4 ms·

> A super earth would require exponentially more Polynomially, right?

• pfdietz 5y ago
  No, exponentially. I used that word precisely, because the mass ratio in the rocket equation is exponential in (delta V)/(exhaust velocity).
  • foobarian 5y ago
    Thanks for the reply. Context: there are so few exponential processes in nature, especially around classical physics that it really stuck out here, so I made the comment. I should have searched and read up on it instead, but thought there is still some value in others seeing the conversation. And lastly: that is really depressing :-(
    • nayuki 5y ago
      This phenomenon is called "The Tyranny of the Rocket Equation": https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped...
      • ncmncm 5y ago
        Saturn, Uranus, and Neptune all have surface (well, cloud level) gravity nearly equal to Earth's. But try launching anything to orbit from any of them! (Strangely, with hydrogen and helium the majority of all three atmospheres, they have water and ammonia clouds. What holds them up?)
    • pfdietz 5y ago
      That exponential dependence comes from the use of chemical rockets, which have a pretty firm upper limit on their exhaust velocity. Once in space, lower thrust could be used, which admits the possibility of higher exhaust velocity. If one can vary the exhaust velocity then the problem can be evaded (although the specific power (power/mass) of the vehicle must be allowed to become very large, or else acceleration will decrease.) Recent example: https://phys.org/news/2022-02-laser-mars.html https://phys.org/news/2022-02-laser-mars.html Note the very high specific power. High Isp rocketry is all about the heat dissipation.