Ballast

Ballast is weight carried in an aircraft or balloon to adjust mass and balance. In gas balloons it is usually sand or water carried so the pilot can drop some of it to reduce total mass and make the balloon climb. Ballast is used during flight to control altitude when lift decreases, for example after cooling or gas loss. The pilot must carry, secure and use ballast carefully because dropped ballast cannot be recovered and it changes the remaining flight performance.