How much bigger could Earth be before rockets wouldn't work?

Planet size, gravity & chemical rockets

• Core idea: as surface gravity increases, chemical rockets need exponentially more propellant; at some point vehicle size and structural limits make launches impractical.
• Long, multi-stage designs and “hot staging” could theoretically still work on very high‑gravity planets, but might require first stages extending above the atmosphere.
• Shockwaves from enormous exhaust plumes and material strength limits may cap practical sea‑level launch mass even on Earth.

Towers, elevators, and alternative launch architectures

• Extremely tall towers or “first stages” start to resemble space elevators; once you can build that, rockets become optional.
• Purely compressive towers to geostationary heights are considered impossible with known materials; tensile space elevators or active concepts (space fountains) are seen as more plausible, especially on low‑gravity bodies.
• Air‑launch, mountain‑top launch, balloons, and railguns are raised; most commenters think benefits on Earth are modest and engineering challenges large, but they might matter more on high‑g or high‑atmosphere worlds.

Nuclear and exotic propulsion

• Nuclear thermal rockets (NTR) have much higher specific impulse but low thrust‑to‑weight; generally viewed as poor for liftoff but excellent for upper stages and in‑space transfer.
• More extreme ideas (Project Orion, nuclear salt‑water rockets) could in principle overcome deep gravity wells but raise radiation and practicality concerns.
• Some argue that if chemistry couldn’t reach orbit, nuclear options would be developed earlier and high‑g civilizations might start spaceflight with nuclear.

High‑gravity planets, habitability & the Fermi paradox

• Several comments tie launch difficulty into the Drake equation and Great Filter ideas: high‑g “superhabitable” planets might host abundant life that cannot become spacefaring.
• Others counter that advanced civilizations could use non‑chemical methods (nuclear, elevators, beamed sails), so gravity alone is unlikely to be a decisive filter.
• Long debate on the Fermi paradox:
  • One side: even slow interstellar expansion and Dyson swarms should be visible; their absence implies intelligent life is rare, short‑lived, or early.
  • Other side: assumptions about eternal technological progress, motives to colonize, and detectability of megastructures are challenged; we may misinterpret or simply not recognize alien engineering.

Atmospheres, buoyancy, and magnetic fields

• Higher gravity generally compresses atmospheres; thicker air increases drag and makes railguns and high‑speed ascent harder.
• Clarification that buoyancy in nearly incompressible liquids is largely gravity‑independent, but in compressible fluids density changes with g.
• Magnetic fields protect atmospheres from stellar wind over long timescales; examples like Venus and Mars are discussed with differing interpretations of how crucial magnetospheres are.

War, governance, and galactic sociology

• Speculation that difficulty of rocketry could slow weapons development (ICBMs) and alter war dynamics; unclear whether that makes civilizations more or less stable.
• Discussions around “space fascists” note that authoritarian systems and slavery tend to be inefficient and particularly ill‑suited to space, where humans (or biological workers) are expensive to keep alive.

Technology without space access

• Civilizations unable to reach orbit would lack satellites, GPS, and easy global remote sensing.
• However, commenters note that terrestrial networks (cables, radio, land‑based positioning systems) can substitute many functions, albeit more expensively and with different vulnerabilities.

Physics side discussions

• Thought experiment: pushing a very long bar; consensus that mechanical disturbances propagate at the material’s speed of sound, not instantaneously.
• At quantum scales, fields mediate interactions with changes limited by the speed of light; particles like quarks are modeled as pointlike, not extended rods.
• Emphasis that “speed of light” is best understood as a speed‑of‑causality limit.