The "Starship" blew up again in two shots, and the stainless steel "canoe" made of thermos cups can send you to Mars?
Chao News client reporter Tu Chenxin
According to the global network, at about 21 o'clock in the evening of November 18, Beijing time, the "Starship" super-heavy rocket of the American SpaceX (Space Exploration) company was ignited and launched for the second orbit-level test flight. The test flight was planned to fly for 90 minutes, and the "Starship" spacecraft reached space for the first time, but about 10 minutes after launch, contact was lost, and its self-destruct system was forced to trigger, and the test flight was declared a failure.
According to CNN, this time it went further than when it was tried in April this year, but unfortunately, it still did not complete all the scheduled plans and eventually exploded again.
On April 20, the first test flight of the "Starship" in orbit lasted 3 minutes and 59 seconds, and flew up to 39 kilometers, but the first and second stages failed to separate, and soon rolled out of control, disintegrating and exploding after issuing a self-destruct command on the ground for 40 seconds.
Since its maiden flight in April, SpaceX has made more than 1,000 modifications to Starship, including reinforcing the launch pad with more stable engines, upgrading self-destruct devices, and changing the primary and secondary separation from cold to hot.
On April 20, Starship made its first orbital-class test mission. Source: Visual China
In Liu Cixin's sci-fi masterpiece "The Three-Body Problem", the chemical energy rockets possessed by humans today are described as "rowing a canoe across the ocean", which is a "fool's dream". In order to make the future aerospace take the road of "controllable nuclear fusion without working matter", one of the protagonists, Zhang Beihai, did not hesitate to take action to create accidents and promote the birth of stellar-class warships. These starships flew to distant alien galaxies at the life-and-death juncture of the invasion of the three-body civilization, becoming the "starship civilization", preserving the fire for the earth civilization.
Elon Musk in the real world is like an "idiot" rowing a canoe across the ocean. He wants to squeeze the potential of chemical energy rockets to the extreme, and he invites people from all over the world to dream with him, hoping to fast-forward human history to the episode of immigration to Mars.
Musk at SpaceX's headquarters in Hawthorne, California, May 29, 2014. Source: Visual China
And the "canoe" he used to realize the "crazy dream" is named "starship" - in the science fiction world, this usually refers to a spaceship that shuttles between star systems, and is a symbol of a future super interstellar civilization.
This big rocket has an extremely lofty name and target, but the materials and fuel used are extremely down-to-earth - the body of the rocket is made of thermos cup in your hand, the 304 stainless steel of your pressure cooker, and the "oil" burned is the methane that your gas stove burns every day.
Liquid oxygen methane is the most suitable space power to open the door to heaven at the moment, and there is no one. In this regard, Chao News has a detailed description in the report that the Zhejiang-made rocket Suzaku 2 snatched the crown of "the world's first liquid oxygen methane rocket successfully put into orbit" from the "Starship".
Can a rocket made of stainless steel really open the "interstellar door" to the moon and Mars for the earthlings? Chao News invited Yang Yuguang, vice chairman of the Space Transportation Committee of the International Astronautical Federation, to do some science popularization for you.
On April 10, in Boca Chica, Texas, USA, the starship was on the launch pad. Source: Visual China
The big rocket made of stainless steel is not simply "stupid and black"
"The biggest disadvantage of stainless steel is one word: heavy. But there are many advantages, high strength, high temperature and low temperature resistance, and extremely cheap. Yang Yuguang said.
According to calculations, 20% of the surface of Starship II sub-stage is exposed to high temperatures of more than 1470 °C during re-entry, and 20% of the surface has a maximum temperature of more than 1300 °C, and the maximum temperature of the rest of the surface is lower than 1176 °C. The melting point of 304 stainless steel is 1398-1454 °C, which is more resistant to high temperature than any mainstream arrow body material, which makes the "Starship" have more than 15,000 heat insulation tiles, which can withstand high temperatures of 1648 °C, and stainless steel can also be carried. Musk originally wanted to use carbon fiber on the second sub-stage of the "Starship", but the carbon fiber could not resist high temperatures, so he boldly changed it to stainless steel.
