"SpaceX Starship will deliver so much propellant to LEO that fuel efficiency won't matter." --- Statements dreampt up by the delusional
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.
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.
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.
I'm not a science guy, but isn't fuel efficiency like the most central issue of rocket science?
Anything to improve specific impulse. Making the fuel better, optimizing combustion, nozzle geometry, etc etc. This is all way more important than basically any other aspect of a rocket, as far as making the rocket go from point A to point B is concerned.
It is
It's so much the central issue of rocket science that science nerds call it "the tyranny of the rocket equation"
the delivery of propellant to LEO that I endorse:
Despite being a bit of an astronomy nerd, my brain still initially read that as Law Enforcement Officers (rather than Low Earth Orbit) and for the tiniest fraction of a second I thought Musk was directing SpaceX to give rockets to NYPD or some shit.
In context, I support this reading more
While this is a blow to space travel, I am very glad that the US is not yet crazy enough to allow Elon to make a nuclear engine.
It's probably more that they are scared the technology will threaten fossil fuels than any actual concern about Elon fucking things up.
Doubt it would really. We've already had nuclear submarines, aircraft carriers and Arctic icebreakers, which are just niche use cases that justify the cost of the nuclear bit.
The bourgeois aren't afraid of new technologies. As long as they control infrastructure and policy, their fossil fuel rents are secure and will seize the opportunity for new rents. They permitted states to spend several billion on nuclear R&D as a centralised rentier-friendly fallback for the inevitable drop in fossil fuel resource quality. Unless we're talking about urban myths like cold fusion or perpetual motion, several approaches and technologies have been exhaustively attempted. Items like MSRs or hybrid fusion, which were previously mothballed, are being revisited worldwide.
Renewables have outpaced nuclear in the meantime when it comes to the sole goal of curtailing fossil fuel demand. No steam islands, low O&M, and turnaround time short enough for a learning effect to drive down costs. China are breaking emissions records year on year because of the ability to scale up solar in a fraction of the time of new nuclear builds. It's not technology suppression; there is just no technology that adequately displaces fossil fuels in a time frame that actually matters. Only curtailing demand with sane socialist planning.
That's what we call a mixed blessing I suppose. I really don't want Elon near fissile material except if the scenario involves getting pricked by an umbrella.
Musk wasn't involved IIRC, Draco was a DARPA/NASA/Lockheed project (also some company called BWX Technologies I've never heard of that I assume is involved with the nuclear enrichment or something).
With the trajectory of NASA, SpaceX would be who makes it if they ever start such a project again.
Unless SpaceX gets ousted from government contracts for being incompetent.
If I had a nickel for every time the US cancelled a thermal nuclear engine program, I'd have two nickels, which isn't very much but it's weird that it's happened twice.
Are you technically delivering the propellent to LEO if you blow up in LEO?
Ahh yes... "Starship." That piece of crap that has only managed to deliver a flaming banana to the Indian Ocean at mach 10. Once. The rest of the time it breaks up into a debris field before it can even manage that much. Yeah, I'm sure that'll happen any day now. Right around the same time as FSD that was set to be rolling out about 10 years ago.
But no, let's rediscover rocket science from first principles because the last 60 years of established doctrine don't "move fast and break things" enough. Absolute fucking morons.
I'm also reminded of that 1950s slogan of "Energy so cheap you won't even meter it!" Yeah still waiting on that one too 75 years later.
nuclear-electric rockets are woke. we need space x rockets that roll coal and have a dixie horn.
lets just stop advancing tech, because doing what we are now, but more, is easier.
Yhe bro, just one more rocket bro. Please, it's a different engine configuration this time bro. It's different heat shilds bro. just trus me bro just bro different trajectory different more money bro just $10bn more bro its different please
In order to refill the tank of a starship in orbit, they would need to launch at least 15 additional starships back to back, i.e. at least 15 launches have to be carried out all without issues, probably more for redundancy just in case, and it has to be done fast because since the fuel is cryogenic (methane Lox) it boil off over time and has to be dumped overboard.
And all of that is assuming they can even get the starship orbit capable in the first place, which they haven't been able to do at all.
fUel eFfICiEnCY.
once they get it 80% fueled china be like "oops sorry one of our satellites destabilized and booped your rocket our bad"
*Right before they start refuelling China be like "your rocket is in the way of our satellite" but Elon insists they'll be done in time. Once they get it 80% fueled the rocket explodes, clearing the way for the satellite to pass through unscathed.
Me in KSP insisting to my GF that I can "eyeball" that single burn from LKO to a Jool Aerobreake.
Its kind of amazing that Elon isnt hust killing infrastructure on earth, hes also doing it in outer space.
Ions are great once you're up in space, provided time isn't a factor. Unfortunately without investing in launch loops, or space elevators, or orbital rings, or rotavators, or other such technologies, getting out of Earth's gravity well is the really expensive part that will still require liquid-fueled rockets. But I hard agree: we should be investing in getting out into space (rather than blowing each other up.)
We fight over land and territory. Solution: make it easy to just leave. Go make your own territory. Space provides that opportunity. The problem: then the people that do become ungovernable. They might go out into the black and do fully-automated luxury gay space communism. And we can't have that.
The Culture Intensifies
Kessler Syndrome has never been so exciting!
It is hard to overstate how delusional it is to think that chemical rockets could ever compete with nuclear thermal. It's in the same category as scoffing at computers because you can just hire more people with slide rules to do your calculations.
oh my god what a fucking COOL ASS website, instant firefox pinned link honestly
This is what the web was like when it was actually good.
SO GOOD
I know what you mean but a fun fact here is that the people with the slide rules had the job title of "computer", what they did was "computing".
Please, I had plans later!
Hehehe, enjoy the rabbit hole