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this post was submitted on 19 Jul 2025
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chapotraphouse
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The rocket equation means that even a modest improvement in the efficiency of the fuel or combustion is worth an exponential improvement in payload mass. What that means in practice is that if you can squeeze out improvements in your propulsion that make it 5% better, it's equivalent to making your whole payload much more than 5% lighter (exactly how much depends on where you started, but it easily could be 20%).
The math behind this is actually really cool. The intuitive explanation is that making your payload lighter is the same as just adding more fuel (the mass ratio gets larger). If you think about what happens as you add more and more fuel, you'd expect that you'd eventually reach a point where nearly all the additional fuel you're adding is spent on pushing other fuel rather than the payload. Only the last bit of fuel in the tank is spent only accelerating payload, so the tradeoff between using fuel to push fuel vs pushing payload is inevitable, but the tradeoff means that there's diminishing returns to improving the mass ratio.
So think about how much money is spent trying to make rockets lighter. Making propulsion technology more efficient is exponentially as important. These people hate science.
Differential equations are hard. Let's just make it bigger.
Average KSP rocket
The nice thing in KSP is that you can add more fuel in a much less punishing way than IRL. You can add radial tanks to a stage and jettison them when empty. This still only makes your mass ratio larger rather than improving specific impulse (i.e. fuel efficiency) so it has diminishing returns, but you at least don't have to haul around the mass of the empty tanks. IRL, there's various reasons why you can't get away with that, so it's an even bigger problem.
Setting all the other issues aside, this strategy seems a lot more effective in Kerbal Space Program than it is in real life due to the dry mass of "liquid fuel" tanks and engines in the game being a lot higher than they should be (3-8 times higher, according to modders who have "corrected" this). The gains from dropping this mass are over-exaggerated as a result.
You probably already know, but I found out about orthogrids in rocket tanks recently. I saw the inside of a fuel tank in AlphaPhoenix's latest video (wait I just realized he never shows it here, maybe he edited it out?) and it's really cool how they make the surface rigid with as little structural support as possible with thin, vertical struts that run across the back of the surface of the tank.
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy:
Just one more lane bro
And this is literal physics 1 stuff. We were tasked to come up with the rocket equation basically on our own, with minimal setup. Like we walked in and we tasked with it ~before~ the lecture on it. He walked around with the TAs helping us along. Even my groupwas able to give a good answer. With a level of physics described by KSP, and we were like C-B students at best. Its so basic I'd expect the "average" (willing) person to be able to understand the concepts.
Deriving that really was a fun moment, because even though we didn't get it all by ourselves, it felt like we ~could~ have given a bit of time. Really made me feel like I had passed some basic level of understanding of how the world works. I couldn't tell you the equation at this point, but I don't work with rockets, physics, or much advanced math daily. Really a joke that I feel more qualified then these clowns.
You should pursue a physics degree if possible, if you haven’t already. It’s that for four years (plus stress but that’s normal)
lowest rate of employment after graduation of any other degree currently. there is a higher rate of employment in their field of study for journalists than physicists and its not even close
Correct, there aren’t that many jobs with the title of “physicist.” It’s very employable however, if one is willing to branch out into applied fields like engineering. I.e I don’t think there are many impoverished physicists (by education) at least in the west. It’s the path I took at least.
Education always has a tension between abstract advancement of knowledge (academia) and application. In the capitalist countries, the latter will always win out. I don’t think it is a bad choice to learn about something that both interests you and sets you up for employment, even if your employment won’t directly fall within that area.
sorry, i miquoted the statistic. not highest unemployement rate in their field. also second highest unemployment rate overall for recent graduates. physicists having trouble getting jobs, period.
I’m assuming US job market. I googled around and found this that seems to be where that statistic comes from
Frankly I still don’t believe it or consider it alarming. Even at face value, if it’s a difference of 6% and 8% unemployment, it is not that meaningful. It’s still 92% vs 94% employment. Once employed, a physicist can expect a good or great salary. Lifetime earnings are great even if it can be hard for some people to find a job straight out of college. Everyone in my program is gainfully employed, usually not as an academic, but in software development, engineering, finance, or education. It’s far from a “do not recommend” field even if the latest CNN fad is to doom and gloom about the fall of STEM (usually simultaneously hyping AI as the replacement, which is rubbish)
Consider the rise of LLMs. Because it is a novel field, there are not many people with an education tailored it. Physicists are generalists. That makes them desired for industries in uncharted territory where a strong analytical and theoretical mindset is more important than a particular certification or knowledge of a computer program.
this number changes yearly. physicist is often the worst employed.
and when talking about large populations and unemployment the difference between 6% and 8% is MASSIVE
also anthropology being #1 is no surprise i actually know someone with a masters in it. went to a specialized school abroad and everything. she is a librarian now. completely respectable field and she enjoys it. but it is not in her field whatsoever
This is also why faster than light travel is impossible. You need more and more fuel the faster you go because your mass increases, which requires more fuel that causes your mass to increase, which....and on and on and so on and so forth. There isn't a fuel with that kind of exponential efficiency, because you would be getting more energy than you're putting in. Energy (like matter) cannot be created nor destroyed, only moved and stored. You would need a perpetual motion machine in order to go faster than light.
You’re right that the behavior is similar, but the physical explanation is different, and the rate of increase for required fuel is different as a result.
The classical rocket equation is well, classical, and derived from non-relativistic Newtonian physics. Fuel requirement increases exponentially because each additional ounce of fuel itself has mass that needs to be accelerated. But importantly, according to the classical equation, it would be possible to accelerate to light speed and faster, if you could find enough fuel.
For the relativistic rocket equation, fuel requirement increases along a different curve (not exponential but hyperbolic) which results in asymptotically approaching light speed. The reason has to do with the Lorentz factor gamma (γ) which expresses the degree to which time dilates and length contracts as you approach light speed. It takes more fuel as you speed up because spacetime itself changes form so that this is true - in addition to the exponential part of the classical equation.