Stainless steel retains sufficient ductility and strength even at minus 160 °C, and can easily navigate the surface of Mars at an average temperature of minus 63 °C. What's even more amazing is that stainless steel will increase its strength by 50% at low temperatures, even higher than that of aluminum-lithium alloys, and stainless steel with chromium-nickel will increase ductility by 12-18%, and carbon fiber is also strong.
And then there's the cheapness, and stainless steel is simply too cheap. 304 stainless steel is very common in our lives, pressure cookers, thermos cups, cabinets at home... Everywhere.
Workers inspect stainless steel vacuum utensils at the Hals plant in Jinhua on October 29, 2020. Source: Visual China
In terms of the price that Musk is most concerned about, he has calculated an account - the cost of building a rocket with carbon fiber is more than $135 per kilogram, and at the same time, carbon fiber has a 35% loss, which costs $200 per kilogram overall, and it costs thirty or forty dollars per kilogram to use aluminum alloy, and the same rocket is only $3 per kilogram to build the same rocket with 301 stainless steel sheets!
And that's not all, the carbon fiber manufacturing process is complex, and a technician earns $250 an hour, while the average welder who welds stainless steel plates earns less than $50 an hour. Musk once said that NASA's SLS heavy rocket cost enough money to bomb the "Starship" 100 times.
"However, being too heavy is indeed a big flaw, because aerospace materials are all pursuing a 'light' word, striving for every gram of weight loss. Yang Yuguang introduced, "The rocket body is too heavy, and the thrust remains the same, the payload is small, and the fuel and cargo that can be carried are less." ”
Therefore, if you want to use stainless steel as the body material, there must be prerequisites. "The engine has to be good enough. Starship's 'Raptor II' full-flow staged combustion cycle liquid oxygen methane engine is made small, with large thrust and high specific impulse, which makes up for the weight loss caused by stainless steel. Yang Yuguang said.
Another point, if the rocket is made particularly large, it can also partially compensate for the shortcomings of stainless steel being too heavy. In other words, it focuses on a "miracle of great force", which is also the design idea of "Starship".
However, Yang Yuguang emphasized that we can't simply think that the "starship" is "stupid, big, black and coarse", in fact, the stainless steel arrow body of the "starship" is very technical, "it is very thin, large, thin and pressure-resistant, and the material technology and processing level behind it are very high."
Although the first launch of the "Starship" failed on 20 April, it rolled in the sky for a long time before disintegrating, which just shows that the strength of its stainless steel rocket body is quite large.
The picture above shows the 30 engines of the first stage of the N1 rocket, and the picture below shows the 33 engines of the first stage of the Starship. Source: Visual China
Choosing a Soviet moon rocket, will it repeat the mistakes of the past?
Since the "Starship" program was revealed in 2016, it has been called "the most powerful rocket in history". Its take-off weight of 5,000 tons greatly exceeds the 3,039 tons of the former world champion American moon landing rocket "Saturn V", and its 7,590-ton take-off thrust also greatly exceeds the 4,620 tons of the former world champion Soviet moon landing rocket N1.
What is particularly topical is that the "Starship" stage boldly adopts 33 parallel engines, which can simply cause some people's "dense phobia". This is considered to be a continuation of the N1's first-stage 30 parallel connection half a century ago.
The N1 was not a successful example, and from February 1969 to November 1972, the N1 rocket was blown out of the field and the Soviet Union lost the race to the moon. The first launch of the "Starship" also exploded, and the rocket was also out of control, which makes people wonder whether this technical scheme of using dozens of units in parallel has a future.
In fact, the Soviet Union put so many engines on the moon rocket out of desperation. The F1 liquid oxygen kerosene engine used in the "Saturn V" has a thrust of up to 680 tons per unit, and only five units are needed in the first stage to produce 3,400 tons of thrust. At that time, the Soviet Union could not build such a powerful engine, and its NK-15 engine thrust was only 154 tons, and in order to obtain more than 4,000 tons of thrust, 30 units had to be connected in parallel.
Soviet N1 moon rocket.
