4 ms·

As I understand it, it's a practicality issue: with enough extra stages you can always escape, but the payload size rapidly approaches zero. (See: http://space.

by qrendel 11y ago

As I understand it, it's a practicality issue: with enough extra stages you can always escape, but the payload size rapidly approaches zero. (See: http://space.stackexchange.com/a/5383 http://space.stackexchange.com/a/5383) The size, complexity, and costs of extra stages make it impossible once you add in the actual real-world constraints. As said in Terr_'s link: "Rockets at 85% propellant and 15% structure and payload are on the extreme edge of our engineering ability to even fabricate (and to pay for!). They require constant engineering to keep flying."

avmich 11y ago
Thank you for your reply - and thank all the others who replied. This is a link on a NASA website :) and that organization is known to err in questions related to space. Seriously, guys - Don Pettit wrote it for general audience, and skimming the article I spotted this - > Hydrogen-oxygen is the most energetic chemical reaction known for use in a human rated rocket. Chemistry is unable to give us any more. This can be understood in a certain way - but also can be argued, as here - http://yarchive.net/space/rocket/fuels/hydrogen.html http://yarchive.net/space/rocket/fuels/hydrogen.html > The highest measured Isp ever achieved with chemical propellants was with LH2/LF2/LLi (yes, liquid lithium), at 542s in vacuum. Next, 15% structure certainly doesn't apply to some first stages - particularly recent Falcons from SpaceX. The point which I was trying to make is I doubt that big of a difference. Sure, it's pretty hard to get to orbit from, say, Jupiter-like planet. However orbital speed for a planet with constant density is linear by the planet radius, and to get to New Horizons' ~16 km/s delta V as orbital speed the Earth would have to be 2 times bigger - 8 times heavier. And New Horizon's ain't cubesat either. And, on top of that, we still have other readily available tricks up our sleeve. So I think even with rather large variations of Earth size we'd get in time to the stars.

by qrendel 11y ago

avmich 11y ago

Thank you for your reply - and thank all the others who replied. This is a link on a NASA website :) and that organization is known to err in questions related to space. Seriously, guys - Don Pettit wrote it for general audience, and skimming the article I spotted this - > Hydrogen-oxygen is the most energetic chemical reaction known for use in a human rated rocket. Chemistry is unable to give us any more. This can be understood in a certain way - but also can be argued, as here - http://yarchive.net/space/rocket/fuels/hydrogen.html http://yarchive.net/space/rocket/fuels/hydrogen.html > The highest measured Isp ever achieved with chemical propellants was with LH2/LF2/LLi (yes, liquid lithium), at 542s in vacuum. Next, 15% structure certainly doesn't apply to some first stages - particularly recent Falcons from SpaceX. The point which I was trying to make is I doubt that big of a difference. Sure, it's pretty hard to get to orbit from, say, Jupiter-like planet. However orbital speed for a planet with constant density is linear by the planet radius, and to get to New Horizons' ~16 km/s delta V as orbital speed the Earth would have to be 2 times bigger - 8 times heavier. And New Horizon's ain't cubesat either. And, on top of that, we still have other readily available tricks up our sleeve. So I think even with rather large variations of Earth size we'd get in time to the stars.