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I have read that the issue with a 1g rocket is that no fuel in existence is powerful enough to provide a constant acceleration of 9.8 meters per second for years on end, and it would take hundreds of tons of fuel just to reach our nearest star.

I have also read that metallic hydrogen would be the most powerful and efficient rocket fuel we've ever seen.

Would metallic hydrogen be powerful and efficient enough to make a 1g rocket feasible?

Qmechanic
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Ben Warner
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Achieving an acceleration of 1g is not difficult - a Formula 1 car can easily achieve accelerations in excess of 1g. Maintaining that acceleration for years rather than seconds is going to be a problem for any fuel, no matter how efficient it is. Even if we assume a super-fuel that is a hundred times more efficient than any conventional propellant, a back-of-the-envelope calculation says that maintaining an acceleration of 1g for years at a time will require millions of tons of propellant, not hundreds.

Of course, there are also theoretical exotic fuels such as antimatter (as discussed in the comments below). But if you plan to launch yourself to the stars on top of many tons of antimatter, I will wave you off from a very great distance.

gandalf61
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    FWIW, an ideal antimatter drive running at 1 g has a half-life of just over 35 weeks. I.e., a ship with such a drive has to convert half its mass to photons every 35 weeks. See https://physics.stackexchange.com/a/345492/123208 for details. – PM 2Ring Aug 13 '22 at 12:43
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    There's an important word in PM 2 Ring's comment that does not appear in your answer. The word is "mass." Your racing car accelerates by pushing against the ground, but a rocket has nothing to push against apart from the reaction mass that it must carry. Using a "super-fuel" to eject that mass is helpful, but you can not escape the harsh reality of the rocket equation. – Solomon Slow Aug 13 '22 at 13:35
  • @Solomon Hydrogen is nice reaction mass because it has the lowest atomic mass, so it maximizes the exhaust momentum for a given temperature. The primary advantage of MH (metallic hydrogen) is its density, but it's pointless if MH doesn't have a stable state. Allegedly, it's been produced in milligram quantities a couple of times, but those experiments are difficult to reproduce: diamond anvils tend to shatter when subjected to pressures ~250 GPa... – PM 2Ring Aug 13 '22 at 16:39
  • I haven't done the calculations for MH, but an ideal deuterium cycle engine converts around 260 kg of fuel to 259 kg of exhaust and 1 kg * c² energy. Such a ship running at 1 g has a half-life of just under 21.9 days, reaching a speed of ~0.0618 c, but it needs to have a comparable mean exhaust speed to achieve that. (And of course a real engine will have various losses). – PM 2Ring Aug 13 '22 at 17:05