American private enterprises use 30 1 stainless steel to build spacecraft to Mars! Musk did this just to save money?

At the end of 20 18, elon musk, the boss of Space Exploration Technology Company, an American space exploration company, showed the world the largest spaceship in human history, and he gave it a very sci-fi name "Starship". In the PPT presented by Musk, the starship was dark and flew over Mars like darth vader in Star Wars. Because space exploration technology company intends to use the most advanced material carbon fiber to build this future spacecraft.

Only two months later, at the beginning of 20 19, 19 10, Musk showed a new picture to the media. In this new picture, the starship on the 18 floor becomes silvery white. Musk called it "looks like liquid silver" because Space Exploration Technology decided to build a starship with stainless steel. Of course, the spacecraft needs a lot of tests, and it is obviously a bit wasteful to use expensive carbon fiber to make the shell from the beginning-Musk fans think so.

However, the following starship prototype test made the faces of horse fans a little sore, and the media raised questions one after another: Ma Lao, you are not here to be funny!

The starship test section looks like the lower part of the "liquid silver" spacecraft. It is indeed made of stainless steel. However, the surface of this big iron drum named "Stars" is pitted, and obviously the welding process is quite poor.

Appearance is actually not important, because the purpose of space exploration technology company is to use it to test the engine and flight control system, as long as it can leave the ground without exploding.

On July 26th, 20 19, this 9-meter-thick stainless steel barrel flew to an altitude of 20 meters and fell back to the ground 22 seconds later. Musk excitedly announced on social media: "Starhopper flew successfully and the water tower can fly haha! ! "

Starhopper can fly, which is not difficult for space exploration technology companies, because the "Falcon 9" rocket's housekeeping skills are hovering in the air and horizontal displacement. For most space powers today, similar technologies are not complicated.

As time goes by, the shape of space exploration technology company starship is getting closer and closer to the original PPT sketch. Although the shell is still stainless steel, the welding process is much better. At the end of 20021,Musk officially announced that the future starship spacecraft flying to Mars will only use stainless steel and completely abandon the idea of carbon fiber!

Why is this happening? Does Musk even risk the lives of Martian immigrants to save money?

Indeed, from the first day of the establishment of Space Exploration Technology Company, Musk played the word "saving money" to the extreme, because the goal of Space Exploration Technology Company is to "reduce the cost of space transportation" and do the biggest thing with the least money. In order to save money, this space company is against the image of all space agencies. They set up tents on wasteland, hired ordinary welders, found the cheapest raw materials and made rockets on the ground full of dirt and dust. If I don't tell you that it is the most famous aerospace enterprise in the world, you will definitely think that a township enterprise has won a big order for tinplate steamer.

Some readers said, don't care about the environment, the works are good, and the things made are exquisite.

Not much to say, one more. This is a starship that has just been manufactured by Space Exploration Technology Company. It has stood on the launch tower and is ready to be tested. Let's look at the process:

No wonder NASA complained about Musk's stainless steel rocket: didn't you smash my brand by playing like this?

But stainless steel is cheap, which is a fact that no one can deny. Musk calculated an account: making rockets with carbon fiber costs more than 135 US dollars per kilogram, while carbon fiber materials have a loss of 35%, totaling 200 US dollars per kilogram; The same 30 1 stainless steel plate is only $3! The manufacturing process of carbon fiber is complicated, and the hourly salary of professional technicians is $250, while the hourly salary of ordinary welders welding stainless steel plates is less than $50.

In this way, it takes tens of millions and hundreds of thousands of stainless steel plates to build a100t spacecraft shell with carbon fiber.

Musk abandoned carbon fiber not only because it is expensive, but because it is really not suitable for the mission requirements of starships.

The advantages of carbon fiber material are light weight and high strength. With the price getting cheaper and cheaper, carbon fiber is widely used not only in mainstream civil aircraft, but also in family cars and bicycles.

However, the strength of carbon fiber is directional and can bear great pressure in some directions, but it is very fragile in another dimension. If it is made into a rocket shell with a diameter of 12 m, additional reinforcement structure is needed, which will increase the total weight and the advantage of thin carbon fiber will no longer exist.

Carbon fiber cannot be welded. If you want to use it to make a starship shell, you need a huge reel with a diameter of 12 m and a length of more than 50 m to wind the fiber filament, and then vacuum bake it with larger equipment for several hours or even days before curing. This is unimaginable for Musk who wants to save money. In contrast, welding with 3 mm thick stainless steel plate hardly needs any equipment and investment, and can be completed in the open air, which is much faster.

The high and low temperature performance of stainless steel is better than that of carbon fiber. 30 1 stainless steel has good thermal insulation performance and is suitable for storing ultra-low temperature liquid oxygen at 8.5 atmospheres. At the same time, it can withstand the high temperature caused by the friction when the rocket enters the atmosphere, and only when the temperature exceeds 8 15 will it lose its strength, so it is necessary to lay insulation ceramics at the position where the friction with air is the most intense.

Carbon fiber has good thermal conductivity and needs a double shell to isolate liquid oxygen, which means extra weight; Although it can also withstand high and low temperatures, when it re-enters the atmosphere, the flame from the engine will continue to bake the outer shell of the spacecraft. There is liquid oxygen in the spacecraft, which will turn the whole spacecraft or rocket into a burning fireball.

Having said that, you should understand that Musk doesn't just use 30 1 stainless steel to make starship spacecraft. Stainless steel does have many advantages: it has higher strength under the same weight, can adapt to extremely low temperature environment, has low processing and maintenance costs, is fast in manufacturing, and even doesn't need painting ... The most important thing is that it is really too cheap.

In contrast, carbon fiber is too high, the material cost is 70 times that of stainless steel, the processing technology is complex and expensive, and the precision requirement is high. In fact, if you want to achieve the strength required for starship missions, the weight advantage of carbon fiber is not obvious. What is more troublesome is that this thing is too easy to burn in a high-oxygen environment and may kill people.

So the decision of space exploration technology company to give up carbon fiber is reasonable, but I don't know whether their stainless steel starship can really fly to the moon and return safely in 2024.

# Musk Starship Project #