Why do we still expect “successful failures” on rocket launches and not just scale up or scale down the same design on successful rocket ships and launch pads to make bigger or smaller ships with more stable structural material?
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Can’t break the sound barrier with a biplane. Can’t make an indestructible plane fly. Can break new things scientifically until it’s a proven design (just add money).
Can’t break the sound barrier with a biplane. Can’t make an indestructible plane fly. Can break new things scientifically until it’s a proven design (just add money).
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You’d think that it’d be that simple. Unfortunately the scaling here is non-linear, it is often exponential, if it scales at all. That is to say, if you double the height of the rocket, you don’t double it’s weight. That kind of scaling would be linear (proportional) but in fact, if you double it’s height you increase it’s volume (ergo its mass, ergo its weight) EIGHT times.
That’s just one simple issue with the scaling. The forces involved do not scale proportionally, nor does the amount of fuel. Nor do the aerodynamics since the volume of air that needs to be displaced is also related exponentially. All this combined means that the materials used in construction won’t be subjected to linear transformations of the stresses. Same is true for the fuel seals and just about every other component.
With something as complex as a rocket (this IS rocket science after all) it’s incredibly difficult to build a reliable mathematical model and scale it to suit. There are so many variables and so many unknowns. And every mathematical model, by its very nature, is a simplified one.
The recent launch was a test, so they can gather data. Now that they have that data, they feed it back into the mathematical model and refine it, tweak the papameters, add or change variables etc. it’s a highly iterative process. Build, test, refine, repeat. That’s why the launch is being considered a success even though the rocket itself failed. If we can understand the failure points, we can engineer them out. Next time that won’t fail, but something else now will. Reset and go again.
Usually these process are not so public and not on such a huge scale. Which is why the failure seems more of a failure than it actually is. To the engineers it’s just part of the process and not deemed a failure at all.
You’d think that it’d be that simple. Unfortunately the scaling here is non-linear, it is often exponential, if it scales at all. That is to say, if you double the height of the rocket, you don’t double it’s weight. That kind of scaling would be linear (proportional) but in fact, if you double it’s height you increase it’s volume (ergo its mass, ergo its weight) EIGHT times.
That’s just one simple issue with the scaling. The forces involved do not scale proportionally, nor does the amount of fuel. Nor do the aerodynamics since the volume of air that needs to be displaced is also related exponentially. All this combined means that the materials used in construction won’t be subjected to linear transformations of the stresses. Same is true for the fuel seals and just about every other component.
With something as complex as a rocket (this IS rocket science after all) it’s incredibly difficult to build a reliable mathematical model and scale it to suit. There are so many variables and so many unknowns. And every mathematical model, by its very nature, is a simplified one.
The recent launch was a test, so they can gather data. Now that they have that data, they feed it back into the mathematical model and refine it, tweak the papameters, add or change variables etc. it’s a highly iterative process. Build, test, refine, repeat. That’s why the launch is being considered a success even though the rocket itself failed. If we can understand the failure points, we can engineer them out. Next time that won’t fail, but something else now will. Reset and go again.
Usually these process are not so public and not on such a huge scale. Which is why the failure seems more of a failure than it actually is. To the engineers it’s just part of the process and not deemed a failure at all.
Simply scaling does not work, as explained in other comments, but there is also another big aspect: We don’t want to be stuck with the technology from 50 years ago. We want better rockets – more reliable, cheaper, flying more often and so on.
One big development is reuse: Most rockets are completely thrown away every launch. They crash into the ocean or break up in the atmosphere. That means you need to build a full new rocket for the next flight, which is very expensive.
The Space Shuttle was the first rocket to reuse some components, but the system was so complex and the components needed so much work between each flight that it didn’t end up being cheaper than building a new rocket.
SpaceX developed Falcon 9 to be partially reusable: The big and expensive booster lands and can be reused, while the smaller and cheaper upper stage is still thrown away. They had to develop a lot of new things to make that work as no other rocket did that before. It now saves them a lot of money and lets them fly extremely often – once to twice a week recently, while other rockets of that size typically fly a few times per year at most. But they still need a new upper stage each time and the booster needs some refurbishment in between flights. To fix both SpaceX is developing Starship.
Starship is designed to be rapidly reusable, pretty much like aircraft: Land, refuel, fly again. You can’t achieve that with just minor changes to existing designs, you need a completely new design. The overall shape is new, the engines are new, even the fuel type is new. The design of the launch pad is completely new because it needs to work as landing pad, too.
SpaceX started it but now many other companies are also working on reusable rockets. The benefits are just too big to ignore.
Simply scaling does not work, as explained in other comments, but there is also another big aspect: We don’t want to be stuck with the technology from 50 years ago. We want better rockets – more reliable, cheaper, flying more often and so on.
One big development is reuse: Most rockets are completely thrown away every launch. They crash into the ocean or break up in the atmosphere. That means you need to build a full new rocket for the next flight, which is very expensive.
The Space Shuttle was the first rocket to reuse some components, but the system was so complex and the components needed so much work between each flight that it didn’t end up being cheaper than building a new rocket.
SpaceX developed Falcon 9 to be partially reusable: The big and expensive booster lands and can be reused, while the smaller and cheaper upper stage is still thrown away. They had to develop a lot of new things to make that work as no other rocket did that before. It now saves them a lot of money and lets them fly extremely often – once to twice a week recently, while other rockets of that size typically fly a few times per year at most. But they still need a new upper stage each time and the booster needs some refurbishment in between flights. To fix both SpaceX is developing Starship.
Starship is designed to be rapidly reusable, pretty much like aircraft: Land, refuel, fly again. You can’t achieve that with just minor changes to existing designs, you need a completely new design. The overall shape is new, the engines are new, even the fuel type is new. The design of the launch pad is completely new because it needs to work as landing pad, too.
SpaceX started it but now many other companies are also working on reusable rockets. The benefits are just too big to ignore.
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Most things in engineering can’t just be scaled like that. Square cube law, material properties, etc. as others have said. You can ask why we don’t just dye cast cars from zinc like scaled Matchbox cars? Those little toy cars can survive crashes at scaled speeds of hundreds of miles an hour without a dent. Or why don’t we make airliners out of paper if paper planes work so well and are so cheap? But in those cases you understand that it doesn’t work like that.
If this is related to the SpaceX crash, I think the more pertinent question is – is this the effect of privatizing something that should not be looked at as a means of profit, thus cutting corners etc? Because let’s be real that’s what it is for him.
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