Skip the rocket. Build a kilometer-wide vacuum chamber, mount a long arm on a central hub, spin it up over hours using cheap grid electricity, and at exactly the right millisecond, release the payload through a hatch in the wall. It exits at orbital velocity. SpinLaunch in Spaceport America already throws 100-kg dummies at ~2.4 km/s from a 33-meter arm. Why not scale it to actual orbit?

The orbital velocity target is v ≈ 7.8 km/s. The first wall we slam into isn't aerodynamic — it's materials science.

The hoop-stress ceiling

A spinning arm experiences tensile stress that depends only on tip speed and density, not on length. For a thin rotating rod, the peak stress at the hub is:

σ = ½ ρ v_tip²

Solving for the maximum tip speed before the arm rips itself apart:

v_max = √(2σ / ρ)

Plugging in real numbers:

• Maraging steel (σ≈2 GPa, ρ=7800): v_max ≈ 720 m/s
• T1100 carbon fiber (σ≈7 GPa, ρ=1800): v_max ≈ 2,790 m/s
• Zylon PBO (σ≈5.8 GPa, ρ=1540): v_max ≈ 2,740 m/s
• Theoretical CNT yarn (σ≈50 GPa, ρ=1300): v_max ≈ 8,770 m/s ✓

Carbon fiber tops out at about 35% of orbital velocity. Only hypothetical defect-free carbon nanotube yarn — which nobody has manufactured at meter-scale — clears the bar. The arm length doesn't matter. You can't outrun this with engineering; it's a property of the atoms.

The g-force ceiling

Centripetal acceleration is a = v²/r. For 7.8 km/s release:

• r = 100 m arm: 62,000 g (silicon liquefies, basically)
• r = 1 km arm: 6,200 g (artillery shells survive ~15,000 g — possible for solid metal slugs only)
• r = 10 km arm: 620 g (heavily potted electronics survive)
• r = 100 km arm: 62 g (humans pass out but live)

A 100-km-radius vacuum centrifuge is a ring 628 km around. The Large Hadron Collider's tunnel is 27 km. We're talking civil engineering on a scale that dwarfs every accelerator ever built.

The atmosphere problem

Even assuming you solve materials and g-loading, the payload exits into sea-level air at Mach 23. Stagnation pressure scales as ½ρv²: at v=7800 m/s and ρ=1.225 kg/m³, that's 37 MPa — five times the pressure at the bottom of the Mariana Trench, applied as a hammer-blow to the nosecone. Aerodynamic heating peaks near 30,000 K. The payload needs an ablative shield heavier than what it's carrying.

The fix: site the launcher at 6 km altitude (air density halved) and aim 30° above horizontal. You still lose ~1.5 km/s to drag — meaning the arm must throw at 9.3 km/s. Now nothing works, even hypothetically.

The honest tradeoff

SpinLaunch's pitch is suborbital boost — fling a payload at 2.4 km/s, let a small rocket on the projectile handle the final 5.4 km/s in vacuum. That's a 30% propellant savings, not a rocket replacement. Going full-orbital with a centrifuge requires either CNT yarn that doesn't exist or a launcher the size of a metropolitan area, in vacuum, at altitude. The spinning-arm bottleneck is the same one that limits flywheels and turbine blades: √(σ/ρ), the universal speed limit of rotating matter.