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A 737-800 has a max take off weight of 175,000lbs Super Heavy Dry Mass: 350,000-440,000lbs Super Heavy Fuel Weight: 7,500,000lbs Starship Dry Mass: ~200,000lbs

A 737-800 has a max take off weight of 175,000lbs Super Heavy Dry Mass: 350,000-440,000lbs Super Heavy Fuel Weight: 7,500,000lbs Starship Dry Mass: ~200,000lbs Starship Fuel Weight: 2,600,000lbs Starship+Booster total: 10,695,000lbs 175,000lbs vs 10,965,000lbs! There is no such thing as a similarly sized aircraft!

ceejayoz 5y ago
A 747-8's MTOW is about a million pounds. Ten-ish 747s for a Starship, as a roughly worst case estimate. Only so much carbon you can stuff into a ton of fuel. A single-digit percentage global increase in aviation emissions. (I'm also very skeptical of that level of Starship launches. By the time you're getting anywhere near that, you're likely to have captured some comets and are processing fuel for interplanetary missions in an orbital refinery. Net zero emissions except for getting the people and Earth-only parts up to LEO.)
- ben_w 5y ago
  > By the time you're getting anywhere near that, you're likely to have captured some comets and are processing fuel for interplanetary missions in an orbital refinery. I think you’re underestimating both the mass of a comet and that the geopolitical implications of a private company being one industrial accident away from replicating something several orders of magnitude closer to Chicxulub than to Tsar Bomba would prevent them being allowed to even try it. I did a napkin estimate a while back, and even optimistically 10,000 Starship launches is just where you start going “hmm, perhaps we should think about starting to seriously plan the basics of an orbital ring or a launch loop” — a 40Mm circumference steel loop with a cross section of 1m^2 is still about 30 times less massive than 67P/Churyumov–Gerasimenko.
  - ceejayoz 5y ago
    > I think you’re underestimating both the mass of a comet and that the geopolitical implications of a private company being one industrial accident away from replicating something several orders of magnitude closer to Chicxulub than to Tsar Bomba would prevent them being allowed to even try it. Meh, you could regulate it fairly effectively. Changing the path of a comet is something that's gonna have to be done years out. Deviating from the planned course would be obvious long before it'd hit anything.
    - ben_w 5y ago
      Bet your life? If it was a naïve straight-line path with no funky orbital mechanics to make things even harder to get right, the difference between hitting the Earth at 90° and missing by the orbit of the moon is a sideways delta-v of 13 m/s one year in advance. The sideways Δv between a 45° impact and LEO, 7 days in advance, is 3.5 m/s. I’m curious: Even ignoring engine errors, given near-Earth solar orbital velocities, what’s the mass of the smallest asteroid which, if it impacted that comet 7 days before the comet reached Earth, could cause it to hit Earth? For whatever orbit you want to put it in, and whatever mass of comet you want to suggest using.
      - ceejayoz 5y ago
        > The sideways Δv between a 45° impact and LEO, 7 days in advance, is 3.5 m/s. In other words, the larger the comet, the better. You'd need a fairly obvious number of rockets to impart that sort of velocity change on a large one, right? And if you're doing it to a pebble, it doesn't matter too much?
        ben_w 5y ago
        > In other words, the larger the comet, the better. I don’t think so? If you’re bringing in a big one you need more engines to push it into the right orbit to start with, so I think the risk is always things that scale up directly with the comet’s mass, e.g. “the engines are misaligned by $foo degrees”. Also, a pebble in space terms is still a potential city-killer, and no nation in their right mind is going to want to let a private company — not one of their own, let alone a private company in another nation if they have even the slightest say in the matter — wield that kind of potential: https://en.wikipedia.org/wiki/Meteor_Crater https://en.wikipedia.org/wiki/Meteor_Crater
        ceejayoz 5y ago
        In the "whoops" scenario (i.e. non-malicious), an engine misalignment would be apparent with enough time to correct. You're a year out. We watch asteroids zing by regularly. The ones we know about have their chances of hitting calculated years or decades out.

ceejayoz 5y ago

A 747-8's MTOW is about a million pounds. Ten-ish 747s for a Starship, as a roughly worst case estimate. Only so much carbon you can stuff into a ton of fuel. A single-digit percentage global increase in aviation emissions. (I'm also very skeptical of that level of Starship launches. By the time you're getting anywhere near that, you're likely to have captured some comets and are processing fuel for interplanetary missions in an orbital refinery. Net zero emissions except for getting the people and Earth-only parts up to LEO.)

ben_w 5y ago
> By the time you're getting anywhere near that, you're likely to have captured some comets and are processing fuel for interplanetary missions in an orbital refinery. I think you’re underestimating both the mass of a comet and that the geopolitical implications of a private company being one industrial accident away from replicating something several orders of magnitude closer to Chicxulub than to Tsar Bomba would prevent them being allowed to even try it. I did a napkin estimate a while back, and even optimistically 10,000 Starship launches is just where you start going “hmm, perhaps we should think about starting to seriously plan the basics of an orbital ring or a launch loop” — a 40Mm circumference steel loop with a cross section of 1m^2 is still about 30 times less massive than 67P/Churyumov–Gerasimenko.
- ceejayoz 5y ago
  > I think you’re underestimating both the mass of a comet and that the geopolitical implications of a private company being one industrial accident away from replicating something several orders of magnitude closer to Chicxulub than to Tsar Bomba would prevent them being allowed to even try it. Meh, you could regulate it fairly effectively. Changing the path of a comet is something that's gonna have to be done years out. Deviating from the planned course would be obvious long before it'd hit anything.
  - ben_w 5y ago
    Bet your life? If it was a naïve straight-line path with no funky orbital mechanics to make things even harder to get right, the difference between hitting the Earth at 90° and missing by the orbit of the moon is a sideways delta-v of 13 m/s one year in advance. The sideways Δv between a 45° impact and LEO, 7 days in advance, is 3.5 m/s. I’m curious: Even ignoring engine errors, given near-Earth solar orbital velocities, what’s the mass of the smallest asteroid which, if it impacted that comet 7 days before the comet reached Earth, could cause it to hit Earth? For whatever orbit you want to put it in, and whatever mass of comet you want to suggest using.
    - ceejayoz 5y ago
      > The sideways Δv between a 45° impact and LEO, 7 days in advance, is 3.5 m/s. In other words, the larger the comet, the better. You'd need a fairly obvious number of rockets to impart that sort of velocity change on a large one, right? And if you're doing it to a pebble, it doesn't matter too much?
      - ben_w 5y ago
        > In other words, the larger the comet, the better. I don’t think so? If you’re bringing in a big one you need more engines to push it into the right orbit to start with, so I think the risk is always things that scale up directly with the comet’s mass, e.g. “the engines are misaligned by $foo degrees”. Also, a pebble in space terms is still a potential city-killer, and no nation in their right mind is going to want to let a private company — not one of their own, let alone a private company in another nation if they have even the slightest say in the matter — wield that kind of potential: https://en.wikipedia.org/wiki/Meteor_Crater https://en.wikipedia.org/wiki/Meteor_Crater
        ceejayoz 5y ago
        In the "whoops" scenario (i.e. non-malicious), an engine misalignment would be apparent with enough time to correct. You're a year out. We watch asteroids zing by regularly. The ones we know about have their chances of hitting calculated years or decades out.