5 ms·

The 80km line can actually be measured objectively by physical properties and the FAI is considering making that their definition. https://www.fai.org/news/sta

The 80km line can actually be measured objectively by physical properties and the FAI is considering making that their definition. https://www.fai.org/news/statement-about-karman-line https://www.fai.org/news/statement-about-karman-line https://www.sciencedirect.com/science/article/pii/S0094576518308221?via%3Dihub https://www.sciencedirect.com/science/article/pii/S009457651... etc

ianai 5y ago
Just for reference, the news just said they’re going a little over 90km up.
- imglorp 5y ago
  Specifically for VG, it might be trivial to add a little extra thrust--some external drop tanks or small SRB's for example--and hit that line just to match Bezos.
mannykannot 5y ago
As your 2nd. reference shows, there are many objective facts to base a decision on, but drawing any particular line ultimately has an irreducible arbitrary element. Also, when defining spaceflight, one could add an orbital velocity requirement - after all, a falling brick is not normally considered to be flying (even the phrase 'flying debris' implies some lateral motion.) What counts is being able to persuade other people. It looks like the 80km faction is succeeding with the FAI.
- _moof 5y ago
  The Kármán line isn't arbitrary - or at least it wasn't when Kármán first conceived of it. It's supposed to be the altitude at which centrifugal force becomes more significant than aerodynamic lift. That's a definite altitude with significant implications. Whether this definition is meaningful for a suborbital flight is debatable.
  - mannykannot 5y ago
    Yes, but, like all the other factual bases for a definition, it is a concept that does not yield an exact number.
    - _moof 5y ago
      Er, not really. There is a specific, identifiable altitude where this happens.
      - mannykannot 5y ago
        Centrifugal force is a function of angular velocity, and atmospheric density varies with the weather and seasons. From the paper imglorp linked to: "in reality the von Karman criterion defines a line whose altitude varies with position and time (because of variations in atmospheric density due to solar activity) and with the lift coefficient of the spacecraft." https://www.sciencedirect.com/science/article/pii/S0094576518308221#bib12 https://www.sciencedirect.com/science/article/pii/S009457651...
        _moof 5y ago
        I'm aware. I'm not saying the altitude is the exact same altitude at all times under all conditions. I'm saying there is a specific altitude where centrifugal force becomes the dominant force if you want to stay aloft. And that was Kármán's original conception. Yes, that altitude will vary with the atmospheric tides (and with C_L, as another commenter points out). But it is still a definite altitude and not at all arbitrary. arbitrary: "based on random choice or personal whim, rather than any reason or system" It is not based on random choice or personal whim. It is the result of a systematic analysis of the relationship between the forces required to sustain flight.
        mannykannot 5y ago
        >I'm not saying the altitude is the exact same altitude at all times under all conditions. You were disputing a post in which this was literally the only point I made: https://news.ycombinator.com/item?id=27801257 https://news.ycombinator.com/item?id=27801257

ianai 5y ago

Just for reference, the news just said they’re going a little over 90km up.

imglorp 5y ago
Specifically for VG, it might be trivial to add a little extra thrust--some external drop tanks or small SRB's for example--and hit that line just to match Bezos.

mannykannot 5y ago

As your 2nd. reference shows, there are many objective facts to base a decision on, but drawing any particular line ultimately has an irreducible arbitrary element. Also, when defining spaceflight, one could add an orbital velocity requirement - after all, a falling brick is not normally considered to be flying (even the phrase 'flying debris' implies some lateral motion.) What counts is being able to persuade other people. It looks like the 80km faction is succeeding with the FAI.

_moof 5y ago
The Kármán line isn't arbitrary - or at least it wasn't when Kármán first conceived of it. It's supposed to be the altitude at which centrifugal force becomes more significant than aerodynamic lift. That's a definite altitude with significant implications. Whether this definition is meaningful for a suborbital flight is debatable.
- mannykannot 5y ago
  Yes, but, like all the other factual bases for a definition, it is a concept that does not yield an exact number.
  - _moof 5y ago
    Er, not really. There is a specific, identifiable altitude where this happens.
    - mannykannot 5y ago
      Centrifugal force is a function of angular velocity, and atmospheric density varies with the weather and seasons. From the paper imglorp linked to: "in reality the von Karman criterion defines a line whose altitude varies with position and time (because of variations in atmospheric density due to solar activity) and with the lift coefficient of the spacecraft." https://www.sciencedirect.com/science/article/pii/S0094576518308221#bib12 https://www.sciencedirect.com/science/article/pii/S009457651...
      - _moof 5y ago
        I'm aware. I'm not saying the altitude is the exact same altitude at all times under all conditions. I'm saying there is a specific altitude where centrifugal force becomes the dominant force if you want to stay aloft. And that was Kármán's original conception. Yes, that altitude will vary with the atmospheric tides (and with C_L, as another commenter points out). But it is still a definite altitude and not at all arbitrary. arbitrary: "based on random choice or personal whim, rather than any reason or system" It is not based on random choice or personal whim. It is the result of a systematic analysis of the relationship between the forces required to sustain flight.
        mannykannot 5y ago
        >I'm not saying the altitude is the exact same altitude at all times under all conditions. You were disputing a post in which this was literally the only point I made: https://news.ycombinator.com/item?id=27801257 https://news.ycombinator.com/item?id=27801257