Similar to the situation of the Soviet space sector, when SpaceX designed the Starship, the existing liquid oxygen methane engine lacked thrust, and the 230-ton thrust Raptor II was already the strongest in the world.
Yang Yuguang told the Chao News reporter that SpaceX also chooses multiple parallel connections, and so many engines are crammed into one rocket body, so it can't bundle several boosters like the Long March 5 and the "Heavy Falcon", and there is an important reason, that is, for reuse.
"Musk said that no matter how big the rocket is, the control system required is almost the same, so the bigger the rocket, the more cost-effective. A first stage plus two boosters, to recover three rocket bodies, so the cost is much higher than with a large rocket, the process is much more complicated, the more complex the worse the reliability. Yang Yuguang explained.
However, the logic of "adding more water to the surface, and adding more water to the surface" is not entirely applicable to building rockets.
"Rocket engines work in a much harsher environment than car engines and aero engines, and the thrust of rockets is much higher than that of the latter two engines of the same weight. This inevitably leads to strong vibrations due to intense combustion, resulting in coupling resonance. Yang Yuguang said.
If dozens of engines are installed on different rocket bodies, for example, the "Heavy Falcon" also has 27 engines, but it is scattered on three rocket bodies, and there are only 9 engines on each rocket body, and then connected together by an interstage connection device, the coupling resonance is not so serious. "But if dozens of them are mounted on the same arrow body, the coupling is much more powerful. Resonances affect not only the engine, but also from the tank to the lines to the valves. Yang Yuguang analyzed that the several failures of the N1 were not mainly due to engine failure, but resonance caused the pipeline to rupture or the valve to break. When the "Starship" was first fired in April, a large amount of white fog came out of the rocket body, and it may also be that the pipeline was damaged and the liquid oxygen leaked.
White smoke emitted from the starship's first flight. Source: Visual China
But that doesn't mean Starship will follow in the footsteps of N1. "After all, times are different, and the current knowledge of computer application capabilities, dynamics, vibration analysis and control is incomparable to that of half a century ago. Yang Yuguang said, for example, that Boeing can design aircraft without wind tunnel tests, and completely rely on digital simulation to achieve very accurate. In his opinion, theoretically, the problem of multiple engines in parallel can be solved.
After the initial failure, SpaceX made a number of improvements, including changing the nozzle oscillation from hydraulic to electric because hydraulic pressure is more affected by dynamics, adding a number of partitions between the engines to isolate each other, and computer simulations. "But all of this is no substitute for a car interview. Even though the Saturn V had only five engines, all of them were tested on the ground on a full-scale test bench, and there was still coupling resonance during launch. ”
In order to save money, Musk did not build a full-scale interview platform, and the test run of the "Starship" could not reach full power, only 50% thrust. Therefore, it is difficult to say whether the problem can be solved theoretically, but whether it can be passed in reality.
On April 5, 1983, the second U.S. space shuttle "Challenger" made its maiden flight, which was on the eve of its launch. Source: Visual China
Ordinary people take the "starship" to the sky, and there is no drama in the foreseeable future
In SpaceX's "Starship" blueprint, the first and second stages will be fully recovered in the future, and each engine can theoretically be reused 50 times. The ultimate goal is to reduce the launch cost to a very low level of $10 per kilogram of payload, so that ordinary people can realize their space dreams. How far are we from this step at the moment?
Yang Yuguang said frankly: The future is uncertain. He gave the example of the space shuttle to prove that "the ideal is plump, and the reality is skinny".
"The Space Shuttle is reusable in orbit, but it comes at a great cost. According to Yang Yuguang, the take-off weight of the whole system of the space shuttle is more than 2,000 tons, and if it is a carrier rocket of conventional configuration, the low-orbit capacity can be at least sixty or seventy tons, but the space shuttle has a capacity of only 29 tons. Pay so much, the first is to be able to carry people, and the second is to be able to come back and be reused.
