxygen engines YF-77, and the four thrusters are also equipped with eight large 120-ton kerosene engines YF-100."

"When these engines are added together, our first-stage rocket will no longer be light when it returns to the ground, but the weight will become very large, which also means that more fuel must be left for deceleration and recovery."

"But once more fuel is used for deceleration and recovery, in the end, the fuel allocated to the launch mission may not be enough to send the second-stage rocket into space..."

Hearing this, Hu Lai understood completely.

To put it bluntly, for example, the Long March 5 has a maximum take-off mass of 869 tons. When the weight of the engine and other parts is fixed, it must only be able to carry so much fuel.

Once part of the fuel carried is used for "rocket recovery technology", the fuel used for the second-stage rocket will inevitably be reduced. How can a payload of 25 tons be achieved?!

Obviously not.

At that time, it will not be a question of "rocket recyclability technology", but a question of whether it can send a 25-ton payload to low-Earth orbit.

certainly.

Another way to carry more fuel is to reduce the weight of the engine and other spare parts.

For example, if one engine reduces the weight by 5 tons, then 10 engines can reduce the weight by 50 tons, and can carry 50 tons more fuel!

but!
To be continued...