Would cavities of near vacuums in the head (or in the 6 x 6 blocks surrounding the rocket [for reentry temperatures]) of a rocket make it lighter so it can be sent out easier?
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$\begingroup$ I don't know what a "near vacuum (solely with H/He atoms)" means. A vacuum doesn't have (very) many atoms of any kind. You also need to distinguish between the satellite (the payload) and the rocket (the thing which spouts fire and puts the payload in orbit). The space inside the rocket is already occupied by the fuel used to propel it, so there's not much savings of mass there. The satellite is typically small compared to the size of the entire rocket, so again, making the inside a vacuum typically is more trouble than its worth. $\endgroup$– user16622Jun 19, 2016 at 8:33
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$\begingroup$ Would balloons help us getting into space? No, otherwise we would be using them. Getting into space is not a matter of achieving altitude, which balloons are good for, it's a matter of achieving velocity. $\endgroup$– CuriousOneJun 19, 2016 at 8:53
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$\begingroup$ @ user16622 | How would extending the tip of the satellite for a vacuum chamber be hard to do? And thanks for the differentiation, I wasn't aware of that. @CuriousOne | wouldn't being light help, at least until it reached the end of the atmosphere? $\endgroup$– nelomadJun 19, 2016 at 21:23
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$\begingroup$ You are not helping yourself by introducing more drag on a rocket by making it larger. One could imagine filling the fairing with helium, which would give a buoyant force on maybe the 100N scale, but what you really need is on the order of 1 million N for a rocket like the Falcon 9, so that's a 1 in 10,000 effect. Putting a payload in a helium atmosphere is probably not acceptable to the payload provider, anyway. $\endgroup$– CuriousOneJun 19, 2016 at 21:32
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$\begingroup$ I thought that building upward instead would avoid drag. $\endgroup$– nelomadJun 19, 2016 at 21:35
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2 Answers
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In a word, no. Getting into space is a matter of achieving enough velocity to overcome the Earth's gravitational influence, not about buoyancy. You can use buoyancy to get to the edge of the Earth's atmosphere, not beyond. We don't fill a rocket with helium so it'll float into space, nor do we use balloons to get beyond the edge of the Earth's atmosphere.
answered Jun 19, 2016 at 16:23
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$\begingroup$ wouldn't it lighten the rocket before the point where it doesn't help, and it could start thrusting at that point $\endgroup$– nelomadJun 19, 2016 at 20:35
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1$\begingroup$ Sure it would. But hot air balloons make lousy launch pads. Even if they didn't it wouldn't help much. Orbit is about speed not altitude. $\endgroup$ Jun 1, 2017 at 18:13
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No because with practical materials, the structure needed to support a vacuum is heavier than the air it displaces. Here's a description of the principle https://en.wikipedia.org/wiki/Vacuum_airship
Even if you increase the buoyancy, say with a helium balloon, you're still not decreasing the mass, and mass is what's expensive to accelerate with a rocket.
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$\begingroup$ I'd say this is an even better reason than the other answer. It's not easy to hold a vacuum, which is why it's an overly useful feature. $\endgroup$– JMacJun 1, 2017 at 18:04