In order to reuse, the space shuttle not only lost more than half of its capacity, but also had to do very complex overhauls every time it came back, and each of its thermal insulation tiles had a different shape, which was difficult to standardize and mass-produce. The "Starship" is a little better, most of the heat protection tiles are the same shape, but the heat protection tiles near the top and the lifting wing surface are also different, and replacing these will inevitably bring time and talent costs. "Because the technology is too radical, there is a question mark over whether it will succeed in the first place, and even if the complete reuse succeeds in practice, it is difficult to say whether it will save money in the end. ”
In particular, if the "Starship" is to plan a manned flight in the future, safety will be an even greater difficulty. The shuttle carried only seven people and blew up twice in 135 flights (Challenger in 1986 and Columbia in 2003), killing a total of 14 astronauts. On the one hand, the "Starship" has to reduce costs to the extreme, and on the other hand, it has to carry 100 people at a time, and in the event of a serious accident, it is basically certain that none of these 100 people will survive, and the impact on the "Starship" program is unimaginable.
On May 2, 2021, the manned Dragon spacecraft returned to Earth from the International Space Station and splashed down on the Gulf of Mexico. Source: Visual China
Yang Yuguang gave an example: Space X originally wanted to use rocket thrust reverser to land on the manned "Dragon" spacecraft, but it was rejected by NASA and the FAA (Federal Aviation Administration).
"The 'Dragon' spacecraft is very short and thick, and its eight engines only need to work for four to land, so the United States officials do not allow it. The second sub-class of the 'Starship' is much more slender than the 'Dragon' spacecraft, and it may fall or explode if it is slightly crooked, which is too risky, and has only been successfully recovered once so far. If you don't carry people, forget it, if you carry people, how can the official give the green light?"
Yang Yuguang reminded that if the second substage of the "Starship" manned class wants to be reused, its only landing method is the rocket thrust reverser, because its empty weight is 120 tons, which is far beyond the load-bearing limit of the parachute.
If the administration does not allow it, then the manned flight of the "Starship" is only a castle in the air, not to mention landing and immigrating to Mars, even if it is impossible to carry passengers from New York to Shanghai.
Starship on April 15. Source: Visual China
Starship is better at orbiting the Earth than flying to the Moon and Mars
Yang Yuguang further pointed out that the "Starship" is actually not very suitable for sending people to the moon and Mars, and the most suitable work for it is to orbit the earth, such as launching satellites into low-earth orbit.
"Because the launch of deep space payloads requires higher speeds, the speed can only be added if there are more stages. For example, the Saturn 5 is a three-stage rocket, and the N1 has reached the fifth stage; for example, the Long March 5 that launched the Tianwen-1 Mars probe is a two-and-a-half-stage basic model, and the Long March 5B, which is dedicated to launching the space station, is a one-and-a-half-stage rocket. Yang Yuguang believes that in order to be 100% reusable, the "Starship" has chosen a bipolar configuration, which is cost-effective and efficient for low-earth orbit, but extremely inefficient for deep space transportation.
Therefore, the statement that "Starship is the most powerful rocket ever built by mankind" is problematic in his opinion. "You say that it is the largest and heaviest rocket, there is no problem, the low earth orbit capacity of 250 tons is definitely the largest, but if it is a lunar orbit, the 'Starship' does not replenish propellant in orbit, I am afraid it is not as good as the 'Saturn V'. ”
According to Yang Yuguang, according to SpaceX's plan, the "Starship" will first fill up liquid oxygen methane propellant in low-earth orbit as many as five times to go to Mars, and if it goes to the moon, it will have to make up for it eight to 10 times, because the speed required to go to the moon will increase even more. The "space tanker" used to refuel the "Starship" has only 1-2 launch windows and 1-2 return windows per day, and the entire system and mission are too complicated, and its cost and failure rate will increase exponentially.
"There is also a big problem: how to store liquid oxygen methane in orbit for a long time? Although it is much easier than liquid hydrogen, human beings have not done it, and liquid oxygen has not been stored in outer space for more than a day. Yang Yuguang analyzed that in the same space, spacecraft in low-earth orbit can be protected by a strong earth's magnetic field, and the deep space environment is much harsher.
No matter how magnificent and romantic this expedition to the "sea of stars" is, human beings can only take one step at a time and grope their way forward.
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