Why does a speace elevator have higher energy cost than a rocket? Is the rocket fuel so cheap compared to electricity, or does the space elevator do things differently?

@PaŭloEbermann Rocket engines are very efficient at turning chemical energy into motion, while the elevator involves a power plant converting it into motion, then into electrical power, then into a laser beam trained on a climber, then back into electricity and then finally into the needed motion. That second to last step, beaming it from the ground to a climber tens of thousands of km away, is quite a lossy one.

@ChristopherJamesHuff Rocket engines are extremely inefficient at turning chemical energy into motion above ground level, because they first have to physically lift the chemicals to the height you want the motion at. I'm reading the Edwards document, and it appears using already-existing lasers with 3% efficiency and not the 30% proposed efficiency design is why it has a 2% overall efficiency - the distance problem is solved by adaptive optics.

These are a number of very good arguments; particularly scalability and suitability for a wide range of orbits are fairly compelling. I think that around 2000, launch cadences achieved and proposed today were not in the picture yet.

@Yakk Rocket engines are among the most efficient heat engines ever built. "Lifting the chemicals" would be an imprecise way of describing gravity losses, which are only 1-2 km/s. In reality, carrying their propellants is exactly what allows rockets to accelerate by delta-v's far greater than their exhaust velocity. Yes, the required mass ratio increases exponentially with delta-v, but staging is a highly effective way of dealing with this.

@phil1008 that is a grossly incorrect claim. Crew Dragon missions are a completely different service including delivery of crew and cargo to and from the ISS and lifeboat services at the ISS.

So are you saying Starship will be cheaper because it will never be tasked to do a mission that resembles delivering crew and cargo to the ISS?

No, I am not. Try again.

There's a preponderance of hard evidence that supports the cost of ISS resupply, both crewed and uncrewed. See space.stackexchange.com/questions/10350/…. There is a lot of hype about SpaceX lowering launch costs, and lots of circular reporting, but I have yet to see any hard data that supports that assertion. Just do some quality research on that.

Unsure why you are providing obvious misinformation here. Anyone who looks can see that's clearly not saying what you claim it is.

I've cited several reputable sources of information. Do you have a source to back up your $100 per-kg for Falcon 9 number? Allow me to help: esquire.com/news-politics/a5077/elon-musk-1008

You've repeatedly tried to misrepresent Dragon ISS services as cargo launch costs. And there is no "$100 per-kg for Falcon 9 number".

@Yakk It's not "lifting the chemicals" and gravity losses. It's accelerating the chemicals. Fuel use is literally exponential in terms of delta-V; rockets don't have fuel tanks, they are fuel tanks. But space elevator climbers are powered from the ground and do not suffer this problem. Also, modern laser diodes are 50+% efficient and PV cells tuned to one frequency are more efficient than white-light PV cells. A >20% overall efficiency is quite likely.

I haven't read the study in-depth, but from an "only energy" perspective, \$220 seems very expensive. Consider that the absolute floor calculated by lifting a 1kg mass to 400km and then speeding it up to orbital velocity only requires about 10KwH of energy, which is like \$1.50 at current industrial electricity prices. Granted, this is highly idealized, but I would expect orbital-infrastructure kg-to-orbit prices to land in the two-digit dollar range. Assuming that's \$220 today-dollars, the efficiency of the system is still absolutely abysmal.

Additionally, while Edward's works are no-doubt the source of many modern space-elevator ideas and debates, I'd be careful taking his word as gospel. His space elevator work was just him alone cranking out content, and there are some "yellow flags" in the work that make me leery (for a physicist, there is a lot of non-physics that he's very sure). Also, the paper ends with "What we have found is that an extremely valuable space elevator can be built in the near future with acceptable risk and less funding than some current space programs", which, wow, those are fighting words.

@Dragongeek Yes, he uses a laser-lift system with 2% power transfer efficiency, and it lifts it to geostationary orbit. That is 75 MJ/kg. At 3 cents per MJ and 50% of amount lifted isn't payload, we hit 225$. That 2% power transfer efficiency uses y2k era solar cells and y2k era lasers; the paper mentions that much more efficient lasers will shortly exist, and solar cells have easily doubled in efficiency since then.