: The distance from the thought to the starry sky (middle)

"In fact, if it's just exploration, it actually started when the first satellite was launched."
　　 A high-altitude island-like mountaintop, sitting around the bonfire under the magnificence of the Milky Way, when Fang Ran asked such a question, Klim answered with a smile.
　　 But I can guess that "Exploring the Universe" he said should be able to travel between stars, and I am a little embarrassed:
　　 "But if you refer to what Fang Ran you think, it is probably the foreseeable future development, which will definitely not be realized within a few centuries, and the subsequent time is unpredictable."
　　 Hearing his rigorous answer, Fang Ran nodded and asked very simply and straightforwardly:
　　 "Is it because you can't build a spaceship?"
　　 "Hahaha, that's true."
　　 I couldn’t help but laugh when I heard this, Klim raised his head and looked up at the flourishing starry sky above his head, even though there were several astronomical observation activities,
　　 But it was the first time he saw such a clear and beautiful Milky Way with his own eyes.
　　 "But in the final analysis, we know too little about the universe and too many unknowns, which leads to no theoretical knowledge before we can create it."
　　 "And face it's huge, small and helpless."
　　 Speaking of this, Klim lowered his head and looked at Fang Ran with a chuckle, telling a little about the hugeness.
　　 "In the theory of relativity, the speed of light is the limit of the speed of the universe, but the size of the Milky Way galaxy is measured in 100,000 light-years, and the local galaxy group to which it belongs is measured in millions of light-years,"
　　 "And above that there are the Virgo Supercluster, and the higher-level Rania Kea Supercluster, and other superclusters of the same level."
　　 also looked at the bonfire in front of him and made a small statement.
　　 "But we don't even have a theory that can reach the speed of light, let alone the nearest star a few light years away,"
　　 "Even activities in the solar system are difficult to achieve."
　　 And Fang Ran's face was stunned. He just barely knew the fairy galaxy, and it was the first time he knew the name of the superior galaxy in the universe.
　　 The scale of one hundred thousand, one million light-years, the country, economy, earthquake, race, culture... everything seems small when compared with the astronomical distance.
　　 "Is it because no one studies it?"
　　 Every time I chat with Kerim, Fang Ran will be troubled by my lack of knowledge and cannot ask any decent questions.
　　 But perhaps because of this, he likes to chat with Klim.
　　 "It is mainly limited by the current level of scientific theory, but there are also some complicated reasons for this,"
　　 As for Fang Ran’s curiosity, Kerim still answered with a smile, and then continued to explain softly and gently:
　　 "The research and development of science and technology needs a purpose. The appearance of rockets during World War II made the great powers feel a sense of military crisis, so they competed for talents in the form of a space race."
　　 "Let the space technology advance by leaps and bounds during that period, and the end of the Cold War naturally slowed down the pace greatly, and more people focused on research in other fields."
　　 Like Fang Ran likes to chat with him, he also likes this kind of small chat very much. Compared with the knowledge that is used as a tool by others,
　　 is used to answer the curiosity of the most precious friend, making Klim even more happy.
　　 "After all, to the extent that global resources have not yet been fully exploited and utilized, it has not yet developed to the point where space navigation is considered, due to various factors such as politics, capital, and productivity."
　　 "This field is still in the development and exploration of human beings under the premise of social abundance."
　　 Speaking of this, seeing Fang Ran's ‘oh oh oh’ face unclearly, Kerim chuckled at him again and added:
　　 "If there is an alien one day, or the earth’s life is hanging by a thread and we need to seize the life-saving straw of space, then maybe we will soon enter the era of interstellar voyage."
　　 "No, I always feel that I might not survive that time..."
　　 Hearing Klim’s "comfort", Fang Ran said helplessly, but soon he looked up at the beautiful Milky Way above his head and laughed again.
　　 I can't see the disappointment at all, but the expectant happy voice comes out.
　　 "Space navigation is not realistic yet..."
　　 "Although the distance to the deep space level is still far away, there are still some more realistic ideas at close range."
　　 also sat on the tree stump, playing with the bonfire with the branches, Li Ze, who had been listening quietly, spoke at this moment, and was immediately asked by the curiosity Fang Ran's upper body shaking the novelty:
　　 "Eh! More realistic? What is it?"
　　 "For example, a space elevator."
　　 "Space elevator?"
　　 Hearing Li Ze's answer, Fang Ran's mind first came up with the "Metal Giant Pillar" that he had forgotten in which work he had seen. His eyes flashed with curiosity:
　　 "Isn't this stuff made up in film and television, is it useful?"
"Very useful..."
　　 repeated Fang Ran's statement again, and Li Ze pondered for a while before speaking slowly:
　　 "It should be said that it has an epoch-making effect."
　　 To understand Fang Ran’s level more clearly, Klim gave him a more detailed explanation.
　　 "At the current aerospace level, the most troublesome thing about entering space is to overcome the gravity of the earth. For this reason, most of the rockets are fuel for acceleration, and there are very few cargo and people."
　　 recalled the papers he had read before, and he gave a simple and clear example:
　　 "To transport a kilogram of payload into space, even if it is very economical, it costs about 20,000 U.S. dollars, and it costs at least one million U.S. dollars to transport one person.
　　 "But if there is a space elevator, the price can be reduced to one percent, of course, not counting the cost of the elevator itself."
Eh! ? so cheap?
While surprised at this point, Fang Ran heard Li Ze say some more far-reaching significance ~EbookFREE.me~ The simpler way to enter space means that people can transport resources more easily and build space bases more easily. It’s easier to acquire knowledge and theories about space,"
　　 "Realize the first step for mankind to leave the cradle."
　　 Listening to their explanation, looking at the starry sky above, I imagined a building that directly leads to the sky. People can go straight to space when they sit on it.
　　 Fang Ran looked at Li Ze and Klim, was incredibly surprised and asked:
　　 "Is this really more realistic? Directly into space, how heavy is the weight of such a tall building, and how much support does it need to stand on the ground?"
　　 "No, the design theory of the space elevator does not require ground support. Like a synchronous satellite, it relies on gravity and the inertial centrifugal force on the synchronous orbit."
"Eh?"
Hearing Fang Ran’s voice, he knew that he must not understand. Li Ze opened a projection on the campfire surrounded by the three of them, and drew two nested circles on it with his fingers, giving him a simple graphical explanation basis principle.
　　 "Assuming that the angle of view is over the North Pole, this circle is the earth's equator, and the outer circle is a synchronous orbit."
　　 "Synchronous orbit is the object in this altitude orbit. Because of the equal gravity and centrifugal force, it will maintain an orbit relatively stationary with the earth."
I know this!
　　 Regarding Krimkop’s concern, Fang Ran made a stubborn cry in his heart that high school physics has not yet forgotten...