It has been two months since SpaceX’s explosion on September 1st, and the accident investigation report has not yet been released. However, in the process of accepting CNBC’s exclusive interview, Eron Musk revealed the final cause of the accident, in order to explain Qing has never had a strange explosion accident in the history of aerospace. We specially translated a foreign-language analysis article, hoping to answer your questions. The latest news about the resumed launch after the investigation is completed is detailed in the daily slogan of the home page after the text.
Annotation: The cause of the accident gradually surfaced, because a small amount of ultra-cold liquid oxygen directly in contact with COPV solidified during the helium filling process. As the helium gas was filled, the metal liner gradually expanded and squeezed into the solid oxygen. In the outer carbon fiber, the chemical reaction between the two causes an explosion. This eliminates our previous concerns about design flaws. We only need to modify the filling process a little. This tragedy can be avoided. It seems that the go-around in December is getting closer.
So far, I have not seen the final investigation report for the bizarre accident on September 1. But when Eron Musk recently mentioned a few words in CNBC's interview with him, this time detonated my thinking. - He is talking about liquid helium and solid oxygen. This important interview allowed us to understand what their current situation is and why SpaceX is so confident that their Falcon-9 rockets will resume launch next month (December).
The September 1 accident shattered more than just a launch, but the ideal of rocket reuse.
It’s been a while, and we know that the explosion was caused by the Composite Overwrapped Pressure Vessel (COPV). (Annotation: The COV of the Falcon-9 rocket consists of an aluminum lining and a carbon fiber casing, lining The role is to isolate the inside and outside of the container, the strength is provided by the carbon fiber wrapped around the outside.). COPV is a tank used to hold gas under high pressure. In the Falcon-9 rocket, it is used to store helium. Helium has a wide range of uses in the Falcon-9 rocket, such as tank pressurization and interstage separation.
COPV is not a new thing, it has been used in rockets for decades. COPV has excellent mechanical properties and extremely light structural weight. It is mainly composed of fibers, so in some respects its properties tend to be more fabric rather than metal.
The COPV of the Falcon 9 rocket that descended from the sky after a launch mission can clearly see the exposed carbon fiber at the bottom. The fiber-wrapped liner is made of aluminum alloy. The specific process and alloy grades are unknown.
I want to say here, another thing that SpaceX does is that it adds the liquid oxygen to the rocket near freezing point instead of the near-boiling liquid oxygen that is commonly used by other rockets. Therefore, this constitutes the second important factor in the explosion accident - liquid oxygen close to the triple point. Sometimes, COPV will absorb a small amount of liquid oxygen. But things don't add up simply. Liquid oxygen has cooled cooler, but it's still liquid. How do the two things that are not related to the original solid oxygen come from?
Normally, if you inflate a fixed-size tank without stopping, the gas will release a lot of heat. We can see that when I pump up the bicycle tires, the tires become very hot. This can be described by the ideal gas law pV=nRT, which generates a lot of heat when the COPV is filled to 5500 psi of the Falcon-9. (Homepage Note: p is the pressure of the ideal gas, V is the volume of the ideal gas, n is the amount of gas, and T is the thermodynamic temperature of the ideal gas; R is the ideal gas constant. The unit of psi is pounds per square. Inches, a common pressure unit of the old beauty)
If in ordinary rockets, COPV is immersed in a low-boiling liquid oxygen tank, this is not a problem. The liquid oxygen will be heated as the COPV gas is inflated, and the superheated liquid oxygen will evaporate away this extra heat. Then, the ground equipment will inject additional liquid oxygen into the rocket to make up for this loss.
The United States launches the "Centre Centau" upper class, its helium bottle is suspended at the end of the tank.
Let's compare it. The picture shows the secondary liquid oxygen tank of the Falcon-9 rocket. The liquid oxygen level has been reduced a lot in the picture, and the COPV is immersed in the full liquid oxygen before the second stage ignition. This design is quite rare and can even be called SpaceX's first.
