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> Self-landing reusable rockets were impossible too according to pretty much the entire aerospace industry. I guess they didn't ask the people who designed and

> Self-landing reusable rockets were impossible too according to pretty much the entire aerospace industry. I guess they didn't ask the people who designed and built the Apollo lunar landing modules in the 1960s?

acover 9y ago
There is an implicit "on earth". Gravity wells being vastly different. If the earth was bigger then we wouldn't even be able to get to orbit.
- dalanmiller 9y ago
  Wouldn't we just need to generate more velocity?
  - URSpider94 9y ago
    Easier said than done. Rockets have to carry their own fuel, so they are heaviest at launch. If you’re in a deeper gravity well, then you need a longer burn to reach escape velocity, and then also more thrust at launch because you have to carry more fuel (which means still more fuel...) It never becomes mathematically impossible to achieve escape, but it can become engineering-impossible, ie the propellant fraction becomes so high that it’s impossible to build a structure that can contain the propellant and maintain mechanical stability. Just for reference, modern rockets are 90+ percent propellant by mass. For more, see https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped...
greenyoda 9y ago
The lunar module was neither self-landing nor reusable. The lunar module was navigated and landed by a human pilot (with computer assistance). The descent stage stayed on the Moon, and wasn't reused (except as a launch platform for the ascent stage). The ascent stage also wasn't reused - after the astronauts exited from the ascent stage into the command module, the ascent stage was jettisoned to crash into the lunar surface (or sent into solar orbit). Only the command module returned to Earth. https://en.wikipedia.org/wiki/Apollo_Lunar_Module https://en.wikipedia.org/wiki/Apollo_Lunar_Module

acover 9y ago

There is an implicit "on earth". Gravity wells being vastly different. If the earth was bigger then we wouldn't even be able to get to orbit.

dalanmiller 9y ago
Wouldn't we just need to generate more velocity?
- URSpider94 9y ago
  Easier said than done. Rockets have to carry their own fuel, so they are heaviest at launch. If you’re in a deeper gravity well, then you need a longer burn to reach escape velocity, and then also more thrust at launch because you have to carry more fuel (which means still more fuel...) It never becomes mathematically impossible to achieve escape, but it can become engineering-impossible, ie the propellant fraction becomes so high that it’s impossible to build a structure that can contain the propellant and maintain mechanical stability. Just for reference, modern rockets are 90+ percent propellant by mass. For more, see https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html https://www.nasa.gov/mission_pages/station/expeditions/exped...

greenyoda 9y ago

The lunar module was neither self-landing nor reusable. The lunar module was navigated and landed by a human pilot (with computer assistance). The descent stage stayed on the Moon, and wasn't reused (except as a launch platform for the ascent stage). The ascent stage also wasn't reused - after the astronauts exited from the ascent stage into the command module, the ascent stage was jettisoned to crash into the lunar surface (or sent into solar orbit). Only the command module returned to Earth. https://en.wikipedia.org/wiki/Apollo_Lunar_Module https://en.wikipedia.org/wiki/Apollo_Lunar_Module