In the past three months, Tang Yue and Lao Mao have discussed this issue privately more than once.

After all, the self-sustaining ability of the joint space station is limited, although it is still far from reaching its own structural life, but no one knows how long the space station can last in the case of supply cut-off, leaving Mai Dong alone Tang Yue is really not at ease, in case something goes wrong, he and the old cat can't help.

Another more serious problem is Mai Dong's body, to be honest, the United Space Station is really not a suitable place to live for a long time, no one likes to live in a narrow pipe, and if there is claustrophobia, it is a nightmare. In this oppressive desperate situation, the negative effects of weightlessness and radiation exceeded Tang Yue and the old cat's expectations, Mai Dong's weight was rapidly decreasing, and she even began to lose her hair.

Tang Yue is on Mars, but he still has a gravity of 0.38 G, while Mai Dong is on the space station, and the gravity is almost zero, and the latter's living environment is much harsher.

Seeing that the girl was losing weight day by day, Tang Yue pulled the old cat and racked his brains, trying to find a way to make Mai Dong land safely.

The old cat said that it was technically impossible, and that neither the space station nor the Orion spacecraft were designed to enter the atmosphere - the day they entered the atmosphere was the moment they were scrapped and burned out. The Union Space Station is a giant truss-like structure, like a giant Lego building block, which can only survive in a weightless orbit, and if it is subjected to gravity and air resistance, the space station will quickly collapse.

Whether on Earth or on Mars, re-entry is the most difficult and dangerous hurdle in aerospace engineering, and I don't know how many spacecraft probes have been planted in this step. In an unpowered re-entry, the returner had to be designed as a blunt cone or bell in order to slow down and cool down, and the Soviets briefly adopted a spherical re-entry capsule, which was later abandoned as too dangerous.

"The average flight speed of the Joint Space Station is now 3.5 kilometers per second, which is equivalent to ten times the speed of sound." The old cat said leisurely, "Do you know what this concept is? With just one tick, the space station has already traveled seven miles, and it only takes five minutes to fly from Beijing to Shanghai. ”

"The total weight of the Joint Space Station is six hundred tons, and we can calculate its momentum...... 2.1x10∧9kgm/s, which is a very scary number. The old cat continued, "It takes a lot of energy to slow it down, and slowing down is the first hurdle we face. ”

"Orion II's rocket engine can be used for thrust reversing." Tang Yue said.

"I'm not sure how much fuel is left on Orion 2, the last time we had the space station violently change orbit, one drop and one liter, it already consumed too much fuel." The old cat shook his head, "But what if we could get the station to lower altitude?" This is self-defeating...... As I said, the structure of the space station cannot withstand such large overloads and high temperatures, and the surface temperature of the space station can exceed 1,000 degrees Celsius after entering the atmosphere, and it will burn into a pile of debris. ”

"Isn't there a single cabin on the space station that can withstand such temperatures?" Tang Yue asked.

"Maybe there will be...... But just because the cabin can withstand it doesn't mean that the occupants in it can withstand it. "That cabin will become a can that is roasted at a high temperature, and whatever is in it will be cooked, like a smoldering pot of chicken." ”

"Overload and high temperatures are the second hurdle we face."

Tang Yue was silent for a long time.

He knew that this problem was difficult to solve, and the aerospace pioneers on Earth racked their brains to overcome the ablation problem of the return capsule, and finally it was materials science that gave the answer, and the engineers coated the heating surface with high-temperature resistant ablative materials, and took away the heat through the peeling of the insulation materials, which saved the return capsule from the fate of being incinerated by high temperatures.

But there is no such thing on the shell of the space station, the shell of the joint space station is metal, engineering plastics, thermal insulation film and all kinds of bits and pieces, the irregular shape will greatly increase the air resistance, and at the same time form a high-temperature accumulation area in some parts, if the space station plunges headlong into the atmosphere, the final result is like throwing wax into the fire.

This is almost a replica of the accident of the space shuttle Columbia.

"The last level is to slow down, even if your luck goes against the sky and you have passed the difficulties ahead, but the space station is descending from the sky at a hypersonic speed several times the speed of sound, how can you guarantee that the crew in it will not fall to their deaths?" "There's no oversized parachute on the space station." ”

Tang Yue grabbed his hair and took a deep breath, "We still have the engine of Orion II, ......"

"It's just a chemically powered rocket, not a fusion engine, and you have to realize that our fuel is limited." The old cat interrupted him, "That rocket isn't big enough to hold up the spacecraft to land safely in the atmosphere." ”

Tang Yue was a little helpless, how he hoped that the old cat would change his mind in the next second, come up with a "but", and then give a plan that worked.

"So if you want to land the space station safely, it's completely technically infeasible." The old cat has the final word.

In the final analysis, the human body is too fragile, and if there is a problem with one link, it can be fatal, if it is not Mai Dong but Optimus Prime in the United Space Station, then there is no need to be so troublesome.

What do you want to slow down?

What to talk about overload?

What are you afraid of high temperatures?

Just let him jump straight down.

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Tang Yue was frustrated, even though the result was what he expected.

He and the old cat can't always make possibilities out of the impossible.

"Isn't it possible to bring people down safely without thinking about carrying any supplies and supplies?"

"I can't do it." "It doesn't matter if the cans are round or flat, but the living are not the same as the dead," said the old cat, "and the unlucky Comrade Komarov, when the rescuers dragged him out of the Soyuz spacecraft's return capsule, he burned to the point that only such a piece remained." ”

The old cat compared it with both hands, a rectangle tens of centimeters square.

Tang Yue covered his face, he had promised to take Mai Dong next, but this promise may never be realized, Mai Dong can only stay on it until he dies.

"Mr. Cat, I'm looking at this evolutionary history...... Was there a relationship between Neanderthals and modern humans? They're not our direct ancestors, are they? Mai Dong asked.

"Strictly speaking, there is a certain genetic relationship, whether it is an Asian or a European, there are three percent Neanderthal genes in the body." The old cat put on his headphones and turned to answer Mai Dong's question, "But Neanderthals belong to a different subspecies from ordinary humans, that is, late Homo sapiens, and they are not your ancestors. Humans originated in Africa, the first group to leave the continent was Homo erectus, the second group to leave Africa was Neanderthals, and the third group to leave Africa was Homo sapiens, that is, the ancestors of modern humans. ”

"So Neanderthals became extinct?"

"Yes." The old cat nodded.

"Why is it extinct?"

"That's a long story......"

Tang Yue sat on the chair, his chin was clubbed, his eyes were staring at the computer screen, on the screen was a three-dimensional model of the joint space station, the model was rotating repeatedly, Tang Yue looked at it in a daze.

It is really an unsolvable problem to make Mai Dong successfully land.

This time, unlike the last time to deliver supplies, the delivery of supplies was only due to the difficulties of natural conditions and mechanical failures, and the Eagle spacecraft itself was capable of transporting supplies, and it was completely wishful thinking to land the space station safely, and the space station did not have this ability at all......

Tang Yue suddenly frowned.

"Old cat." Tang Yue stretched out his hand and pulled the old cat.

"What for?"

"I ...... I have an idea to overcome the difficulties you mentioned. Tang Yue said slowly, "Maybe there is a play, you can see if it's okay." ”

"What?" The old cat was taken aback.

"Eagle." Tang Yue turned his head, his eyes flashing with light, "Eagle spaceship!" ”