However, SpaceX, which pursues technological advancement, often does not take the usual path. SpaceX uses ultra-low temperature liquid oxygen close to the three-point point (Homepage Note: that is, we often say "pre-cooled liquid oxygen" or "supercooled liquid oxygen", Falcon-9 fills the liquid oxygen temperature than the normal rocket It is also used low, intending to use the high-density characteristics of supercooled liquid oxygen, storing more liquid oxygen propellant under the premise of the same tank size, thus draining the rocket's capacity, kerosene pre-cooling is similar) Low temperatures do not allow COPV heat to enter the liquid oxygen. The release of heat will cause the temperature of the propellant to rise, while the density is related to temperature. Higher temperatures mean that only less propellant can be carried, resulting in a decrease in the rocket's carrying capacity. Therefore, SpaceX, which pursues greater carrying capacity, will not adopt the current conventional COPV inflation method.
So how does helium fill the COPV? How does solid oxygen come into being? Before we did, we didn't know how SpaceX handled the problem of liquid oxygen heating. Until yesterday, Musk in the interview mentioned that they would fill the COPV with liquid helium instead of completely filling the hernia. This filling procedure ensures as low a temperature as possible of liquid oxygen: the liquid is injected into the COPV to absorb the heat generated by the heating. The heat will boil the liquid without heating the liquid oxygen outside of it. (Homepage Note: That is to say, SpaceX does not affect the pre-cooling effect in order to prevent the helium gas from pressurizing, and it uses the liquid helium with a boiling point as low as -268.9 degrees Celsius to fill the COPV, so that the liquid oxygen will not The heat absorption evaporates, but the melting point of liquid oxygen is only -214.4 degrees Celsius. The liquid helium absorbs the heat of liquid oxygen, which causes the pre-cooled liquid oxygen partially infiltrated into the gap between the COPV carbon fibers to become solid oxygen.
As long as we look at the table, we all know that the liquid helium triple point is lower than the liquid oxygen. Obviously, SpaceX knows the difference, why their rocket scientists don't think it will be a problem?
It turns out that liquid helium is a very strange substance. One of its characteristics is that it has a very low specific heat capacity. In general, it requires only a small amount of heat to heat it to a very high temperature. Clearly, SpaceX engineers believe that liquid oxygen does not condense into solids as long as enough heat is left in the liquid oxygen. Sadly, only most of the time, they are correct.
When liquid oxygen close to the three-phase point is immersed in the COPV fiber, it undergoes a very small amount of freezing, which is a disaster. The COPV has a pressure of 5,500 psi and the fibers are strongly compressed. At this time, if the oxygen intertwined with the COPV fiber is a liquid or a gas, it will be extruded. But it is not, it is solid oxygen.
The cross section of the COPV after cutting, the silver is the aluminum alloy liner, and the liquid oxygen is infiltrated into the gap of the material indicated by the arrow.
A typical carbon fiber winding process.
To make matters worse, carbon fiber reacts with liquid or solid oxygen and is very easy to explode, which we already know. Moreover, all this requires only a little mechanical stress to trigger. All these carbon fibers and solid oxygen need only a little bit (Home Note: According to the original, liquid oxygen will also react, but because it can be extruded under pressure, it will not explode. In fact, carbon fiber composites are compatible with liquid oxygen. Sexual issues have been well known since the 1990s, but they are not this form.) When this combination is formed, carbon and oxygen will explode and subsequently spread to the entire COPV.
From the preliminary investigation report, we can know that the explosion damaged the COPV, and a large amount of helium gas rushed into the secondary rocket storage tank, and the overpressure caused the entire secondary explosion.
In the words of Musk, this is an unprecedented accident. Yes, there will always be sacrifices on the road to the pursuit of new technologies. This little setback is a little elementary school fee for the journey to the universe.
When the accident is over, the bombing is actually blown up. Musk’s current tuition on composite materials is much cheaper than going to Mars in any case! And the latest news is that SpaceX has already taken an important step in the accident investigation. - The accident reappears. (If the conclusion of the final accident is different from the analysis of our translation, we will write another article)
Of course, it is certainly not a new Falcon-9 secondary to do the experiment, but similar to the destructive test simulation environment shown in the figure, simulating the COPV rupture explosion caused by solid oxygen during the pre-cooling filling process.
