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So , i was watching a interview with Elon Musk and something he said caught my attetion. He said that if the world's gravity was 10% stronger, it would be impossible to have a reusable rocket. Is that ideia correct?

If so, i was wondering why? It has something to do with the equipment that would be required to escape earth's gravitational field? It has something to do with the Rocket equation? Or it has something to do with Newton's Third Law?

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  • $\begingroup$ Scott Manley has an interesting practical (insofar as KSP is practical) exploration of this topic, but in the much more extreme 500% stronger case: youtube.com/watch?v=RD5WAldIe5A $\endgroup$ – probably_someone Jun 25 '17 at 1:53
  • $\begingroup$ I would interpret Elon Musk's statement as: "If Earth's gravity was 10% stronger, the methods Spacex currently uses for a reusable rocket just couldn't work." He's probably factoring in a million and one financial, practical, and engineering factors. $\endgroup$ – user12029 Jun 25 '17 at 5:01
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I would not literally believe what he said. Obviously, he would have said this based upon what his engineers/scientists told him.

It could have been much more challenging than it is with current gravity. The factors that would come into play are as follows -

  1. More fuel required to launch and then to slow down and land

  2. Higher orbital speed, so harder re-entry

  3. Thicker atmosphere, so more heat, and even harder re-entry.

  4. More difficult design for the heavier take-off and higher escape velocity, you might need more/multiple thrusters.

  5. Stronger material requirements to overcome the re-entry stress and heat.

Without going into calculations, it could be much harder, but not impossible. I am not even sure at what value of gravity, it would become impossible, if at all.

On the other hand, we could have possibly had stronger materials available due to stronger gravity.

What he may have meant is that it may not have been economically viable to do so. But we do not know what kind of economy we would have with 10% stronger gravity.

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    $\begingroup$ "We could have possibly had stronger materials available due to stronger gravity" - what's your reasoning here? $\endgroup$ – probably_someone Jun 25 '17 at 1:14
  • $\begingroup$ @probably_someone: No concrete reasoning, but for example, due to higher gravity, atom arrangement may be possibly slightly different giving same material different strength. Everything gets impacted by gravity in general. $\endgroup$ – kpv Jun 25 '17 at 2:11
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It is definitely not true. You'd need a substantially larger, more powerful, and more expensive rocket to achieve any particular payload-to-orbit specification, making the economics more challenging, and for a large enough planet even a project Mercury style one-man-to-orbit mission might be impractically expensive, but a 1.1 g surface gravity Earth wouldn't be a complete show-stopper.

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