Each balloon's lift comes from Archimedes' principle: buoyant force = ρair(h)·V(h)·g. Because a latex balloon is unsealed to pressure, its gas obeys the isothermal ideal gas law as it rises, so V(h) = V₀·e^(h/H) — and since ρair(h) = ρ₀·e^(−h/H), the two exponentials cancel and net lift stays roughly constant with altitude, exactly why real weather balloons climb at a near-steady rate.
V(h) = V0 · e^(h/H), H ≈ 8500 m
Burst when V(h) ≥ V0 · burst× → h_burst = H·ln(burst×)
Drag = ½·ρ_air(h)·Cd·A(h)·v·|v|
- Envelope expansion × — how many times its launch volume the balloon stretches before the latex tears; sets the burst altitude directly (H·ln(×)).
- Jet-stream wind — peak horizontal wind speed, strongest around the tropopause (~10–12 km), that drifts the balloon downrange.
- Station range — the radio equipment's rated maximum; actual coverage also needs geometric line-of-sight, which grows with √altitude, so low balloons need stations directly below them.
After burst the payload falls on a parachute: drag now opposes descent, so fall speed is fast in the thin high air and slows automatically as the parachute reaches denser air near the ground.