As a result, the theory that the COPV and the tank filling in the previous period formed a sonic resonance caused the COPV to break can only be swept into the pile of paper. However, it is good to prove that the design of COPV itself is no problem. The design of the rocket itself is not the root cause of the accident (this conclusion may be slightly arbitrary). But the strange thing is that the level of the Falcon-9 rocket is also a similar filling mode, but there has not been such an accident. There is no evidence that the first and second levels of COPV are different in the filling process. SpaceX also does not explain the difference between the two. However, SpaceX believes that we have found the problem and found a solution to the problem - to modify the filling process of the helium gas to avoid the phenomenon of liquid oxygen curing, and no hardware changes are involved.
As a result, SpaceX should be preparing to resume the launch, because the customers underneath are anxious like the ants on the hot pot. . . Among them, the company can be called "scrapping in the toilet". It was originally launched twice at the end of the year. A total of 20 comets were in orbit. As a result, even the hairs are not visible. The satellites in the warehouse are everywhere. Staying on the ground for a day, the white flowers will keep flowing. In addition, according to the "Wall Street Journal" report, SpaceX is likely to launch orders for the launch of the satellite Instarsat PLC (a famous maritime satellite), which was previously reported by the European satellite communications company. There is no way to restart the confidence of the satellite launch plan. After all, time is not waiting for people.
Since SpaceX did not choose to return the traditional model of the soaked cooled helium cylinder used by the predecessors, the titanium alloy helium cylinder, the recovery launch seems to be just around the corner, and the reason continues to take risks, because COPV is relative to titanium cylinders. There are still outstanding advantages in both weight and cost. Everyone knows that Lao Ma is more fascinated by drugs than money. . .
As a result, all current sources point to SpaceX will resume transmission in December, the specific time and specific tasks to be determined!
At the end of October, the Texas test site ushered in a new rocket number 031, the full-time ignition test has been completed, the level has been shipped to the LC-39A launching station in Cape Canaveral, becoming a rocket to resume launch.
The second level of recovery launch before the ignition test, in fact, the most striking is the structure test arrow on the right red box. According to the foreign media news, the heavy-duty Falcon rocket booster structure test arrow is now standing here. The core test arrow has been tested and pulled away.
Of course, there is even more amazing news - the two boosters of the heavy Falcon rocket's first flying arrow will be refitted with the recovered Falcon 9 rocket! (Red box) I really want to say, Ma S, can you tell me more? I didn't believe it when the news came out, but now more and more internal news confirms this practice.
Secondary ignition test screen
Spacecom, Israel: Amos-6 satellite manufacturer IAI said it will receive $196 million from insurance companies, and Xinwei’s acquisition will continue. Of course, as I predicted, the valuation will definitely change.
In addition, for the next year's manned dragon mission, in order to free up more energy to prepare for the manned dragon launch tentative next year, SpaceX decided to start with the CRS-11 replenishment mission (the next mission is CRS-10). The reclaimed and refurbished cargo dragon spacecraft is used to resupply the International Space Station. SpaceX official said that the most difficult problem in the process of reusing the cargo dragon spacecraft is the corrosion of seawater, which is one of the reasons why the next generation of dragon spacecraft uses land-based reverse thrust landing, but in any case, the reuse of cargo dragons is also human space. A new attempt in history is equally commendable.
The picture shows the cargo ship that was recovered from the sea. The bottom spit is the Draco engine. The next uncle is Tom Muller, the founder of the Merlin engine. He was the chief designer of TRW.
Seriously, following the footsteps of the predecessors, the design can really take a lot of detours, but the old Ma Ning can pay tuition, risk, and face constant innovations in various aerospace history. Although paying tuition is almost a matter of course, we still hope that he will have less interaction. After all, there are really not many people who are willing to do this now.
Our banknote handling machines mainly include following
BC -30: basic piece counter with only one UV
BC-35: piece counter with UV MG
BC-40: value counter with one CIS, support 4 currencies, Auto recognition, multi-currency mix counting
BC-55: value counter with two CIS, support 40 currencies at the same time, serial number reading, Auto recognition, multi-currency mix counting, remote software upgrading via network
Those 4 models have similar structure, passage can be opened from reat side, easy for maintenance and cleaning
BCS-160: 1+1 pockets banknote sorter with two CIS, support 20 currencies at most, serial number reading
Banknote Deposit Machine,Mixed Denomination Cis Banknote Counter,High Speed Euro Banknote Counter,Mixed Denomination Cis Banknote Counter
Suzhou Ribao Technology Co. Ltd. , https://www.ribaoeurope.com