6 ms·

https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped...

duskwuff 7y ago
Nice find! Near the end, the author directly addresses this question: > If the radius of our planet were larger, there could be a point at which an Earth escaping rocket could not be built. Let us assume that building a rocket at 96% propellant (4% rocket), currently the limit for just the Shuttle External Tank, is the practical limit for launch vehicle engineering. Let us also choose hydrogen-oxygen, the most energetic chemical propellant known and currently capable of use in a human rated rocket engine. By plugging these numbers into the rocket equation, we can transform the calculated escape velocity into its equivalent planetary radius. That radius would be about 9680 kilometers (Earth is 6670 km). If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport.
- acidburnNSA 7y ago
  Not using chemical rockets. Nuclear propulsion would be able to do it with the ~1000000x energy density advantage of nuclear fuel over chemical fuel.
  - nine_k 7y ago
    The problem is that the super-dense energy of a nuclear blast also evaporates solids and rains gamma rays on everything around. Imagine how hard space exploration would be if the only practical rocket were a Project Orion.
  - Baeocystin 7y ago
    I remember seeing a simple demonstrator some years back of a laser pulsing against the backside of a spinning disc, the geometry of things causing the heat from the laser to provide thrust. I can't find the video I saw, but here's a general link on the topic: https://en.wikipedia.org/wiki/Laser_propulsion#Laser_energized_rocket https://en.wikipedia.org/wiki/Laser_propulsion#Laser_energiz... This comes with many problems, but it does bypass the rocket equation, while not requiring Project Orion levels of trouble.
    - rocqua 7y ago
      I mean you still need to carry propellant: the stuff that is ablated away. It's just that the exhaust velocity is much higher.
      - king07828 7y ago
        Air from the atmosphere may be the propellant [1]. If sufficient velocity can be achieved before leaving the atmosphere, then no propellant is needed to be carried up on the way to orbit. [1] https://www.youtube.com/watch?v=XhUasBcoj-Q https://www.youtube.com/watch?v=XhUasBcoj-Q
  - jccooper 7y ago
    Nuclear would be better, but it's not quite as good as it seems. Nuclear engines are rather heavier than chemical.
- wolf550e 7y ago
  There are more efficient propellants than hydrolox, but extremely toxic [1]. With a bigger planet, we would have been forced to use either those or nuclear propulsion to get to space. 1 - https://space.stackexchange.com/questions/19852/where-is-the-lithium-fluorine-hydrogen-tripropellant-currently https://space.stackexchange.com/questions/19852/where-is-the...

duskwuff 7y ago

Nice find! Near the end, the author directly addresses this question: > If the radius of our planet were larger, there could be a point at which an Earth escaping rocket could not be built. Let us assume that building a rocket at 96% propellant (4% rocket), currently the limit for just the Shuttle External Tank, is the practical limit for launch vehicle engineering. Let us also choose hydrogen-oxygen, the most energetic chemical propellant known and currently capable of use in a human rated rocket engine. By plugging these numbers into the rocket equation, we can transform the calculated escape velocity into its equivalent planetary radius. That radius would be about 9680 kilometers (Earth is 6670 km). If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport.

acidburnNSA 7y ago
Not using chemical rockets. Nuclear propulsion would be able to do it with the ~1000000x energy density advantage of nuclear fuel over chemical fuel.
- nine_k 7y ago
  The problem is that the super-dense energy of a nuclear blast also evaporates solids and rains gamma rays on everything around. Imagine how hard space exploration would be if the only practical rocket were a Project Orion.
- Baeocystin 7y ago
  I remember seeing a simple demonstrator some years back of a laser pulsing against the backside of a spinning disc, the geometry of things causing the heat from the laser to provide thrust. I can't find the video I saw, but here's a general link on the topic: https://en.wikipedia.org/wiki/Laser_propulsion#Laser_energized_rocket https://en.wikipedia.org/wiki/Laser_propulsion#Laser_energiz... This comes with many problems, but it does bypass the rocket equation, while not requiring Project Orion levels of trouble.
  - rocqua 7y ago
    I mean you still need to carry propellant: the stuff that is ablated away. It's just that the exhaust velocity is much higher.
    - king07828 7y ago
      Air from the atmosphere may be the propellant [1]. If sufficient velocity can be achieved before leaving the atmosphere, then no propellant is needed to be carried up on the way to orbit. [1] https://www.youtube.com/watch?v=XhUasBcoj-Q https://www.youtube.com/watch?v=XhUasBcoj-Q
- jccooper 7y ago
  Nuclear would be better, but it's not quite as good as it seems. Nuclear engines are rather heavier than chemical.
wolf550e 7y ago
There are more efficient propellants than hydrolox, but extremely toxic [1]. With a bigger planet, we would have been forced to use either those or nuclear propulsion to get to space. 1 - https://space.stackexchange.com/questions/19852/where-is-the-lithium-fluorine-hydrogen-tripropellant-currently https://space.stackexchange.com/questions/19852/where-is-the...