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I have hope that SpaceX BFR will break past the sonic boom problem by doing the zoomy stuff outside the sound transmitting parts of the atmosphere.

detritus 9y ago
As much as I like what SpaceX are doing, I'm personally dubious about the idea of tens or hundreds of large scale ballistic rocket launches every day and their affect on the atmosphere, purely for consumer travel. The thought of making a colander out of our ozone and ionosphere sends shudders down my spine.
- JulianMorrison 9y ago
  They are LOX/kerosene so it's not as bad as hydrazine or something. And it's less fuel for a suborbital lob and subsequent braking burn than for LEO. And a good portion of the journey is unpowered ballistic drift. But yeah, it probably isn't ideal for the atmosphere.
  - Robotbeat 9y ago
    SpaceX are using methane for BFR point to point, not kerosene. Burns cleaner, and they're planning on synthesizing it eventually like they need to do for Mars. Although I suspect that long-term, if you're synthesizing your fuel, you're better off using hydrogen instead of methane. Structural mass is generally higher if you use hydrogen, but there is a performance boost especially at higher velocities. And you avoid the inevitable energy loss from the Sabatier Reaction. And generally better for the climate than methane, particularly if you're running fuel-rich.
    - theothermkn 9y ago
      From a conservation of mass standpoint, synthesizing methane would be better for the climate. The stored fuel represents temporarily sequestered carbon. The exhaust, whether the engine runs rich or lean, only represents carbon that was in the atmosphere before the Sabatier reaction was run. However, the total size of the launch vehicle market renders these speculations superfluous, for now.
      - Robotbeat 9y ago
        The problem isn't just carbon mass (i.e. CO2 in the atmosphere), but the fact that methane is a much stronger greenhouse gas than CO2 per unit carbon. The total size of the launch market today is infinitesimal (~100 launches per year and vast majority less than a tenth the payload capacity of BFR). But BFR is being built to change that by orders of magnitude. Long-haul point-to-point transport of people means potentially hundreds of thousands to millions of flights per year. Long road to get there, though, and the primary obstacle may just be the incredible airline safety record (to make it close, you probably need to include lifetime saved by making the trips shorter).
        theothermkn 9y ago
        It's not a stronger greenhouse gas than CO2 when it's sitting in a tank, and it's not a stronger greenhouse gas when it's emitted as hot, reactive exhaust into the atmosphere, where it is immediately reduced to CO2, CO, H2, H, H2O, HO, and so on. But, like I said, premature and superfluous, even though we should still do our accounting carefully, and not rely on "OMG methane!" as the guiding principle of our thinking.
    - BrandonMarc 9y ago
      Hydrolox will always be a more efficient fuel, but it's a nightmare to store and manage, and destructive to engine components, fuel lines, storage tanks, and, well, everything it touches. It may be tough to have a reusable hydrolox rocket that's efficient from a total cost of ownership perspective.
- hinkley 9y ago
  I think we should consider the cost benefit analysis and maybe it makes sense to mandate that boosters throttle back when transiting the ionosphere. Especially if we are going to increase launches by a factor of ten or more.

detritus 9y ago

As much as I like what SpaceX are doing, I'm personally dubious about the idea of tens or hundreds of large scale ballistic rocket launches every day and their affect on the atmosphere, purely for consumer travel. The thought of making a colander out of our ozone and ionosphere sends shudders down my spine.

JulianMorrison 9y ago
They are LOX/kerosene so it's not as bad as hydrazine or something. And it's less fuel for a suborbital lob and subsequent braking burn than for LEO. And a good portion of the journey is unpowered ballistic drift. But yeah, it probably isn't ideal for the atmosphere.
- Robotbeat 9y ago
  SpaceX are using methane for BFR point to point, not kerosene. Burns cleaner, and they're planning on synthesizing it eventually like they need to do for Mars. Although I suspect that long-term, if you're synthesizing your fuel, you're better off using hydrogen instead of methane. Structural mass is generally higher if you use hydrogen, but there is a performance boost especially at higher velocities. And you avoid the inevitable energy loss from the Sabatier Reaction. And generally better for the climate than methane, particularly if you're running fuel-rich.
  - theothermkn 9y ago
    From a conservation of mass standpoint, synthesizing methane would be better for the climate. The stored fuel represents temporarily sequestered carbon. The exhaust, whether the engine runs rich or lean, only represents carbon that was in the atmosphere before the Sabatier reaction was run. However, the total size of the launch vehicle market renders these speculations superfluous, for now.
    - Robotbeat 9y ago
      The problem isn't just carbon mass (i.e. CO2 in the atmosphere), but the fact that methane is a much stronger greenhouse gas than CO2 per unit carbon. The total size of the launch market today is infinitesimal (~100 launches per year and vast majority less than a tenth the payload capacity of BFR). But BFR is being built to change that by orders of magnitude. Long-haul point-to-point transport of people means potentially hundreds of thousands to millions of flights per year. Long road to get there, though, and the primary obstacle may just be the incredible airline safety record (to make it close, you probably need to include lifetime saved by making the trips shorter).
      - theothermkn 9y ago
        It's not a stronger greenhouse gas than CO2 when it's sitting in a tank, and it's not a stronger greenhouse gas when it's emitted as hot, reactive exhaust into the atmosphere, where it is immediately reduced to CO2, CO, H2, H, H2O, HO, and so on. But, like I said, premature and superfluous, even though we should still do our accounting carefully, and not rely on "OMG methane!" as the guiding principle of our thinking.
  - BrandonMarc 9y ago
    Hydrolox will always be a more efficient fuel, but it's a nightmare to store and manage, and destructive to engine components, fuel lines, storage tanks, and, well, everything it touches. It may be tough to have a reusable hydrolox rocket that's efficient from a total cost of ownership perspective.
hinkley 9y ago
I think we should consider the cost benefit analysis and maybe it makes sense to mandate that boosters throttle back when transiting the ionosphere. Especially if we are going to increase launches by a factor of ten or more.