6 ms·

That's not realistic simply because of the carbon requirements. Long haul aviation only burns a couple hundred kg of jet fuel per passenger. (I don't know how t

That's not realistic simply because of the carbon requirements. Long haul aviation only burns a couple hundred kg of jet fuel per passenger. (I don't know how the top-level comment is calculating 1-3 tonnes of CO2 per passenger, Contrail effects? Construction of the plane? Altitude? Incomplete combustion? but a 250-passenger 787 doesn't carry 750,000 kg of fuel, it only fits 100,000 kg at most, plus plenty of reserve capacity). The flight only costs $100-$200 per person in fuel. Rocketry is far less efficient than a modern high-bypass turbofan. NASA can afford to buy 75,000 kg of methane per astronaut. Even if the rocket was amortized to zero over infinite flights, and had zero maintenance costs, even if crew cost nothing and airport/spaceport leases cost nothing, thermodynamics insists that you still have to buy $100,000 worth of RP-1 rocket fuel. A business class ticket cannot buy enough carbon to support 75,000 kg of emissions.

bryanlarsen 3y ago
Starship has the size to carry about 400 passengers. Both stages together carry about 5,000t of propellant. But over 3/4 of that is liquid oxygen, and most of that is the first stage. The second stage alone with 1200t of propellant can't put humans into orbit, but it does have a range comparable to that of a 787. So 300t of liquid methane will get 400 passengers about as far as a 787 can get 250 passengers with 100t of kerosene. A starship ticket could theoretically cost <3x the price of an airline ticket. A rocket may be less efficient than a turbofan but it gains it back by coasting through space for all but 3 minutes rather than pushing through air for the entire flight.
- pi-e-sigma 3y ago
  It doesn't gain anything back, what are you on. Before landing it has to shed all the speed it gained that was needed for the ballistic trajectory. That energy is lost. Orbital or suborbital flights will never, ever be competitive to flying with regards to required energy expended.
  - bryanlarsen 3y ago
    It gains efficiency compared with an airplane by spending most its trajectory outside of atmosphere with no air resistance.
    - pi-e-sigma 3y ago
      No it does not, because thanks to atmosphere wings on an airplane generate lift. And they do it more efficient than any kind of engine known to the mankind
      - bryanlarsen 3y ago
        Yes, an airplane can climb much more efficiently than a rocket. So on a 300km flight where all it is doing is climbing and descending it's way more efficient than a rocket. But for a 10,000km flight the airplane expends almost all of its fuel coasting rather than climbing. Luckily we don't have to rely on assertions. If I'm wrong, there should be an obvious error in my math (which is trivial) or facts (which is on Wikipedia). Please point it out.
        pi-e-sigma 3y ago
        You think an airplane doesn't need lift when in a level flight? :) Thanks to the atmosphere an airplane doesn't need to carry its own oxidizer, either. I'll leave to you to check how much oxidizer a Falcon rocket needs to carry for every ton of fuel.
        bryanlarsen 3y ago
        We don't have to wait long to prove you wrong. Starship using just ~1200t of Methane and 150t of payload capacity will fly East (the long way) from Texas to Hawaii in 90 minutes. That's 8x as much payload 3x as far as a 787 can do with its 100t of fuel.
        mensetmanusman 3y ago
- tsimionescu 3y ago
  Starship has nowhere near the capacity to carry 400 passengers - people are not sardines you can just stuff into the rocket like you can satellites. You need plenty of equipment per person for manned spaceflight. Much more so if you want to compete with business class flying. Also, the total travel time would be horrible, since you can't have a rocket launch/landing facility anywhere near a city, and loading and unloading a rocket is an immensely time consuming process. Plus, you never ever load people into a an already fuelled rocket.
  - bryanlarsen 3y ago
    It's not as if 40,000 feet is survivable without a flight suit and parachute, yet airliners don't provide those. And 400 people per starship is much more spacious than the area you get in economy class. Travel time is the main reason to use Starship. It might add 30 minutes extra on either end, but if it saves 10 hours of flight tine... Loading people into an already fueled rocket is standard operating procedure for every rocket except Falcon.

bryanlarsen 3y ago

Starship has the size to carry about 400 passengers. Both stages together carry about 5,000t of propellant. But over 3/4 of that is liquid oxygen, and most of that is the first stage. The second stage alone with 1200t of propellant can't put humans into orbit, but it does have a range comparable to that of a 787. So 300t of liquid methane will get 400 passengers about as far as a 787 can get 250 passengers with 100t of kerosene. A starship ticket could theoretically cost <3x the price of an airline ticket. A rocket may be less efficient than a turbofan but it gains it back by coasting through space for all but 3 minutes rather than pushing through air for the entire flight.

pi-e-sigma 3y ago
It doesn't gain anything back, what are you on. Before landing it has to shed all the speed it gained that was needed for the ballistic trajectory. That energy is lost. Orbital or suborbital flights will never, ever be competitive to flying with regards to required energy expended.
- bryanlarsen 3y ago
  It gains efficiency compared with an airplane by spending most its trajectory outside of atmosphere with no air resistance.
  - pi-e-sigma 3y ago
    No it does not, because thanks to atmosphere wings on an airplane generate lift. And they do it more efficient than any kind of engine known to the mankind
    - bryanlarsen 3y ago
      Yes, an airplane can climb much more efficiently than a rocket. So on a 300km flight where all it is doing is climbing and descending it's way more efficient than a rocket. But for a 10,000km flight the airplane expends almost all of its fuel coasting rather than climbing. Luckily we don't have to rely on assertions. If I'm wrong, there should be an obvious error in my math (which is trivial) or facts (which is on Wikipedia). Please point it out.
      - pi-e-sigma 3y ago
        You think an airplane doesn't need lift when in a level flight? :) Thanks to the atmosphere an airplane doesn't need to carry its own oxidizer, either. I'll leave to you to check how much oxidizer a Falcon rocket needs to carry for every ton of fuel.
        bryanlarsen 3y ago
        We don't have to wait long to prove you wrong. Starship using just ~1200t of Methane and 150t of payload capacity will fly East (the long way) from Texas to Hawaii in 90 minutes. That's 8x as much payload 3x as far as a 787 can do with its 100t of fuel.
        mensetmanusman 3y ago
tsimionescu 3y ago
Starship has nowhere near the capacity to carry 400 passengers - people are not sardines you can just stuff into the rocket like you can satellites. You need plenty of equipment per person for manned spaceflight. Much more so if you want to compete with business class flying. Also, the total travel time would be horrible, since you can't have a rocket launch/landing facility anywhere near a city, and loading and unloading a rocket is an immensely time consuming process. Plus, you never ever load people into a an already fuelled rocket.
- bryanlarsen 3y ago
  It's not as if 40,000 feet is survivable without a flight suit and parachute, yet airliners don't provide those. And 400 people per starship is much more spacious than the area you get in economy class. Travel time is the main reason to use Starship. It might add 30 minutes extra on either end, but if it saves 10 hours of flight tine... Loading people into an already fueled rocket is standard operating procedure for every rocket except Falcon.