Abstract
Spaceport site selection is bounded by overlapping geographic, regulatory, and political constraints. The single most important factor is latitude: rockets launched near the equator gain ~465 m/s of "free" eastward velocity from Earth's rotation, reducing propellant requirements substantially. The minimum orbital inclination achievable from a fixed launch site equals the site's latitude — so high-latitude sites cannot deploy payloads to low-inclination orbits. Coastal locations are strongly preferred to allow rockets to launch over open water rather than populated areas, with downrange exclusion zones of order tens to hundreds of kilometres. Equatorial coastline with suitable downrange ocean is finite. Current global active launch sites number ~30. Plausible mature global pad count, even with extensive expansion, is bounded by available equatorial coastline (which excludes most of Africa's interior coastline, much of South Asia, populated portions of South America and northern Australia).
Key claims
- equatorial-rotation-bonus: ~465 m/s eastward velocity at the equator, decreasing with cos(latitude).
- minimum-orbital-inclination-equals-latitude: cannot launch to inclination below site latitude.
- coastal-downrange-required: rockets launched over open water; downrange exclusion zones tens to hundreds of km.
- current-active-sites: ~30 active launch sites globally.
- equatorial-coast-finite: suitable equatorial coastal sites are geographically limited; not every coastline is usable (population density, weather, infrastructure access).
Reviewer notes
Pad infrastructure has a fundamental geographic ceiling that is NOT willingness-to-scale: equatorial coastline with downrange ocean and low population density is finite. Realistic mature global count of high-cadence-suitable pad sites is probably 50-100 — and approaching that ceiling requires sites in less-than-ideal latitudes (further from equator → propellant penalty for non-equatorial launch) or offshore platforms (entirely new infrastructure class). At 1-3 launches/pad/day, the pad geographic ceiling is ~18,000-110,000 launches/yr — sitting in the same range as before but now reframed as a fundamental constraint, not a willingness-to-scale one. However — pads are not the binding constraint until LOX/electricity become a more fundamental scaling issue at the Tt/yr cosmic scale.