Die on Mars

"The next work is very complicated. I need to explain it to you in detail, Miss Maidong."

The old cat sat up straight and looked serious.

"Yeah, I'm listening, Mr. Cat." Maidong floated in front of the camera, looking like a good student listening carefully.

Tang Yue sat on the edge and didn't know what to say. He looked at the pen and paper on the table in a daze. He knew that there was no hope. It was completely impractical to use the Eagle spacecraft to return to Kunlun Station, whether it was to install a rocket engine or not. , it is impossible for the lander to land successfully.

The Raptor 10D engine on the Orion 2 spacecraft was not designed for landing. Even the Orion 2 spacecraft itself cannot re-enter the atmosphere. Its huge and fragile propellant tanks can withstand very low overloads before entering the atmosphere. Can cause structural cracks.

As for disassembling the rocket engine, it is even more wishful thinking. It can be done by asking a team of workers to drive a crane, but letting a little girl from Maidong hold the wrench. This is ridiculous - those huge rocket engines on the Orion spacecraft The nozzles are thicker than the entire body of Ophiopogon japonicus.

Whether it is himself or Lao Mao, the only answer he can give Ophiopogon japonicus is "It's hopeless, girl, we can't do it."

"We still have hope."

Tang Yue was stunned, what?

He turned his head to make sure he heard correctly. What was the cat saying? Is there still hope? What hope is there?

It had just completely rejected its plan, saying it was completely hopeless.

Now that the topic has changed, why is there hope again?

"Ms. Maidong, you should have a basic understanding of spacecraft re-entry into the atmosphere. Generally speaking, it is a process of deceleration and landing. Although the public likes to describe it as very complicated and dangerous - of course it is indeed extremely dangerous. It is dangerous, but essentially it is a process of deceleration." Lao Mao said, "As long as we can successfully decelerate and reduce the speed to a low enough level... many problems will be solved."

"Uh-huh."

Tang Yue stared. Seeing this situation, the old cat didn't seem to be joking. Could it really be anything he could do?

"Slowing down requires power, and as long as there is enough power, we can solve seemingly unsolvable problems very simply and crudely."

"The engine on the Orion spacecraft?" Maidong asked.

The old cat nodded.

"Old Cat, you just said that it is impractical to dismantle the engine!" Tang Yue shouted, "You said yourself that you have failed in so many simulations, and you have never been able to cross the height of 10,000 meters!"

"Of course it's impractical to dismantle the engine." The old cat rolled his eyes, "Have you seen the rocket engine on Orion? Is that thing something that can be dismantled by humans? Your thinking has fallen into a misunderstanding. Miss Maidong really wants to ride on it. Eagle spacecraft, but the Eagle spacecraft is not the key... Think about Apollo 13 back then, was the space lifeboat that saved everyone's lives the command module?"

Apollo 13?

Tang Yue was stunned, and then his scalp felt numb.

His thinking did fall into a misunderstanding. The Eagle spacecraft was a lander. Tang Yue subconsciously believed that the Eagle spacecraft was the key to everything.

Everything had to revolve around the Eagle lander, so he wanted to dismantle the engine and install it on the lander, and then he thought hard about how to make the lander stable.

But what can really save Maidong's life... was never the Eagle spacecraft!

"What we want to dismantle is not the rocket engine." Old Cat whispered, "What we want to dismantle is the Eagle lander and Orion!"

Tang Yue suddenly understood that this was another really crazy plan, even crazier than the last time he drove the space station to catch the lander - the reason why he could not land successfully was because of insufficient thrust. If the thrust was insufficient, then it would be impossible. To increase power, if one engine cannot meet their needs, then use all nine engines!

I really don’t know whether this idea is inherited from the Falcon Heavy or N1.

If it's the former, then Tang Yue is still relieved.

if the latter one……

"You said that the Orion spacecraft would crash when it entered the atmosphere!" Tang Yue grabbed the old cat.

"That's right." The old cat said with a stern expression, "What we want is for it to crash!"

A robot is a robot, and when it's crazy, it's not a human being at all.

Later the old cat said:

Ninety-nine percent of the problems faced by humans in aerospace engineering are caused by insufficient power. As long as there is sufficient power, these are not problems.

The last one percent takes the blame for the system as usual.

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"We all know that if an object is dropped from a high altitude on the Earth, it will move in a state close to free fall, but it will not be a true free fall."

"Because of air resistance?" Maidong said.

"Yes, this object will continue to accelerate, but it will not continue to accelerate forever." Old Cat said, "When it falls, gravity and air resistance will balance out at a certain point, and then it will fall at a constant speed."

Maidong and Tang Yue both nodded. This is easy to understand, as it was taught in high school physics classes.

"This is affected by air density. In physics, there is a word called 'ballistic coefficient'. The ballistic coefficient in the Martian atmosphere is very low, which means that it is difficult for the atmosphere to give you enough resistance to allow you to reach an equilibrium state." Old The cat continued, "If we drop the unpowered Eagle spacecraft, it will decelerate very slowly. When the altitude drops to 40,000 meters, its speed will still exceed fifteen times the speed of sound, and the surface temperature will rise to 2,000 meters. Celsius – that’s why we need insulated tiles.”

"In the last century and the beginning of this century, many Mars probes failed because of this. The speed was too fast and they could not land."

The old cat shrugged.

The most typical example of a Mars probe that crashed during landing is ESA's Beagle 2. That poor lander is still lying dead in the wilderness.

"The normal landing process of the lander is as follows: it begins to enter the atmosphere at an altitude of 125 kilometers. At this time, its speed is about five kilometers per second." Old Mao once again demonstrated to the two people with a pen. He raised the pen in his hand high, and then plunged down, "After eighty-five seconds, the deceleration air cushion will be opened and the first deceleration will be carried out. In these eighty-five seconds, its altitude will drop by ninety kilometers and survive." The worst heat barrier.”

"The deceleration air cushion will reduce the speed of the Eagle spacecraft to less than twice the speed of sound, which is an acceptable Mach number for parachute opening. At an altitude of 10,000 meters, the lander will open a ring parasail with a diameter of 30 meters. The old cat spread its paws at the end of the pen to indicate the parachute, "The parachute can reduce the speed of the Eagle spacecraft to below the speed of sound. Until the altitude of the lander drops to less than one thousand meters, it will abandon the parachute and turn on the rocket engine to adjust." Attitude, perform reverse thrust to decelerate, and finally land vertically."

The old cat finally slowly put the pen vertically on the table.

Both Maidong and Tang Yue also knew that the working principles of the spacecraft had been explained in detail by people on the ground during the training before the mission.

The old cat repeated it again today.

"Why is this process so complicated?" Old Cat asked, "Why is it so complicated?"

Before Maidong and Tang Yue could speak, the old cat answered by himself.

"Because we don't have enough power, we can't use rocket engines for reverse thrust from beginning to end. The efficiency of chemical rockets is too low." Lao Mao said, "Most of the thrust of the engine is pushing itself, thousands of tons. The mass is all fuel, and the remaining fraction can be used as a load."

"During a normal landing process, it is impractical to use rocket reverse thrust throughout the entire process. In that case, the Eagle spacecraft would also have to be filled with propellant in the cargo hold and command module, and the lander would become a flying fuel tank." Lao Mao Then he said, "But that is a normal situation. We are going to have an abnormal landing... We don't care about efficiency, we don't care about cost, we don't care about hundreds of tons of fuel, we only want that fraction!"

The old cat raised his paw, pointed at Ophiopogon japonicus on the screen, and said word by word:

"A fraction of sixty kilograms!"